Dams – Latest levels: Winelands and Cape Town

 

Latest report (updated 19th June 2017) on the main dams serving

Cape Town City and nearby Boland/Overberg towns

Net inflows continued as further rainfall swelled river run-off into the dams last week. Total stored water in the main dams reportedly rose by 15.7 M.cuM (1.8% of capacity).

The combined effect of savings plus rainfall means that since 1st November 2016, together we have, after consumption, used 41.4 M.cuM less water than in the same period the previous year.

How many days of water are left? arithmetically calculated, using the recent moving average estimated water consumption rate of 6.2 M.cuM per week  the usable water left could now last 18 weeks, i.e. 126 days, through to until mid-October 2017; a gain of 3 weeks due to rain run-off. Planned interventions at Theewaterskloof Dam could stretch the supply until end-October.

Are we out of trouble yet? …….. Definitely Not!

We need to be grateful for this rain that is stretching out our supplies. But to place it in context; in order to be secure that we can cope with a dry summer and still have enough supplies to last well into the following 2018 winter, ideally we need to exit this winter with 60% or more of capacity in the main dams; i.e. collectively storing around 520M.cuM of water (as happened last year). At the moment we have some 202M.cuM of water stored in the dams, so to be safe we would need to harvest another 320M.cuM of additional water, net after on-going consumption.

Given that there are only 10-12 weeks of recognised southern winter left at this stage, it means that we require an average net run-off that is roughly double that which we have received over the past two weeks. I.e. we need a net fresh water average replenishment rate of 30-32M.cuM per week, sustained week after week for 10-12 weeks. Frankly, if the South Atlantic high pressure systems continues in its present position it is unlikely that enough depressions will force their way through to bring us that much rain.

Until that 60% of capacity level is reached the authorities will be correct to maintain water restrictions at level-4.

A matter of fact!

Furthermore, it must be understood and accepted that the 6 main dams do not supply Cape Town alone; their water is designed for and committed to the entire SW Cape (i.e. area south of the mountains); including residential, industry and agriculture.

And here is the challenge. Commercial irrigation starts up each year in a small way during August but gets strongly underway in September. The agricultural sector cannot avoid watering the plants and trees. Part of the main dam storage capacity was built for this purpose and the farms are entitled to that water. Without the water, irrigated crops will fail, farms will stumble, many jobs would be lost and general food security would be weakened.

I don’t know precisely where total agricultural irrigation water use will stand after application of tolerable restrictions as it varies for many reasons, but it is certain that there is only limited scope for cuts before the produce is irreparably harmed. Conservatively, it appears that agricultural use may add over 4M.cuM of water consumption per week from September onward. And, if that is the case then combined use in the SW Cape may likely climb over 10M.cuM per week by October heading for 12McuM by November and higher figures by December/January,when the tourist season usually commences and related water demand begins.

A question of balance – if there is not enough water ……. ?

Of the 320McuM of water that we need to store between now and the end of winter, 150+M.cuM will be consumed by agriculture between September 2017 and April 2018, with the balance going to residential and industrial use.

If we somehow receive the required full 320M.cuM by end of this winter, then good and well. Starting with 500M.cuM, similarly to 2017, we should be able to survive through to mid-winter 2018 by which stage presumably more rain will arrive. Also special interventions being undertaken should be starting to produce additional supplies of fresh water by that time.

But if we “only” manage to continue to accumulate water at the current rate of around 16McuM per week for the coming 12 weeks through to mid-September then we would end winter with 394M.cuM of water collected in the dams. At usage rates similar to those experienced last season, that amount of water would be consumed and all gone by end-March 2018.

Worse still; what happens if we “only” collect, say, another 120McuM and finish with 304M.cuM on hand at end-winter? That amount of water could all be gone as early as end-January, 2018.

……….. what then? 

At some point a debate will have to start as to what should and will be done. No doubt authorities will be thinking it through carefully but perhaps at some point the public needs to be included in the process. We will be in uncharted territory, with a whole array of unique issues to be faced and unprecedented  questions to be decided. The situation could be extremely fraught.

I have been thinking about this and related matters for some time. It is not my aim to spread concern but rather to initiate some debate by those who are expert in their fields for the benefit of those who are not; once more to help provide clarity and understanding now, while the situation is still somewhat unpressurised. Here are just a few “thought starters” on issues that may arise and need resolution in a looming very low near zero or zero water situation:

• should a humanitarian crisis be declared and the agricultural allocation diverted for human consumption? if so, only that of the export producers? or only the wine farmers and not the fruit farmers? or cut all fruit and leave only the vegetables? or what?
• is the tourism season to be curtailed? or stopped? or should hospitality establishments be limited to some percentage of the water they used last season? or cut them down to zero and channel all water for consumption only by proven residents?
• what happens to industry? do all heavy users of fresh water (e.g. laundries) get stopped completely? or do water supplies to all industries get cut by 50% and leave them  to  decide what processes to suspend or reduce?
• what happens to residential users? how far can water usage targets be reduced? how tough do we get on those that still do not reduce consumption? do we register and commandeer pools for the water in them? is rationing introduced? how do we administer and control whatever systems are introduced?
• should installation of tanks and sumps be encouraged with subsidies? or loans? if so, how do we decide to allocate subsidies (FIFO? deserving? communal?)? how are loans to be made and at what interest rates and re-payment terms?
• what about water-related unemployment? job losses? social security services and payments? who receives what? who decides and who administers? if so, on what basis? can the unemployed be set to work helping create new or rehabilitate old water sources?
• what about security? should martial law be declared? what about looting from businesses and houses that may have been locked and left by those fleeing? theft of water from those that have stored water by those that haven’t? black markets? extortion? gangsterism? is there a point where one starts applying violent means to quell unrest?
• is the current political dispensation capable of dealing with such issues? of making the hard decisions? at what point does humanitarianism outweigh politics? how should the public be involved? what steps are desirable, optimal, defensible, justifiable, viable? how do we decide? do prevailing laws and regulations allow what is necessary to be done?

There are many, many questions in every imaginable discipline that will have to be asked and answered in such a situation. Many bedrock principles upon which society is founded and operates may need to be suspended, changed or replaced.

How would such issues be resolved and who would do this? [Please comment either in the Facebook post comments section or to me directly in the block at the bottom of my articles.]

What ought you to be doing?

If you have a house, then we recommend that you install or arrange some form of rainfall capture and water storage system. Such a system can range from large tanks with automatic pumping systems to simple “wheely bins” drilled and fitted to allow an outflow hose to be attached. Read here about how to size such a system as well as likely financial benefits that you can enjoy.

Clearly, you should continue to introduce and follow waters savings methods:

• Read our Indoors Water Savings Ideas here.
• Read our Outdoors Water Savings Ideas here

What are the authorities doing now?

The Think Water Exhibition of water conservation, rainwater harvesting, storage and related technologies arranged by the City of Cape Town has moved to the Civic Centre. The exhibition will visit other malls across the city. Keep an eye open for announcements of these useful events.

All possible interventions to “produce” more fresh water, e.g. drilling boreholes” are being accelerated as fast as funds permit.

However, as hopes for heavy rain this winter start to recede, “the city would formally post a request for ideas/information (RFI) to the market for proposed solutions that would enable the city to temporarily establish several small, intermediate and possibly even large plants to supply potable water. It was contemplated that these plants could use reverse osmosis, desalination, or similar technology from sea water, other surface water sources or treated run-off. The city was looking for solutions that could produce between 100 million litres and 500 million litres of potable water per day.”

The City may soon consider moving to a yet more severe water restriction,  targeting water usage rates of 80 litres per day or less.

Higher fines will apply and possible jail time may befall repeat transgressors who use in excess of the target amounts of water each month.

Read main details of the current level-4 water restrictions here. The present aim is to reduce water consumption to 100 litres per person per day.

Will the weather help?

Snow melt is feeding the Breede River, with some going to the Berg River and Wemmershoek Dams.

The South Atlantic high pressure cell is once more back in its previous position close to the west of the Cape and is deflecting low pressure fronts past the tip of the country.

.

We should get a nice burst of rain on Thursday 22nd June. The South Atlantic high pressure cell will have moved away to the west and left an opening through which a cold front is forecast to deliver a sharp ‘right hook’ to the ‘jaw’ of the Cape.

Unfortunately the high has already knocked this cold front “on its back” so it doesn’t pack much frontal energy any more.

.

.

Nevertheless, as this cumulative 3-day forecast chart from NOAA/CPC shows, it should deliver some good 15-25mm falls of rain, also in the mountains catchments.

At this stage,  it seems that rain will be concentrated around the Berg River and Wemmershoek Dams, with some benefit reaching the Steenbras dam area, but less so in the Voelvlei and Theewaters catchments.

.

What else may we expect?

The previously tracked unstable weather predicted for end-June seems to have slowed and will now only strike around 2nd July but with good falls of rain possibly in the 40-80mm range.

Another delayed system that we have been watching is now forecast to settle in between 7th and 9th July to supply 35-55mm widepread rain. This system might deepen with attendant thunderstorms.

Hopefully these and other smaller systems flicking through – like that which rattled the windows this Monday evening as I was writing – will be sufficient to keep rivers flowing into the main dams and that net inflows will be maintained.

The flattening pattern of the Central Pacific surface temps as recorded by NOAA/CPC continues. While El Niño is still expected to emerge later it is increasingly unlikely that it will affect our 2017 winter weather. 

How much rain has fallen in the dam catchment areas? All the main dams received good inflows and continued recharging. It appears that June will see many areas having above-average rainfall.

In Summary: last week net inflows continued with a collective rise of 15.7M.cuM in the dams levels, up from 21.1% to 22.7% of capacity. Water reserves improved but in reality the dams remain nearly empty. Every savings effort must be continued.

Here are the levels of the six main dams that serve the Cape Town/Overberg/Boland area. 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.

Read about South Africa’s desalination policies and initiatives.

Cape Town water tariff effective 1st June 2017 for 2017/2018 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.