Diep River Estuary management plan

City finalising management plan for Diep River Estuary

The City of Cape Town facilitated a public participation process on the draft management plan for the Diep River Estuary in Milnerton by mid-2022.

The public participation process formed part of the review of the draft Diep River Estuary Management Plan. The estuary is the point where the Diep River meets the ocean in Milnerton. This is the fourth review of the plan and is a legal requirement in terms of the National Estuarine Management Protocol of 2021. “The latest revision is extremely important. It intends to identify interventions that are pragmatic and realistic to improve the state of the Diep River Estuary given the many pressures it is facing. One of these is its location within a heavily altered and urbanised environment. For example, approximately 33% of the estuary is situated within developed land, and the channel has been stabilised by roads and embankments, which reduces the estuary’s natural ability to meander. “The revised plan includes new information and recommendations and was workshopped with external experts and independent scientists in the field of coastal and estuarine science,” said Alderman Eddie Andrews, deputy mayor and MMC for Spatial Planning and Environment, City of Cape Town. There are systemic pressures on the estuary. Some of these pressures originate from the Diep River’s wider catchment area, which falls outside of the City of Cape Town’s metropolitan boundaries. “The Diep River originates in the Riebeek Kasteel Mountains north-east of Malmesbury and flows for about 65 km towards Cape Town. Thus, the river meanders through many communities and past several neighbouring towns. What happens along the river before it reaches Cape Town has a profound impact on the river’s health. Once it reaches Cape Town, the river flows through the Rietvlei wetlands, including Flamingo vlei and Milnerton Lagoon which form part of the estuary, covering an area of about 900 ha, before it finally reaches the ocean,” said Alderman Andrews.

Estuarine Management Plan The City’s Environmental Management Department is responsible for the management of the estuary and must develop an Estuarine Management Plan that assesses its current state and determines management and monitoring actions. The purpose of the plan is to improve the water quality of the Diep River Estuary, which currently faces multiple sources of pollutants entering the system including agricultural run-off, treated effluent from the Potsdam Wastewater Treatment Works (WWTW), the illegal disposal of substances in the local stormwater system from formal and informal residential areas, stormwater run-off from industrial areas, the disposal of foreign items into sewer systems and subsequent sewer spills, litter, and so forth. The draft management plan divides the Diep River Estuary into six distinct zones with various objectives and priority actions. These are developed to be specific and tailored for each zone, but simultaneously recognise the interlinkages and dependencies between the different zones. It also outlines a number of capital-intensive projects to address the current challenges, among which the planned upgrade of the Potsdam WWTW to progressively add capacity and new treatment technology, upgrades to bulk sewage infrastructure and construction of treatment wetlands.

Overall, the plan intends to manage the estuary in a manner that ensures its sustainability, and is aligned with pragmatic conservation goals befitting a heavily altered and rapidly changing urban ecosystem.

Priority actions These include some high-priority actions to improve the water quality with: • upgrades to the Potsdam WWTW to progressively add capacity and new treatment technology • upgrade to the Montague Gardens bulk sewer to reduce sewage spill events • constructing a stormwater to sewer diversion at Dunoon and Doornbach • constructing a treatment wetland/ pond at the Erica Road stormwater system outfall • constructing the treatment wetland at the Bayside Canal outfall • developing a sewer pump station protocol • ensuring all pump stations within the catchment function optimally.