Cape Water and Dams Report – 2July2018
(Steenbras Dam. Now at 102% of capacity. Photo : DWS)
Dams – Latest levels: Winelands and Cape Town
Report nr. 111 (updated 2nd July 2018) on the main dams serving
Cape Town City and nearby Boland/Overberg towns
Another great week! Fresh rain plus steady run-off caused combined dam levels to increase by 53.4 M.cuM (6.0%). Stored water rose from 42.3% of capacity to 48.3%.
In the same week of 2017 the dam levels lifted by just 5.5 M.cuM (0.6%) to 24.9% of capacity.
How long will the water last?
The increase in stored water smashed through expectations and in 10 weeks since 23rd April the combined storage has grown by nearly 30% to just under 50% of maximum capacity. A much improved situation, but we still need to take care.
We now have 100 M.cuM more water stored than we had at the end of last winter, so we know that we can make it through to winter 2019 if we have to. But we also know that to do so last year we withheld that amount of water from agriculture. So, if we end up at about the current level and instead give agriculture its full allocation of irrigation water this coming 2018 summer season then we could be stuck on the same 50L/p/d restrictions for another 12 months. And in the (admittedly unlikely) event that the balance of winter 2018 proves to be dry and winter 2019 arrives late and starts dry, then we could be in trouble again; particularly as augmentation is advancing very slowly.
As outlined last week the best will be if we can get to around 60% of capacity (530-540 M.cuM). That means we still need another 100 M.cuM in the main dams by end-October. Then we can give agriculture its full share and still be very sure of making it through to the following winter even if nature turns hard against us and the drought returns.
Will the authorities relax restrictions? They are committed to drop restrictions should combined dam levels reach 85% (755 M.cuM) of capacity. If not, the fall-back position is that they will meet monthly from July onward, review the situation and decide if relaxation of restrictions may be implemented.
Note that only DWS can change the amount of water allocated to the municipalities, and only then can the municipalities, in turn, change restrictions and amend tariffs.
(Here is our model predicting the amount of water likely to be stored in the dams.)
Putting it into context!
The final change in dam levels across month of June 2018 alone, was just 10 M.cuM short of the entire 176 M.cuM increase received across the whole of 2017 winter – a phenomenal outcome.
But we should be cautious, at least for another two months or so. We have been extremely fortunate with the heavy rains and also that they have fallen in the catchments. It is noteworthy that at the moment the total rainfall predicted by the long-range forecasts for both July and August combined is less than the rainfall that the catchments received just last week.
One lesson that we have surely learned over the past few years is that historical weather patterns no longer necessarily apply in the future. So it is not a given that this winter, having started well, may be relied upon to continue and end the same way. But we obviously do hope it will bring the relief that we all long for.
Good rises were also seen in levels of the inland big irrigation dams – Brandvlei 27.1% (23.7%); Kwaggaskloof 28.6% (22.2%); Clanwilliam 67.7% (57.5%). Why is this important? Well a solid water supply means that those farming areas will be under less stress and the possibility of disruption to the rural population, and possible consequent unmanageable migration to the city, is avoided. And this consideration underscores why it is also important to be able to give the SW Cape irrigation areas their full water allocation this season.
How will this water bounty be managed?
Readers often ask if water can be moved around to minimise wastage; are the dams connected?
The answer is that some are and some aren’t.
1) Steenbras. The Upper and Lower dams are effectively one storage system at two levels. Water from the catchment runs mainly into the upper dam. From there the water can be sent for purification and on to Cape Town. And if the upper dams fills (as it has at present), water can be spilled under gravity into the lower dam and from there also be sent for purification and on to Cape Town.
The two dams also form part of a pumped water hydro-electric scheme in that at peak demand times, water can be run down from Upper to Lower through turbines to generate some 180 MW of power. Then later at night when demand falls away, excess power generated, e.g. by Koeberg, can be used to pump water back to the Upper dam, stored ready for use in the next high demand period.
Lastly, Steenbras Upper Dam is usually kept relatively full as a backup in case anything disables the water supply to Cape Town through the tunnel from Theewaterskloof Dam.
2) Palmiet. Up to 25 M.cuM of surplus water can be pumped across from the Palmiet river basin to Upper Steenbras dam via the Rockview reservoir or from the Kogelberg irrigation dam to Steenbras, as was done in Feb/Mar of this year. The Palmiet-Rockview pumped storage system can generate a nominal 400 MW of electrical power.
3)Theewaterskloof. Water can be pumped between Berg River Dam and TWK Dam at 4 cuM/second through a large 6.7 km tunnel. This enables water from Berg River Dam, which tends to fill first and spill by end of winter, to be transferred to TWK and stored there until summer when it can flow back through the tunnel for purification at Faure and on to Cape Town.
4) Berg River Dam. Apart from transferring water to TWK, water released by BRD flows down-river to Misverstand Weir (as was done in April) from where it can be abstracted for the local West Coast municipal purification plants. Of course, water from the Berg River Dam is also supplied to Cape Town via the Kleinplaas balancing dam and Faure purification plant.
5) Voelvlei. Water from this dam can be supplied to the Misverstand Weir. Voelvlei is an off-channel dam and is actually supplied by the 24 Rivers canal and Klein Berg canal.
In the near future an augmentation scheme will be built to take surplus water from the Berg River at the Lorelei Weir and pump this up to the Voelvlei dam. An extra 26 M.cuM of water may be stored in the system in this way.
However, notwithstanding these interconnections, the primary way in which water is conserved in the overall system is by drawing water first from those dams which, based on water levels and predicted rainfall models, are most likely to spill so that the dams lose as little water as seldom as possible. This is practical because a further layer of interconnections exist within the system at the level of the purification and treatment works.
Thus ultimately, except for some west coast locations tied to the Voelvlei Dam, water from any dam can reach virtually any tap in the system.
What about augmentation?
The contribution of extra water from augmentation was little changed at 34 ML/d as reported by CoCT today. What was odd is that, as may be clearly seen from the following graphic, the water reported produced from ‘all sources’ seemingly fell sharply to 481 ML/d (527 ML/d) and that drawn ‘only from the dams’ dropped by a similar daily amount to 447 ML/d (492 ML/d).
We have enquired as to the cause. The City believes the main reason for the improved water usage figure is weather-related. People could have decided to delay doing their laundry and other water-intensive chores because of the heavy rains. Recently improved pressure management will also have contributed. So it is possible that these volumes may partly rebound in coming weeks.
(Graph tracking overall use and production of extra water through the augmentation efforts)
See our report on the status of Cape Town City’s augmentation efforts here.
To place augmentation in context, I expressed it this way in a recent radio interview. At the present level of usage of around 500 ML/d, of every 10 glasses of water that you drink, until recently half a glass was from augmentation sources and nine and a half glasses came from the dams. Soon that will rise to 1 glass out of 10 and by end of 2018 it is planned it will rise to 2 glasses out of 10. By year-end 2020 the intention is that 3-4 glasses will be from augmentation (assuming that overall water usage is higher again by then).
How well are we actually doing?
CoCT have produced this new graph which clearly shows the current level of water stored relative to the levels representing various risk scenarios. This excellent graphic shows at a glance where we stand and that we have in fact moved away from any immediate danger.
I agree totally that as shown here, in order to be effectively out of danger we need to get above the 60% capacity level by the end of winter. If we do not then some or other group of users of water in the SW Cape will need to be short supplied through the summer. It will not be until summer of 2019 that augmentation of extra water will start to materially supplement supplies.
Will the weather help?
The past week saw heavy rains fall across the whole area and all the dam catchments received solid downpours, with Berg River and Wemmershoek dams doing particularly well. Most spectacular was Dwarsberg where a total of 230 mm fell last week. Good run-off may be expected to keep the rivers flowing into the large dams during this week.
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What rain ought we to now expect?
1) The Antarctic Oscillation is turning positive and is forecast to remain so for the coming two weeks, permitting the S. Atlantic High to slide into place once more off the west coast. This in turn means that the on-coming low pressure systems will tend to be deflected away to the south resulting only in lighter occasional rain passing over the Cape. This will apply on 10th July and again on 15th-16th July when only scattered light rain is expected.
2) Per NOAA/CPC, the La Nina phase is over and El Nino is starting to re-emerge, in fact somewhat earlier than expected. Although still in upper neutral range it may soon pop up higher into full El Nino territory, perhaps thereby working to truncate our winter rains.
3) Around 25th-26th July the High may move away somewhat and allow an unstable system to bring some 20-40 mm of rain. 10-20 mm of rain is expected during the first week of August, hopefully in the catchments.
Otherwise no large unstable systems are predicted for the SW Cape during the coming 4 to 8 weeks.
What are the authorities doing?
1) From 1st July, Cape Town introduces a fixed water delivery charge of either R64.40 per month or R115.00 per month depending upon whether your house has a 15 mm or 20 mm water supply line. A small adjustment in the lowest tariff from R26.25/KL to R28.90/KL for the first 6KL will be applied.
2) Deputy Mayor Ian Nielsen has declared that provided restrictions are adhered to, “Day Zero” will not occur in 2019. This is a bold declaration. In order to be absolutely sure of this one must assume that agriculture will once more be starved of irrigation water if needed to relieve the Metro and towns. But as this decision lies with DWS and not the municipalities, it may not work out this way. Let us hope that his forecast is correct.
3) When mayor De Lille announced the level-6B restrictions back in January, it was said that these would apply for 150 days from February and that they would then be reviewed. Ian Nielsen has accordingly indicated that he will seek to meet with Minister Nkwinti with a view to possible easing of the water allocation, related restrictions and tariffs. A statement by CoCT reads “Any decision by the City of Cape Town to lower current water restrictions and thus the tariffs associated with them is dependent on National Government relaxing the restriction on water releases from the dams. The City believes that current conditions warrant a relaxation of restrictions“.
4) The Metro has announced that it is modifying several municipal swimming pools to use salt water instead of drinking water. The four coastal pools targeted for conversion are the Strand indoor pool as well as the Mnandi, Monwabisi and Muizenberg swimming pools.
5) It was announced that 399,675 Metro households earned their green dot status (using less than 10,500 L/month) during May, with 217271 of them using less than 6000 L/month. Well done all these Capetownians
Read the full City Cape Town release about Water By-law amendments here.
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 of the six main reservoirs rose from 42.3% to 48.3% 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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