Estimation of Effective Roughness for Water-Worked Gravel Surfaces

Abstract

There is no accepted standard equation for predicting flow resistance in gravel rivers. This is mainly because of the lack of an effective approach for describing the roughness of the gravel surface. This paper aims at describing the roughness of gravel surfaces based on characteristics of the elevation field rather than conventionally used grain size distribution. A new parameter—the coarseness parameter—in addition to the steepness parameter and standard deviation of the elevation field is proposed for characterizing the roughness of gravel surfaces. Two groups of rough surfaces (A and B) were generated using unconditional Gaussian simulation to study the influence of the coarseness and steepness parameters on effective roughness. The effective roughness of groups A and B was calculated by a two-equation turbulence model, and a quantitative relationship between the effective roughness and proposed parameters was derived. The resulting relationship derived from groups A and B was validated using data from flume experiments (group C). The results confirm the dependence of the effective roughness on the proposed parameters.