High-Density Integrated GNSS and Hydrologic Monitoring Network for Short-Scale Hydrogeodesy in High Mountain Watersheds

We installed a purpose-built network of co-located Global Navigation Satellite System (GNSS) stations and meteorological instrumentation to investigate water storage in a high-mountain watershed along the Idaho-Montana border. Twelve GNSS stations are distributed across the Selway-Lochsa watersheds at approximately 30-40 km spacing, filling a critical observational gap between localized point measurements and regional geodetic and satellite data sets. The unique coupling of geodetic and hydrologic observations in this network enables direct comparison between co-located GNSS measurements of the elastic response of the solid Earth and local changes in measured water storage. This network is specifically designed to address questions of hydrologic storage and movement at the mountain watershed scale. Here, we describe technical details of the network and its deployment; introduce new hydrologic, meteorologic, and geodetic data sets recorded by the network; process and analyze the source data (e.g., time series of daily three-dimensional GNSS site positions, removal of non-hydrologic signals); and characterize basic empirical relationships between water storage, water movement, and GNSS-inferred surface displacement. The network shows preliminary evidence for spatial differences in displacement resulting from a range of snow loads across elevations, but longer and more complete data records are needed to support these initial findings. We also provide examples of additional scientific applications of this network, including estimations of snow depth and snow water equivalent from GNSS multipath reflectometry. Finally, we consider the challenges, limitations, and opportunities of deploying GNSS and weather stations at high elevations with heavy snowpack and offer ideas for technical improvements.