Hindcast Modeling of Morphodynamic Changes and UXO Burial Caused by Hurricane Matthew 2016, Fort Pierce, Florida

Abstract

We simulate the burial and exposure of potential UneXploded Ordnance (UXO) during Hurricane Matthew 2016 on the Fort Pierce Naval Amphibious Training Base, Florida (USA). We used a large-scale model to simulate currents, waves, and morphodynamics, and coupled it to DRAMBUIE 3.0, a newly developed UXO burial model, to predict the vertical movement of UXOs in the near shore zone at depths between the depth of closure and the shoreline, considering both a gently sloping beach and a barred beach profile. The effects of Matthew took place mostly in a short window of 10 h before and after the passage of the storm. Within this window, large variability occurred in the significant wave height (from 1 to 4.8 m), near bed turbulence (KC numbers from 20 to 83) and sediment fluxes (up to 2 kg/m/s). Local bedforms influenced the evolution of waves from offshore to the beach, and these bedforms migrated offshore as their stoss side accreted and their lee side was eroded. In the model, exemplar UXOs were placed on the seabed at depths between 3 and 10 m below mean sea level. The model showed that the slope of the beach profiles and in particular the presence of a submerged bar affect the burial or exposure of the UXO. UXOs located in the breaker zone and on a submerged bar were buried the deepest (0.2 m) after the passage of the storm (more than the exemplar reference munitions diameter, 0.155 m). UXOs along the rest of the model domain finished at shallower burial depths, roughly equivalent to the objects’ diameter. The results of the research identified areas where UXOs are most likely to be buried after storms, which will help coastal managers to more efficiently clean up and make safe the near shore seabed. Significant amounts of unexploded ordnance (UXO) and discarded military munitions are present on or beneath the seabed. The action of waves and currents causes UXO to become buried due to scour, settlement, and sediment accretion, or exposed when the bed sediment undergoes rapid or severe erosion. Prediction of UXO burial and exposure requires information on waves and currents, and seabed changes caused by hydrodynamic forcing mechanisms. This paper describes how a hydrodynamic model of coupled wind, waves, and currents was combined with a model to predict scour around UXO objects and self-burial of those objects during Hurricane Matthew. The results showed a variation in space and time in the interactions between the seabed and the objects. In the model, an object was buried in one location during the hurricane, yet an identical object was partially exposed at another location. Elsewhere, burial followed by partial exposure occurred during different stages of the hurricane. The results of the research identified areas where UXOs are likely to be buried after storms, which will help coastal managers to clean up the near shore seabed more efficiently.