Baffle designs to facilitate fish passage in box culverts: a preliminary study

Waterway culverts and road crossings are very common structures along water systems, ranging from rural roads to national highways and urban drainage networks. Present expertise in environmental hydraulics of culverts is deficient because of the many empirically-based design guidelines, which are sometimes outdated and often inadequate for fish passage. Engineers and biologists need better, more reliable prediction 'tools' during the design stages to compare the bio-engineering performances of a range of design options. In all the cases, the turbulence of the flowing waters must be optimized efficiently to maximize fish migration. This project focused on the development of simple solutions to retrofit existing box culverts, with the aim to maximize slow flow regions suitable for small fish passage and to minimize the afflux increase. Herein, a physical study of a standard box culvert was performed under controlled flow conditions, and six baffle designs were tested. Two baffle configurations presented promising results: the corner baffles and the streamlined diagonal baffles. The streamlined diagonal baffles assisted with the development of a large recirculation region immediately downstream of each baffle, with a moderate increase in afflux for a given discharge. The optimum design appeared to be the corner baffle system. It produced little additional afflux, while creating excellent recirculation both upstream and downstream of each baffle. However, further testing must be conducted to develop quantitative design guidelines and to assess the impact on real fish passage