Using Groundwater Flow Model (MODFLOW) As a Management Tool for Targeted Sub-Basins in Sana’a Basin

Abstract

The numerical modelling (MODFLOW) has emerged as an effective tool for managing groundwater resources and predicting future responses, especially when dealing with complex aquifers systems and heterogeneous formations. MODFLOW model has been used herein as a management tool for the targeted sub- basins (Wadi Bani Hawat sub-basin, Wadi Dhahr & Al-Ghayl sub-basin , Wadi Hamdan & As Sabrah sub-basin and Wadi Ghayman sub-basin); the most important groundwater resources for domestic and agricultural sectors in Sana’a basin . Groundwater extraction from this basin has already exceeded the safe yield of the aquifer, a sharp drop in the water table, and a dry out of most wells. Currently, more than 13000 wells including governmental, private and unauthorized wells are operating within the basin boundary. A conceptual model was designed according to the actual groundwater dynamic flow system in the 2010 Hydrosult Sana’a Basin Model. Also, the governing partial parabolic differential equation was defined, including the vertical conductivity flow between the aquifers. Total groundwater abstraction values were compiled after filtering the available data, including the 2015 NWRA-SB wells inventory data. These data were documented in a database and stored in soft copy (excel form). In this study, three simulations of groundwater development scenarios were distinguished. The first scenario is applied for evaluation of the present status and till 2025. The second and the third scenarios are focused on the effect of water augmentation i.e. decrease the present rate of groundwater abstraction to 30% and 50% respectively, with considering the highly intervention of IWRM structure of Sana'a basin on the on-going activities related to change land use, change crop pattern, value chain, marketing, modern irrigation techniques, water harvesting techniques, etc….. Scenario 3 gives a remarkable improvement of the water resources system in the four sub-basins within a reasonable period (in the year 2025), thus, it will keep the water resources sustainability. It is recommended that irrigation systems should be improved with the usage of harvesting water methods to reduce the losses and increase the groundwater recharge respectively in the targeted four sub-basins