A numerical experiment of cold front induced circulation in Wax Lake Delta: evaluation of forcing factors

Abstract

The effects of passing atmospheric cold fronts with different orientations and moving directions on the hydrodynamics of the Wax Lake Delta (WLD) were analyzed by considering the influence of river discharge, cold front moving direction, wind magnitude, and Coriolis effect. The study employs numerical simulations using the Delft-3D model and an analytical model to explore water volume transport, water level variations, water circulation, and particle trajectories during nine cold front events. Results indicate that cold fronts cause a decrease in the average contribution of the water transport through western channels and an increase of that in central and eastern channels. A westerly cold front with an average wind speed of ~12 m/s can increase water transport through eastern channels by about 35%. During the passage of a cold front, the intertidal islands between the main channels and East Bay experience the largest fluctuations in subtidal water levels, which can be attributed to the influence of local wind stress. For example, a westerly cold front can result in a water level variation of approximately 0.45 m over some of the intertidal Islands and 0.65 m in the East Bay. Results also show that the subtidal water circulation in the WLD is correlated with the Wax Lake Outlet (WLO) discharge and wind magnitude. The findings illustrate that when WLO discharge is low, the impact of cold fronts is more pronounced, and cold fronts from the west have a greater impact compared to those from the northwest and north. This study identifies the significance of WLO discharge and Coriolis force by the trajectories of particles in the water column. The results of the simulations indicate that under low WLO discharge (less than 2000 m3/s), the majority of particles are found to exit through Campground Pass instead of Gadwall because of the dominance of Coriolis force. To summarize, this study assesses the impact of cold fronts on the hydrodynamics of the Wax Lake Delta, underscoring the contributions of multiple factors, including the cold front moving direction, river discharge, wind strength, and Coriolis force.

Response of river delta hydrological connectivity to changes in river discharge and atmospheric frontal passage

“…The Manning's n bottom friction scheme was chosen due to its capability to yield lower drag coefficients compared to the Chezy formulation, particularly in deep waters. The specific Manning coefficient value used is 0.023 m -1/3 s (Shafiei et al, 2022;Feizabadi et al, 2023). Feizabadi et al 10.3389/fmars.2024.1387180…”

“…In river deltas, the concept focuses on the pathways and mechanisms through which water is exchanged or transported primarily between distributary channels and deltaic floodplains (Passalacqua, 2017). Numerous studies have shown that hydrological connectivity regulates landscape evolution, water and material transport, and water quality in river deltas and other water bodies (e.g., Hiatt and Passalacqua, 2015;Coffey and Shaw, 2017;Christensen et al, 2020;Olliver and Edmonds, 2021;Feizabadi et al, 2022bFeizabadi et al, , 2023. The need to understand deltaic hydrological connectivity and its impact on deltaic ecogeomorphology is motivated by the necessity to address challenges associated with the continued loss of coastal wetlands (Engle, 2011;Wu et al, 2017), heightened nutrient loading in receiving waters (Rabalais et al, 2002;Wurtsbaugh et al, 2019), and anthropogenic impacts (Moon et al, 2022;Constantinescu et al, 2023).…”

“…The coastal Louisiana water is a microtidal system and as such the river discharge has a major role in controlling the overall water level on seasonal time scales. The periodic passages of atmospheric cold fronts are known to generate significant winds that modulate water levels and impact coastal and deltaic circulation patterns (Li, 2013;Huang and Li, 2017;Feizabadi et al, 2023). The cold front wind generates short term effect to the water level (e.g., drying effect post front, Huang et al, 2024).…”

“…The pre-frontal phase, occurring approximately 24-48 hours before the frontal passage, is characterized by robust southerly and easterly winds. These winds generate waves and currents that drive water towards the coast, causing water level elevations of more than 0.5 meter above predicted levels (Roberts et al, 1989;Feng and Li, 2010;Li et al, 2011;Feizabadi et al, 2023). This process also leads to the resuspension of sediment from coastal bays and deltaic wetlands.…”

“…Concurrently, these winds contribute to the transport of suspended sediments (Walker and Hammack, 2000), nutrients, and organic matter from coastal bays, and adjacent wetlands onto the continental shelf of the Gulf of Mexico (Childers and Day, 1990;Perez et al, 2000;Huang and Li, 2017). For example, water and sediment transport processes associated with cold-front passages have been identified as beneficial for accretion along the eastern section of the chenierplain on the central Louisiana coast (Draut et al, 2005;Jaramillo et al, 2009;Zhang et al, 2022;Feizabadi et al, 2023). Therefore, the incorporation of cold fronts into numerical models designed for morphodynamics and hydrodynamics applications in the northern Gulf of Mexico is essential.…”