The nature of the fluid boundary layer and the selection of parameters for benthic ecology

Abstract

SUMMARY 1. The nature of flow structure close to a river bed is reviewed and suggestions made as to appropriate equations to apply to given hydrodynamic regimes. 2. It is emphasized that in natural rivers the laminar sublayer observed immediately above the bed in some experimental studies is completely disrupted for flows characterized by high turbulence levels. 3. Instead of resorting to direct topographical measurement of bed undulations, the roughness of the river bed also can be quantified using hydraulic data obtained from velocity profiles. 4. Ambuhl's experimental findings of 1959 underpin modern ecological research into the nature of the benthic boundary layer. Common misconceptions concerning Ambuhl's contribution are corrected and it is shown that his results only apply to certain prescribed hydrodynamic conditions. 5. The adoption of a consistent approach to describing the benthic boundary layer is to be preferred, so that diverse studies can be usefully compared.