Severe Weather-Induced Exchange Flows through a Narrow Tidal Channel of Calcasieu Lake Estuary

Jie Wang,Fumin Xu,Wei Huang,Chunyan Li

doi:10.3390/jmse8020113

Abstract

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.

Highlights

The Louisiana coast along the northern Gulf of Mexico contains 40% of the U.S wetlands [1,2]
Aimed at a further understanding of wind-driven exchange flows through the narrow tidal channel of Calcasieu Lake Estuary, some hydrodynamic data (ADCPs & conductivity-temperature-depth sensors (CTDs)) from Calcasieu Lake Estuary and meteorological data from a nearby station were analyzed
Sixteen cold fronts occurred between 4 Dec. 2013 and 4 Feb. 2014, among which six of the strongest were selected for a more detailed examination

Summary

Introduction

The Louisiana coast along the northern Gulf of Mexico contains 40% of the U.S wetlands [1,2]. About 80% of the coastal erosion and wetland loss of the U.S occur in this region [2]. Estuarine processes are important to long-term coastal erosion and sediment transport. The estuarine flows include the gravitational [3,4,5,6,7,8,9], tidally-driven [10,11,12,13,14], and wind-driven circulations [15,16,17,18,19]. It is found that the gravitational circulation can be overwhelmed by wind-driven flows [15], and the tidally-induced flows can be overwhelmed by wind-driven flows as well [20]. In the Louisiana estuaries, wind-driven flows are important because of the micro-tidal environment [21]

Objectives

Findings

Discussion

Conclusion