A deeper understanding of river habitat-scale ecohydraulics: interpreting the relationship between habitat type, depth and velocity using knowledge of sediment dynamics and macrophyte growth

Late spring/summer depth and velocity conditions of 16 ‘functional habitats’ were investigated in lowland rivers. The habitats significantly associated with shallower, faster areas were 'submerged, fine-leaved macrophytes' (20-40 cm deep, >0.45 ms-1) and 'macroalgae' (10-30 cm, >0.60 ms-1). 'Cobbles' were associated with slightly slower, shallower conditions (0-20 cm, 0.45 ms-1), 'gravels' with slower conditions again (around 0.15 ms-1, depths from 0-30 cm). The slowest velocity class (0-0.05 ms-1) was associated with 'silt' (depths 20-70 cm), ‘marginal plants' (0-20 cm deep), 'emergent macrophytes' (10-80 cm deep), 'submerged, broad-leaved macrophytes' (40-110 cm deep), 'floating leaved macrophytes' (40-150 cm deep) and a second mode of ‘macroalgae’ (145-180 cm deep). The factors thought to be behind these findings are discussed.