Boca Raton (Fla.)

Tropical storms and mid-latitude cyclones are major drivers of coastal change and damage in coastal communities. Beaches act as a first line of defense against storms, as well as provide recreation, contribute to the economy, and serve as ecological habitat for coastal flora and fauna. Throughout the year, meteorological event-driven increases in wave energy result in higher amounts of sediment transport that cause rapid coastal zone morphology alterations and threaten these beach functions. This study uses streamer traps to evaluate cohesionless sediment dynamics in the surf zone and storm-induced morphology change in Boca Raton, Florida. The quantitative and sedimentological characteristics of sediment collected in the bottom streamer trap bins was larger grains with a higher capture weight near the seabed compared to sediment captured in the middle and upper streamer trap bins during both the cold front and the tropical storm. A greater quantity of sediment was captured in transport due to the tropical storm compared to the cold front. Morphology change observed as a result of the cold front included berm erosion, swash zone and foreshore accretion, and erosion beyond the -1.0m contour elevation. Analysis of the morphology observed post-tropical storm included berm accretion, and swash zone and foreshore erosion that continued seaward to the end of the profile. Dean number calculations using pre-cold front sediments and wave parameters predicted erosion, and the post-cold front BMAP measurements confirmed this prediction. Dean number calculations using pre-tropical storm sediments and wave parameters predicted accretion and the post-tropical storm BMAP measurements invalidated this prediction at all capture locations, although above the 1.0m contour the berm did exhibit accretion. Results of this study aim to quantify granulometric differences in event-driven sediment transport in Boca Raton, FL for improved prediction capabilities. Given the current trajectory of climate change, sea-level rise, and increased storm intensity, better understanding the morphological impact of different classes of storms is necessary to ensure and improve coastal resiliency and management.

Beach morphology changes naturally with seasonal and event-driven variability in the wave climate, as well as due to anthropogenic activities such as erosion mitigation efforts. In 2017, category four Hurricane Irma caused beach erosion and dune overwash in Boca Raton, FL. Immediate post-storm perigean spring tides coupled with typical winter high-wind conditions imposed a regime of spatially and temporally extended meteorologic and morphologic variability. This study evaluates the morphologic evolution and post-storm recovery in the first year following Hurricane Irma. Time-series topographic surveys and surface sediment samples were collected. Patterns of accretion and erosion were evaluated with regionally measured water and wind levels. Recovery morphology was generally through berm-building, but lacked shoreline stability. Storm impact regime, mitigation structures, and sediment transport patterns drove the recovery. Total volume lost above the 0 m contour due to the storm was not fully recovered within the year, with a large volume measured in the south.