This ledge outcrop serves as the control at the USGS station on the Mousam River near West Kennebunk, Maine.
USGS streamflow stations measure water level. Our database takes that water level and inputs it into a table that converts water level to the corresponding discharge. This stage-discharge relationship varies for every station, and is dependent on the control at each site. The control is a hydraulic feature that could be a natural ledge or cobble riffle, a man-made structure, or the river channel itself. Any changes to the control feature would result in a change to the stage-discharge relationship. What commonly changes this relationship? Scour or fill from high water events, aquatic growth, ice, leaves and beaver debris are some of the common culprits and the reason we confirm this relationship throughout the year at varying flow ranges.