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An investigation of past and present stormwater management practices within the City of Johannesburg

The City of Johannesburg (CoJ) has implemented a new stormwater design manual which aims at treating stormwater as a resource and to render urban spaces usable for urban environment through design networks that convey stormwater safely to the environment. The Soil and Water Assessment Tool (SWAT), SWATCup, and Rational Method, were used to investigate and assess the past (1886 to 1900) and present (1990 to 2016) stormwater management practices within the City of Johannesburg. The current stormwater management infrastructures were investigated as green and grey, with a focus on the benefits of green infrastructure. The study showed a lower simulated quantity of runoff in the pre-development era and higher simulated quantity of runoff in the post-development era, with varying land use land cover percentages. The post-development time shows that 35% of land use land cover is used for settlements and 65% is for open fields and other uses. However, in the pre-development time, only 10% of this land was used for urban settlement while 90% was dedicated to farmland. Pre-development condition also showed an annual precipitation of 757 mm of which 28% ended up as surface runoff while 45% was lost due to evaporation and transpiration. On the other hand, the post-development time showed 772 mm of annual precipitation with 29% of this precipitation resulting in surface runoff and 50% lost due to evaporation and transpiration. This study also confirms that indeed the LULC changes over the years have affected the quantity of runoff in CoJ. This paper is essential in assisting CoJ in determining the practicality of utilising the new stormwater design manual.