Cape Water and Dams Report

(Clanwilliam Dam.   Now full with sluice open. Photo : DWS)

 Dams – Latest levels: Winelands and Cape Town

Report nr. 112 (updated 9th July 2018) on the main dams serving

Cape Town City and nearby Boland/Overberg towns

The improvement continues! Despite little additional rain, run-off continues and combined dam levels increase by 41.9 M.cuM (4.7% of capacity).  Stored water rose from 48.3% of capacity to 53.0%.

In the same week of 2017 the dam levels crept up by just 2.0 M.cuM (0.6%) to 25.1% of capacity.

How long will the water last?

We now have over twice as much water stored in the main dams as at the same time in 2017.

Our near-term goal remains to get to around 60% of capacity (530-540 M.cuM). That means we still need to gather another 70 M.cuM in the main dams by end-October. This will enable full distribution to agriculture while leaving a safe amount for the municipalities.

At this stage it is reasonably certain that we will be able to make it through to winter 2019 without the danger of rationing (“Day Zero”) being imposed.

Although the authorities have stated that they will only consider a full relaxation in restrictions if stored water levels reach 85% of capacity, once 60% of capacity is passed, it would not be irresponsible of DWS to consider permitting the municipalities to sell more water and to thereby lower the water tariffs to some extent, reducing the financial pressure on hard-pressed consumers.

(Here is our model predicting the amount of water likely to be stored in the dams.)

Putting it into context!

This winter has started well and the situation seems to just keep getting better.

But can we rely on this pattern continuing? No, not yet; we need to accept that a shortage of rain might return. Several past years (2009, 2010) have seen good early rains followed by months of relatively low rainfall, with the total volume of stored water stabilising and even actually declining during the second part of winter (2014), as may be seen from the following CoCT graph.

The inland big irrigation dams also continued to rise strongly – Brandvlei 31.7% (27.1%); Kwaggaskloof 32.74 (28.6%); Clanwilliam 98.3% (67.7%).

The 31% rise in Clanwilliam Dam in one week was spectacular. It is indeed a pity that the opportunity was not taken by DWS to raise this dam’s wall as had been planned to happen over the past few years. As a result water that by now could have been stored up will instead spill down to the sea.

What about augmentation?

The amount of water contributed by augmentation rose further to 37 ML/d last week, according to the City’s report today. That is the highest total amount of extra water produced per day so far.

As discussed last week, it was anticipated that the drop in consumption the week before was likely to have been influenced by the heavy rain and therefore was likely to rebound during last week. This indeed happened, with water reported produced from ‘all sources’ climbing back to 510 ML/d (481 ML/d) while that drawn ‘only from the dams’ to a daily amount to 473 ML/d (447 ML/d).

What is gratifying to see is that the broad consumption of water in the Metro is continuing to decline. In stock market parlance, the values are moving in a downward channel characterised by a series of lower ‘highs’ and lower ‘lows’. Perhaps not a pattern of “stock price” that one might invest in but certainly a satisfactory trend in falling water consumption.

(Graph tracking overall use and production of extra water through the augmentation efforts)

The outcome is that augmented water supplies are permitting residents of the City to steadily use a daily amount of water that is higher than is being drawn from the dams. This differential will slowly grow as the augmentation efforts show increasing results. across the coming 24-36 months.

See our report on the status of Cape Town City’s augmentation efforts here.

How well are we actually doing?

CoCT graph reproduced below clearly shows the combined level of water stored in the 6 main dams relative to the danger zones. The Metro continues to do well.

Will the weather help?

Little rain fell last week with very little falling in the catchments.

In overall terms, so far this is at best an average rainfall year with only the smaller mountain dams being ahead of averages and the two large storage dams, Voelvlei and Theewaterskloof, still being ‘behind the curve’. Also, as time passes transfers from Berg River Dam and the Banghoek and Wolwekloof rivers to TWK Dam make TWK seem to have received more rain than it actually has.

 .

What rain ought we to now expect?

1) The Antarctic Oscillation is forecast to remain positive over the coming two weeks, except for a brief spell between 12th and 14th July which should see the south Atlantic High pressure cell move aside. This should permit the coincidentally on-coming low pressure system to penetrate and bring general rains to the Cape on 12th-13th July.

General falls of 15-20mm are expected, with 30-40mm in mountain catchments.

What is also interesting is the unusually high surface pressure that could build up in the following high pressure cell. This is predicted to ridge in strongly around the Cape following that low pressure and climb to a core pressure of 1044mb to the South-East of the country. At that stage the pressure at Cape Town could be around 1024-1026mb. The last time that sea level pressure got to 1024mb was in July 2011, a year that saw little increase in dam levels during July/August due to high pressure dominance. By comparison the normal air pressure at sea level is 1015 millibars.

This forecast high pressure is exceptional for this time of year and will very successfully block any Lows from reaching the Cape during that period.

2) Around 21-22 July an unstable system may bring some 15-20 mm of rain. Rainy spells of 15-25 mm are also predicted for 3rd week of August and again during 3rd week of September. Occasional light rain will occur from time to time.

Otherwise no large unstable systems are predicted for the SW Cape during the coming 4 to 8 weeks

Per NOAA/CPC, El Nino continues to emerge, but is not yet fully in place. There is no good correlation between ENSO and rainfall in SW Cape, but El Nino tends to favour more stable, high pressure weather, moderate Lows, lighter rains in the Cape.

What are the authorities doing?

1)  New tariffs and water accounts. The City has issued the following statement:

“The City’s issues hundreds of thousands accounts per month. Although inaccurate billing is always regrettable, in fact only a very small percentage of accounts contain billing errors.

We have noticed reports of customers who have been receiving significantly higher accounts than what they may be used to. We will investigate any account query sent to us on its merits and advise the complainant(s) accordingly of the outcome. However, the reason for some significantly higher bills is likely due to underground leaks. These are the responsibility of private property owners to fix. However, customers may apply to the City for a rebate if there are mitigating circumstances. We have also enhanced our programme of fixing leaks for our low-income residents.

In light of the tariff increases, it is reasonable to assume that under the low tariffs of say a year ago, if one had a substantial underground leak, the cost for that water loss would be substantially lower than what one would pay for the same water loss under the Level 6 tariffs of this year.

A customer’s account may be the first warning that something could be amiss. If a customer notices that water consumption is repeatedly high despite his or her best efforts to conserve water, it may be due to an underground leak. Some underground leaks are easy to detect, while others require an expert leak detection professional or plumber.  Customers are encouraged to read their own water meters at least weekly to monitor their consumption and pick up any problems that may arise, as soon as possible.”

2)  Deputy Mayor Ian Nielsen has sought a meting with Minister Nkwinti regarding possible easing of the water allocation, related restrictions and tariffs. The City awaits a reply.

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 48.3% to 53.0% 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

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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