HYDRAULIC EFFECTS OF COVERAGE WIDTH OF DOUBLE-LAYER VEGETATION ON OPEN-CHANNEL FLOWS: EXPERIMENTAL STUDY

Aquatic vegetation is an essential component of both urban and rural ecosystems. Investigating the effect of aquatic vegetation on water flow is an important topic in hydraulics since it affects hydraulic characteristics that provide rivers with many functions. Due to the complexity of the effect, previous researchers have explored the submergence, density, and arrangement of aquatic vegetation and established some models for predicting the velocity distribution of flow with vegetation. However, natural rivers have more complex aquatic vegetation conditions: the shallow region grows more vegetation, while the deep region has less vegetation. The change of vegetation cover in a channel can result in significant differences in the effect of aquatic vegetation on water flow. Still, such influence has not been fully understood in previous studies. This paper explores the impact of the coverage width of double-layer aquatic vegetation on the river flow. The experiments were conducted to understand the impact of different vegetation widths on the velocity and discharge distribution. The dowels of two heights were used to simulate aquatic rigid vegetation and lay partially on the bed of a water flume. The width of vegetation coverage was set at 50% to simulate different vegetation in a natural river. The mixed vegetation's flow depth was set under partial and full submergence conditions. The velocity at different positions was measured using a micro propeller meter, which enables the calculation of the discharge in different flow regions for comparison. The results of the experiments show that aquatic vegetation affects the velocity distribution and discharge in many aspects. In 50% covered conditions, the average velocity in vegetated zones is one-third of that in the free flow zone, and the vegetated zone discharge is about one-quarter of the whole flow discharge. These conclusions allow the establishment of analytical models to predict velocity distributions in different coverage.