Future water options from within the Cape Flats Aquifer: poorly understood risks

By Dr. Kevin Winter

Cape Town’s pre-winter rainfall cannot come quickly enough in this drought stricken region. Since 2015 records show a below average rainfall for the southern Cape which has result in a reduced storage capacity of the major dams supplying the City of Cape Town, together with some smaller towns and the agricultural sector. The succession of droughts since 2000 is now a familiar occurrence. This is the third drought since 2000 – we have been here before. The reality is that an over reliance on surface water supply, treated to potable standards, is longer sustainable in meeting the total water demand. The drought has sent a clear message that is prompting water resource managers to consider a range of options that will augment the supply on and above the Western Cape Water Supply Services that sets out plans for the next 15 years. Cape Town will continue to be vulnerable to water scarcity largely due to its excessive reliance on stressed surface water resources, urbanisation, population growth, increasing water demand and climate change to name a few core elements that impact on the water resource system.

One water resource option, perhaps the lowest hanging fruit that is immediately available, is to abstract water from the underground that is stored in the Cape Flats Aquifer (CFA) for the common good. There is nothing new in this suggestion. At least 40 years of research exists on this subject, although the science of managing the process and risks to the integrity of natural wetland and surface systems is not well understood. While researchers tend to agree that the potential water yield from the CFA is approximately 20 Mm3 per annum, a mere 5% of total bulk water allocated to the City, it is uncertain exactly how an abstraction programme would affect surface systems and ecosystems. Researchers generally conclude that the CFA is a valuable resource, however the ecological risks have received less attention. If the aquifer becomes actively managed through recharge and flood control, and is used as ‘fit for purpose’ water resource, then the ecological risks will need to be understood and the implications for supporting and improving ecological services within the city. Tensions immediately arise that raise legitimate concerns about the ability to managing systems within the constraints of natural biophysical processes. Dare we try?

New research is suggesting that it is possible to manage the recharge of the aquifer not only to improve the groundwater storage capacity, but to reduce the flooding in low lying areas that occur every winter during the rainfall season. Recent research by a UCT PhD student, Ben Mauck, shows that water could be abstracted from selected parts of the CFA during the winter at a maximum rate of 5 ℓs-1 while at the same time ensuring that groundwater levels do not recede to below 1.5 m below the surface. If these models are correct then it might be possible to do two things: draw water to surface, and transfer this water to wetlands and detention ponds for use during the summer; and also to draw sufficient water during the pre-winter rainfall period from low lying areas to reduce the potential for flooding. These models also show that it is possible to inject or infiltrate water from urban stormwater or treated wastewater into the CFA to double the yield by a further 18 Mm3 which would extend the overall yield to nearly 40 Mm3. In theory, a Managed Aquifer Recharge (MAR) could augment non-drinking water requirements. A map of the storage capacity of the CFA shows that the highest volume of storage capacity is found in the northern parts of the CFA followed by areas such as Philippi and Mitchells Plain (Figure 1). Injecting stormwater to selective regions within the CFA would require a substantial investment in new infrastructure.

Figure 1: MAR potential for the Cape Flats Aquifer (B. Mauck, 2017)

The drought has prompted a welcome urgency to examine alternative water options. In turning to the CFA as one possible source, researchers are recognising the whole of the CFA as a complex wetland system. There is potential to manage the recharge and to extract water in a managed aquifer approach, but the impact on surface water systems and ecological services requires further research and analysis. There is opportunity and risk that must be understood and it must begin with research that is able to understand ground- and surface water interactions within strategic regions of CFA and across the city.

 

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Waiting for the rain

Extremely low levels of water currently in the Theewaterskloof Dam, the largest dam serving the City of Cape Town.

Extremely low levels of water currently in the Theewaterskloof Dam, the largest dam serving the City of Cape Town.

 

Cape Town residents are increasingly familiar with the constraints of water use – the region is in the grip of its third major drought since 2001.

In April 2005, for example, the water storage capacity of the main supply dams reached an all-time low of just 26% overall. In this case, the City of Cape Town (CoCT) had already imposed Level 2 water restrictions (1 January 2005) in an effort to reduce consumption by 20%. Records show that consumers did adhere to the restrictions and the City was able to meet the intended reduction. There was some relief on 20 April when an intense, localised thunderstorm brought about 130 mm of rain to the catchment that feeds the Theewaterskloof Dam. By late June 2005 the overall dam storage capacity was a little over 50%, which is usual for mid-year early winter conditions.

The current conditions in 2017 appear to be similar to that of 2005, but in the present moment there is heightened uncertainty. The overall storage capacity of the dams decreases by between 1.5 and 1.8% each week under the current weather conditions and demand. Given the current water storage capacity of approximately 40% (23 January 2017), and with limits on the drawdown for most dams being between 10 and 15%, and if there is no significant rainfall ahead, the risk level could be serious. There is no doubt that it will rain, but waiting is uncomfortable and unsettling for all. Short term rainfall forecasts are unable to provide answers to three of the most important questions right now: When will it rain? How much will it rain? Where will the rain fall?

The CoCT receives about 98.5 % of its potable water supply from surface water resources. The Western Cape Water Supply System (WCWSS) comprises a network of major and minor dams, which are all used to store winter runoff. Six major dams, located in the mountain catchments areas in the Boland and Hottentots-Holland mountain ranges, supply 99.6% of CoCT’s raw water. The WCWSS has an annual yield of 556 million cubic metres of which 399 million cubic metres is allocated to the CoCT, while the remaining yield is allocated to other urban areas and for agriculture. There are plans to augment surface water resource by 2020, but this might be too long to wait.

The imposition of water restrictions by the City is uncomfortable and it creates uncertainty among consumers, but it is clearly necessary. The City has stepped up the restrictions from Level 2 to Level 3 restrictions (1 December 2016) and are likely to implement Level 3B restrictions soon. At the same time, the City has struggled to inform consumers about the requirements of each level, and each level requires a response that is increasingly nuanced. To the credit of the City, policies and weekly updates on the water supply have been well managed on the City’s website.

Water resource options

The official response is that taps will not run dry before the winter rainfall period although there are many views that are being expressed to the contrary on social media and other media platforms. Hopefully it will rain in time, but it is an anxious wait.

Given the three droughts that have occurred over the past 15 years, in relatively quick succession, there should be more than enough motivation to actively commit to incorporating a variety of water supply and treatment options into the overall water resources mix.

Over the last 10 years and more, a variety of water resource options have been explored, for example, augmenting supplies from the Table Mountain Group aquifer, including the Cape Flats aquifer; the Reclaim Camissa project, which utilises spring water from Table Mountain; domestic rainwater harvesting and grey-water systems; the use of storm water as a resource; and improving the quality, supply and distribution of treated effluent for business enterprises, golf courses and large institutions.

These options are all reasonably well researched both in Cape Town and elsewhere. It is time to test and implement many of these systems. These options have the potential to enable Cape Town to become a water-resilient and water-sensitive city that is capable of dealing with the uncertainty of water supply in an increasingly water scarce region.

In future we should not be caught waiting for the rain.

Download, print and display the CoCT water-saving tips poster…

Story Kevin Winter. Photo Johnny Miller / Code For Africa.

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Research results: Liesbeek Parkway stormwater biofilter

Read the executive summary reporting on the efforts to improve the constructed wetland opposite Rhodes Office Park, Mowbray.

CONSTRUCTED_WETLAND_BARRY

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Peninsula Paddle 2015: Sunday 7th June

Each year the Friends of the Liesbeek helps to organise the Peninsula Paddle. This event has had an important impact on rivers, vleis and canals of Cape Town. The paddle brings attention to the state of the waterways by raising public attention through the media and also drawing public officials to address the problems together with the public themselves.

Anyone can take part in the paddle. You can do a short section or join up to 80 paddlers who will be doing the full route. There is no cost, but you must register on the webside: www.peninsulapaddle.wordpress.com

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Milnerton lagoon: Peninsula Paddle 2013

 

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Mowbray wetland needs attention

When the wetland on the western bank of the Liesbeek River in Mowbray, opposite Rhodes Office Park, was built in 1997, the intention was to provide an aesthetically pleasing public environment and perhaps a secondary thought was to intercept and treat urban stormwater runoff. This development was funded by Rhodes Office Park complex as a contribution to the environment. I understand that the developers agreed to maintain the wetland for the first two years, thereafter it would revert to a City’s Parks and Recreation department.

Want to read more and see some options? Click on the link to read a two-page document:Constructed wetlands need attention WETLAND3 20141022_183118

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Liesbeek Life Plan

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Liesbeek Lake

Liesbeek Lake

 

 

 

 

 

 

 

 

 

The Liesbeek Life Plan is a recently formed collaborative effort between the Friends Of the Liesbeek and UCT’s Urban Water Management research unit to contribute to plans and designs for restoring and offering better support to social and ecological life of the Liesbeek River.

Aims
The primary aim is to provide a framework plan which will guide the building of ecological and social resilience in the Liesbeek River catchment while providing an “insurance policy” in order to safeguard and enhance the Liesbeek. This framework will also aim to address the relationship between ecology and human behavior by enhancing amenity and social value of the river.A secondary aim is to work together in a community of practice where we explore new ways of thinking from the knowledge and experiences of participants. This community of practice will include the knowledge and resources from various academic and professional bodies as well as from first-hand knowledge with community groups.
Objectives
The Liesbeek Life Plan will use the concept of “Landscape Urbanism” as a means to allow social and ecological interactions to be translated into design. In this manner it will consider the urban, natural and social processes within the catchment and will aim to align them through design interventions at a framework level with associated principles and guidelines. These interventions will then be designed further as applicable at a site specific level so that plans and designs can be implemented in a practical manner. Emphasis will be placed on design which guides interventions in an appropriate and holistic manner rather than a prescriptive set of constraints.Reference will also be made to precedent examples elsewhere which illustrate the manner in which the “Urban River Syndrome” is being managed in other parts of the world.

Newsletters about the concept and progress of the project

No 1.  Making room for an urban river The Liesbeek Life #1

No 2. The urban river syndrome – what could be done about it? Liesbeek Life Plan #2 August 2014 (2)

No 3.  AIMS, OBJECTIVES AND OUTCOMES Liesbeek Life Plan #3 September 2014

No 4. Landscapes that enrich and enable public attitudes and actions The Liesbeek Life #4

No 5. Leading change in urban water management Liesbeek River Life Plan # 5

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FOL Annual General Meeting 24th June 2014

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Sunbirds in the Western Cape rely on summer flowering plants for food during the hot dry summers. Summer flowering Erica verticillata became extinct in the 1930s and its reintroduction means an important summer food source is available for these lovely birds on the Cape Flats.


 

Annual General Meeting 2014

Thank you to everyone who attended the meeting. Every seat was filled and the presentations and discussions were lively. Chairman Phil McLean gave us a short summary of the year’s challenges and successes; Grant Irlam, our treasurer, explained to everyone how our funds have been managed; and the members were satisfied that the Friends of the Liesbeek had once again done a great job this year. Our speaker, Dalton Gibbs, had everyone “yaying” and “awing” during his talk on the rollercoaster ride of plant conservation, namely the restoration of extinct Erica verticillata. We also had a chance to hear what our Liesbeek Maintenance Project Manager, Nick Fordyce, had achieved in the 8 months that he has been on the river. Well done to Nick for having taken over so ably. Kevin Winter treated us to a slideshow of the 2014 Peninsula Paddle and Landscape architect Clare Burgess gave us a taste of the “Plan” that is being drafted for the Liesbeek and updates will be posted here and sent out to members as the project progresses. Finally we could tuck into the delicious snacks provided by The Fat Cactus (Dave), Players Restaurant (Sharon) and The Wild Fig (Trevor). A big thank you for the generous donations and support from these restaurants on the Liesbeek.

 

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WINTER NEWSLETTER and AGM

Liesbeek Lake

The view over the weir towards Devil’s Peak at Liesbeek Lake in Observatory

The Friends of the Liesbeek AGM

Tuesday 24 June

18h00

Enviro Centre

Dalton Gibbs will be speaking on Erica verticillata and the restoration of wetlands.

Please join us for this important meeting. We are looking forward to seeing you again.

You can read the latest newsletter by clicking on the link below.

FOL Newsletter MAY

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Valkenberg Redevelopment

Final BAR of the Proposed Redevelopment Of Valkenberg Hospital, (D:EA&DP Reference Number: 16/3/1/1/A7/17/3064/12)

YOUR INVITATION TO PARTAKE IN THE PUBLIC REVIEW PERIOD OF THE FINAL BASIC ASSESSMENT REPORT AND ENVIRONMENTAL MANAGEMENT PROGRAMME.

DATES:              29 November 2013 – 9th January 2014

VENUES: 1.      Observatory Library: Opp. Cnr Station and Drake Roads,Observatory,7925

Tel:021 447 9017(Contact person: Cleo Delmore)

2.     Mowbray Library: 31 Main Road,Mowbray,7700

Tel: 021 689 1201(Contact person: Michelle Venter)

3.    Chand Website:

http://www.chand.co.za/valkenberg2.asp

4.      Chand Environmental Consultants: Contact person: Kim Wyngaardt, 021-762 3050, Richmond Centre, 174-206 Main Road, Plumstead.

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The Envirocentre

The Envirocentre on the Valkenburg Hospital grounds has always been an important base for environmental groups, facilitating open discussion and innovation for almost two decades. Read Emma Bryce’s report Envirocentre_Bryce.

The recent Open House held by Chand to comply with the Public Engagement Process for the proposed redevelopment of the Valkenberg Hospital raised many concerns. The interested and affected parties were able to speak to the project team but many issues were still not resolved. One of these is the future of the Envirocentre.

The building is the old Valkenberg Dispensary, an attractive 65 year old building, with lovely wooden floors, high ceilings and original doors and window frames. It commands an inspiring view of Devil’s Peak and the Liesbeek Lake, and has a long open space in front of the building where seasonal ponds and grassy fields give refuge to frogs and toads, as well as numerous bird species.

However, as is clearly stated in the report, the Envirocentre is far more than an attractive building set in open grounds, it is in fact, where a space was created where diverse groups could interact and energise civil society.

The Chand proposal for their client, the Western Cape Provincial Administration and the Department of Health, does not preserve this important space. Instead the whole area is to be covered by extensive new buildings, destroying the heritage centre and the open areas leading to Liesbeek Lake.

It seems to be a sad waste of a lovely, historical  community space.

 

 

The view from the Envirocentre

The view from the Envirocentre

 

 

 

 

 

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