Hydraulic characteristics of embedded circular culverts

On small rivers and streams, culverts are the most common form of stream crossing in Manitoba. However, conflicting interests arise between the need to balance economical installations with proper stewardship of our aquatic resources, most notably fish and fish habitat. Current models intended to ensure that culvert installations include proper consideration for fish passage are based on conservative average velocity criteria because there are currently no methods to adequately predict the velocity distribution in culverts. Therefore, this report details a physical modeling study to investigate the flow characteristics of circular corrugated structural plate (CSP) culverts with 10% embedment and projecting end inlets using a 0.62 m diameter corrugated metal pipe under a range of flows (0.064 m3/s to 0.254 m 3/s) and slopes (0%, 0.5% and 1.0%).;An automated sampling system was used to record detailed velocity measurements at cross-sections along the length of the model. The velocity data was then used to develop isovel plots and observations were made regarding the effect of water depth, average velocity, boundary roughness and inlet configuration on the velocity structure. Strong trends were observed when the percent flow area was related to velocity suggesting a regression based velocity prediction method may be feasible. The distribution of shear velocity and equivalent sand roughness was measured and the Manning's roughness coefficient of the model was determined. Existing methods to predict bed roughness and composite roughness were evaluated using the measured water surface profiles. Simulations made using HEC-RAS were found to agree well with model results although inlet losses were underestimated by an average of 9%. An analytical method was used to estimate an 11% reduction in maximum discharge caused by 10% embedment with a rough gravel bed.;Based on a review of existing literature and model results, recommendations are presented to focus future research and to highlight areas where a better understanding of the velocity structure in culverts may lead to design improvements for fish passage.