Sustainable Water Management in Kalu River Basin of Sri Lanka: Comparison of Watershed Yield Computations for Water Security

Irrigation reservoir design associated with ungauged watersheds requires reliable watershed streamflow estimations. In practice, designs are either based on the empirical model of Department guideline or recent conceptual mathematical models. Use models require appropriate levels for calculation streamflow. Popular adequate guidance application safety factors to outputs. The two aspects that need attention are, reliability estimations by and incorporation when converting outputs as main gap in literature is a critical evaluation importance these real-life applications. authors, review paper, identified best available method yield estimation Guideline Method (IGM) but pointed necessity verification field observations. Accordingly, present study compared most commonly used IGM, HEC HMS Unit Hydrograph (UH) carrying out an Kalu Ganga at Ellagawa. This study, while focusing availability parameters assessments watersheds, aimed demonstration comparison which has data established parameters. It expected this would facilitate selection not only wet zone also dry Sri Lanka. Spreadsheet were developed each using reported incorporating engineering judgment. Comparison observed was done annual seasonal water balance, flow duration curves, Mean Ratio Absolute Error (MRAE) numerical indicator. Evaluation from three methods showed IGM estimates monthly closely matched data. MRAE Overall Hydrograph, in-case HMS, UH 0.35, 0.58 0.4, respectively. thresholds modern hydrological updating guidelines highlighted. revealed establishing guides computing watersheds. recognized amongst selected estimation. results create significant ambiguities because unreliability processes considering factors, clearly guidelines. vital