Dams – Latest levels: Winelands and Cape Town
Latest report (updated 26th June 2017) on the main dams serving
Cape Town City and nearby Boland/Overberg towns
River run-off into the dams continued but net inflows slowed. Combined stored water in the main dams rose by 13.7 M.cuM (1.6% of capacity) and as at Monday 26th stood at 24.3% of full capacity.
The table below shows that cumulative net water consumption since 1st November 2016 (8 months) stands at 316.5 M.cuM. However, the difference to same period a year before has reduced sharply due to very heavy rains experienced at this time in 2016. A spike in current usage is reportedly also happening as people mistakenly think that one big spell of rain has solved the crisis.
Why watch these numbers? Well, before winter we had saved some 50M.cuM versus the previous year (“this year” figure was smaller by that amount). But the difference is closing due to two factors; at this stage of winter 2016 the savings were growing due to raised restrictions and we had received more rain at this time in 2016.
At the moment there is around 130 M.cuM of accessible water left in the dams. Last year it stood at 201 M.cuM – 60% higher. And last year, strong winter rains were recharging the dams quickly (this week last year the weekly increase was a strong 38 M.cuM vs only 13.7 M.cuM this year).
Therefore, in simple terms, for us to be gaining vs last year, the difference between these two figures should by now be 75 M.cuM (the figure for “this year” should be smaller). Clearly, at the moment, we are steadily falling further behind. And that is why, faced with what now appears to be possibly below average rains in 2017, the authorities have to try to further increase the rate of water savings while also seeking to implement methods to “produce” more water.
How many days of water are left? arithmetically calculated, using the recent estimated water consumption rate of 6.2 M.cuM per week, the usable water left could now theoretically last 20 weeks, i.e. 140 days, through to until mid-November 2017.
From August onward, two new factors will increasingly start to pull in opposite directions.
- Agricultural irrigation normally begins in August/September, with 4 M.cuM more consumed per week – a negative impact; it is not clear at this time what limits may be placed on irrigation.
- Interventions by CoCT drawing underground water from boreholes as well as implementation of small-scale desalination will “produce” additional fresh water – a positive impact. It remains to be seen how much extra water will become available through these methods within the coming 12 months.
In order to be safe until mid-2018, stored water in the main dams must increase by 300 M.cuM more to reach over 500 M.cuM (of which around 410 M.cuM would be easily accessible). With only 10-11 weeks of normal winter left, we are going to need torrential rain if this goal is to be reached.
If we “only” manage to continue to steadily accumulate water at the current rate of around 14 M.cuM per week for the coming 10-11 weeks through to mid-September then we could end winter with 360 M.cuM of water stored in the dams (of which about 170 M.cuM would be accessible). Assuming continued restrictions, that water could be consumed with dams empty by end-January 2018!
What ought we to be doing?
I may sound repetitive but cannot emphasise enough that the best individual intervention is for every household that can afford it to install some level of rainfall capture and storage systems.
Why?
- Our rain does not always fall in the dam catchments but rain does always fall over the low-lying residential areas every year.
- It’s impractical to capture and store rain falling in town areas on large scales (no suitable place for a big dam), but it is practical to capture and store water at the level of every household.
- By capturing rainfall we not only “produce” additional fresh water but we simultaneously reduce our draw of water from the dams. Indirectly, by capturing water at household level, we transfer that saving ‘back to the dams’ through the reduction in demand for municipal water.
- Effectively we would be following the policy of saving water while one still has water (rain) to be saved. Every cuM of water saved will reduce the draw on the dams and stretch out the water that we do have in the dams for longer.
Read here about how to size such a system as well as likely financial benefits that you can enjoy.
Read here how Dani N installed a rainwater capture and tank storage system.
Why else is household-level water harvesting and storage important?
- It is under your direct control; so you decide:
- what water to store for which specific purpose.
- when and how to use or consume that water.
- You are responsible for the water quality and can maintain your desired standard.
- Storage investment can be scaled precisely to your household’s ability to harvest water.
- A properly installed system will be a long-term asset and add to the value of the house.
- Municipal cost of water and of sewerage is reduced.
- Your household contributes to stretching the number of days of water stored in the dams.
- Household’s awareness to save water is maintained, even when rains again fill the dams.
Possible downsides of central (communal) water production facilities.
- Projects are subject to possible political influences
- Supply may be diverted for party political and/or corrupt reasons
- Costs may escalate beyond expectation due to inefficiency and corruption.
- Budgets may be cut and/or diverted.
- Once drought is over facilities may be mismanaged and fall into disrepair.
- Central systems are more easily sabotaged and vulnerable to disaster.
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 is rotating through different malls and centres.
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 winter rains start to recede, CoCT is seeking alternative methods of producing fresh water. “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 (from 1st July 2017) move to more severe Level-4B water restrictions, setting water usage targets of possibly 80 litres per person per day or less.
The City is finalising its operational plan for eventual “Zero water” conditions and has indicated that this will be published in about three weeks’ time.
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?
Precisely as forecast by NOAA/CPC last week, solid rains fell last week around the Berg River, (66mm) Steenbras (35mm) and Wemmershoek (49mm) Dams, with some benefit reaching the Voelvlei Dam but little pushing through to the Theewaters (2mm) catchment.
This week there should be a brief burst of rain when an approaching cold front flicks past the Cape during the early hours and morning of Wednesday, 28th June.
Unfortunately, as today’s synoptic chart from WeatherSA shows, the high pressure(s) is once again pressing this front away to the south.
15-20mm of rain is predicted.
What else may we expect?
Looking further ahead, a spell of solid rain (20-30mm) is expected across 6-7th July. This system might still deepen.
But, better still, a major spell of unstable weather is forecast for the period of 12-15th July. At this stage 80-100mm of rain is expected accompanied thunder storms and strong winds. Hopefully this major depression will arrive as predicted and that the strength of the storm will be sufficient to also force through to the Theewaters catchment.
The pattern of the Central Pacific surface temps ticked up but are still forecast to remain largely neutral. El Niño is expected to emerge later in 2017 but it is unlikely that it will affect our 2017 Cape winter weather.
How much rain has fallen in the dam catchment areas? All the main dams received good inflows with the Berg River and Wemmershoek catchments receiving the most rain. June 2017 should end up as an above-average rainfall month and the first two weeks of July promise more very solid rain in the mountain catchments.
In Summary: last week net inflows continued with a collective rise of 13.7 M.cuM in the dams levels, up from 22.7% to 24.3% of capacity. Rainfall run-off continues recharging the dams. However, levels are still low. 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 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
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.
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