Zandvlei in the drought

The drought is affecting the Zandvlei estuary in two major ways: the water quality and quantity as a potential source of water.

The important message here is that Zandvlei is under stress, like all other local wetlands, due to the low water levels from the drought. The nutrients that have accumulated in wetland systems over time can now be expected to be manifested in algae blooms , excessive plant growth and in this case a new weed species coming to the fore. Wetland systems can be expected to manifest water quality issues in response to the stress imposed upon them by years of city runoff, pollutants and the drought conditions. What we are seeing are symptoms of underlying stresses placed upon our wetlands.

Water quality

The condition of the Zandvlei estuary is currently a cause for closer monitoring. It is not as dire as some may suggest, considering what it has to accommodate:
1.         There is a larger than usual amount of stringy algae. This is due to the hot temperatures, and also a nutrient build up because there is not enough flow to flush the system, because of the extreme  drought.   Lower water levels concentrate nutrients already in the system – high temperatures spurn algal growth.
2.         The drought also means that there is a larger build-up of nutrients higher up in the catchment. When rain does come it washes large amounts of nutrients off the catchment into the estuary in one or two events, as opposed to continued rain with small amounts of nutrients over a long period.
3.         The biggest challenge the system currently faces is sediment build up which is impairing the functioning of the estuary as a nursery. The annual maintenance dredging has been redirected to drought emergency measures.
4.         The mouth opening depends on flow into the system to manage the salinity, and the flow has been low due to the extreme drought. The build-up of sand in the mouth of the estuary means that when there is tidal interchange the amount of water exchanged with the sea is limited. In addition, the budget for this is also constrained due to drought emergency measures. The sand bar, coupled with the long drought, means a decrease in sea water exchange and a decrease in flushing of the system. Thus the conditions seem to be set for poor water quality issues in the summer ahead.

The top priority of the ZPAAC currently is to dredge the estuary. While this will have a positive impact on the nutrient balance and hence pond weed growth, the pond weed management is not the main topic under scrutiny. Any help obtaining funds or assistance in getting any amount of dredging done will be welcomed.

Water extraction

There has been reports of water being extracted from the estuary. It is illegal (see below), but people removing water by hand from Zandvlei wouldn’t be a huge ecological disaster; there may be health consequences but this would probably be out of the ambit of the City to resolve.

In terms of the Marina; the first 2m of water is owned by the adjacent property and is not Council property. Thus Council permission is not needed as they are not the land owners. The person however still needs a water use licence from National Government and be registered as a water user.

The Zandvlei water has a high salt content (about half sea water) so it won’t be too good as drinking water.

Below is an extract of the present legislation – it is old and outdated but still in effect. If you witness water extraction, please call the reserve ranger staff (24/7) at 083 499 1717 (please note this is for ENVIRONMENTAL emergencies only).



Dream Zandvlei – members wishlist

An excerpt from the minutes of the ZPAAC working meeting held on 17 January 2018. In due course this will be regrouped per topic and worked into a detailed, timelined subsidiary plan to the management plan. Please add your thoughts and comments below!

The reasoning is that we need significant amounts of funding, which can only realistically be obtained through private-public partnership and that requires significant economic incentive. This requires a strategy that likely includes commercial development.

The input from the meeting participants are noted below. Going forward, DG noted that many of the desired things are already legally required and built into the management plans. BV noted that this is encouraging for investment. The risk of irresponsible development is limited because of extensive legislation and a vibrant local community. Enforcement of basic rules like fishing equipment and public order policing is challenging.

DG suggested after the meeting that the management plan is vague, and that more detailed subsidiary plans are needed with timelines and defined objectives. These include specific topics, like invasive flora, development, sediment management schedules, littertrap and litter management etc. DG, BV and the new reserve manager will meet and formulate these with input from the ZPAAC.

Obtaining funding for these plans to supplement city budgets is a full time exercise, GL noted we need a full time fundraiser. GL developed a job description for this. To pay the salary for this person, BV suggests entering the Dream Zandvlei into global competitions, for example. GL shared the #cocreate design festival as example, after the meeting.  It would be great to get a landscape architect volunteer on board for the visualisation.

Preamble: Andy: sewer line: if moved make a dramatic change, but doesn’t bring it back to natural, because it’s so constrained. But it is likely the best we can do.
Can we put the sewer pipe below the low spring tide? Drop 2m? May cause small leaks, would require an additional pump station. The most expensive part is the power line to the pump station. The sewage from Clovelly, St. James, Muizenberg, Lakeside goes through this pipe.


Rebuild estuary roadbridge – traffic, restore canals,

More natural estuary mouth – seem to fit well with the estuary roadbridge

Build the Steenberg extension at the bottom of the M5. If this road is landscaped properly, it would still be an environmental asset. – bridge over railway line there. Allow to develop the northern part of the reserve better, currently underutilized.

Environmental reserve, platformed tented camp. – Can get to this nature reserve by train!

Perhaps café, open on weekends.

The old campsite revamped, including a very special amenity centre, special sort of restaurant (like Harbour house)

Source to Sea pathways – connecting the catchment (good already in Constantia valley, Tokai), have started in Muizenberg and Lakeside, need to connect them in Westlake, and consider issues of safety. It’s a short distance to connect to Kirstenbosch

Water quality,

An enhanced aesthetic value to Cape Town

A financial audit of what the estuary is worth from a fishing perspective.

Educationally worth optimized.

Marketing programme for students and learners, learn, understand, take ownership of this area.

Set of behavioural rules – a code of conduct for how people should behave in this environment.

Better signage



Investment, investors

A mini waterfront, having a market, restuarants, not too upmarket

Nothing noisy



Look at what is already happening, working with that rather than designing something new

Investors look at maximizing profit at the exclusion of the people who live here, so need to manage that, keep the people and council involved.


David Roux

The banks around the sea cadet base, the eastern side of the yacht club, something permanent. The sand bag idea worked well.

Better utilization of areas – e.g. next to caravan park, e.g. light environmental centre, camping centres

Move on the bowling green



Source to Sea is very important, creating connectivity out of the vlei, drawing people in.

Security concerns follow this,

Also False Bay source to sea efforts. But we need to open up the community. The more people using it, the safer it will become, and yes we need to upgrade the security.

Improving awareness. Not just this community, but everywhere, catchment management, catchment and upwards. Strong community involvement.

Improved amenities, making use of space that isn’t used properly Look at what GreenPoint park has achieved.

Sufficient budget from council for management. Not only from a staffing perspective.

Office facilities, education centre (co-working spaces) that budget need to be allocated

Naturalisation of the litter traps

Don’t: harden the edges of the vlei. A hybrid system is important.

Connectivity to the mountain, from a natural flow of flora and fauna.



The management plan – 2011. The proclamation has now formally been proclaimed. These ideas are only ideas until they are encapsulated into the plan.

“Zandvlei usage is a valuable component of the CT network. Appropriately used for education … “

These ideas are not short on thought or on plans – these are in place! Institutionally we are one of the better managed in the Western Cape.

Code of conduct – we have a recreational water use by-law Section 23

Economic study was done in early 2000 – in terms of property values, link economic benefits to natural systems

Suggest: A natural function estuary cycle bearing in mind we are in an impacted cycle. Fix the water levels etc. It will always be a ‘novel ecosytem’

Manage the impact – big one is water quality, solid waste and chemicals. Not that badly affected by water quantity.

The system needs to be better integrated in the surrounding environment, e.g. the caravan park has no connection to the external environment.

Zandvlei is very well studied.

All the work has been done! It is ripe for investment.



Operating as close to a naturally functioning estuary as possible. We need to do remedial dredging

Relocate sewer pipe

Allow water to fluctuate more

Maintain passage to allow fish

Water depth at about 1.5m at spring tide

The money and budget to achieve these



The destruction of Zandvlei as a fishing nursery

Motorised craft

Urban or industrial development along the normal edge of the vlei


Nutrients, polluted entering from the North

Imbalanced weeds



Similar to Cherry’s

Royal Bridge road needs to be triple its present span

The promenade walkway needs to come down – this is the part that constricts the mouth

Open up the mouth to four times it’s current width, allow it to self-regulate

Is in the plan, but Phase 2 onwards need to be implemented

Need a full-time fundraiser

Elegant, big windows restaurant that has great benefit from the sunset.



All my points covered

Having one representative in the city to deal with



Children to engage with nature, sport

Adequate management

Sensitively and appropriate

Non-motorised boating


Awareness – showcase eco stuff

The by-laws are there, but difficult to enforce them – need manpower and money – Dalton: the new by-law gives users the ability to manage their own by-laws



Water reticulation of the ends of the waterways (Boksburg has a mobile unit to reticulate this water)

(Ask Tamsin about law of taking water from vlei to sell)

Fishing – endangered – Chapter 3. Better enforcement. More security officers, more staff.

More notice board. Better signage. (That doesn’t get stolen in two hours)

We need full time law enforcement – lobby local council! In Zandvlei and in Zeekoevlei. It is an important recreational space and need law enforcement (only the beaches seem to have them)

Walkway between Uitsig waterway and  the <> – Sandriver, that boom gate is not working to prevent undesirable traffic (only for emergency)

Agriwaste – diffuse pollution, pollutants in the ground – integrated nutrient management,



Not have Green algae!

Different weed harvester design? Dalton: tenderized model may have faster turnaround. Privately owned, leased to the city. If the machine is too specialized it may be useless in the near future.



World class water (sports) tourism destination

Vibrant fish

Vibrant birds

Nutrient managed

Softened banks, rehabilitated riverbeds

Softened catchment – WSD

Clear waters

Ferry fun stuff between caravan park and sports club

Zip line


Dynamic mouth management – vibrant estuarine habitat

Promenade, night time walks, LED lighting (not light pollution), perhaps powered through wetland/microbial fuel cells (MFCs)

Dredged vlei, sediment used for award winning architecture and landscape architecture

Lots of otters!

A new “Otter trail” including sections of the Hoerikwaggo

Safe hiking

Vibrant community – also including the “homeless” to live the life they are comfortable with

Multifunctional, productive spaces

More animals, e.g. eland

Science! High tech integrated but also educational, it’s tech, but it’s not about the tech, it’s about the people.

Inclusive, resilient

Food gardens, allotment plots? => wider than Zandvlei, incorporate open areas everywhere, extend the green corridor, integrate with the cycle routes, down to Cape Point, up to various places, the V&A, the PHA

Link with the catchment – articulate and visualize the relationship with the catchment

Access and support for multiple activities – horses, dogs cycles, yacht, canoe, fish, integrated, responsible hiking.

Less lawns!

Win awards, world famous

Inclusive also to light industry – showcase the circular economy

Better circulation in Marina da Gama – connect with Capricorn business park, as per the original development plan

“liveable neighbourhoods”

Public-private research, engaged research

Park Island higher profile

Permanent orienteering course(s)

Build community between and within neighbourhoods – e.g. Muizenberg, Lakeside, Westlake and beyond.

Don’t want litter, motorboats


Sediment management in Zandvlei

Why is it necessary to manage sediment in the Vlei? The benefits of sediment removal

By dredging or other methods.

Zandvlei’s location in an urban environment has necessitated that the water level be maintained between certain limits to meet the needs of the residents and recreational users, but should not unduely disturb the function of the Vlei as an estuary. Unfortunately, the infrastructure put in place by the City Council to manage the water level has had the unnatural consequence of trapping large volumes of sediment in the lower reaches of the Vlei. A study done in 2014 showed that the sheet of accumulating sediment was advancing away from the mouth into the Vlei at an average rate of more than 2 metres per month, leaving behind a shallow area much of which is above water level at low tide.

Too much sediment in the Vlei is bad for recreational activities – canoeing and yachting in particular, as well as for fishing. It is also bad for some of the creatures calling the Vlei home. The Zandvlei estuary is the last remaining functional estuary in False Bay, and as such represents the only nursery for the fish that live in this area. If the estuary fills up with sediment, not only will the fish in the Vlei be threatened, but there is also likely to be a negative impact on the fish population of False Bay.

It is generally accepted that the silting up of the Narrows is due to the artificial raising of the base level of the Vlei by a rock weir constructed just below the Royal Road bridge to protect a sewerage pipe located just above the bridge. The long-term solution is to re-engineer the mouth and relocate the pipe and remove the rock weir, thereby enabling tidal ebb to cut a channel back down to the low water level. This will avoid the accumulation of sand in the narrows.

As the re-engineering of the mouth could not be funded by the Council in the near future, options for remedial action in the interim was to;

  1. Lower the rock weir to try and reduce the level of the sand sheet behind it.
  2. Dredge a channel through the accumulated sediment to the mouth.

Passive sediment removal through mouth management: reduce the weir or more dynamic measures?

From an estuary management perspective, free flowing tidal movement with an unconstrained, meandering mouth is the ideal scenario, for fish activity as well as sediment movement. Due to the current constraints on the vlei, being built up at all sides, this is not currently possible. Keeping the weir to maintain a stable water level is also not good because it cuts off access for fish to the nursery, and it gives no option for the coarser fractions of sediment (coming from upstream or introduced through the mouth by flood tide) to leave the estuary into the sea. Furthermore, removing any constriction to the mouth would minimize flooding that might arise as a result of heavy rain in the catchment area to Zandvlei.

The next best thing is to manually manage the mouth at certain times of the year, depending on rain and tidal movement, which is the current practice. With the prolonged drought this is difficult.

When the mouth is open, there may be some sediment removal through tidal ebb and rainstorms in the catchment. Unfortunately, there is a weir in the way that hampers this action and, on balance, the tidal inflow will deposit more sediment above the weir than is removed. Lowering the rock weir increases the volume of saltwater entering the Vlei and also reduces the level to which the sand sheet will accumulate. But it will not stop the advance of the sand sheet into the Vlei.

The rock weir has now been lowered to the minimum level at which it still affords acceptable protection to the sewer line. The sewer line could be moved, but currently it only relies on gravity to transport the wastes and any alternative option would require pumps and introduce more risk of failure. With the lowering of the rubble weir, there has been increased tidal inflow which has pushed the stability of the building foundations of Marina da Gama to the limit.

Before the drought there was a small net sediment removal in response to lowering of the weir. With the extended drought there has been insufficient rain to create enough flow to remove the sediment that arrives in suspension and it is collecting in the body of the vlei. Even in periods of good rain the weir stops bed-load sediment from being removed from the vlei.

The benefits of dredging

Sediment removal specifically through dredging.

Considering all the options, the need for dredging is clear. It provides all the benefits of working towards Water Sensitive Design except water supply including:

  • Flood prevention
  • Improved water quality
  • Improved Biodiversity
  • Increased property values
  • Maintaining blue flag beach status
  • The maintenance of a well utilised, truly multi-racial public space

Dredging is not regarded as the optimal remedial action to the unnatural build-up of sand in the lower reaches of the Vlei and should not be regarded as a long-term solution. However, if re-engineering the mouth is not presently affordable, it does offer some relief to the problem in the shorter term.

Although there are potential negative impacts to dredging there are several benefits;

  • It will enable salt water to penetrate further into the estuary, and this should improve the flushing of the Vlei and also discourage pondweed growth.
  • Research (reported in Whitfield, 1998) has shown that estuary mouth channels with depths greater than 1.5m have greater diversity and numbers of piscivorous fish. Thus, the deteriorating fishing experienced could be due to the shallowing water for hundreds of metres above the mouth. Dredging may ameliorate this situation.
  • Canoeists will be able to resume paddling, without getting stuck, from the vlei to the sea.
  • The Narrows, one of the most popular fishing sites in the Vlei, would be reinstated and once more expanded as a fishing venue.

Evaluating the potentially negative consequences of dredging

Water stratification is an undesired possibility, due to the more dense (heavier) sea water taking up the deeper channels. On the other hand, estuaries are dynamic: seawater will fill the channels in the Narrows, but it will be exchanged with every tide when the mouth is open. Furthermore, our prevailing winds, induce currents in the Vlei and these result in both horizontal and vertical mixing of the water body. Nevertheless, dredging should be undertaken in a manner so as not to create pockets which may become anaerobic. The front-end shovel used in 2015 is not an optimal tool in this regard. However, in the Narrows these pockets will be short-lived and ironed out by redistribution of the sediment by tidal and fluvial currents, which was indeed observed with the holes created by the front-end shovel in 2015. The only area where dredged depressions are likely to persist is in the middle section of the Vlei, distant from fluvial and tidal action.

The sandprawn population and other benthic organisms would clearly be negatively impacted by removal of the sand bodies. If everything is dredged all at once this could be devastating to the prawns. Consequently, the current dredging plan leaves undisturbed areas of sand flats adjacent to the dredged channel, where the prawns and other benthic fauna would remain. Anecdotally, the prawn population of Zandvlei has been found to be remarkably resilient. This is not surprising as sand prawns live in the dynamic lower reaches of estuaries and have to cope with rapid changes. Not to dredge for the sake of a few prawns and allow degradation of the remainder of the ichthyofaunal nursery does not seem wise.


Dredging is not an optimal solution, but would combat the advance of sediment from the mouth into the basin, thereby keeping the estuarine system functional in the meantime. To be effective dredging would have to be undertaken at regular intervals until the infrastructure at the mouth has been re-engineered.

Littertrap progress

This piece was written for the Marina News and The Zandvlei Trust Newsletters and submitted to them on 17 August 2017. It was written by the ZPAAC chair at the time – Bernelle Verster, in a volunteering capacity.

The issue of litter is a highly emotive topic and a very difficult one to solve. The Zandvlei Protected Areas Advisory Committee (ZPAAC) has been trying to address this issue for some time.

Apart from the bigger problem of how we as a society live and dispose of waste, two more immediate issues make dealing with litter hard: As Councillor Aimee Kuhl reiterated in a ZPAAC meeting in October 2016, problems like litter management have to be balanced against the needs of the massive influx of people into the Cape Metropolis, who needed housing, water and sanitation. In short and as can be seen in this article, the City simply does not have the funding to build and maintain litter traps to the extent that it is required. Secondly, to the credit of members of the public who live, work and enjoy the vlei and its surroundings, many people are contributing in their private capacity through for example litter clean ups. This is, however, of limited value. Litter is an easy and visible thing for people to complain about, but it is also easy to misjudge the scale and scope of the interventions required. We are dealing with immense inequality issues and poor design decisions from the 60’s and 70’s which result in what we see in the waterways.

As a recently appointed chair to the ZPAAC, I had a look over the minutes of the ZPAAC since inception (mid 2015) to track the progress towards better litter management. It is important to note here that ZPAAC is a statuary advisory body to the City Council and that as such it does not deal with members of the general public. The ZPAAC is not obliged to furnish any information to individuals but connects with the public through the organisations represented on ZPAAC.

Note: the minutes of ZPAAC meetings are available on this website.

The timeline of addressing the litter problem since June 2015:

June 2015:                    Bob Crask of Marina da Gama Association (MDGA) tables the state and future plans of the litter traps in Sand River canal. Heavy rain results in the litter bypassing the existing litter traps. It is acknowledged that funding is a challenge. MDGA would like cities backing to retrofit the existing litter traps.

September 2015:           Abdullah Parker (City of Cape Town) met with Bob Crask, and supports the initiative.

February 2016:              The meeting discusses the repair, cleaning and maintenance of litter traps along the river(s) feeding into the vlei. More traps were needed, and an awareness campaign was ongoing. The incidents of dumping were increasing. Dredging and rubbish collection were ongoing. A long term solution to improving the river was proposed of proactive environmental education. Currently approximately 6000 children per year attend environmental education at Zandvlei. It was also noted that the cleaning of litter traps is not always done correctly, resulting in litter escaping over the top or through the bars.

April 2016:                    Abdullah Parker provided a feedback email about the litter traps

May 2016:                     This is the first meeting I attended. Litter traps were not being maintained due to insufficient funding.

August 2016:                Litter Traps were still ‘not working’; in the absence of Bob and Abdullah there was no further feedback. In this meeting I agreed to look into options for sediment removal, which in my view was the most pressing need. Through discussions about the management of the vlei I became aware that all the matters are related, and thus became more involved in the litter trap discussions.

During this time the Zandvlei Trust received an anonymous donation to investigate an improved litter trap.

November 2016:            No specific mention of litter traps. At this meeting the Friends of the Liesbeek were invited as it was hoped to learn about their strategy, seeing the success in managing to rehabilitate the Liesbeek river. They have also more recently suffered from funding shortfalls.

During this time Anchor Environmental did a report for the Stormwater and Sustainability Branch Planning Department – Transport for Cape Town, which is to be appended to the Integrated Reserve Management Plan (IRMP).

January 2017:               Litter traps feedback had been received from Abdullah Parker.

March 2017:                  Joshua Gericke, the Zandvlei Reserve Manager, had a preliminary design for a litter trap and needed a pilot study done. He had spoken to two students, but there had been little interest shown.

May 2017:                     An emotional discussion about the litter traps ensues, but with not enough personpower to address. A few people had a workshop and worked through Prof Neil Armitage’s 1998 WRC report as well as Kyle Kriel’s 2014 report (a student of Neil Armitage). From this it was established that the ground work has been done, but that a student is not appropriate for the final design. The next step is to obtain quotes/expression of interest from consulting engineers.

Litter reduction upstream: The conversation then went towards reducing the problem at source, either through recycling or through global initiatives. Peter Kruger has looked at this at a local level with a nearby recycling depot and Angus Hemp was advised to get in touch with him.

At this meeting I am also elected chair of the ZPAAC.

July 2017 (the most recent meeting):     Following the last meeting and working with Prof Neil Armitage (Future Water Institute and Urban Water Management Group at the University of Cape Town) (who has been contributing pro bono) quotes were sent to several engineering companies. Two companies replied with quotes, JG Afrika and ZAA Engineering Projects & Naval Architecture. ZAA then met with Joshua and myself discussing the project scope and limitations. Following this ZAA revised their quote and informed us that they have selected the Sand River Litter Trap as a ZAA Corporate Social Investment Project, to be executed as a  team effort between all parties involved.

The approach was further discussed, including approaching the litter from multiple interventions, and modifying the current trap to only capture large items, allowing another litter trap downstream to be designed to capture smaller items with less potential for damage. Neil considers the cascade of interventions as a good idea, but expressed concern that the current litter trap is bad design. Neil kindly offered to advise during the project.

At this meeting the concerns expressed by some members of the public of an ‘over-engineered approach’ was also discussed. There was some concern that the litter trap is expensive and will take long to build, which does not address the immediate problem. I took input from all members attending. Neil’s response “If you are not going to do it properly you can’t do it at all” and that “it will have to be an engineering solution as we can’t deal with the social source of the challenge”, was met with agreement all round.

The committee further agreed that “You are not going to solve the problem in one go, it needs to be an iterative solution” particularly as it relates to larger and windblown litter.

Litter reduction upstream

A social approach to litter reduction around the Blue Route mall involving the Keysers river, a WESSA project in the 1990’s were mentioned. While it was noted that there is very little in that river that contributes to the litter in the Sand area, it was lauded as a good approach that we should consider for the catchment at large.

Neil also noted that the litter can be an order of magnitude higher than what we see. Nets can work but it really is about the maintenance and only works at low flow. The better litter traps is where a machine can empty it: it’s not a nice job, people start to ‘pretend not to clean it’.

As part of an integrated and iterative strategy, we need to find ways to reduce litter at source. One low hanging fruit is to get a working relationship with a recycling centre. There is apparently such an initiative underway in Noordhoek, and we are busy investigating this.

Dream Zandvlei: Meeting with Barry Clark

After the first Dream Zandvlei presentation (18 January 2017), Barry Clark from Anchor Environmental offered to discuss the merits of dredging the vlei, following work they did for the Department of Water Affairs, in collaboration with Aurecon and Southern Waters, on environmental flow requirements for the Zandvlei estuary along with several other systems in the Western Cape. Following this meeting some of the findings from that report was also presented at the Estuary Management Workshop, as reported at a Dream Zandvlei presentation on 15 March 2017.

As part of this work, Barry and his team looked at a number of options for restoring ecological health of Zandvlei including considering merits of dredging the vlei. Bernelle met with him on 27 February 2017.

Barry works in marine and estuary management. The work they were doing was required as part of a Department of Water Affairs classification study on the significant water bodies. The classification study broadly means to decide on a future desired state of health of these bodies, which takes into account its environmental, human, agricultural and industrial impacts. Significant bodies broadly fall along the Catchment Management Agencies (CMAs) and Zandvlei falls in the Berg/Steenberg area. This study will be publicly available once published.

The bodies are classified along 3 levels:
1. Natural
2. Moderately used
3. Fully developed.
Further, the bodies are classified along their current ecological health, where A corresponds to largely natural, and E being completely trashed.

“Zandvlei is probably the third most important estuary in the Berg catchment area”
(First Berg, then Langebaan, then Zandvlei, then Diep…)

“It is critically important that we conserve Zandvlei”
– Barry Clark, Anchor Environmental

Generally water abstraction is a large factor in water bodies, with about 60% of the Berg taken out for human use, for example. Zandvlei, in contrast, does not have a large water use, with it’s current runoff about 95% of the reference (or only about 5% of the water taken away). All the degradation seen in Zandvlei is human related, with a large portion recreational. But it is an estuary that is improving. In 1995 when Barry did his PhD on it, the vlei, especially in the Narrows, was filled with dark sludge. Now it has clean marine sand and an abundance of fish. This is due to good management, and specifically to Joshua Gericke’s input.

“Encouragingly, the transformation of Zandvlei from 1995 to now has been most amazingly good”
– Barry Clark, Anchor Environmental

As part of the classification study, reserve determination studies were done, which include water quality records. The present health of Zandvlei is classified as a ‘D’, about 50% degraded, and the best attainable state is advised as a “C”, given the pressures on the system. This is to acknowledge that the vlei will always have a large human component and cannot return to its natural state for a variety of reasons.

Improvement strategies included four scenarios (to be included in the Dream Zandvlei project):
1. Removing the weir
Removing the current rubble weir is desired for better tidal flow into the estuary. This is predicted to have a modest positive impact on water quality. The importance of water depth for recreational events are acknowledged, but Barry recommends that the weir be managed in a more dynamic way, similar to the mouth opening. It should be removed most of the time, for example in the week when people are less likely to be sailing. An option is to have a movable weir (like a sluice?). This would allow for (even) higher water levels when recreational activities take place, and extensive flushing more often per year, which would improve the water quality and reduce the silt buildup – it’s a potential win-win.
Another alternative to maintain a higher level constantly, especially for the rivets of the Marina da Gama residences is to install weirs where the Marina channels join the main water body.
One complicating factor is a sewer pipe that is currently protected by the existing rubble weir.

2. Restoring habitat
The area most requiring this is the shallow intertidal salt margin, which is currently lined with concrete. Rehabilitating this is not expected to really have an impact on water quality, but it would contribute to the biodiversity of the region.

3. Improving water quality
Difficult because of diffuse urban water runoff, but we spoke about the potential for biological means, biomass cultivation rather than chemical or physical means, – and the importance of harvesting the biomass as a means to remove the nutrients from the system.

4. Dredging
Dredging did not have a positive outcome in this study, but the scenario that was considered was a deep, 1.5m channel through the middle of the water body. The main function of this is to entrain more salt in the system to reduce the growth of invasive grasses. But, through modelling this is predicted to cause stratification in this channel of the more dense salt water, leading to hypoxic conditions.
In retrospect, however, Barry comments that dredging 0.5m everywhere rather than a single deep channel should still invoke a tidal prism allowing for better flushing. This, in combination with a re-think of the weir may yield better results, but needs more hydrodynamic modeling.
A point to mention is the potential impact of dredging on prawn stocks. Dredging sections over longer periods of time would allow the prawns time to adapt and move to new areas. “Artisinal dredging”. – See Port Owen’s set up in the Bergriver.

“The Zandvlei estuary has huge potential as a fish nursery and in terms of biodiversity once the system is restored”

Closing remarks touched on monitoring stations, linking to nutrient inflows into specifically the Westlake Wetlands. The City apparently has about 20 monitoring stations in the Zandvlei catchment. – listed in Candice Haskins’s presentation at the Estuary Management Workshop (notes at the feedback meeting). From Josh, this data gives an indication on the concentrations, but not the total flows and hence total amounts of nutrients incoming. Flowmeters could be a good project here.

We then briefly discussed rehabilitation of the Westlake Wetlands generally, and Barry noted that the city’s preference for the concrete canals is to reduce the risk of backflooding. But he agreed on the need to have the wetland meander to remove nutrients and design for sediment traps, as the sediment holds most of the Phosphorous. Barry agreed that the nutrient levels are a large potential risk, and agreed that if the larger plants (polymechetons??) are successfully removed, this opens up opportunities for algal blooms which are potentially more dangerous. The nutrients need to be captured into biomass and then removed from the system (harvested). If this can be done with economic yield, even better. Bernelle mentioned her work on wastewater biorefineries.

About the Dream Zandvlei Group

The Dream Zandvlei Group is an informal, collaborative collective of individuals working together to improve the Zandvlei Estuary and the catchment leading into it, with specific projects of personal interest, and independent of imposed mandates.

The current projects are mainly focused on installing litter traps in the Zandvlei catchment and promoting awareness of the Estuary through sport.

The core individuals represent several groups, and actively maintain communication between these groups:

The Zandvlei Trust  aims to conserve the indigenous fauna and flora of the Zandvlei and
to enhance this natural resource for the benefit of all  since 1988.

The Zandvlei Protected Areas Advisory Committee (ZPAAC) is a government mandated body and made up of groups and individuals with a common interest in the ongoing management of the vlei.



Dream Zandvlei: Meeting with Sarah Chippendale

Sarah was project manager of the Source to Sea project a year ago. We met on the 4th of March to talk about how her time there influenced what she would like to see in the Zandvlei catchment.

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Dream Zandvlei: meeting 16 February 2017


This is the minutes of a meeting that forms part of a series of conversations to take care of Zandvlei. In 2017 the plan is to develop a ‘dream’ of what all the various stakeholders want to see or experience in and around the Zandvlei Nature Reserve, and wider, the Zandvlei catchment. Towards the later half of 2017 and into 2018 this dream will then be interrogated with feasibility analyses and shaped into a plan. This is a highly participative, somewhat informal, dynamic process. If this interests you, please get in touch:

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