1. Integrated groundwater modeling study in Addis Ababa area: Towards developing decision support system for well head protection
Tenalem Ayenew And Molla Demelie Department of Earth Sciences, Addis Ababa University

2. Outline of presentation
Introduction
Objective and Methodology
Results/Discussion
Conclusions and Recommendation

3. Justification
Problem of Groundwater level decline & pollution as the Metropolis grows in size and population.

4. Study area

5. Akaki Basin

6. Objective
To understand the groundwater flow system and its relation with surface water
To indentify vulnerable areas to pollution
Scenario analysis

7. Methodolgy Conventional Hydrogeological Mapping
Hydro-meteorological data analysis
Hydrochemistry
Establishing interactive database in a GIS
Numerical Groundwater Flow Modelling
The groundwater model used for the study is the popular three-dimensional finite difference groundwater flow model called MODFLOW (MacDonald and Harbaugh, 1988).-

8. Geology

9. Aquifer Parameters

10. Recharge Zones

11. Aquifer Classification

12. Boundary conditions and calibration

13. Groundwater contours

14. Scenario Analysis

15. Flow system

16. Hydro Chemistry

17. Scatter plots

18. Pollution susceptible zones

19. Groundwater pollution vulnerability map

20. Akaki Well Field

21. DEM
Akaki
Wellfield

22. Geological map

23. Evolution of the water table May 1999- Jan 2002

24. Comparison of logs - Reclassified log of BH05A

25. Comparison of logs – original geologic log of BH05a

26. Distribution of Akaki boreholes
EP04
BH06
BH20
BH11
EP7
BH05a?
EP8
BH19
MW01b
BH23
TW1
BH16 P1
BH12
EP6
BH09
BH18
BH14
BH10
BH1
BH21
BH17
BH13
BH08
MW04
BH26
BH05
BH25
BH22
BH04
BH02
BH07
BH01
MW01
BH03a
MW03
Deep well = TW1
Abandoned well = BH05a & BH03h

27. N E W S SW SE NW NE EP04 BH06 BH20 BH11 EP7 BH05a BH03b EP8 BH19 MW01b
TW1
BH16 P1
BH12
EP6
BH09
BH18
BH14
BH10
BH1
BH21
BH17
BH13
BH08
MW04
BH26
BH05
BH25
BH22
BH04
BH02
BH07
BH01
MW01
BH03a
MW03 N E W S NE SW SE NW

28. West- East (2.2 Kms)
BH No 16
BH No 07
BH No 12
BH No 20
BH No 23

29. North-South (2.2 Kms) BH No 16 BH No 17 BH No 18 BH No 04 BH No 20

30. Northwest-Southeast (1.8 Kms)
BH No 12
BH No 08
BH No 16
BH No 19

31. Northeast-Southwest (3.4 Kms)
BH No 05a(dry)
BH No 12
BH No 09
BH No 17
BH No 26
BH No 22

32. Fence Diagram 1

33. Fence Diagram 2

34. TW1, 2003
MW04, 2022
EP6, 2018
EP4, 2026
BH13,2024 N

35. Conclusions
Model simulations made under different pumping scenarios indicate that an increase in pumping rate results in substantial regional groundwater level decline, which will lead to the drying of springs, and shallow hand dug wells. This causes reversal of flow from contaminated rivers in to productive shallow aquifers close to highly polluted rivers draining through the city of Addis Ababa.
Excessive pumping and luck of considerations on issues of wellhead (recharge area) protection will likely lead to large-scale groundwater pollution. The vulnerable areas are close to major aquifers.
The study clearly indicates the importance of numerical groundwater flow models in identifying the most susceptible areas, groundwater and surface water interactions.
This work is believed to have far-reaching impactions for many urbanized areas established on fractured aquifers.

38. Alemaya Catchment

39. DEM and Drainage

40. Groundwater level decline (mismangement!?)

41. Borehole locations

42. Groundwater flow

43. Cross-section showing pumping wells from the lake bed

44. Groundwater level monitoring

45. One year groundwater level trend

46. Dried chat plant as a result of water level decline