Identification and estimation of ecologically relevant flow indices for non-perennial rivers, South Africa

Abstract

The importance of environmental flows and establishing the balance between hydrological response and ecological functioning of rivers has been globally recognised. Methods for determining environmental flows range from simplistic hydrological methods, to complex holistic approaches. Extensive research has been conducted to understand the dynamics of perennial rivers. However, non-perennial rivers remain among the least studied freshwater systems. Although these rivers only flow during certain periods of the year, these river systems are still of ecological significance. This study therefore aims to characterise the flow regime of non-perennial rivers in an ecologically meaningful way and to assess the spatial variation of these flow attributes. This study identified a subset of ecologically relevant flow indices that provided the opportunity to characterise the flow regime in an ecologically meaningful way, which was based on recommendations of previous studies. Redundancy analysis was used in the study to assess factors that account for the spatial variation of ecologically relevant flow indices of non-perennial rivers. The results identified that mean annual rainfall and the slope equalled or exceeded 90 % of the time were the only catchment characteristics found to be significant at explaining the variance of flow characteristics. The final objective of the study explored methods that can be used to predict flow characteristics in ungauged catchments. Most catchments around the globe are ungauged or poorly gauged, which is a core issue in hydrology.