Swash overtopping and sediment overwash on a truncated beach
New experimental laboratory data are presented on swash overtopping and sediment overwash on a truncated beach, approximating the conditions at the crest of a beach berm or inter-tidal ridge-runnel. The experiments provide a measure of the uprush sediment transport rate in the swash zone that is unaffected by the difficulties inherent in deploying instrumentation or sediment trapping techniques at laboratory scale. Overtopping flow volumes are compared with an analytical solution for swash flows as well as a simple numerical model, both of which are restricted to individual swash events. The analytical solution underestimates the overtopping volume by an order of magnitude while the model provides good overall agreement with the data and the reason for this difference is discussed. Modelled flow velocities are input to simple sediment transport formulae appropriate to the swash zone in order to predict the overwash sediment transport rates. Calculations performed with traditional expressions for the wave friction factor tend to underestimate the measured transport. Additional sediment transport calculations using standard total load equations are used to derive an optimum constant wave friction factor of fw=0.024. This is in good agreement with a broad range of published field and laboratory data. However, the influence of long waves and irregular wave run-up on the overtopping and overwash remains to be assessed. The good agreement between modelled and measured sediment transport rates suggests that the model provides accurate predictions of the uprush sediment transport rates in the swash zone, which has application in predicting the growth and height of beach berms. D 2005 Elsevier B.V. All rights reserved.
MODELING AND MANAGING THE LONG-TERM EFFECTS OF ARTIFICIAL DUNE CONSTRUCTION IN THE OUTER BANKS OF NORTH CAROLINA
The goal of this paper is to gain a better understanding of long-term interactions between natural processes and human activities, and how protective measures produce long-term, unintended consequences. Protective measures can disrupt natural processes in such a way that can intensify property damages from natural hazards. Current management practices aimed at defending transportation infrastructure in the Outer Banks of North Carolina are creating such long-term effects. A numerical model examines the long-term, coupled geomorphic and economic consequences of constructing and maintaining artificial dunes. By subjecting a simulated barrier island to a probabilistic storm climate, storm impacts are described in terms of probability distributions of outcomes, which can be translated into quantifiable risk to coastal development. Furthermore, the evolution of this risk over time is investigated as economic activities-and subsequent mitigation measures-are impacted by and alter natural processes of barrier island evolution. Given the magnitude of change that coastal systems will be subject to under climate change, current management strategies designed to maintain system stability are certainly unsustainable and may even be self-defeating in the long-term.
The potential vorticity flux through the Yucatan Channel and the Loop Current in the Gulf of Mexico
Two‐year‐long time series of current and density structure measurements across the Yucatan Channel's main section allow the calculation of the time‐dependent potential vorticity flux between the Gulf of Mexico and the Caribbean Sea, which is characterized by alternating periods of positive (cyclonic) and negative (anti‐cyclonic) vorticity influx. Periods of negative cumulative vorticity influx are related to the Loop Current extending into the Gulf of Mexico, whereas periods of positive cumulative vorticity influx relate to a Loop Current retraction, sometimes coincident with the shedding of an anti‐cyclonic eddy.