Table 3. Some possible links between flow categories and ecosystem functioning in Western Cape rivers, South Africa. Flow category Ecosystem link Dry-season low flows Maintain perenniality and thus wet habitat for survival of aquatic species, trigger emergence of some insect species Wet-season low flows Maintain wetbank vegetation and fast-flow habitat Intra-annual flood 1 Trigger fish spawning in mid-dry season, flush out poor-quality water Intra-annual flood 2 Trigger fish spawning in early dry season, flush out poor-quality water Intra-annual flood 3 Sort sediments by size, maintain physical heterogeneity, flush riffles, scour cobbles Intra-annual flood 4 Sort sediments by size, maintain physical heterogeneity, flush tree seedlings from edge of active channel 1:2 yr flood Maintain tree line on banks, scour out sedimented areas in active channel 1:5 yr flood Maintain lower part of tree/shrub vegetation zone on banks, deposit sediments in riparian zone 1:10 yr flood Maintain channel, reset physical habitat, maintain middle part of tree/shrub zone ≥1:20 yr flood Maintain channel, reset physical habitat, maintain top part of tree/shrub zone