Environmentally significant morphological and hydraulic characteristics of cobble and boulder bed rivers in the Western Cape

[摘要] ENGLISH ABSTRACT:The interaction between moving water and the physical attributes of a river, as displayed bythe channel morphology, determines the availability of physical habitat for aquatic speciesand thus also the condition of the ecosystem. As such, the environmental flow assessmentprocess requires knowledge on how changes in the flow regime will affect both themorphological and hydraulic conditions within a river channel. With the increasingdevelopment of water-related infrastructure in mountain regions, knowledge of themorphological and hydraulic characteristics of rivers in the upper catchment areas is veryimportant. Cobble and boulder bed rivers in the Western Cape are typical examples. They arecharacterized by steep gradients, great variability in sediment size and relatively low flowdepths. The bed configuration contains a series of pools, steps, rapids, riffles and plane beds,while energy losses are high as a result of turbulence and hydraulic jumps. Due to their widerangingmorphological and associated hydraulic attributes, the physical habitats within theserivers are extremely diverse, both on a spatial and temporal scale. This study addresses theinteraction between moving water and the physical attributes of cobble and boulder bedrivers. Empirical, semi-empirical and theoretically based models are developed which definethe hydraulic and morphological related characteristics of environmental flow components incobble and boulder bed rivers. They cover macro scale channel deformation, the scouring ofsand from the interstitial spaces between the cobbles as well as velocity-depth relationships,which prove to be key components in the assessment of environmental flow requirements incobble and boulder bed rivers.

[发布机构] Stellenbosch University