Professorial Inaugural Lecture Extended Summary

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					Professorial Inaugural Lecture: Extended Summary

Hydrodynamics of the Ethiopian Rift
Lakes Basin and Environmental Changes
                      By

Tenalem Ayenew
Department of Earth Sciences
Addis Ababa University




1. General



The Ethiopian Rift Valley (ERV) is part of the Great East African Rift (EAR), which is the largest,
longest, and most conspicuous feature of its kind on Earth. Astronauts call it the most significant
physical detail of the world visible from outer space. The ERV landscape ranges from wide faulted
salt plains lying 120 m.b.s.l in the north to the elevated central Main Ethiopian Rift (MER) occupied
by a series of large lakes localized within volcano-tectonic depressions.

The MER has three major lake basins: Ziway-Shala, Awassa and Abaya-Chamo. The study focuses
on the first two basins that include lakes Awassa, Sahala, Langano, Abiyata and Ziway. The ERV
lakes are boarded to the east and west by highlands where the main tributary rivers originate.
Magnificent volcanic centres dot the floor of the rift separating the different lakes. The MER is home
for many endemic animals. An extraordinarily rich fauna inhabits the rift lakes and associated
wetlands. The rift lakes are home to many endemic animals and migratory birds of global importance.


The hydrology and hydrogeology of the MER lakes basin has been studied for over a decade using
converging evidence approach involving conventional hydrometeorological data analysis, isotope and
hydrochemistry, numerical modelling and remote sensing and GIS techniques. The result
demonstrated the extreme variability of the hydrological and hydrogeological setting of the region
with dramatic changes having far-reaching negative environmental repercussions.

The hydrodynamics of the lakes and their catchments will be presented including the environmental
changes. In this case the term hydrodynamics refers the dynamics of natural waters with particular
reference to the interaction of groundwater and surface waters. Emphasis is given to the interaction of
the rift lakes with the groundwater and the subsurface hydraulic connection among the lakes and the
relative importance of the components of the hydrologic cycle in the water balance of the lakes and
anthropogenic factors.

2. Major findings

The result of the work can be categorized in to three broad aspects: water balance and lake levels,
surface water and groundwater interactions and the influence of anthropogenic factors on the
dynamics of the lakes and their catchments.

A. Water Balance and lake levels - One of the most important aspects of the study is establishing the
water balance of the lakes and assess the relative importance of the different components of the
hydrologic cycle. The result clearly demonstrates that the existence of the rift lakes is strongly
dependent on the highland rainfall that feeds them through rivers and large groundwater flux that
comes preferentially through large regional faults.

Often many water balance study of lake watersheds ignore or gives little attention to groundwater. In
most of the Ethiopian rift lake basins this was found to be not the case. Groundwater is the major part
of the water balance of lakes, especially those located in a terminal position. This has important
practical implication indicating that any sustainable water management practise in the region must
give serious attention to groundwater.

B. Groundwater - Surface water interactions - The relation of the lakes with local and regional
groundwater has been established using satellite images, isotope and hydrochemical techniques and
numerical models. The result shows that the lakes are strongly linked to regional and local flow
systems and have subsurface links among the them.

               The existence of the rift lakes is strongly controlled by the hydrodynamics of the

                adjacent highlands and escarpments. Any factor that affects the highland hydrology

                affects the rift lakes.


               Large groundwater fluxes supply the rift lakes from the western highlands than the

                eastern highlands. This is especially the case for lakes Ziway and Langano.


               All evidences suggest that there are no large lakes in the Ethiopian rift which are

                having a closed system from the point of view of the dynamics of groundwater. The

                lakes have strong subsurface hydraulic link.


               Classical regional groundwater flow models indicates that in areas where there is

                large topographic gradient, regional flow systems follow long flow paths and gets
                more saline as depth of groundwater circulation increases. The numerical flow

                models demonstrate that the dominant flux of groundwater circulates from the

                highlands to the rift is in the upper few tens of meters.


               The hydrological and hydrogeological setting of the lakes has been affected by

                neotectonism. In few cases this has resulted in the expansion of few lakes by

                increasing the groundwater inflow into the lakes against the general trend of lake

                level reduction in the EAR.


               Spectral satellite data analysis indicates large spatial variability in temperature and

                evapotranspiration rates. The spectral satellite data shows also zones of large

                groundwater inflow sites illustrated by the change in lake surface temperature.


               Conventional open-water evaporation estimation methods usually assume that the surface

                temperature of lakes remains uniform and that instantaneous evaporation proceeds more or

                less at the same rate over the total lake surface area. However, this study shows that

                temperature varies widely depending on surface temperature and reflectance, and on the

                incoming fluxes from groundwater and surface waters.


C. Anthropogenic influences – The rift lakes and major tributary rivers are being used for agricultural and
industrial purposes. Large scale irrigation and pumping of lake water for soda ash abstraction resulted in the
shocking reduction of the size and level of few lakes. Clearing of vegetation and expansion of farmlands
caused widespread soil erosion and subsequent siltation of lakes. In few cases the hydrochemical setup of the
lakes has changed. Improper utilization of water resources resulted in substantial changes in the hydrological
and hydrogeological setting. The changes are more pronounced in terminal lakes without surface water
outlets. The study clearly indicates these changes with undisputed scientific evidences.



3. Environmental Implications


The improper utilization of water and land resources brought about noticeable negative changes in the region,
which have far-reaching environmental implications. The Ethiopian rift lakes basin is known by its rich
biodiversity. The lakes form an important migration route for Palaearctic birds during the northern winter.
Particularly the muddy shore of lake Abiyata supports a wealth of bird life almost unequalled perhaps in the
whole of Africa. The lake is part of the Rift Valley Lakes National Park, which is expected to play an
increasing role in the promotion of Ethiopia's tourism industry. The high density of flamingo around the lake
is able to subsist directly on the blue green algae in the surface waters while many other birds are dependent
on fish. Abiyata also forms a vital feeding ground for Pelicans and other fish-eating birds. The increase in the
alkalinity of the lake and its shrinkage will result in the reduction of the fish population ultimately leading to
the death of birds.

With broad shallow margins fringed with swamp, dense floating vegetation and a high concentration of
phytoplankton, Lake Ziway is the principal source of commercial fishing in Ethiopia. Therefore, the main
economic consideration of altering the volume of Ziway for irrigation is the impact on its considerable
potential as a freshwater fishery. The other more subtle effect of lake level reduction is on the vegetation
around the lake edge, which plays an important role in providing food and shelter for numerous animals.
Some species are apparently sensitive to short-term fluctuations and disruptions to their environment (the
marginal vegetation). Irrigation around the lake and deforestation have already been profoundly affected the
larger mammalian population.

The highly productive rim of grassland close to the shore of most lakes is the principal source of dry season
grazing at high stocking densities. Lowering of lake level may also result in an increase of the transpiration
loss from the marginal vegetation and lowering of the groundwater level which intern leads to the drying up of
springs used for community water supply purposes; especially in the eastern shore of Ziway.

The transformation of lake Cheleleka to a swampy area has completely changed the aquatic ecosystem and
lead to the loss of its regulating capacity of the level of Awassa. Tall papyrus like grasses grow in the swampy
area indicating that the deposition of transported sediment from the uplands has been in a continuous process
of filling the natural reservoir of this small lake.

The highlands where major feeder rivers originate are highly cultivated and the deforestation rate is growing
every year. The use of fertilizers is also growing with time; this will increase the rate of supply of nutrients in
to the lakes ultimately leading to eutrophication




In general the existing problems demand integrated watershed management practise. Mostly

utilization of water in the region has proceeded without basic understanding of the complexity of the

hydrologic system. This has become a major problem in water resources management. In the past

development plans were implemented with short-term interests. Now a days, there is a general

consciences at various levels on the prevalence of negative environmental changes demanding urgent
intervention and developing water management strategies which will lead to ‘wise use’ of lakes and

rivers.

The ‘wise use’ of lakes is their sustainable utilization for the benefit of the people in a way
compatible with the maintenance of the natural properties of the ecosystem. The term ‘wise
use’ encapsulates the need to safeguard the integrity of the lakes while at the same time
providing sustenance to the natural and human communities around them. The wise use of
lakes involves the maintenance of their ecological character as a basis not only for nature
conservation, but also for sustainable development. It goes without saying that the wise use of
lakes is impractical if the people who make use of them are not involved in one way or
another. The involvement of such people and knowledge of their values is the basis for the
implementation of wise use strategies.



4. Future Plan

Currently there are efforts of establishing river basin authorities including the rift valley at the federal
level. The authorities are expected to address the burning environmental issues and pave the way for
the sustainable utilization of the water resources of the region. The Department of Earth Sciences
through the Hydrogeology Unit has played a positive role in addressing the existing problems at a
national and international level through publications, training and building capacity for scientific
research. The Department has established hydrochemical and isotope hydrology laboratory together
with other stakeholders which is playing important role in water sciences. There is an effort to launch
PhD program which will focus on the burning issues of the rift valley lakes basin and other river and
lake-basins that are given utmost priority for water and land resources development. There is a plan to
establish hydrological monitoring stations together with the launching of the PhD program. In the
long-term the Department has a vision to establish centre of water sciences and geo-engineering
which is expected to play important role in the conservation of the rift valley lakes.



Acknowledgements


I am greatly indebted to the Department of Earth Sciences (my Department) for its
continuous and remarkable support during the long and difficult journey. My research
projects were funded by both national (Addis Ababa University, Ethiopian Science and
Technology Commission) and International organizations. Among others the most important
ones are the Alexander von Humboldt Foundation (AvH), National Science Foundation
(NSF), STaRT, the MAWARI project, Sardinian Local Government Fund (Italy). I am very
much grateful to all of them. All my close friends have stood by my side and gave me too
much comfort during my difficult and challenging times that I passed after my PhD. I have
no words to express my heartfelt appreciation. There are also various personalities who have
encouraged me one way or another to come to this level. Last but not least, owe much of my
academic success to my wife Almaz Shitie and our sweet kids Mahlet and Mikias. Take my
bunch of flowers!!



Publications


Excluding book chapters, technical documents and conference proceedings Prof. Tenalem has
published the following books and scientific articles most of which focus on the Ethiopian rift
lakes.



Books

   1. Tenalem Ayenew, 1988. Principles of Stratigraphy (text Book). Asmara University Press.
      Asmara. 240p.
   2. Tenalem Ayenew, 1998. The hydrogeological system of the lake district basin, Central Main
      Ethiopian Rift. Published PhD thesis (Book, ISBN. 9061641586), Free University of Amsterdam,
      The Netherlands. 259p.
   3. Tenalem Ayenew, Tamiru Alemyaheu, 2001. Principles of Hydrogeoloy (Text Book). Addis
      Ababa University Press. 279 pp.
   4. Tenalem Ayenew, 2004. Principles of Engineering Geology (Text book). Addis Ababa
      University Press. 280 pp.
   5. Tenalem Ayenew, 2008. Natural lakes of Ethiopia (commercial book in press). Addis Ababa
      University Press. 280 pp.



Scientific articles

1. Acharya, S., Mulugeta Alene, Tenalem Ayenew, 1989. Geology of Adola- Moyale areas with
   special reference to controls of Gold Mineralization, southern Ethiopia. Asmara University. 1
   Unpub. Report, 45p.
2. Acharya, S., Mulugeta Alene, Tenalem Ayenew, 1989: Geology in relation to water potentiality
   in Asmara. Asmara University. Unpub. Report, 23p.
3. Tenalem Ayenew, 1991. Water resources potential assessment of the Domail river basin,
   Northwestern Frontier Province, Pakistan, IHE PGD thesis, Delf, The Netherlands. 89p.
4. Tenalem Ayenew, 1992. Hydrogeological Investigation of the Bergantes River Basin,
   Northeastern Spain, ITC, M.Sc thesis, 184p.
5. Tenalem Ayenew, 1996. Application of TM band 6 for the study of groundwater and surface
   water interaction with the lakes of Ziway-Shala basin. Abstracts, programs of the third Ethiopian
   Geoscience and Mineral Engineering Congress, 15-17 November 1996, Addis Ababa.
6. Hailu, D., Martina, H., Tenalem Ayenew, 1996. The problem of high rise groundwater in
   Amibara Irrigation Project, Ethiopian Science and Technology Commission unpublished report.
   42p., Addis Ababa, Ethiopia.
7. Gieske, A.S.M.; Tenalem, A., 1999. Estimation of hot spring discharge in Lake Ziway (Ethiopia)
   by thermal infrared remote sensing techniques Proceedings of the 24th European Geophysical
   Society General Assembly (April 19-23, 1999). Den Haag, The Netherlands.
8. Tenalem Ayenew, 2001. A new approach of evapotranspiration estimation using spectral satellite
    data: A case study in Ethiopian Rift lakes Basin. International Journal of ITC.
9. Tenalem Ayenew, 2001. Surface kinetic temperature mapping of the central main Ethiopian rift
    lakes, SINET: Ethioian Journal of Science. 24(1): 241-252.
10. Tenalem Ayenew, 2001. Numerical groundwater flow modeling of the Central Main Ethiopian
    Rift lakes basin, SINET: Ethiopian Journal of Science 24(2):167-184.
11. Tenalem Ayenew, 2001. Numerical groundwater modelling and hydrochemical study of the Main
    Ethiopian Rift lakes basin. Proceedings of the XXXIth Congress of the International Association
    of Hydrogeologists "New Approach to Characterizing Groundwater Flow", 14-18 September
    2001. Munich, Germany.
12. Tenalem Ayenew, 2001. Recent changes in the level of Lake Abiyata, Central Main Ethiopian
    Rift. Journal of Hydrological Sciences, 47(3):493-503.
13. Tenalem Ayenew, 2001. Integrated Hydrological and hydrogeological study of some Ethiopian
    rift lakes. SEARCH workshop proceedings. 22-28 September 2001. Nairobi, Kenya.
14. Seifu Kebede, Tenalem Ayenew, Mohammed Ummer, 2001. Application of isotope and water
    balance approaches for the study of the hydrogeological regime of the Bishoftu crater lakes,
    Ethiopia. SINET: Ethiopian Journal of Science 24(2):151-166.
15. Tenalem Ayenew, 2002. Application of environmental isotopes for the study of the
    hydrogeological system of some Ethiopian Rift lakes. Proceedings of the 4 th International
    Conference on Isotopes. 10-14 March 2002. Cape Town South Africa.
16. Tenalem Ayenew, 2002. Integrated groundwater flow system analysis in the Central Main
    Ethiopian Rift lake basin. Proceedings of the Australian National Chapter of the Internationa
    Association of Hydrogeologists " balancing the groundwater budget". 12-17 May, Darwin,
    Australia (Proceedings in CD-ROM).
17. Tenalem Ayenew, 2003. Environmental isotope-based integrated hydrogeological study of some
    Ethiopian rift lakes. Journal of radioanalytical and nuclear chemistry. Vol. 257 No 1 (2003): 11-
    16.
18. Tenalem Ayenew, 2003. Evapotranspiration estimation using thematic mapper spectral satellite
    data in the Ethiopian rift and adjacent highlands. Journal of Hydrology, Volume 279, Issues 1-4,
    25 August 2003, Pages 83-93
19. Tenalem Ayenew and Molla Demlie, 2004. Bathymetric survey and estimation of the water
    balance of lake Ardibo, Ethiopia. Sinet: Ethiopian Journal of Science. 27(1):61-68.
20. Tenalem Ayenew, 2004. Environmental implications of changes in the levels of lakes in the
    Ethiopian rift since 1970. Regional Environmental Changes.4:192-204.
21. Tenalem Ayenew, Giulio Barbieri, 2004. Inventory of landslides and susceptibility mapping in
    the Dessie area, northern Ethiopia. Engineering Geology 77:1-15.
22. Tenalem Ayenew, 2004. Comparison of different groundwater recharge estimation methods and
    characterization of the hydrological behavior of the Meki river catchment. Proceedings of the
    Fourth EGMEA Congress. December 19-21, 2003. Addis Ababa. Pp. 209-225.
23. Tenalem Ayenew, Paulos Masresha, 2005. Study of socio-ecology and utilization of groundwater
    resources in Ethiopia. Technical document. International Water Management Institute (IWMI).
    135 pp.
24. Tamiru Alemayehu, Tenalem Ayenew., Seifu Kebede, 2006. Hydrochemical and lake level
    changes in the Ethiopian Rift. Journal of Hydrology Vol. 316, No. 1-4:290-300.
25. Tamiru Alemayehu, Dagnachew Legesse, Tenalem Ayenew, Yirga Tadesse, Solomon
    Waltenigus, and Nuri Mohammed, 2005. Hydrogeology, water quality and the degree of
    groundwater vulnerability to pollution in Addis Ababa, Ethiopia. UNEP/UNESCO report.
    Nairobi, Kenya. 118 pp.
26. Tamiru Alemayehu, Dagnachew Legesse, Tenalem Ayenew, Yirga Tadesse, Solomon
    Waltenigus and Nuri Mohammed, 2005. Hydrogeology, Water quality and the degree of
    groundwater vulnerability to pollution in Addis Ababa, Ethiopia. UNEP/UNESCO report. Book
    in press. Nairobi, Kenya. 118 pp.
27. Seifu Kebede, Yves Travi, Tamiru Alemayehu, Tenalem Ayenew, 2005. Groundwater recharge,
    circulation and geochemical evolution in the source region of the Blue Nile river, Ethiopia,
    Applied Geochemistry 20 (9):1658-1676.
28. Tenalem Ayenew, Seifu Kebede, Tamiru Alemyahu, 2005. Environmental isotopes and
    hydrochemical study for groundwater exploration and development in the Afar Depression,
    Northeastern Ethiopia. Proceedings of 5th international conference on isotopes. 25-29 April 2005.
    Bussels, Belgium.
29. Zerihun Woldu, Assefa Mebrate, Seyoum Mengistou, Tenalem Ayenew, Dagnachew Legesse,
    2005. A review of the current status and an outline of a future management plan for lakes Abijata
    and Ziway. Oromia Environmental Protection Burea. Unpublished Technical Report. Addis
    Ababa, Ethioipia. 80 pp.
30. Tenalem Ayenew, 2005. Major ions composition of the groundwater and surface water systems
    and their geological and geochemical controls in the Ethiopian volcanic terrain. Sinet: Ethiopian
    Journal of Science. 28(2):171-188.
31. Tenalem Ayenew, Yemane Gebreegziabher, 2006. Application of a spreadsheet hydrological
    model for computing the long-term water balance of Lake Awassa, Ethiopia. Hydrological
    Sciences Journal. 51(3): 418-431.
32. Dagnachew Legesse, Tenalem Ayenew, 2006. Effect of improper water and land resources
    utilization on the central Main Ethiopian Rift lakes. Quaternary International: 148: 8-18.
33. Tenalem Ayenew, T., Alemyahu, T., Kebede, S., 2006. Environmental Isotopes and
    Hydrochemical Studies as Applied to Water Resources Assessment in Central and Southern Afar
    and Adjacent Highlands. Ethiopian Science and Technology Agency. Unpublished Report of the
    International Atomic Energy Agency Project (ETH/8/008). Addis Ababa, Ethiopia. 128 pp.
34. Alemayehu, T., Legesse, D., Ayenew, T., Mohammed N., Waltenigus S., 2006. Degree of
    groundwater vulnerability to pollution in Addis Ababa, Ethiopia. In: Yongxin Xu and Brent
    Usher (Eds). Groundwater pollution in Africa. Taylor and Francis Publishers, USA.pp. 203-212.
35. Tenalem Ayenew, 2007. Some improper water resources utilization practices and
    environmental problems in the Ethiopian rift. African water Journal. Volume 1 No. 1.
    March 2007- ISBN 92-1-125089-7 UN-Water Africa. Addis Ababa, Ethiopia.
36. Tenalem Ayenew, 2007. Water management problems in the Ethiopian rift: Challenges
    for development. Journal of African Earth Sciences 48:222–236.
37. Molla Demlie, Tenalem Ayenew, Stefan Wohnlich, 2007 Hydrological system analysis of
    topographically closed lakes in highland Ethiopia: the case of Hayq and Ardibo. Journal of
    hydrology. Volume 339, Issue 3-4, page 145-158.
38. Lamb, H.F., M.J. Leng, R.J. Telford, Tenalem Ayenew, Mohammed Umer, 2007. Oxygen and
    carbon isotope composition of authigenic carbonate from an Ethiopian lake: a climate record of
    the last 2000 years. The Holocene. 17(4):517-526.
39. Tenalem Ayenew, Robert Becht, Arno van Lieshout, Yemane Gebreegziabher, Dagnchew
    Legesse, Japheth Onyando (2007). Model-based study of the hydrodynamics of topographically
    closed lakes in the Ethio-Kenyan Rift: The case of lakes Awassa and Naivasha. Journal of Spatial
    Hydrology. Volume 7. No. 1.
40. Tenalem Ayenew and Dagnachew Legesse (2007). The changing face of the Ethiopian rift lakes:
    Call of the time. Lakes and reservoirs: research and mangament. 12 (3): 149–165
41. Tenalem Ayenew (2007). Hydrogeological controls and distribution of fluoride in the
    groundwaters of the central Main Ethiopian rift and adjacent highlands. Environmental geology
42. Tenalem Ayenew, Seifu Kebede, Tamiru Alemyahu Published online: DOI: 10.1007/s00254-007-0914-4).
    Environmental isotopes and hydrochemical study as applied to surface water and groundwater
    interaction in the Awash river basin. Hydrological processes (published online)
43. Tenalem Ayenew, Robert Becht (in press). Comparative Assessment of the hydrology of
    selected Ethio-Kenyan rift lakes. Journal of Hydrological Sciences.
44. Tenalem Ayenew (accepted and in press). Groundwater recharge estimation using semi-
   distributed hydrological models and river discharge measurement in the Meki river basin. Sinet:
   Ethiopian Journal of Science.
45. Seifu Kebede, Yves Travi, Asfawossen Asrat, Tamiru Alemayehu, Tenalem Ayenew,
    Zenaw Tessema accepted and in press). Groundwater origin and flow along selected
    transects in Ethiopian rift volcanic aquifers. Hydrogeology Journal.
46. Tenalem Ayenew, Molla Demlie, Stefan Wohnlich (accepted and in press). Hydrogeological
    framework and occurrence of groundwater in the Ethiopian volcanic terrain. Journal of African
    Earth Sciences
47. Tenalem Ayenew, Molla Demillie and Stefan Wohnlich, 2008. Application of numerical
    modeling for groundwater flow system analysis in the Akaki catchment, central Ethiopia.
    Mathematical Geosciences. DOI: 10.1007/s11004-008-9144-x
48. Molla Demlie, Stefan Wohnlich, Tenalem Ayenew, 2007. Major ion hydrochemistry and
    environmental isotope signatures as a tool in assessing groundwater occurrence and its dynamics
    in a fractured volcanic aquifer system located within a heavily urbanized catchment, central
    Ethiopia. Journal of Hydrology (2008) 353, 175– 188.
49. Tewodros Rango, Gianluca Bianchini, Luigi Beccaluva,Tenalem Ayenew,Nicolo`
   Colombani, 2008. Hydrogeochemical study in the Main Ethiopian Rift: new insights to
   the source and enrichment mechanism of fluoride. Environmental Geology. DOI
   0.1007/s00254-008-1498-3
50. Tenalem Ayenew, 2003. Evapotranspiration estimation using thematic mapper spectral satellite
    data in the Ethiopian rift and adjacent highlands. Journal of Hydrology. 279(1-4): 83-93.
51. Tenalem Ayenew, 2003. Environmental isotope-based integrated hydrogeological study of some
    Ethiopian rift lakes. Journal of radioanalytical and nuclear chemistry. 257(1): 11-16.
52. Tenalem Ayenew and Molla Demlie, 2004. Bathymetric survey and estimation of the water
    balance of lake Ardibo, Ethiopia. Sinet: Ethiopian Journal of Science. 27(1):61 - 68.
53. Tenalem Ayenew, 2004. Environmental implications of changes in the levels of lakes in the
    Ethiopian rift since 1970. Regional Environmental Changes. 101(13-14):192-204.
54. Tenalem Ayenew, Giulio Barbieri, 2004. Inventory of landslides and susceptibility mapping in
    the Dessie area, northern Ethiopia. Engineering Geology 77:1-15.
55. Tamiru Alemayehu, Tenalem Ayenew., Seifu Kebede, 2006. Hydrochemical and lake level
    changes in the Ethiopian Rift. Journal of Hydrology. 316(1-4):290-300.
56. Seifu Kebede, Yves Travi, Tamiru Alemayehu, Tenalem Ayenew, 2005. Groundwater recharge,
    circulation and geochemical evolution in the source region of the Blue Nile river, Ethiopia,
    Applied Geochemistry 20(9):1658-1676.
57. Tenalem Ayenew, Yemane Gebreegziabher, 2006. Application of a spreadsheet hydrological
    model for computing the long-term water balance of Lake Awassa, Ethiopia. Hydrological
    Sciences Journal. 51(3): 418-431.
58. Dagnachew Legesse and Tenalem Ayenew, 2006. Effect of improper water and land resources
    utilization on the central Main Ethiopian Rift lakes. Quaternary International: 148: 8-18.
59. Tenalem Ayenew, 2007. Water management problems in the Ethiopian rift: Challenges for
    development. Journal of African Earth Sciences 48:222-236.
60. Molla Demlie, Tenalem Ayenew, Stefan Wohnlich, 2007 Hydrological system analysis of
    topographically closed lakes in highland Ethiopia: the case of Hayq and Ardibo. Journal of
    Hydrology. 339(3-4): 145-158.
61. Lamb, H.F., M.J. Leng, R.J. Telford, Tenalem Ayenew, Mohammed Umer, 2007. Late Holocene
    climate variability in Africa: a 2500-year stable isotope record from Lake Hayk, northern
    Ethiopia. The Holocene. 17(4):517-526.
62. Tenalem Ayenew and Dagnachew Legesse, 2007. The changing face of the Ethiopian rift lakes:
    Call of the time. Lakes and Reservoirs: Research and Management. 12(3): 149–165.
63. Tenalem Ayenew, 2007. Hydrogeological controls and distribution of fluoride in the
    groundwaters of the central Main Ethiopian rift and adjacent highlands. Environmental Geology.
    54(6):1313-1324.
64. Tenalem Ayenew, Robert Becht, Arno van Lieshout, Yemane Gebreegziabher, Dagnchew
    Legesse, Japheth Onyando, 2007. Model-based study of the hydrodynamics of topographically
    closed lakes in the Ethio-Kenyan Rift: The case of lakes Awassa and Naivasha. Journal of Spatial
    Hydrology. 7(1):81-100.
65. Tenalem Ayenew, Seifu Kebede, Tamiru Alemyahu, 2007. Environmental isotopes and
    hydrochemical study as applied to surface water and groundwater interaction in the Awash river
    basin. Hydrological processes. 22(10): 1548-1563.
66. Molla Demlie, Stefan Wohnlich, Tenalem Ayenew, 2008. Major ion hydrochemistry and
    environmental isotope signatures as a tool in assessing groundwater occurrence and its dynamics
    in a fractured volcanic aquifer system located within a heavily urbanized catchment, central
    Ethiopia. Journal of Hydrology. 353: 175-188.
67. Seifu Kebede, Yves Travi, Asfawossen Asrat, Tamiru Alemayehu, Tenalem Ayenew, Zenaw
    Tessema, 2008. Groundwater origin and flow along selected transects in Ethiopian rift volcanic
    aquifers. Hydrogeology Journal. 16(1):55-77
68. Tenalem Ayenew, Molla Demillie and Stefan Wohnlich, 2007. Application of numerical
    modelling for groundwater flow system analysis in the Akaki catchment, central Ethiopia.
    Journal of Mathematical Geosciences. Available online (DOI. 10.1007/s11004-008-9144-x).
69. Tenalem Ayenew, Molla Demlie, Stefan Wohnlich, 2008. Hydrogeological framework and
    occurrence of groundwater in the Ethiopian volcanic terrain. Journal of African Earth Sciences.
    52(3):97-113.
70. Tenalem Ayenew, Robert Becht, 2008. Comparative assessment of the hydrology of selected
    Ethio-Kenyan rift lakes. Journal of Lakes and Reservoirs: Research and Management.13:191-
    196.
71. Tenalem Ayenew, 2008.Hydrogeological system analysis and groundwater recharge estimation
    using semi-distributed models and river discharge in the Meki river basin. Sinet: Ethiopian
    Journal of Science 31(1):21-28.
72. Tamiru Alemayehu, Dagnachew Legesse, Tenalem Ayenew, Nuri Mohammed and Solomon
    Waltenigus, 2006. Degree of groundwater vulnerability to pollution in Addis Ababa, Ethiopia. In:
    Yongxin Xu and Brent Usher (Eds). Groundwater pollution in Africa. Taylor and Francis
    Publishers, USA. pp. 203-212.
73. Tenalem Ayenew, Molla Demillie and Stefan Wohnlich, 2007. Application of numerical
    modelling for groundwater flow system analysis in the Akaki catchment, central Ethiopia.
    Journal of Mathematical Geosciences. 40(8):887-906.
74. Tenalem Ayenew, Molla Demlie, Stefan Wohnlich, 2008. Hydrogeological framework and
    occurrence of groundwater in the Ethiopian volcanic terrain. Journal of African Earth Sciences.
    52(3):97-113.
75. Tenalem Ayenew, Robert Becht, 2008. Comparative assessment of the hydrology of selected
    Ethio-Kenyan rift lakes. Journal of Lakes and Reservoirs: Research and Management.13:191-
    196.
76. Tewdros Rango, Luca Bianchini, Luigi Becaluva, Tenalem Ayenew, 2008. Water quality
    problem in main Ethiopian rift, a new insight to fluoride problem. Journal of Environmental
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