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A coupled one-dimensional (1D) and two-dimensional (2D) hydrodynamic model for small rivers and streams on a large background area using an immersed boundary method (IBM) was developed and implemented for a simple flooding case in a previously published study. In this study, the IBM model was applied for simulations on a real geographical area, the Calcasieu Lake and its surrounding area in Southwest Louisiana. The simulation area ranges from the city of Lake Charles on the north to Gulf of Mexico on the south, and two National Wildlife Refuges (NWR) on the east and west side of Calcasieu Lake. A small change in the natural state of Calcasieu Lake, i.e., the change in the water surface elevation or flooding, can have a drastic impact on the ecosystem of its surrounding wetlands. The flooding to the wetlands is mainly through small rivers connected to the lake. In order to study the effects of coastal flooding to the wetlands, the IBM 1D-2D coupled model was implemented in the simulation package. The main purposes of this study are to: (1) determine the appropriate number of immersed boundary points to be used for this simulation and (2) test the applicability and validate the IBM model for an actual geographical region. Due to the lack of measurement data for the small rivers, the validation was conducted by comparing simulated results from IBM to the results from a non-IBM approach (i.e., manually carved rivers). Data from NOAA and USGS were used for the boundary conditions for the 2D model. [ABSTRACT FROM AUTHOR]

Exchange flows between estuaries and the coastal ocean are important for land-ocean interactions and ecosystem health. This study is aimed at resolving severe weather-induced exchange flows between the Calcasieu Lake Estuary and Gulf of Mexico. For that purpose, we use data from a long-term deployment of side-looking acoustic Doppler current profilers (ADCPs) and conductivity-temperature-depth sensors (CTDs) as well as flow velocity data from a boat operated survey. Regression between the transport measured from a boat mounted ADCP and the velocity data from a fixed side-looking ADCP is done to calculate a long-term transport along the Calcasieu Pass. Analyses have been done for the hydrodynamic response to 16 cold fronts passing the study area. Effects of six strongest cold fronts are discussed in more detail. Results have confirmed that the hydrodynamics is highly correlated with the frequent cold fronts. The highest correlation coefficient is r ~0.75 between the north wind and along channel transport. In general, winds from the southern quadrants push water into the estuary before each frontal passage; after the passage of the front, a rapid change of wind direction to the northern quadrants produces strong outward flows. A quasi-steady state balance between the wind stress and water level difference proposed in recent studies for different systems is further confirmed and discussed in this system. The quasi-steady state balance leads to a relatively high R2 value of greater than 0.8 between the modeled water level gradient and actual observed gradient. We have also applied a regression model, derived from the momentum balance requirement, for the subtidal exchange flow as a function of wind components and their squares which yield an R2 value greater than 0.7. With a confidence in the regression model, we further implement it for twelve years from 26 February 2007 to 10 April 2019. Four extreme events during this 12-year period of time are discussed−they include the Hurricane Ike (2008), Tropical Storm Lee (2011), a warm front, and a cold front. This hindcast of the exchange flows over multiple years can provide a useful tool for coastal management and research for estuarine channels where continuous observations of velocity are not always available.

Exchange flows between estuaries and the coastal ocean are important for land-ocean interactions and ecosystem health. This study is aimed at resolving severe weather-induced exchange flows between the Calcasieu Lake Estuary and Gulf of Mexico. For that purpose, we use data from a long-term deployment of side-looking acoustic Doppler current profilers (ADCPs) and conductivity-temperature-depth sensors (CTDs) as well as flow velocity data from a boat operated survey. Regression between the transport measured from a boat mounted ADCP and the velocity data from a fixed side-looking ADCP is done to calculate a long-term transport along the Calcasieu Pass. Analyses have been done for the hydrodynamic response to 16 cold fronts passing the study area. Effects of six strongest cold fronts are discussed in more detail. Results have confirmed that the hydrodynamics is highly correlated with the frequent cold fronts. The highest correlation coefficient is r ~0.75 between the north wind and along channel transport. In general, winds from the southern quadrants push water into the estuary before each frontal passage; after the passage of the front, a rapid change of wind direction to the northern quadrants produces strong outward flows. A quasi-steady state balance between the wind stress and water level difference proposed in recent studies for different systems is further confirmed and discussed in this system. The quasi-steady state balance leads to a relatively high R2 value of greater than 0.8 between the modeled water level gradient and actual observed gradient. We have also applied a regression model, derived from the momentum balance requirement, for the subtidal exchange flow as a function of wind components and their squares which yield an R2 value greater than 0.7. With a confidence in the regression model, we further implement it for twelve years from 26 February 2007 to 10 April 2019. Four extreme events during this 12-year period of time are discussed–they include the Hurricane Ike (2008), Tropical Storm Lee (2011), a warm front, and a cold front. This hindcast of the exchange flows over multiple years can provide a useful tool for coastal management and research for estuarine channels where continuous observations of velocity are not always available. [ABSTRACT FROM AUTHOR]