Abstract
Atmospheric cold fronts can periodically generate storm surges and affect sediment transport in the Northern Gulf of Mexico (NGOM). In this paper, we evaluate water circulation spatiotemporal patterns induced by six atmospheric cold front events in the Wax Lake Delta (WLD) in coastal Louisiana using the 3-D hydrodynamic model ECOM-si. Model simulations show that channelized and inter-distributary water flow is significantly impacted by cold fronts. Water volume transport throughout the deltaic channel network is not just constrained to the main channels but also occurs laterally across channels accounting for about a quarter of the total flow. Results show that a significant landward flow occurs across the delta prior to the frontal passage, resulting in a positive storm surge on the coast. The along-channel current velocity dominates while cross-channel water transport occurs at the southwest lobe during the post-frontal stage. Depending on local weather conditions, the cold-front-induced flushing event lasts for 1.7 to 7 days and can flush 32–76% of the total water mass out of the system, a greater range of variability than previous reports. The magnitude of water flushed out of the system is not necessarily dependent on the duration of the frontal events. An energy partitioning analysis shows that the relative importance of subtidal energy (10–45% of the total) and tidal energy (20–70%) varies substantially from station to station and is linked to the weather impact. It is important to note that within the WLD region, the weather-induced subtidal energy (46–66% of the total) is much greater than the diurnal tidal energy (13–25% of the total). The wind associated with cold fronts in winter is the main factor controlling water circulation in the WLD and is a major driver in the spatial configuration of the channel network and delta progradation rates.
Highlights
Atmospheric cold fronts have an average interval of 3–7 days in the late fall to spring and dominate regional weather along coastal Louisiana [1]
Both the Atchafalaya and Wax Lake deltas continue to prograde by filling extensive areas across the south-central region of the Atchafalaya Bay as they advance into the continental shelf [26,27]
The correlation coefficients are generally larger than the skill scores, consistent with [67], which showed that the skill scores are generally smaller than the square of the correlation coefficients
Summary
Atmospheric cold fronts have an average interval of 3–7 days in the late fall to spring and dominate regional weather along coastal Louisiana [1]. Water level fluctuations, and winds associated with atmospheric cold fronts are responsible for the resuspension of fine-grained sediments and their subsequent transport to the adjacent continental shelf Both the Atchafalaya and Wax Lake deltas continue to prograde by filling extensive areas across the south-central region of the Atchafalaya Bay as they advance into the continental shelf [26,27]. These severe weather events can produce excess flooding during high storm surges and subsequent drainage of the system that controls delta morphological evolution and wetland structural and functional properties [11,29] Within this deltaic region, distributary channels bounded by the vegetated lobes or islands, may be submerged or emergent depending on the Mississippi River stage, wind (magnitude/direction), and the local wetland hydroperiod regime (frequency/duration of inundation and water depth [24]). We ignore the overall river discharge effect on water level change inside the delta since the first order variability of river discharge is seasonal in terms of its magnitude, i.e., the impact occurs over a much longer time scale than that of individual cold front events; most of the cold front induced circulation and water level fluctuations are wind-dominated
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