Influences of Common Anthropogenic Modifications on Tidal Circulation in a Shallow Microtidal Estuary: Applications of Basin-scale Nature-based Solutions

Abstract Typical of a shallow estuary, McKay Bay located at the northeastern end of Tampa Bay, Florida, USA, has been heavily altered by anthropogenic activities partially due to its proximity to the Port of Tampa. A bridge and causeway were built crossing the mouth of the bay, along with numerous dredge-and-fill projects within the bay. These common engineering activities have altered tidal circulation by concentrating flow in the deep and wide dredged channel in the middle and weakening the currents in the nearshore area leading to deteriorating environmental conditions along the low-income underserved Palmetto Beach community coast. The objective of this study is to restore the natural tidal circulation pattern by applying basin-scale nature-based solutions, using numerical modeling to evaluate various solutions. A calibrated and verified numerical model was constructed to quantify the impacts of engineering alterations on tidal circulation in this shallow estuary. Based on the numerical modeling results, the present channelized tidal circulation is significantly different from the rather spatially uniform flow pattern under natural conditions with relatively strong flow in the nearshore area. The bridge and causeway system at the entrance to the bay created a stagnant zone at the two corners. The dredging of the natural bayhead delta at the mouth of a tidal creek, which guided tidal flow along the shoreline, played a dominant role in altering bay-wide circulation. The large protruding landfill along the northern shoreline created a corner and a large shadow zone for tidal flow. By restoring the historical bayhead delta, although at a different location, the natural circulation can be restored except at the corners created by irreversible engineering activities. The McKay Bay engineering modifications are quite common. Our approach, based on a key natural feature that was removed by human alteration, can be considered a nature-based solution and have broad applications.