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UNESCO-IHE Institute for Water Education, Delft (2011)

Modelling and optimization for groundwater resources development : case study of Akaki catchment well fields in Addis Ababa, Ethiopia

Wagena, M.B.

Titre Modelling and optimization for groundwater resources development : case study of Akaki catchment well fields in Addis Ababa, Ethiopia

Auteur : Wagena, M.B.

Etablissement de soutenance : UNESCO-IHE Institute for Water Education, Delft

Grade : Master of Science (MS) 2011

Résumé
Groundwater resource is main source of water supply for many countries in the world. Likewise groundwater is used as source of potable water in the city of Addis Ababa, the capital of Ethiopia, in addition to surface water resources. The abstraction of groundwater resource in well fields of Akaki catchment is currently not based on understanding of drawdown levels and available potential groundwater resources in the area. Meanwhile, this mismanagement of groundwater resource and over exploitation in the Akaki catchment has caused continuous decline of groundwater level. The objective of this study is to find the maximum groundwater drawdown and optimal abstraction rates for each well within the well fields. Different techniques for developing groundwater management models (coupled simulation-optimization approaches) are proposed by a number of researchers, which enable determination of optimal abstraction rates of wells given certain constraints. In this study the groundwater management model (MODMAN) which links the groundwater simulation model (MODFLOW) with the optimization model (LINDO) is used to find optimal abstraction rates and well locations. For this study a regional single layer groundwater model of Akaki catchment developed in 2000E.C by BCEOM in cooperation with SEURECA and Tropics consulting Engineers Plc (later, in 2004 E.C- adjusted by enlarging the model span) is used as groundwater simulation model. This regional model was adjusted with additional grid refinement in the area of interest addressed in this study. To determine the optimal abstraction rates and well spacing- two objectives are formulated for both steady and transient state condition. These are maximization of abstraction rate and minimization of operational, drilling and pipe costs. To achieve these objectives minimum and maximum drawdown constraints of 15 and 30 m are imposed at twenty three control locations. Balance constraints are also imposed for cost minimization. Linear optimization and mixed-integer programming techniques are used for formulating and solving the optimization problems. The research led to new insights on specification of reduced number of drawdown constraints, depending on transmissivity values of the aquifer.

Sujets  : groundwater resources ; wells ; modelling ; catchment areas ; case studies ; Ethiopia

Présentation

Page publiée le 7 janvier 2017, mise à jour le 20 octobre 2018