1. GROUNDWATER RECHARGE AND FATE OF GROUNDWATER STORAGE OF
THE WEYBO RIVER CATCHMENT
WELAYITA-HADIYA ZONES SOUTHERN ETHIOPIA

2. BACKGROUND
  Most activities come to rely on groundwater resources than on surface water resources mainly due to their sustainability and quality 
 The Potentialities of Groundwater resource is mainly factored by the Rate of Recharge
 Changes in the Geo-Environment of the catchment and the entire Omo-Gibe Basin is manifested by changes in Recharge Rates

3. OBJECTIVES
Estimating the Optimum Groundwater Recharge
Showing the Temporal-Trend of Recharge w.r.t. the Temporal Changes of the Hydro- Meteorological Parameters
Assessing the Fate of Groundwater Storage
To Show the Major Controlling Parameter of Groundwater Recharge in the Catchment

4. 60 55’ 42 - 7010’28N 370 31’ 39 - 37046’40E AREAL EXTENT = 574Km2
PERIMETER = 124Km
60 55’ ’28N
370 31’ ’40E
DISTANCE FROM ADDIS ABABA AND ALTERNATIVE ROADS
Along Addis Ababa – Butajira – Hosaina Road = 300Km
Along Addis Ababa – Shashemene – Welaita Road = 410Km
Along Addis Ababa – Durame – Areka = 440Km
PERIMETER = 124Km
AREAL EXTENT = 574Km2
DISTANCE FROM ADDIS ABABA AND
ALTERNATIVE ROADS
Along Addis Ababa – Butajira – Hosaina Road = 300Km
Along Addis Ababa – Shashemene – Welaita Road = 410
Along Addis Ababa – Durame – Areka = 440Km

5. Elevated areas are found in the boundaries of the area
PHYSIOGRAPHY
 50% of the area has a slope 2-6%,
 25% has 0-2%,
15% has 6-12%,
 6% has 12-24%
Elevated areas are found in the boundaries of the area
Topographic relief ranges from m from the highest peak Damota to the lowest Weybo valley

6. GEOLOGY
The main lithologic units that are outcropped in the study area and near to its adjacent watersheds are the teritiary volcanics
The Nazareth Groups (of Miocene to Pliocene age) and the flood basalts (Eocene to early Miocene age) are the dominant units that widely cover the study area
About 90% of the area is covered by the Nazareth Group, which comprises of a series of rhyolite-trachyt flows, ignimbrites, pumice and ash falls
The Nazareth Group unconformably overlies the early flood basalts

8. HYDROGEOLOGIC UNITS AND AQUIFER SYSTEMS AQUIFER FORMATION
HYDROGEOLOGY
HYDROGEOLOGIC UNITS AND AQUIFER SYSTEMS
AQUIFER FORMATION
-Weathered and fractured ignimbrite/welded tuff
-Sediments associated with weathered pumice
-Weathered and fractured rhyolites and Trachytes
TYPES OF AQUIFERS IN THE CATCHMENT
-Dominantly leaky aquifers

9. HYDROGEOLOGICAL MAP OF THE STUDY AREA

10. Geological structures and hydraulic conductivity values
HYDRAULIC CHARACTERISTICS
  Correlation has been made between
Geological structures and hydraulic conductivity values
 A greater extent of the study area possesses
a low permeability zone.

11. GROUND WATER FLOW SYSTEMS AND POTENTIOMETRIC CONTOURS
Regional, intermediate and local flow systems

12. RECHARGE AND DISCHARGE ZONES
 Zonation based on topography

13. Flow lines tend to diverge from recharge areas and
 Zonation based on peizometric patterns
Flow lines tend to diverge from recharge areas and
converge toward discharge zones

14.  Zonation Based on Hydro chemical Trends

15. POTENTIAL EVAPOTRANSPIRATION = 1074.4mm
HYDROMETEOROLOGY
PRECIPITATION = 1340 mm
TEMPRATURE = C
RELATIVE HUMIDITY = 63.5%
MEAN WIND SPEED = 2.45m/s
POTENTIAL EVAPOTRANSPIRATION = mm
ACTUAL EVAPOTRANSPIRATION (AET) = 960.3mm

16. STREAM DISCHARGE OF WEYBO RIVER
(i) Scaling up the stream flow values
Qmouth = (A2/A1) Qgauged
Q = Qan (Pan/P)
(ii) The analogue method

18. GROUNDWATER RECHARGE (GWR)
 CONVENTIONAL WATER BALANCE APPROACH
GWR = 88.19mm/annum
 STREAM HYDROGRAPHS ANALYSES
Mean long-term minimum flow = 62.5mm/year
Seasonal recession method = 74.5mm/year
 CHLORIDE MASS BALANCE = 123.5mm/year

19. THE OPTIMUM GROUND WATER RECHARGE
ESTIMATION BASED ON GROUNDWATER BUDGET
ESTIMATED GROUNDWATER OUTFLOW = 78.56
GW INFLOW ESTIMATED FROM WATER BALANCE AND SEASONAL RECESSION METHOD = 81.5mm
THE OPTIMUM GROUND WATER RECHARGE = 81.5

20. TREND OF GROUNDWATER RECHARGE

21. FATE OF GROUNDWATER STORAGE
Equating the linear equation: y = -587x
Groundwater storage will be heavily affected and appreciable change in storage will be seen after 30 years now on

22. RECHARGE TREND W.R.T. CONTROLLING
HYDRO-METEOROLOGICAL PARAMETERS
Mean precipitation is slightly decreasing,
however, its rate of declination is not comparable

23. mean temperature shows an increasing trend
mean wind speed shows an increasing trend

24. potential evapotranspiration is slightly increasing

25. CONCLUSION -Groundwater recharge is computed using 4 different Methods
-Groundwater recharge is computed using 4 different Methods
and four different values are obtained. The optimum=81.5mm
-The decline in groundwater recharge is highly attributed to
changes in the environment
-Measurable changes in groundwater storage will be seen in
a 30 years period of time if environmental changes are
keeping on the same rate
CONCLUSION
CONCLUSION
-The groundwater recharge estimated from measurements of chloride yields an over estimated result.

26. THANK YOU!!