Geodetic Lysimetry: GPS/GNSS observations to measure continuous, time-dependent water mass in mountainous watersheds

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Every winter, water is stored in the mountains as snow. This snow feeds streams and rivers as it melts. Measuring the amount of water stored and drained in the mountains is very difficult, but it is important for predicting water available to humans and the environment. Recently, scientists have observed that the weight of the water collected during winter pushes the surface of the earth down, and that the surface rebounds as the water drains out. Highly accurate, Global Positioning Systems (GPS) measure these changes to the Earth's surface. This project measures the up and down movement of the earth to estimate the volume of water stored in the mountains. GPS stations are installed in the mountains of Idaho and Montana to measure the up and down movement of the Earth. Snow depth and water content are also measured. These data determine the best methods for calculating the amount of water in the mountains. Approximately 100 undergraduate students are trained during immersive learning experiences in summer classes. In regions of substantial topographic relief, the water loading and unloading is highly heterogeneous due to nonlinear feedbacks among weather, landscape morphology, and water exchange among terrestrial reservoirs. This project tests techniques for removing long wavelength regional hydrologic load and downscales geodetic water loading to 10-100 km. A network of Global Positioning Systems (GPS) and weather stations are installed across a watershed in northern Idaho and western Montana. High-precision observations of the watershed hydrologic load using a combination of field and remotely sensed measurements is used to constrain the local hydrologic load independent of GPS measurements. The project tests the spatial and temporal sensitivity of GPS observations, and investigates time constants for different loading and unloading mechanisms including: snowpack dynamics, surface runoff, shallow and deep groundwater flux, and evapotranspiration. The quantitative methods produced here facilitate advances in the basic understanding of watershed function as well as produce new tools for monitoring hydrologic resources. Undergraduates are trained in field geophysics and data Integration courses. This project is jointly funded by the Hydrologic Sciences, Geophysics, and Established Program to Stimulate Competitive Research (EPSCoR) programs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.