The Influence of Floodplain Vegetation Patches on Hydrodynamic Characteristics: A Case Study in the Old Course of Fuhe River

Abstract

As an important part of the river ecosystem, vegetation has a significant influence on hydrodynamic characteristics, water quality, river morphology, and ecological habitat. Combining vegetation survey with the verified numerical model, this study aims to analyze the impact of floodplain vegetation patches on hydrodynamic characteristics in the old course of Fuhe River under various combinations of incoming flow discharges, and flood diversion discharges, and changes in the land use type. The equivalent Manning coefficient was adopted to quantify the additional resistance induced by plants in the vegetation module of the numerical model. According to simulating results, vegetation patches would cause the water level to rise and velocity to decrease, which mainly affects the upstream of the old course of Fuhe River. And with the increase in incoming discharge, water level difference and velocity difference have an upward trend. It is also found that the resistance of Zizania latifolia to river flow is strongest followed by sugarcane, crops, and weeds because of the differences in vegetation characteristics. Furthermore, compared with existing vegetation conditions, converting farmland to Zizania latifolia and expanding farmland induce a moderate rise in water level upstream while the decreasing velocity happens in the area where land use type is changed. And there are areas where velocity increases located opposite to the velocity decreasing area because of the adjustment of cross-section velocity distribution caused by plants.