Past work has not sufficiently integrated the sciences of hydrology and fisheries. Therefore, streamflow, sediment transport, and channel morphology were used to describe the present state of our knowledge of interactions between physical and biological (fishery) processes. These three physical factors (and certainly others) dictate both habitat quantity and quality for different life stages of fishes, and their inclusion in habitat assessments will enhance the quality of investigations. Interaction of the hydraulic and morphologic factors creates either dynamic equilibrium or disequilibrium. Indicators are given for determining the type of equilibrium condition. Thus, stream reaches in disequilibrium can be avoided for enhancement or channel stabilization projects. Neglect of the equilibrium condition increases the probability of failure of enhancement projects. Examples of enhancement measures and possible failures are described. Investigators are also urged to use additional hydrodynamic parameters, such as the Froude or Reynolds number, to quantify objectively the type of flow for improved mathematical–statistical analysis of fish–flow relationships. Land managers and researchers are encouraged to design future projects to improve our understanding of the very complex interactions between fish and their hydraulic and morphologic environment. Characteristics offish habitat must be modified with great care, and then only if (1) the causes for an undesirable condition are known and (2) the measures will be compatible with future stream development. In such an evaluation of fish habitat, the inclusion of hydrodynamic and fluvial morphologic variables should provide more precise quantification of habitat characteristics.
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Heede et al. (1990) studied this question.