Flood risk assessment of the Crocodile River, Mpumalanga

A dissertation submitted to the School of Geography, Archaeology and Environmental Studies, Faculty of Science at the University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2016.The Crocodile River East in Mpumalanga Province, South Africa, has seen three major floods in a twenty-four-month period, specifically January 2011, January 2012 and January 2013. The damage included the loss of life, damage and/or loss of public or private properties, agricultural land loss, and damage to biodiversity and river geomorphology. The purpose of this study was to understand the consequences and risks to livelihoods and river basin systems due to flooding of the river. The study focused on a segment of the Crocodile River East, between Riverside and Tekwane. The study used historic hydro-climatic data for the Crocodile River to determine the critical threshold for past flood events and to predict the extent of future flood events. Hydrological modelling coupled with the HEC-RAS hydraulic model enabled the simulation of these future flood events. The use of orthophotos and digital elevation models (DEMs) allowed for a spatial representation of the areas affected during the flood events. Flood hazard maps and flood risk maps were then developed for the identified flood events within a Geographical Information System (GIS). The maps enabled the identification of high risk and flood prone areas along this segment of the Crocodile River Basin. The results showed that when discharge reaches 241.75 m3/s, both locations (Riverside and Tekwane) are at risk to flooding. This is therefore the threshold for which the two locations are likely to be flooded. This study provides a methodology to determine the spatial extent of past and modelled future river flood events. As such, outcomes of this study may aid in the understanding of flood hazard extent and flood prone areas, and may thus help catchment management authorities and institutions in flood reconstruction and flood risk management. The employed methodology can aid effective spatial planning, and can also be extended at the basin scale through integration with the existent flood warning system to gain an estimate of flood extent and flood risk.TG201