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					Quantifying Impact Of Rainfall On Shallow Groundwater
    Table In The Wakool Irrigation District, NSW
                                                                                                                                                                              (Final Draft)
                                 Rainfall gauging station with no missing data for the specified time                                                                                                                                             Rainfall gauging station with missing data for the specified time
                                 interval.                                                                                                                                                                                                        interval and thus disregarded for the specified time interval.

                                 Boundary of the Wakool Irrigation District.                                                                                                                                                Irrigation
                                                                                                                                                                                          Boundary of the area under Murray LWMP. Ltd.                                                                                                                                            Main road.
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                                                                     Butian Wang, Shahbaz Khan, Natalie O’Connell

                                                                                                 CSIRO Land and Water, Griffith Laboratory

                                                                                                                                                                              Version: Oct 2003
Quantifying Impact Of Rainfall On Shallow Groundwater
    Table In The Wakool Irrigation District, NSW
                         (Final Draft)



           Butian Wang, Shahbaz Khan, Natalie O’Connell




              CSIRO Land and Water, Griffith Laboratory

                          Version: Oct 2003
                Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                          Executive Summary

Water table rise and salinity are major threats to the sustainability of agriculture in the
Wakool area. In order to improve groundwater and salinity management in the Wakool area,
it is necessary to quantify impact of both climate and management on shallow groundwater
table.

Rainfall as a major climate indicator and hydrology component plays an important role in
regional hydrology and environment, as well as in water table change. This study attempts to
quantify the impact of rainfall as a major climate indicator on shallow groundwater in the
Wakool area based on the piezometric data in this area and the rainfall data in a wider area.

GIS techniques have been extensively used in this study for data processing and analysis,
especially for generating the spatial distributions of rainfall and groundwater table over the
study period, for analyzing the spatial extent of groundwater table changes, and for
calculating relevant volumes for various time intervals.

This study has developed a method for isolating the impact of climate on shallow watertables.
The method has been proven particularly effective in assessing the impact of rainfall for
summer seasons which are the major irrigation periods in the study area.

Statistical relationships were established to understand and quantify the impact of climate
represented by rainfall on groundwater tables for different seasons in the year.

The statistical relationships between rainfall and groundwater storage change derived from
this study revealed some interesting bench mark rainfall figures:
    • For summer seasons, the bench mark rainfall is around 200mm, above which, it will
        likely to have an addition effect on groundwater storage; below which, it will likely to
        have a reduction effect on groundwater storage;
    • For the winter season, that bench mark rainfall is around 170mm

The results of this study indicate that climate represented by rainfall, which is also a major
source of flood, has a significant impact on the shallow groundwater tables in the Wakool
area, as the correlations (R2) between rainfall and water table change are in the range of
0.7~0.9 for all the time intervals considered.


Keywords: groundwater, water table, GIS, climate, flood, rainfall, Murray, Wakool.




                                                       -i-
                            Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                                              Table of Contents
Executive Summary ··························································································································i

Table of Contents ···························································································································· ii

List of Tables ···································································································································· iv

List of Figures ·····································································································································v

List of Figures in Appendix A ········································································································· vi

List of Figures in Appendix B ·······································································································viii

List of Figures in Appendix C ···········································································································x

List of Figures in Appendix D········································································································ xii

List of Figures in Appendix E ······································································································· xiv

List of Figures in Appendix F ······································································································· xvi

1. Introduction ···································································································································1

2. The Study Area ·····························································································································2

3. Data Collection ····························································································································6
   3.1. Piezometric data ··················································································································6
   3.2. Rainfall data ······················································································································ 10

4. Differentiation of Climatic and Management Impact
   on Shallow Water Table ········································································································ 11

5. Data Processing ························································································································ 13
   5.1. Quantifying water table change from average change ······································· 13
   5.2. Calculating corresponding rainfall ··········································································· 16

6. The Results ································································································································· 17
   6.1 Rainfall and relative net groundwater storage ······················································· 17
   6.2 Comparison with correlation between rainfall and net absolute
       groundwater storage change ························································································ 20

7. Summary and Conclusions ··································································································· 22

Acknowledgement ··························································································································· 23

Reference ·········································································································································· 23

                                                                             - ii -
                         Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




Appendix A. Maps Showing Spatial Distribution of Relative Water Table Change
in Summer Season Estimated due to Climate Factors Represented by Rainfall ········· 24

Appendix B. Maps Showing Spatial Distribution of Relative Water Table Change
in Winter Season Estimated due to Climate Factors Represented by Rainfall ············ 43

Appendix C. Maps Showing Spatial Distribution of Yearly Relative Water Table
Change Estimated due to Climate Factors Represented by Rainfall ······························ 62

Appendix D. Maps Showing Summer Rainfall Spatial Distribution around the
Murray Irrigation Area ················································································································· 81

Appendix E. Maps Showing Winter Rainfall Spatial Distribution around the
Murray Irrigation Area ··············································································································· 100

Appendix F. Maps Showing Yearly Rainfall Spatial Distribution around the
Murray Irrigation Area ··············································································································· 119




                                                                      - iii -
                  Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                                      List of Tables


Table 1.   Average water use by different categories. ·········································································· 3

Table 2.   Summary of piezometric data collected. ·············································································· 7

Table 3.   Spatial coverage of the piezometers and season delineation based on piezometric data. ···· 14




                                                              - iv -
                     Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                                               List of Figures

Figure 1.    Location of the Wakool area and major irrigation areas in south NSW.······························ 3

Figure 2.    Monthly average daily temperature at Moulamein Post Office. (Data source: BOM).········· 5

Figure 3.    Monthly pan evaporation at NSW Water Resources Commission’s observation station
             in Wakool (Data source: BOM). ························································································· 6

Figure 4.    Monthly rainfall statistics at Moulamein Post Office (Data source: Bureau of
             Meteorology. Data period: 1888 - 1999).············································································ 6

Figure 5.    Temporal distribution of the number of piezometers with data available for Wakool
             area.···································································································································· 8

Figure 6.    Accumulated percentage of number of piezometers vs. number of readings over the
             data period (1963 Dec ~ 2001 Mar). ··················································································· 9

Figure 7.    Spatial distribution of rainfall stations selected for this study (total: 84). ·························· 10

Figure 8.    Annual rainfall at Moulamein Post Office (Station no: 75046). (Data source: Bureau of
             Meteorology)···················································································································· 11

Figure 8.    Annual rainfall at Moulamein Post Office (Station no: 75046). (Data source: Bureau of
             Meteorology)···················································································································· 11

Figure 10.   Illustration of average water table change for irrigation seasons (summer seasons) for a
             piezometer.······················································································································· 13

Figure 11.   Average water table change in summer season. ································································ 15

Figure 12.   Average water table change in winter season.··································································· 15

Figure 13.   Average yearly water table change. ·················································································· 16

Figure 14.   1974 winter rainfall spatial distribution around the Murray irrigation area in NSW.
             (1974 Mar – 1974 Aug inclusive). ···················································································· 17

Figure 15.   Seasonal net groundwater storage change assumed due to impact of rainfall. ··················· 18

Figure 16.   Correlation between summer net groundwater storage change due to climate impact
             and corresponding summer rainfall over the whole Wakool area ······································ 19

Figure 17.   Correlation between winter net groundwater storage change due to climate impact and
             corresponding winter rainfall over the whole Wakool area. ·············································· 19

Figure 18.   Correlation between yearly net groundwater storage change due to climate impact and
             corresponding yearly rainfall over the whole Wakool area. ·············································· 20

Figure 19.   Correlation between summer net absolute groundwater storage change and
             corresponding summer rainfall over the whole Wakool area.············································ 21

Figure 20.   Correlation between winter net absolute groundwater storage change and
             corresponding winter rainfall over the whole Wakool area. ·············································· 21

Figure 21.   Correlation between yearly net absolute groundwater storage change and
             corresponding yearly rainfall over the whole Wakool area. ·············································· 22



                                                                         -v-
                       Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                             List of Figures in Appendix A

Figure A1.      Relative water table change in 1965 summer season (between Sep-64 and Mar-65)
                estimated due to climate factors represented by rainfall. ···················································· 25

Figure A2.      Relative water table change in 1966 summer season (between Sep-65 and Mar-66)
                estimated due to climate factors represented by rainfall. ···················································· 25

Figure A3.      Relative water table change in 1967 summer season (between Sep-66 and Mar-67)
                estimated due to climate factors represented by rainfall. ···················································· 26

Figure A4.      Relative water table change in 1968 summer season (between Sep-67 and Mar-68)
                estimated due to climate factors represented by rainfall. ···················································· 26

Figure A5.      Relative water table change in 1969 summer season (between Sep-68 and Mar-69)
                estimated due to climate factors represented by rainfall. ···················································· 27

Figure A6.      Relative water table change in 1970 summer season (between Sep-69 and Mar-70)
                estimated due to climate factors represented by rainfall. ···················································· 27

Figure A7.      Relative water table change in 1971 summer season (between Sep-70 and Mar-71)
                estimated due to climate factors represented by rainfall. ···················································· 28

Figure A8.      Relative water table change in 1972 summer season (between Sep-71 and Mar-72)
                estimated due to climate factors represented by rainfall. ···················································· 28

Figure A9.      Relative water table change in 1973 summer season (between Sep-72 and Mar-73)
                estimated due to climate factors represented by rainfall. ···················································· 29

Figure A10. Relative water table change in 1974 summer season (between Sep-73 and Mar-74)
            estimated due to climate factors represented by rainfall. ···················································· 29

Figure A11. Relative water table change in 1975 summer season (between Sep-74 and Mar-75)
            estimated due to climate factors represented by rainfall. ···················································· 30

Figure A12. Relative water table change in 1976 summer season (between Sep-75 and Mar-76)
            estimated due to climate factors represented by rainfall. ···················································· 30

Figure A13. Relative water table change in 1977 summer season (between Sep-76 and Mar-77)
            estimated due to climate factors represented by rainfall. ···················································· 31

Figure A14. Relative water table change in 1978 summer season (between Sep-77 and Mar-78)
            estimated due to climate factors represented by rainfall. ···················································· 31

Figure A15. Relative water table change in 1979 summer season (between Sep-78 and Feb-79)
            estimated due to climate factors represented by rainfall. ···················································· 32

Figure A16. Relative water table change in 1980 summer season (between Aug-79 and Jan-80)
            estimated due to climate factors represented by rainfall. ···················································· 32

Figure A17. Relative water table change in 1981 summer season (between Aug-80 and Feb-81)
            estimated due to climate factors represented by rainfall. ···················································· 33

Figure A18. Relative water table change in 1982 summer season (between Aug-81 and Feb-82)
            estimated due to climate factors represented by rainfall. ···················································· 33

Figure A19. Relative water table change in 1983 summer season (between Aug-82 and Feb-83)
            estimated due to climate factors represented by rainfall. ···················································· 34



                                                                 - vi -
                       Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW



Figure A20. Relative water table change in 1984 summer season (between Aug-83 and Feb-84)
            estimated due to climate factors represented by rainfall. ···················································· 34

Figure A21. Relative water table change in 1985 summer season (between Jul-84 and Feb-85)
            estimated due to climate factors represented by rainfall. ···················································· 35

Figure A22. Relative water table change in 1986 summer season (between Jul-85 and Feb-86)
            estimated due to climate factors represented by rainfall. ···················································· 35

Figure A23. Relative water table change in 1987 summer season (between Jul-86 and Feb-87)
            estimated due to climate factors represented by rainfall. ···················································· 36

Figure A24. Relative water table change in 1988 summer season (between Jul-87 and Feb-88)
            estimated due to climate factors represented by rainfall. ···················································· 36

Figure A25. Relative water table change in 1989 summer season (between Jul-88 and Feb-89)
            estimated due to climate factors represented by rainfall. ···················································· 37

Figure A26. Relative water table change in 1990 summer season (between Jul-89 and Feb-90)
            estimated due to climate factors represented by rainfall. ···················································· 37

Figure A27. Relative water table change in 1991 summer season (between Jul-90 and Feb-91)
            estimated due to climate factors represented by rainfall. ···················································· 38

Figure A28. Relative water table change in 1992 summer season (between Jul-91 and Feb-92)
            estimated due to climate factors represented by rainfall. ···················································· 38

Figure A29. Relative water table change in 1993 summer season (between Jul-92 and Feb-93)
            estimated due to climate factors represented by rainfall. ···················································· 39

Figure A30. Relative water table change in 1994 summer season (between Jul-93 and Feb-94)
            estimated due to climate factors represented by rainfall. ···················································· 39

Figure A31. Relative water table change in 1995 summer season (between Jul-94 and Feb-95)
            estimated due to climate factors represented by rainfall. ···················································· 40

Figure A32. Relative water table change in 1996 summer season (between Jul-95 and Feb-96)
            estimated due to climate factors represented by rainfall. ···················································· 40

Figure A33. Relative water table change in 1997 summer season (between Jul-96 and Mar-97)
            estimated due to climate factors represented by rainfall. ···················································· 41

Figure A34. Relative water table change in 1998 summer season (between Aug-97 and Mar-98)
            estimated due to climate factors represented by rainfall. ···················································· 41

Figure A35. Relative water table change in 1999 summer season (between Aug-98 and Mar-99)
            estimated due to climate factors represented by rainfall. ···················································· 42

Figure A36. Relative water table change in 2000 summer season (between Aug-99 and Mar-00)
            estimated due to climate factors represented by rainfall. ···················································· 42




                                                               - vii -
                       Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                             List of Figures in Appendix B

Figure B1.      Relative water table change in 1965 winter season (between Mar-65 and Sep-65)
                estimated due to climate factors represented by rainfall. ···················································· 44

Figure B2.      Relative water table change in 1966 winter season (between Mar-66 and Sep-66)
                estimated due to climate factors represented by rainfall. ···················································· 44

Figure B3.      Relative water table change in 1967 winter season (between Mar-67 and Sep-67)
                estimated due to climate factors represented by rainfall. ···················································· 45

Figure B4.      Relative water table change in 1968 winter season (between Mar-68 and Sep-68)
                estimated due to climate factors represented by rainfall. ···················································· 45

Figure B5.      Relative water table change in 1969 winter season (between Mar-69 and Sep-69)
                estimated due to climate factors represented by rainfall. ···················································· 46

Figure B6.      Relative water table change in 1970 winter season (between Mar-70 and Sep-70)
                estimated due to climate factors represented by rainfall. ···················································· 46

Figure B7.      Relative water table change in 1971 winter season (between Mar-71 and Sep-71)
                estimated due to climate factors represented by rainfall. ···················································· 47

Figure B8.      Relative water table change in 1972 winter season (between Mar-72 and Sep-72)
                estimated due to climate factors represented by rainfall. ···················································· 47

Figure B9.      Relative water table change in 1973 winter season (between Mar-73 and Sep-73)
                estimated due to climate factors represented by rainfall. ···················································· 48

Figure B10. Relative water table change in 1974 winter season (between Mar-74 and Sep-74)
            estimated due to climate factors represented by rainfall. ···················································· 48

Figure B11. Relative water table change in 1975 winter season (between Mar-75 and Sep-75)
            estimated due to climate factors represented by rainfall. ···················································· 49

Figure B12. Relative water table change in 1976 winter season (between Mar-76 and Sep-76)
            estimated due to climate factors represented by rainfall. ···················································· 49

Figure B13. Relative water table change in 1977 winter season (between Mar-77 and Sep-77)
            estimated due to climate factors represented by rainfall. ···················································· 50

Figure B14. Relative water table change in 1978 winter season (between Mar-78 and Sep-78)
            estimated due to climate factors represented by rainfall. ···················································· 50

Figure B15. Relative water table change in 1979 winter season (between Feb-79 and Aug-79)
            estimated due to climate factors represented by rainfall. ···················································· 51

Figure B16. Relative water table change in 1980 winter season (between Jan-80 and Aug-80)
            estimated due to climate factors represented by rainfall. ···················································· 51

Figure B17. Relative water table change in 1981 winter season (between Feb-81 and Aug-81)
            estimated due to climate factors represented by rainfall. ···················································· 52

Figure B18. Relative water table change in 1982 winter season (between Feb-82 and Aug-82)
            estimated due to climate factors represented by rainfall. ···················································· 52

Figure B19. Relative water table change in 1983 winter season (between Feb-83 and Aug-83)
            estimated due to climate factors represented by rainfall. ···················································· 53



                                                                - viii -
                       Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW



Figure B20. Relative water table change in 1984 winter season (between Feb-84 and Jul-84)
            estimated due to climate factors represented by rainfall. ···················································· 53

Figure B21. Relative water table change in 1985 winter season (between Feb-85 and Jul-85)
            estimated due to climate factors represented by rainfall. ···················································· 54

Figure B22. Relative water table change in 1986 winter season (between Feb-86 and Jul-86)
            estimated due to climate factors represented by rainfall. ···················································· 54

Figure B23. Relative water table change in 1987 winter season (between Feb-87 and Jul-87)
            estimated due to climate factors represented by rainfall. ···················································· 55

Figure B24. Relative water table change in 1988 winter season (between Feb-88 and Jul-88)
            estimated due to climate factors represented by rainfall. ···················································· 55

Figure B25. Relative water table change in 1989 winter season (between Feb-89 and Jul-89)
            estimated due to climate factors represented by rainfall. ···················································· 56

Figure B26. Relative water table change in 1990 winter season (between Feb-90 and Jul-90)
            estimated due to climate factors represented by rainfall. ···················································· 56

Figure B27. Relative water table change in 1991 winter season (between Feb-91 and Jul-91)
            estimated due to climate factors represented by rainfall. ···················································· 57

Figure B28. Relative water table change in 1992 winter season (between Feb-92 and Jul-92)
            estimated due to climate factors represented by rainfall. ···················································· 57

Figure B29. Relative water table change in 1993 winter season (between Feb-93 and Jul-93)
            estimated due to climate factors represented by rainfall. ···················································· 58

Figure B30. Relative water table change in 1994 winter season (between Feb-94 and Jul-94)
            estimated due to climate factors represented by rainfall. ···················································· 58

Figure B31. Relative water table change in 1995 winter season (between Feb-95 and Jul-95)
            estimated due to climate factors represented by rainfall. ···················································· 59

Figure B32. Relative water table change in 1996 winter season (between Feb-96 and Jul-96)
            estimated due to climate factors represented by rainfall. ···················································· 59

Figure B33. Relative water table change in 1997 winter season (between Mar-97 and Aug-97)
            estimated due to climate factors represented by rainfall. ···················································· 60

Figure B34. Relative water table change in 1998 winter season (between Mar-98 and Aug-98)
            estimated due to climate factors represented by rainfall. ···················································· 60

Figure B35. Relative water table change in 1999 winter season (between Mar-99 and Aug-99)
            estimated due to climate factors represented by rainfall. ···················································· 61

Figure B36. Relative water table change in 2000 winter season (between Mar-00 and Aug-00)
            estimated due to climate factors represented by rainfall. ···················································· 61




                                                               - ix -
                        Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                                 List of Figures in Appendix C

Figure C1.       Relative water table change in 1965 (between Sep-64 Sep-65) estimated due to climate
                 factors represented by rainfall.··························································································· 63

Figure C2.       Relative water table change in 1966 (between Sep-65 and Sep-66) estimated due to
                 climate factors represented by rainfall. ·············································································· 63

Figure C3.       Relative water table change in 1967 (between Sep-66 and Sep-67) estimated due to
                 climate factors represented by rainfall. ·············································································· 64

Figure C4.       Relative water table change in 1968 (between Sep-67 and Sep-68) estimated due to
                 climate factors represented by rainfall. ·············································································· 64

Figure C5.       Relative water table change in 1969 (between Sep-68 and Sep-69) estimated due to
                 climate factors represented by rainfall. ·············································································· 65

Figure C6.       Relative water table change in 1970 (between Sep-69 and Sep-70) estimated due to
                 climate factors represented by rainfall. ·············································································· 65

Figure C7.       Relative water table change in 1971 (between Sep-70 and Sep-71) estimated due to
                 climate factors represented by rainfall. ·············································································· 66

Figure C8.       Relative water table change in 1972 (between Sep-71 and Sep-72) estimated due to
                 climate factors represented by rainfall. ·············································································· 66

Figure C9.       Relative water table change in 1973 (between Sep-72 and Sep-73) estimated due to
                 climate factors represented by rainfall. ·············································································· 67

Figure C10. Relative water table change in 1974 (between Sep-73 and Sep-74) estimated due to
            climate factors represented by rainfall. ·············································································· 67

Figure C11. Relative water table change in 1975 (between Sep-74 and Sep-75) estimated due to
            climate factors represented by rainfall. ·············································································· 68

Figure C12. Relative water table change in 1976 (between Sep-75 and Sep-76) estimated due to
            climate factors represented by rainfall. ·············································································· 68

Figure C13. Relative water table change in 1977 (between Sep-76 and Sep-77) estimated due to
            climate factors represented by rainfall. ·············································································· 69

Figure C14. Relative water table change in 1978 (between Sep-77 and Sep-78) estimated due to
            climate factors represented by rainfall. ·············································································· 69

Figure C15. Relative water table change in 1979 (between Sep-78 and Aug-79) estimated due to
            climate factors represented by rainfall. ·············································································· 70

Figure C16. Relative water table change in 1980 (between Aug-79 and Aug-80) estimated due to
            climate factors represented by rainfall. ·············································································· 70

Figure C17. Relative water table change in 1981 (between Aug-80 and Aug-81) estimated due to
            climate factors represented by rainfall. ·············································································· 71

Figure C18. Relative water table change in 1982 (between Aug-81 and Aug-82) estimated due to
            climate factors represented by rainfall. ·············································································· 71

Figure C19. Relative water table change in 1983 (between Aug-82 and Aug-83) estimated due to
            climate factors represented by rainfall. ·············································································· 72



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                        Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW



Figure C20. Relative water table change in 1984 (between Aug-83 and Jul-84) estimated due to
            climate factors represented by rainfall. ·············································································· 72

Figure C21. Relative water table change in 1985 (between Jul-84 and Jul-85) estimated due to
            climate factors represented by rainfall. ·············································································· 73

Figure C22. Relative water table change in 1986 (between Jul-85 and Jul-86) estimated due to
            climate factors represented by rainfall. ·············································································· 73

Figure C23. Relative water table change in 1987 (between Jul-86 and Jul-87) estimated due to
            climate factors represented by rainfall. ·············································································· 74

Figure C24. Relative water table change in 1988 (between Jul-87 and Jul-88) estimated due to
            climate factors represented by rainfall. ·············································································· 74

Figure C25. Relative water table change in 1989 (between Jul-88 and Jul-89) estimated due to
            climate factors represented by rainfall. ·············································································· 75

Figure C26. Relative water table change in 1990 (between Jul-89 and Jul-90) estimated due to
            climate factors represented by rainfall. ·············································································· 75

Figure C27. Relative water table change in 1991 (between Jul-90 and Jul-91) estimated due to
            climate factors represented by rainfall. ·············································································· 76

Figure C28. Relative water table change in 1992 (between Jul-91 and Jul-92) estimated due to
            climate factors represented by rainfall. ·············································································· 76

Figure C29. Relative water table change in 1993 (between Jul-92 and Jul-93) estimated due to
            climate factors represented by rainfall. ·············································································· 77

Figure C30. Relative water table change in 1994 (between Jul-93 and Jul-94) estimated due to
            climate factors represented by rainfall. ·············································································· 77

Figure C31. Relative water table change in 1995 (between Jul-94 and Jul-95) estimated due to
            climate factors represented by rainfall. ·············································································· 78

Figure C32. Relative water table change in 1996 (between Jul-95 and Jul-96) estimated due to
            climate factors represented by rainfall. ·············································································· 78

Figure C33. Relative water table change in 1997 (between Jul-96 and Aug-97) estimated due to
            climate factors represented by rainfall. ·············································································· 79

Figure C34. Relative water table change in 1998 (between Aug-97 and Aug-98) estimated due to
            climate factors represented by rainfall. ·············································································· 79

Figure C35. Relative water table change in 1999 (between Aug-98 and Aug-99) estimated due to
            climate factors represented by rainfall. ·············································································· 80

Figure C36. Relative water table change in 2000 (between Aug-99 and Aug-00) estimated due to
            climate factors represented by rainfall. ·············································································· 80




                                                                    - xi -
                         Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                                 List of Figures in Appendix D

Figure D1.       1964 summer rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1963 Sep – 1964 Aug inclusive). ···················································································· 82

Figure D2.       1965 summer rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1964 Sep – 1965 Feb inclusive).······················································································· 82

Figure D3.       1966 summer rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1965 Sep – 1966 Feb inclusive).······················································································· 83

Figure D4.       1967 summer rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1966 Sep – 1967 Feb inclusive).······················································································· 83

Figure D5.       1968 summer rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1967 Sep 1968 Feb inclusive).·························································································· 84

Figure D6.       1969 summer rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1968 Sep – 1969 Feb inclusive).······················································································· 84

Figure D7.       1970 summer rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1969 Sep – 1970 Feb inclusive).······················································································· 85

Figure D8.       1971 summer rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1970 Sep – 1971 Feb inclusive).······················································································· 85

Figure D9.       1972 summer rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1971 Sep – 1972 Feb inclusive).······················································································· 86

Figure D10. 1973 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1972 Sep – 1973 Feb inclusive).······················································································· 86

Figure D11. 1974 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1973 Sep – 1974 Feb inclusive).······················································································· 87

Figure D12. 1975 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1974 Sep – 1975 Feb inclusive).······················································································· 87

Figure D13. 1976 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1975 Sep – 1976 Feb inclusive).······················································································· 88

Figure D14. 1977 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1976 Sep – 1977 Feb inclusive).······················································································· 88

Figure D15. 1978 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1977 Sep – 1978 Feb inclusive).······················································································· 89

Figure D16. 1979 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1978 Sep – 1979 Jan inclusive). ······················································································· 89

Figure D17. 1980 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1979 Aug – 1979 Dec inclusive). ····················································································· 90

Figure D18. 1981 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1980 Aug – 1981 Jan inclusive). ······················································································ 90

Figure D19. 1982 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1981 Aug – 1982 Jan inclusive). ······················································································ 91



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Figure D20. 1983 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1982 Aug – 1983 Jan inclusive). ······················································································ 91

Figure D21. 1984 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1983 Aug – 1984 Jan inclusive). ······················································································ 92

Figure D22. 1985 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1984 Jul – 1985 Jan inclusive).························································································· 92

Figure D23. 1986 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1985 Jul – 1986 Jan inclusive).························································································· 93

Figure D24. 1987 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1986 Jul – 1987 Jan inclusive).························································································· 93

Figure D25. 1988 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1987 Jul – 1988 Jan inclusive).························································································· 94

Figure D26. 1989 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1988 Jul – 1989 Jan inclusive).························································································· 94

Figure D27. 1990 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1989 Jul – 1990 Jan inclusive).························································································· 95

Figure D28. 1991 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1990 Jul – 1991 Jan inclusive).························································································· 95

Figure D29. 1992 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1991 Jul – 1992 Jan inclusive).························································································· 96

Figure D30. 1993 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1992 Jul – 1993 Jan inclusive).························································································· 96

Figure D31. 1994 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1993 Jul – 1994 Jan inclusive).························································································· 97

Figure D32. 1995 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1994 Jul – 1995 Jan inclusive).························································································· 97

Figure D33. 1996 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1995 Jul – 1996 Jan inclusive).························································································· 98

Figure D34. 1997 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1996 Jul – 1997 Feb inclusive).························································································ 98

Figure D35. 1998 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1997 Aug – 1998 Mar inclusive). ····················································································· 99

Figure D36. 1999 summer rainfall spatial distribution around the Murray irrigation area in NSW.
            (1998 Aug – 1999 Mar inclusive). ····················································································· 99




                                                                    - xiii -
                        Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                                List of Figures in Appendix E

Figure E1.       1964 winter rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1964 Mar – 1964 Aug inclusive). ·················································································· 101

Figure E2.       1965 winter rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1965 Mar – 1965 Aug inclusive). ·················································································· 101

Figure E3.       1966 winter rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1966 Mar – 1966 Aug inclusive). ·················································································· 102

Figure E4.       1967 winter rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1967 Mar – 1967 Aug inclusive). ·················································································· 102

Figure E5.       1968 winter rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1968 Mar – 1968 Aug inclusive). ·················································································· 103

Figure E6.       1969 winter rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1969 Mar – 1969 Aug inclusive). ·················································································· 103

Figure E7.       1970 winter rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1970 Mar – 1970 Aug inclusive). ·················································································· 104

Figure E8.       1971 winter rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1971 Mar – 1971 Aug inclusive). ·················································································· 104

Figure E9.       1972 winter rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1972 Mar – 1972 Aug inclusive). ·················································································· 105

Figure E10. 1973 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1973 Mar – 1973 Aug inclusive). ·················································································· 105

Figure E11. 1974 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1974 Mar – 1974 Aug inclusive). ·················································································· 106

Figure E12. 1975 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1975 Mar – 1975 Aug inclusive). ·················································································· 106

Figure E13. 1976 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1976 Mar – 1976 Aug inclusive). ·················································································· 107

Figure E14. 1977 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1977 Mar – 1977 Aug inclusive). ·················································································· 107

Figure E15. 1978 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1978 Mar – 1978 Aug inclusive). ·················································································· 108

Figure E16. 1979 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1979 Feb – 1979 Jul inclusive).····················································································· 108

Figure E17. 1980 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1980 Jan – 1980 Jul inclusive).······················································································ 109

Figure E18. 1981 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1981 Feb – 1981 Jul inclusive).····················································································· 109

Figure E19. 1982 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1982 Feb – 1982 Jul inclusive).····················································································· 110



                                                                   - xiv -
                        Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW



Figure E20. 1983 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1983 Feb – 1983 Jul inclusive).····················································································· 110

Figure E21. 1984 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1984 Feb – 1984 Jun inclusive). ···················································································· 111

Figure E22. 1985 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1985 Feb – 1985 Jun inclusive). ···················································································· 111

Figure E23. 1986 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1986 Feb – 1986 Jun inclusive). ···················································································· 112

Figure E24. 1987 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1987 Feb – 1987 Jun inclusive). ···················································································· 112

Figure E25. 1988 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1988 Feb – 1988 Jun inclusive). ···················································································· 113

Figure E26. 1989 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1989 Feb – 1989 Jun inclusive). ···················································································· 113

Figure E27. 1990 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1990 Feb – 1990 Jun inclusive). ···················································································· 114

Figure E28. 1991 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1991 Feb – 1991 Jun inclusive). ···················································································· 114

Figure E29. 1992 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1992 Feb – 1992 Jun inclusive). ···················································································· 115

Figure E30. 1993 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1993 Feb – 1993 Jun inclusive). ···················································································· 115

Figure E31. 1994 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1994 Feb – 1994 Jun inclusive). ···················································································· 116

Figure E32. 1995 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1995 Feb – 1995 Jun inclusive). ···················································································· 116

Figure E33. 1996 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1996 Feb – 1996 Jun inclusive). ···················································································· 117

Figure E34. 1997 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1997 Mar – 1997 Jul inclusive). ···················································································· 117

Figure E35. 1998 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1998 Mar – 1998 Jul inclusive). ···················································································· 118

Figure E36. 1999 winter rainfall spatial distribution around the Murray irrigation area in NSW.
            (1999 Mar – 1999 Jul inclusive). ···················································································· 118




                                                                   - xv -
                        Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                                List of Figures in Appendix F

Figure F1.       1964 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1963 Sep – 1964 Aug inclusive).··················································································· 120

Figure F2.       1965 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1964 Sep – 1965 Aug inclusive).··················································································· 120

Figure F3.       1966 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1965 Sep – 1966 Aug inclusive).··················································································· 121

Figure F4.       1967 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1966 Sep – 1967 Aug inclusive).··················································································· 121

Figure F5.       1968 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1967 Sep – 1968 Aug inclusive).··················································································· 122

Figure F6.       1969 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1968 Sep – 1969 Aug inclusive).··················································································· 122

Figure F7.       1970 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1969 Sep – 1970 Aug inclusive).··················································································· 123

Figure F8.       1971 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1970 Sep – 1971 Aug inclusive).··················································································· 123

Figure F9.       1972 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
                 (1971 Sep – 1972 Aug inclusive).··················································································· 124

Figure F10. 1973 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1972 Sep – 1973 Aug inclusive).··················································································· 124

Figure F11. 1974 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1973 Sep – 1974 Aug inclusive).··················································································· 125

Figure F12. 1975 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1974 Sep – 1975 Aug inclusive).··················································································· 125

Figure F13. 1976 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1975 Sep – 1976 Aug inclusive).··················································································· 126

Figure F14. 1977 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1976 Sep – 1977 Aug inclusive).··················································································· 126

Figure F15. 1978 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1977 Sep – 1978 Aug inclusive).··················································································· 127

Figure F16. 1979 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1978 Sep – 1979 Jul inclusive).····················································································· 127

Figure F17. 1980 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1979 Aug – 1980 Jul inclusive). ···················································································· 128

Figure F18. 1981 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1980 Aug – 1981 Jul inclusive). ···················································································· 128

Figure F19. 1982 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1981 Aug – 1982 Jul inclusive). ···················································································· 129



                                                                   - xvi -
                         Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW



Figure F20. 1983 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1982 Aug – 1983 Jul inclusive). ···················································································· 129

Figure F21. 1984 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1983 Aug – 1984 Jun inclusive). ··················································································· 130

Figure F22. 1985 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1984 Jul – 1985 Jun inclusive). ····················································································· 130

Figure F23. 1986 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1985 Jul – 1986 Jun inclusive). ····················································································· 131

Figure F24. 1987 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1986 Jul – 1987 Jun inclusive). ····················································································· 131

Figure F25. 1988 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1987 Jul – 1988 Jun inclusive). ····················································································· 132

Figure F26. 1989 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1988 Jul – 1989 Jun inclusive). ····················································································· 132

Figure F27. 1990 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1989 Jul – 1990 Jun inclusive). ····················································································· 133

Figure F28. 1991 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1990 Jul – 1991 Jun inclusive). ····················································································· 133

Figure F29. 1992 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1991 Jul – 1992 Jun inclusive). ····················································································· 134

Figure F30. 1993 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1992 Jul – 1993 Jun inclusive). ····················································································· 134

Figure F31. 1994 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1993 Jul – 1994 Jun inclusive). ····················································································· 135

Figure F32. 1995 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1994 Jul – 1995 Jun inclusive). ····················································································· 135

Figure F33. 1996 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1995 Jul – 1996 Jun inclusive). ····················································································· 136

Figure F34. 1997 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1996 Jul – 1997 Jul inclusive). ······················································································ 136

Figure F35. 1998 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1997 Aug – 1998 Jul inclusive). ···················································································· 137

Figure F36. 1999 yearly rainfall spatial distribution around the Murray irrigation area in NSW.
            (1998 Aug – 1999 Jul inclusive). ···················································································· 137




                                                                   - xvii -
                  Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




1. Introduction

Water table change is dominated by the groundwater recharge and discharge process affected
by many factors. The groundwater balance for a region for a given period can be expressed as:

 Inflow to Groundwater - Outflow from Groundwater = ± Groundwater Storage Change (∆S)

Or:
                                     Recharge – Discharge = ± ∆S                       (1)

Water inflows (recharge) to a regional groundwater system, according to their sources, can be
classified as:
     Isw - inflow from surface water in the natural waterways (rivers, creeks, etc.);
     Iirr.ch - inflow from water in the irrigation channel system;
     Iswb - inflow from static surface water bodies such as reservoirs and farm dams;
     Iirr - inflow from irrigation water applied to the farmland;
     Ir      - inflow from rainfall fallen directly to the region;
     If      - inflow from floodwater in the inundated area other than natural waterways;
     Ig      - inflow from regional groundwater system into the area, including possible upward
               flow from deep groundwater;

While outflows (discharge) from regional groundwater system according to their outlets can
be classified as:
    Osw - outflow from groundwater to surface water in the natural waterways (rivers, creeks,
    etc.), which could be significant during low streamflow period when groundwater table is
    higher than the streamflow level in the adjacent areas to the streamflow;
    Oirr.ch - outflow from groundwater to the irrigation channel system, which could happen
    during non-irrigation season;
    Oswb - outflow from groundwater to static surface water body such as reservoirs and farm
    dams;
    Oe - outflow by evapotranspiration through water supply by capillary upflow and
    vegetation uptake;
    Op - outflow by groundwater pumping;
    Odra - outflow through artificial drainage system other than groundwater pumping, where
    depth of drainage channel is greater than the depth of groundwater table;
    Og - outflow through groundwater flow underground out of regional boundary and
    through possible leakage to deep groundwater system further down below.

Thus the groundwater balance can be expressed as:

(Isw + Iirr.ch + Iswb + Iirr + Ir + Ig + If) – (Osw + Oirr.ch + Oswb + Oe + Op + Odra + Og) = ±∆S       (2)

For certain length of time interval, for example on yearly basis, under average weather
conditions some of the inflow terms could offset their outflow counterparts or their combined
effect could be relatively constant, for instance:
        (Isw + Iirr.ch + Iswb) - (Osw + Oirr.ch+ Oswb) ≈ C
        Ig - Og ≈ 0
        If ≈ 0 (suppose no inundating flood happened)


                                                         -1-
                Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




Where C is assumed to be a constant. Thus the groundwater balance equation can be
simplified as:

                         (Iirr + Ir) – (Oe + Op + Odra) + C ≈ ±∆S                      (3)

For areas such as Wakool with a very flat ground slope and relatively heavy soil type
therefore with a low hydraulic conductivity over the area, horizontal groundwater movement
within the soil can be expected to be very slow for most of the area. The average storage
coefficient or specific yield (Sy) for the shallow aquifer in this area is estimated in the range
of 0.03 ~ 0.05 (Wang, et al, 2003; Smith, et al, 1943). This is reflected by the high salinity of
shallow groundwater in this area due to the poor groundwater circulation conditions and
having been a discharge area in the geological history. The shallow groundwater quality
survey in 2000 showed that more than 90% of the area had shallow groundwater salinity
greater than 10,000EC (approximately equivalent to 6.2g/l total dissolved solid) (WCLWMP,
2001).


2. The Study Area

The Murray Irrigation Area (most part of the Murray LWMP area) is one of the largest
irrigation areas in the well-known Murray Darling Basin and is located in the south NSW, just
north of the Murray River across NSW – Victoria border (Fig. 1).


                                                                                             Murrumbidgee
                                                                                             Irrigation Area

                                                                          Griffith
                                              Hay



                                                                                              Coleambally
                                                                                             Irrigation Area



   Wakool                       Wakool

                                                    Deniliquin
                                                                 Finley
                                                                                     Murray Land and Water
                                                                                     Management Plan Area



                                                             Shepparton



                 Murray Darling Basin
            Figure 1. Location of the Wakool area and major irrigation areas in south NSW.



                                                       -2-
                 Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




The Wakool area, which is also known as Wakool Irrigation District, is the northwest part of
the Murray Irrigation Area and is one of its four irrigation districts consisting of Berriquin,
Cadell, Denimein and Wakool. Wakool is also the name of the major town established in the
Wakool area in 1927. The total area of the Wakool area is around 230,000 hectares (Fig. 1).

Irrigation diverted from a surface water source was started in 1935 in this area. Rice has been
grown in this area since as early as 1943. Due to the success of rice crop in this area, irrigated
area and water use were expanded significantly from the 1970’s to the 1980’s and stabilized
since then (WCLWMP, 2001). Based on data from 1984 to 1992, the average amount for each
water use in percentage to total water use in this area is given in Table 1 (WCLWMP, 2001).

                       Table 1. Average water use by different categories.
                                 Crop            Water Use (%)
                        Rice                             55
                        Annual Pasture                   29
                        Permanent Pasture                 8
                        Cereal                            4
                        Other                             3
                        Stock and Domestic                1
                        Total                          100


Rice is the major crop and income source for the farmers in this area. The highest annual total
water use ever recorded is around 400,000ML, which happened in 1992. The average annual
total water use from late 1970’s to late 1990’s is around 250,000ML. (WCLWMP, 2001).

While increase in irrigated area has brought benefit to the economy, it also brought land and
water management problems with the increased irrigation water brought into this area. The
topography, geological structure, soil type makes this area prone to water logging due to poor
natural drainage conditions.

This area is located in the converging area of several rivers and creeks (see Fig. 1). Due to its
flood plain nature and flatness, the hydraulics of flood could easily expand and change the
waterways. This is reflected by the well-developed and relatively dense natural waterways in
this area, with waterways of the same source being divided into several branches in some area
and converged together at other area. The major natural surface waterways wandering around
this area include:
    • the Murray River;
    • the Edward River (also known as Kyalite River, a branch of the Murray River);
    • the Wakool River (a branch of the Edward River and could also get its water from the
        Goulburn River);
    • the Billabong Creek (also known as Moulamein Creek with one of its upstream
        tributaries, the Yanko Creek, branched from the Murrumbidgee River);
    • the Niemur River (developed within the Wakool area and could also receive water
        from the Edward River).

The nature of its geographical location makes this area flood prone. The 1956 flood inundated
around 50% of this area. With the development of the Murray Irrigation Area and other
irrigation areas, several dams have been built in the upstream areas. This has increased
security of irrigation water supply and reduced chances of flooding.

                                                        -3-
                Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




The climate around this area can be described as warm temperate and transitional from
semiarid zone to arid zone with average annual rainfall within the range of 350mm ~ 400mm
(see Fig. 2, 3, 4).

The rainfall generally decreases from southeast towards northwest with a high temporal
variability from year to year. The annual rainfall in extreme wet years could be 7~8 times as
much as that in extreme dry years (see Fig.4, Fig. 7-8).

The mean monthly rainfalls for each month in the year are relatively evenly distributed with a
little bit more in the winter months than that in the summer months (see Fig. 4). However, the
actual monthly rainfalls are highly variable from month to month and from year to year. Fig. 4
shows that zero rainfall could happen in any month in the year and the maximum monthly
rainfall could be 8~9 times as much as the mean monthly rainfall.

Extreme monthly rainfall could also happen in relatively closely adjacent months. For
example, as recorded at Moulamein Post Office, the maximum monthly rainfall ever recorded
for the month of October, January, and April happened in Oct. 1973, Jan. 1974 and Apr. 1974,
which caused serious flood contributed by both local rainfall and rainfall in the upstream
areas. The similar rainfall pattern also happened in 1956 in which 152.6mm rain fell in March
and 101mm fell in May with large portion of the rain fallen in a short period. The maximum
daily rainfall ever recorded at Moulamein Post Office is 130.8mm, which happened on Nov.
17 1889.

Under extremely dry weather conditions there could be no rain at all for several consecutive
months as happened from August to October in 1914 and from December 1925 to February
1926. Without irrigation, agriculture in this area would be much more vulnerable to weather
conditions.

Determined by its location, latitude and elevation, the temperature in this area is warm to hot
in the summer and cool to mild in the winter. The maximum temperature recorded for the
period of 1971-1975 was 43°C (Dec. 21-22, 1972) and the minimum was -2.8°C (July 1,
1971). In some extremely hot days, the daily minimum temperature can go as high as 26°C as
has happened in Jan. 24, 1973. Due to its inland location, daily temperature range can be over
20°C with 25.6°C recorded on Jan. 2, 1973 (maximum 42.1°C, minimum 16.5°C for that day).
Mean monthly temperature is shown in Fig. 2.

Temporal distribution of monthly pan evaporation shown in Fig. 3 has the similar pattern to
that of monthly temperature, which reflects the effect of temperature on evaporation.




                                                       -4-
                                              Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                                          Monthly Average Daily Temperature
                                                              At Moulamein Post Office
                                                                             (1971 - 1975)
                                  35

                                  30                                              Max
                                                                                  Min
   Temperature (oC)




                                  25
                                                                                  Average
                                  20

                                  15

                                  10

                                   5

                                   0
                                    Jan       Feb      Mar      Apr      May       Jun      Jul      Aug      Sep       Oct         Nov    Dec
                                                                                     Month

Figure 2. Monthly average daily temperature at Moulamein Post Office. (Data source:
          BOM).



                                             Average Observed Monthly Pan Evaporation At Wakool
                                                                            (1974 - 1979 average)
                                  300.0


                                  250.0
       Monthly Evaporation (mm)




                                                                            (Annual average = 1552.6mm)
                                  200.0


                                  150.0


                                  100.0


                                   50.0


                                       0.0
                                             Jan    Feb      Mar      Apr    May      Jun      Jul     Aug     Sep      Oct     Nov       Dec
                                                                                         Month

Figure 3. Monthly pan evaporation at NSW Water Resources Commission’s observation
          station in Wakool (Data source: BOM).




                                                                                     -5-
                                   Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                                   Monthly Rainfall Statistics At Moulamein Post Office
                                                                                                                                     Dec 1930
                    200.0    Jan 1974                                                                                                (190.2mm)
                            (180.8mm)
                    180.0                                                 Jun 1923
                                               Mar 1906
                                                                         (160.3mm)
                    160.0                     (154.2mm)

                    140.0             Feb 1946                                                    Aug 1958
                                     (151.1mm)                                                   (123.7mm)                 Nov 1889
    Rainfall (mm)




                                                                                                                          (145.9mm)
                    120.0
                                                        Apr 1974
                    100.0                              (122.4mm) May 1906                                 Sep 1906 Oct 1973            Avg
                                                                                      Jul 1936           (111.7mm) (114.9mm)
                                                                 (110.4mm)                                                             Max
                     80.0                                                            (103.3mm)
                                                                                                                                       Min
                     60.0                                                                                                              StDev

                     40.0

                     20.0

                      0.0
                             Jan        Feb      Mar      Apr     May        Jun           Jul     Aug       Sep    Oct        Nov       Dec
                                                                                   Month


Figure 4. Monthly rainfall statistics at Moulamein Post Office (Data source: Bureau of
          Meterology. Data period: 1888 - 1999).



3. Data Collection

3.1. Piezometric data

All piezometric data for the study area are obtained from Murray Irrigation Limited (MIL).
There has been a total of 1480 piezometers established and monitored around the Wakool area
with data available for some of them since as early as 1963. The piezometric data has been
collected upto March 2001.

These piezometers may have been established for different purposes at different times and
thus there is some inconsistency in the number of readings taken in a year and times at which
the readings were taken. In other words, data density varies both temporally and spatially.
Some statistics about the piezometric data are listed in Table 2 and the temporal distribution
of the data is shown in Fig. 5, Fig. 6.

Table 2. Summary of piezometric data collected.
Total number of monitored piezometers:                                                                1480
Total data period:                                                                                    1963 Dec ~ 2001 Mar
Total number of years (up to 2001 Mar) the data covered:                                              38
Number of months in which readings were taken:                                                        112
Maximum number of readings taken for a single piezo:                                                  106
Minimum number of readings taken for a single piezo:                                                  0 (i.e. data n/a)
Maximum frequency of readings taken per a year:                                                       7 (in 1982)
Frequency of readings taken for most of the period:                                                   Quarterly or biannually
Average number of readings taken per piezo over the                                                   33.9
whole data period (1963 Dec ~ 2001 Mar):
Number of piezos with no data (or data not available):                                                4.3%




                                                                             -6-
                Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




Before 1978, the readings were normally taken once every quarter in the year in the month of
Mar, Jun, Sep, and Dec respectively, with months in which data available the most being Mar.
and Sep which approximately delineates the end and start of peak irrigation season.

After 1978, the readings have been generally taken twice a year. The months in which the
readings were taken were not same for each year, with majority of the readings taken in Feb
and July while in some years readings were taken in Mar and Aug. Occasionally readings
were taken in Jan and Aug.

As shown in Table 2 and Fig. 5-6, among the 1480 piezometers 4.3% has no data or data not
available, around 60% has the available data less than the average readings per piezometer,
and around 70% has less than 40 readings out of the maximum possible of 112 over the whole
data period.

The piezometric data obtained from MIL were in several separate files collated for different
period at different times. These data are re-collated and compiled into one file by matching
the data by its bore number with the unique bore number or site ID listed in the master bore
file for each of the piezometers. The data are further assessed for frequencies of readings per
year, months in which readings were taken, period of available data, etc., as summarized in
Fig. 5-6.

After bores without any data or coordinate information were removed, the data is converted
into an ArcView GIS database by geo-coding of the master bore file which has bore location
coordinates. This GIS database consists a total number of 1417 bores with each bore having at
least one reading for the period of 1963 Dec ~ 2001 Mar.




                                                       -7-
                                                                                                                        Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                                                                                                                 Number of Piezos with Data Available over the Time
                                                                                                                                                                               Total Number of Piezos = 1464
                                1300

                                1200

                                1100

                                1000
   Number of Piezos with data




                                 900

                                 800

                                 700

                                 600

                                 500

                                 400

                                 300

                                 200

                                 100

                                  0
                                       63-Jan

                                                64-Jan

                                                         65-Jan

                                                                  66-Jan

                                                                           67-Jan

                                                                                    68-Jan

                                                                                             69-Jan

                                                                                                      70-Jan

                                                                                                               71-Jan

                                                                                                                        72-Jan

                                                                                                                                  73-Jan

                                                                                                                                           74-Jan

                                                                                                                                                    75-Jan

                                                                                                                                                             76-Jan

                                                                                                                                                                      77-Jan

                                                                                                                                                                                78-Jan

                                                                                                                                                                                         79-Jan

                                                                                                                                                                                                  80-Jan

                                                                                                                                                                                                           81-Jan

                                                                                                                                                                                                                    82-Jan

                                                                                                                                                                                                                             83-Jan

                                                                                                                                                                                                                                      84-Jan

                                                                                                                                                                                                                                               85-Jan

                                                                                                                                                                                                                                                        86-Jan

                                                                                                                                                                                                                                                                 87-Jan

                                                                                                                                                                                                                                                                          88-Jan

                                                                                                                                                                                                                                                                                   89-Jan

                                                                                                                                                                                                                                                                                            90-Jan

                                                                                                                                                                                                                                                                                                     91-Jan

                                                                                                                                                                                                                                                                                                              92-Jan

                                                                                                                                                                                                                                                                                                                       93-Jan

                                                                                                                                                                                                                                                                                                                                94-Jan

                                                                                                                                                                                                                                                                                                                                         95-Jan

                                                                                                                                                                                                                                                                                                                                                  96-Jan

                                                                                                                                                                                                                                                                                                                                                           97-Jan

                                                                                                                                                                                                                                                                                                                                                                    98-Jan

                                                                                                                                                                                                                                                                                                                                                                             99-Jan

                                                                                                                                                                                                                                                                                                                                                                                      00-Jan
                                                                                                                                                                                                   Year and Month

                                                                                                                                                                                         Total Number of Years: 37

Figure 5. Temporal distribution of the number of piezometers with data available for Wakool area.

                                                                                                                                                                                                     -8-
                                               Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                                        Number of Readings vs Number of Piezos

                        120




                        100




                         80
   Number of Readings




                         60




                         40




                         20




                          0
                              0%   10%   20%            30%              40%              50%              60%               70%     80%   90%   100%
                                          Number of Piezos (%) with Number of Readings Less Than Corresponding Number


Figure 6. Accumulated percentage of number of piezometers vs. number of readings over the data period (1


                                                                                      -9-
                                 Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW



3.2. Rainfall data

The rainfall data is sourced from the Bureau Of Meteorology (BOM) and collected via
Horizontech Pty Ltd. A software package, MetAccess for Windows Version 1.04
developed by CSIRO, was used to access the data. The minimum time interval of the
rainfall data in the database is daily. The rainfall data can be easily extracted via
MetAccess in monthly or yearly form for any station in the database for any period
within the period from the date the station started collecting data upto 1999 or the date
the station ceased.

In order to generate spatial distribution of rainfall to calculate the total volume of rain
water fallen onto Wakool area, those rainfall gauging stations around the MIL area with
data available for the study period (1963 –2000) were selected, a total of 84 stations.
Monthly rainfall data were extracted for the 84 stations via MetAccess. The extracted
data were examined to remove questionable numbers by comparing with data from
adjacent stations before used in the analysis.

The information about these stations along with their data is then converted to GIS
databases in a format that is ready for use in the analysis. Fig. 7 shows locations of the
selected rainfall gauging stations.

                                                                                                                                                                                                    #
                                                                                                                                                                                                    S
                S
                #
                                                                                                                                                                  S
                                                                                                                                                                  #                                         #
                                                                                                                                                                                                            S       S
                                                                                                                                                                                                                    #
                                         S
                                         #
                                                                                                   Selected Rainfall Stations
#
S
            10          0   10 20 30 40 50
                                                                                               #
                                                                                               S

                            Kilometres                                                         Moulameim Post Office
                                                                                               (Station no: 75046)            S
                                                                                                                              #                                                         #
                                                                                                                                                                                        S
                                                                                                                                                     S
                                                                                                                                                     #
                                                                                                             S
                                                                                                             #
                                             #
                                             S
                                                                                   S
                                                                                   #
                                                                                                                                                  Wakool (Calimo)
                                                                   S
                                                                   #                                                      S
                                                                                                                          #                       (Station no: 75012)
        #
        S                    S
                             #   S
                                 #

                                 #
                                 S                                                                                S
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        S                                                                                                             S
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    S
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#
S                                                              #
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                                                                                                                                              S


                                                     Selected rainfall gauging station.                                           Main road.


                                                     Boundary of the Wakool Irrigation District.                                                                    Irrigation
                                                                                                                                  Boundary of the area under Murray LWMP. Ltd.


Figure 7. Spatial distribution of rainfall stations selected for this study (total: 84).


Fig. 8 and Fig. 9 show the annual rainfall recorded in two of the long-term rainfall
stations (see Fig. 7) in this area since rainfall gauging started at the two stations
indicated in the figures, reflecting temporal rainfall variability in this area.

                                                                                                                 - 10 -
                                        Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                                               Yearly Rainfall At Moulamein Post Office

                        900
                                                                           Average:     356mm
                        800                                                Median:      347.9mm
                                                                           Maximum:     762.4mm (1974)
                        700                                                Minimum:     118.9mm (1967)
                                                                           Range:       643.5mm
 Annual Rainfall (mm)




                                          Average
                        600               (356mm)                          Std. Dev:    124.2mm

                        500

                        400

                        300

                        200


                        100

                         0
                              1889
                              1891
                              1893
                              1895
                              1897
                              1899
                              1901
                              1903
                              1905
                              1907
                              1909
                              1911
                              1913
                              1915
                              1917
                              1919
                              1921
                              1923
                              1925
                              1927
                              1929
                              1931
                              1933
                              1935
                              1937
                              1939
                              1941
                              1943
                              1945
                              1947
                              1949
                              1951
                              1953
                              1955
                              1957
                              1959
                              1961
                              1963
                              1965
                              1967
                              1969
                              1971
                              1973
                              1975
                              1977
                              1979
                              1981
                              1983
                              1985
                              1987
                              1989
                              1991
                              1993
                              1995
                              1997
                              1999
                                                                                           Year

Figure 8. Annual rainfall at Moulamein Post Office (Station no: 75046, rainfall for
          years with incomplete data are not shown). (Data source: Bureau of
          Meterology)



                                                                  Yearly Rainfall At Wakool (Calimo)

                        1000                                 Average:    379.6mm
                                                             Median:     364.1mm
                         900
                                                             Maximum:    873.2mm (1956)
                                                                                                                              1973
                         800
                                                             Minimum:    118.2mm (1934)
                                                             Range:      755.0mm
 Annual Rainfall (mm)




                         700                                 Std. Dev:   150.1mm
                                   Average
                                  (379.6mm)
                         600

                         500

                         400

                         300

                         200

                         100

                              0
                                  1896
                                  1898
                                  1900
                                  1902
                                  1904
                                  1906
                                  1908
                                  1910
                                  1912
                                  1914
                                  1916
                                  1918
                                  1920
                                  1922
                                  1924
                                  1926
                                  1928
                                  1930
                                  1932
                                  1934
                                  1936
                                  1938
                                  1940
                                  1942
                                  1944
                                  1946
                                  1948
                                  1950
                                  1952
                                  1954
                                  1956
                                  1958
                                  1960
                                  1962
                                  1964
                                  1966
                                  1968
                                  1970
                                  1972
                                  1974
                                  1976
                                  1978
                                  1980
                                  1982
                                  1984
                                  1986
                                  1988
                                  1990
                                  1992
                                  1994
                                  1996
                                  1998




                                                                                           Year

Figure. 9. Annual rainfall at Wakool (Calimo) (Station no: 75012, rainfall for years
           with incomplete data are not shown ). (Data source: Bureau of Meterology)



4. Differentiation of Climatic and Management Impact on Shallow Water Table

As indicated in the section of introduction, there are many factors affecting water table
changes. In order to differentiate between climatic and management impact on water
table, there is a need to define a way to achieve it based on the data collected. For most


                                                                               - 11 -
              Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW

of the years within the data period, the detailed process of water table change can hardly
be defined due to the low frequencies of piezometric readings. This means the highest
and lowest water table in the year may not be reflected by the piezometric readings
taken.

However, with majority of the piezometric readings were taken at around the start and
end of the peak irrigation seasons, which are also normally around low and high water
table period in this irrigation area, the difference between the readings taken at start and
end of a peak irrigation season reflects the combined impact of both management and
climate on water table for that season.

Based on the available data and the common water table change pattern in irrigation
areas, a simple method was developed to define water table change from that under
average climatic conditions and management practices within the period between the
two piezometric readings.

It is assumed that the average seasonal water table change, winter or summer, can be
used to represent the combined impact under average climatic conditions and
management practices. It is further assumed that for any given season or year, there has
been no significant change in management practices over the data period. Thus, water
table change from that of average reflects climatic impact.

Based on the above assumptions, the average water table change for a particular
piezometer can be expressed as:
                          1 n                               1 n
                    ∆x p = ∑ ( x pi _ end − x pi _ start ) = ∑ ∆x pi (4)
                          n i =1                            n i =1
where: ∆x p is the average water table change for piezometer p;
       n is the number of seasons or years;
       x pi _ end is the reading of piezometer p at the end of the season or year in year i;

        x pi _ start is the reading of piezometer p at the start of the season or year in year i.

        ∆x pi is the water table change for the season or year in year i;

Then the climatic impact on shallow groundwater reflected by the piezometric readings
for a particular piezometer in year i can be expressed as:

                                      ∆X pi = ∆x pi − ∆x p          (5)

where: ∆X pi is the water table change from the average water table change for
piezometer p for the season or year in year i, and assumed to be the change due to the
climatic impact.

Fig. 10 illustrates average water table change for a piezometer for peak irrigation
seasons, which is normally consistent with summer seasons, over the years. The same
concept can also be applied to the winter seasons and whole years.




                                                    - 12 -
                                             Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                                                                                            Illustration of Average Water Table Change

                          1.80
                          1.60
                                                                                                                                                                                        x p (i+4 )_ end

                          1.60
                          1.80                                                 x p (i+1)_ end                   x p (i+2 )_ end                 x p (i+3 )_ end                    x p (i+4 )

                                                                                                                   x p (i+2 )             x p (i+3 ) x p (i+4 )_ s tart
  Water Table Depth (m)




                          2.00
                          1.40
                                                                                           x p (i+1)
                                                                                                                       x p (i+3 )_ s tart
                                          x p (i)_ end                                            x p (i+2 )_ s tart
                          2.20
                          1.20

                                                                 x p (i+1)_ s tart
                          2.40
                          1.00
                                                                                                                          1 n                             1 n
                                                     x p (i)                                                        ∆x p = ∑(x pi _ end − x pi _ start ) = ∑∆x pi
                          2.60
                          0.80                                                                                            n i =1                          n i=1
                                      x p (i)_ s tart
                          2.80
                          0.60
                                            Jan-66

                                                        May-66




                                                                                  Jan-67

                                                                                              May-67



                                                                                                                  Jan-68

                                                                                                                           May-68



                                                                                                                                                   Jan-69

                                                                                                                                                            May-69



                                                                                                                                                                              Jan-70

                                                                                                                                                                                        May-70



                                                                                                                                                                                                          Jan-71

                                                                                                                                                                                                                   May-71



                                                                                                                                                                                                                                     Jan-72
                                 Sep-65




                                                                      Sep-66




                                                                                                       Sep-67




                                                                                                                                       Sep-68




                                                                                                                                                                     Sep-69




                                                                                                                                                                                                 Sep-70




                                                                                                                                                                                                                            Sep-71
                                                                                                                                                Date


Figure 10. Illustration of average water table change for peak irrigation seasons
           (summer seasons) over the years for a piezometer.


5. Data Processing

5.1. Quantifying water table change from average change

Based on the above concept, the piezometric data are further examined and processed.
There is a wide range of the total number of readings for different piezometers in the
available piezometric data (see Table 2). In order to balance the spatial and temporal
coverage of the piezometric data, those piezometers with less than 10 readings were
removed from the database to be used in the analysis.

The spatial distribution of the piezometers with data varies with different reading
months. The periods, for which piezometers with data covered the whole Wakool area
and seasonal water table change for both peak irrigation and non-peak irrigation seasons
can be derived, are 1971-1976 and 1979-1986. Most of the piezometers with data after
1987 have been located in the southern half of the Wakool area.

The total number of piezometers in the final GIS database is 819. The number of years
for which summer, winter and yearly water table change can be derived from a
piezometer is different for different piezometers, ranging from 7 to 35. Delineation of
the seasons, or time intervals, is based on the availability of piezometric data. The
delineation of seasons, number of piezometers with data from which the seasonal water
table change can be derived, and description of spatial coverage of the piezometers with
data in relation to the whole Wakool area are summarized in Table 3.

                                                                                                                                    - 13 -
            Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




Table 3. Spatial coverage of the piezometers and season delineation based on
piezometric data.
                        Time Delineation
            Summer           Winter              Year          Number of                           Spatial
 Year
         Start    End    Start     End     Start      End     Piezometers                         Coverage
         Month   Month  Month     Month    Month    Month
 1965    Sep-64 Mar-65 Mar-65     Sep-65 Sep-64       Sep-65       67                              partial
 1966    Sep-65 Mar-66 Mar-66     Sep-66 Sep-65       Sep-66      105                              partial
 1967    Sep-66 Mar-67 Mar-67     Sep-67 Sep-66       Sep-67       99                              partial
 1968    Sep-67 Mar-68 Mar-68     Sep-68 Sep-67       Sep-68      123                              partial
 1969    Sep-68 Mar-69 Mar-69     Sep-69 Sep-68       Sep-69      137                              partial
 1970    Sep-69 Mar-70 Mar-70     Sep-70 Sep-69       Sep-70      223                              partial
 1971    Sep-70 Mar-71 Mar-71     Sep-71 Sep-70       Sep-71      267                               full
 1972    Sep-71 Mar-72 Mar-72     Sep-72 Sep-71       Sep-72      285                               full
 1973    Sep-72 Mar-73 Mar-73     Sep-73 Sep-72       Sep-73      191                               full
 1974    Sep-73 Mar-74 Mar-74     Sep-74 Sep-73       Sep-74      173                               full
 1975    Sep-74 Mar-75 Mar-75     Sep-75 Sep-74       Sep-75      241                               full
 1976    Sep-75 Mar-76 Mar-76     Sep-76 Sep-75       Sep-76      373                               full
 1977    Sep-76 Mar-77 Mar-77     Sep-77 Sep-76       Sep-77       97                              partial
 1978    Sep-77 Mar-78 Mar-78     Sep-78 Sep-77       Sep-78       95                              partial
 1979    Sep-78 Feb-79 Feb-79     Aug-79 Sep-78       Aug-79      353                               full
 1980    Aug-79 Jan-80 Jan-80     Aug-80 Aug-79       Aug-80      407                               full
 1981    Aug-80 Feb-81 Feb-81     Aug-81 Aug-80       Aug-81      391                               full
 1982    Aug-81 Feb-82 Feb-82     Aug-82 Aug-81       Aug-82      392                               full
 1983    Aug-82 Feb-83 Feb-83     Aug-83 Aug-82       Aug-83      622                               full
 1984    Aug-83 Feb-84 Feb-84       Jul-84 Aug-83      Jul-84     673                               full
 1985     Jul-84 Feb-85 Feb-85      Jul-85  Jul-84     Jul-85     699                               full
 1986     Jul-85 Feb-86 Feb-86      Jul-86  Jul-85     Jul-86     695                               full
 1987     Jul-86 Feb-87 Feb-87      Jul-87  Jul-86     Jul-87     610                              partial
 1988     Jul-87 Feb-88 Feb-88      Jul-88  Jul-87     Jul-88     628                              partial
 1989     Jul-88 Feb-89 Feb-89      Jul-89  Jul-88     Jul-89     642                              partial
 1990     Jul-89 Feb-90 Feb-90      Jul-90  Jul-89     Jul-90     637                              partial
 1991     Jul-90 Feb-91 Feb-91      Jul-91  Jul-90     Jul-91     573                              partial
 1992     Jul-91 Feb-92 Feb-92      Jul-92  Jul-91     Jul-92     583                              partial
 1993     Jul-92 Feb-93 Feb-93      Jul-93  Jul-92     Jul-93     601                              partial
 1994     Jul-93 Feb-94 Feb-94      Jul-94  Jul-93     Jul-94     595                              partial
 1995     Jul-94 Feb-95 Feb-95      Jul-95  Jul-94     Jul-95     579                              partial
 1996     Jul-95 Feb-96 Feb-96      Jul-96  Jul-95     Jul-96      88                              partial
 1997     Jul-96 Mar-97 Mar-97    Aug-97    Jul-96    Aug-97      289                              partial
 1998    Aug-97 Mar-98 Mar-98     Aug-98 Aug-97       Aug-98      313                              partial
 1999    Aug-98 Mar-99 Mar-99     Aug-99 Aug-98       Aug-99      349                              partial
 2000    Aug-99 Mar-00 Mar-00     Aug-00 Aug-99       Aug-00      350                              partial



After all of the ∆Xpi (see Equation (5)) were calculated, surfaces representing water
table change assumed resulting from climatic impact are generated for each of the
seasons and years in the ArcView GIS application from the GIS database, which are
shown in Appendix A, B, and C. The corresponding recharge, discharge, and total net
groundwater storage change are also calculated in the ArcView GIS. Fig. 11-13 show
the spatial distribution of the average water table change ∆x p (see Equation (4)) on
seasonal and yearly basis.


                                                  - 14 -
                Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                     Average water table change in summer season



                                                                                            River, Ck
                                                                                            Main Rd




                Relative WT
                Change (m)
                       <-1
                       -1- -0.8
                       -0.8--0.6
         up




                       -0.6--0.4
                       -0.4--0.2
                       -0.2-0
           WT
                       0- 0.2
                       0.2- 0.4
         down




                       0.4- 0.6
                       0.6- 0.8
                       0.8- 1
                       >1
                                     5   0      5   10 15 20

                                             Kilometers
Figure 11. Average water table change in summer season.



                    Average water table change in winter season



                                                                                            River, Ck
                                                                                            Main Rd




                Relative WT
                Change (m)
                       <-1
                       -1- -0.8
                       -0.8- -0.6
        up




                       -0.6- -0.4
                       -0.4- -0.2
                       -0.2- 0
          WT
                       0- 0.2
                       0.2- 0.4
        down




                       0.4- 0.6
                       0.6- 0.8
                       0.8- 1
                       >1
                                     5   0      5   10 15 20

                                           Kilometers
Figure 12. Average water table change in winter season.




                                                          - 15 -
                Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW




                    Average yearly water table change



                                                                                            River, Ck
                                                                                            Main Rd




                Relative WT
                Change (m)
                       <-1
                       -1- -0.8
                       -0.8- -0.6
         up




                       -0.6- -0.4
                       -0.4- -0.2
                       -0.2- 0
           WT
                       0- 0.2
                       0.2- 0.4
         down




                       0.4- 0.6
                       0.6- 0.8
                       0.8- 1
                       >1
                                     5   0    5   10 15 20

                                           Kilometers
Figure 13. Average yearly water table change.


Fig. 11-13 reflects the average combined effects of management and climate on shallow
water table in the Wakool area over the data period. It is shown that in most of the area
water table change in the summer season was compensated by water table change in the
winter season. On a yearly basis, shallow groundwater in most of the lower Wakool
area has been discharging and most of the upper Wakool area (northern part) has been
in a state of recharging.


5.2. Calculating corresponding rainfall

Computer programs were developed to extract and calculate total rainfalls for each of
the time interval listed in Table 3 for each of the selected 84 rainfall stations. Rainfall
accounted for each of the time intervals listed in Table 3 is determined by the start and
end month of that interval.

For example, if a winter season starts in March and ends in September in a year, then
the rainfall accounted for that season is the total rainfall from the beginning of March to
the end of August. If an irrigation year starts in September and ends in August in the
following year, then the rainfall accounted for that year is the total rainfall from the
beginning of September to the end of July in the following year.

Further GIS databases were developed to incorporate the calculated rainfalls. Surfaces
representing spatial distributions for each of the rainfalls were generated in the GIS
application. Fig. 14 shows an example of the spatial distribution of the total rainfall
fallen in the winter season of 1974 interpolated from the 84 rainfall stations. Maps


                                                        - 16 -
                                                Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW

showing the spatial distribution of rainfalls generated in the same way for each season
and year over the data period are attached in Appendix D, E, and F.


                                  Rainfall gauging station with no missing data for the specified time                                                                                                                                             Rainfall gauging station with missing data for the specified time
                                  interval.                                                                                                                                                                                                        interval and thus disregarded for the specified time interval.

                                  Boundary of the Wakool Irrigation District.                                                                                                              Boundary of the area under Murray LWMP. Ltd.
                                                                                                                                                                                                                             Irrigation                                                                                                                                            Main road.
                                                                                                                                                                                                                                                                                                                                                                                                                                           #
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                                                                                  #                   1974 Winter Rainfall
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                                                                                                                                                                                                                                                                                                                                                                                                                                               Rainfall (mm)
                         0 - 25
                                      25 - 50
                                                 50 - 75
                                                           75 - 100
                                                           75 - 100
                                                           75 - 100
                                                           75 - 100
                                                           75 - 100
                                                                      100 - 125
                                                                                      125 - 150
                                                                                                   150 - 175
                                                                                                               175 - 200
                                                                                                                               200 - 225
                                                                                                                                           225 - 250
                                                                                                                                                       250 - 275
                                                                                                                                                       250 - 275
                                                                                                                                                       250 - 275
                                                                                                                                                       250 - 275
                                                                                                                                                       250 - 275
                                                                                                                                                                   275 - 300
                                                                                                                                                                               300 - 325
                                                                                                                                                                                           325 - 350
                                                                                                                                                                                                           350 - 375
                                                                                                                                                                                                                       375 - 400
                                                                                                                                                                                                                                   400 - 425
                                                                                                                                                                                                                                               425 - 450
                                                                                                                                                                                                                                               425 - 450
                                                                                                                                                                                                                                               425 - 450
                                                                                                                                                                                                                                               425 - 450
                                                                                                                                                                                                                                               425 - 450
                                                                                                                                                                                                                                                           450 - 475
                                                                                                                                                                                                                                                                       475 - 500
                                                                                                                                                                                                                                                                                       500 - 525
                                                                                                                                                                                                                                                                                                   525 - 550
                                                                                                                                                                                                                                                                                                               550 - 575
                                                                                                                                                                                                                                                                                                                           575 - 600
                                                                                                                                                                                                                                                                                                                                           600 - 625
                                                                                                                                                                                                                                                                                                                                           600 - 625
                                                                                                                                                                                                                                                                                                                                           600 - 625
                                                                                                                                                                                                                                                                                                                                           600 - 625
                                                                                                                                                                                                                                                                                                                                           600 - 625
                                                                                                                                                                                                                                                                                                                                                       625 - 650
                                                                                                                                                                                                                                                                                                                                                                   650 - 675
                                                                                                                                                                                                                                                                                                                                                                                   675 - 700
                                                                                                                                                                                                                                                                                                                                                                                   675 - 700
                                                                                                                                                                                                                                                                                                                                                                                   675 - 700
                                                                                                                                                                                                                                                                                                                                                                                   675 - 700
                                                                                                                                                                                                                                                                                                                                                                                   675 - 700
                                                                                                                                                                                                                                                                                                                                                                                                   700 - 725
                                                                                                                                                                                                                                                                                                                                                                                                               725 - 750
                                                                                                                                                                                                                                                                                                                                                                                                                               750 - 800
Figure 14. 1974 winter rainfall spatial distribution around the Murray LWMP area in
           NSW. (1974 Mar – 1974 Aug inclusive, number of rainfall stations with no
           missing data for the period: 82).


Equivalent volumes of total rainfall over the Wakool area for each of the seasons and
years were then calculated based on the spatial distributions of the rainfall.


6. The Results

6.1 Rainfall and relative net groundwater storage

The net groundwater storage change assumed due to climate impact (or relative net
groundwater storage change) and the corresponding rainfall for each of the summer and
winter seasons with full data coverage over the whole Wakool area (see Table 3) are
presented in Fig. 15. Sy=0.03 is used to derive the net groundwater storage change
displayed in Fig. 15 (Wang et al, 2003).




                                                                                                                                                                                                                       - 17 -
                                         Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW


                                                              Seasonal Net Groundwater Storage Change
                                              (Note: Rainfall is spatially averaged rainfall over whole Wakool area for the same season )
                             80,000                                                                                                                0
                             70,000                                                                                                                100
Net GW Storage Change (ML)



                             60,000                                                                                                                200
                             50,000                                                                                                                300




                                                                                                                                                          Rainfall (mm)
                             40,000                                                                                 Summer Rain                    400
                                                                                                                    Winter Rain
                             30,000                                                                                                                500
                                                                                                                    Summer GW Change
                             20,000     Recharge                                                                                                   600
                                                                                                                    Winer GW Change
                             10,000    (WT rising)                                                                                                 700
                                  0                                                                                                                800
                             -10,000    Discharge                                                                                                  900
                                       (WT falling)
                             -20,000                                                                                                               1000




                                                                                                                                    1985

                                                                                                                                            1986
                                                                              1976




                                                                                                                    1983
                                       1971

                                               1972

                                                       1973

                                                                1974

                                                                       1975




                                                                                        1979

                                                                                               1980

                                                                                                      1981

                                                                                                             1982




                                                                                                                            1984
                                                                                           Year

Figure 15. Seasonal net groundwater storage change assumed due to impact of rainfall.
           (Note: Sy=0.03 is used to derive the net storage change.)


The correlations between the rainfalls and the net storage changes are shown in Fig. 16-
17. For comparison purpose those net storage changes derived by using Sy =0.05 are
also presented in these figures. The type of the trend lines presented in these figures is
the one that gives the highest correlation coefficient among the available types in MS
Excel.

The statistical relationships shown in Fig. 16-18 indicate strong correlations between
the net storage change and the corresponding rainfall for all the three selected time
intervals – summer, winter, and year. The highest correlation coefficient is the one for
winter seasons with R2=0.84, suggesting that impact of rainfall on groundwater is more
significant during winter seasons than that during summer seasons and whole years.
This also suggests that there are less management interferences and unaccounted
climatic fluctuations on the rainfall – groundwater relationship during winter seasons
than that during summer seasons and whole years.




                                                                                     - 18 -
                                                               Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW


                                                                     Summer Net Groundwater Change - Rainfall Relationship For Whole Wakool Area
                                                                                       (Average equivalent water depth over whole Wakool area)
                                                                                                                                                                                     (x10-2ML/ha)
                                             15.0                                                                                                                                         15.0

                                                                                                              y = -9E-05x2 + 0.101x - 17.04
Summer Net Groundwater Storage Change (mm)




                                                                                                                       R2 = 0.7034                           Sy=0.05
                                             10.0                                                                                                                                         10.0

                                                                                                                                                              Sy=0.03

                                              5.0                                                                                                                                         5.0

                                                                                                                                      y = -5E-05x2 + 0.0606x - 10.224
                                                           WT up                                                                                R2 = 0.7034
                                              0.0                                                                                                                                         0.0
                                                           WT down


                                              -5.0                                                                                                                      Sy=0.03           -5.0

                                                                                                                                                                        Sy=0.05

                                             -10.0                                                                                                                      Sy=0.03           -10.0

                                                                                                                                                                        Sy=0.05

                                             -15.0                                                                                                                                       -15.0
                                                     0.0       50.0       100.0       150.0      200.0       250.0         300.0         350.0         400.0            450.0        500.0

                                                                                                      Summer Rainfall (mm)

Figure 16. Correlation between summer net groundwater storage change due to
           climate impact and corresponding summer rainfall over the whole Wakool
           area



                                                                      Winter Net Groundwater Change - Rainfall Relationship For Whole Wakool Area

                                                                                                                                                                                    -2
                                                                                                                                                                                (x10 ML/ha)
                                             30.0

                                                                                                                                                                 Sy=0.05
                                             25.0                                                                                                                                        25.00
Winter Net Groundwater Storage Change (mm)




                                                                                                                       2
                                                                                                            y = 0.0002x + 0.0127x - 8.8889
                                                                                                                      R2 = 0.8393
                                             20.0

                                                                                                                                                                 Sy=0.03
                                             15.0                                                                                                                                        15.00

                                                           WT up
                                             10.0


                                              5.0                                                                                                                                        5.00
                                                                                                                                                  y = 0.0001x2 + 0.0076x - 5.3334
                                                                                                                                                            R2 = 0.8393
                                              0.0
                                                                                                                                                                          Sy=0.03

                                              -5.0                                                                                                                        Sy=0.05        -5.00

                                                                                                                                                                          Sy=0.03
                                             -10.0
                                                           WT down
                                                                                                                                                                          Sy=0.05

                                             -15.0                                                                                                                                      -15.00
                                                     0.0           50.0       100.0           150.0         200.0            250.0             300.0            350.0               400.0

                                                                                                      Winter Rainfall (mm)

Figure 17. Correlation between winter net groundwater storage change due to climate
           impact and corresponding winter rainfall over the whole Wakool area.




                                                                                                            - 19 -
                                                           Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW

                                                                 Yearly Net Groundwater Change - Rainfall Relationship For Whole Wakool Area
                                                                                  (Average equivalent water depth over whole Wakool area)
                                                                                                                                                                               (ML/ha)
                                             40.0                                                                                                                                 0.40

                                             35.0
                                                                                             y = -0.0001x2 + 0.1947x - 55.55
Yearly Net Groundwater Storage Change (mm)



                                                                                                                                          Sy=0.05
                                                                                                       R2 = 0.7539
                                             30.0                                                                                                                                 0.30

                                             25.0

                                             20.0                                                                                        Sy=0.03                                  0.20

                                             15.0

                                             10.0                                                                                                                                 0.10
                                                                                                                                    y = -6E-05x2 + 0.1168x - 33.33
                                                                                                                                             R2 = 0.7539
                                              5.0
                                                         WT up
                                              0.0                                                                                                                                 0.00
                                                         WT down                                                                                                     Sy=0.05
                                              -5.0
                                                                                                                                                                     Sy=0.03
                                             -10.0                                                                                                                                -0.10
                                                                                                                                                                     Sy=0.05

                                             -15.0                                                                                                                   Sy=0.03

                                             -20.0                                                                                                                              -0.20
                                                100.00      200.00       300.00          400.00          500.00            600.00         700.00            800.00         900.00

                                                                                                  Yearly Rainfall (mm)

Figure 18. Correlation between yearly net groundwater storage change due to climate
           impact and corresponding yearly rainfall over the whole Wakool area.


These relationships also revealed some interesting messages:
   • If the total rainfall for a summer season is around 200mm, the climate will have
       little impact on groundwater storage over the summer period. In other words, the
       water table change will be mainly caused by management actions. If the total
       summer rainfall is greater than 200mm, it will be likely to cause an extra net
       recharge to the groundwater on top of the net recharge or discharge due to
       management actions. If summer rainfall is less than 200mm, groundwater
       storage would likely to be reduced if there were no management impact.
   • Similarly, if the total rainfall for a winter season is around 170mm, it won’t
       affect net groundwater storage significantly for that season. If winter rainfall is
       greater than 170mm, it is likely to cause an extra net recharge to the
       groundwater on top of that caused by management. If winter rainfall is less than
       170mm, the climate will likely to have a reduction effect on groundwater storage;
   • For a whole year, the benchmark rainfall is around 350mm.


6.2. Comparison with correlation between rainfall and net absolute groundwater
storage change

In order to justify the effectiveness of the method used to screen out factors affecting
water table other than climate represented by rainfall, the correlation between rainfall
and net absolute groundwater storage change based on ∆x pi (water table change under
the combined effect of both management and climate, see Equation 4 and Fig. 10) are
also carried out. The correlations are shown in Fig. 19-21.




                                                                                                       - 20 -
                                              Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW


                                           Rainfall vs Abs olute Ne t Groundw ate r Storage Change for Sum m e r Se as on
                                                                                                           Sy=0 .0 3

                                       2 0 0 0 0 .0 0

                                        150 0 0 .0 0
    Summer Absolute Net Groundwater
         Storage Change (ML)           10 0 0 0 .0 0

                                         50 0 0 .0 0

                                              0 .0 0

                                        -50 0 0 .0 0
                                                                                                                                  y = -155.6 4 x 2 + 14 2 4 9 8 x - 2 E+0 7
                                                                                                                                              R 2 = 0 .4 2 3 3
                                      -10 0 0 0 .0 0

                                       -150 0 0 .0 0

                                      -2 0 0 0 0 .0 0

                                      -2 50 0 0 .0 0
                                                        0 .0   50 .0      10 0 .0             150 .0     2 0 0 .0      2 50 .0          3 0 0 .0      3 50 .0        4 0 0 .0      4 50 .0          50 0 .0

                                                                                                          Summer Rainf all (mm)


Figure 19. Correlation between summer net absolute groundwater storage change and
           corresponding summer rainfall over the whole Wakool area.



                                             Rainfall vs Abs olute Ne t Groundw ate r Storage Change for Winte r Se as on
                                                                                                           Sy=0 .0 3

                                       6 0 0 0 0 .0 0

                                       50 0 0 0 .0 0
    Winter Absolute Net Groundwater




                                       4 0 0 0 0 .0 0
           Storage Change (ML)




                                       3 0 0 0 0 .0 0

                                       2 0 0 0 0 .0 0

                                        10 0 0 0 .0 0

                                               0 .0 0
                                                                                                                                                         y = 758 .3 2 x 2 - 10 4 6 0 2 x - 7E+0 6
                                                                                                                                                                     R 2 = 0 .9 0 53
                                       -10 0 0 0 .0 0

                                      -2 0 0 0 0 .0 0

                                      -3 0 0 0 0 .0 0
                                                        0 .0      50 .0             10 0 .0            150 .0          2 0 0 .0             2 50 .0          3 0 0 .0           3 50 .0             4 0 0 .0

                                                                                                           Winter Rainf all (mm)


Figure 20. Correlation between winter net absolute groundwater storage change and
           corresponding winter rainfall over the whole Wakool area.




                                                                                                           - 21 -
                                               Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW


                                                 Rainfall vs Abs olute Ne t Groundw ate r Storage Change for Whole Ye ar
                                                                                           Sy=0 .0 3

                                        70 0 0 0 .0 0

                                        6 0 0 0 0 .0 0
     Yearly Absolute Net Groundwater
                                        50 0 0 0 .0 0
            Storage Change (ML)
                                        4 0 0 0 0 .0 0

                                        3 0 0 0 0 .0 0

                                        2 0 0 0 0 .0 0
                                                                                                        y = -2 6 7.8 6 x 2 + 4 3 54 0 2 x - 1E+0 8
                                        10 0 0 0 .0 0                                                                R 2 = 0 .72 8 4
                                               0 .0 0

                                       -10 0 0 0 .0 0

                                       -2 0 0 0 0 .0 0

                                       -3 0 0 0 0 .0 0

                                       -4 0 0 0 0 .0 0
                                                    2 0 0 .0 0   3 0 0 .0 0   4 0 0 .0 0    50 0 .0 0      6 0 0 .0 0           70 0 .0 0            8 0 0 .0 0   9 0 0 .0 0

                                                                                           Y early Rainf all (mm)


Figure 21. Correlation between yearly net absolute groundwater storage change and
          corresponding yearly rainfall over the whole Wakool area.


Compared with the correlations between net absolute groundwater storage change and
corresponding rainfall for different time intervals, the relative water table change
method has significantly improved the correlation between rainfall and water table
change for summer seasons, with the R2 being 0.703 and 0.423 respectively (see Fig. 16
and Fig. 19), indicating the method used has been very effective in identifying impact of
climate on water table for summer seasons, using rainfall as a climate indicator.

For winter season, the method actually deteriorated the correlation relationship a little
bit (see Fig. 17 and Fig. 20), with the R2 being 0.839 and 0.905 respectively, suggesting
that during winter seasons the management effect on water table is much less significant
than that during summer seasons.

On yearly basis, the method has no significant impact on the rainfall and groundwater
change relationship (see Fig. 18 and Fig. 21), mainly due to the compensating effect of
summer and winter seasons.

The benchmark rainfalls for determining whether climate represented by rainfall would
have an addition or a reduction effect on net groundwater storage are around the same
for both correlations.


7. Summary and Conclusions

This study has developed a concept and method for estimating climate impact on
shallow groundwater for the Wakool area, based on the available data and by applying
GIS techniques in the data processing,

The results show that the method is more effective for summer seasons than for winter
seasons. For summer seasons, the method improved the rainfall ~ groundwater change
correlation from R2=0.42 to R2=0.70.


                                                                                           - 22 -
             Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Area, NSW

The results of this study indicate that climate represented by rainfall, which is also a
major source of flood, has a significant impact on the shallow groundwater tables in the
Wakool area, as the correlations (R2) between rainfall and water table change are in the
range of 0.7~0.9 for all the time intervals considered. The statistical relationships
between rainfall and groundwater storage change derived from this study revealed some
interesting bench mark rainfall figures:
    • For summer seasons, the bench mark rainfall is around 200mm, above which, it
        will likely to have an addition effect on groundwater storage; below which, it
        will likely to have a reduction effect on groundwater storage;
    • For the winter season, that bench mark rainfall is around 170mm

It should be noted that climate conditions are determined by many factors in a region.
The combined climate and weather conditions are often reflected by rainfall to some
degree. For example, in wet years, the temperature tends to be lower, the relative
humidity tends to be higher, and consequently the potential evaporation tends to be
lower, leading to a reduction of groundwater discharge through evapotranspiration.
Although the relationship presented in this study is between rainfall and groundwater,
the rainfall contains messages of many other climate components.

Restricted by the available data, there are some unavoidable weaknesses in this study.
For example, the number of the available data is different for different piezometers,
causing some data inconsistency in deriving the average water table change. The other
obvious weakness is that the sample number for the statistical relationships is small.
Thus when considering using the results in land and water management practice,
discretion should apply.


                                         Acknowledgement

This study is funded by Rice CRC. The piezometric data and base GIS layers (roads,
rivers, and boundaries of the Murray LWMP area and the Wakool Irrigation District)
used in this study are supplied by Murray Irrigation Ltd (MIL). Rainfall data is obtained
from Bureau of Meteorology (BOM) via Horizontech Pty Ltd.

The authors acknowledge the feedback and suggestions from Mr. Ary van der Lely, a
prominent hydrogeologist in the NSW Riverina region.


Reference:

Smith, R., Herriot, R. I., and Johnston, E. J. (1943). The Soil and Land-Use Survey of
the Wakool Irrigation District, New South Wales. Australian Council for Scientific and
Industrial Research, Bulletin No. 162, Melbourne.

Wakool LWMP Working Group (2001). Wakool Community’s Land & Water
Management Plan. Wakool LWMP Working Group, Wakool, NSW.

Wang, B., Khan, S., and O’Connell, N. (2003). Impact of Flooding on Shallow
Groundwater Levels in the Wakool Irrigation District. CSIRO Land and Water, Griffith,
draft report.


                                                   - 23 -

				
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