*Civil and Hydraulic Englneering Department, Indian Institute of Science, Bangalore-12.
**University College of Engineering, Bangalore-1.
Experiments were performed on friction blocks with and without passages, and, with passages of different diameters in a horizontal, rectangular flume. The flow in the flume was supercritical throughout. It was observed that at higher upstream Froude numbers, rectangular blocks with larger diameter passages were better than the ones with smaller diameter passages, which in turn were more effective than rectangular blocks without passages. Similarly. at higher upstream Fronde numbers, wedges with convergent passages were found to be more effective than the ones with straight passages, which in turn dissipate more energy than the wedge without passages.
