This research project will examine how the evolution of the nearshore profile determines beachface erosion and accretion through changes in both the supply and transport of sediment within the swash zone. The lack of information about this set of processes remains a central barrier to the development of theories regarding coastal evolution and beach-dune interaction that can be translated across scales and field sites. Most swash zone studies have considered hydrodynamics and transport without explicit consideration of the beach-state in which the field observations were collected and the dynamic nature of this boundary condition. In this project, the researchers will assess how swash-zone hydrodynamics and sediment transport are dependent on the transformation of the incident wave field across the evolving nearshore profile. The project will involve a complex field-study that simultaneously monitors swash-zone hydrodynamics, sediment transport, and bed elevation change in response to changes in beach-state and nearshore morphology. Field instruments that will be used include ultrasonic distance sensors and current meters in the swash zone, wave and tide sensors in the inner-surf zone, and a terrestrial laser scanner and remote cameras to monitor beachface evolution. The project is expected to yield a rich dataset of evolving swash-zone hydrodynamics and sediment transport in response to changes in the nearshore profile, an important and unique first step to developing a predictive model of beachface evolution.
The impact of a tropical storm or hurricane on a barrier island is dependent on the ability of the beach and dune system to recover since the last storm. The recovery of dunes is dependent on the transfer of sediment from the nearshore to the beachface, where it may become available for aeolian transport to the backshore and dunes. The factors that control the rate and mechanism of swash-zone evolution therefore are of great interest to coastal managers who need improved information and models for predicting the type of impact expected during succeeding storms and for determining whether beach or dune restoration is required to protect property and infrastructure. This project also will provide valuable education and training for a promising graduate student.
This research project examined how the evolution of the nearshore profile determines beachface erosion and accretion through changes in both the supply and transport of sediment within the swash zone. The lack of information in this regard remains a central barrier to the development of a theory of coastal evolution and (indirectly) beach-dune interaction that can be translated across scales and between field sites. The majority of past swash zone studies consider the hydrodynamics and transport, without explicit consideration of the beach-state in which the field observations were collected and the dynamic nature of this boundary condition. This study considers that swash zone hydrodynamics and sediment transport is dependent on the transformation of the incident wave field across the evolving nearshore profile. The study involved a complex but viable field-study that simultaneously monitored swash zone hydrodynamics, sediment transport and bed elevation change in response to changes in beach-state and nearshore morphology. The field instruments included ultrasonic distance sensors and current meters in the swash zone, wave and tide sensors in the inner-surf zone, and a terrestrial laser scanner and remote cameras to monitor beachface evolution. We also used Ground Penetrating Radar to characterize the evolutionary history of the beach face and to use the sedimentary structures as a proxy for beach-dune interaction. Field experiments conducted in Texas, Puerto Rico and Costa Rica provided a rich dataset of evolving swash zone hydrodynamics and sediment transport in response to changes in the nearshore profile, an important and unique first step to developing a predictive model of beachface evolution. Specifically, we found evidence to suggest that the evolution of the beachface is dependent on the nearshore boundary with distinct evolutionary sequences observed for dissipative, intermediate and reflective beaches. While we are continue to analyze the data from all beaches, we believe that the key outcome will be a new conceptual model for the swash zone that shows how it is dependent on the behavior of the nearshore morphology. Combined with the results of a previous NSF grant, the results of this study will clarify the process linkages amongst the nearshore, beach and dune. The impact of a tropical storm or hurricane on a barrier island is dependent on the ability of the beach and dune system to recover since the last storm. The recovery of dunes is dependent on the transfer of sediment from the nearshore to the beachface, where it may become available for aeolian transport to the backshore and dunes. In this respect, the factors that control the rate and mechanism of swash zone evolution is of great interest to coastal managers who need a means to predict the type of impact expected during succeeding storms and in determining if beach or dune restoration is required to protect property and infrastructure.
