Incredibly, there is one area in the Western Cape, close to Cape Town, that is not experiencing the drought to the same debilitating degree. The Overberg region, comprising towns like Grabouw, Hermanus and Swellendam is coming to the aid of Cape Town.
The Groenland Water User Association (GWUA) in the Overberg has offered to transfer between 7 and 10 million m³ of water from their water system to one of the major dams supplying Cape Town, the Upper Steenbras Dam. The water is only earmarked for urban use. “It says a lot for the agricultural community in the Grabouw Overberg area that they have managed their water resources in such a manner that there is spare capacity to be used in this way,” says André Roux, coordinator of the province’s drought-management activities in the Office of the Premier.
However, the City is reticent about announcing the plan too enthusiastically as it is contingent on a raft of uncertainties and the City doesn’t want water users to conclude that there will always be a back door. This is the last current option to augment the city’s water supply from surface water sources.
According to a Hortgro press release, Johan Groenewald, CEO of the GWUA, Grabouw and Elgin producers have enough water for the current season. “We are in a different catchment area than the City of Cape Town, and although our rainfall has been much lower than what we are used to, farmers in the area realised that we are currently in a more favourable position than the City of Cape Town. Thus, they decided to ‘pay-it forward’. ”
Ross Heyns, chairperson of the Elgin, Grabouw, Vyeboom, Villiersdorp Agricultural Association, says that the donation could put farmers in a difficult position at the end of the current season. “We will be dependent on a good winter rainfall to replenish reserves for the next season.”
How the water will be transferred
The Eskom Palmiet Pump Storage Scheme consists of two dams i.e. the Rockview Dam on the mountain side and one at the bottom in the Palmiet River, the Kogelberg Dam. Over weekends when electricity demand is lower, water is pumped to the upper dam to enable the system to generate electricity in the next week during day time. Every day of the week water is released down to the bottom dam, generating electricity in the process and at night some of the water is pumped back into the Rockview Dam. Every day the level in the upper dam is a bit lower, getting quite low by Friday, which is why weekends are used to replenish the upper dam’s levels.
As part of the Western Cape Water Supply System, 30 million m3 of water is transferred from the Palmiet River to the Upper Steenbras Dam during the winter by making use of the pump storage scheme. More water than is required to fill the upper Rockview Dam is pumped to allow the Rockview Dam to spill into the 3 km connecting canal between the Rockview and Upper Steenbras dams. This is done to augment the water supply to the Greater Cape Town area.
The Groenland Water User Association has now offered to pump more water than is needed by the pump storage scheme itself to the upper dam, in order for that dam to reach overflow levels. The overflow will then run via a canal – not long, only about two or three km – to the important Steenbras Dam.
Depending on the available pump capacity, the process of transferring 10 million m³ of water will occur over a period of two to three weeks. This volume of water is estimated to last the City of Cape Town for about 20 days – if inhabitants were to keep to their combined daily quota of 450 million litres, but that total is unfortunately far from being reached currently. According to city authorities, inhabitants’ daily water use hasn’t even come down to 500 million litres yet. By 2 February it was still at 560 million litres per day.
It won’t be the first time that water has been transferred to the Steenbras Dam in this way; the same was done during this past winter when 30 million m³ was extracted from this system for use in Cape Town.
Meanwhile, irrigation water supply to access for all farmers along the Berg River has been cut off for the season. Two weeks ago FreshPlaza reported that farmers in the Upper Berg River were anxiously awaiting the command from the Department of Water and Sanitation Affairs that would close the sluice gates at the Berg River and Voëlvlei Dams, which they were expecting at any moment.
The effect of evaporation on this 200 km-long river on water losses is significant, and all of the streams feeding into the river is dry.
Cape Town’s Day Zero has been much in the news; it is just been moved ahead to 11 May 2018, in part because agricultural water usage has declined. André Roux makes it clear that it doesn’t mean that Cape Town’s six large dams are empty when Day Zero is reached, but that their combined capacity lies at 13.5%, At this level water can no longer flow to outlets by itself but will have to be pumped to the outlet works, which, apart from the extra electricity demand, will also mean that less water is available because the flow tempo is lower when pumped than when water flows naturally.
The City is busy preparing around 200 water collection points where inhabitants will have to collect their 25 litre per person daily allowance. This will bring major disruption to the lives of Capetonians who will have to queue for water, while the city is working on a system to prevent people from filling their quota repeatedly during the day at different water points.
André mentioned that it is important to realise that Day Zero can be avoided if Capetonians reduce their water use to 50 litres per person per day of 450 million litres per day combined use and the City of Cape Town’s augmentation options of desalination, ground water use and the use of treated effluent is implemented as planned by the end of March or early April.