Boundary Effects of Uniform Size Roughness Elements in Two-Dimensional Flow in Open Channels

Tests were conducted to investigate the characteristics of the vertical velocity distribution in flow in wide channels with large relative roughness. The study was basically a two-dimensional investigation of the boundary roughness effects in turbulent flow. The investigation was conducted in a 48-ft-long, 2-1/2-ft-wide flume with 1/8-, 1/2-, 3/4-, and 1-in. crushed limestone and 3/4-in. concrete cubes as the boundary roughness. Results indicate that the root-mean-square value of the boundary roughness heights is related to the Nikuradse equivalent sand grain roughness and that the root-mean-square value can be treated as a roughness parameter for boundaries of densely spaced, irregular, randomly placed roughness elements of uniform size. Appendix A includes the experimental data. Appendix B describes the special instrumentation used for measuring the vertical velocity profiles within the flow.