Cape Water and Dams Report
(Stettynskoof Dam. Now 100% full. Photo : DWS)
Dams – Latest levels: Winelands and Cape Town
Report nr. 120 (updated 3rd September 2018) on the main dams serving
Cape Town City and nearby Boland/Overberg towns
General rains, particularly in all the catchments, raised the levels of the main dams by 35.7 M.cuM (a very healthy 4.0% of capacity) last week. Total water in storage improved from 61.9% to 66.0%.
Last year, the same week saw levels rise by only 7.4 M.cuM (0.8%) to 34.7% of capacity.
Much improved. This latest burst of rain has lifted us away from the below-average results of July and August. All the dams rose, but this time the two major dams, Theewaterskloof and Voelvlei, also gained sharply. Voelvlei in particular gained 6.6% to end the week at 74.4% of capacity.
Here is my model projecting the percentage full state of the six main dams. August/early-September was better than expected, also because of the cut-over date. So the model has revised the likely peak storage level upwards to 67%, and it could easily end up even better.
(Here is our model predicting the amount of water likely to be stored in the dams each month)
Putting it into context!
The net result is that the combined amount of water stored has increased to 586 M.cuM. With more rain still to come this week as well as predicted for early October, there is now a chance that the total water stored could climb to 650+ M.cuM (73% of capacity) by end of winter.
If this was to happen then 2018 could turn out to have been the best year since 2012 in terms of the extent to which the main dams recharged (around 50% of combined capacity). And it would be the outright best rainfall year out of the past 4 years. To everyone’s relief the rainfall this winter would have returned to normal levels. And hopefully it will now stay this way.
Augmented water supplies i.e. the difference between the water drawn from the six main dams (491 ML/day) and that consumed from all sources (535 M.cuM) this week stood at 44 ML/day.
(Graph tracking overall use and production of extra water through the augmentation efforts)
Read full report on status of Cape Town’s augmentation efforts here.
How well are we actually doing overall?
This CoCT graph of the combined dam levels evidences further strong improvement .
Of interest to irrigation farmers, Brandvlei Dam has reached 49% and Kwaggaskloof Dam is up to 48% of capacity. Clanwilliam Dam and the lower smaller Bullshoek Dam both stand at over 99%.
The south-eastern Cape and Klein Karoo are still very short of water (you can assist through a donation here to a charity helping the farmers – donations go to cover some costs of distributing animal feed).
Will the weather help?
As predicted, the cold front that arrived over the weekend roundly boosted the mountain dams. Here is our chart of rain that actually fell right at the dams, as measured by DWS.
Click here to see ShowMe Winelands Weather forecast of possible near-term rain.
What rain ought we to now expect?
1) A cold front could bring 40-70 mm of widespread rain across SW Cape, commencing today (4th) and continuing through to Saturday (8th), with the heaviest rain expected on Friday. This NOAA/CPC chart shows that on 7th/8th September, falls of 40-60 mm rain could be enjoyed in the south-east stretch from Caledon to Mossel Bay (hope it’s now your turn Swellendam).
Somewhat unusually, this rain will be approaching from the south-east. Much of the rain may stay just offshore.
2) Scattered showers are expected occasionally, with 5-10 mm forecast for 3rd week September.
3) The long-range forecast has improved and a thunder storm with heavy rain in places is presently predicted for end of the first week of October.
ENSO continues to remain in neutral range and it increasingly seems that even if it does emerge, the El Nino condition is likely to be mild.
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What are the authorities doing?
The proposal by Cape Town City to DWS for a gradual easing of water restrictions fell on deaf ears and DWS decided to keep the restrictions in the Western Cape unchanged. This proposal was reportedly supported by the other municipalities and agricultural irrigation users.
It is hoped that this does not represent a fixed position on the part of DWS.
Various dam capacity levelling actions by DWS are taking place.
1) Water is being transferred from Berg River Dam at 3.5 cuM/sec to Theewaterskloof Dam. Water from the Banhoek and Wolwekloof rivers is also being diverted to TWK. All this will be helping to prevent the Berg River Dam from overflowing while storing the excess water in TWK for later use.
2) 19 M.cuM of water has been transferred from the Kogelberg and Rockview Dams to Steenbras Upper Dam.
3) Upper Steenbras Dam is spilling into Steenbras Lower Dam, which is now also rapidly filling.
4) Cape Town is currently drawing water mainly from Berg River and Steenbras dams.
It is planned that these diversions of water to TWK will continue through to end-October.
The new debate: when to start easing restrictions and by how much?
The recent good rains permit us to now think seriously about this next step. In order to do so it will probably be useful to recap some of the prevailing circumstances:
1) DWS determines how much water will be allocated to the municipalities and agriculture. Cape Town is operating on level-6B restricted to a target of 450 million litres per day for all purposes. This has translated to a limit on residential water use of 50 L/person/day at a charge of R33.24/Kl for up to 6 Kl. Cape Town’s average draw from the main dams has recently been in the range of 470-490 ML/day; i.e. somewhat above target.
2) DWS has stated that if the dams serving the SW Cape recharge to above 85% of capacity, restrictions will be immediately lifted.
3) DWS and the users comprising the Western Cape Water Supply System [WCWSS] meet monthly to consider the situation. Now that the stored water levels have risen above danger levels, Cape Town has proposed a step-wise gradual easing of the restrictions. The other municipalities and agriculture have supported this proposal, but to date DWS has refused to change the restrictions.
4) Depending upon where it falls, there is a risk that rains predicted for this week could well cause the smaller dams to start spilling, with such overflows running away to the sea.
5) If personal restrictions are eased to 70 L/p/d, the resultant extra water consumption would increase by some 2 M.cuM of water per month which, over the 7 months from October 2018 to April 2019, would amount to less than 15 M.cuM in total (rainfall delivered that much water to the dams in just one day last week). This modest increase in consumption would have only a marginal impact on the dam levels at the end of Summer 2019. Even if we receive no more rain this winter (very unlikely) the combined dam levels would still be above 300 M.cuM in May 2019; a reasonably safe position of 35% storage at the start of winter. To enable the easing, DWS would need to increase the restricted target for Cape town to around 560 ML/day.
6) Such a quantitative easing would be of immediate benefit to the older community and also larger families – reducing the burden of re-using water – and the extra water sales will enable the municipalities to reduce the tariffs, thereby bringing costs of water down. For those 400,000 ‘green dot’ homes who could maintain reduced water usage, the benefit would be a reduction in their monthly charges for the same amount of water consumed.
7) It would also make sense to reduce the connection fee to one single charge for all residential properties, irrespective of what the incoming pipe diameter happened to be.
8) Increasing water supplied primarily from the smaller dams will help prevent them from spilling and losing excess water to the sea. That water can instead be used to reduce the burden on users.
9) Last but not least, such an easing would be acknowledgement of the extraordinary job the SW Cape has done in reducing its water usage and a deserved ‘reward’ for the community’s efforts.
To sum up: I advocate that we support the municipalities’ proposal to ease restrictions from 50 L/p/d to 70 L/p/d from 1st October 2018.
Summary: Combined levels of the six main reservoirs serving the Cape Town/Overberg/Boland area rose from 61.9% to 66.0% of capacity.
Watch me answer the often asked question: “why do you write this report?“
Read the full City Cape Town release about Water By-law amendments here.
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
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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