Combined 1D Modelling with HEC-RAS for Delineation Floodplain Area: A Case Study of Hennops River in the Centurion Area

Abstract

Flooding is among the most extreme weather events, endangering lives and causing significant property damage each year. Flood events in the Centurion area occur every year during the rainy season. This causes considerable damage to road infrastructure in both residential and commercial areas. The objective of this study is to incorporate hydraulic/hydrological (i.e., HEC-RAS/HEC-GeoRAS) models with geo-spatial techniques to predict flood extent and depth along Hennops River in Centurion area, Tshwane Metropolitan Municipality, Gauteng Province. In this study, floodplain inundation areas with different return periods were predicted in a 3.1 km distance of the Hennops River that passes through the Centurion area. Flood hazard analysis indicated that areas at close proximity to the Hennops River were submerged by a minimum and maximum flood depth of 0.4 m to more than 1.1 m for both 50 and 100 year flood recurrence interval. The study’s findings show that integrating GIS with HEC-RAS/HEC-GeoRAS techniques is a useful tool for floodplain mapping and analysis. Hence, the findings of this study are expected to be used as a foundation for the identification of causative factors of flash floods and the prediction of flash floods within the study area in future. The floodplain delineation maps developed in this study will be useful to policy-makers and the relevant authorities, as well as to local residents, in finding suitable measures for residential development along the floodplain while reducing flood risk in the study area.