Flood inundation modelling on agricultural land in Legonkulon Sub-district, Subang Regency, Indonesia

Abstract

Flood has been an issue in many sectors, including agricultural land. The disaster has been severe to many places in Indonesia, including Subang Regency, and in particular Legonkulon Subdistrict, where the area was traversed by Cipunagara River. The study showed the flood inundation projections for various return periods and portrayed the significance of flood occurrences from Cipunagara River on agricultural lands within the area. The model was established using DEMNAS topographic data, where Lognormal Distribution was selected for the design rainfall based on goodness of fit tests. Afterwards, Snyder SUH Method was performed to estimate the peak discharge for Q2, Q10, Q50, and Q100, resulting 1,568.24 m3/sec, 2,228.89 m3/sec, 2,754.87 m3/sec, and 2,968.74 m3/sec, respectively. As for the inundation model, HEC-RAS 5.0.7 (one-dimensional Saint-Venant equation) was utilized to construct the model. Finally, the study showed that from a total agricultural land area of 2,385.45 Ha within the Legonkulon Sub-district, areas that were inundated by the overflow of Cipunagara River for Q2, Q10, Q50, and Q100 were 738.53 Ha, 792.33 Ha, 816.74 Ha, and 825.15 Ha, respectively. It was concluded that the agricultural land in Legonkulon Subdistrict was prone to the overflow of Cipunagara River even from low return period floods.