APPLICATION OF THE ANALYTIC HIERARCHY PROCESS (AHP) AND TECHNIQUE FOR ORDER PREFERENCE BY SIMILARITY TO IDEAL SOLUTION (TOPSIS) FOR SELECTING SUITABLE RESERVOIR CONSTRUCTION SITES: A CASE STUDY OF THE NAM LAI WATERSHED, LOEI PROVINCE

Abstract

This study aimed to determine the weights of criteria for selecting a suitable dam site in the Nam Lai Watershed, Loei Province, using the Analytic Hierarchy Process (AHP); rank three candidate headwork sites using the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS); and examine the sensitivity of the rankings under alternative weighting scenarios. Engineering, environmental, social, and economic data were obtained from the Initial Environmental Examination report and project documents. All alternatives had an equal storage capacity of 27.99 million m³. Pairwise-comparison judgments from four experts were aggregated using the geometric mean after retaining matrices with consistency ratios not exceeding 0.10. Social criteria received the greatest weight (0.3742), followed by environmental (0.2415), engineering (0.2012), and economic criteria (0.1831). Affected agricultural land had the largest global weight (0.2010). Under the baseline scenario, Alternative 2 ranked first (Ci = 0.7230), followed by Alternatives 1 (0.7146) and 3 (0.3117). Sensitivity analysis showed that Alternative 2 ranked first in five of six scenarios, whereas Alternative 1 ranked first when environmental criteria were prioritized. The findings support transparent assessment of trade-offs among engineering feasibility, environmental and social impacts, and economic returns.

Keywords: Analytic Hierarchy Process, TOPSIS, Sensitivity Analysis, Reservoir Site Selection, Nam Lai Watershed