Author(s): Matthew Lueker; Omid Mohseni; John S. Gulliver; Nathan Cox; Harold Huff
Linked Author(s): John S. Gulliver
Keywords: No Keywords
Abstract: Stepped spillways present some advantages over the traditional spillway, including reduced downstream stilling basin dimensions and less tendency for cavitation damage on spillway and basin surfaces. A 1:26 Froude scaled model of the proposed stepped spillway and stilling basin at the Folsom Dam was constructed and tested at the St. Anthony Falls Laboratory. The stepped spillway follows a 610 meter long 2% sloped chute. The physical model was 40.2 meters long and 2.74 meters wide with a discharge in excess of 2.59 m3/s for the probable maximum flood (PMF) condition. One objective of the model study was to estimate the boundary layer development length along the spillway. Our approach was to measure boundary layer development length on the model, then use the information to calibrate a generic form of an internal boundary layer growth equation due to a step change in roughness. The equation was then applied to other discharges on the model. The dynamic roughness was found to be 0.24 times the tangential step height using the velocity profiles. This is in general agreement with literature (Kondo, 1986). Artificial roughness was also used to shorten the boundary layer development length. Three different roughness enhancements were tested: 1) added roughness elements on the spillway steps, 2) added roughness elements in the chute upstream of the spillway, and 3) both nos. 1 and 2. Added roughness elements in the upstream chute were almost as successful as the combination of elements in the chute and on the steps. Adding roughness elements on the spillway steps alone was not as successful at decreasing the boundary layer development length.
Year: 2009