Turbulence Characteristics of Flow in a Culvert with Sloped-Weir Baffles

The problem of culverts that block fish from freely moving up and downstream is becoming a critical environmental issue. Agencies often retrofit culverts with baffles to aid in fish passage, but little is known about the detailed flow characteristics within a baffled culvert. During August and September, 2005, fine-scaled measurements were taken at the Skookumchuck hatchery near Tenino, WA on the flow field inside a 6-foot diameter corrugated metal culvert fitted with sloped-weir baffles. The culvert was 40 feet long and set at a 1.14% slope, and the data were collected for flow rates 1.5, 2.0, 3.0, 4.0, and 8.0 cubic feet per second. Flow field measurements were collected using a Sontek acoustic Doppler velocimeter at 50 Hz. Preliminary data were used to understand the turbulence characteristics of flow within a culvert fitted with baffles, and to compare the flow field caused by sloped-weir baffles to experiments of other baffle types recorded in literature. It has been found that the turbulent kinetic energy (TKE) dissipates as the flow moves downstream from a baffle. At flows less than 3.0 cfs, the sloped-weir baffles cause higher TKE values on the left side of the flow (looking upstream) due to plunging flow. As the flow rate increases, the TKE becomes equal on both sides of the culvert, and are higher on the edges due to shear stress caused by the culvert boundary. The flow is also described using dimensionless discharge, and data from this experiment are compared to dimensionless discharge equations given by previous researchers. This research provides new information on the turbulence characteristics of flows within culverts retrofitted with sloped-weir baffles, and will be useful in recognizing which areas of the flow field could be too turbulent for fish passage.