Lessons from Fish Passage Waterways in Oregon and Factors for Improving Their Construction

Stream enhancement in Oregon is primarily focused on improving fish passage conditions. Oregon state law requires that hydraulic structures located in water properly provide fish passage. Increasingly stringent state and federal require fish passage designers to become more cognizant of hydraulic conditions over a range of flows to avoid expensive structural failure of hydraulic structures. These hydraulic structures may include culverts, bridges or roughened channels. Roughened channels are man-made stream channels utilized for retrofitting a hydraulic structure for fish passage when an existing hydraulic structure is structurally sound but deemed inadequate for fish movement through the passage. A variety of methods are utilized for the design of fish passages such as no impedance, geomorphic simulation, hydraulic simulation and hydraulic design. Mixtures of materials are used to construct the bed of roughened channels from fines such as sand, silt and gravel to coarse elements like cobble and boulders. Fines are a critical element in limiting permeability of the constructed bed thus keeping stream flow concentrated in the roughened channel during low flow periods. Our study focuses on the tendency for structural failure in roughened channels. The study goals are to determine the significant hydraulic design factors affecting the success or failure of roughened channels, particularly the loss of fines from the channel structure by examining actual fish passages in the region. Improving fish passages to enhance fish movement through the passage is a priority for government agencies such as Oregon Department of Transportation (ODOT) and Oregon Transportation Research and Education Consortium (OTREC) who have to use less funding more effectively.