Numerical Groundwater Flow Modeling Of The Adelle Haromaya Dry Lakes Catchment (east Hararghe Oromia Regional State)

Groundwater of the Adelle – Haromaya dry lakes catchment, an area of aroundrn240km2 in Eastern Oromia, is the primary source of drinking water for Harar,rnHaromaya and Awaday towns, and used also for irrigation and industrial purposes.rnThe demand for this water source is increasing from time to time since the last fewrnyears as the surface water source became scarce and rapid population growth.rnThe groundwater flow system of the area was conceptualized as it consists twornaquifers and one confining units, based on the geo-hydrologic properties of thernsediments and rocks: the upper low permeability aquifer which includes poorly sortedrnalluvial sediments, weathered basement complex and weathered and fracturedrnsedimentary formations; the lower high permeability aquifer which consists the wellrnsorted alluvial sediment, and the confining bedrock. The well sorted sandy gravelrnsediment in the basin is the high yield but localized in the central part of the threernwatersheds. The poorly sorted alluvial, weathered basement and weathered andrnfractured Mesozoic formations, found at the outer part of the study area, are low yieldrnaquifers and overlies in most parts the high yield alluvial aquifer.rnGroundwater inflow to the area is mostly from infiltration of precipitation surplus leftrnfrom evapotranspiration, surface runoff and soil moisture deficit to reach the waterrntable. Groundwater outflow of the study area is mostly through withdrawals from wellsrnfor water supply, irrigation and industries. Natural discharges by two perennial springs,rnand seasonal outflows along the streams to the surface water bodies (seasonal lakes)rnalso contribute to the groundwater outflow of the area. The monitored groundwaterrnlevel and the information obtained from local people showed that groundwater level inrnHaromaya sub-basin declines starting from the development of wells in the area. The two-layer steady-state and transient groundwater flow models were developedrnusing the numerical modeling code MODFLOW 96 + interface with advective transportrnto help better understand the aquifer system, assess the long-term availability ofrngroundwater and evaluate groundwater conditions owing to current pumping and tornplan for future water needs. Boundary conditions, hydraulic conductivity, altitude of thernbottom of the layers, vertical conductance, storage coefficient, recharge, andrndischarge were determined from the existing data and estimated from literatures. Thernmodels were calibrated to water levels of the Feb, 2006 and drilling report static waterrnlevels for steady-state simulation and 13 months water level monitoring data from Feb,rn2005 to Feb, 2006 at Harar water supply observation boreholes for transientrnsimulation.rnModel calibration was accomplished by varying parameters within plausible range tornproduce the best fit between simulated and observed hydraulic heads. For steadystaternsimulation, the root mean square error for simulated hydraulic heads for all wellsrnwas 9.038m. Simulated hydraulic heads were within ±10m for observed values of 80%rnof the wells. For the transient simulation, the difference between the simulated andrnobserved for the four wells was within 10m. The potentiometeric surface calculated byrnsteady-state simulation established initial conditions for the transient simulation.rnWater management alternatives were evaluated by simulating scenarios ofrngroundwater pumping for the next five years under two pumping conditions. Result ofrnpredictive simulation indicate that in five years, if the pumping condition of Dec, 2005rncontinues, groundwater decline by around 6m for Haromaya sub-basin which mayrnaffect the groundwater flow system of the area.

Get Full Work

Report copyright infringement or plagiarism