Dams – Latest levels: Winelands and Cape Town
Latest report (updated 14th August 2017) on the main dams serving
Cape Town City and nearby Boland/Overberg towns
Predicted rains last week in the mountain catchments saw both the Wemmershoek and Berg River dams recharge further. Useful rain in the Villiersdorp area contributed to a lift in the Theewaterskloof dam. The combined net inflows climbed to 15.3 M.cuM for the week (1.7% of capacity) causing the total stored water to rise above 30% for the first time this winter.
During this week last year the dams rose by a similar 16.6 M.cuM to reach 55.4% of capacity.
The year-on-year comparison shows the reduction in net water stored in 2017 to be 119.4 M.cuM compared to the same period in 2016.
[Why since 1st November 2016? that was when level 4 restrictions were imposed].
Current status?
There is now 273 M.cuM (188 M.cuM of easily accessible) water in the dams (last year same time this stood at 492 and 407 M.cuM respectively).
The accessible water now equates to only 46% of that available at the same time last year.
Although rains have been useful, relatively the overall situation continues to deteriorate. The unpleasant fact is that, according to current NOAA/CPC climate forecasts, only average to below-average rain is probable through August to end-September. So it is increasingly probable that we may not even reach 300 McuM of total water stored in the 6 main dams by the end of 2017 winter.
This chart produced by UCT Climate Systems Analysis Group (as at 8th August) shows that the cumulative rainfall year-to-date (measured at CT Airport) is the lowest across the past 12 years.
How long will the water last?
It is now seems that nature is letting us down and that we may therefore end winter with only around 300 M.cuM of water in the dams; way below the hoped for “safe level” of 500 M.cuM. Absent surprise heavy rains and allowing for normal ramping summer consumption levels, under ‘worst case’ conditions that water could be exhausted by end-December, 2017.
Clearly this situation is not viable; something must be done! (Read here what steps we believe authorities need to take to ensure sufficient potable water is available until winter of 2018).
How long can the available water be made to last?
Three factors will surely become critical in containing the situation:
- Action by the authorities to target and motivate further sharp reductions in water consumption.
- Cooperation by the population, residents and visitors, to reach the new reduced target.
- Interventions by the authorities to produce extra potable water before the dams run empty.
Given the circumstances, the authorities will have no option but to soon introduce further sharply reduced water consumption targets. An emerging problem is however, that it is proving extremely difficult to even get down to the current target of 500,000 cuM/day, with total consumption “sticking” in the range of 600,000 cuM/day; i.e. 20% too high. What then will happen if the CoCT has to try to halve consumption down to, say, 250,000 cuM per day? What will they do if such a reduction is the only way to ensure survival but the population cannot (or will not) achieve it? What further steps will be needed to enforce adherence to lower targets?
The City has yet to announce its plans.
But we are now getting the first indications that DWAF may cut agricultural irrigation allocations by 30%. That appears prudent to us and should still allow a reasonably productive growing season and manageable job losses while stretching out the available water supplies. If implemented, this step could save around 40-45 M.cuM that would otherwise be used by agriculture in SW Cape between September and next April.
Thereafter, the holiday season spike and summer heat factors will bear down between December and February – it remains to be seen how the authorities can throttle this usual summer ramp in water consumption.
An announcement is promised soon from mayor De Lille as to how Cape Town City plans to deal with both the general crisis and this specific summer challenge.
What ought households to be doing?
Prepare to deal with further sharp reductions in water availability – targets may soon be reduced to 50L/person/day or even lower and at some stage water stopages may start to occur.
What to do? focus on one thing – make your household more water-resilient, meaning;
- Practice getting by using far less water (read my suggestions on how to).
- Install some means to harvest and store water that is under your direct control (see here).
The warning signs are clear; it is up to you to prepare as best you can to cope with a likely crisis. There are stacks of ideas and experiences being shared at the Facebook Group Water Shedding Western Cape – join the group, follow the debate and get valuable ideas from fellow citizens.
What are the authorities doing now?
Mayor De Lille recently stipulated that the City “will not run out of water”. She mentioned four specific interventions that would be used to achieve this, but made no mention of what each would produce by way of additional water and by when this would start to flow. The mayor’s stipulated interventions were:
- Emergency drilling of boreholes into the Table Mountain Group Aquifer.
- A small-scale desalination package plant.
- A small-scale water re-use for drinking use plant.
- Drilling and expanding a well field into the Cape Flats Aquifer
STOP PRESS (midday 17th August).
Mayor De Lille’s announcement on planned “Water Resilience” was issued by CoCT in Cape Town today (17th August) – read it here. The interventions listed are much as was expected above. The potable water yields predicted for the different actions add up to 500 M.litres/day, the current target for fresh water consumption by the City. It looks good, but the announcement is short on detail as to what may be expected by when.
I have requested more specific clarification from her office and will report back if and when a reply is received. It is important to know if these interventions can have a practical effect before the feared water shortage arrives.
We are just told that the City is considering recent RFI responses but without giving any indication where they may be leading or what relief any of the proposed measures may bring.
One solution possibly under consideration is the proposed installation of mobile seawater desalination (reverse osmosis) units, each capable of producing 20,000 cuM of water per day. Reportedly five such units could be made operational by the end of 4 months (by December 2017?) capable together of producing 100,000 cuM/day of potable water. This would amount to around 17% of CoCT’s total daily consumption or some 25litres/day for each of 4 million people. Apparently the incremental costs are bearable and the units can be de-installed and removed once no longer needed. More details will no doubt emerge if this solution is selected by CoCT.
We still await the City’s promised operational plan for possible “Zero water” conditions.
Will the weather help?
The remaining 4 weeks of traditional Cape winter are all important. August may yet surprise:
There is the possibility of a cut-off low developing this week on 15th through 17th that may help recharge Theewaters dam (but risk is that this front may rather lie further east, beyond the catchments) – it could bring 10-20 mm rain with cold, windy conditions.
Another small front arriving on 21st could bring a further 5-10 mm of rain.
This NOAA/CPC chart shows the likely cumulative rainfall pattern by 21st August.
A much larger unstable weather spell between 23rd and 26th August may help more with a possible cumulative 40-60 mm of rain in some areas.
The main recipient of this burst of rain is likely to be the two Steenbras dams as well as the Palmiet river system.
This NOAA/CPC chart shows the likely cumulative rainfall pattern for 7 days ending 28th August.
What else may we expect?
Looking further out into September:
- a storm with about 10 mm rain on/about 2nd September
- 7-10 mm of rain on/about 9th September
- 10-15 mm of rain between 19-20th September.
And once the South Easter sets in, that will probably be the lot. A long look into October indicates nothing special at this stage. So at best we may expect average rainfall for September and October.
Curiously, El Niño which had seemed to return to a very neutral state, has again indicated a dip towards La Niña status. If this continues it might just bring greater instability to our weather, and the possibility of late rains.
How much rain has fallen in the dam catchment areas? The useful rains that fell in the mountains last week kept the rivers flowing to the benefit once more mainly of Wemmershoek and Berg river dam. DWS is still pumping water through to Theewaters dam.
In Summary: with fresh rains, net inflows prevailed resulting in a 15.3 M.cuM rise in the dams levels, up from 29.0% to 30.7% of capacity. Further rains are expected this week and next. Dam levels are still way below safe levels. Constant water savings is essential.
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.
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.
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