Characterization of Turbulent Open Channel Flow in a Full Scale Spiral Corrugated Culvert

Abstract

As part of a larger study of juvenile fish passage, a micro-Acoustic Doppler Velocimeter (ADV) was used to characterize the three-dimensional velocity and turbulence characteristics in a full-scale culvert with spiral corrugations. The culvert was set up in a test bed constructed to examine upstream passage success of juvenile salmon under various culvert conditions. The test culvert was 12.2 m long and 1.83 m in diameter, and set at a 1.14% slope. The corrugations were 2.54 cm deep by 7.62 cm peak to peak with a 5° right-handed pitch. Tailwater elevation was adjustable with a stop-log system and was set slightly above the water surface level at the culvert exit. Cross-sectional grids of ADV measurements were taken at discharges of 28, 57, 113, 227, and 453 lps at nine locations within the culvert barrel and just inside the headwater and tailwater tanks. Results revealed asymmetries in the velocity and turbulence distributions. These asymmetries caused a Reduced Velocity Zone (RVZ) on the right side of the culvert as seen looking upstream. Velocity and turbulence levels in the RVZ were found to be less than in mid channel or on the left side of the culvert, and the difference became greater as flow rates increased. Lateral and vertical velocity components were very small relative to the axial component, while lateral and vertical turbulence intensities were comparable to the axial component. Inlet loss coefficients were calculated as well and ranged from 0.32 to 0.42. Relationships between the average velocity and the velocity and turbulence intensity in the RVZ were developed, which may be useful for evaluating whether the barrel of a culvert is passable for juvenile fish. The RVZ could be beneficial to juvenile salmon during upstream passage.