4. Catchment parameters

4.1 Analysis of the catchments

4.1.1 Catchments

Cape Town metropolitan area is dived into 18 catchments, see adjacent diagram. The Diep River catchment being spatially the largest.

The study area spans over three catchments, the Salt River, City and Diep River catchments. Originally, the Salt River estuary spanned over all three of these catchments and with this combined the Diep and Salt River catchment into one. “A catchment being a three-dimensional land system or drainage basin, which converts precipitation and groundwater inputs to stream flow and whose components are assessed in terms of their influence on these processes.”(Smithson, The Physical Environment, 2002). For the status quo assessment of the catchment only the Salt River catchment is described as it has influence on the Salt River canal. The other 2 catchments are influencing the Old Salt River canal and the Zoarvlei wetland. It was not possible to gain the same depth of information for these as part of this study, due to the lock down period and the closure of government departments as part of the Covid-19 pandemic.

4.1.2 City catchment

The City catchment comprises of the streams originating on Table Mountain and Signal Hill draining north or west from it into the CBD or the Atlantic Seaboard suburbs. In these dense urban areas streams are in general piped. Table Mountain provides a platform that receives some of the highest precipitation in the Peninsula, and is the source of countless streams and springs. “There are four main perennial streams flowing into Table Valley, namely the Platteklip Stream, Molenwater, Third Stream and Zwaartrivier. There are also several small seasonal streams draining the slopes of Devil’s Peak and the saddle to the east, and Tamboerskloof to the west. All these streams are piped at some point, where they hit the urban edge of the city” (Cate Brown and Rembu Magoba, 2009) . These mountain streams where one of the reasons for ships to stop and settlers to stay in the Cape 300 years ago . “Over the years, as polluted stormwater and untreated sewage entered the system, the waters of the stream became unfit for consumption. To reduce stenches and misuse, and to improve access over the canals, the entire system was covered over with stonework barrel arches” (Cate Brown and Rembu Magoba, 2009). These system exist until now and are in parts tourist attractions. Today the rivers coming off the mountain have been diverted into stormwater drains. “All streams coming from table mountain and Devils Peak are today no more than drains, beneath the City” (Cate Brown and Rembu Magoba, 2009). The two unnamed streams (in Save to Sea, one was called Platteklip stream) influencing the study area are emerging from Devils Peak and are piped from Philip Khosana Drive through Woodstock and Salt River. They resurface on 2 different points where they enter the Old Salt canal. Their fresh water gets polluted with stormwater along the way before it discharges into the harbour.