Dams – Latest levels: Winelands and Cape Town
Latest report (updated 6th June 2017) on the main dams serving
Cape Town City and nearby Boland/Overberg towns
Net outflows reduced sharply, indicating that the first winter rainfall run-off has reached the dams. The combined level of stored water in the main dams reportedly fell by only 2.0 M.cuM (2.2% of full capacity) last week.
With Cape Town reportedly having consumed some 4.6M.cuM last week it seems that total consumption for the SW Cape would have been around our expected level of 6M.cuM. This implies that the run-off into the dams from the recent rains amounted to some 4M.cuM, compensating for 2/3 of water consumption last week. Not enough to start recharging the dams, but at least stretching out how long the existing water supplies will last.
How many days of water is left? Using the moving average estimated water consumption rate of 6.2 M.cuM from the last weeks, arithmetically calculated, the usable water left will last 13.0 weeks, i.e. 91 days, through to until 2nd September 2017; a gain of 4-5 days versus last week due to rain run-off.
Taking into account planned interventions to access more water in Theewaterskloof Dam, the available accessible water should stretch until end September.
Further assessment of the current situation!
Small drops in the levels of most of the dams indicates that DWS is again drawing more widely from the system. The gain in level of the Steenbras Upper Dam was due to water pumped up from the Steenbras Lower Dam.
Anticipated heavy rains this coming week should see some dams start to recharge. Nonetheless, the situation remains extremely grave as the real challenge is how to survive the following dry summer period where no significant rain may be relied upon. Severe restrictions seem sure to remain in effect. and all possible efforts must be made to continue saving water.
Negative accusations are often levelled that the authorities have no plans. This is obviously not true. Read extracts from a recent presentation by City of Cape Town Councillor Limburg, responsible for water matters, outlining current water consumption patterns and the city’s near-term plans to produce and distribute additional water.
What ought you to be doing?
We have previously advised to install the biggest household water tank system that you can afford. We explore the rationale for you doing so in this article – read more here. The key advantages are:
- At a household level, the cost of doing so should typically be paid back within 3-5 years through saving the costs of water no longer taken from the taps; and savings continue.
- One personally takes responsibility for one’s own water usage and contributes to the conservation of communal water resources.
- Personal water security is enhanced in the event of future droughts.
- If the water harvesting and storage system is correctly planned and installed, it will add to the resale value of the property.
In so doing greater water security, at both individual household and collective community levels, would be achieved.
Do take a look a practical example of rainwater harvesting calculated using a real property. Then try it for your own property.
Read about a D-i-Y household rainwater harvesting and tank system here
What are the authorities doing now?
An exhibition of water conservation, rainwater harvesting, storage and related technologies has been arranged by the City of Cape Town and will take place at Canal Walk between Saturday 10th to Sunday 11th June. Do visit this event and learn of the many ways in which you may harvest and store water as well as reduce consumption in your household. All residents who want to explore ways in which they can conserve water are encouraged to attend.
Cape Town Mayor Patricia De Lille has announced change to level-4 water restrictions from 1st June 2017. Read the mayor’s statement here.
Read main details of level-4 water restrictions here.
Will the weather help?
During the first days of June widespread rain fell across the SW Cape with many experiencing 10-15mm. Gratifyingly particularly heavy falls were recorded at Berg River Dam and Wemmershoek Dam. Importantly this rain damped the soil, enabling more run-off when the next rain arrives.
A “perfect storm” is now approaching. Tracked for several weeks, it is due to strike land around midnight on Tuesday 6th June and, although deflected slightly southwards, this depression has deepened to 980mb, enough to ‘kick down the door’ and cause sustained widespread rain. It is predicted to rain solidly for 36+hours. Many places may receive 60-80mm rain and, importantly, the heaviest rain at 80-120mm is forecast to fall in the mountain catchments and beyond.
Pressures in Cape Town could drop to 994mb (vs sea level norm of 1015mb) a “valley in the atmosphere” deep enough to cause very strong winds. Expect some hard driving rain; batten down the hatches.
The Synoptic chart shows very clearly how this depression has got positioned firmly between two high pressure cells. Following our comparison of highs as “hills” and lows as “valleys”, looking down on this diagram gives the sense that one is looking into a deep steep-sided hole.
This forecast chart from NOAA/CPC indicates the predicted cumulative rainfall across three days 7th-9th June. It shows how widely the rain may fall and the concentration around Berg River and Wemmershoek Dams, with solid rainfall also extending to the Voelvlei and Steenbras dam areas.
What else may we expect?
Apart from occasional light showers in between, some rain may occur towards June month-end. More encouraging , a strong depression is predicted for around 10th July and then again for the end of July. However, these will not be enough to recharge the dams so we must hope that some of them develop more venom and bring heavier rainfall.
NOAA/CPC, has recorded an up-tick in surface temp in the Pacific. An upward pattern seems to be developing. The effect of El Niño during Cape winters is uncertain and associated weather instability sometimes brings heavier rain
However, NOAA/CPC predicts that the El Niño will arrive later and shouldn’t influence our winter rain.
How much rain has fallen in the dam catchment areas? After a disappointing month of May, the early June rainfall run-off will now be reaching the dams, with Berg River Dam and Wemmershoek likely to be the main recipients.
However the on-coming heavy rain should cause still greater run-off, so the levels on Monday next week should be more informative. All the dams, with possible exception of Theewaters, should enjoy strong rains in their catchment areas.
In Summary: net outflows continued last week but at a sharply reduced rate due to compensating rainfall run-off into the dams. Stored water reportedly fell to 19.1% of full capacity.
Here are the levels of the six main dams that serve the Cape Town/Overberg/Boland area. Also shown is the total water storage level of all the dams in the whole greater Western Cape.
SPECIAL UPDATE – dams water levels 10June2017 report after the big storm.
Read about a D-i-Y household rainwater harvesting and tank system here
Our water-wise landscaping and water-wise gardening suggestions.
Read about South Africa’s desalination policies and initiatives.
Draft services pricing plan for 2017/2018 and proposed water tariff structure here.
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).
Note: To calculate number of days of water left we first reduce reported water stored volume by 10% of capacity (i.e. 89 Million cuM) to allow for water that usually can’t be extracted or processed and then divide the remainder by the net outflow rate during the previous week.
Tom.
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