Observations of Restratification after a Wind Mixing Event in a Shallow Highly Stratified Estuary

Abstract

In stratified estuaries susceptible to wind mixing events, the changes in stratification have important implications for estuarine dynamics. Understanding the timescale associated with these mixing events and indirect wind impacts is dependent on estimating the restratification timescale. Bay-wide stratification observations, turbulence time series, and long-term data were examined to quantify the response mechanisms and restratification times in Mobile Bay. Observations showed moderate increases in stratification occurred over 2–3 days after the mixing event and were spatially variable. Turbulence data and model results that further highlight the period of returning stratification had changes in the relative contribution of tidal straining and gravitational exchange for the residual circulation in the estuary. Estimates of dissipation for the two ADVs averaged 2.6–3.1 × 10−5 m2 s−3 prior to the mixing event and increased to 1.4–8.5 × 10−4 m2 s−3 after the mixing event. These changes showed with increasing stratification; the turbulent dissipation decreased. These results highlight initial high returns in stratification are slowed over time as the exchange and mixing in the bay develop, and stratification returns to its premixed state.