Flow through Non-submerged Vegetation: a Flume Experiment with Artificial Vegetation

Vegetation growing in the water along rivers plays an important role on the hydrodynamic behavior, on the ecological equilibrium and on the characteristics of the river. It has effects on the flow resistance and, as a result, has a large impact on water levels. The influence of non-submerged vegetation on flow is not so clear as yet; it needs to be further studied. The Acorus Calmus L is a kind of typical non-submerged vegetation, it is widely planted in river, but few researches have been done on the effects of these plants on the flow. A laboratory experiment using artificial vegetation selected to simulate Acorus Calmus L, was carried out in a water flume to investigate its influence on flow resistance and velocity distribution. A flow resistance model based on concepts of drag is developed to evaluate the Manning’s (n) roughness coefficient for non-submerged vegetation. Experimental tests have shown that the relationship between flow depth and discharge depends significantly on the vegetation density and patterns. Manning resistance coefficient depends strongly on vegetation density and the depth of flow far more than in unvegetated channels; it increases with increasing water depth. Within vegetation, the mean velocity decreases with flow for which the vegetative roughness increases with decreasing velocity.