Author(s): Ngangbam Romeji; Zulfequar Ahmad; Nayan Sharma
Linked Author(s): Ngangbam Romeji Singh
Keywords: Macro-roughness; Boulder concentration; Uniform; Non-uniform; Energy dissipation
Abstract: Block ramps are a cost-effective assembly in river restoration projects to sustain river morphology. This experimental study determines the various energy dissipation factors with uniform and non-uniform (NU) configuration of boulders, with the objective to translate the dissipation of excess energy in the flow to minimize river bed aggradation or degradation. Semi-hemispherical blocks of 5 sizes representing boulders in staggered pattern is adopted on 3ramp slopes as it was established that this arrangement is more effective in energy dissolution than the row or random arrangements. Energy dissipation increases as the spacing decreases for various sets of uniform arrangements. NU configuration of the boulders has been so far not investigated by previous researchers. This study incorporates experiments on the NU configuration and it was found that energy dissipation is greater in NU configuration than uniform arrangement in majority of the test conditions and that alternate spacing inherits the flow accordingly producing quantitative loss of energy due to increased localized energy dissipation. An empirical relation has been developed incorporating the uniform and non-uniform configurations for evaluating the relative energy dissipation, in terms of length of ramp, ramp height, critical flow depth, boulder concentration, and coefficients representing the relative boulder configuration. The relation is found to hold good within the ± 5% deviation and may be conservatively used for formulation of design guidelines that can aid water resources engineers in practical applications of boulder block ramps for stream restoration works.
Year: 2020