Temporal and Spatial Sequencing of Destratification in a Coastal Plain Estuary

Abstract

Periodic destratification of the York River estuary of Virginia was noted by Haas (1977) to closely follow the fortnightly neap/ spring cycling of tides. Continued investigations of this tributary to Chesapeake Bay prompted Hayward, Welch and Haas (1982) to formulate a conceptual model (henceforth referenced as the HWH model) of destratification-restratification based on limited observations in the lower York River. The HWH model progresses through the following steps: 1) Relatively fresh water is advected into the York River from Chesapeake Bay as a result of tidal current phase relationships and increased tidal excursion during spring tides. 2) This reduces (and may reverse) the horizontal pressure gradient which drives normal estuarine circulation thereby limiting the importation of relatively saltier bottom water from the bay. 3) Normal mixing processes enhanced by stronger currents during spring tides and the limited availability of saltier bottom water combine to produce a well-mixed water column. 4) Restratification of the water column starts when reduced post-spring tidal currents fail to advect fresher water into the York from the bay.