Zandvlei Trust

SAND RIVER CATCHMENT FORUM

Speaker presentations from meeting on Tuesday 04 th October 2011.

Alien water weeds in the Westlake Wetlands by John and Sandra Fowkes.

The immediate focus of our story is about a water plant – water hyacinth, Eichhornia crassipes, a plant that arrived in South Africa in 1884. (How it got the name “squirrel” heaven only knows or even more puzzling, named after a Prussian official who died in 1856) However, there is a much bigger story of the challenges of assisting a whole system to work, the importance of collaboration between a whole range of partners, and given that we are dealing with a living system, always knowing that there is going to be yet another challenge.

1. How it began
Our interest in the Westlake wetlands is that we have lived there for 26 years and watched the changes with a mixture of delight, fascination, concern.

In the late 1980swe first noticed water hyacinth plants coming down the Keyser’s River. Just one or two individual plants floating along. We thought nothing of it. The summer winds then blew these plants up the Westlake River.

The hyacinth is a native of the Amazon. It is a very beautiful plant with dark green leaves and an upright spike of lovely mauve flowers. Because of this it attracted the attention of gardeners and then horticulturalists and has been transported for sale all over the world. It is easy to see how the water orchid – another name for it - seduced so many to want to have it in their garden ponds. Unfortunately water hyacinth grows prolifically in the absence of natural controls and has become a major problem in many parts of the world. But at the time that our story starts we did not immediately read the warning signs.

And then, suddenly, we had a major problem on our hands. Water hyacinth doubles in size every 38 days. By the early 1990s we had water bodies that were closed by a solid mat of weed.

These choked the Westlake and Keyser’s Rivers and were expanding into the Westlake Pond, the major body of open water around which the houses had been built.

In fact the weeds were so thick at one point that one family took two canoes, climbed out of the canoes and father and two sons crawled across the surface of the weed dragging their canoes and then got into the water under the railway bridge.

The City Council moved to address this problem and deployed the Kingfisher weed machine. We celebrated a clear water body.

But our celebrations were premature. The Kingfisher clears bulk weed but leaves behind many pieces in the reed beds along the sides of the water – remember that doubling in 38 days. We suddenly had a new infestation on our hands.
We tried clearing by hand but could not keep up with the growth.

We realized that we needed to act to avoid losing access to this water body and that the City was not going to be able to do the “hands on” constant clearing that was needed. Working through the Zandvlei Trust we mobilized resident’s in the area to develop “A PLAN”.

We had no money and although there was plenty of scientific expertise there was little experience of what to do.

2. The boon of booms
We decided to erect floating booms. These would need to be able to rise and fall with the water body, be able to cope with winds and be strong enough to hold back the weeds.

Where to start? Well one of the community members worked for Marine and Coastal Management. He knew that they had lots of old rope and damaged nets from their research work. So off to MCM – “oh yes, how much would you like? We are only too glad to be able to get rid of it”.

O.K. what about floats? The very nice fishing net floats were very expensive. Well there were lots of 2 liter cold drink bottles floating in the Zandvlei. So we launched a programme to collect used cold drink bottles.

Now how to keep the bottom of the nets down so the weed did not break free. The railways had recently been replacing cables along the railway line. Someone remembered that the used cables had been dumped into the vegetation along the side of the water. A search found several coils of heavy cable – ideal to be the weight along the bottom of the boom... These we recovered and added to our pile of components.

We then called a “boom party” inviting people living along the edge of the water to come and help us make up the booms. The booms comprised a sleeve of net at the top through which we ran the lengths of rope and then sewed the 2 titer cold drink bottles in place. Then along the bottom we sewed another sleeve in which the railway cable was enclosed. We now had booms which could be tied to the banks, floated on the surface and had a bottom edge which trailed on the bottom of the water.

An armada set forth and we installed our booms to hold back the weeds. They worked well. But we still had dense infestation of hyacinth.

One of the impacts of the mat of thick hyacinth was that if formed a barrier to birds and fish. It was a dead zone with no light and no air.

3. City actions
The City Council had realized that the weed presented a potential problem if it built up at the railway bridge and blocked up the flow of flood waters out into the main vlei.

An operation was launched where the rivers were cleared by means of the drag line (which lifted the hyacinth out of the rivers and swung across to dump it in the wetlands).

Another clearing project was launched but this time we were better prepared. One of the Kingfisher weed clearing craft was again brought across and put onto the Westlake Pond at a cost, we understand, of some R20 000. This then cleared the hyacinth and brought it to the end of Rutter Road from where it was collected and removed.

We realized we needed to compartmentalise the weed, i.e. create boomed off cells that could be cleared and then move on to the next area. The Nature Reserve staff put in substantial metal stakes that could be used to secure the booms to create these cells. After the Kingfisher came back in to do bulk clearing we had the booms to put in place to contain the small pieces of weed that were left floating. We then organized a flotilla of small craft to go out and “pick up the pieces”.

The impact of the clearing of the water bodies soon became apparent. Fish moved back in. With the fish came the fishing birds and the local fishermen. With the fish for food otters moved back in.

4. Background to the problem
The Zandvlei and the associated wetlands have undergone some radical changes. At the turn of the century the water body passed under the railway line and there was boating on the Westlake water body. Then the foundation of the railway line was hardened and a solid barrier was created between the main body of the Zandvlei and the wetlands.

The Westlake Wetlands were cut off from the main body of the Zandvlei when a solid base was created for the railway line from Cape Town to Simonstown. Prior to that the railway had been on top of a wooden structure and there was a free flow of water between the main body of the Zandvlei and the wetlands. Indeed there was an active boating club at the Blue Moon Hotel on the western side of the water body. When we first settled in Lakeside in the early 1980s the banks of the Westlake and Keyser’s Rivers were porous – that is they had numerous gaps and channels that fed from the main river flow into the surrounding wetlands. The banks of the rivers were covered in alien trees. These provided roosts for various groups of birds. Below the railway bridge there was a wooden pole barrier across the river which slowed down the water flow. We later heard that this had been used to help in water flow for irrigation canals. The effect of this was that the rain induced flood waters rose, flowed sideways into the wetlands and then drained away slowly through the railway bridge as the weather cleared.

With increasing suburban commercial and industrial development in the catchment areas surfaces were hardened and run-off increased. As we understand it, the City became concerned about the prospects of flooding and moved to “improve” the water flow. This led to clearing of the north bank of the Westlake River and the west bank of the Keyser’s River and the trucking in of land fill to create a surface track along which trucks and a drag line could travel. This track was extended into the pool west of the railway bridge to allow the drag line to “reach” for clearing purposes.

The effect was that the sideways seepage of water into the northern part of the wetlands stopped and the speed of the water flow in the rivers increased.

Today the Westlake Wetlands form a part of the Greater Zandvlei Nature Reserve in Cape Town. The GZNR is on the False Bay coast and the Zandvlei estuary is the only functioning estuary in the False Bay. As such it plays an important role in the breeding cycle of marine fish in the False Bay.

4.1 Catchment perspective
The Westlake Wetlands are fed by four sources of water – two river systems; subterranean flow and tidal back flow from the main water body. If we want to look at the problems of the wetland we have to look at the sources of the water that flow into it.

The logic of looking at the problem from a catchment point of view was to start at the top of the catchment and work your way down. The booms enabled a local group to make a significant difference on their local scale. It was treating symptoms and not the underlying cause but it showed the potential etc. etc.

The two river systems which feed the wetlands are the Westlake, which rises in the Silvermine Nature Reserve, flows through Pollsmore Prison, through the suburban area, under the Main Road and into its junction with the second river, the Keyser’s. The Keyser’s River rises just below the Elephant’s Eye cave on the Constantiaberg. It passes through the Tokai forest plantations. Here it is joined by tributaries that come from the wine farms and then into suburbia. It then passes into the business / industrial area of Tokai and down to the west of the railway line.

The two rivers join just before the railway line. There they pass under a railway bridge and flow into the main body of the Zandvlei. The railway bridge is quite narrow and has solid sides and a relatively high concrete sill at its base. As such it forms a “choke” on the flow of water into the main body of the vlei.

We will come back to the importance of these aspects later.

An unmeasured, but fairly major source of water flow into the Westlake Wetlands is the subterranean water flow from the Muizenberg Mountain, Silvermine, and Constantiaberg. The mountains that make up these features are frequently cloaked in cloud and water seeps down and into the wetland system.

The final source of water is a back flow that occurs when the mouth of the Zandvlei lagoon is opened and sea water comes in pushing water back into the system. The water flow into the wetlands is minimal. We have only once seen a flow back into the wetlands under the railway bridge. But the effect of the backing up of water in the main body of the vlei is to stop the outflow of water through the railway bridge and a consequent rise in the height of water in the wetlands. Because of a sand bank and the concrete sill at the railway bridge any water flow from the main body of the vlei will be fresh surface water as the salt water sinks into the depths of the main vlei.

This is quite an important component of the ecology of the wetlands as they are totally different to the main body of the vlei. The water is predominantly fresh water with only occasional periods of brak water from the salts carried in the subterranean water. This means a very different environment from that found in the main water body where salt water has an influence. This is particularly relevant when talking about invasive alien water plants.

5. Recent initiatives
In 2009, four things happened which changed the picture. One there was a concerted community effort to collect as much of the broken hyacinth as we could.

5.2 we made contact with Rhodes University. They have a Department of Zoology and Entomology Aquatic Weed Biocontrol unit. This was led by Prof Martin Hill with Dr. Julie Coetzee as Senior Research Officer. They were looking at biocontrol agents that could be used for invasive aquatic weeds. Martin Hill, Julie Coetzee and Dieter Schlange came to the Westlake and looked at what we were doing. They were then able to supply us with biological control agents not only for the hyacinth but for some other weeds that had arrived.

5.3 Working for Wetlands put in a team to help in hand clearing weed in the two rivers.

5.4 the Zandvlei Trust was successful in a fund raising application to the Peninsula Beverage Company, PenBev. They are the major bottlers of cold drinks in the peninsula and they were intrigued by the recycling use that we were making of their 2 liter bottles. The PenBev funds enable us to employ and train a young man to go out every month to do clearing of the hyacinth. These funds have been renewed for three years now and this contribution has had a major impact on the success of the project. Whilst volunteers still put in time being able to have a person on a regular scheduled programme has made a world of difference. So thank you PenBev.

Two amusing aspects of employing Michael Melikaya Mangwata. Michael knew nothing of boats. When he first started in a rowing boat he insisted in rowing stern first so that he could see where he was going! Then he fell into the Keyser’s and developed swelling and a rash. His medical certificate said “Fell into the water and drowned. Is allergic to salty water”.

What has been the result? The first signs of change were when we saw an increase in fishing birds, kingfishers, cormorants, darters etc. Then the fishermen were back on the banks. Otters and water mongoose then arrived.

As far as the hyacinth is concerned the wetlands are virtually clear of the weed. We had one major concentration in the central wetlands. We could not get into this area manually because of the density of the reeds and deep mud with shallow water. We boomed it off, put in the weevils and let them do their work. The results are impressive.

However, during the winter rains we have had fresh clumps of hyacinth coming down the Keyser’s River. We think we know the source and are now working to remove this infestation. Hyacinth seeds are viable for up to 20 years so now it is a question of going out and constantly checking for any new plants. By and large – between constant surveillance and with the help of the biocontrol agents we think we have the hyacinth under control.

6. Post hyacinth challenges
BUT. We mentioned earlier the course of the two inflow rivers. Both come through areas of farming, up market gardens and informal settlements. This means that they carry a high nutrient load. The hyacinth was doing an excellent job in taking out these nutrients. Remove the hyacinth and something else will take its place.

So we now have a whole suite of the bad invasive aquatic water plants in the wetlands – Parrots Feather Myriophyllum aquaticum, Red water fern, Azolla filiculoides, Kariba Weed, Salvinia, Water lettuce, Pistia stratiotes, Yellow hybrid water lily, Nymphaea, Water Cress, Nasturtium officinale.

But things have changed. The City now has an invasive species programme which is looking at the control of invasive alien plants. Fortunately there are biological control agents for several of the weeds we have in the system. These have been introduced and are having an impact on the weed population. This is, of course, an on-going initiative. The biocontrol agents beat back the weeds and then there is no food for them so they die out and the weed comes back. The biocontrol agents then have food so the population grows again and eats itself out of house and home. So there is a continuous pulse in the system. The Invasive Species Unit now has its own nursery for biocontrol agents in Cape Town so we are in a position to introduce them as and when they are needed.

The “Source to Sea Project” which looks to rehabilitating the water courses from Constantiaberg to the coast is now looking to a broader based approach to addressing problems of eutrophication and pollution. The Zandvlei Trust is actively participating in this as the Westlake Wetlands have been selected as a pilot site.

The Sand River Catchment Forum is creating a meeting place for key players to come together. The Zandvlei Trust ZIMP project is collecting important data to contribute to future management decisions.

The Zandvlei Advisory Group meetings enable interested and affected parties to express their views on the management processes in the Zandvlei.

A new Zandvlei Estuary Management Programme has been agreed.

Hopefully these programmes will give us a home in which the control of alien water plants in the Westlake Wetlands can be based. It is now an ongoing programme of watching, clearing and being vigilant.

7. The future    What’s different today?

• The lessons learned over 20 years

• The use of booms

• Funding from PenBev to employ someone +/- 3days per month

• Introduction of biocontrol agents

• Greater awareness of the problem of invasives, new institutions and initiatives.

We live in a dynamic environment. Because of the nutrient inflow plants will grab these nutrients and grow. If we want to create a natural water body with an appropriate plant level we must filter out those nutrients as close to their source as possible.

8. Conclusions

• There have been significant changes in thw weed density and species in the Zandvlei and its wetlands in the last 30 years.

• These changes are having a negative impact on the maintenance cost to the City and the recreational value of the water body

• Current management practices do not appear to be providing a long term solution to the problem

We need to recognize that we need to work at catchment level, treating causes not symptons

• How do we more effectively implement those things that are working?

• How can we stimulate a new way of addressing the problems – doing something different which is more cost effective and sustainable?

• Can we set up a process whereby we get user groups into free thinking workshops to come up with new ideas?