API TR 1153-2-2016

Tidal inlets occur along most barrier coasts and therefore these dynamic systems must be considered separately when designing an overall strategy for oil coming towards the coast. Inlets are the gateways that can allow oil to enter extensive, sensitive marsh, mangrove and sheltered tidal flats environments that dominate back-barrier lagoons, bays, and estuaries. Reversing tidal flow, wave-current interaction, and periodic exposure of tidal sand bodies make advance planning a necessity if oil is to be contained. Important attributes of tidal inlets and how these relate to the development of response strategies are provided below:

– Tidal currents dominate areas adjacent to the inlet throat and inside the inlet, whereas the shoals seaward of the inlet are dominated by waves and wave-generated currents.

– Currents at tidal inlets can reach high speeds where the entire tidal prism must flow through the narrow channel. Flooding tides can transport oil into bays and lagoons and surrounding sensitive tidal flat, marsh, and mangrove habitats.

– Response operations at tidal inlets face numerous challenges, the most important of which are the constantly changing water depths and reversing current directions. At large inlets, wind-generated currents also can affect oil transport.

– Recognition of the morphological features of an inlet system enables planners and responders to understand how water depth and current pattern change through the tidal cycle.

– Determination of morphological features and current patterns provide the basis for selecting realistic and practical response strategies for minimizing oil transport through an inlet during flooding tides.

– With a basic understanding of the hydrology and morphology of a tidal inlet and dedication of resources, it is possible to implement a number of protective actions which can mitigate risk and reduce oil spill impacts.