The role of in-channel aquatic vegetation on hyporheic exchange

河道内植被（IAV）是以藻类或植物的形式广泛存在于河道中的一种植物。它提供了许多重要的生态和水文形态功能，并正在成为河流恢复的主要工具。对IAV的研究主要集中在泥沙输移和水流阻力方面，而忽略了它在诱导潜流交换中的作用。潜流交换是连接河流与河床的主要过程，其方式是通过充当地表水与地下沃茨之间界面的潜流带HZ，使河流中的水进出河床沉积物。高海拔地区促进重要的生物和化学过程，影响河流和河床沃茨的质量。因此，模拟由于IAV导致的潜流通量将为提倡种植的河流恢复实践提供关键信息，这是一个每年10亿美元的行业。此外，潜流交换和过程的预测是必不可少的量化溶质运输和转化沿着溪流和河流。因此，本研究的目标是模拟由于IAV的潜流。这将提供一个基本的和预测性的理解的过程，控制由于流动和IAV相互作用的低流交换。它将促进根际附近的潜流流场的知识，沉积物的区域直接影响根分泌物和相关的土壤微生物和模拟溶质，养分，污染物和病原体运输的能力沿着流网络，包括IAV的影响。在这个项目中开发的模型将被用来预测在溪流与植被的潜流过程，并将被纳入流域尺度的溶质和营养物质的传输模型。将开发一个新的变革性课后计划，通过实践活动和使用移动的教育水槽的课程，向5 - 6年级的学生介绍STEM学科。此外，本科和研究生土木工程专业的学生将接受培训。该项目的科学目标是机械地理解，量化和模拟IAV对潜流交换的影响，作为IAV密度，斑块大小和斑块分布在不同流动条件下的函数。IAV将被认为与三个schematizations：1）流量和一个单独的挺水和沉水植被干之间的相互作用，2）流量和一个单一的沉水植被斑块之间的相互作用，和3）流量和多个沉水植被斑块之间的相互作用。这将解决与新的示踪剂试验水槽实验，耦合匹配指数反射，粒子图像测速，分析和数值模拟，并通过测试三个具体的假设：（1）IAV密度、（2）IAV斑块大小、（3）IAV斑块大小、（4）IAV斑块大小、（5）IAV斑块大小、（6）IAV斑块大小、（7）IAV斑块大小、（8）IAV斑块大小、（9）IAV斑块大小、（10）IAV斑块大小（3）多个密集IAV斑块覆盖河床的百分比。

In-channel vegetation, IAV, is ubiquitous in watercourse as plants or algae. It provides many vital ecological and hydromorphological functions and is becoming a major tool in river restoration. Research on IAV has chiefly focused on sediment transport and flow resistance, while its role in inducing hyporheic exchange has been neglected. Hyporheic exchange is the main process connecting streams with streambeds by moving in-stream water in and out of the streambed sediment through the hyporheic zone, HZ, which serves as an interface between surface and ground waters. The HZ promotes important biological and chemical processes, which affect the quality of both stream and streambed waters. Consequently, modeling hyporheic fluxes due to IAV will provide key information for river restoration practices in which planting has been advocated, a $1B per year industry. Additionally, predictions of hyporheic exchange and processes are essential to quantify solute transport and transformation along streams and rivers. Thus the goal of this research is to model hyporheic flow due to IAV. This will provide a fundamental and predictive understanding of the processes that control hyporheic exchange due to flow and IAV interaction. It will advance knowledge on hyporheic flow field near the rhizosphere, the region of sediment directly influenced by root secretions and associated soil microorganisms and the ability to model solute, nutrient, contaminant, and pathogen transport along stream networks by including the effect of IAV. The models developed in this project will be used to predict hyporheic processes in streams with vegetation and will be incorporated into basin-scale transport models of solute and nutrients. A new transformative after school program will be developed to introduce 5th-6th grade students to STEM disciplines through hands-on activities and lessons with a mobile educational flume. In addition undergraduate and graduate Civil Engineering students will be trained. The scientific goal of this project is to mechanistically understand, quantify, and model the effects of IAV on hyporheic exchange as a function of IAV density, patch size, and patch distribution under different flow conditions. IAVs will be considered with three schematizations: 1) interaction between flow and an individual emergent and submerged vegetation stem, 2) interaction between flow and one single submerged vegetation patch, and 3) interaction between flow and multiple submerged vegetation patches. This will be addressed with novel tracer test flume experiments, coupling Matching Index Reflectometry, Particle Image Velocimetry, and analytical and numerical modeling, and by testing three specific hypotheses: hyporheic exchange has an inverse U-shaped (increases to a maximum and then decreases with increasing value of the independent variable) relationship with: (1) IAV density; (2) IAV patch size; and (3) the percent of streambed covered by multiple dense IAV patches.