ENVIRONMENTAL HYDRAULICS OF LARGE WOODY DEBRIS IN STREAMS AND RIVERS

Although awareness of the habitat value of large woody debris in streams has promoted a more environmentally sensitive approach to its management, present guidelines are Largely intuitive and do not contain advice for conducting quantitative hydraulic investigations. This review of the literature provides information to assist management, and highlights deficiencies in current knowledge. Hydraulically, debris act as large roughness elements that provide a varied flow environment, reduce average velocity, and locally elevate the water-surface profile. This can significantly increase flood travel time. The significance of debris is scale-dependent. For example, the hydraulic effects are often drowned out in a large flood on a large river. Some hydraulic models can be used to predict the effect of debris removal or reinstatement. A challenge for research is the development of a hydraulically and biologically meaningful definition of debris geometry that can be readily used in the field. When more is known about the physical and biological significance of debris in rivers, a detailed cost-benefit analysis on its management should be undertaken.