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Abstract
The main objective of this study was to examine the hydraulic performance of knickpoint‐control structures (i.e., riprap weirs, grouted‐riprap weirs, baffled and non‐baffled fish ladders) to facilitate unimpeded fish passage. The hydraulic performance of these structures, located in Midwestern streams, was evaluated by determining the mean and turbulent flow characteristics in the vicinity of the structures via detailed field tests. Non‐intrusive mean flow measurements were performed using a 3‐dimensional sidelooking Flowtracker handheld Acoustic Doppler Velocimeter (ADV) and by utilizing the newly developed Large Scale Particle Image Velocimetry (LSPIV) technique. Non‐intrusive turbulent flow measurements were performed using a field ADV with a high sampling frequency. Results from the mean flow measurements illustrated that the mean flow depth (Y) and velocity (V) atop the structures were critical for evaluating the performance of the structures. In addition, the present study suggested that the (Y, V) should be viewed in conjunction with the drainage area (DA), slope (S) of the structure, and structure type. The DA size affected (Y, V) in the streams, S affected the power of the water action, and the structure type could cause flow acceleration/deceleration. Results from the turbulent flow measurements illustrated that the flow approaching the structures became 3‐dimensonal, while the size of eddies in the baffled fish ladder were found to disorient fish in the transverse direction due to sudden constriction. In short, the results presented herein illustrated that a complete assessment of the hydraulic performance of structures should include not only the conventional permissible criteria for (Y, V) but also the turbulent flow characteristics at the locations atop the structures.