Cape Water and Dams Report
Dams – Latest levels: Winelands and Cape Town
Report nr. 90 (updated 19th February 2018) on the main dams serving
Cape Town City and nearby Boland/Overberg towns
Combined levels of the main dams dropped by only 4.2 M.cuM, or 0.5% of total capacity (vs the preceding week’s higher 5.8 M.cuM) during last week from 24.5% of capacity to 24.0% of capacity.
The net result is now obscured by the water transferring in from the Kogelberg-Palmiet system as well as rainfall experienced at Steenbras, Theewaters and Wemmershoek dams during this week; while the Berg River dam benefited from rainfall run-off from Dwarsberg. The transfer obviously makes the overall result appear better than it otherwise would have done.
In 2017, the main dams dropped by a far larger 15.6 M.cuM, falling 1.7% to 34.0% of full capacity.
All-in-all an outstanding week, making attainment of the mid-year goals more likely. The following week-to-week water consumption chart shows the dramatic change achieved. Given that evaporation was estimated at around 1.7 M.cuM, the net drop of water levels in the main dams was only 2.5 M.cuM for the week.
Current status?
Combined water stored in the 6 main dams fell to 214 M.cuM (129 M.cuM of easily accessible water) (last year, levels dropped to 312 and 227 M.cuM respectively over the same period).
How long will the remaining fresh water last?
DWS managed to cut off water flows to agriculture at almost precisely the agreed 40% level. But the Metro’s average consumption still remains too high at ave. 523 ML/day. [I think there may have been an error in their figures this past week. I have queried this and await an answer].
Nevertheless, net improvement is such that I can make a mid-month correction to my forecast chart, reducing predicted consumption for February down from 37.8 M.cuM to 27.5 M.cuM.
The net end-result is to make it yet more likely that we will attain our “Success Day” target, being to reach 30th June with 100 M.cuM or more water in the 6 main dams. What it requires is for households to hold water consumption down at the goal of 50L/p/day or less until winter arrives.
What actually is going on to make the available water last?
1) As mentioned above, agricultural draws for irrigation purposes have almost completely ceased.
2) Modifications – essentially dams within dams – at Theewaters and Voelvlei dams – are almost complete. This photo taken last Friday shows the berm across TWK above the road bridge is almost right across. This will hold water from the Sonderend River above the berm at a higher level to enable abstraction towards the Berg River. Water may also be pumped up from the deeper part of the dam if needed; intention is that this will enable the dam to be drawn down to 6% (i.s.o. 10%) of capacity if needed.
3) As at last Friday, 16th February, the Metro had reduced its overall water production to 505 ML/day with only 479 ML/d actually coming from the main dams. Cape Town is targeted to get down to water production of just 450 ML/d with perhaps only 420 ML/d or less being drawn from the main dams. Good work all who are making such a special effort.
Here is our altered CoCT tracker chart displaying graphically what seems to be happening (see here for a detailed explanation of how the chart is to be read).
Importantly, the City of Cape Town last week pushed out its prediction of “Day Zero” to 4th June 2018 (point red ‘X’ in the chart). This estimate now coincides closely with my long-standing prediction. It is encouraging as it means that the Metro’s water management team, while remaining cautious, recognise that provided we meet our reduced water usage targets, then we are now likely to survive until the winter rains arrive without invoking stage-2 collection/rationing.
We are today at point red ‘Y’ (24.0% of capacity on 19th February) – the small yellow circles with ‘x’ mark the previous positions of ‘Y’ over the immediate past. Now that the reduced use by agriculture has fully kicked in (blue-striped zone marked ‘E’), the final outcome is entirely in the hands of all SW Cape households to achieve the saving depicted by the blue zone labelled ‘H’. We are now firmly following the dotted red line trending from ‘Y’ toward point “I” on the revised lower line “C” at which the authorities would finally have to implement stage-2 collection/rationing of the disaster plan.
But our expectation is that arrival of winter rains (‘J’) together with production of extra water through the augmentation initiatives (‘K’) will cause us to shift across to the lifting red dotted line ‘L’ rising up again as the dams start to recharge; where, although we will still need to keep our use of water reduced, we should pass into a safer, more water-secure phase.
The positive fixed target that I call “Success Day” means getting to 30th June with sufficient reserves of water in the dams such that even if winter rains are weak, we could reach the end of 2018 under a rationing regime, by which time a number of augmentation initiatives should be producing extra water to start to relieve the situation.
Thinking ahead!
Now that it appears we may survive through to winter, our thoughts should perhaps start to turn to what next? How should the SW Cape be made more water-secure? How can it become more resilient to deal with possible similar water shortages in the future.
And if it does become water-secure and more resilient, what could the blended cost of water become as a result? Combining the augmentation initiatives currently being pursued by DWS and the Metro at the various costs per KL ex the water treatment plants as published by the Metro, this is what a blended augmented outcome could look like. The following table indicates an estimate of the average produced cost of water exiting the water treatment plants. The cost of getting the water to the consumers taps would thereafter be the same irrespective of the original source.
Given that the standard at the moment is apparently R5.20/KL for purified dam water, it shows that the new blended cost of producing this amount of water in this specific mix would be some 40% higher at R7.04/KL, ex the treatment plants.
Note; I have not taken capital costs into account but assumed that the capital needed could be raised for these projects and the cost thereof recovered through the water pricing. I have focused rather on how cost-effective a resilient water production system could be. Main elements could be:
1) Encourage installation of rain water capture tanks in every household and business. Property owners would own the installations, adding value to the properties. Assume ave 100ML/day captured and contributed across a year at zero cost to the metro.
2) Draw (reduced) amount of water from dams. Assume 650ML/day drawn at R5.20/KL processed.
3) Abstract water from the aquifers; 70ML/day from the Atlantis and Cape Flats aquifers at R7.00 processed together with 40 ML/day from the TMG aquifer at R15.00/KL processed.
4) Permanent recycling. 165 KL/day at R7.50 and 100 KL/day at R15.00/KL processed.
5) Permanent desalination. 80KL/day for a medium-sized plant running 24/7 at R15.00/KL supplied.
What are the authorities doing now?
DWS engineers have delivered on the promise to “manage the system so as to not fail“.
- Agricultural irrigation has been stopped at the gazetted level of 40% of unrestricted supply (i.e. around 58 M.cuM for this year).
- Voelvlei and Theewaterskloof dams have been modified to permit additional water to be abstracted.
Helen Zille reports about the thwarted plans to increase capacity of Clanwilliam Dam and the reasons why the Lambert’s Bay desalination plant is lying idle. Read this important article here.
Last week City of Cape Town reported that 505 ML/day of water was consumed from all sources but that it only used 479 ML/day drawn from the main dams. This implied an augmentation flow of 26 ML/day of fresh water during last week.
While encouraging people to continue using less water, by adjusting its estimated date for “Day Zero” to 4th June, the Metro recognises the various savings being effected as well as the transfer of the 8-10 M.cuM of water from the Groenland Water Users Association to WCWSS.
CoCT had announced that it intended to release details of the Points of Distribution on Sunday 18th February. However, nothing has been announced yet.
The water quality compliance is being maintained at better than 99.4% vs minimum goal of 98%.
See details of Cape Town’s planned interventions to produce fresh water here.
Learn about water savings efforts by other Cape municipalities – read more here.
Hear me interviewed on Bok Radio here about the overall water situation in the western Cape
Do visit the City of Cape Town website to see additional graphically presented information regarding the water situation – very helpful.
1) See the full water status presentation here and
2) Check out water usage for your property and of neighbours, friends, using this interactive map.
What ought you to be doing?
1) Reduce use of water wherever possible. The biggest items to focus on are showers and laundry.
2) Remain reliably informed of developments. Benefit from tips and suggestions on how to reduce use of water. Have a look at this link.
3) Install some form of rainwater capture. As the year progresses we will tend to get increasing amounts of precipitation and you will benefit by storing water every time it rains.
Will the weather help?
It was odd weather last week. Spinning clockwise, that low pressure system brought thunderstorms and bursts of rain down across the extreme west and central SW Cape. So much so that there was sadly some loss of life of people caught in local flash floods. Otherwise, you may have had decent rain if you were under a cloud. Unfortunately, not much fell in the dam catchments.
Next weekend is starting to look as though a similar burst of unstable weather could develop, although this time in connection with an approaching low pressure system. 5-10 mm of rain is predicted for most areas with perhaps a bit more in the mountain catchments.
Our rainfall chart for the dam catchments for the period since 1st April 2017 shows that the rains falling at the dams at the moment are much in line with the long-term averages.
In Summary: outflows exceeded inflows by 4.2 M.cuM and combined dam levels fell to 24.0%.
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.
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.
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