Abstract
The ecological functioning of the Nyl River floodplain in the Limpopo Province of South Africa depends on water supplied by catchments which are experiencing continuing water resource development. Hydrological and hydraulic models have been produced to assist in future planning by simulating the effects of developments on ecologically relevant flooding characteristics. The models are applied here to predict the impacts of different development scenarios on the areal extent of suitable habitat for a key species, the Wild Rice (Oryza longistaminata), which can be characterised in terms of the depth, duration and timing of flood events. The results show that historical developments in the contributing catchments have already significantlyreduced the area suitable for Wild Rice growth, particularly in relatively dry years, and increased the likely dry period between flooding events. Dam construction on one of the tributaries would reduce the suitable area further in dry to average years and increase the inter-event dry period. Careful dam operation could ameliorate impacts in very dry years, however.
Highlights
The Nyl River floodplain in the semi-arid Limpopo Province of South Africa is an internationally recognised conservation area, supporting a large proportion of the breeding population of inland water birds in Southern Africa (Tarboton, 1991), as well as a wide variety of mammals, reptiles, fish and insects (Tarboton, 1987)
The impact on inundation frequency of suitable areas of the historical catchment developments (Scenario 2) compared with pre-development hydrological conditions (Scenario 1) is greatest for inundation areas less than 2.5 km2, where the reduction in frequency was as much as 56% for 2.3 km2
Hydrological modelling and one-dimensional hydraulic modelling can simulate the impacts of catchment developments on the hydraulic conditions in the Nyl River floodplain with sufficient resolution for meaningful ecological interpretations to be made
Summary
The Nyl River floodplain in the semi-arid Limpopo Province of South Africa is an internationally recognised conservation area, supporting a large proportion of the breeding population of inland water birds in Southern Africa (Tarboton, 1991), as well as a wide variety of mammals, reptiles, fish and insects (Tarboton, 1987). Impacts on suitable habitat areas relative to the pre-development (Scenario 1) and historically developed (Scenario 2) conditions are presented in Table 1 for typical wet (1995/96), dry (1991/92) and intermediate (1981/82) years, as well as the overall average impact.
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