Cape Water and Dams Report
Dams – Latest levels: Winelands and Cape Town
Report nr. 93 (updated 11th March 2018) on the main dams serving
Cape Town City and nearby Boland/Overberg towns
Levels of the main dams dropped more quickly by 4.7 M.cuM, or 0.5% of capacity (vs the preceding week’s 4.2 M.cuM) and from 23.2% to 22.7% of capacity.
The benefit of the transfer from Kogelberg dam of about 2 M.cuM per week is diminishing but does continue to reduce the apparent water usage. This effect will fade away by end of March. Agricultural allocations are now almost completely stopped for 2018. Weekly consumption is reverting to ‘normal’ anticipated under level-6B restrictions.
During the same week in 2017 the dams dropped by 13.1 M.cuM (1.4%) to 31.0% of full capacity.
Current status?
Combined water stored in the 6 main dams fell to 202 M.cuM (117 M.cuM of easily accessible water) (last year, levels dropped to 262 and 177 M.cuM respectively over the same period).
There is sometimes confusion as to why we are in this seemingly continuous water shortage situation. How did this happen? What have we done wrong?
Well, an analysis of figures provided by UCT makes the situation clear. For the past four years, each and every year we have consumed more water than the preceding winter provided us by way of net recharge of the dam levels.
- In winter 2014, dams recharged 284 M.cuM but by June 2015 we had consumed 489 M.cuM
- In winter 2015, dams recharged 229 M.cuM but by June 2016 we had consumed 401 M.cuM
- In winter 2016, dams recharged 297 M.cuM but by June 2017 we had consumed 385 M.cuM
- In winter 2017, dams recharged 169 M.cuM and by June 2018 we could consume 227 M.cuM
No doubt, as each year passed the assumption was made that the rains in the following year would recharge the dams. But it didn’t. So every year we have ‘spent more than we received in the water bank’. And, although the present restrictions are so stringent, in 2018 we are doing it again. Every year we ended winter with less water in the dams than the previous year. Quite unsustainable.
Given that the current drought has been so unexpectedly extreme, the authorities could be forgiven once for expecting the rainfall to revert to normal at an earlier stage.
However, now that the risk of such extreme weather patterns has become clear, far more swiftly reacting management methods must be adopted in future to introduce restrictions earlier and more stringently to ensure that such continuously growing deficits do not happen again. We should never again delay firmly implementing the appropriate restrictions.
How long will the remaining fresh water last?
If the current reduced rate of water usage is maintained, then it seems reasonably sure that we will reach the end of June with some 120 M.cuM of water stored in the main dams. If this materialises then we will have succeeded to make it to winter without having to introduce rationing (“Day Zero”) and we will be ready to receive the fresh rains.
But what happens after winter?
Recent political utterances have tended to muddy the picture. So what are the issues facing us?
1) To be useful, rain must fall in the dam catchments to recharge the dams. Last year that did not happen for either Voelvlei or Theewaterskloof, so they are both very low. This may happen again!
2) Regarding winter rain, three outcomes are possible:
- Lots of rain in the catchments, in which case restrictions can soon be eased.
- Little or no rain in the catchments in May/June will mean rationing introduced by end-July.
- Some rain, similar to the poor 2017 to partly recharge the dams; restrictions remain in force.
3) In all cases the situation will be managed through winter and then, at the end of October when the winter rains are finished, we will know for sure how much water is stored in the dams. The authorities will model the situation in November and decide how much water to allocate to the different users.
4) If we consider our “some rain” scenario in detail, assume that after similar rainfall to 2017 we end winter with 320 M.cuM of water stored in the dams. That would mean we can allocate approx. 200 M.cuM of that water plus whatever can be produced extra via the on-going augmentation initiatives. So then (working in M.cuM of water):
200 = available water, mid-October 2018
-117 = metro water at 450 ML/d for 8.5 months to end-June following year
– 12 = other SW Cape municipalities likewise
– 40 = evaporation
+16 = augmentation, estimated for June to October 2018
+36 = augmentation, estimated for November 2018 to June 2019
83 = left available for agriculture, commencing late September 2018.
It is not certain that this would be enough water for agriculture to make good the ravages of previous cuts (usual allocation is 160 M.cuM pa) – they may need more water to avoid large loss of productive orchards and vineyards from which the agriculture industry may never fully recover.
If any less rain is received in the catchments than that assumed above, then the authorities will need to further restrict to, say, 40L/p/day or from November to implement level-7 collection/rationing (“Day Zero”).
It can be seen that this situation would in all events be very marginal and would call at least for the same level-6B restrictions to be maintained all the way through to winter 2019. It remains to be seen how much rainfall winter will deliver to the dam catchment areas.
Here is our model predicting the amount of water likely to be stored in the dams by mid-year.
Are we winning?
Consumption in the Metro at the most recent daily average of 506 ML/d is still too high and the goal remains to get water consumption reduced to 450 ML/d
Here is the altered CoCT tracker chart showing how we are progressing towards our “Success Day” target. We are today at point red ‘X’ (22.7% of capacity on 12th March). Although consumption has risen slightly, we remain “ahead of the game” above the dotted black line and therefore are more likely to reach our “Success Day” goal.
(see here for a detailed explanation of how the chart is to be read).
What are the authorities doing now?
Here is our new graph tracking progress being made by the City to produce extra water through the various augmentation initiatives.
At the moment the average fresh water being produced amounts is holding steady at some 35ML/d. This should climb to over 40ML/d as the new small desalination plants commence production toward month-end. The declared goal of the Metro is to be producing over 100ML/d by end-June.
The Metro produces a useful map showing water usage by property. Click here, find your area and zoom in. Compare your water usage with that of other households in your area.
DWS continues preparation at Voelvlei and Theewaterskloof to be able to abstract some of the last 10% of water from those dams. At TWK, the temporary berm/coffer dam will be closed as soon as the natural back-flow from the deeper section to the shallower section stops. At that stage the pumping up of water to the abstraction point towards Cape Town will commence.
(Strandfontein desalination plant 8th March – ostensibly 72% completed, but still some way to go.)
See updated details of Cape Town’s planned interventions to produce fresh water here.
Learn about water savings efforts by other Cape municipalities – read more here.
Do visit the City of Cape Town website to see additional graphically presented information regarding the water situation – it is very helpful. See the full water status presentation here.
What ought you to be doing?
1) Check your house water meter. Make sure that it is clean and readable (it is your responsibility to keep it accessible to meter readers). Take a note of the meter reading and compare it with your municipal account. Make sure that you are being fairly charged for water used. If in doubt, contact your municipal office.
2) Maintain a high standard of hygiene in the home. Keep hands clean and, most particularly, wash all food carefully before use. There are indications that gastro-related problems increasing.
3) We are now only three months away from when the rains are due to arrive. Consider your budgets carefully and endeavour to install some form of rainwater capture and storage at your house so that you are ready. Design and prepare the site foundation area to accommodate at least one (or two) large (5000L?) tanks. Even if you cannot afford them initially you may be able to upgrade later by swapping tanks. Once you have created the gutter rain capturing system, then install at least a small tank as this will help in the meantime by collecting some water when it rains.
4) Reduce your water usage where you can. Everyone’s efforts are making a great difference.
Will the weather help?
La Niña condition appears to be levelling out. Predictions are that it will start moving back toward neutral during April/May. However, it has held on longer this year and our hope is that it will cause a cooler Autumn and earlier start to winter rains.
Light rain should fall across the Peninsula and adjacent areas on Wednesday/Thursday 15th/16th. Otherwise occasional rain is forecast with more extensive rain indicated for 1st week of April.
Our chart of rainfall for the dam catchments shows no meaningful rain at the dams last week.
In Summary: outflows normalised and exceeded inflows by 4.7 M.cuM. combined dam levels fell to 22.7% of full capacity
Here are the levels of the six main dams serving the Cape Town/Overberg/Boland area.
Plan ahead for possible water outages; here are points that could help.
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 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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