Tracking Baseflow Supply Dynamics Using <scp>SWOT</scp> Data From Small Groundwater‐Dominated Lakes

ABSTRACT In situ surface‐water monitoring strategies are biased towards larger perennial streams and lakes and are generally not designed to track mechanisms of baseflow supply contributed by the dynamic storage of aquifers. Additionally, small (&lt; 1 km 2 ) groundwater‐influenced lakes and wetlands globally have little in situ monitoring infrastructure. We explored the utility of remotely sensed Surface Water Ocean Topography Satellite (SWOT) data, collected from 2023 onward, to characterise the seasonal and multi‐year water‐level trends of groundwater flow‐through kettle lakes distributed across the permeable sediments of eastern Massachusetts, USA. This analysis indicated that water levels for kettle lakes with areas down to approximately 0.05 km 2 are resolvable in the study area. Our examination of 17 kettle lakes found that SWOT water‐surface elevation data closely tracked groundwater levels in adjacent monitoring wells where available, including the timing of seasonal patterns (highest levels generally in late spring), although there was some variation between years and there was a substantial lag in the timing of high water levels for a lake located downgradient from a 30‐m‐thick vadose zone. Furthermore, SWOT‐observed water‐level increases in kettle lakes tracked with baseflow increases in two adjacent groundwater‐dominated streams, as would be expected from increased hydraulic gradients. Unlike spectral remote sensing, SWOT data are generally not affected by cloud cover, resulting in a potential for groundwater‐dominated lakes to be sentinels of dynamic storage patterns, including identification of baseflow drought lags, which are currently ill‐defined hydrological processes. SWOT monitoring of groundwater‐influenced surface waters shows potential for augmenting existing monitoring wells and streamgages as continuous monitors of groundwater levels and baseflow supply in permeable terrain.