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.
This is a preview of subscription content, log in to check access.
Buy single article
Instant access to the full article PDF.
Price includes VAT for USA
Subscribe to journal
Immediate online access to all issues from 2019. Subscription will auto renew annually.
This is the net price. Taxes to be calculated in checkout.
Burchard, H. 2009. Combined effects of wind, tide, and horizontal density gradients on stratification in estuaries and coastal seas. Journal of Physical Oceanography. https://doi.org/10.1175/2009JPO4142.1.
Burchard, H., and R. Hetland. 2010. Quantifying the contributions of tidal straining and gravitational circulation to residual circulation in periodically stratified tidal estuaries. Journal of Physical Oceanography. https://doi.org/10.1175/2010JPO4270.1.
Burchard, H., and R. Hofmeister. 2008. A dynamic equation for the potential energy anomaly for analysing mixing and stratification in estuaries and coastal seas. Estuarine, Coastal and Shelf Science. https://doi.org/10.1016/j.ecss.2007.10.025.
Canuto, V., A. Howard, Y. Cheng, and M. Dubovikov. 2001. Ocean turbulence. Part I: One-point closure model - momentum and heat vertical diffusivities. Journal of Physical Oceanography. https://doi.org/10.1175/1520-0485(2001)031<1413:OTPIOP>2.0.CO;2.
Chen, S., and L. Sanford. 2009. Axial wind effects on stratification and longitudinal salt transport in an idealized, Partially Mixed Estuary. Journal of Physical Oceanography. https://doi.org/10.1175/2009JPO4016.1.
Coogan, J., and B. Dzwonkowski. 2018. Observations of wind forcing effects on estuary length and salinity flux in a river-dominated, microtidal estuary, Mobile Bay, Alabama. Journal of Physical Oceanography. https://doi.org/10.1175/JPO-D-17-0249.1.
Davis, K., and S. Monismith. 2011. The modification of bottom boundary layer turbulence and mixing by internal waves shoaling on a barrier reef. Journal of Physical Oceanography. https://doi.org/10.1175/2011JPO4344.1.
Du, J., K. Park, J. Shen, B. Dzwonkowski, X. Yu, and B. Yoon. 2018. Role of baroclinic processes on flushing characteristics in a highly stratified estuarine system, Mobile Bay, Alabama. Journal of Geophysical Research: Oceans. https://doi.org/10.1029/2018JC013855.
Dzwonkowski, B., K. Park, H. Ha, W. Graham, F. Hernandez, and S. Powers. 2011. Hydrographic variability on a coastal shelf directly influenced by estuarine outflow. Continental Shelf Research. https://doi.org/10.1016/j.csr.2011.03.001.
Friedrichs, C., L. Wright, D. Hepworth, and S. Kim. 2000. Bottom-boundary-layer processes associated with fine sediment accumulation in coastal seas and bays. Continental Shelf Research. https://doi.org/10.3354/meps192219.
Geyer, W. 1993. The importance of suppression of turbulence by stratification on the estuarine turbidity maximum. Estuaries. https://doi.org/10.2307/1352769.
Geyer, W., and P. MacCready. 2014. The estuarine circulation. Annual Review of Fluid Mechanics. https://doi.org/10.1146/annurev-fluid-010313-141302.
Geyer, W., and D. Ralston. 2015. Estuarine frontogenesis. Journal of Physical Oceanography. https://doi.org/10.1175/JPO-D-14-0082.1.
Geyer, W., J. Trowbridge, and M. Bowen. 2000. The dynamics of a partially mixed estuary. Journal of Physical Oceanography. https://doi.org/10.1175/1520-0485(2000)030<2035:TDOAPM>2.0.CO;2.
Gibson, C. 1986. Internal waves, fossil turbulence, and composite ocean microstructure spectra. Journal of Fluid Mechanics. https://doi.org/10.1017/S0022112086000307.
Ha, H., and K. Park. 2012. High-resolution comparison of sediment dynamics under different forcing conditions in the bottom boundary layer of a shallow, micro-tidal estuary. Journal of Geophysical Research: Oceans. https://doi.org/10.1029/2012JC007878.
Hansen, D., and M. Rattray. 1966. Gravitational circulation in straits and estuaries. Journal of Marine Research 23: 104 122.
Holleman, R., W. Geyer, and D. Ralston. 2016. Stratified turbulence and mixing efficiency in a salt wedge estuary. Journal of Physical Oceanography. https://doi.org/10.1175/JPO-D-15-0193.1.
Huang, C., H. Ma, J. Guo, D. Dai, and F. Qiao. 2018. Calculation of turbulent dissipation rate with acoustic Doppler velocimeter: calculation of turbulent dissipation rate. Limnology and Oceanography: Methods. https://doi.org/10.1002/lom3.10243.
Jones, N., and S. Monismith. 2008. The influence of whitecapping waves on the vertical structure of turbulence in a shallow estuarine embayment. Journal of Physical Oceanography. https://doi.org/10.1175/2007JPO3766.1.
Kaimal, J.C., J.C.J. Wyngaard, Y. Izumi, and O.R. Coté. 1972. Spectral characteristics of surface-layer turbulence. Quarterly Journal of the Royal Meteorological Society 98 (417): 563–589.
Kim, C., and K. Park. 2012. A modeling study of water and salt exchange for a microtidal, stratified northern Gulf of Mexico estuary. Journal of Marine Systems. https://doi.org/10.1016/j.jmarsys.2012.02.008.
Kim, S., C. Friedrichs, J. Maa, and L. Wright. 2000. Estimating bottom stress in tidal boundary layer from acoustic Doppler velocimeter data. Journal of Hydraulic Engineering. https://doi.org/10.1061/(ASCE)0733-9429(2000)126:6(399.
Li, Y., and M. Li. 2011. Effects of winds on stratification and circulation in a partially mixed estuary. Journal of Geophysical Research. https://doi.org/10.1029/2010JC006893.
Li, M., L. Zhong, W.C. Boicourt, S. Zhang, and D.L. Zhang. 2007. Hurricane-induced destratification and restratification in a partially-mixed estuary. Journal of Marine Research. https://doi.org/10.1357/002224007780882550.
MacCready, P., and W. Geyer. 2010. Advances in estuarine physics. Annual Review of Marine Science. https://doi.org/10.1146/annurev-marine-120308-081015.
MacCready, P., W. Geyer, and H. Burchard. 2018. Estuarine exchange flow is related to mixing through the salinity variance budget. Journal of Physical Oceanography. https://doi.org/10.1175/JPO-D-17-0266.1.
Noble, M., W. Schroeder, W. Wiseman, H. Ryan, and G. Gelfenbaum. 1996. Subtidal circulation patterns in a shallow, highly stratified estuary: Mobile Bay, Alabama. Journal of Geophysical Research. https://doi.org/10.1029/96JC02506.
Park, K., C. Kim, and W. Schroeder. 2007. Temporal variability in summertime bottom hypoxia in shallow areas of Mobile Bay, Alabama. Estuaries and Coasts 30 (1): 54–65. https://doi.org/10.1007/BF02782967.
Peters, H., and R. Bokhorst. 2000. Microstructure observations of turbulent mixing in a partially mixed estuary. Part I: Dissipation rate. Journal of Physical Oceanography. https://doi.org/10.1175/15200485(2000)030<1232:MOOTMI>2.0.CO;2.
Pritchard, D. 1956. The dynamic structure of a coastal plain estuary. Journal of Marine Research 15 (1): 33–42.
Ralston, D., and M. Stacey. 2006. Shear and turbulence production across subtidal channels. Journal of Marine Research. https://doi.org/10.1357/002224006776412359.
Rodi, W. 1987. Examples of calculation methods for flow and mixing in stratified fluids. Journal of Geophysical Research: Oceans. https://doi.org/10.1029/JC092iC05p05305.
Ryan, H., M. Noble, E. Williams, W. Schroeder, J. Pennock, and G. Gelfenbaum. 1997. Tidal current shear in a broad, shallow, river-dominated estuary. Continental Shelf Research. https://doi.org/10.1016/S0278-4343(96)00053-2.
Schroeder, W., S. Dinnel, and W. Wiseman. 1990. Salinity stratification in a river dominated estuary. Estuaries. https://doi.org/10.2307/1351583.
Scully, M., W. Geyer, and J. Trowbridge. 2011. The influence of stratification and nonlocal turbulent production on estuarine turbulence: an assessment of turbulence closure with field observations. Journal of Physical Oceanography. https://doi.org/10.1175/2010JPO4470.1.
Shih, L., J. Koseff, G. Ivey, and J. Ferziger. 2005. Parameterization of turbulent fluxes and scales using homogeneous sheared stably stratified turbulence simulations. Journal of Fluid Mechanics. https://doi.org/10.1017/S0022112004002587.
Simpson, J., and P. Linden. 1989. Frontogenesis in a fluid with horizontal density gradients. Journal of Fluid Mechanics. https://doi.org/10.1017/S0022112089001072.
Simpson, J., J. Brown, J. Matthews, and G. Allen. 1990. Tidal straining, density currents, and stirring in the control of estuarine stratification. Estuaries. https://doi.org/10.2307/1351581.
Stacey, M.T., and D.K. Ralston. 2005. The scaling and structure of the estuarine bottom boundary layer. Journal of Physical Oceanography. https://doi.org/10.1175/JPO-2672.1.
Stacey, M., J. Burau, and S. Monismith. 2001. Creation of residual flows in a partially stratified estuary. Journal of Geophysical Research: Oceans. https://doi.org/10.1029/2000JC000576.
Umlauf, L., and H. Burchard. 2005. Second-order turbulence closure models for geophysical boundary layers. A review of recent work. Continental Shelf Research. https://doi.org/10.1016/j.csr.2004.08.004.
Valle-Levinson, A. 2010. Definition and classification of estuaries. In Contemporary issues in estuarine physics, ed. A. Valle-Levinson, 1–11. New York: Cambridge University press.
Voulgaris, G., and J.H. Trowbridge. 1998. Evaluation of the acoustic Doppler velocimeter (ADV) for turbulence measurements. Journal of atmospheric and oceanic technology. https://doi.org/10.1175/1520-0426(1998)015<0272:EOTADV>2.0.CO;2.
Long-term data were collected by the Tech Support Group at the Dauphin Island Sea Lab, including Kyle Weis, Roxanne Robertson, Alan Gunter, Mike Dardeau, G. Lockridge, Hunter King, Y. Hintz and L. Linn and R. Collini (Data available at www.mymobile.com). The authors would like to acknowledge Steve Dykstra, Kara Gadeken, Cy Clemo, Jacob Blandford, and Jenine Brideau for their help with field data collection. This research was made possible in part by NOAA RESTORE program (NA17NOS4510101) and the Center for Environmental Resiliency at University of South Alabama. We acknowledge commentsprovided by the two program (NA17NOS4510101) and the Center for Environmental Resiliency at University of South Alabama. We acknowledge comments provided by the two anonymous reviewers that helped to improve this manuscript.
Communicated by Stephen G. Monismith
About this article
Cite this article
Coogan, J., Dzwonkowski, B., Park, K. et al. Observations of Restratification after a Wind Mixing Event in a Shallow Highly Stratified Estuary. Estuaries and Coasts 43, 272–285 (2020). https://doi.org/10.1007/s12237-019-00689-w
- Tidal straining
- Highly stratified
- Estuarine hydrodynamics
- Wind mixing