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Hydraulic Characteristics of
Fully Developed Flow in Circular Culverts

Nicholas Kehler

Throughout the world, particularly in water abundant countries such as Canada, water crossings are a significant part of the infrastructure system. For both financial and practical reasons, the majority of small to medium sized streams crossings will be designed with some type of culvert system. Since corrugated metal pipe (CMP) culverts are a reasonably inexpensive choice, as well as hydraulically efficient, they are a very appealing option to designers.

In order to ensure that the natural ecosystem is not adversely affected, culverts must be designed so that throughout the year fish can migrate upstream to feeding and spawning grounds without significant delay. Current design practices and regulations are based on the average velocity within the culvert and by comparing it to the prolonged swimming speed of the fish species present. In order to examine the validity of this approach, a physical modeling study was undertaken using a 0.8 m diameter circular CMP culvert with 68 by 13 mm annular corrugations.

It was found through analysis of the velocity measurements that there is significant cross sectional area below average velocity, and that gravel embedment further increases this area. In addition, through detailed analysis of radial velocity profiles, the distribution of shear stress along the wetted perimeter, and several fitted values, a technique was developed that produced very agreeable streamwise velocity predictions over a two dimensional cross section in the developed region.

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