Beaches

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.

A novel, 'near-real' time technique; peptide nucleic acid chemilumiscent in situ hybridization (PNA CISH), was developed and validated for detecting, enumerating and identifying potential indicators (Staphyloccus aureus and Pseudomonas aeruginosa) of beach quality. To understand the dynamics of bacterial indicators a plethora of physical, chemical and biological parameters were tested under field and lab conditions. Escherichia coli tagged with green fluorescence protein (GFP) was used to assess the impact of wave energy and rainfall on seawater counts. PNA CISH and plate counts correlated strongly (r = 0.94 to r = 0.86). Temperature, salinity, nutrient availability and predation significantly influenced the survival of indicators. Rainfall and wave energy affected the re-suspension of bacteria from sand onto overlying water. Overall PNA CISH provides a reliable rapid method for beach monitoring. The implications of beach topography and sampling time on the numbers of Clostridium perfringens and other potential indicators are discussed. Data suggest a revision of policy for tropical sandy beaches.