Lake St Lucia: mathematical modelling and evaluation of ameliorative measures

Abstract

Connected to the sea by a narrow estuary, St Lucia lake is a shallow, generally saline water body situated on the sub-tropical east coast of northern Natal. The lake constitutes an internationally renowned nature reserve, rich in freshwater and marine flora and fauna. A popular tourist resort, it has great appeal to naturalists and scientists. With the advent of man, development of the catchments of the rivers feeding the lake has disturbed the delicate balance between the freshwater supply and evaporation losses. To an ever-increasing degree the system has now to rely on salt water from the sea to replace the water lost by evaporation. Consequently, during drought, salinities may rise to several times that of sea water, with dire consequences to the flora and fauna. The work reported in the paper was aimed primarily at establishing the effect of man's activities on the water level and the salinity regimes in the lake and, secondly, at selecting and testing feasible engineering measures aimed at preserving or enhancing the nature reserve environment. No attempt was made, however, to perform a benefit cost analysis of the lake system as a whole.