HAZARD ASSESSMENT FOR THE CONSTRUCTION SITE OF THE GRAND ETHIOPIAN RENAISSANCE DAM

The Grand Ethiopian Renaissance Dam, constructed in NW Ethiopia across the Nile River, brings a geopolitical conflict between the upstream country (Ethiopia) and the downstream countries (Sudan and Egypt). The potential negative impacts of the dam on the downstream countries are obvious and have been addressed comprehensively in numerous previous studies; however, this is out of focus of this research. The dam is located in the tropical zone with heavy rain and is surrounded by steep slopes, erodible soils, and unconsolidated rocks. So, the area is naturally prone to mass wasting and seismic events. Once the reservoir behind the dam is filled with water to its full capacity, reservoir-induced earthquakes, flash floods, and landslides are likely to occur. In this study, we assess hazards for the dam site and its surroundings using a GIS (Geographic Information Systems) model. Nine factors, including earthquakes, volcanoes, faults, fractures, lithology, slope, soil, precipitation, and groundwater depth, are considered in this investigation based on our familiarity with the study area. Factor weights are assigned according to their relative importance using the AHP (Analytic Hierarchy Process) approach, and then the weighted factors are incorporated together in the geospatial analysis to create a hazard index for the study area. Three zones of low, moderate, and high hazard are determined, and it is not a surprise that the dam is found in the high hazard zone. Unfortunately, natural hazards in the study area are nearly impossible to avoid, so strategies that deal with scenarios of future dam failure should be developed and become readily available before completing the dam construction and filling its reservoir.

Keywords: GIS, dam, GERD, AHP, hazard assessment.