Open-access digital elevation model (DEM) selection for flood inundation modelling using HEC-RAS in Capital City of Nusantara

Abstract

Flood is a classic but complex issue in most regions of Indonesia. Nusantara, the future capital of Indonesia, is now undergoing construction but the site continues to experience flooding due to high intensity rainfall. To overcome this challenge, identification of flood points in those areas needs to be done. Digital Elevation Models (DEM) are the most important component in modeling flood inundation in data-sparse areas. High-accuracy DEMs have been found to give better flood estimation but the availability of such data is very limited. Therefore, open-access DEMs, such as SRTM, DEMNAS, and MERIT-Hydro, are the most common choices used in modeling flood inundation in Indonesia. Each data set may provide varying model outcomes, due to different data processing methods. These results often lead to confusion as to which result should be used in subsequent studies. In this study, flood inundation in Nusantara will be generated using different DEMs and HEC-RAS hydraulic modeling with 25-, 50-, and 100-year return period rainfall events. The return period rainfall was obtained by calibrating Global Precipitation Measurement (GPM) satellite rain data. The results provide various flood inundation conditions, MERIT-Hydro tends to present higher flood depths. Followed by DEMNAS and SRTM which have lower flood depths. On the other hand, the use of return period variation gives a linear increase in flood depth for the DEMNAS model. While a decline in increment occurred in the SRTM and MERIT-Hydro models when the two big year return periods were applied. This research can be considered for the Nusantara development planning.