Cape Water and Dams Report
(Steenbras Upper Dam. Now 98% full. Photo : DWS)
Dams – Latest levels: Winelands and Cape Town
Report nr. 115 (updated 30th July 2018) on the main dams serving
Cape Town City and nearby Boland/Overberg towns
A brief spurt of rain coupled with the last of the run-off from earlier July rains lifted the combined level of the dams by another 3.4 M.cuM (0.4% of capacity). Overall water in storage climbed from 56.1% of capacity to 56.5%.
In the same week of 2017 the dam levels lifted by 4.0 M.cuM (1.0%) to 27.5% of capacity.
How long will the water last?
The goal remains to have at least 60% of capacity (530-540 M.cuM) stored on hand by end of winter. At 502 M.cuM we are quite close. Unfortunately hoped-for late July rains failed to materialise but expectation is that good showers in the catchments during August should see us meet this goal.
As established previously, a level of 60% would permit a full allocation to be made to agriculture while holding enough left in storage to see the SW Cape through to winter 2019 with restrictions perhaps relaxed back to level 5.
(Here is our model predicting the amount of water likely to be stored in the dams.
My revised estimate for July seems accurate and we will have gained 72 M.cuM in stored water.
Putting it into context!
For now, not much more can be done than is already being done. We are in a reasonably secure position but hope for more rains to boost the dams further by end-winter. In the background the CoCT push to produce extra water continues to improve volumes. Efforts by everyone to continue saving water is reflected the CoCT report that over 400,000 households currently earn the green dot for using less than 10500 L/month of water. While in the background, actions of the authorities to throttle demand and reduce wastage all help to minimise water consumed.
What progress is Cape Town making towards augmented ‘resilience’?
The latest report from CoCT indicates the contribution of augmentation stands at 44 ML/day.
This graph shows gross potable water ‘produced’ by the Metro (498 ML/d) vs the part (454 ML/d) that is drawn from the dams. The Metro has now moved into the range of 450 ML/d set by DWS.
(Graph tracking overall use and production of extra water through the augmentation efforts)
Here is our summary of the latest status of the Metro’s augmentation efforts! Red text indicates a change since the last update in May (click on the table to open a full-sized version).
What is not shown on here, but for completeness must be taken into account is that the dams will continue to play a very important role. If we assume that they will continue to supply at least one third of their capacity in water each year, then Cape Town’s share of that should, even in low rainfall years, equate to at least 550 ML/day. If we add to that, say, 300 ML/d of augmentation water then Metro citizens should from year 2022 onward be able to depend on 80-100 L/p/d of water without stressing the system; and of course purchase and use much more in normal good rainfall years. While industry and agriculture can rely on sufficient water to maintain production and job growth.
Read full report on status of Cape Town’s augmentation efforts here.
How well are we actually doing overall?
This CoCT graph showing the combined level of the 6 main dams clearly evidences that the recharge rate has slowed sharply.
In fact levels of both the Steenbras dam pair and the Wemmershoek dam have dropped slightly this past week as the authorities draw more water from those three dams; they are fullest and most likely to spill water first. Water from the Berg River Dam continues to be transferred to TWK dam.
Will the weather help?
A small amount of rain fell in the catchments this past week, with the Steenbras dams the primary beneficiaries as the rain systems were pushed down and around the southern tip of the continent. The rainfall for July is in total still below average overall.
Click here to see ShowMe Winelands Weather forecast of possible near-term rain.
What rain ought we to now expect?
1) As expected and was charted last week, a mild low pressure system has worked its way past the S. Atlantic High and lined up with the west coast. Per the synoptic chart, a strange arrangement has emerged with the High to the west, a small ridge of high pressure to the south-east and a general zone of high pressure over the land to the east holding this Low stationary off the west coast preventing it from making landfall. This may remain so over the coming few days until the low is broken up and squeezed into a sausage of cloud that will slither away along the south coast, bringing maybe 10-15 mm to the Peninsula and 20-30 mm to Steenbras.
2) As the Antarctic Oscillation is predicted to remain negative for the coming two weeks, it should permit the penetration by a block of unstable weather due to arrive on 7th and last through to 9th August bringing widespread rains, potentially heavy in the catchments, with Steenbras possibly receiving up to 80 mm and 30-35 mm falling in the Theewaterskloof catchment.
3) Beyond that, general rain – at this stage forecast to total some 20-30 mm each – should fall across SW Cape between 20th-22nd August and again between 30th August to 2nd September. Unstable thundery weather is forecast to bring 20-30 mm of rain between 6th and 8th September.
4) ENSO remains neutral. The NOAA/CPC chart indicates that the warmer El Nino condition has not developed fully yet (still below +0.5degC above average) so we can expect mainly weaker low pressure systems to continue to work through to the SW Cape over the coming weeks.
Some thoughts on water-related climate matters.
During this past week the pattern of extreme weather events has continued in the northern hemisphere with numerous out-of-control wildfires raging in Europe and the USA and burning through towns in California and Greece, the latter sadly causing substantial loss of life.
My comments last week about possible effects of climate change drew some sharp responses, so in case I confused anyone, permit me to digress and explain why I personally believe that climate change is important and could increasingly influence future fresh water supplies.
1) Caveat: I am not a climatologist so my opinions are based on what I read of the science of others.
2) According to scientific studies, the world appears to have gone through many cycles of low average temperatures, glaciation and low sea levels followed by periods of high average temperatures, melted ice and high sea levels. Left to their own devices, such climate cycles could be expected to continue to oscillate out into the future following varying time-lines driven by natural events such as movement of continents, volcanism, celestial mechanics, changes in the behaviour of the sun and occasional asteroid bombardment from space. Life on earth has and would continue to change and evolve sometimes influenced by or responding to climate variations. The geological record seems to indicate that, apart from the occasional catastrophe, such changes happened gradually over long time spans; the Earth, and life, has had sufficient time to adjust.
3) The Earth has gone through several such cycles since human-like folks have been around, the most recent being a period of glaciation which seems to have come to an end around 12-15 thousand years ago. Since then the Earth has been warming, the ice has been melting and the sea level has been rising. All other things being equal, this pattern would probably have continued out into the future until the cycle once more naturally reversed. So it is reasonable to assume that such climate changes would have anyway impacted the rainfall patterns and availability of water in various parts of the world. Some speculate that it was long, very persistent droughts thousands of years ago that disrupted the early Anasazi and later Inca populations in the Americas. It can happen again.
4) Most recently, since advent of the industrial revolution, humankind has for the first time been in a position to itself seriously influence the pace and direction of climate change. It does so indirectly through the results of its various activities, such as converting and consuming resources, denuding forests and vegetation, powering ever-expanding industries by burning fossil fuels, building massive herds of methane-emitting cattle and creating concentrations of people in large heat-emitting cities. Swiftly rising concentrations of gases like sulphur, CO2 and methane generally are trailing indicators of such human activities. But when coupled with rapidly rising average temperatures, these gasses contribute to self-reinforcing “greenhouse” conditions that generate yet more warming and additional natural out-gassing of CO2 and methane from the oceans and melting permafrost.
(This graph shows the change in global average temperatures across the industrial age. Note acceleration)
5) One effect of all this seems to be problems led by climate change that are besetting areas lying in the mid-latitudes, 30-40 degrees both north and south of the equator. Generally spreading from west to east, it appears that rainfall is diminishing, average temperatures are rising and a general drying-out tendency is taking hold. Surface and ground water is lessening, plant growth patterns are changing, crops are weakening, negative economic impacts are growing, costs are rising, health issues are emerging, living standards are faltering, political instability is burgeoning. It isn’t clear that our fractured, cynical and unbalanced ZA society will be capable of dealing with these challenges.
6) I have not read anywhere that humankind is believed to be the root cause of climate change. However, virtually everything that humans presently do has the effect of compounding increasing greenhouse gas levels and rising average temperatures. In doing so, humans appear to be accelerating the natural rate of climate change and are believed to have doubled and sometimes trebled the likelihood of more extreme weather events occurring. It follows then that apart from the growing population-driven consumption of and demand for fresh water, human activity must be increasingly having an impact on the availability of fresh water; also here in the SW Cape.
Looking to the future, in the SW Cape water will obviously be a key resource. If managed well and if it keeps up with population growth and industrial development, then water availability will be supportive of growth and contribute to social and economic well-being. But if it is not, …………..
Somehow we need to elevate the matter of fresh water supply to an even higher priority, to extricate water management from the realms of petty political partisanship and to resolutely and consequently build an economical but resilient water supply system for the best future for all.
Am I confident that we will do so? Yes, I am. I believe that this severe drought has been salutary and focused our collective minds on the facts that we have a substantial challenge to overcome but also that we live in an area which almost uniquely provides us with multiple potential solutions to the problem, provided that we take the correct actions. And good science today informs us as to likely future climate change effects that we need to take into account.
Nature gave us all a good fright but has now also provided some breathing space – we need to seize the opportunity and keep driving hard until we achieve adequate water resilience. For many reasons, this may be the last solid opportunity that we get to solve the SW Cape water issues.
What are the authorities doing?
Work continues. No new developments have been announced on the water front.
Summary: Combined levels of the six main reservoirs serving the Cape Town/Overberg/Boland area rose from 56.1% to 56.5% of capacity. Some useful rain is expected next weekend.
Watch me answer the often asked question: “why do you write this report?“
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.
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
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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