Variability in infragravity wave processes during estuary artificial entrance openings

Abstract

Intermittently open/closed estuaries (IOCE) are wave-dominated estuaries with entrances that temporarily close to the ocean. Wave-current interactions play a major role in estuary entrance morphodynamics and influence the degree of energy transfer from the ocean into the lagoon. This study utilizes artificial entrance openings of multiple ICOE in Victoria, Australia, to capture continuous hydrodynamic and geomorphic data throughout the opening cycle. We illustrate that water level oscillations in the infragravity (IG) band) are present in the basin during open entrance conditions. IG waves were observed to propagate up to 1.8 km upstream of the mouth while the entrance was open. Our work identifies that changes in cross-sectional area, bed depth at the berm position, and offshore wave height control the magnitude of IG waves within the estuary basin. IG wave magnitude is also tidally modulated and increases with high tides when the nearshore water level is higher. Late during the drainage phase, waves were observed to track the margins of the channel, away from the thalweg, and reach the basin. IG wave energy was highest immediately after the basin had ceased draining and while channel dimensions at the mouth were within 10% of their maximum value. As the entrance aggrades, IG wave magnitude decreases in the absence of energetic offshore wave conditions. We relate the changes in IG wave magnitude and frequency to a six-stage conceptual model of the opening-closure sequence. Within the basin, IG wave energy, height and frequency were also consistently highest closer to the mouth and decreased with distance upstream. Our findings indicate that water level oscillations in the IG band are a persistent feature in IOCE and may be the norm rather than the exception in these systems. As IG waves were captured serendipitously as part of a larger field campaign, future work will focus on instrumenting IOCE to gain high-resolution data to quantify IG wave processes during entrance openings.

InletTracker: An open-source Python toolkit for historic and near real-time monitoring of coastal inlets from Landsat and Sentinel-2

“…Existing monitoring and survey techniques for coastal inlets include RTK-GPS and echo-sounding surveying (e.g., Mcsweeney and Stout (2020); Morris and Turner (2010)), stationary coastal imaging systems such as Argus (e.g., Harley et al (2011)) as well as more recent techniques such as UAVs (Turner et al, 2016) and airborne water penetrating LiDAR (Kinsela et al, 2020). While these techniques are suitable for surveying coastal inlets at a high resolution, they remain costly and their suitability for reconstructing historical inlet dynamics depends on when corresponding surveys were initiated.…”

“…Information on the long-term spatial and temporal dynamics of coastal inlets would enable researchers to further advance the existing knowledge on the mechanics and drivers of inlet opening/closure (e.g., Behrens et al, 2013;Bertin and Mendes, 2019;González-Villanueva et al, 2017;Mcsweeney et al, 2018;Mcsweeney and Stout, 2020;Morris and Turner, 2010;Ranasinghe and Pattiaratchi, 2003;Slinger, 2017;van Ormondt et al, 2020;Velasquez Montoya et al, 2018), the hydrology (e.g., Gale et al, 2007) and ecology (e.g., Gladstone et al, 2006;Scanes et al, 2020) of intermittent estuaries, or the impacts of climate change on coastal inlet dynamics (e.g., Duong et al, 2016;Duong et al, 2017Duong et al, , 2018. To date, however, the potential of satellite remote sensing remains poorly explored and there is need for an automated and transferable method to monitor intermittent coastal inlets worldwide.…”

Hydrodynamic Variability of an Intermittently Closed Estuary over Interannual, Seasonal, Fortnightly, and Tidal Timescales

“…Recent work has focused on the influence of infragravity (IG hereafter) waves on sediment transport within tidal inlets (Dodet et al 2013;Bertin et al 2019Bertin et al , 2018. Multiple ICE observational studies and numerical simulations (XBeach) have shown that the strength of IG motions is correlated with offshore wave heights, and that the IG energy depends on the tidal phase and connectivity between the ocean and estuary (Williams and Stacey 2016;McSweeney et al 2020;Bertin and Olabarrieta 2016). Additionally, observations have found that the magnitude of IG orbital motions can be on the same order as tidal velocities (Uncles et al 2014;Williams and Stacey 2016;Bertin and Olabarrieta 2016).…”

River Plume Modulation by Infragravity Wave Forcing

“…Similarly, Bertin et al (2019) reported high currents during the passage of IG waves crests at a shallow tidal inlet, which resulted in an increase of the sand flux by at least two orders of magnitude that favored inlet closure. IG wave frequencies and amplitudes have been linked to variability in estuary entrance morphologies and offshore wave conditions (e.g., McSweeney et al, 2020;Williams & Stacey, 2016).…”

“…The effects of infragravity (hereafter IG) motions are not considered in the above formulations. Infragravity waves, while small offshore, have been shown to influence the hydrodynamics and morphodynamics of beaches, small tidal inlets and estuaries (Bertin et al., 2019; Bertin & Olabarrieta, 2016; Brocchini, 2020; Elgar et al., 1992; McSweeney et al., 2020; Melito et al., 2020; Mendes et al., 2020; Williams & Stacey, 2016). IG waves result in surface water level fluctuations with periods of 30–300 s that are typically associated with wave groups and result from nonlinear interactions in the incident short waves (Bertin et al., 2018; Henderson et al., 2006; Schäffer, 1993).…”