Assessment Of The Impact Of Urban Development On Flood Peaks In The Acacia Suburb, Arebbusch Sub-Catchment Windhoek, Namibia

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ABSTRACT

Climate change is affecting global weather patterns, more so by exacerbating the sporadic nature of Namibia’s rainfall patterns. This has negative consequences on urbanization as increased rainfall in certain rainy seasons coupled with increased urban development could lead to dangerous flooding in low-lying areas, as was the case with Acacia residential, Windhoek, in 2004. Increased urban development has the potential to increase runoff and flood peaks by 20% to 50% of those under natural conditions. This study investigated the urban development in the greater Arebbusch catchment, and its impact on the Acacia suburb. Employed methods and techniques comprised remote sensing, GIS, SANRAL Drainage manual and hydraulic modelling software (HEC-RAS). Landsat and Sentinel images were used to produce and determine land cover changes in the study area between 1989 and 2018, respectively. Furthermore, computer models of the Acacia River section, the steady and unsteady flow simulations and flood inundation area were carried out in the Acacia residential area and compared with the existing, regulatory 1:50-year flood line that the City of Windhoek uses as reference for urban development. Results indicate that the flood peaks in the study area increased by 13% over the past 30 years. This suggests that urban development influenced flood peaks in the study area, whilst the 1:50-year flood line remains static. It is therefore recommended that more assessment be done on the hydraulic flow of all constructions in close proximity to the 1:50-year flood line, whilst taking into greater consideration the accumulative effects of urban development on urban flood peaks.

Key words: Urban development, SANRAL, City of Windhoek, flood peaks, remote sensing.