GROUNDWATER POTENTIAL MAPPING USING GIS AND REMOTE SENSING: A CASE STUDY IN WELMEL WATERSHEDE, GENALE-DAWA RIVER BASIN, SOUTHEAST ETHIOPIA

Abstract

To fulfil the demand of a rapidly growing population in drought-prone areas with high rate of urbanization, identification and management of groundwater resources are required. In the welmel catchment, a search for an alternative source of water has been always a major issue. The current practice of groundwater potential zone (GWPZ) identification is time consuming and uneconomical. This study applied integration of GIS-Remote Sensing (RS) and Analytical Hierarchy Process (AHP) for mapping the GWPZ of welmel catchment , Southeast Ethiopia. This technique is a fast, accurate, and feasible technique. Groundwater potential zone influencing parameters were derived from Operational Land Imager 8, digital elevation model(DEM) 20*20 resolution and secondary sources were utilized in this research. These were geomorphology, lineament density , lithology, rainfall, drainage density , slope , elevation , LULC, and soil texture were prepared . Borehole data were used for results validation. All thematic layers were reclassified based knowledge based analysis that was reviewed from different kinds of literature. Then the weight for each factor was assigned according to their relative importance as per suitable based on Saatty's scale of AHP. The important factors result show that geomorphology and lineament density have a higher weight and soil texture has the lowest weight for identifying groundwater potential zone . For weights allocated to each parameter, the consistency ratio obtained was 0.061, which is less than 0.1, showing the weight allocated to each parameter is acceptable. The resulting GWPZ of the study area indicates four zones representing Very Low, Low, Moderate and High . The areal extent of high and moderate GWPZ is 350 km2 and 2256 km2 , respectively. low and very low GWPZ covers 10356 km2 and 1547km2 areas. The particular direction of groundwater flow is towards the NE and SE, coinciding with the direction of surface water flow. The validation result of 82.08% confirms the very good agreement among the groundwater record data and groundwater potential classes delineated. Thus, the identification of GWPZ by using GIS and RS through AHP is reliable for conducting similar studies.