iSimangaliso – Healing nature
11 Sep 2017
iSimangaliso’s bold management strategy is paying dividends. During a R65 million St Lucia Estuary restoration project, some 1.4 million cubic metres of dredge spoil have been removed and water levels in Lake St Lucia are at the highest level since 2002.
The Restoration story – in a nutshell
For 60-odd years, dredge spoil was artificially deposited in the natural course of the uMfolozi River by then conservation managers as it was thought that silt exacerbated from the canalisation of the uMfolozi River was the biggest man-induced risk to the 350km2 estuarine system.
In 2010, a multi-disciplinary research team drawing on independent peer-reviewed research was pulled together by iSimangaliso to concretise solutions towards resolving the acute hydrological problems facing the Lake St Lucia system. While silt is an issue, the science identified that the critical issue is fresh water and the uMfolozi River’s ability to act as the powerhouse that drives the natural process of the mouth. With support from the Global Environmental Facility and World Bank, iSimangaliso initiated this R63 million Lake St Lucia restoration project. (Note: A further R2 Million was subsequently added to the budget for work now in progress)
The health of iSimangaliso’s Lake St Lucia ecosystem is critical for some 80 000 people who use it extensively as part of their livelihood strategies. Tourism related directly to the Lake employs an estimated 8000 people locally. Income from iSimangaliso’s 510 000 visitors, 42% of whom are international, contributes some 7% to KZN Tourism GDP. The contribution to fisheries of the Lake St Lucia system is also significant locally, nationally and for Mozambique.
It is expected that over time with good river flows, the rest of the obstacle between the uMfolozi and Lake St Lucia Estuary will erode and wash out to sea, as it would have during floods. The removal of thorn trees off the remainder of the dredger-created ‘island’ is being done to assist this. “The scene is now set for Mother Nature to continue the rehabilitation process. Good rainfall will be a key driver,” says iSimangaliso’s Senior Manager Research and Planning, Bronwyn James.
According to Professor Derek Stretch of the Civil Engineering Department at the University of KZN, the mouth restoration work “is very significant and will enable us to reverse some of the negative impacts of decades of dumping dredge spoil in that area and facilitate the more natural functioning of Lake St Lucia Estuary. At the moment, with a closed mouth from the drought and as the first part of the restoration work is underway, we are very likely in a sediment accumulation phase. This is however only the short term view, because once we enter a period with more rainfall, floods and tidal flushing associated with an open mouth this will result in a net loss of silt from the estuary.”
“While we have completed the main rehabilitation, the story of Lake St Lucia is far from over – a further R2 million of restoration is currently in process and includes the removal of stands of thorn trees. This is expected to increase the erodibility of those areas during floods, which will in turn assist the natural processes that shape the morphology of the mouth area. Casuarina trees between the uMfolozi River and the Lake St Lucia Estuary are being removed as these obstruct the flow of water,” says Bronwyn James.
The examples shown from the 1984/87 floods are good illustrations of the problems caused by casuarina trees. Estuarine ecologists recommend that the remnants of that flood control levee should also be removed or flattened to allow unencumbered flood flows and facilitate their role in reshaping the area. The late Dr Nolly Zaloumis, whose speciality was wetlands, was on the Board of the Natal Parks Board at the time of Cyclone Domoina and reported that the impact of these casuarinas contributed to the northern side of the Maphelane dune – which is the highest forested coastal dune in Africa – being eroded during the floods.
Rainfall and water levels
Water levels are measured at various stations within the estuary and are included in the plot below. Water in the Narrows is around Mean Sea Level and the higher levels in the Narrows have supplemented the southern lake levels. Despite the dryness of winter, water even remains in the northern parts of the estuary with North Lake, False Bay and the Wilderness water quality stations all registering some water depth.
The salinity remains low reflecting conditions that developed after the onset of the 2016/2017 summer rains and most of the system has remained fresh through to the beginning of September 2017. The exceptions are slightly elevated salinities in the northern parts of the system which remain below that of half seawater (below 15). These brackish water conditions are ideal for Macrobrachium spp, brackish water shrimp which require these conditions for hatching and larval development prior to upstream migration to freshwater. These are now being found in numbers in the northern parts of the estuary where these favourable conditions are currently occurring.
Since the closure of the estuary mouth in 2002 the estuary has only had connection with the marine environment intermittently; once in 2007 after the large surf associated with the March 2007 storm surge carved its way through the sand barrier and again during 2012-2014 when the mouth opened naturally after heavy rains. Estuarine functioning will continue to be impacted until a more natural mouth dynamic is set up but it is anticipated that the movement of the uMfolozi after the completion of the restoration activities and the development of higher summer flows will begin to effect these changes.
Another action taken by iSimangaliso in preparation for the anticipated opening and northward movement of the mouth, once good rains fall in the catchment is the imminent removal of old ablution facilities and casuarinas at the Estuary beach along with the relocation of the vehicle/boat access ramp to its new ecologically suitable position at Ingwe Beach. The new ramp has been constructed and will be commissioned shortly. This work forms part of 14 planned St Lucia Estuary precinct projects for which the Environmental Impact Assessment Record of Decision is now in place. The projects include upgrades from Sugarloaf campsite to and including the St Lucia Ski Boat Club. A larger picnic area, new facilities, improved access and parking are in the plans. Construction will start shortly.
A first for South Africa
For the first time, real-time monitoring is to take place in the Lake St Lucia Estuarine system. “This is a huge step forward for management and research,” says Estuarine Ecologist for the rehabilitation iSimangaliso project, Nicolette Forbes. Monitoring was previously done once a week in person – a labour and time-intensive process. The real-time monitoring of the Lake St Lucia system has been put in place and tested over the past 24 months. In addition to managers and eco-advice, it will be made available to scientists and researchers who are doing work with iSimangaliso on the estuarine system. This telemetry system automatically collects physico-chemical data from points and transmits them to receiving equipment for monitoring. Observing the changes in the physico-chemical parameters of the estuary and lake is intended to support the tracking of the state of the system, including the restoration process.
Eight stations are distributed along the Lake St Lucia estuary to measure water level, salinity, water temperature, specific conductivity and pH, with four of these probes also measuring dissolved oxygen and turbidity. The stations provide real-time data on these parameters, uploading the data to a website via a cell-phone signal approximately every 15 minutes.
“The restoration of the Lake St Lucia Estuary mouth is the culmination of pro-active leadership and good hard science along with extensive consultation – an excellent synergy between natural and social sciences,” says James.
Socioeconomics of Lake St Lucia
The health of the Lake St Lucia ecosystem is directly linked to the livelihoods of people in the area. The Park is situated in the uMkhanyakude District Municipality, one of the poorest and most underdeveloped local authorities in South Africa. Over 80% of households live below the poverty line and only about 16,5% of the population is formally employed. Some 80 000 people living in 15 000 households within 15km of the Lake St Lucia estuarine system and use the system extensively. Harvests of raw materials, particularly estuarine sedges, is estimated to be worth around R7,5 million a year. The contribution of the estuarine floodplain areas to livestock grazing is estimated at R3,6 million per year.
Tourism related to iSimangaliso’s Lake St Lucia area creates an estimated 8000 permanent jobs. There are about 510 000 visitors to the study area per annum, of whom 42% are foreign visitors, that spend R46 million on an estimated 157 000 tourism activities from local operators.
The contribution to fisheries of the Lake St Lucia system is also significant. Of the 155 fish species have been recorded in the St Lucia estuarine system 71 species use St Lucia as a nursery area and at least 24 of these are important in marine line fisheries. During the extended period of closed-mouth conditions from 2002 to 2012, there was virtually no exchange of fish between the estuary and the marine environment. Recruitment failure due to drought conditions and the closure of the St Lucia estuary mouth from 2002 to 2012 resulted in collapse of the Thukela Bank prawn fishery. Similar losses were experienced in other fisheries, for example, R19.3 million in 2009/10 loss from shore angling fishery and R1.06 million loss in the commercial line fisheries at the same time due to reduced estuarine functioning of the Lake St Lucia system.
For media enquiries and photographs contact Bronwyn Coppola on 083 450 9111 or email@example.com.