Zeekoevlei / Rondevlei Rehabilitation Study ... - Southern Waters

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Southern Waters Ecological Research and Consulting future aquatic health of the vlei would not only be immediately profound, but likely to be sustainable for a very long period of time. 4.4.5 Options for modifying the timing and rate of the drawdown procedure The present timing of the drawdowns at Zeekoevlei corresponds with the time of year when the water levels would naturally have receded. However, the current drawdown procedure suddenly exaggerates this cycle, but at a point towards the natural end of the low water period. This is not an ideal ecological scenario. Zeekoevlei, and to a lesser degree Rondevlei, provide very little in the way of shallow, exposed shorelines for migrant waders. By the time that the drawdowns are implemented, usually late-April, it is too late for wading birds to benefit. Furthermore, the shorelines of Zeekoevlei are rather abrupt, either bordered by reed beds extending into relatively deep water, or by houses and lawns extending to the water’s edge. These features also reduce the availability of suitable habitat for wading birds. A benefit of increasing wading bird populations would be additional predation on midge larvae and other aquatic invertebrates, a dynamic that is currently precluded by the present policy of water level management. The earlier implementation of a gradual drawdown process, i.e. by progressively reducing water levels by increments of approx 100 mm between November and April, such that the vlei is fully drawn down (1 m ) by the end of the process, would be a more representative simulation of natural events, and provide a greater range of habitat for birds. This process would further benefit from compositional restructuring of the certain of the reed bed areas to provide exposed or sparsely-reeded areas away from high recreational usage zones. In the case of Rondevlei, drawdowns should be timed so as to not connect islands to the mainland too early in the breeding cycles of birds. 4.4.6 Impact of the drawdowns on bird populations The drawdowns have invoked certain predictable responses in terms of the effect on bird populations. These have largely centred on increases in counts due to habitat provision (flamingoes) and food availability (pelicans). Other changes or influences have not been 22 Zeekoevlei / Rondevlei Rehabilitation Study: Action Plan
Southern Waters Ecological Research and Consulting discernible as a consequence of the absence of count data (Zeekoevlei), or the short study period (Rondevlei). It is, however, deemed likely that, should the proposed phased drawdowns be implemented, positive benefits will accrue to both vleis insofar as their bird populations are concerned. Recommendation 4: 4.1 Create or re-create deep water habitat areas in Zeekoevlei (existing basins) and Rondevlei (as desired) – see also Recommendation 2.1. 4.2 Continue to implement the annual drawdowns in a gradual and phased manner over a period of six months, and at an incremental rate of 100 mm per interval of 10% of the total drawdown period. 4.3 In conjunction with 4.2, restructure the vegetation of reeded areas of shoreline so as to enhance the quality of habitat for migrant wading birds. Zeekoevlei / Rondevlei Rehabilitation Study: Action Plan 23
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Zeekoevlei / Rondevlei Rehabilitation Study ... - Southern Waters

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