Cape Water and Dams Report
Dams – Latest levels: Winelands and Cape Town
Report nr. 96 (updated 3rd April 2018) on the main dams serving
Cape Town City and nearby Boland/Overberg towns
Net outflows from the main dams totalled 3.6 M.cuM, or 0.4% of capacity (vs the preceding week’s 4.4 M.cuM), and combined storage dropped from 21.8% to 21.4% of total capacity. Note that due to the holidays this result is for 8 days and thus will be slightly overstated (by the same token the result next week will be slightly understated).
The tail-end of inward water transfers from Groenland Water Users plus scattered rainfall offset some draw-down from the dams.
During the same week in 2017 the dams dropped by 8.8 M.cuM (1.0%) to 25.8% of full capacity.
How long will the water last?
We marginally beat the prediction and passed end-March with 191 M.cuM (vs. expected 187 M.cuM) of water in storage. The model now predicts that we should reach early-June with 140 M.cuM or more water in storage just ahead of commencement of winter rains. This is well above the critical cut-off of 120 M.cuM (13.5% of capacity) at which rationing would be introduced “Day Zero”).
We continue to improve against our “Success Day” target to have at least 100 M.cuM of water in storage at end-June 2018.
(Here is our model predicting the amount of water likely to be stored in the dams by mid-year.)
Putting it in context!
The latest average daily draw from the dams by the Metro is 492 ML/d and the water used from “all sources” dropped to 515 ML/d. This implies that the augmentation contribution remained a subdued 22 ML/d. It seems that no additional extra water was added to the system from any additional groundwater or desalination augmentation project last week.
(Graph tracking overall use and production of extra water through the augmentation efforts).
The tracker chart shows that we are today at point red ‘X’ (now 21.4% of capacity on 2nd April) with consumption being eased by the useful rains received in the mountain catchments last week.
(see here for a detailed explanation of how the chart is to be read).
What are the authorities doing now?
1) Cape Town City announced that it conducted a test of a Point of Distribution (POD) to check how the system works and to iron out aspects that may slow passage of consumers collecting water through such an installation. The aim of the exercise was to test different layouts to see which configuration is most efficient and safe; to collect data on how long it will take to fill containers; and to assess staffing and other operational requirements. The exercise will further evaluate the impact of potential traffic congestion on the on-site operations and the surrounding area.
The desired outcome is that the PODs can be effectively managed. This involves anticipating what strategies households and businesses will employ to meet their water needs in the event of Day Zero and how these strategies can be supported by designing and managing the PODs in a way that ensures water collection can be made quickly and safely.
2) At Theewaterskloof Dam, DWS is holding off closing the temporary berm across the dam until it is certain that the pumping effort will be needed to lift water up from the deep section to the point of abstraction through to the Berg River side. This makes sense as the pumps would consume costly electricity and it is best to wait until absolutely sure that they are needed before switching them on.
3) Cape Town City has presented its draft budget for the coming year. This includes increases in many cost areas, most significant of which is a 26.9% increase for water. The budget also envisages the implementation of a fixed monthly charge for all metered connections. Increased revenues are needed to fund over R3 billion to meet water augmentation initiatives. A period for comments has now opened. Be sure to make your feelings known by submitting comments and suggestions.
How is the City’s long-term water augmentation plan developing?
Contrary to what many people think, a considerable amount of planning is going into developing a sound, resilient and cost-effective solution to the Metro’s growing water demand.
According to the Water Outlook Report 2018 published by the City on 23rd March, the planned production of extra water by source is as follows:
1) Surface water = 60 ML/d through lower Berg River to Voelvlei pumped storage scheme.
2) Groundwater = 100 ML/d (more could be abstracted from ground water sources in dry years).
3) Re-use = 70 ML/d to be produced through one large reclamation plant (economies of scale).
4) Desalination =120 ML/d – the optimal scale for desalination considered to be 120-150 ML/d.
Total extra water to be produced through these means would be 350 ML/d.
This planned mix of additional water sources was supported by an international review of the program facilitated by National Treasury’s Cities Support Programme, undertaken during November 2017, which took into account Cape Town’s unique combination of available water sourcing opportunities and advised the following: (quoted from a Metro publication).
- “Manage demand and dam draw-down. Assuming it will not rain again is not realistic. Augmentation would not make a significant difference to dam levels during 2017-2018 summer and there was therefore no alternative but to ensure effective demand management during summer. Ensuring agriculture was restricted was very important and the city should also pursue opportunities for water transfers from agriculture. The critical point for dam levels is June 2019 if there is poor rain in the winter of 2018.”
- “Prioritise ground water. Ground water is much quicker to exploit and is cheaper. There is a large resource available. It is possible to over-exploit the groundwater resource in the short-run as part of the emergency, taking future recharge into account.”
- “Do not pursue temporary desalination and reuse. Temporary desalination and reuse is very expensive. Multiple small plants are logistically complex, and are not sustainable. Providing temporary desalination at scale is not a quick solution, It will take longer than planned and anticipated.”
- “Do not use ship or barge-based marine desalination plants. Current experience shows that such plants are very costly and have a poor track record of producing target fresh water quantity due to the source seawater challenges when the plant is docked in ports located in an urbanized or industrial area.”
- “Re-use is cheaper than desalination and may be faster to execute. Pursue the most promising opportunities for re-use in a cost-effective and time-effective way, in parallel to permanent desalination.”
- “Pursue permanent desalination at optimal scale. Plan and execute permanent desalination at a optimum scale, at a plant size or in modules of 120-150 million litres per day. Do not build desalination plants of capacity larger than 200 million litres per day.”
- “Procure time- and cost-effectively. A competitively bid turnkey approach for reuse and desalination, using the private sector and with a water purchase agreement, will yield the lowest cost per unit of water compared to the alternatives and be quicker to implement provided regulatory processes are fast-tracked as part of the emergency.”
- “Make decisions on the long term now and implement. Do not delay decisions on permanent reuse and desalination, and implementation.”
The New Water Program is aligned to recommendations from this International Review.
See updated details of Cape Town’s planned interventions to produce fresh water here.
Learn about water savings efforts by other Cape municipalities – read more here.
Do visit the City of Cape Town website to see additional graphically presented information regarding the water situation – it is very helpful. See the full water status presentation here.
What ought you to be doing?
Simply keep working to get water usage down to 50L/p/d while giving thought to installing a rainwater capture and storage system.
Will the weather help?
According to NOAA/CPC, La Niña seems to be reverting toward the predicted slightly below-neutral temperature range. Hopefully it will hang on long enough to also benefit winter rainfall in SW Cape (as it has done on the Highveld).
As predicted, useful rains fell between 28th and 30th March with 15-20 mm falling in the mountain catchments.
Regrettably the South Atlantic high pressure cell has come skidding back into position off the west coast and has succeeded in deflecting those approaching powerful depressions further south of the land, with the rain falling uselessly over the sea. At the moment it seems that we may expect only light rain of 4-8 mm on morning of Friday 6th April.
Long-range forecasts at this time show no major weather systems being expected during April. Let us hope that this changes during the month, particularly as climatologist Piotr Wolski’s study showed that April rainfall gives some indication as to how the year’s rains may turn out.
In Summary: outflows exceeded inflows by 3.6 M.cuM. Combined levels fell to 21.4% of capacity.
Here are the levels of the six main dams serving the Cape Town/Overberg/Boland area.
Plan ahead for possible water outages; here are points that could help you.
Read our Indoors Water Savings Ideas here.
Read our Outdoors Water Savings Ideas here
Read about a D-i-Y household rainwater harvesting and tank system here
Read about South Africa’s desalination policies and initiatives.
Click here to see Winelands Weather forecast of possible near-term rain.
Report instances of piping failures and incorrect use to municipalities.
In Cape Town the contact details of the 24-hour Technical Operation Centre are: Email: waterTOC@capetown.gov.za Telephone: 0860103089 (choose option2: water-related faults) or SMS: 31373 (max 160 characters).
Tom Brown.
Retired international businessman with a background in Finance and IT; and now a fruit farmer, with a passion for the weather and climate.
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