Collaborative Research: Mapping Changes in the Active Stream Channel Network in Mesoscale Watersheds in order to Understand Distinct Signatures in Event Recession Curves

研究流域内的水流通常是通过测量流域出口的水流或在流域内的井中进行点测量。这两种方法都不足以获得分水岭功能的完整图像，因为在出口处的测量可能太宽，而点测量可能太局部。该项目旨在通过绘制整个流域活动河道的扩张和收缩图，并深入了解流域的哪些区域为流域出口提供或不提供流量，来填补知识空白。这将为更好地理解水、土壤和化学物质如何在流域中移动以及河流流量如何变化提供新的知识，特别是在降水少的时期。作为该项目的教育和推广工作，该项目将为初高中理科学生提供动手学习的机会，并帮助培养研究生。在水文科学中，长期以来一直使用观测到的降雨结束后河流流量下降率对（即衰退流量）和同期河流流量值来推断流域尺度上的含水层性质。然而，新的研究表明，在整个集水区，水流源区域的空间变化可能比含水层性质和水力学更好地解释衰退。因此，关于什么才是真正控制经济衰退的争论正在兴起。解决这一争论可以为分水岭功能提供根本性的见解。为了研究对衰退的控制，该项目将在美国不同地点的六个中型流域安装高密度传感器网络，以绘制活动河道网络范围的变化。对流量的传感器测量将辅以对活动水系网络的可视化测绘、对可能流入溪流的地下水的热成像和土壤湿度测量。该项目可能会对预测未测量流域的流量和了解溶质在流域内移动的过程产生更广泛的影响。

Water flow in watersheds is most often studied by either measuring stream flow at the watershed outlet or by making point measurements in wells within the watershed. Neither is adequate for gaining a complete picture of watershed function because measurements at the outlet can be too broad and point measurements too localized. This project seeks to fill the knowledge gap by mapping the expansion and contraction of active stream channels throughout the watershed and providing insights into which areas of a watershed are or are not contributing flow to the watershed outlet. This will provide new knowledge for better understanding how water, soil, and chemicals move through watersheds and how stream discharge will change, particularly during periods of little precipitation. As an education and outreach effort of this project, the project will develop hands-on learning opportunities for middle and high school science students and help train graduate students. Pairs of observed rates of stream flow decline after rainfall ends (i.e. recession flow) and the concurrent stream flow value have long been used in the hydrologic sciences to infer aquifer properties at the watershed scale. However, new work has shown that spatial variation in stream flow source areas across a catchment may explain recession as well or better than aquifer property and hydraulics. Thus, there is an emerging debate on what really controls recession. Resolving this debate can provide fundamental insights into watershed function. To investigate the controls on recession, this project will install high-density sensor networks at up to six medium-sized watersheds at different locations throughout the U.S. to map changes in the extent of the active stream channel network. Sensor measurements of discharge will be supplemented with visual mapping of the active stream network, thermal imaging of likely groundwater inputs to streams, and soil moisture measurements. The project could have broader implications for predicting discharge in ungauged basins and understanding processes of solutes moving through watersheds.