Design and Assessment Techniques for Fish Passage at Culverts and Bridges

Research at Washington State University is bringing together state-of-the-art and state-of-practice fish passage design criteria from across the nation — covering culvert and bridge installations or retrofits. A Federal Highways manual entitled Hydraulic Engineering Circular 26 "Design of Fish Passage at Bridge and Culverts" (HEC-26) will be the amalgamation of a comprehensive literature review, input from state departments of transportation, non-governmental organizations, and other interested parties. HEC-26 will include a compilation and comparison of design methods, culvert and stream assessment techniques, case studies, and design examples. The manual will provide a set of guidelines to any party interested in the design or retrofit of culverts and bridges to meet fish passage requirements, and is intended to streamline the design process. This paper presents a summary and comparison of design, retrofit and field assessment techniques employed to evaluate the barrier status of existing culverts. A number of alternatives have been developed for the design of fish-crossings, and although the exact specifications of each method vary from state to state, the overarching concepts remain the same. General methodologies fall into two categories, which meet the needs of most crossing structures: Stream Simulation and Hydraulic Design. The appropriateness of the design method is dictated by the level of stream-reach connectivity required and project budget. Fish passage assessment is essential to prioritize culvert improvement projects, and shows many similarities across the nation. The results presented within this paper will be used to shape the discussion of design procedure and culvert assessment techniques within HEC-26.