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Water SA

On-line version ISSN 1816-7950
Print version ISSN 0378-4738


RIVERS-MOORE, NA; SCHULZE, RE  and  DAVIS, NS. A regional flow type classification for South African perennial rivers. Water SA [online]. 2020, vol.46, n.3, pp.383-392. ISSN 1816-7950.

Flow classification provides a statistically robust method of defining an expected range of variability for flow metrics describing frequency, magnitude, duration and timing of events. Here, we characterised reference mean daily flows for 1950-1999 for all 5838 quinary catchments of South Africa based on 150 metrics. Using a two-tiered approach, where sub-catchments were classified into similar flow types using principal components and cluster analyses, we defined 6 to 12 flow types for each of 8 hydrological regions reflecting rainfall seasonality. Redundancy between variables was 87% on average, so that site variability could be accounted for using 8-28 metrics. In general, flow volume metrics accounted for Axis 1 variability, while coefficients of dispersion had 1.8 times less leverage in Axis 2. With the incorporation into a spatial product and an associated database, this study provides a basis for defining statistically robust reference flow conditions for multiple flow metrics, against which current observed flows at specific sites may be compared.

Keywords : environmental flows; flow metrics; flow variation; regional flow assessments; spatial heterogeneity.

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