The Rooi River, which runs through the Kingswood Estate in George, is being rehabilitated back to its natural state. Environmental integration is part of Kingswood’s development philosophy and the Rooi River banks and wetland areas are included in the rehabilitation programme.
When Kingswood Estate was started, the river was completely degraded and infested by alien vegetation, mainly in the form of Black Wattle, Pampas Grass and Bugweed. In some areas, the river could not be seen at all and at the onset of the rehabilitation programme, tests indicated hardly any life in it.
The rehabilitation programme being implemented by Hilland Associates and Cape Nature is in accordance with river health programmes, where badly degraded systems are restored to their former state of ecological health. This process recreates the natural riverine environment and allows indigenous vegetation to return by following Cape Nature’s guidelines for such programmes. Hilland Associates and the scientific services of Cape Nature have devised a programme for those sections of the Rooi River (and its tributary) which run through the estate. They are monitoring implementation of the process which covers the entire length of the river, wetland areas, the river banks and 40m beyond on either side – a total distance of approximately 3.25 km.
The process involves six steps:
- Removing the alien invasive species;
- Having a continual follow-up programme to remove the young alien seedlings (Black Wattle seedlings germinate at a rate of 3500 seedlings per m2);
- Removing all the debris within the river (logs, litter, tyres);
- Identifying areas where wetlands need to be created in order to reverse the erosion cycle which the river is in. This involves infilling the gulley erosion which is occurring;
- Creating a variety of riparian habitats along the river which will promote and support the various fresh water organisms required to help the river restore itself;
- Replanting the key indicator riparian plant species which will assist the natural process of plant succession (movement from pioneer plants to the climax plants).
Riparian channel free from alien vegetation in the foreground. The natural vegetation is returning to the channel. Alien vegetation regrowth is evident in the distance and will be removed as part of the fourth rotational follow-up of alien clearing.Section of wetland being created where previously a deep erosion gully occurred. This section of the river was totally infested by a black wattle forest.
The South African Scoring System (SASS) is a monitoring system devised to rapidly assess the quality of water within a river, thereby assessing its ecological status. This is being used to monitor the river health and works by sampling the river at various locations to determine the presence of aquatic organisms and insects. The presence ofdifferent insects gives an indication of the quality of the water, for example insects sensitive to pollutants will be absent in polluted water and present in clean water.
Six months into the rehabilitation programme, a marked improvement was noticed and it is expected that a full recovery will take place in approximately two years. Monitoring is ongoing.
River channel after extensive clearing of alien trees, logs and stumps. Rehabilitation of the riparian habitat is about to commenceRiver channel section after extensive clearing of alien trees, logs and stumps, with rehabilitation of the bank vegetation now well established. The far section show logs and stumps still blocking the channel. However they will be removed to allow for re-vegetation of this section. Small mammal and bird footprints can be seen in the deposited fines in the foreground.
Plant rescue nursery
Before construction started, a plant rescue nursery was established on site and indigenous plants which were present were collected to be replanted later. This was a condition of the EIA phase and the developers were obliged to train and employ staff to rescue the plants and establish the nursery.
To begin with, all Black Wattle trees were removed and to prevent destabilising the soil (which causes erosion), this was done by hand rather than by mechanical means. A local crew of eight people was specially trained in alien vegetation removal to do the work which entailed cutting down the trees and treating the stumps with herbicide to prevent regrowth.
Cathy Avierinos of Hilland Associated says:“Because seeds can remain in the ground for as long as forty years and indigenous plants grow slower and are less competitive than aliens, the follow-up phases of removing alien seedlings and saplings are critical. The young alien plants will be removed continuously until the indigenous vegetation has become well established and alien species no longer grow.
The importance of this is highlighted by the fact that in certain areas, an initial regrowth of as many as 3000 seedlings per m2 was counted. Substances that are biologically safe to other organisms are used to control areas of high density to prevent further growth. After the first germination of indigenous pioneer plants, intervention will again become necessary to remove weeds and any remaining alien vegetation.
In the wetland areas of the river, key species were planted to speed up the process of recovery. The forested areas along the river are being planted with indigenous species such as Yellowwood, White Stinkwood, Cape Chestnut, Ironwood and Milkwood trees. There are also fynbos areas being replanted with key fynbos species such as Ericas, Proteas and Restios. Some of these plants came from the rescue nursery.
Area below the gabions used to create the wetland shown in the previous photo. Here the previously eroded gully is being transformed to a section of rapids where additional habitat is being created within the water course. This will prevent the continued downward erosion of the river. The peat layer which would historically have formed the base of the river is clearly evident on the eroded banks. The erosion occurred due to the previous wattle infestation and the challenge is now to prevent continued erosion through this peat layer.Rapids – A section of well-established rapids where the erosion has now stopped and the banks are once again stable. These areas of fast flowing water through a rocky substrate provide valuable micro-habitats for the riverine invertebrates and pool sections between the rocky sections are suitable habitat for the re-introduction of the indigenous fish, Cape Galaxis.
Information for this article was provided by Hilland Associates, Odev Developments and Errieda Du Toit PR. Photos courtesy of Cathy Avierinos, Hilland Associates.
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