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St Lucia 2001 to 2012: A Decade of Drought
Expanded Title:This document is a record of the impacts of the 2001 - 2012 drought on the St Lucia estuarine system. In addition to documenting the impacts of the drought on the estuarine system, details of the management interventions are provided. In 2000 rainfall in the catchments of Lake St Lucia was above average, and the rivers entering the lake were flowing strongly, the St Lucia mouth was open, and salinity in the system was low. Water levels were high, boating was easy and angling was good. Two years prior to this the area had been awarded World Heritage Site status in recognition of its global status as a superlative natural area. Then the situation changed. Below average rainfall was recorded, most years, for the period 2001 to 2012. There was little flow in the rivers, and the St Lucia mouth closed but the authorities decided against dredging it open. This was a controversial management decision. The cumulative freshwater deficit manifested as lowered water levels and hypersalinity. There were a number of physical changes. Large portions of the St Lucia lake bed dried and estuarine fish died off with little opportunity for them to recruit from the sea. With the lack of competition, the Tilapia populations increased exponentially. So much so that thousands of Great White Pelicans were consuming an estimated 15 tonnes of these fish each day during peak periods. Groundwater seepage along at least 40 km of St Lucia’s 400 km of shoreline supported a rich groundwater-dependent vegetation, and in other areas there were large ‘fields’ of succulent salt-marsh. New areas of reed beds lined the Narrows and the mangroves were still healthy. However, in the northern part of the lake, where salinity was at its highest, the food chain was reduced to a simple form with only few species and characterised by a bloom of orange-coloured cyanobacteria. In March 2007 there were extreme high seas, caused by the coincidence of very high tides, storm surges and the influence of Cyclone Gamede. The St Lucia Mouth was breached and stayed open for six months before closing naturally. At this time a large quantity of seawater flowed into St Lucia, raising water levels and introducing salt. Since 2008, management experimented with small-scale linkages of the Mfolozi River via the Back Channel – a disused channel excavated in about 1970. This proved to be a highly successful management intervention, albeit only at a small-scale. In March 2012 Cyclone Irina brought a lot of rain to St Lucia, but not to the inland catchment areas. In July 2012 a canal to link the Mfolozi along the beach into St Lucia was opened. Then, from early September 2012, heavy and consistent rains caused the rivers to flow and the drought to break. For the first time in many years all the rivers entering St Lucia carried water .The Mfolozi River overtopped into the abandoned Link Canal bringing huge quantities of freshwater into St Lucia. The water level in St Lucia increased by more than a metre by late 2012 and salinity levels dropped. St Lucia still has a shortage of freshwater and controversy about management continues. A project funded by the Global Environment Facility (GEF) is currently underway to assess the situation and to make recommendations about various long-term options. Areas of concern that require investigation include freshwater supply, altered water quality, accelerated sedimentation, alien invasive species as well as the effect of increasing human activities in the catchment.
Date Published:01/10/2013
Document Type:Research Report
Document Subjects:Water Resource Management/IWRM - Planning and development, Water Resource Management/IWRM - Water Governance, Ecosystem - Biodiversity protection
Document Format:Report
Document File Type:pdf
Research Report Type:Technical
WRC Report No:TT 576/13
ISBN No:978-1-4312-0475-5
Authors:Taylor RH
Project Leader:Taylor R
Project No:K8/1011
Originator:WRC
Document Size:13 092 KB
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