Dams – Latest levels: Winelands and Cape Town

Latest report (updated 2nd October 2017) on the main dams serving

Cape Town City and nearby Boland/Overberg towns

It seems that we may have reached the high point for 2017 with no meaningful change in the total dam storage levels occurring as inflows once more balanced outflows. Total water stored rose only 0.1 M.cuM (0.01% of capacity) vs 0.2 M.cuM (0.02% capacity) during the prior week. Total stored water essentially stayed unchanged at 37.2% of full capacity.

During this week in 2016 total dam levels also remained virtually unchanged at 61.6% of capacity.

[Why since 1st November 2016? that was when harsher level 3 restrictions were imposed].

Current status?

Total water in the dams has levelled off at 330 M.cuM (245 M.cuM of easily accessible) water (last year this also stood unchanged at 548 and 463 M.cuM respectively). So, to see us through, we have only 53% of the accessible potable water available compared to the same time last year.

How long will the remaining fresh water last?

Here is our progressive estimate for 2017 compared with what actually happened in 2016.

We ended September with 330 M.cuM stored collectively in the dams, as forecast. There is, therefore, essentially no change to the present estimate that all easily accessible water in the main dams may be exhausted by 3rd week of February, 2018.

While one can never be absolutely sure, climate predictions currently point to only average rainfall during the coming spring and summer months; i.e. no exceptional rains are predicted.

So everything now turns on the ability of the City of Cape Town to implement planned additional water production interventions and further consumption restrictions; the available water supply must be stretched to last until the 2018 winter.

Placing this situation in some context.

As the stresses of a diminishing water supply manifest themselves, some folks will inevitably cast around for persons or entities to blame. Permit me to add some context for the debate.

Capture/storage/supply of bulk water is actually a central government responsibility, while metros are responsible for treatment and distribution of water allocated to them by government as well as for disposal of waste. Cities simply cannot roam around building dams and interfering with the water rights of others. This must be centrally regulated.

Local population growth is inevitable. Older readers will remember when the population of Cape Town was well below a million people, and now stands at nearly 4 million; a result of the global trend toward urbanisation and the special issue of movement of population groups in South Africa. This is neither to be halted nor deflected, and must be accommodated through extensive new water projects.

Climate change is likely to result in an increasing frequency of increasingly longer dry spells in the Western Cape. Under usual circumstances the storage of surface (rainfall run-off) in existing dams has in the past provided sufficient potable water. However, as bulk water storage opportunities are now essentially exhausted, other more innovative forms of fresh water production have become essential.

Cape Town City is currently using less water than it is allocated by way of bulk supply from DWS. The basic problem is that DWS is unable to deliver that allocation of bulk water supplies. The City has actually been doing the only thing that it independently could do within its powers, namely increasing water efficiency (reducing waste and losses) while progressively reducing potable water demand.

The looming problem of insufficient water across SW Cape has been identified and studied for decades. Clearly, at various points over past years decisions were taken, based on then prevailing priorities and budgets, to rely on average weather patterns to estimate supply while restricting consumption to strike the balance from time to time when existing stored supplies fell short. And it worked through to 2014 when the dams last overflowed.

But looking back through the 20:20 lens of the current drought, it can now be seen that logic was faulty and risky – at some point constantly growing population pressure would inevitably outstrip not only the total water storage capacity but worse, the total amount of surface water available from all the rain normally falling in the catchments.

A 20-year plan to resolve this does exist. It includes all the interventions now being actioned but with hindsight, implementation by central DWS, the City and other metros may be judged to have been too slow. The resulting vulnerability has been exposed by this current 100-year+ extreme drought.

So the City of Cape Town is now (perhaps somewhat belatedly) intervening and taking it upon itself to do what it can to mitigate the situation. In doing so it’s concentrating on those aspects within its jurisdiction (e.g. recycling, temporary desalination, groundwater abstraction) but in order to do so still needs to navigate many environmental regulations.

In summary then, the history is complex and past decisions, good and bad, local and non-local, have brought us to where we are. The short-term problem is survival. Although it is not yet clear if the severity of this drought can be linked to climate change, gratifyingly CoCT is approaching the problem with the intention, this time, of also permanently addressing the long-term strategic water needs. Hopefully they will get appropriate central government support to do so. Read our thoughts here on how the water supply may be stretched to last until next winter.

What ought households to be doing?

There is a misconception that once winter is over, no more rain falls. This is not normally the case.

Although it may be unlikely in 2017, according to UCT figures (see chart below), 21% of the median annual rainfall at CT airport (108 mm out of 515 mm) falls between 1st October and 31st December.

Furthermore, a recent statement by the Deputy Mayor (read it here) included this advice for households and business: “Prepare for the possibility of intermittent supply and low water pressures by ensuring sufficient onsite storage and effective operation of [any] pumping systems“.

We recommend that all households – that have not already done so –  still consider installing some  form of water storage system to capture rainfall. Having some water stored under your own control could prove vitally important if more severe water consumption restrictions are imposed and/or water supply stoppages commence at any time.

As we showed last week, for example a house in Pinelands with a tiled roof of which 150 sqM capturing rainfall to a 5000 litre tank, could capture and make available 5000 litres by the year end.

What are the authorities doing now?

On Thursday 19th October, 2017 there will be a meeting at which the City of Cape Town will provide a “Water Resilience Update“. Amongst other things, the meeting will cover:

• Latest on resilience plan implementation, including supply and demand side solutions
• Introduction of draft guidelines for installation of alternative water systems
• Practical guidance for businesses e.g. contingency plans, support tools etc.

We may at this meeting learn more about progress with tenders being issued to contractors to commence potable water production.

The City has indicated that the Contingency Plan, to be implemented if and when the combined level of water stored in the dams falls to 15% (i.e. only 5-7% of easily accessible water remains), should be released by second week October. This may also coincide with the above meeting.

I will attend the meeting and provide a report-back.

The National Department of Water and Sanitation, the custodian of national water resources, has instructed all water users of the Western Cape Water Supply Scheme, such as the metro, the agricultural sector and other municipalities in the Western Cape, to reduce usage further.

“For City of Cape Town, water usage must be cut immediately to 500 million litres of collective usage per day. The city states it will increasingly intervene to force consumption down. Collective usage is currently 618 million litres per day, 118 million litres above the consumption target.”

“According to the new National Government restriction targets, the City must reduce its usage by 40%. To date, the national restriction has been 20%, which the City met successfully. A reduction of 40% would equate to about 520 million litres of collective usage per day. The City has been ahead of the curve by having a target in place that is even lower than the new restriction target.”

“Note that normal supply could be disrupted in order to lower demand. This is part of the aggressive pressure reduction programmes in place which are set to be intensified.”

Regarding public swimming pool access, a decision has been made to open 12 of 35 municipal swimming pools during the peak summer season. These facilities are distributed across the city to ensure equitable access. The Atlantis, Strand, Blue Downs Indoor, Khayelitsha, Bellville, Vulindlela, Retreat, Mnandi, Eastridge, Kensington and Hanover Park swimming pools will be open from 1 December 2017 until 31 January 2018, between 10:00 and 16:00 daily. The Sea Point swimming pool uses seawater and will open from 1 November between 07:00 and 19:00 daily during summer.

All water back-washed from the pools will be stored, treated, and reused and any water lost through evaporation will be replaced with water from the surrounding pools that remain closed this season. The use of recycled water, along with the reduced operating hours, will ensure that no water is wasted and that no drinking water is used to top up swimming pools, in line with Level 5 restrictions.

Will the weather help?

As expected, the 50mm of rains that fell in the Dwarsberg area caused a nice lift in the Berg River dam.

The SA Weather Services synoptic chart shows a respectable low pressure system that has forced its way past the high pressure system and should make landfall over the Cape tonight (3rd October).

It holds the promise of dumping 15-20 mm in the mountain catchments

This forecast is confirmed by the NOAA/CPC forecast chart (right), which has for some weeks now predicted that this rain would fall.

From this can also be seen that the summer rainfall pattern is now very firmly in place. All indications are that the summer rainfall areas may expect good above-average rains again this coming summer season.

Long-range forecasts presently indicate possible thunderstorms with 10-15 mm rain around 17-18th October and then another 5-10 mm of rains around 20th October.

All-in-all, October is starting to look like it may bring useful rain also in the catchments.

It appears that sea surface temperatures in the Pacific Ocean are ‘bouncing around’ and that a steady La Niña condition has not yet set in. It is still predicted to prevail during southern spring and summer.

Here is the rainfall experienced at the dams for the period since 2017 winter began. September 2017 was slightly better than 2016 but still well below the long-term averages. The rains have favoured mainly the Berg River and Steenbras dams.

In Summary: the dams experienced negligible net inflows of 0.1 M.cuM and levels effectively stayed the same at 37.2% of total capacity. There is always the possibility of unseasonal spring rain but only successful implementation of water production initiatives by City of Cape Town can stretch water supplies through to next winter. A briefing meeting is planned by CoCT for 19th October.

This table shows the levels of the six main dams that serve the Cape Town/Overberg/Boland area as reported by Dept Water and Sanitation. It seems that we may be approaching the peak level of combined water stored ahead of summer. The state of other dams across the Western Cape also remained unchanged.

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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