Conservation of Pinulot-Caulaman River Watershed using GIS and RUSLE-based Soil Erosion Risk Assessment in Central Luzon, Philippines

Abstract

Soil erosion is a serious environmental issue which can drastically impact watersheds like the case of Pinulot-Caulaman River Watershed (PCRW) in Central Luzon, Philippines. PCRW is a critical watershed for agricultural and domestic purposes covering Zambales Range and Mt. Natib to the west and lowland areas to the east. This study investigated the biophysical and socioeconomic conditions of PCRW to estimate the overall soil erosion risk and recommend conservation strategies appropriate for the watershed. The methodology involved data mining online and processing of secondary information through Geographic Information System (GIS). This was followed by applying Revised Universal Soil Loss Equation (RUSLE) model to compute soil erosion and delineate risk zonation by analyzing the temporal and spatial changes in the watershed on three selected periods, i.e., 2014, 2017, and 2024.

The PCRW is characteristically fragmented showing declining forest cover across complex topography with young and clay-rich soil types that received abundant rainfall, however, there were minimal conservation practices employed. Based on RUSLE, soil erosion with more than 300 tons ha-1 annually was considered very severe, particularly in steep and sparsely vegetated western areas of the watershed. In 2014, these severely eroded areas covered 20% of PCRW which increased to 28% with 11,696 hectares erosion coverage a decade after. Considering the status of the watershed, these critically erodible areas should be prioritized for restoration through the enhanced National Greening Program (NGP). Furthermore, moderate to very high erosion risk categories require conservation measures while intact forested slopes should be delineated as protected zones that will altogether form part of the watershed management plan.

This study highlighted the applicability of GIS techniques and RUSLE model in providing data-driven and evidence-based decision-making tools for soil conservation. Furthermore, erosion results can be verified through ground validation to enhance the accuracy of the model in assessing the PCRW, together with future watershed assessment of erosion in other parts of the country.