Dams – Latest levels: Winelands and Cape Town
Latest report (updated 2nd January 2018) on the main dams serving
Cape Town City and nearby Boland/Overberg towns
Over the past two holiday weeks, little data was available for reporting, and that which was published was not entirely consistent; but the picture is stabilising again.
During the week leading up to Xmas total consumption was reported as 6.9 M.cuM, whereas last week, before New Year, consumption reportedly climbed to 11.9 M.cuM. In reality, variations in reporting periods introduced distortions so it is perhaps best to look at the aggregate net outflow of 18.8 M.cuM for the two weeks, an average net usage of 9.4 M.cuM per week. During the same two-week period in 2016, levels of the main dams dropped by a substantially higher 26.8 M.cuM (ave. 13.4 M.cuM per week).
Combined dam levels dropped 2.1% from 32.7% of capacity to 30.6% across the two weeks. During the same period in 2016, total dam levels declined by 3.0% to 46% of full capacity.
Here’s the graph of the weekly change in stored water, 2017 versus 2016, commencing from end of winter. As already mentioned, Dec-25 is probably under-stated while Jan-01 is likely over-stated.
The red-brown line shows changes for this year while the grey-shaded area shows what happened during the same weeks last year. Minus figures mean net dam outflows.]
Current status?
Last week combined water stored in the 6 main dams fell to 272 M.cuM (187 M.cuM of easily accessible water) (last year, levels dropped more quickly to 409 and 324 M.cuM respectively over the same period).
How long will the remaining fresh water last?
As may be seen from the table below, actual consumption across December was only 36 M.cuM, considerably lower that the 45 M.cuM we predicted and fully1/3rd lower than the 56.6 M.cuM used during December 2016.
Commencing 1st August 2017, had water simply been used on the same “business as usual” basis as in 2016, then we could now have been down to just 191 M.cuM stored in the dams and heading for “Day Zero” by end-January. Instead, we ended December 2017 with 273 M.cuM of water in hand.
This is a great result and all those who have saved so vigorously are to be applauded.
We predict that we now could end January 2018 with 209 M.cuM of water still stored and hope that this may actually end up as high as 230 M.cuM.
Our estimate shows that, provided water consumption remains cut to a minimum, then currently stored water should last into June 2018. And if this month, January 2018, proves to be another low consumption month of say, 45 M.cuM (instead of the 64 M.cuM that we have predicted (green columns) and versus the 81 M.cuM historically consumed in January 2017 (blue columns)), then most importantly, the authorities should be able to hold off introduction of water collection/ rationing to June; by which time relieving winter rains should arrive and also fresh water production by the various augmentation initiatives should be coming into production.
And as consumption continues to reduce we can hopefully move past assured survival and start building safety reserves just in case 2018 winter rains are disappointing and yet more time is needed to bring new water production capacity on line.
Why is this? How has it come about?
- Reduction in water consumption achieved by the residents has on average been excellent and is gradually edging even lower. Most gather and re-use “grey water”. Many residents have given up on their gardens and some have installed rainwater harvesting and storage systems while most seem to have introduced water efficiency mechanisms and follow requirements to not use potable water for outside purposes. Those that can afford it are installing well-points or boreholes. Businesses have introduced water efficiency and savings methods and encourage their work forces to be sparing with water use. The overall aim being to cut water usage by 45%.
- Other municipalities have played their part, reportedly matching Cape Town’s 40% water savings rate. They are also rehabilitating old and drilling new boreholes both to improve water security as well as to reduce their reliance on the dams for fresh water supplies. Storage facilities have been perked up while recycled water is being made available for businesses and farms in substitution for reduced use of potable water. One location, Veldrif, is planning a small local desalination plant. Read more about what other municipalities are doing here.
- Cape Town has world-class low water loss rates due to sustained maintenance and effective ‘break-fix’ efforts. It encourages all water savings and has various ground-water, recycling and desalination initiatives in process to produce fresh water. It reduces pressure and throttles supply to reduce water usage. Read more here.
- Potable water use for agricultural irrigation has been reduced by 60%. In the near term this will become the largest single contributor to reducing demand on the dams. At present the agricultural sector is using all the water it has available to maximise crops but total consumption is nearing the newly gazetted limits and supplies from the dams should start to be be cut off relatively soon (see CoCT graph below).
What lies ahead?
Agriculture has a normal water allocation of some 150 M.cuM per annum, now cut to just under 60 M.cuM. Presently farmers are using all water available to maximise early crops, but orchards and vineyards are being pulled out and crops are being written off. Massive financial losses lie ahead and job lay-offs are likely to be widespread. At the moment it appears that the agricultural allocation will be largely consumed by end-January and use of fresh water for irrigation purposes will then fall away. Once that happens monthly water consumption by agriculture should taper off sharply and “flat line” as shown.
Once agricultural irrigation demand terminates (in my model I conservatively allow for this to happen during February), the remaining combined draw from the dams by City of Cape Town and the other municipalities in SW Cape should should settle around 4.5 M.cuM per week. Unfortunately the “gorilla in the room” remains evaporation – unchanging as consumption reduces (being simply a function of dam surface area, humidity, temperature and wind, evaporation does not ‘scale’) – at this time of year total evaporation can be as high as 3.0 M.cuM per week. This implies total combined non-agriculture drain on the dams reducing to 25-28 M.cuM of water per month, declining further as evaporation slows in the cooler months and new water production commences.
What are the authorities doing now?
Level-6 restrictions become applicable from 1st January 2018 across the SW Cape in line with DWS instructions (read details of the restrictions here). All previous restrictions still apply so there is no major change for residents of Cape Town except that:
- unless exemption is obtained, a household’s water consumption may not exceed 10,500 litres per month (=4 persons x 87 litres/day x 31 days).
- the 87 litres limit per person/day must also include water used in places other than the home. E.g. do not shift consumption by flushing and/or using water wastefully at work or taking a long shower at the gym after morning exercise; such water still comes from the dams.
In Cape Town 60+% of households use more than 87 litres per person per day. Why? What needs to be done to sensitise all water users to the problem. The municipality must do more but we can all help. Talk to your family and friends. Discuss the issues and share ideas and ways to save water.
Be aware that the municipality is able to to see the water consumption for every household/ water user and are closing in on all wasters, installing water restriction devices and applying fines.
Cape Town has proposed a “Drought Levy/Charge” (see City’s summary here and my assessment here). The principle is a fixed monthly amount based on the municipal valuation of each property, and in force for three years. Clearly, use of water and consequently the revenues that it generated have been more than halved. Unfortunately the City needs to replace this lost revenue otherwise it will not be able to continue to provide us all with high quality fresh water through our taps; the cost must be covered in some way and must be paid by us, the residents. OUTA argues that this should not take the form of a stealthy tax. Most feel it should be linked to usage, not property values. Opinions differ strongly. If you are interested to see what I submitted, you can read it here. Have your say – email any concerns and recommendations to drought.charge@capetown.gov.za.
Cape Town’s website now shows two water consumption figures:
- one is water drawn from the dams (target is to reduce this to 500 ML/day) and last week this had reduced to average 561 ML/day, and
- the other is total dam water consumed plus water from other sources such as underground and recycled water – last week this amounted to average 578ML/day.
This means that Cape Town City is already producing between 17 and 20 ML/day of water from sources other than the main dams. This figure is expected to rise to over 200 ML/day when all new projects come into production.
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.
Will the weather help?
The La Niña Pacific Ocean cool water condition is expanding; to the east, in zone NINO 3.0, temperatures are already down in the range of 1.5 degC below average.
There is a close correlation between La Niña and the severe wet weather being experienced in the summer rainfall area. Links between the winter rainfall patterns and La Niña are less certain. However, in 2013/2014 a La Niña condition similar to the current one prevailed and it was noticeable that in 2013 strong winter rains came unusually late in August-November followed by good rains that then arrived more normally in June-August in 2014. So my hope is that this current La Niña holds on long enough into autumn to bring good strong rains early in winter 2018.
Many places enjoyed some refreshing rains over New Year weekend. A wet morning with 5-10 mm is also forecast for 7th January. The medium range forecast points to an unstable weather system of three days duration 19th – 22nd February possibly bringing 15-20 mm of rain accompanied by thunderstorms. Otherwise the weather is generally predicted to be hot and dry with occasional rain.
New Years 30 mm rains around Dwarsberg will offer some small run-off into Berg River Dam, while the cooler weather will have slowed evaporation from all the dams.
In Summary: outflows exceeded inflows by 11.9 M.cuM and combined dam levels fell to 30.6%.
Here are the levels of the six main dams serving the Cape Town/Overberg/Boland area. Note that all four mountain dams now hold more water than they did this time last year.
Here are some of our thoughts of possible implications of “Day Zero”.
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.
Views expressed in this article, and comments in response, are those of the writer and commenters alone and do not necessarily reflect the views and opinions of ShowMe, nor is any warranty hereby given as to suitability for any purpose of a reviewed enterprise or as to the quality of offered advice, products, services or value. Copyright ShowMe Paarl. All rights reserved. Copy only with prior permission.
2 Comments
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prd1923
Hi Tom,
I am working on a community water project task force in the Cape South Peninsula and have been looking for some of the data exactly as you have presented it. Could I please email you directly to discuss some of the detail?
Thank you.
Peter
tombrown
Hi Peter.
I am not sure how I may help but feel free to contact me. Email what you have in mind or call me on 0824564206. Best will be before Friday evening – after that I shall be on my farm and harder to reach.
Tom.