Experimental study on flow structure characteristics behind quasi-flexible vegetation patches

In river and wetland ecosystems, vegetation exerts diverse and complex influences on water flow. By altering flow structure and sediment deposition patterns, vegetation plays a crucial role in regulating and maintaining these ecosystems. This study investigates the interaction between quasi-flexible vegetation (inhabiting salt marshes and estuaries) and water flow through physical flume experiments, specifically examining flow characteristics downstream of vegetation patches. The primary focus is on the effects of lateral channel, submergence condition, and patch length on downstream velocity distribution, turbulence intensity, and deposition zones. The results reveal that: (1) Channel presence significantly impacts flow. For emergent channel-spanning patches, longer patch lengths result in less pronounced velocity reduction within the wake region. Bleed flow and associated sediment deposition zones do not develop under these conditions. Meanwhile, the turbulence intensity within the vegetation and velocity recovery regions is significantly higher than observed for emergent finite-width patches. (2) The submerged channel-spanning scenario exhibits a velocity structure distribution closely resembling that of the emergent finite-width scenario. (3) The length of the stable wake region for emergent finite-width patches depends on patch width, whereas for channel-spanning patches, it depends on patch length. (4) The flow-blockage effect of emergent channel-spanning patches is significantly enhanced, resulting in a correspondingly larger drag coefficient.