Integrated rainfall-runoff, HEC‑RAS 2D, and Lidar DEM model for flood simulation in urban ungauged catchment area: case study of Cipinang catchment, Jakarta City, Indonesia

Flooding is the highest frequency natural disaster that causes damage, losses, and casualties. Flood modeling is a disaster management effort to reduce the level of risk. The aim of this research is (1) to analyze the rainfall-runoff using the Synthetic Unit Hydrograph model based on suitability with characteristics of urban watersheds in the ungauged catchment; (2) to evaluate the integration of the rainfall-runoff model, 2D HEC-RAS, and Lidar DEM for rapid mapping of urban flood hazards. The Synthetic Unit Hydrograph models used are the SCS, Nakayasu, Snyder, Limanatara, Gama I, and ITB 1. Evaluation and calibration of the model compared with hydrograph measurement and analyzed using the Nash–Sutcliffe coefficient. Flood simulation uses the 2D unsteady flow method in HEC-RAS, with river geometry constructed from Lidar DEM using RAS Mapper. The results show that the evaluation of the Synthetic Unit Hydrograph model with a Nash–Sutcliffe coefficient value of 0.78 is very satisfactory in the Nakayasu model. However, the model results were overestimated, so calibration is carried out on the Curve Number (CN) parameter, time lag, and Alpha value, with calibration results of 78, 0.35 h, and 2, respectively. The frequency analysis results in maximum discharge predictions for return periods of 2, 5, 10, and 25 years, with peak discharges of 27.3, 44.26, 57, and 75 m3/s each period. Flood simulation results show that the maximum flood depth of the study area is 4 m. The area with the highest flood depth exposure is at the outlet of the Sub-Catchment, where most land is used for settlements. The result of modeled and observed data was in close agreement indicating a successful integration of rainfall-runoff, 2D HEC RAS, and Lidar DEM model. The government can use the flood simulation map in this study area for flood mitigation and urban development planning. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2025.