Abstract:
Floods are a natural disaster that frequently affects Indonesia, including Cilacap Regency, which according to the 2024 Indonesian Disaster Risk Index (IRBI) has a flood risk level of 53%. Kroya District is one of the areas with high vulnerability, particularly in Mujur Lor Village, which is affected by floods almost every year. This situation disrupts community activities, damages infrastructure, and endangers safety, necessitating a study to determine the distribution pattern of floodwater, planned flood discharge, and existing drainage capacity.
In order to evaluate drainage conditions, this study used a quantitative descriptive approach that included field surveys and spatial data processing with ArcGIS 10.8. Topographic maps, land use, rainfall, and direct measurements of channel dimensions were among the data that were studied. The Tipar Sub-watershed's design flood flow was determined using the Rational Method, and the drainage capacity was assessed by contrasting the design discharge with the channel's actual capacity.
According to the research findings, the Kroya Subdistrict's water inundation area is 128.44 hectares and is distributed among seven villages, with Mujur Lor Village having the biggest size (45.18 hectares). With Penjarangan Drainage at 0.653 m³/s, Situmang Drainage at 5.711 m³/s, and Kali Bangsa I Drainage at 7.889 m³/s, the drainage capacity is much less than the design flood discharge with a 5-year return period of 22.23 m³/s. This substantial discrepancy suggests that the channels cannot handle the flood discharge, hence a larger channel layout is required to lessen flooding.
