Model Based Groundwater System Analysisffor Hayk -ardibo Catchment

A research was undertaken to understand better the interaction between the surface andrngroundwater of the Hayk-Ardibo Catchment. A two-dimensional aerial finite-differencerngroundwater flow model was used to simulate the groundwater flow and establish a hydrorngeologic budget of the region .rnThe Hayk-Ardibo Catchment lie on the western Afar rift escarpment, an area with a complexrngeologic history. The geologic history includes volcanic rocks with the major NNE-SSW faultrntrend in the area. Faulting have modified the distribution and thickness of volcanic rocks, theirrnsecondary porosity & permeability and the degree of weathering and fracturing which internrninfluence the occurrence and movement of ground-water in the region. The permeability ofrnthe aquifer which are highly weathered and fractured are associated with high hydraulicrnconductivity value which in most case is the typical nature of the Tertiary volcanic located inrnthe center of the Catchment along lake area that control the gradient of the potentiometricrnsurface and ground water flow in that region. The geology, hydrogeology and water balancernof the study area has been discussed and it helped to understand the groundwater flow systemrnin the study area . These are the basics, which helped to conceptualize and determine the typernof aquifer, its aerial extent and boundaries.rnA Conceptual model was first developed to decide in order to determine the modelingrnapproach .. The model boundaries determined to represent natural hydrological boundariesrnincorporate (1) no-flow boundary along the westem, Eastern and Southern boundaries, (2)rnflux boundary along Northwestern boarder of the study area (3) general head boundary on therntwo lakes and internal boundary along Ankerka River draining the central catchment.rnSeveral simplifying assumptions were made for the conceptualization and simulation of flowrnin the Catchment: 1) Recharge to the groundwater is assumed only from precipitation with inrnthe catchment and there is no additional subsurface inflow across boundary in any part of thernstudy area. Recharge varies spatially, 2) single layer has been used in the model 3) Darcy’srnlaw is applicable to flow through the fractures 4) unconfined aquifer is assumed in the model,rnand 5) evaporation was not explicitly simulated in the model. Recharge rates were consideredrnas ‘net recharge,’ and 6) discharge occurs from the aquifer along the Northern boundaryrnwhere aquifers are hydraulically connected to down Catchment.

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