Natural and Anthropogenic Factors Controlling Circulation at the Terminus of a Seagrass-covered Estuary, Fort DeSoto Bay, West-Central Florida

Abstract

Vickery, C.G.; Wang, P., and Cheng, J., 2022. Natural and anthropogenic factors controlling circulation at the terminus of a seagrass-covered estuary, Fort DeSoto Bay, West-Central Florida. Journal of Coastal Research, 38(4), 681–698. Coconut Creek (Florida), ISSN 0749-0208. Causeway construction and channel dredging are common engineering activities in shallow estuaries and can significantly alter natural circulation patterns. Bridges are often installed on causeways to improve circulation. This study examines the influence of dredged channels, causeways, and bridges on circulation patterns within a shallow estuary with dense seagrass beds using a calibrated and verified numerical model. For the case of Fort DeSoto Bay in west-central Florida, the causeways disrupted the natural east-west flow and reduced current velocities within the seagrass beds in the southern terminus portion of the estuary by up to 76%. The tidal bridges increased velocity in the stagnant areas by up to 226%. Up to 26% of the tidal prism in the lower half of the bay passes through the bridges during a spring flood-tidal cycle. Thus, the bridges significantly improved tidal flushing between the estuarine cells divided by causeways. The unvegetated dredged channels serve as efficient conduits that facilitate penetration of tidal currents into the southern and terminus of the bay, leading to significantly higher current velocity in the channels and corresponding reduced velocity over the adjacent seagrass beds. The channels allow for improved tidal flushing within the otherwise stagnant southern terminus of the bay and therefore can be designed for the purpose of improving circulation.