Nearshore coastal dispersion enhanced through estuarine trapping/pumping

Estuaries are known to exchange water between the ocean and the coast through estuarine exchange flow and tidal pumping. In the classical picture of estuarine exchange, ocean water is brought into estuaries at depth, mixed vertically with fresher surface layers, and exported at the surface in a significantly modified manner. Thus, there is a known transport pathway by which constituents are exchanged between the ocean and estuaries. Moreover, in the absence of estuaries, coastal bathymetric and topographic variations (shoals, headlands, etc.) are known to impact coastal dispersion in the nearshore and over the shelf. Further, nearshore wave-driven circulation is known to impact coastal transport pathways. Here we try to bridge these various perspectives (those focused along the coastline and at estuary mouths) to consider how small estuaries contribute to coastal dispersion. Analogous to tidal trapping enhancing dispersion within estuaries, small estuaries along the coast can trap and subsequently pump coastal water masses and constituents, thus enhancing coastal dispersion. In a series of nearshore dye transport studies, enhanced dispersion was observed after a dye release adjacent to an estuary mouth relative to coastline releases. Measurements appear to highlight dye trapped inside of the estuary and released over multiple tidal cycles. Unfortunately, estuarine fluorometer readings are complicated by the presence of CDOM and sediment, thus realistic as well as quasi-idealized wave-hydrodynamic coupled simulations are used to further investigate and quantify estuarine trapping and the resulting influence on coastal dispersion. Relationships between estuarine size, discharge, tidal range, wave conditions, and residence time with the coastal dispersion impacts are investigated.