ENVIRONMENTAL HYDRAULICS OF LARGE WOODY DEBRIS IN STREAMS AND RIVERS

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