Cape Water and Dams Report
Dams – Latest levels: Winelands and Cape Town
Report nr. 102 (updated 14th May 2018) on the main dams serving
Cape Town City and nearby Boland/Overberg towns
Some residual run-off together with some new bursts of rain, particularly in the mountain catchments boosted the combined dam levels by 4.6 M.cuM, or 0.5% last week according to DWS statistics. Combined storage climbed again from 20.4% of capacity to 20.9%.
During the same week in 2017 the dams dropped by 8.2 M.cuM (0.9%) to 20.8% of full capacity.
So the harsh water saving campaign has paid off. For the first time in 2018, there is more total water stored in the 6 main dams than there was at the same time in 2017 (20.9% vs 20.8%).
How long will the water last?
The way that May-month is starting to unfold with these early rains, there is a growing possibility that we might end up with as much water stored in the dams at end-May as we did at end-April; an unexpectedly good result. This particularly so in light of more rains forecast for the rest of this month (see “will the weather help” below).
Importantly we will have managed to get one month ‘ahead of the game’ with some extra water reserves in case June and July turn out to bring weaker rainfall than usually is the case.
In the next report I will make a mid-month correction to the model, which is unchanged for this week.
(Here is our model predicting the amount of water likely to be stored in the dams by mid-year.)
Putting it in context!
The following most useful charts produced by the Climate Systems Analysis Group at UCT give a very interesting picture of the extreme variability of the rainfall being experienced across the SW Cape. In a way, it shows the extent to which our rainfall pattern seems to have changed across what is relatively small geographical area. This phenomenon is being studied by the CSAG at UCT which may reveal some very interesting insights in due course. [the red line is for 2018 year-to-date].
Voelvlei Dam’s (NW of CoCT) rainfall lies between the very poor 2017 and very good 2014 results. Having remained low through to April the cumulative rainfall in the dam catchment is encouragingly climbing towards the 2014 level and at present must be just below the median for this station.
Theewaterskloof dam, our largest storage dam (NE of CoCT, behind the mountains) is faring worst with the rainfall received slightly less than at the same time in 2017. The poor result for this dam characterises the apparent change in the weather pattern in that the more southerly approach angle of the rain results in it being blocked by the mountains.
The Steenbras dams (SE of Cape town) generally receive steady rainfall and are apparently least affected by changes to the rainfall patterns.
Even when the rains approach more from the SSW, they still tend to get through to the Overberg area and fall generously in the catchment of these two smaller dams.
Far more encouraging has been the rainfall received in the Wemmershoek catchment, (north of CoCT).
Particularly good rain in early May – better even that that received by the same time in 2014 – have fallen over that area resulting in that dam level lifting again.
Similarly the SAEON weather station at Dwarsberg, the highest rainfall area in South Africa, has seen the cumulative rainfall at that location climb to match the levels last seen at the same time in 2014. This holds promise for good run-off into the Berg River and Theewaterskloof dams; both of which rose this past week.
Our mountain dam catchments continue to receive the bulk of the rain while our big dams behind the mountains continue to be starved and to hover at extremely low levels. This includes Brandvlei and Kwaggaskloof dams both under 6% of capacity and Clanwilliam Dam with less than 5% of capacity.
This is a large challenge with which we may have to contend. Why? These 3 dams together with Theewaterskloof Dam comprise 56.5% of the total water storage capacity in the whole of the Western Cape (a total of 1057 M.cuM vs maximum storage of 1870 M. cuM). At the moment these 4 dams contain only 89 M.cuM of water between them, just 8.4% of their capacity.
Constructed mainly to support irrigation schemes, unless these dams receive massive amounts of rain, the agricultural sector might not be able to start up in the new season; a really bad situation.
Looking out into the years ahead, are we just facing unusual weather or is this perhaps the front-edge of climate change. Here are a few ‘thought-starters’.
1) CO2 concentrations on 29 April 2018 (2 weeks ago) on Hawaii were measured at 441.2 ppm
150 years ago CO2 = just 280 ppm.
10 million years ago CO2 = 500ppm and sea levels were 20m higher than today (our future?).
2) The Gulf Stream is reportedly slowing : reportedly it has slowed by 15% since 1950
The overall reduction in its flow is equivalent to stopping all the world’s rivers 3 times.
It is speculated that if the Gulf Stream stopped, Europe could become ice-bound.
3) The hottest daytime temperature on record was 2 weeks ago in Pakistan : 50.2 degC.
What do you think? Just bad weather or climate change?
What of augmentation efforts?
I had hoped to provide a detailed update on the status on the augmentation efforts, but have not yet received the final information – I suspect that the water management team has been deeply focused on the budget issues over the past days.
From what I have understood so far, all the primary augmentation initiatives remain on track.
However, what has happened is that since the overall water situation has latterly become slightly less of an emergency, some extra time is being taken to more carefully test the quality of the water being produced as well as dealing with various environmental issues that are slowing the TMG groundwater extraction program. The main aim is to in all instances produce the best quality water on the most sustainable basis. This has slowed bringing some facilities into production.
Consequently the supply of extra water into the system has not changed and remains at about the level of 26 ML/day.
(Graph tracking overall use and production of extra water through the augmentation efforts).
How well are we actually doing?
As usual, our current position is shown at red ‘X’ on the following graph, i.e. over 20% of capacity.
This situation is becoming ever more encouraging. We certainly are on course to meet our “Success Day” goal. Let us keep saving all the water that we can for now as the real test will come when winter is over. Hard decisions will need to be made as to how the then available water can be allocated and whatever reserves we build up now will add to our resilience at that stage.
(See here for a detailed explanation of how the chart is to be read).Unfortunately, the amount of water used in the Metro from all sources has increased again to 550 ML/d, a disappointing outcome due perhaps to folks relaxing their water saving efforts somewhat because of recent rain.
No doubt also, fatigue and boredom are setting in. But no matter how tiresome it may seem to have to keep saving water, it is a far better option that having the taps run dry. There is no choice; for now we simply have to keep trying to cut personal usage to 50 L/day.
See updated details of Cape Town’s planned interventions to produce fresh water here.
Learn about water savings efforts by other Cape municipalities – read more here.
Do visit the City of Cape Town website to see additional graphically presented information regarding the water situation – it is very helpful. See the full water status presentation here.
Will the weather help?
Particularly good rain fell at the Wemmershoek dam with useful falls also at Steenbras. The Berg River dam should benefit from the 60+ mm that fell at Dwarsberg.
Solid rains seem set to continue during May month;
1) 20th-21st is forecast to see general rains of 20-30 mm.
2) Over 22nd-23rd May, Wemmershoek and Dwarsberg could receive 50-60 mm.
3) Between 27th-30th May unstable conditions could bring thundery weather and 15-30 mm of rain.
4) Another strong system is predicted for 2nd-5th June bringing 60+mm to the catchments.
5) A burst of unstable weather is predicted for 3rd week of July hopefully bringing more heavy rain.
If this rain all eventuates then we may well be at the start of a more normal rainfall Season. This alone would not relieve the situation but at least the pressure could ease somewhat giving more time to get the augmentation efforts operational.
Here is the rainfall measured since April 2018 at the dams.
What are the authorities doing?
Today, Monday 14th May, the Cape Town City Council announced a substantial revision to the previously proposed water and sewage tariffs contained in the draft budget for 2018/19. Importantly, the overall increase is reduced from 26.96% to 19.9%. Key changes are:
1) If using less than 6KL of water per month, the cost increase is reduced from 55,16% to 10,10%.
2) The equivalent 70% sanitaion charge (4.2KL) cost increase is reduced from 78,71% to 9,87%.
The City states that a number of different steps have been taken to reduce and/or re-purpose expenditure. Significantly the total budget allocated for the New Water Program is reduced from R19 billon to R14.1 billion over the coming 5 years.
Read here about Cape Town’s reduced water and sanitation tariff increases.
Here are the levels of the six main dams serving the Cape Town/Overberg/Boland area. Combined levels lifted from 20.4% to 20.9% of capacity.
Plan ahead for possible water outages; here are points that could help you.
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 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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