Modeling Surface Runoff in Surakarta Using HEC-HMS and DEM

Surakarta, Central Java, experiences recurrent urban flooding from impervious surfaces, inadequate drainage, and complex topography. This study applied HEC-HMS with 30-meter DEM data to simulate surface runoff in the Pepe River and Bengawan Solo subbasins. Using January 2018 rainfall and October 2022 streamflow data, the model achieved strong validation. Results showed 488 mm rainfall produced 100% runoff, with peak discharge of 21.0 m³/s. Flow accumulation mapping identified key sinks and high-velocity runoff zones. Findings highlight drainage vulnerabilities and provide a replicable framework for adaptive stormwater management in flood-prone Southeast Asian cities.