Combined Hydrological and Geologic Assessment for Sustainable Management of the Sambunotan Watershed, Dinagat Islands, Philippines

This paper presents a combined hydrological and geological study to support the Sambunotan Watershed Management Plan (SWMP) for Tubajon and Loreto in the Dinagat Islands, Philippines. The primary objective is to integrate the results of the geological assessments with hydrological assessment data to provide a better understanding of the watershed's dynamics to support the development of the SWMP. Utilizing GIS tools and IfSAR DTM, the watershed's precise boundaries, covering 2,819.9125 hectares, were established. Hydrological modeling using HEC-HMS, calibrated with field data, achieved a "Very Good" performance, with a Nash-Sutcliffe efficiency of 0.85. The computed annual baseflow volume is 71,601,871.66 m³, wherein 73.69% is generated during the wet season. Geological assessments revealed that the river networks are influenced by harzburgite and basalt rocks, confirmed through field surveys identifying harzburgite, pillow basalts, and clastic sediments. Regions with clastic sediments and limestone, identified as potential aquifers, are recommended for further groundwater exploration.