IMPACT OF MACROPORES AND SOIL PIPES ON HYPORHEIC EXCHANGE IN STREAMS

溪流和河流是水循环的重要组成部分，是“万物的下游”，受大多数人类活动的影响最大。因此，了解溪流和河流的工作原理非常重要，这样我们就可以解释这些好处，并预测它们如何应对城市化等趋势。潜流带是河流或溪流中的水与河流下面或河边沉积物中的水之间的边界。潜潜带具有独特的特性，包括增强的化学反应（其中许多有助于降低污染物水平）和其他地方无法生存的生物的栖息地。当溪流或河流中的水位波动时，例如由于风暴事件，因为这迫使水流入或流出河岸，所以潜潜区特别活跃。该项目将使用实地调查来确定在美国东部大范围的河流中，这种风暴增强的低环流交换有多大变化。现场数据将与计算机模型相结合，以预测这种交换在其他流中的存在和意义。这将有助于更好地了解这种关于水生生物的交换以及营养物质和污染物的运输。该项目还将加强弗吉尼亚理工大学现有的几门课程，并提高学生在科学、技术、工程和数学（STEM）领域从事职业的兴趣，这些领域对于保护和提高美国的动态经济和生活质量至关重要。该计划将会接触到人数不足的本科生，以提高他们参与计划提供的促进职业发展的研究机会。小溪和河流构成了水圈各部分之间的重要联系。潜流带是水在地表和地下交换的关键界面，对水生生物、生物地球化学反应和污染物衰减具有重要意义。“肺模式”的潜流交换发生在水进入和离开地下的瞬间现象，如风暴、水峰和每日融雪。肺模型交换对水质的影响最近已被证明是实质性的，但高度依赖于交换率。该项目将对河岸大孔隙进行实地调查，以测试大孔隙/土壤管道在美国东部几个省份以及一系列河流大小和土地利用中是否普遍存在。现场调查将包括详细测量大孔隙的几何形状、连通性、沉积和堵塞。这些数据将用于将基于darcy的SUTRA反应和输运模型与计算流体动力学代码Ansys CFX进行比较。建模将确定控制因素（如大孔几何形状、水头梯度、沉积物水力传导率）与大孔促进肺模型交换的程度之间的关系。然后，这些结果将被放大，以估计大孔的存在增加流长度百分比的程度，其中肺模型下潜交换是显著的。

Streams and rivers form a vital part of the water cycle, are 'downstream of everything" and are most affected by most human actions. It is therefore important to understand how stream and rivers work so we can account for these benefits and anticipate how they may respond to trends like urbanization. The hyporheic zone is the boundary between the water in a river or stream and the water in sediment beneath or alongside the river. The hyporheic zone has unique properties including enhanced chemical reactions (many of which are good for reducing pollutant levels) and habitat for organisms that live nowhere else. The hyporheic zone is particularly active when water levels fluctuate in the stream or river, for instance due to storm events, because this forces water into or out of the riverbanks. This project will use field surveys to determine how much this storm-enhanced hyporheic exchange varies through a wide range of streams in the eastern USA. The field data will be combined with computer models to predict the presence and significance of this exchange in other streams. This will allow better understanding of this exchange on aquatic organisms and the transport of nutrients and pollutants. This project will also enhance several existing classes at Virginia Tech and increase student interest in pursuing careers in Science, Technology, Engineering, and Mathematics (STEM) fields which are critical for preserving and enhancing America's dynamic economy and quality of life. The project will reach out to under-represented undergraduates to improve their participation in the career-enhancing research opportunities provided by the project. Streams and rivers form a vital link among compartments of the hydrosphere. The hyporheic zone is a key interface where water exchanges between surface and subsurface, and is important for aquatic organisms, biogeochemical reactions, and contaminant attenuation. "Lung model" hyporheic exchange occurs where water enters and exits the subsurface during transient phenomena such as storms, hydropeaking, and daily snowmelt. The effect of lung model exchange on water quality has been recently shown to be substantial, yet highly dependent on exchange rate. This project will use field surveys of stream bank macropores to test whether macropores/soil pipes are common in several provinces of the eastern USA and a range of stream sizes and land uses. Field surveys will include detailed measurements of macropore geometry, connectivity, sedimentation, and plugging. These data will be used to compare the Darcy-based SUTRA model of reaction and transport to the computational fluid dynamics code Ansys CFX. The modeling will determine the relationships between controlling factors (e.g., macropore geometry, head gradients, sediment hydraulic conductivity) and the degree that macropores enhance lung model exchange. These results will then be upscaled to estimate the degree to which the presence of macropores increases the percent of stream length where lung model hyporheic exchange is significant.