Hydrological Impacts of Land Use-Land Cover Change on Urban Flood Hazard: A Case Study of Jukskei River in Alexandra Township, Johannesburg.

Tshepo Sylvester Mawasha, Wilma Britz

Abstract


Flooding in urban areas is a major natural disaster causing damage to infrastructure, properties and loss of life. In urban areas, the major causes behind the changing hydrological processes (i.e. floods) include topography, increase in precipitation due to climate change and change in land-use/land-cover (LULC) over time. The objective of this study is to evaluate the spatial and temporal LULC change impacts on flooding along Jukskei River in Alexandra Township, Johannesburg. The LULC imageries of 1987 MSS and 2015 OLI derived from Landsat satellite were pre-processed and classified using a supervised classification method. The analysis of LULC revealed that, there is an increase in built-up area from 934.2 ha to 1277.2 ha and reduction in intact and sparse vegetation from 190.5 ha to 62.4 ha and 380.8 ha to 142.1 ha between the years 1987 and 2015. Flood depth map, velocity map and flood depth-velocity for different return period and LULC scenario have been developed by integrated approach of Hydrological Engineering Centre-River analysis system (HEC-RAS) and HEC-GeoRAS with geographic information system (GIS) and remote sensing data. From the analysis, it is observed that there is an increase in flood depth and flood velocity from 2.3 m to 3.0 m and 1.4 m/s to 3.4 m/s, whereas, the depth-velocity for the last 28-year increased by 3.4 m2/s from 2.9 m2/s to 6.3 m2/s for 1987 LULC and 2015 LULC conditions, respectively. The flood hazards maps generated in this study can be used by local authorities and municipal for flood disaster management.


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