Now day GIS based suitable dam site identification has been adaptable in order to minimize the requirement of high cost, time, and many specialists. GISbased sensitivity analysis of factors weights reduces the uncertainty of the final dam site suitability map and increases confidence by avoiding the errors coming due to an expert’s opinion suggestion. According to the GIS-based sensitivity analysis, the cumulative geological fault suitability class difference was the highest value and elevation was the lowest value from different weighting. As the suitability area difference of the geological fault at different weighting is highest; it is the highest sensitive factor for dam site selection in the Birr watershed and elevation was the lowest sensitive factor as the difference of suitability area is relatively lowest. The geological fault is given the highest rank or preference and finally, the highest weight and elevation are given the lowest rank and weight. It indicates that more of the dam site suitability of the watershed is depend on the suitability of the geological fault. The geological fault is the highest weight (31%), foundation geology (21%), soil texture (11%), slope (8%), erosion rate (5%), road proximity (4%), river proximity (3%) and the lowest weight is elevation range (2%). Dominantly the watershed area is suitable (47.57%) and moderately suitable (41.81%) for the dam site. GIS is software that is able to input, manipulate, analyze, and displays the output of spatial data. Therefore when the factor's weight is certainly determined the final map of the watershed dam site suitable map is also certain.

Keywords : GIS, Sensitivity, Weight, Suitable Dam Site.