Observations of Internal Solitary Waves in a Coastal Plain Estuary

Internal solitary waves are commonly found in stratified flows of coastal seas, fjords and lakes but have received little attention in shallow coastal plain estuaries. Here we report first observations of large-amplitude internal solitary waves in Chesapeake Bay which features the channel-shoal bathymetry typical of coastal plain estuaries. The misalignment between the principal tidal-current direction and the axis of the deep channel resulted in cross-channel (lateral) flows. Their interaction with the lateral bathymetry generated internal lee waves in the deep channel and a train of internal solitary waves on the shallow shoal. An internal lee wave in the form of pycnocline depression was generated near the deep channel during the flood tide. This wave propagated over the shallow shoal during the following ebb tide, experienced nonlinear steepening and evolved into a group of internal solitary waves of elevation near the floor. Wind-driven lateral circulations also interacted with the channel-shoal bathymetry to produce isolated large-amplitude internal waves with pycnocline depression or elevation. They subsequently evolved into a group of high-frequency nonlinear solitary waves over the shallow shoal. The internal solitary waves may be ubiquitous in coastal plain estuaries and could make important contributions to turbulent mixing with broad implications for hypoxia and biogeochemical cycling.