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Socio-ecological system management of the lower Phongolo River and Floodplain using Relative Risk Methodology.

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Abstract

The construction of the Pongolapoort Dam in the Phongolo River started in 1960 with the purpose to supply irrigation water for the proposed sugarcane and cotton plantations in the adjacent floodplain, the Makhathini flats. The floodplain of approximately 10 000 ha increases in size to 13 000 ha at full inundation. The floodplain extends to the confluence of the Phongolo and Usutu Rivers in Ndumo Game Reserve (NGR) up to the border with Mozambique. Ndumo was proclaimed a game reserve in 1924 with the primary objective of strict protection of its biodiversity. Today, NGR is a RAMSAR site because of its unique wetlands. Surrounding the NGR is communal areas that are heavily dependent on resources from the floodplain. However, the environmental sustainability of the floodplain has been questioned over time. Following an earlier ecological study of the floodplain system it was suggested that the ecosystem infrastructure of the Phongolo floodplain are maintained through controlled flood releases that were introduced to simulate the flood regime prior to the construction of the dam wall. The controlled flood releases were required to mimic the annual inundation of the floodplain. Although there are proper protocols for water releases it seems to be ignored and therefore not in accord with ecological needs. The environmental flow requirements to maintain the physical and chemical structure, biodiversity, ecosystem processes and functions in the Lower Phongolo River and floodplain may therefore not be met.