Hydrology by wanghonghx

VIEWS: 6 PAGES: 26

									      The Caveat: Hydrology

•   Complex
•   Site specific
•   Difficult to accurately quantify
•   More questions than answers
     Wetland Hydrology

• Wetland Hydrologic Function
  – Flow control
  – Water quality
    Current projects to assess
             function

• Landscape scale diagrams (RSE)

• Wells (Gracz and Coble)

• Conceptual, regional model (Andy
  Reeve)
              A few terms
• Recharge, discharge
  – Recharge = input; discharge = output
• Water Budget
  +   Precipitation
  –   ET
  –   Storage
  –   Average Streamflow
  –   Storm and spring melt Streamflow
  –   Groundwater flow
• Confined/unconfined aquifers
Landscape Diagrams (RSE)

• Geology
• Nature of confined and unconfined
  aquifers
• Basic water budget
Complex, thick glacial sediments, some produce artesian flows
Thick, complex glacial sediments. Note two till units N of Kenai River.
Abandoned, connected channel deposits- withdrawal from these may induce recharge from streams.
Mostly thin glacial sediments.
Groundwater discharge to peatlands from surrounding highlands
Very thin glacial sediments,
most (shallow unconfined) groundwater movement
occurrs in a near-surface zone
    Wells (Gracz and Coble)

• Document Wetland Hydrology over the
  growing season
• Describe nature of precipitation storage
• Begin to understand ET where possible
      Growing Season and Wetland
               Hydrology
• Homer Airport Growing Season: May 8- Oct 2

• In Wellheads:

•   Begin 2006
        • 17 April (Homer Bench)
        • 6 June (Skyline)
        • 4 June (Blackwater Bend)


•   End 2005
        • 24 October (Homer Bench)
        • 2 September (Skyline)
        • 11 October (Blackwater Bend)
                       Wynn Nature Center Bog
                                                            H234 Water level and Precipitation

                    -1.0
                                                                                                                                      1.40
Water Level, Feet




                    -2.0




                                                                                                                                             Precip, Inches
                                                                                                                                      1.20
                    -3.0
                    -4.0                                                                                                              1.00
                    -5.0                                                                                                              0.80
                    -6.0                                                                                                              0.60
                    -7.0                                                                                                              0.40
                    -8.0                                                                                                              0.20
                    -9.0                                                                                                              0.00




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                                                                      Water level       Precip




                       Summer: Water table drops, less in 2006
                       Fall: rapidly rises with onset of rainy period,
                       Winter: remains steady, then slowly lowers during late winter
                       Spring: rapidly rises during snowmelt period
Homer Bench near Beluga Lake

                                            Calvin and Coyle Bluejoint- Willow Discharge Slope (SCS) Precip and Water Level, Well #2
                                                                                 40" deep, fully screened

                1.20                                                                                                                                          1




                                                                                                                                                                   Water Level, Feet
                1.00                                                                                                                                          0
Inches Precip




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                                                                           Precip     Water Level




                                 Summer: Drops to confining layer
                                 Fall: rapidly rises with onset of rainy period
                                 Winter: varies, probably responding to freeze/thaw cycles
                                 Spring: rises with snowmelt period
             Homer Bench below Paul Banks Elem.

                                               Calvin and Coyle Spruce / Alder Discharge Slope (SLA) Precip and Water Level, Well #2
                                                                                  38" deep, fully screened

                 1.20                                                                                                                                          1




                                                                                                                                                                    Water Level, Feet
                 1.00
 Inches Precip




                                                                                                                                                               0
                 0.80
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                 0.60
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                 0.40
                 0.20                                                                                                                                          -3
                 0.00                                                                                                                                          -4




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                                                                            Precip      Water Level




Summer: dropped to confining layer in 2005, but not 2006
Fall: rises rapidly with onset of rainy period
Winter: small drops and rises probably corresponding to thaw cycles
Spring: rises a little, but little storage is available for spring melt
                                Blackwater Bend




Peatland:                                         Discharge Slope: remains close to surface year around
Summer: lots of variation, but general drop       Summer: lots of sharp variation
Fall: rapid rise with onset of rainy period       Fall: general rise, then remains relatively steady near surface
Winter: remains steady, but varies late winter;   Winter: remains steady, but varies late winter
        -discharge to stream during January?              is recharged by peatland above?
Spring: rapid rise during melt                    Spring: drop after melt period.
 Where does the discharge go?


• Atmosphere (ET)
• Adjacent wetlands and streams
• Deeper groundwater
     ET- Evapotranspiration


• Thornthwaite Equation using temperature
  – Found to underpredict actual ET


• Daily water table variations
  – Need specific conditions
Daily Water Table Variations
                                              SLA Water Table, 9 - 16 July 2006




       Depth Below Surface, Feet
                                   -0.5
                                   -0.6
                                   -0.7
                                   -0.8
                                   -0.9
                                   -1.0
                                   -1.1
                                   -1.2

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                                   Plants use water during the day

                                   Recharge occurs at night
               ET Varies
• Equation generally agrees with water table
  variations
• Predictions more or less verified by actual
  stream flow values

• Could be as high as 85% of annual
  precipitation- in forest behind Paul Banks
• Probably low at peatlands
        So far we can GUESS:
• If annual precipitation equals 24”:

  •   14” leaves as ET
  •   3” remains in storage- cycling over the year
  •   ¾” goes to deeper groundwater
  •   2¾” leaves as storm and spring melt run-off
  •   3½” Flows in streams during “normal” periods
Conceptual, Regional Model (Andy
      Reeve, Univ. Maine)
• Generally: How does water move
  throughout the regions shown in the
  Landscape diagrams

• MODFLOW hydrologic computer model
    • Precipitation
    • Elevation/slope
    • Guesses at hydraulic conductivity
Abandoned channel deposits: more or less continuous.

Most discharge (of moisture surplus) is to streams,
 -between 0 and 16% of the moisture surplus is discharged to peat from local uplands.
 -peat remains saturated during dry periods; streamflow suffers

Pumping from shallow wells may induce recharge from streams.
Springs indicate groundwater discharge from highlands to peatland.

Most flow is from shallow unconfined aquifer to confined, but some into river.

Between about 3 and 17% of moisture surplus leaves to deeper aquifers.
           Overall Conclusions
• Diagrams:
  – Thin unconfined aquifer near Homer

• Wells:
  – Storage is significant and can be replenished during
    winter.
  – ET can be large in forested wetlands

• Model:
  – Wetlands remain saturated during dry years;
    streamflow suffers.

								
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