The daily‐scale entrance dynamics of intermittently open/closed estuaries

Abstract

Intermittently open/closed estuaries (IOCE) are a dynamic form of estuary characterised by periodic entrance closure to the ocean. Entrance closure is a function of the relative balance between on and offshore sediment transport with closures occurring during periods of low fluvial discharge whereby the estuary ebb‐tidal prism is reduced. Although the broad scale processes of entrance closure are becoming better understood, there remains limited knowledge on channel morphodynamics during an individual closure event. In this study, the entrance dynamics of three IOCE on the coast of Victoria, Australia, were monitored over a daily timescale following both artificial and natural openings. The influence of changing marine and fluvial conditions on the relative sedimentation rate within the entrance channel was examined. IOCE in Victoria showed two distinct modes of entrance closure: (a) lateral accretion, whereby the estuary gradually closes by longshore drift‐driven spit growth during low river flows; and (b) vertical accretion, where the channel rapidly aggrades under high (> 2 m), near‐normal waves. During storms, when fluvial discharge and wave heights simultaneously increase, large swells will not always close the mouth due to an increase in the ebb‐tidal prism. The estuary water depth and the maximum channel dimensions following opening were not proportional to the opening duration, with this being a function of the wave and fluvial conditions occurring following lagoon drainage. Based on the findings of this work, implementing a successful artificial entrance opening is dependent on reduced onshore sedimentation rates which occur when wave energy is low (< 2 m Hs) relative to river flow. Copyright © 2017 John Wiley & Sons, Ltd.

Coastal flooding thresholds and morphological evolution of a Mediterranean spit-barrier

“…Their development is caused by the effect of prevailing SE waves (northward migration) or during onshore wind events (Tramontane) which generates short NE waves (southward migration) during low flow periods. This behavior matches with the definition of Intermittently Open/Closed Estuaries (IOCESs) (MCSWEENEY et al, 2018).…”

“…Many mouths, with low or variable fluvial discharge during the year, are subject to a seasonal (semi) closure of their channel due to the development of a sand or gravel spit. The spit develops itself when the wave-driven longshore sediment transport exceeds the ability of the river flow to remove sediment from the channel Thème 2 -Dynamique sédimentaire (MCSWEENEY et al, 2018;RANASINGHE & PATTIARATCHI, 2003). During marine storm events, spits are natural coastal defenses acting as protective barriers, but because of their low elevation, they are easily overtopped.…”

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

“…Due to the often sporadic and erratic nature of intermittent coastal inlets, they remain less understood than more mature and permanent coastal inlets (Behrens et al, 2013;Mcsweeney et al, 2018;Velasquez Montoya et al, 2018), pose a challenge for coastal management (Alluvium, 2012;Gordon and Nielsen, 2020;Stephens and Murtagh, 2012) and sometimes feature a heated socio-political debate around management interventions such as mechanical openings/closures (Gladstone et al, 2006;Gordon and Nielsen, 2020;Stephens and Murtagh, 2012;Young et al, 2014). These concerns can be compounded by a lack of datasets on historic inlet states (open vs. closed), which, apart from a few targeted coastal monitoring programs (e.g., DPIE (2020a)), do not exist for many inlets around the globe.…”

“…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.…”

Variability in infragravity wave processes during estuary artificial entrance openings

“…During an opening, water outflow from the lagoon dominates sediment transport and the channel adjusts to the predominantly seaward direction of sediment movement (Stretch and Parkinson, 2006). Once the hydraulic head lessens, ocean waves become a main control on entrance morphodynamics and sediment is again reworked landward (Morris and Turner, 2010; McSweeney et al, 2018). Short waves (i.e., gravity frequency) are dominant, with entrance closure occurring through vertical accretion of the berm or longshore progradation of spits at the mouth (Ranasinghe and Pattiaratchi, 2003).…”