A Model Study of the Hydraulics Related to Fish Passage Through Embedded Culverts

Abstract

This aim of this research program was to provide a better understanding of the hydraulics of embedded culverts. The results of this research may provide support to improving the methods of culvert installation with respect to fish passage requirements. The overall objective of the research program was to quantify the hydraulic conditions, which included flow depths and velocity distributions, for at-grade and embedded culverts.

A physical hydraulic model study was conducted in the Hydrotechnical Laboratory of the Department of Civil and Geological Engineering at the University of Saskatchewan. A culvert with a length of 8 m and a diameter of 500 mm was studied. The culvert slope was set at approximately 0.75% for all tests. The tests consisted of a culvert that did not have backfill material or baffle structures placed within the barrel. Only part-full flow conditions were studied. The hydraulic conditions in the model culvert barrel were altered by using three invert placement configurations (at grade, 0.1D and 0.2D) and three discharges (50 L/s, 70 L/s, and 90 L/s) resulting in nine combinations of culvert invert placement and discharge. For each combination of placement and discharge, the following data were collected along the length of the culvert: velocity distributions within a cross-section of the flow at five locations; vertical velocity profiles along the centerline of the culvert at 10 locations; and flow depths along the centerline of the culvert at 17 locations.

From the results of the study, an embedded culvert has lower velocities than an at-grade culvert provided that the culvert diameter, culvert slope and discharge are the same. On the basis of the work done in this study, the mean velocity of the flow field decreased by approximately 15% when embedding the culvert 0.1D and 30% when embedding the culvert 0.2D. When the culvert was placed at grade, on average approximately 44% of the flow area was less than the mean velocity of the flow. When the culvert was placed at an embedment of 0.1D and 0.2D, on average approximately 70% and 98% of the flow field had a velocity less than the mean velocity of the flow corresponding to the at-grade conditions.