In 2011 iSimangaliso publicised its strategy to let the uMfolozi River and Lake St Lucia rejoin in a bid to restore system functioning to close to its former state, prior to human intervention. This is a change from the practice of the last 60-odd years which has been to actively keep the uMfolozi and the Lake St Lucia system separate through the use of dredgers and the building of berms. This new strategy follows from new scientific findings and monitoring of the Lake system.
“New scientific work has highlighted the importance of re-establishing the link between the uMfolozi River and Lake St Lucia, and has shown that the risk of sediments to the health of the estuary has been overstated. By enabling the two systems to join, iSimangaliso is reversing a 60-year-old management approach which saw extensive manipulation of the Lake St Lucia estuary. Our ultimate aim in the restoration of Lake St Lucia is to protect iSimangaliso’s World Heritage Site without setting up a management regime that includes endless manipulation” says iSimangaliso CEO Andrew Zaloumis.
Since 1952 the uMfolozi River has been artificially cut off from the main system, which has reduced freshwater inflow to the lake. Combined with drought conditions, the St Lucia estuary mouth has remained closed to the sea for the best part of the last decade. This has resulted in St Lucia being unable to function as an estuary.
Following the adoption of the strategy and since the uMfolozi River was breached on the 5 November 2011 it has moved 330 metres. This northward migration of the uMfolozi Rver is a natural process that has been accelerated by a combination of high flows in the river from rainfall in the catchment and big seas generated by Cyclone Dando.
The uMfolozi mouth is now well positioned to re-join the St Lucia Lake system. iSimangaliso, together with Ezemvelo KZN Wildlife, has begun to facilitate the linking of the uMfolozi to Lake St Lucia, with the assistance of a tracked excavator and wheeled dozer. This entails the removal of old dredger spoil and marine sediments that have been deposited on the beach creating an artificial berm that deflects the uMfolozi River away from St Lucia. Heavy swells and rain such as those predicted for this weekend may assist with the re-joining process.
The spillway is being established as far west on the beach as possible. The route has been selected where a natural gradient exists on the beach between the uMfolozi and St Lucia systems. It is anticipated that this will allow the unrestricted flow of the uMfolozi into the St Lucia system. This is particularly important before the upcoming winter period when rainfall is low and it is possible that the uMfolozi mouth will close. The process continues to be carefully monitored by Park ecologists and GEF specialists.
The spillway will provide much needed water for the St Lucia system; lifting lake levels and contributing towards the longer term plan to restore the estuarine functioning of Lake St Lucia which will be of benefit to all users of the 70 km long system which comprises about 60% of South Africa’s estuarine resource. Restoring the link between the uMfolozi river and Lake St Lucia is necessary for this is to occur.
The management strategy is based on a scientific investigation and monitoring of the lake system scientific undertaken. Indicators such as rainfall and lake salinity are monitored regularly. St Lucia received a total of 803.1mm rain from October to date, with the highest monthly rainfall in November (237.9mm).
The rainfall has influenced the salinity levels in the Lake. The salinity level in the Narrows is maintained at a low level by the freshwater inflows from the uMpathe River and local catchment. Salinity in Charters Creek is less than a third of that of seawater. In contrast, the northern parts of the lake are experiencing hyper-salinities (i.e. above the salinity of the sea). This represents a reversed salinity gradient that is not normally found in estuaries.
This process is part of the iSimangaliso Wetland Park Authority’s development of long term solutions to improve the hydrological functioning of Lake St Lucia through the iSimangaliso/Global Environmental Facility (GEF) Project. The objective of the GEF project is to support key studies that improve knowledge of the Lake St Lucia system, and to select the best feasible option to restore estuarine function; and to implement the necessary interventions to achieve this.
For further information and updates on the GEF project please contact GEF@iSimangaliso.com.
Or visit www.iSimangaliso.com and download ‘Lake St Lucia: understanding the problem and finding the solution’.
Newsflash No.: 2012.02.29
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