Estimation of transmissivity across the conterminous US using large water table and surface water datasets

The transmissivity of the subsurface controls groundwater flow but is highly variable and often uncertain. Here we use large datasets of groundwater level measurements and surface drainage to calculate transmissivity for 5000 points in the conterminous US. We designed a new algorithm that uses water table data, elevation and surface water location data to reconstruct the groundwater flow path, the groundwater discharge location and the groundwater divide for each data point. We subsequently calculate the ratio of recharge over transmissivity for each point using an analytical solution of the groundwater flow equation. Finally, we use independent estimates of groundwater recharge to estimate transmissivity. The results demonstrate the viability of combining large sets of water level data to quantify the spatial distribution of transmissivity. The algorithm will be published as an open-source code that can be used to automatically find groundwater flow paths and estimate transmissivity for large water level datasets.