EVALUATION AND DEVELOPMENT OF GROUND WATER RESOURCES OF ADAA BECHO PLAINS FOR IRRIGATION PROJECT

1. 3rd Annual Connference EHA Aug. 23, 2008 1 EVALUATION AND DEVELOPMENT OF GROUND WATER RESOURCES OF ADA'A�BECHO PLAINS FOR IRRIGATION PROJECT Engida ZA*, Tilahun A*, Dr. Seifu K* and Dr. Yilma*

2. 3rd Annual Connference EHA Aug. 23, 2008 2 TABLE OF CONTENT Location Objective and scope of the study Methodology Geology and structures, Hydrology, Geophysics, Drilling of mapping wells Isotope and water quality, Water quality monitoring, Hydrogeology Main study output of the project Developing conceptual models (Inception phase) Preparing hydrogeological map Preparing groundwater flow system of AB Plains

3. 3rd Annual Connference EHA Aug. 23, 2008 3 TABLE OF CONTENT� Evaluation of groundwater potential of Ada'a and Becho plains Interaction of Debre Zeit Lakes with the groundwater system Interaction of Awash river with the groundwater system

4. 3rd Annual Connference EHA Aug. 23, 2008 4 1. LOCATION OF THE PROJECT AREA Central Ethiopia, in Oromia Regional State in Upper Awash river Basin Ada�a plain is found between elevation 1600 and 1900 masl and approximately between Co-ordinates 38050�E - 39015�E and 8030�N - 8053�N (T area-1641 km2 ,223km2M Net area of the plain1418 km2 Becho plain is found between elevation 2040 and 2120 masl and approximately between coordinates 38008�E - 38036�E and 8038�N - 9000�N (T area 1414km2 seasonally inundated area117km2 net area 1297 km2)

5. 3rd Annual Connference EHA Aug. 23, 2008 5 Fig1 LOCATION MAP OF THE PROJECT AREA

6. 3rd Annual Connference EHA Aug. 23, 2008 6 2. OBJECTIVE AND SCOPE OF THE STUDY Previous studies have indicated that there is a possible high groundwater potential, currently agriculture consists mainly of rain fed annual cropping. Crop yields are generally good in the project area, the high population growth has made the available land decreasing from year to year. Unless remedial measures are taken, the standard of living of the farmers will further decline, especially in view of the current rapid population growth rate of about 2.9 % per year. Since the rural population is expected to double in about 25 years, it is increasingly important to deal with these issues as soon as possible by implementing irrigation in the area.

7. 3rd Annual Connference EHA Aug. 23, 2008 7 2. OBJECTIVE AND SCOPE � Determine the hydrogeological condition of the Ada'a-Becho plains groundwater system Qualitative and quantitative evaluation of the groundwater resources of the plain and select potential well fields Carry out analytical and/or numerical model of the main aquifer of the area to recommended appropriate groundwater management Develop strategy of groundwater resources development together with cost estimates

8. 3rd Annual Connference EHA Aug. 23, 2008 8 3. METHODOLOGY Data collection & review of previous works. Geological & geomorphologic mapping Hydrological survey and analysis Hydrogeological investigation (water point inventory, water quality survey, water quality monitoring, mapping well drilling & testing) Geophysical investigation (Resistivity and TEM) Isotope hydrogeology Detail qualitative & quantitative groundwater potential evaluation Prioritization of potential prospective area for Pilot well field development Analytical Modelling 1. 900, 34 2. previous maps, satelitiand areail, field work, drilling of mapping 3. Hydrometer1. 900, 34 2. previous maps, satelitiand areail, field work, drilling of mapping 3. Hydrometer

9. 3rd Annual Connference EHA Aug. 23, 2008 9 3. MAIN OUTPUTS OF THE PROJECT A. Developing conceptual models (In. phase): The hydrogeological and isotope data from Akaki catchment shows the following conditions Most of the deep wells drilled in Addis Ababa and adjacent areas are highly confined. Confining acidic volcanic and the aquifer basic rocks (basalt of different comp. and ages) The upper part of Akaki catchment is steep and composed of dominantly acidic volcanic rocks (which are practically impervious) it is difficult to assume that a recharge that occurred at the upper part of the catchment has formed a confined aquifer in the basalts at the central, eastern and western AA. The upper part of Akaki river catchment is merely runoff generator.

10. 3rd Annual Connference EHA Aug. 23, 2008 10 3. MAIN OUTPUTS OF THE PROJECT� A. Developing conceptual models (In. phase): The hydrogeological and isotope data from Akaki catchment shows the following conditions The tritium value from different sources Yves M. Travi, Kebede S. (2000) shows Except few wells (probably shallow wells) the other wells both cold and thermal wells are depleted in tritium value in general Reconnaissance surveys at Muger and Abbay rivers gorges showed that the Mesozoic sedimentary formation is most likely dipping in SSE direction, which highly favors the Abay plateau groundwater flow to SSE direction into Awash River basin These observations led to conceptualize that the groundwater of Addis Ababa and in general Becho and Ada'a plains groundwater is recharged mainly from outside their surface catchments. The basalt plateau of Abay river basin that is found adjacent to Akaki and Awash rivers catchments could be the main recharge zone of Ada'a plain (as shown the figs 3and 4 below)

11. 3rd Annual Connference EHA Aug. 23, 2008 11 Fig 2 CONCEPTUAL MODEL DEV.

12. 3rd Annual Connference EHA Aug. 23, 2008 12 FIG 3 CONCEPTUAL X-SECTION AP-AA-ADAA

13. 3rd Annual Connference EHA Aug. 23, 2008 13 FIG 4 CONCEPTUAL X-SECTION AP-BECHO-ADAA

14. 3rd Annual Connference EHA Aug. 23, 2008 14 3. MAIN OUTPUTS OF THE PROJECT� B. Preparation of Hydrogeological map and cross-section: Phase I: Inv. and analysis: Hydrogeological conditions of the area is a function of geomorphology and tectonics, on the Plateau older Tertiary volcanic outcrops to the south the younger geological formation over lies the older volcanic unit The recharge condition, groundwater flow and aquifer parameters in the Adaa-Becho plains is highly governed by the general bedding of the sedimentary formation underlying the volcanic unit, the tectonic condition and the hydraulic properties of the different volcanic units that outcrops in the basin There are two basaltic aquifers in the Becho plain and along west-east direction from Becho-Legedadi section which are separated by ignimbrites and welded tuffs

15. 3rd Annual Connference EHA Aug. 23, 2008 15 3. MAIN OUTPUTS OF THE PROJECT� B. Preparation of Hydrogeological map and cross-section: Phase I: Inv. and analysis: Upper Basalt Aquifer composed of Quaternary of Weliso-Ambo basalts, Akaki basalts: scoria and spatter cones, and Tertiary-Neogene�s basalt of Addis Ababa basalts and Tulu ries basalts. one aquifer system in Ada�a plain (south of Dukem) distributed in Upper Awash, where it outcrops at Central Addis Ababa, Weliso and Akaki and it also overlain by ignimbrites and tuffs at Becho plaains, Legedadi area, in general where the ignimbrites and tuff outcrops Varies from more than 200 to 50 m thickness: TDS 400-700 mg/l by water balance method and chloride balance method the recharge of this aquifer is estimated to be 390 Mm3/year

16. 3rd Annual Connference EHA Aug. 23, 2008 16 3. MAIN OUTPUTS OF THE PROJECT� B. Preparation of Hydrogeological map and cross-section: Phase I: Inv. and analysis: Lower Basalt Aquifer composed of tertiary Tarmaber basalt composed of dominantly scoraceous basalt and Amba Aiba basalt. These tertiary basalt formations occupy more than 75% of Abay plateau about 7,000 km2. . mapping wells drilling at Becho Plain, Holota, Melka Kunture, Legedadi areas penetrated at different depth this aquifer. The total confining head more than 220 meters The yield of the well was progressively increasing when the depth of penetration is increased in this aquifer. Water level varies from artesian condition to a depth of 67.5 meters The total annually recharge of the lower aquifer is estimated by different method is about 700Mm3/year.

17. 3rd Annual Connference EHA Aug. 23, 2008 17 Fig 5 Hydrogeological Map of ADAA-BECHO PLAINS

18. 3rd Annual Connference EHA Aug. 23, 2008 18 Fig 6 HYDROGEOLOGICAL X-SECTION ALONG BECHO PLAIN

19. 3rd Annual Connference EHA Aug. 23, 2008 19 Fig 7 Hydrogeological x-section along Kachise �Becho-Ada�a line

20. 3rd Annual Connference EHA Aug. 23, 2008 20 Fig 8 Muger-Holota-Becho

21. 3rd Annual Connference EHA Aug. 23, 2008 21 Fig 9 SEGNO GEBYA-LEGEDADI

22. 3rd Annual Connference EHA Aug. 23, 2008 22 Fig 10 Hydrogeological x-section along Plateau -Legedadi - Akaki section line

23. 3rd Annual Connference EHA Aug. 23, 2008 23 Fig 11 Hydrogeological x-section in Ada�a Plain (Southwest � Northeast direction)

24. 3rd Annual Connference EHA Aug. 23, 2008 24 3. MAIN OUTPUTS OF THE PROJECT� B. Preparation of Groundwater flow system of AB Plains: Phase I: Inv. and analysis: Groundwater level elevation contour map was constructed for the regional basalt aquifer (lower aquifer) applying the data generated from drilling of mapping wells and existing bore holes identified to be representing the regional aquifer water level On the groundwater elevation contour map the following understanding is obtained � Entoto and Wechecha �furi and Bedegebaba ridges acts as local barrier � The recharge at Abay plateau flows to Upper Awash through two main direction i.e. through Becho plain and along Legedadi areas � Almost 100% of Abay plateau is the recharge area of the lower basalt aquifer in Upper Awash basin Bore holes drilled along flow paths have yield and artesian if drilled at lower places

25. 3rd Annual Connference EHA Aug. 23, 2008 25 Fig 12 SIMPLIFIED GROUNDWATER FLOW PATHS IN AB Around Modjo, previously drilled wells depth upto 250 m in pyroclastic rocks, were having a yield not greater than 10 l/s and transmissivity a maximum of 200 m2/day. In the recent drilling for Ada'a project thew pyroclastic rocks was penetrated at depth of 343 meter and the yield of bore holes is very high >100 l/s and the transmsiisvity is >10,000 m2/dayAround Modjo, previously drilled wells depth upto 250 m in pyroclastic rocks, were having a yield not greater than 10 l/s and transmissivity a maximum of 200 m2/day. In the recent drilling for Ada'a project thew pyroclastic rocks was penetrated at depth of 343 meter and the yield of bore holes is very high >100 l/s and the transmsiisvity is >10,000 m2/day

26. 3rd Annual Connference EHA Aug. 23, 2008 26 Fig 13 Drilling at Holeta area

27. 3rd Annual Connference EHA Aug. 23, 2008 27 Fig 14 DRILLING AT ASGORI

28. 3rd Annual Connference EHA Aug. 23, 2008 28 Fig 15 Melka Kunture Pumping test Q=36 l/s

29. 3rd Annual Connference EHA Aug. 23, 2008 29 Fig 16 Artesian flow well drilled south of legedadi

30. 3rd Annual Connference EHA Aug. 23, 2008 30 3. MAIN OUTPUTS OF THE PROJECT� C. Evaluation of groundwater potential of Ada�a plains (ECGPAP): AQUIFER CHARACTERISTICS aquifer composed of scoria, scoraceous Basalt and fractured basalt unconfined extensive with high transmissivity groundwater recharge to Ada�a plain groundwater system is from three direction i.e.i) between Mountains Yerer and Guji, ii) between Bede Gebaba and Ziquala (Qgz) and from Mojo, Wedecha and Belebela catchment (Qmw).

31. 3rd Annual Connference EHA Aug. 23, 2008 31 ADAA PLAIN

32. 3rd Annual Connference EHA Aug. 23, 2008 32 Fig 11 Hydrogeological x-section in Ada�a Plain (Southwest � Northeast direction)

33. 3rd Annual Connference EHA Aug. 23, 2008 33 3. MAIN OUTPUTS OF THE PROJECT� C. ECGPAP: ESTIMATED RECHARGE AP

34. 3rd Annual Connference EHA Aug. 23, 2008 34 3. MAIN OUTPUTS OF THE PROJECT� ESTIMATED EXPLOITABLE GWR OF AP Analytical method Excluding the recharge from Becho plain due to the maximum exploitation of the groundwater resource in the plain the net available exploitable ground water potential is estimated about 1,046MCM/year or 2.9MCM/day or 33 500 l/s

35. 3rd Annual Connference EHA Aug. 23, 2008 35 3. MAIN OUTPUTS OF THE PROJECT� PRIORITIZING GROUNDWATER PROSPECTING SITES IN AP

36. 3rd Annual Connference EHA Aug. 23, 2008 36 3. MAIN OUTPUTS OF THE PROJECT� C. ECGPAP: Fig 17 Prospective groundwater potential sites

37. 3rd Annual Connference EHA Aug. 23, 2008 37 3. MAIN OUTPUTS OF THE PROJECT� C. ECGPAP: Parameters considered The groundwater system as extensive unconfined aquifer. Average transmissivity of the confined aquifer Tavg = 5000m2/day The specific yield of the aquifer is estimated to be about 0.25. Thickness of Aquifer 300 m 100 wells 1km apart in grid

38. 3rd Annual Connference EHA Aug. 23, 2008 38 C. ECGPAP: Fig 18 Proposed PW in prioritized sites

39. 3rd Annual Connference EHA Aug. 23, 2008 39 C. ECGPAP: Calculated Max DD in the WF for different scenario of Abstraction rate and duration of pumping

40. 3rd Annual Connference EHA Aug. 23, 2008 40 C. ECGPAP: Estimated EGWP of prioritized area

41. 3rd Annual Connference EHA Aug. 23, 2008 41 C. ECGPAP: IMPACT ON THE LAKES

42. 3rd Annual Connference EHA Aug. 23, 2008 42 C. ECGPAP: IMPACT ON THE LAKES The result of analysis shows that the maximum drawdown created on the lakes is less than 14 meters on the nearest lake Bishoftu Guda. Here it is found possible to shift further to the east the well field by two kilometers and the draw down on Lake Bishoftu Guda decrease similar to the other lakes. Further Numerical modeling shall be conducted to verify this analytical calculation in the final report. The estimated exploitable resources is estimated about 378 MCM/year on site B.

43. 3rd Annual Connference EHA Aug. 23, 2008 43 C. ECGPAP: NEXT STAGE Drilling of 5 pilot wells each well discharge 100 l/s Detail design of 500 ha Pressurized irrigation Ground water modelling Feasibility design of 10, 000 ha pressurized irrigation

44. 3rd Annual Connference EHA Aug. 23, 2008 44 MAIN OUTPUTS OF THE PROJECT� D. Interaction of Debre Zeit Lakes with the groundwater Hydrogeological method of analysis Water quality monitoring Monthly water balance of DZ lakes (hydrologic method

45. 3rd Annual Connference EHA Aug. 23, 2008 45 MAIN OUTPUTS OF THE PROJECT� D. Interaction of Debre Zeit Lakes with the groundwater Hydrogeological method of analysis Constructing a groundwater level elevation contour: two groundwater flow regimes within Ada�a plain caused by Debre Zeit lakes and Mountain Bede Gababa which they act as a groundwater divide and Barrier to the ground water system (fig 19) Water Quality monitoring (fig 20) Lake Water balance of DZ lakes (fig21)

46. 3rd Annual Connference EHA Aug. 23, 2008 46 Fig 19 Groundwater flow paths at DZ lakes area

47. 3rd Annual Connference EHA Aug. 23, 2008 47 Fig 20 EC versus time monitored BH (WQM)

48. 3rd Annual Connference EHA Aug. 23, 2008 48 Fig 21 Time series of groundwater Inflow-outflow (1000 m3)

49. 3rd Annual Connference EHA Aug. 23, 2008 49 MAIN OUTPUTS OF THE PROJECT� D. Interaction of Debre Zeit Lakes with the groundwater All the methods (Hydrogeological, water quality monitoring and Water balance of DZ lakes showed method the lakes except Kurftu lake acts as groundwater divide (recharge boundary) and Bede gebaba ridge as a barrier.

50. 3rd Annual Connference EHA Aug. 23, 2008 50 MAIN OUTPUTS OF THE PROJECT� Interaction of Awash river with the groundwater Awash river monitored two stations (upstream at Melkakunture and down stream at Ombole river gauging stations) far apart more than 50kms. From July- September, the EC at the two stations are nearly similar (about 100�S/cm). During dry season the electrical conductivity value measured at the two stations shows larger gap (400�S/cm at Melka Kunture and 600-650�S/cm at Ombole respectively). The conductivity of the regional groundwater of the area between Melka Kunture and Ombole vary from 600 to 650 �S/cm. The higher EC value measured at Ombole site verifies the fact that the river is being recharged by regional groundwater and the base flow from November to June at this station is from the regional groundwater

51. 3rd Annual Connference EHA Aug. 23, 2008 51 Fig 22 Interaction of Awash with the groundwater

52. 3rd Annual Connference EHA Aug. 23, 2008 52 TEM Interpretation at Inchini

53. 3rd Annual Connference EHA Aug. 23, 2008 53 Segno Gebeya

54. 3rd Annual Connference EHA Aug. 23, 2008 54 Sululta

55. 3rd Annual Connference EHA Aug. 23, 2008 55 Chancho

56. 3rd Annual Connference EHA Aug. 23, 2008 56 THANK YOUFOR YOUR ATTENTION!!