Study Of The Flow Through Non-submerged Vegetation

Vegetation along rivers plays an important role on the hydrodynamic behavior, on the ecological equilibrium and on the characteristics of the river. It produces high resistance to flow and, as a result, has a large impact on water levels in rivers. The vegetation growing in the water has affects on the turbulent structure such as the mean velocity profiles, the Reynolds stress and the turbulence intensity distributions. For flow of water through nonsubmerged vegetation, previous investigations show different results. Hence, the effect of nonsubmerged 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 or wetland because of its function of improving water quality and economy. But few researches have been done on the effects of theses plants on the flow. In this research, the Acorus Calmus L is chosen to model vegetation to study its effects on water flow.An experimental study using artificial roughness selected to simulate Acorus calamus L, and four densities, has been conducted to investigate its influence on the flow resistance and structure. A simplified model based on drag concepts is developed to evaluate the roughness coefficient for unsubmerged vegetation.Experimental tests have shown that the relationship between flow depth and discharge depends significantly on the vegetation density and patterns. The water depth increases with increasing density. 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. An increase of the vegetation density leads to reduce cross sectional area and increases flow resistance.The velocity increases in the stem zone of the grass, and decreases in the leaf zone, for the four patterns, as demonstrated by experiments. The mean velocity decreases with flow for which the vegetative roughness increases with decreasing velocity. The presence of foliage significantly reduces the mean velocity. Within the vegetation, turbulence intensity distribution is anisotropic, the Reynolds stress is relatively small, and hence vertical turbulent transport of momentum is negligible.