Vaal Dam’s levels are plummeting

A dry early summer, successive heatwaves, Gauteng municipalities’ failure to maintain water infrastructure and ongoing work on the Lesotho Highlands Water Project (LHWP) have led to the precipitous drop in the level of the Vaal Dam.

The dam is at 24.9% capacity, compared with 66.8% during the same period last year, according to the department of water and sanitation’s provincial state of dams report issued on 16 December.

The levels of dams in the Vaal catchment are much lower than is usual in the middle of December, according to water governance adviser Carin Bosman.

“Our rainy season started very late. Our first rain was only on 14 October [and] then it wasn’t a lot of rain, and up to this week Monday and Tuesday, we only had a couple of showers. We didn’t get any proper rain yet; it’s a dry year.”

Bosman said the low inflows into the Vaal Dam as a result of closing the LHWP’s tunnel for planned maintenance work has obviously had an effect on dam levels. But she pointed out that it has to follow a specific maintenance programme: a one-day quick check once a month, a week-long check once a year and then a closure for a month every five years. Then there is a tunnel closure for three months every 10 years and for six months every 20 years. 

“This is planned maintenance that is essential. If you don’t maintain the channel for the water project, it all fails and you have nothing. You have to do maintenance. We’re halfway through the maintenance planned to end in March, before the dry season, so that during the dry season, it will be online again,” Bosman said.

Another reason for low water levels is that municipalities are not reducing their water consumption. 

The department’s water level scorecard recording average consumption from the Vaal Dam by municipalities shows that the City of Johannesburg had “quite a jump in consumption” mostly caused by leaking infrastructure and poor maintenance. 

“Tshwane and Emfuleni do not show similar increases,” said Bosman.

Consumption of water from the Vaal Dam does not necessarily mean the water reaches the consumers, she said, pointing out that if maintenance is not undertaken, the increased leakages mean abstraction from the dam increases. 

“If you have leaks, then you have to keep pumping more and that has had an impact on the availability of water in the Vaal. 

“Drought, heatwaves, which increase evaporation, lack of maintenance by the municipalities — which leads to increased abstraction from the Vaal Dam — all of those factors contributed to the lower levels that we see now.”

 Bosman referred to a graph of the Integrated Vaal River System ­— which consists of 14 dams feeding Mpumalanga, Gauteng, the Free State and Northern Cape ­— which showed that the system’s surface water storage stood at 72.2% on 25  November. 

“We are on the upper edge of the ‘low supplies’ line. The last time we were at the same level was in July/August 2020 — the end of the dry season for that year,” she said. 

“We have not seen the regular increases that are associated with the start of the rainy season in November/December, and there is a small gap before we hit the danger zone red peak at the end of January.” 

Bosman said this meant everything possible had to be done to use water sparingly to have enough water until March next year. 

“We are relying on good rains now to March to keep the levels to such a level that we’re okay.”

There is a backup plan: the Sterkfontein Dam, the level of which was 97.6% this week.

“The operational plan is when the Vaal Dam reaches 18%, then we release water from Sterkfontein. Sterkfontein contains about the same volume as the Vaal Dam; it’s a big dam, but it’s deeper and it’s got a smaller surface area, which means less evaporation. And it is almost full,” said Bosman. 

“I don’t think people should panic because we do have this backup system.”

 But there is uncertainty about whether there will be good rains from January to March, which means that people should remain vigilant and apply water-saving techniques.

“Every drop counts, save every drop that you can,” Bosman said.

This includes only flushing the toilet when it is really necessary; ensuring there are no leaky taps; taking five-minute showers; putting a bucket in the shower to collect water with which to flush the toilet; turning off irrigation sprinkler systems and only watering essential garden plants with a hand-held hose between 6pm and 6am because the water will evaporate at other times.

Further water-saving measures include not washing pets or vehicles with a running tap and instead using a bucket; not cleaning driveways and other hard surfaces with a hosepipe and not filling swimming pools, she said.

Residents should also put pressure on municipalities to fix leaks wherever they are spotted.

“Ask your municipality to set up a leak hotline so that leaks can be fixed as soon as they are identified. The best thing we can do is to keep the pressure on the municipalities, keep holding their feet to the fire so that they can do what they’re supposed to do,” Bosman said.

“In the medium to long term, we have to ensure that we hold municipalities accountable for their infrastructure maintenance and management, and we have to start considering alternatives such as non-waterborne sanitation.”

The department’s spokesperson Wisane Mavasa said the level of the Vaal Dam has been decreasing by 1.5% to 2% weekly. 

She said this is primarily caused by low inflows to the dam because of low rainfall in the Vaal catchment area and elevated temperatures, which have led to increased evaporation losses. 

The surface area of the Vaal Dam is wide and shallow and “therefore susceptible to high evaporation losses”, Mavasa said. 

Another cause for the drop in the water level is the low inflow from the LHWP tunnel closure. The tunnel usually transfers 780 million cubic metres of water a year into the Integrated Vaal River System, but there was a shortfall of 80 million cubic metres this year because of the shutdown.

Mavasa said the primary objective for the augmentation of the Vaal Dam is to ensure that it does not go below the minimum operating level of 18% of full supply capacity, Mavasa said. 

“This is to ensure that the water requirements of water users that depend on the Vaal Dam are met as stipulated in the operating rules,” she said.

Low water levels can cause erosion of the exposed areas of the dam that were once filled with water, she added. As a result, reduced dam levels can diminish the variety of habitats for a range of animals and plants.

“Furthermore, lower dam levels can prevent fish from migrating to spawn and reproduce, which can affect fish populations and other species in the food chain,” Mavasa said.

The department has not imposed restrictions on water use from a water resources perspective so the effect will be minimal regarding water supply for domestic, industrial and agricultural use. 

“All users abstracting water from the dam continue to do so within their authorised allocation. [But] our water availability resilience is affected in the medium term when we start using our strategic reserves. 

“To determine the extent of the use of these reserves requires a detailed economic impact assessment,” said Mavasa.

Kathy Manten, the owner of Manten Marina in Deneysville in the Free State, said the harbour on the Vaal Dam is dry. 

“We had beautiful rains this week, which were really good up at Grootdraai Dam, which is in the catchment area, so hopefully we’ll be getting water coming through from the system,” she said.

“With the Katse Dam tunnel closed from the beginning of October to the end of March, we’re not getting any water from that system, and we get the bulk of our water from there,” Manten said. 

“We’re really dependent on rain and, up until now, we’ve had very little rain in the catchment areas. Hopefully this is the turning point — you never know though.”