The Use of GIS Techniques and Geophysical Investigation for Flood Management at Wadi Al-Mafraq Catchment Area

The rapid expansion of urban areas over the past two decades within Mafraq City has affected the surface hydrology runoff. Developments in Mafraq City have changed the land coverage from vegetation to impervious surface (Asphalt and Buildings) which covers most of the urban areas within Mafraq City. This reduced the ability of the land to absorb rainfall and force the excess rainfall-runoff to flow faster over the surface. As a result, the West and central regions of Mafraq City recently experienced floods that have affected hundreds of people. In order to control flood and minimize its impacts on local people, it is necessary to manage such floods. The present study aims at identifying the potential sites for water harvesting dam within the Wadi Al-Mafraq watershed to control the flood that pass through the city using GIS techniques. In order to select the potential site for the water-harvesting dam, five physical criteria that affect the water harvesting were identified based on a literature review. These criteria are rainfall, soil texture, slope, material of vadoze zone and drainage density. Based on the use of the Weighted Linear Combination (WLC) method, a water harvesting potential map was generated. The outcome of the GIS analysis was validated by fieldwork investigations carried out using Time Domain Electromagnetic Geophysical method (TDEM). The TDEM results show that (10 - 25) m of silty clay, soil and alluvium deposits are dominated the proposed site as the topmost layer. Moreover, three to four distinctive subsurface geo-electrical layers were identified in terms of their resistivity, thicknesses and structures. The present study proves the importance of the integration of different techniques GIS and TDEM in water harvesting and flood management studies.