AHP and FAHP-based multi-criteria analysis for suitable dam location analysis: a case study of the Bagmati Basin, Nepal

The Bagmati River Basin is experiencing significant water stress due to a reduction of surface and groundwater resources, especially during the dry season. The basin's heavy reliance on monsoon-dominated precipitation, without the buffer of snow or glacier melt, exacerbates these issues. Dam construction is seen as a viable solution for maintaining river flow and regulating river ecosystems. Thus, this study leveraged multi-criteria decision-making tools, particularly the analytical hierarchy process (AHP) and fuzzy AHP (FAHP) in conjunction with the Geographic Information System(GIS), to identify suitable dam construction sites in the Bagmati River Basin. Through an extensive literature review, nine criteria were identified: stream density, rainfall, slope, land use, elevation, soil type, distance from faults, distance from settlements, and distance from roads. Pairwise comparison matrices, based on expert surveys, were used to assign weights to each criterion, with validation against existing and proposed dams. Results show that approximately 31% of the basin area is suitable for dam construction, with about 4.45% area being highly suitable. FAHP only slightly outperforms AHP in assessing existing dam locations, demonstrating the robustness of both methodologies. For the validation of suitability analysis, location of existing dams are compared. While Nepal is not generally water-stressed, inter-seasonal water availability is high. Dam construction for multiple uses is nascent in Nepal, and location analysis studies are rare. The methodology used here can be replicated in other regions, offering valuable insights for decision-makers.