GROUNDWATER RECHARGE AND FATE OF GROUNDWATER STORAGE OF THE WEYBO RIVER CATCHMENT WELAYITA-HADIYA...
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Transcript of GROUNDWATER RECHARGE AND FATE OF GROUNDWATER STORAGE OF THE WEYBO RIVER CATCHMENT WELAYITA-HADIYA...
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 Hydro- Meteorological Parameters
Assessing the Fate of Groundwater Storage
To Show the Major Controlling Parameter of Groundwater Recharge in the Catchment
Legend
Tow ns
A ll w eather roads
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H osaina
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Study area
O m o-G ibe Basin
Location of the study area in the O m o-G ibe Basin
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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
AREAL EXTENT = 574Km2
PERIMETER = 124Km
60 55’ 42 - 7010’28N370 31’ 39 - 37046’40E
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 1800-1900m 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
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Legend
Flood basalt
Rhyolite
Trachyte
Ignim brite
A lluvium
Inferred faults
Known fault
E levation contoursm eter1800
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
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LegendH ydraulic conductiv ity zones
Low H ydraulic conductiv ity
M oderate hydraulic conductiv ity
H igh hydraulic conductiv ity
(K<=0.3)
(0.3<K<0.5)
(0.5<K>0.8)
Know n fault
In ferred fault
G roundw ater contours 1850
R egional groundwater flow d irection
Local groundw ater flow direction
Inferred region of groundwater outflow
Inferred region of groundwater inflow
D rainage netw orks
Sub-catchm ent boundary
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Know n region of groundw ater outflow
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Boreholes
Springs
W ater type and TD S rangesNa-C a-HCO 3-Type(70-100m g/l)Ca-M g-HC O 3-Type(25-80m g/l)C a-Na-HC O 3-Type(200-300m g/l)Na-Ca-HCO 3-Type(100-190m g/l)Na-Ca-HCO 3-Type(80-185m g/l)
HYDROGEOLOGICAL MAP OF THE STUDY AREA
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Boreholes and their d istribution used to m ap hydraulic conductivity o f the area
Legend
Correlation has been made between Geological structures and hydraulic conductivity values
A greater extent of the study area possesses a low permeability zone.
HYDRAULIC CHARACTERISTICS
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Legend
R egional groundw ater flow d irections
Local groundwater flow directions
G round w ater table e levation contours1850
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Fig. R egional and local ground w ater flow system s as in ferred from ground w ater e levation contours
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GROUND WATER FLOW SYSTEMS AND POTENTIOMETRIC CONTOURS Regional, intermediate and local flow systems
RECHARGE AND DISCHARGE ZONES
Zonation based on topography
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RECHARGE & DISCHARGE ZONES AS INFERRED FROM ELEVATION CONTOURS
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Zonation based on peizometric patterns
Flow lines tend to diverge from recharge areas and converge toward discharge zones
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Fig. C onvergence and d ivergence zones of flow lines show ing recharge and d ischarge zones
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Legend
Zones of converging flow s
C atchm ent boundary
G round water flow d irections
G round w ater table contours
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Same clusters showing aquifer interactions
Recharging zones, Na-Ca-HCO3-Type waters(cluster-2)
Discharging zone, reprasented by Na-Ca-HCO3-W ater Type(Clusters 1,4,5)
Legend
C atchm ent boundary
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Hydrochemical clustrs showing aquifer interconectivity and 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
Q = Qan (Pan/P)
(ii) The analogue method
SUMMARY OF WEYBO RIVER DISCHARGE,m3/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 7.230 1.878 0.666
1997 0.424 0.345 0.528 3.113 3.575 2.152 4.180 5.406 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 7.310 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
MEAN 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
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
Trend of Ground Water Recharge, 1992-2005
y = -5.8718x + 93.078
0
10
20
30
40
50
60
70
80
90
100
1992-1993 1993-1994 1994-1995 1995-1996 1996-1997 1997-1998 1998-1999 1999-2000 2000-2001 2001-2002 2002-2003 2003-2004 2004-2005
FATE OF GROUNDWATER STORAGE
Groundwater storage will be heavily affected and appreciable change in storage will be seen after 30 years now on
Equating the linear equation: y = -587x + 93.07
RECHARGE TREND W.R.T. CONTROLLING HYDRO-METEOROLOGICAL PARAMETERS
Mean precipitation is slightly decreasing, however, its rate of declination is not comparable
mean temperature shows an increasing trend
mean wind speed shows an increasing trend
TREND OF PET, 1988-2005
850
900
950
1000
1050
1100
1150
1200
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
PE
T, m
m
potential evapotranspiration is slightly increasing
-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
-The groundwater recharge estimated from measurements of chloride yields an over estimated result.