Tidal Hydrodynamics under Future Sea Level Rise Scenarios with Coastal Morphology along the Northern Gulf of Mexico

Abstract:

This study examines the integrated influence of sea level rise (SLR) and future morphology on tidal hydrodynamics along the Northern Gulf of Mexico (NGOM) coast with particular focus in three estuaries: Grand Bay, MS, Weeks Bay, AL, and Apalachicola, FL. A large-domain hydrodynamic model was used to simulate astronomic tides for present (circa 2005) and future conditions (circa 2050 and 2100) to understand how sea level and morphology affect tidal heights and velocities. The model was modified with SLR scenarios and projections of morphology obtained from a Bayesian Network (BN); the BN relates driving forces and geological constraints to produce probabilistic projections of shoreline change and dune heights under SLR. Tidal amplitudes within the bays increased as much as 67% (10.0 cm) under the highest SLR scenario. There was a linear correlation between the change in the inlet cross-sectional area under SLR and the change in the tidal amplitude in each bay. Changes in harmonic constituent phases indicated faster tidal propagation in the future scenario in all of the bays except St. Andrew. Tidal velocities also increased in all of the bays, especially in Grand Bay where current velocities doubled under the highest SLR scenario. In addition, the ratio of the flood to ebb velocity decreased (i.e., currents became more ebb dominant) in all of the future scenarios within Weeks Bay and Apalachicola, by as much as 26% and 39%, respectively. Under the higher SLR scenarios, currents those two estuaries reversed from flood-dominant to ebb-dominant. In Grand Bay, the flood-ebb ratio increased (i.e., currents became more flood dominant) by 25% under the lower SLR scenarios, but decreased by 16% under the higher SLR as a result of the offshore barrier islands being overtopped. Results from this study can be used to inform future storm surge and ecological assessments of SLR, and improve monitoring and management decisions within the NGOM estuaries.