Baffle Designs to Facilitate Fish Passage in Box Culverts: A Preliminary study

Waterway culverts and road crossings are very common design in water systems, ranging from rural roads to national highways and urban drainage networks. Engineers and biologists need better, more reliable prediction \u27tools\u27 during the design stages to compare the bio-engineering performances of a range of design options. 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hydraulics of culverts is deficient because of the many empirically-based design guidelines which are sometimes outdated and often inadequate for fish passage. In all the cases, the turbulence of the flowing waters must be optimised efficiently to maximise fish migration. This project focused on the development of simple solutions to retrofit of existing box culverts, with the aim to maximise slow flow regions suitable for fish passage and to minimise 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 baffles. The streamlined diagonal baffles assisted with the development of large recirculation region immediately downstream of each baffle, with a moderate increase in afflux for a given discharge. Based upon physical modelling, the optimum design appeared to be the corner baffle system. It produced little additional afflux, while creating excellent recirculation regions both upstream and downstream of each baffle. Further testing must be however conducted to develop quantitative design guidelines,and to assess the impact on real fish passage