Weather-Induced Transport through a Tidal Channel Calibrated by an Unmanned Boat

Abstract

An unmanned surface vehicle (USV) was designed and constructed to operate continuously for covering both flood and ebb and preferably a complete tidal cycle (e.g., ~24 h) to measure the vertical profiles of horizontal flow velocity. It was applied in a tidal channel at Port Fourchon, Louisiana. A bottom-mounted ADCP was deployed for 515 days. The first EOF mode of the velocity profiles showed a barotropic type of flow that explained more than 98.2% of the variability. The second mode showed a typical estuarine flow with two layers, which explained 0.47% of the variability. Using a linear regression of the total transport from the USV with the vertically averaged velocity from the bottom-mounted ADCP, with an R-squared value of 98%, the total along-channel transport throughout the deployment was calculated. A low-pass filtering of the transport allowed for examining the impact of 76 events with cold, warm, or combined cold–warm fronts passing the area. The top seven most severe events were discussed, as their associated transports obviously stood out in the time series, indicating the importance of weather. It is shown that large-scale weather systems with frontal lines of ~1500–3000-km horizontal length scale control the subtidal transport in the area. Cold (warm) fronts tend to generate outward (inward) transports, followed by a rebound. The maximum coherence between the atmospheric forcing and the ocean response reached ~71%–84%, which occurred at about a frequency f of ~0.29 cycle per day or T of ~3.4 days in the period, consistent with the atmospheric frontal return periods (~3–7 days).

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

“…In this period, data were obtained from two stations with the first station being at a USCG Tower (29.8307 • N, 93.3497 • W) in the southern part of the Calcasieu channel and northern Calcasieu Pass [38], which is labeled as CLAK3 in Figures 1 and 2, where two horizontal ADCPs were deployed to measure 2-D horizontal current velocity: the along channel current (positive toward the north) and the cross channel current (perpendicular to the axis of the Calcasieu channel, positive toward the east). This is similar to our recent work in Barataria Bay [21] and Vermillion Bay [33] but different from another recent study in Port Fourchon [25] in which a vertical ADCP, rather than a horizontal one, was used. The two ADCPs were deployed roughly at~1.4 m and~4.7 m below the surface, respectively.…”

“…The transport can then be used to study the impact of the weather, particularly, in our case, the cold front events. This method has been used in a channel of the Port Fourchon in Louisiana successfully with an R 2 value of 0.96-0.99 [25].…”

“…Following some recent studies [21,25,34,36], the relationship between local wind and the water level differences is examined for the Calcasieu Lake Estuary. We start from the 2-D shallow water momentum equations:…”

Flow Regimes and Adjustment to Wind‐Driven Motions in Lake Pontchartrain Estuary: A Modeling Experiment Using FVCOM

“…While wind can also produce significant flows, mostly at frequencies lower than those of tides-the so-called subtidal flows (Valle-Levinson et al, 2007;Wong & Wilson, 1984), the effect is more challenging to predict because weather is much more variable and less regular than tides. Among the weather events, there are the hurricanes or cyclones (e.g., Kumar et al, 2017;Weaver, Johnson et al, 2016), winter storms (e.g., Beardsley et al, 2013), atmospheric fronts (e.g., Feng & Li, 2010;Li et al, 2018;Walker & Hammack, 2000;Weaver, Taeb et al, 2016), and sea breezes (Mohanty & Panda, 2009). The effect of wind has been recognized and studied in various estuaries and lagoons (e.g., Elliott, 1978;Smith, 1985;Sternberger, 1983;Weisberg, 1976;Winant et al, 2014;Wong, 1994;Wong & Moses-Hal, 1998;Wong & Wilson, 1984).…”

A Survey on Unmanned Surface Vehicles for Disaster Robotics: Main Challenges and Directions

“…Li et al [75] deal with the problem of measuring the vertical profiles of horizontal flow velocity for estimations of flushing time, fluxes of water, salt, suspended sediments, and other waterborne materials. These measures can be used to understand and predict floods in case of extreme weather events in water channels—traditional methods to measure the current fixes the instrument at a specific location to collect a long time series of flow data.…”