Incorporating Floodplain Functions into River Restoration Engineering: The Role of Floodplain Vegetation on Channel-Floodplain Hydrodynamics

由于其在连接河流和陆地生态系统中的独特作用，泛滥平原为自然和人类系统提供了许多好处或服务，如洪水波衰减、污染物的生物地球化学减少和营养物质的转移。这些服务依赖于洪水事件期间河道和泛滥平原表面之间的水转移，也称为水文交换流。滩地植被在控制河滩水力和水文交换流量方面起着特别重要的作用，因此会影响许多滩地的服务和航道稳定。然而，大多数河流恢复工作很少考虑滩地植被的影响，因为我们没有充分了解植被对稳定恢复设计的水力控制，也没有充分了解植被对交换流量和滩地服务的影响程度。因此，这项研究的目的是加深我们对滩地植被对恢复的曲折河道中的水动力和对滩地服务至关重要的水文交换流量的耦合影响的理解。为实现上述目标，本研究的目标是完成以下核心目标：(1)推进与自然河床地形曲折河道动量交换相关的植被流水动力学的概念性知识；(2)研究滩地植被对滩面水文交换流的影响；(3)评价河滩恢复设计中河道水动力与滩面水文交换流的关系。这项研究将结合当地河流修复项目的特点，利用水槽实验和数值模拟相结合的方法来解决这些目标。通过水槽试验，系统地研究了滩地植被特征变化时，曲流河漫滩水流的水动力特性。水槽试验期间收集的水力学测量将被用来更好地了解滩地植被和河床形态对漫滩水流中和滩地水力条件的影响，包括二次流的分布、湍流特性和水文交换流量。水槽实验的结果将被用来为数值模拟提供依据。对科罗拉多州波德雷河的当地修复地点的实地数据的收集和分析将补充数字和物理实验。这项研究的工作将与柯林斯堡密切相关，该市已经花费近1000万美元对当地波德雷河进行修复投资，并制定了改造波德雷河的宏伟目标，以加强沿河自然和人类系统之间的联系。这项研究将通过参与许多当地的外展活动与利益攸关方接触，包括波德雷河艺术节和该市的“风景背后的科学”计划。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Because of their distinct role in linking riverine and terrestrial ecosystems, floodplains provide numerous benefits or services to natural and human systems, such as floodwave attenuation, biogeochemical reduction of pollutants, and transfer of nutrients. These services rely on the transfer of water between a river channel and floodplain surface during flooding events, also known as hydrologic exchange flows. Floodplain vegetation plays a particularly important role in controlling river-floodplain hydraulics and hydrologic exchange flows, and therefore can influence many floodplain services and channel stability. However, most river restoration efforts rarely consider the influences of floodplain vegetation because we do not adequately understand the hydraulic controls of vegetation on stable restoration designs nor the degree to which vegetation influences exchange flows and floodplain services. Therefore, the goal for this research is to improve our understanding of the coupled effects of floodplain vegetation on hydrodynamics in restored meandering channels and on hydrologic exchange flows that are important for floodplain services. To meet the above stated goal, this research targets accomplishing the following core objectives: (1) advance conceptual knowledge of the vegetation-flow hydrodynamics related to momentum exchange in meandering channels with natural bed topography; (2) investigate the influence of floodplain vegetation on hydrologic exchange flows on floodplain surfaces; and (3) evaluate relationships between channel hydrodynamics and hydrologic exchange flows on floodplain surfaces pertaining to river-floodplain restoration design. This research will address these objectives using a combination of flume experiments and numerical modeling that are linked to characteristics of local river restoration projects. Flume experiments will be conducted to explore the hydrodynamics of overbank flows in meandering channels while systematically varying floodplain vegetation characteristics. Hydraulic measurements collected during the flume experiments will be used to better understand the influence of floodplain vegetation and channel bedform on in-channel and floodplain hydraulic conditions during overbank flows, including distributions of secondary currents, turbulence characteristics, and hydrologic exchange flows. Results from the flume experiments will be used to inform numerical modeling. The numerical and physical experiments will be complemented by the collection and analysis of field data from local restoration sites on the Cache la Poudre River, Colorado. Work conducted in this research will closely involve the City of Fort Collins, which has already spent nearly $10 million on restoration investments on the local Poudre River and has large goals for transforming the Poudre to provide a greater connection between natural and human systems along the river. This research will engage with stakeholders by participating in numerous local outreach events, including the Poudre River Fest and the City's "The Science Behind the Scenery" program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.