A Weighted Basin-Scale Susceptibility Framework Integrating River Morphology, Soil Erosion, and Hydrological Alteration in a Tropical Regulated River System

Abstract

Understanding watershed susceptibility in regulated tropical river systems requires integrating geomorphic predisposition, sediment generation, and hydrological modification within a unified analytical framework. This study proposes a weighted basin-scale watershed susceptibility framework that synthesizes soil erosion (RUSLE), hydrological alteration (IHA/HAI), and geomorphic maturity (Hypsometric Integral) into a normalized composite index. Unlike conventional single-parameter assessments, the framework applied min–max normalization and a theoretically rationalized weighting scheme (0.40 soil loss, 0.35 flow alteration, 0.25 morphology) to enable cross-parameter comparability and basin-wide prioritization. Application to a multigradient tropical regulated river system revealed pronounced spatial heterogeneity, with composite susceptibility values ranging from 0.15 to 0.92. Batang Padang Catchment recorded the highest index (0.92, Very High), driven by concurrent extreme soil loss and substantial hydrological alteration, while downstream depositional reaches exhibited consistently low susceptibility. The resulting spatial pattern demonstrated a clear upstream-to-downstream gradient consistent with geomorphic first principles. Robustness testing through equal-weight and ±10–20% perturbation scenarios produced minimal classification shifts (average index ratio variation <3%), confirming stability of sub-basin rankings. Comparative analysis with prior erosion studies in the basin further supported consistency in magnitude and spatial patterning. The proposed framework advances watershed assessment by transforming standalone erosion and flow metrics into an interpretable basin-scale susceptibility synthesis. Because the methodology relies on widely available DEM, discharge, and land-use datasets, it is transferable to other regulated tropical river systems seeking integrated geomorphic–hydrological prioritization for management and conservation planning.