Nearshore-offshore exchanges in multi-basin coastal waters: Observations and three-dimensional modeling in Lake Erie

Nearshore-offshore exchanges through upwelling events and subsequent formation of internal Kelvin waves and coastal-jets are expected in the multi-basin coastal waters of Lake Erie; however, these phenomena have yet to be confirmed in the field or numerically modeled. Here, we demonstrate these physical processes in Lake Erie through extensive field data analysis and high-resolution three-dimensional hydrodynamic modeling. The validated model successfully reproduces dominant physical processes in the offshore and nearshore waters including surface seiches (~14 h), near-inertial waves (~17 h) and upwelling events (5–10 days). We show that upwelling events are the predominant nearshore physical processes, and are energized when winds accelerate the epilimnetic waters to the south, causing the thermocline front to move up into the north shore. After the wind subsides, the elevated thermoclines simultaneously form two separate cyclonically propagating internal Kelvin waves in the central and the eastern basins following by two coastal-jets at phase speeds of 0.22 ms−1 and 0.37 ms−1 within 5–15 km off the shoreline, respectively. The predominant south-west winds limit the presence of Kelvin waves only to the northern parts of each basin, where the bathymetry allows, and disappear when shoreline morphology no longer maintain these waves due to nonzero cross-shore transports at the coastal boundary layer. Intrusions of hypolimnetic waters through upwelling events contribute 10–30% to the net cross-shore transport, and are most pronounced in May and June when the offshore thermocline is shallow. The intermittent strong westward nearshore currents by Kelvin waves are in the opposite direction of seasonal eastward currents.