Transcript Document
GROUNDWATER RECHARGE AND FATE OF GROUNDWATER STORAGE OF THE WEYBO RIVER CATCHMENT WELAYITA-HADIYA ZONES SOUTHERN ETHIOPIA 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 OBJECTIVES Estimating the Optimum Groundwater Recharge Showing the Temporal-Trend of Recharge w.r.t. the Temporal Changes of the HydroMeteorological Parameters Assessing the Fate of Groundwater Storage To Show the Major Controlling Parameter of Groundwater Recharge in the Catchment AREAL EXTENT = 574Km2 PERIMETER = 124Km 60 55’ 42 - 7010’28N 370 31’ 39 - 37046’40E 1000000 950000 900000 850000 800000 750000 DISTANCE FROM ADDIS ABABA AND ALTERNATIVE ROADS 700000 650000 Legend Study area 600000 Omo-Gibe Basin 550000 0 500000 100000 150000 200000 250000 50000 300000 100000 350000 Location of the study area in the Omo-Gibe Basin Along Addis Ababa – Butajira – Hosaina Road = 300Km Along Addis Ababa – Shashemene – Welaita Road = 410 150000 mAlong Addis Ababa – Durame – Areka = 440Km 400000 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 18001900m from the highest peak Damota to the lowest Weybo valley 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 795000 790000 785000 780000 775000 Legend 770000 Flood basalt Rhyolite 765000 Trachyte Ignimbrite 760000 Alluvium 755000 Inferred faults Known fault 750000 Elevation contours 1800 0 10000 20000 30000 40000 meter 335000 340000 345000 350000 355000 360000 365000 370000 375000 380000 3 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 HYDROGEOLOGICAL MAP OF THE STUDY AREA 795000 790000 785000 780000 775000 770000 765000 760000 0 10000 20000 30000 meter 795000 HYDRAULIC CHARACTERISTICS 790000 0.8 785000 0.7 0.6 780000 0.5 775000 0.4 0.3 770000 0.2 765000 0.1 335000 340000 Legend 0 345000 350000 10000 355000 360000 20000 365000 30000 370000 375000 380000 40000 meter Boreholes and their distribution used to map hydraulic conductivity of the area Correlation has been made between Geological structures and hydraulic conductivity values A greater extent of the study area possesses a low permeability zone. GROUND WATER FLOW SYSTEMS AND POTENTIOMETRIC CONTOURS Regional, intermediate and local flow systems 795000 790000 785000 780000 775000 Legend 770000 765000 Regional groundwater flow directions Local groundwater flow directions Ground water table elevation contours 1850 760000 335000 340000 345000 0 10000 350000 355000 20000 360000 30000 365000 40000 meter 370000 375000 RECHARGE AND DISCHARGE ZONES Zonation based on topography 790000 785000 2880 780000 2200 775000 770000 e g r a h c Re 765000 e n zo 335000 340000 345000 350000 355000 360000 365000 370000 375000 0 10000 20000 30000 40000 meter 1900 800 Zonation based on peizometric patterns Flow lines tend to diverge from recharge areas and converge toward discharge zones 790000 785000 780000 775000 Legend Zones of converging flows Catchment boundary 770000 Ground water flow directions 765000 Ground water table contours 340000 345000 0 350000 355000 10000 360000 20000 365000 30000 370000 375000 380000 40000 meter Fig. Convergence and divergence zones of flow lines showing recharge and discharge zones Zonation Based on Hydro chemical Trends HYDROMETEOROLOGY PRECIPITATION = 1340 mm TEMPRATURE = 19.210C RELATIVE HUMIDITY = 63.5% MEAN WIND SPEED = 2.45m/s POTENTIAL EVAPOTRANSPIRATION = 1074.4mm ACTUAL EVAPOTRANSPIRATION (AET) = 960.3mm STREAM DISCHARGE OF WEYBO RIVER (i) Scaling up the stream flow values Qmouth = (A2/A1) Qgauged (ii) The analogue method Q = Qan (Pan/P) 3 SUMMARY OF WEYBO RIVER DISCHARGE,m /s, 1992 - 2005 WAT. YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC TOTAL 1992 0.873 0.742 1.116 2.475 5.521 3.785 5.754 27.050 35.044 34.221 26.519 10.400 1993 1.235 1.942 0.787 1.907 8.330 7.991 8.415 17.491 11.366 4.984 1.654 0.781 1994 0.622 0.548 1.014 1.751 3.505 3.776 17.453 27.442 12.739 4.436 1.430 0.713 1995 0.548 0.557 0.534 3.310 2.833 2.426 11.675 14.278 21.995 11.761 1.996 0.669 1996 0.569 0.348 1.618 3.855 6.759 30.334 22.546 21.688 28.892 1.878 0.666 1997 0.424 0.345 0.528 3.113 3.575 2.152 3.001 11.454 18.458 7.985 1998 2.662 1.598 1.509 2.043 5.394 6.252 14.847 26.248 14.988 16.848 6.432 2.054 1999 1.318 0.928 1.223 2.302 2.553 2.856 9.367 11.557 10.602 19.428 5.146 1.483 2000 0.525 0.427 0.545 1.760 4.710 1.509 2.564 8.012 12.695 6.160 1.556 2001 0.704 0.542 0.545 1.350 5.071 6.535 13.131 26.761 19.498 12.598 3.060 0.848 2002 0.878 0.793 1.940 1.350 0.943 0.973 1.512 2.673 2.187 0.843 0.366 0.610 2003 0.539 0.454 1.630 2.635 0.914 2.043 6.841 20.403 5.671 0.843 0.365 0.628 2004 0.873 0.742 1.116 2.453 4.051 1.229 3.260 5.208 4.572 5.777 1.129 0.510 2005 0.448 0.422 1.515 4.032 2.554 1.231 3.259 5.207 4.571 5.778 1.128 0.510 0.873 0.742 1.116 2.453 4.051 5.221 8.915 15.623 13.081 10.636 5.408 2.101 70.219 MEAN 4.180 5.406 7.310 7.230 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 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 TREND OF GROUNDWATER RECHARGE FATE OF GROUNDWATER STORAGE Equating the linear equation: y = -587x + 93.07 Groundwater storage will be heavily affected and appreciable change in storage will be seen after 30 years now on RECHARGE TREND W.R.T. CONTROLLING HYDRO-METEOROLOGICAL PARAMETERS MEAN PPT,mm TREND OF PRECIPITATION IN THE STUDY AREA 1500 1400 1300 1200 1100 1985-1989 1990-1994 1995-1999 2000-2004 Mean precipitation is slightly decreasing, however, its rate of declination is not comparable mean temperature shows an increasing trend 16 0 Minimum T( C) 15 14 13 12 11 10 1988 1989 1990 1991 1995 1996 1997 1998 1999 2000 2001 2002 2003 9 8 7 6 5 4 3 2 1 0 19 88 19 89 19 90 19 91 19 92 19 93 19 94 19 95 19 96 19 97 19 98 19 99 20 00 20 01 20 02 20 03 20 04 20 05 Mean Wind Speed(m/s) I n c r e a s i n g T r e n d o f M e a n W i n d Sp e e d mean wind speed shows an increasing trend 2004 TREND OF PET, 1988-2005 potential evapotranspiration is slightly increasing 1200 1150 PET, mm 1100 1050 1000 950 900 850 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 CONCLUSION -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 -The groundwater recharge estimated from measurements of chloride yields an over estimated result.