Dams – Latest levels: Winelands and Cape Town
Latest report (updated 10th July 2017) on the main dams serving
Cape Town City and nearby Boland/Overberg towns
Net inflows to the main dams reduced and total water stored rose by only 2.0 M.cuM (0.2% of capacity) and as at Monday 10th July stood little changed at 25.1% of full capacity.
During the same week last year the dams levels rose by a much, much greater 38.7 M.cuM.
As I wrote a few weeks back, the table below acts as our “canary in the coalmine”…….. why? Well it shows whether we are gaining or losing ground relative to the same period in the prior year.
This week it is showing that:
- Net consumption for 1st Nov. 2016 to this point in July, 2017 has been 309.0 M.cuM of water.
- By comparison, the net consumption for the same period in 2015-2016 was just 275.4 M.cuM.
At first it seems that, although restrictions have been tougher this year, we have apparently saved less water than we did last year.
How can that be? The apparent lower net usage in 2016 is actually due to fact that far greater rains fell in the dam catchments this time last year and offset more consumption. Hence the apparent lower net usage in 2016.
Thus, comparatively, we are losing ground and our situation is worsening because less rain is falling in the dam catchments this year.
This is key; and it shows how severe the problem has become.
At present we have just 138 M.cuM of easily accessible water left in the dams, whereas at the same time last year the level stood at 273 M.cuM – 97% higher. So, last year we had almost double the amount of available fresh water stored and the dams were also filling far more quickly.
To drive that point home; last year was already marginal but nonetheless, this year we have just half the amount of accessible water available as we had at the same time in 2016.
How many days of water are left? Calculated arithmetically using the recently estimated water consumption rate of 6.2 M.cuM per week, the usable water left could theoretically last 22 weeks, i.e. 154 days, until first week December 2017. And more water is still to run off the mountains from recent rain while more rain is sure to fall before end-October; all of which would further stretch out the supplies.
But the situation is far more challenging than that simple interpretation.
Here is the split in 2014-2015 between the three primary users of water stored in the 6 main dams.
Now let us realistically assume that household/industrial consumption is sustainably reduced by 35%; that agricultural use commencing September can be reduced by 15%; and that incremental holiday season use is also reduced by 30%.
That would give us total consumption by end-November of some 145 M.cuM of water, which could mean that the currently available 138 M.cuM would be exhausted by 3rd week October, 2017.
But of course it will rain some more. And if the rain recharges the dams at the rate of 10 M.cuM of water per week through to end-September, then that would provide another 100 M.cuM of water supply. However, the above assumed consumption rate would use 50 M.cuM of that by end-November and, as consumption then climbs to about 50 M.cuM per month across the December to February holiday season, the remaining water would be gone by end-December, 2017.
And what if we received double that amount of rain (= approximately that which fell in 2016) then that would boost the dams by 200 M.cuM of water (instead of just 100 M.cuM). But at a holiday season consumption rate of, say, 50.M.cuM per month, that extra water would then only last until end-February 2018.
Unfortunately, at this time the long-range weather forecasts only predict average rainfall for the remainder of winter. And according to published figures, the interventions planned by CoCT at best will add about another 1.5 days worth of fresh water by year-end.
Some really tough decisions could lie ahead.
Can we still attain a secure water level …………… ?
Our “safe” target is to reach 500 M.cuM or more water stored in the dams by mid-September, of which around 410 M.cuM would be easily accessible (last year we stood at 551 M.cuM of stored water at mid-September).
In view of the current prevailing consumption patterns and long-range climate predictions that only average rains are expected, it seems that the SW Cape could now end September 2017 with around 250 M.cuM of fresh water in storage, equivalent roughly to a total of approximately 170 M.cuM of easily accessible water. Some smaller bursts of rain can (and do) fall in October and November but this cannot be relied upon and may anyway not fall in the catchments.
I hope that I am wrong, but circumstances increasingly indicate the answer will probably finally be:
………. no we won’t.
What are the authorities doing now?
Interventions to “produce” more fresh water, are being accelerated. However, don’t hold your breath; even if all planned boreholes and waste water recycling was to miraculously be fully operational by 4Q2017 (highly unlikely) then the total additional potable water produced would amount to some 200,000 cuM (= some 8 hours per week (1/3 of 1 day) of the total water consumed by the City). Desalination will add to this but may take longer to bring into operation. These interventions are all worthwhile and could have a greater beneficial effect once fully operational by mid-2018.
But, even at maximum effort, this extra production will only progressively come on line, mainly during the first half of 2018.
The city’s RFI call for suggested solutions closed yesterday and responses will now be evaluated and considered for possible implementation.
From 1st July 2017 Level-4B water restrictions have been implemented by Cape Town City (read full details of restrictions and tariffs here). Essentially this mean reduce potable water usage to below 87 litres per person per day or less.
If generous rains do not fall in the next 6 weeks then further tough water restrictions may be enforced, i.e. perhaps reducing consumption down into the range of 25-50 litres per person.
Western Cape Government is instructing all other Cape municipalities to implement similar levels of water restrictions unless local water supply circumstances permit otherwise.
The City of Cape Towns operational plan for possible “Zero water” conditions should be ready to publish within a few weeks.
What ought individual households to be doing?
- install some form of rainfall harvesting and storage system – it’s not too late (read more here).
- save water wherever possible (read savings ideas here).
- give some serious thought to what you may do should “zero water” day arrive (read more about possible implications and issues here).
Will the weather help?
There is fresh cold front is approaching that should strike and bring some solid rain, on 15th/16th again benefiting the Steenbras, Wemmershoek, and Berg River dams.
This NOAA/CPC chart predicts 20-30mm of rain to fall in the mountain catchments across next weekend.
What else may we expect?
Encouragingly, a sustained spell of unstable weather is forecast for the period of 20-22 July, with sometimes heavy rains with NW winds gusting over 70 Kmph hopefully forcing the 30-40mm rain through also to the Theewaters and Voelvlei catchments.
Then the first week of August promises 4-5 days of rainy weather, possibly including thunderstorms.
Otherwise August is presently predicted to be generally fine and mild with occasional rain.
If you are interested in the historic rainfall patterns for Cape Town airport, then this chart produced by UCT gives good comparative information. The dark red line is the rainfall so far this year. The heavy black line is the average. Find it here and look at what interests you. Remember this does not relate directly to rainfall at the dams which are quite far away from the airport. Thanks UCT.
How much rain has fallen in the dam catchment areas? Good rains fell last weekend with Steenbras, Wemmershoek and Berg River Dams benefiting most. Voelvlei and Theewaters also received some rainfall so the levels of all the dams should move upwards this coming week.
In Summary: net inflows continued at a low rate resulting in only a 2.0 M.cuM rise in the dams levels, up from 24.9% to 25.1% of capacity. More rainfall run-off is expected this week but levels are still very low. Continued savings effort must be made.
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.
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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