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

研究流域中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来进行的。这两种方法都不足以全面了解分水岭的功能，因为出水口的测量范围可能太广，而点测量的范围太小。该项目试图通过绘制整个分水岭内活跃河道的扩张和收缩情况，并深入了解分水岭的哪些区域对分水岭出水口的流量有贡献或没有贡献，来填补这一知识空白。这将为更好地理解水、土壤和化学物质如何通过流域以及河流流量将如何变化提供新的知识，特别是在降雨量较少的时期。作为该项目的一项教育和推广工作，该项目将为初中和高中理科学生提供实践学习机会，并帮助培养研究生。长期以来，水文科学一直使用降雨结束后观测到的河流流量下降对(即后退流量)和并行河流流量值来推断分水岭尺度上的含水层特性。然而，新的工作表明，一个流域的水流源区域的空间变化可以解释衰退，或者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衰退的因素，出现了一场新的辩论。解决这一争论可以提供对分水岭作用的基本见解。为了调查对经济衰退的控制，该项目将在全美不同地点的最多六个中型流域安装高密度传感器网络，以绘制活跃的河流河道网络范围的变化。流量的传感器测量将得到活跃河流网络的可视测绘、可能输入到河流的地下水的热成像以及土壤湿度测量的补充。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中的流动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.