Analisis Kapasitas Sungai Tuntang Terhadap Debit Banjir Rencana Menggunakan Hec-Ras di Desa Baturagung, Kabupaten Grobogan

Abstract

The Tuntang River is one of the major rivers in Grobogan Regency that plays an important role as a natural drainage channel. However, several sections of the river, particularly in Baturagung Village, frequently experience overflow during the rainy season. This study aimed to determine the design flood discharges for 2-, 5-, 10-, 25-, 50-, and 100-year return periods, evaluate the capacity of the Tuntang River to convey the design flood discharges, and assess the potential for river overflow using HEC-RAS. Hydrological analysis was conducted using annual maximum daily rainfall data from 2011 to 2025 collected at the Tuntang, Rawa Pening, and Jragung rainfall stations. Areal rainfall was calculated using the Thiessen Polygon method, while the design flood discharges were generated using the HEC-HMS model, which was calibrated with an RMSE of 0.42, a PBIAS of 0.00%, and an NSE of 0.820. The resulting design flood discharges were subsequently used as input for hydraulic modeling in HEC-RAS. The results showed that the design flood discharges for the 2-, 5-, 10-, 25-, 50-, and 100-year return periods were 22.7 m³/s, 28.3 m³/s, 32.1 m³/s, 36.9 m³/s, 40.5 m³/s, and 44.0 m³/s, respectively. The HEC-RAS simulation indicated that river overflow occurred from STA 9 to STA 18 for the 2- to 25-year return periods and extended to STA 8 for the 50- and 100-year return periods. These findings indicate that the existing capacity of the Tuntang River within the study area in Baturagung Village is insufficient to convey the design flood discharges, thereby increasing the potential for flooding.