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.
