Dams – Latest levels: Winelands and Cape Town
Latest report (updated 10 April 2017) on the main dams serving
Cape Town City and nearby Boland/Overberg towns
There seems to be a problem with the levels reported for Wemmershoek Dam which could be distorting the whole water consumption result this week. According to DWS information, 5 of the dams levels fell, but Wemmershoek Dam rose up by 8% compared to the prior week??
As you can see from the table below, when compared to previous weeks this results in total water net consumption dropping to a level that implies almost all of Cape Town did not use any water at all last week. Clearly impossible.
So what is going on?
Was it perhaps inflows from rainfall? SA Weather Services rainfall stats for the preceding 10 days show Paarl 1mm, Franschhoek 1mm, Jonkershoek 6mm. So it can’t have been rainfall run-off!
Did authorities perhaps move water to Wemmershoek from another dam? Maybe, but none of the other 5 dams show a drop that could allow for such a movement of water. Anyway, if they had, it would then leave the problem that the overall consumption for the week would be improbably low.
Here is another oddity. Except for last week’s reading of 28.2%, the level of Wemmershok has for some 8 weeks been sitting steadily at around 36.2% of capacity. Very strange. I did flag this some weeks ago. Initially I thought that water was being pumped to Wemmershoek for whatever reason and the higher usage at the time masked this. Then when the level dropped a week back it appeared that the water was being released at last. But now a week later it has jumped back up to that same 36.2% level. That is simply too much of a coincidence. See this DWS graph for the dam itself.
What has happened at Wemmershoek since the end of January? One can only conclude that it is an error or something unannounced is going on. I will try to get to the bottom of this.
[13th April update. It turns out that the previous week’s lower figure for Wemmershoek Dam was in fact wrong. CoCT Dept. of Water and Sanitation confirm that the Wemmershoek Dam level is indeed (since end of January) being held at about 36% of full capacity as a primary reserve while the other dams slowly run down. If there are no rains within about two weeks then Wemmershoek Dam will also start to drop as its water begins to be used.]
What actually did happen last week?
If we examine the stats for the other 5 main dams, they reflect a total consumption of 8.92 McuM or around 1.1% of full capacity – this is exactly what one would expect at this stage of the cycle. If one takes an educated guess that Wemmershoek Dam fell by a similar percentage, then the total water consumed would have been around 10.2 McuM or some 1.1% of capacity.
That would be a good outcome in line with the recent trend indicating that some 126McuM of accessible water remains. And at this estimated reduced consumption rate of 10.2 McuM, it indicates that the remaining water should still stretch out for some 86 days to mid-June.
Where are the good savings coming from compared to previous months? General reduction in water use, of course. But a key contributor will be that demand for agricultural irrigation water will be diminishing sharply as the summer season draws to a close. This will be a once-off reduction. Remember that agricultural irrigation at times reportedly accounts for up to as much as 40% of the water used from these dams.
What are the authorities doing?
City of Cape Town advises that water pressure has been reduced in the central and southern suburbs – saving a reported 25,000 cuM per day – and that the plan is to roll this pressure reduction out along the False Bay seaboard this week. Households are cautioned that variations in water flows may be experienced as these adjustments are made.
The other important thing to be aware of is the draft services pricing plan for 2017/2018 that has been announced. Two components of this warrant special mention:
* City of Cape Town plans, in all but the most deserving cases, to eliminate the current free monthly allowance of 6,000 litres of water per household. This means all water used must be paid for from the very first litre.
* The price of water will climb sharply, from 12% at the low usage end through 27% to 250% at the top usage range.
Note that similar changes are being implemented in other large metros and most municipalities are likely to follow suit.
See the new proposed water tariff structure here. Proposed service charges are open for comments; email these to the City Manager at email address: city.manager@capetown.gov.za.
One question that is asked is if everyone is saving so hard, why are we being “punished” with higher costs. There are two reasons, one obvious and one not so obvious:
* By raising prices, we will all be motivated to take steps to reduce water consumption. This must happen, as available fresh water will in future become increasingly limited.
* Not so obviously, as users reduce consumption, water revenues fall but the cost of producing and distributing water continually increases for the authorities. This gives rise to a growing deficit. The strange situation that arises from this is that as households successfully use less and less water they will have to pay more for each Kilolitre consumed so that the authorities can balance their books. To illustrate the point, at its most extreme, if there were just one user left, then that one user would theoretically have to pay for the cost of the entire water distribution system. Hopefully the savings from our reduced usage will offset the rising prices.
I continue to encourage all to look at installing some form of rainwater capture system; storage tanks become an increasingly financially viable option as prices rise.
It is said “a picture tells a thousand words”.
Here is a photo taken recently by Wimpie Stapelberg. It looks like a beach scene, doesn’t it? But the water here should in fact be several metres deep. Judging from the plant growth is hasn’t been there for several years.
It is, of course, the eastern part of Theewaters dam. Take a look at other superb photos from Wimpie; they highlight so well what is happening to this vitally important dam.
Read more about the water savings that can effectively be made here.
Read about D-i-Y household rainwater harvesting and tank system here.
Will the weather help?
As forecast, we all enjoyed some welcome rain this past weekend. More is predicted for the coming 24 hours. It seems that the winter rainfall pattern is gradually arriving.
As this NOAA chart for actual rainfall shows, SW Cape rainfall during March 2017 was disappointingly once more below average.
Occasional rain showers have been arriving as predicted but the rainfalls have mostly been light and of short duration. Unstable weather is expected between 23rd and 27th April with the possibility of some general rain and thunderstorms on the latter occasion. A sustained period of unstable weather is foreseen for middle May and, encouragingly, a spell of rain is still being predicted for early in June.
The latest report from USA NOAA’s Climate Centre still predicts normal average winter rainfall with re-emergence of a weak “El Niño” event still possible during the second half of the southern hemisphere winter. Hopefully this will only impact after the full winter rainfall has been obtained.
Our concern remains that predictions are still no better than average, or chance – no solid, widespread and sustained heavy rainfall is predicted at this stage during the coming 90 days to recharge the dams. So, even with wide rains, dam levels could still continue to fall.
Read ShowMe’s ideas to reducing indoors use of water here.
Read ShowMe’s ideas to reducing outdoors use of water here.
In Summary: net outflows appear to have diminished last week and stored water fell from 25.3% to around 24.1% of full capacity. At the presently reducing consumption rates, some 86 days supply of generally accessible fresh water is estimated to remain in the main dams.
Here are the levels of the six main dams that serve the Cape Town/Overberg/Boland area, including that doubtful reading for Wemmershoek Dam. Also shown is the total water storage level of all the dams in the whole greater Western Cape.
Read about a D-i-Y household rainwater harvesting and tank system here
Our water-wise landscaping and water-wise gardening suggestions.
Guide to reducing outdoors use of water here.
Guide to reducing indoors use of water here.
Read about South Africa’s desalination policies and initiatives.
Details of level-3B water restrictions 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.
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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mushroom
Good detective work, and have you seen this post. The city was warned in 2004 that we’d start having problems by 2014, but instead of doing something, they seemingly ignored the advice of experts, and did nothing.
https://www.facebook.com/SaveCapeTown/photos/a.1130277946990593.1073741828.1094085777276477/1463722770312774/?type=3&theater
tombrown
Hi Mark.
As it turns out, the previous week’s report on the level of Wemmershoek was incorrect. It stayed at around 36% throughout, a specific strategy by the bulk water supply department to hold that as a reserve while levels of the other shallower dams fall.
Regarding the history of water use in Cape Town, some of those old records make interesting readings. I wounder if there has in history ever been an instance where any politicians took the tough decisions to properly prepare for the future – Singapore perhaps :-). CoCT is clearly no exception.
Tom.