Sediment transport

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.

For the last several decades, beach nourishment has been a widely implemented erosion mitigation strategy along many developed coastlines. Measuring subsequent patterns of erosion and accretion can help elucidate local sediment transport trends, improve time scale predictions of profile equilibration, decrease renourishment intervals, and adjust future engineering design of nourishments. This study evaluates the morphologic evolution of two beach nourishment projects (e.g., characterized as a full and partial nourishment) at the same location in Boca Raton, Florida using time series beach profiles, surface sediment samples, and wave data. More than 85% of sediment volume was retained within the full nourishment six months after project completion, compared to 50% retained eight months after completion of the partial nourishment. Wave energy largely influenced immediate post nourishment change. Profile equilibration was controlled by high-energy events (i.e., hurricanes) for both nourishments.

Due to the fact that most of closed-end canals are protected from high energy inputs, these canals tend to act as sediment traps. Accumulation of deposited material creates navigational and flood problems. Shoaling in closed-end canals is caused mostly by fine sediments. The behavior of fine sediments can be quantitatively described by means of a mass balance equation. More specifically, the advection-dispersion equation including proper sink/source terms can be used. The sink/source terms represent the processes of deposition and erosion respectively. The purpose of this thesis is to develop analytical solutions of the unsteady advection-dispersion equation as applied to free surface closed-end canals. Solutions are obtained under various initial and boundary conditions, by using the finite transformation analysis. The simulation results are validated against laboratory data.