One of SA’s most important rivers is running out of water — and there’s not much time left to save it.
The once mighty Berg River, which gave birth to many of the Cape’s vineyards, is wilting under the combined pressure of climate change, pollution and thirsty humans.
The 294km river, which rises in the Drakenstein mountains outside Franschhoek, is not delivering enough water to its estuary at Velddrif on the West Coast. A significant portion of Cape Town’s water supply comes from the Berg River Dam near Franschhoek.
Shock findings of a new study show that water flow reaching the estuary in summer has dropped more than 80% compared with the historical average, and the river stopped flowing for the first time in recorded history during the recent Western Cape drought.
The amount of water now reaching the estuary near Velddrif is below the legal requirement, according to the study published in Water SA.
• 80%-86%: Reduction in Berg River flow during summer compared with historical average
• 39%-42%: Reduction in winter
— IN NUMBERS
The Berg River is one of many SA rivers in trouble. The latest State of Rivers survey painted a bleak picture, with half of the 364 river sites tested classified as “moderately modified”. About 16% were classified “natural” or “largely natural” while 5% — generally those in urban areas — were “unsustainable”.
Some river sites were so altered that the survey team could not do water quality assessments. There were health and safety concerns at 12 sites and two testing sites had been discontinued “due to the consistent high level of raw sewage, which constitutes a major health risk to staff”, the report said.
The plight of the Berg is of particular concern partly because it has been consistently monitored for more than 50 years.
Deteriorating water quality in the Berg estuary following the 2015-2017 drought prompted the government to downgrade its official ecological category in 2019 from “largely natural” to “partially modified”.
The latest estuary water readings suggest the changing climate is only part of the problem; the river no longer meets its legal flow and quality requirements.
“Data presented in this study suggest that this requirement has not been upheld and that the health of this important estuary has been allowed to degrade further,” the new study says.
Lead author Barry Clark said scientists have long warned of reduced river flow, particularly in the low-rainfall summer months. Strong runoff is needed to clear silt and “reset” a river system.
The large Berg River Dam, opened in 2009 after five years of construction, affected the volume of runoff, and not enough had been done to mitigate this impact by ensuring compliance among water users, Clark told the Sunday Times this week.
“The idea was that there was supposed to be post-construction monitoring [of water extraction], but I’m not sure that ever really happened,” he said.
The National Water Act requires the government to protect scarce water resources, particularly sensitive wetland areas such as the Berg.
The first known European record of the Berg River was made by bailiff Abraham Gabbema in 1657 when Dutch Governor Jan van Riebeeck sent him to trade with the Khoikhoi for meat for the settlement at the Cape
— Wikipedia
Clark said the Berg River estuary was required to be “close to natural” due partly to its vital role as a fish nursery and bird habitat. “It is considered to be one of the most important estuaries in the country because there are so few along the arid West Coast,” he said.
Fertiliser washing into the estuary is of particular concern because of its nutrient load. The reduction of fresh water during periods of drought also increases salt levels, to the detriment of flora and fauna.
“Zero fresh water coming into the estuary during the most recent drought caused some very severe impacts on the estuary, which became more salty than the sea. High levels of salt are toxic to most organisms. It was clear that this has never happened before, according to historical records,” Clark said.
Jeremy Shelton. a conservation biologist at Cape Town’s Freshwater Research Centre, said minimum flow requirements were not being met. “I’m observing rivers that used to be perennial now drying up, which affects the ecology.”
Neil Griffin, a scientist at the Rhodes University Institute for Water Research, said the government’s ecological reserve estimates — the amount of river water required to ensure adequate ecosystem function — needed to be updated with current weather data informed by climate change modelling.
“These [ecological reserve estimates] are worked out in a modelling process that uses historic data to calibrate the model. But that’s not working as rainfall drops when the model is based on previous, better rain,” Griffin said.
“Modelling of flow is a big part of South African water management so this will be an issue in the Western Cape, where the models that are used to make decisions are liable to be optimistic.”
Pierre de Villiers, senior manager at CapeNature's marine and coastal programmes, said the Berg River improvement plan, led by the province, helped address problems within the river’s catchment area.
“This involves but is not restricted to alien tree removal, river bank restoration, improved management of waste water treatment works, water quality monitoring and other activities,” he said.
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