Application of Remote Sensing and GIS for Groundwater Potential Zone Mapping in Northern Ada'a Plain (Modjo Catchment)

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Addis Ababa Universty


An integrated approach with remote sensing, Geographic Information Systems (GIS) and more traditional fieldwork techniques was adopted to map the groundwater potential sites in the central rift valley area of Northern Ada`a Plain (Modjo Catchment). Catchment delineation was done in ILWIS 3.3 DEMHYDROPROCESSING module. Digital image processing of enhanced color from Landsat ETM+ was interpreted to produce thematic maps such as lithology, lineaments, land use/cover and geomorphology. Contours and drainage lines were digitized for slope and drainage density mapping. GIS analysis of distance for lineaments, density for drainage, slope for elevation and reclassification were done for each factor maps. Selected springs and wells were visited to study their topographic and hydrogeological setting. Digital Elevation Models (DEM) derived from contours and acquired in the Shuttle Radar Topographic Mission (SRTM V-3) were compared in relation to drainage and lineaments extraction, landform mapping and catchments delineation. DEM derived from SRTM V-3 using DEMHYDROPROCESSING are better for catchments delineation and landform mapping than those derived from contours. A model that incorporates Weighted Linear Combination (WLC) was built using ARCGIS 9 model builder engine. The model was executed and groundwater potential map was generated. The spatial distributions of the various ground water potential zones obtained from the model generally show regional patterns of lithology, landform and lineaments. Spatially the very good and good categories are distributed along plain geomorphic units, near to lineaments, less dense drainage density and where the lithology is affected by secondary structure and having interconnected pore spaces. Groundwater potential zones demarcated through the model are in agreement with borehole data collected from the area. The validity of the model developed was tested against the borehole data, where out of 107 boreholes 50 are on very good and good zones, 37 on moderate zones, 14 on fair and 6 on poor zones. Moreover out of 52 bore holes with discharge rate from 24 l/s to 69 l/s are on the very good and good zones, which reflects the actual ground water potential. Although some wells exist in all ground water potential zones, the best yielding wells lie in the very good and good ground water prospect zone. The results demonstrate that the integration of remote sensing, GIS, traditional fieldwork, and geomorphology provide a powerful tool in the assessment and management of water resources and development of groundwater exploration plans.



Modjo Catchment