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.
Wave run-up and wave overtopping at dikes and revetments
This paper summarizes newly obtained results of wave run-up on and overtopping at dikes and similar structures as sloping revetments and seawalls. The contents is focussed on formulae for conceptual design. Various influences are incorporated in the formulae in the form of reduction factors. These include the influence of a berm, a shallow foreshore (depth limited waves), roughness elements on the slope and obliquely incoming waves, both short­ crested and long-crested. The wave run-up can be described as a function of the breaker parameter and reduction factors. Wave overtopping is given by two formulae, one for breaking waves, the other for non-breaking waves. In addition, a distribution is given for overtopping volumes per wave. The maximum volume of overtopping by the highest wave may be thousand times larger than the average overtopping discharge. Wave runup Introduction Dikes or revetments usually have a rather mild slope, mostly of the order of 1:2 or milder. A dike consists of a toe construction, an outer slope, often with a berm, a crest of a certain height and an inner slope, see Figure 1. The outer slope may consist of various materials such as asphalt, a revetment of concrete stones, or grass on a clay cover layer. Combinations of these are also possible . ........................ ­
Atmospheric drag effects on the KOMPSAT-1 satellite during geomagnetic superstorms
We examine the atmospheric drag on the low earth-orbiting satellite, KOMPSAT-1 in a sun-synchronous orbit at ~685-km altitude starting in 1999, during a 3-month (October-December) period in 2003. This 3-month interval includes the October 29-30 and November 20 magnetic superstorms and weak to moderate storms. We observed that the daily KOMPSAT-1 drag acceleration transiently responses to transient storm-time disturbances. That is, there is an one-to-one correspondence between the KOMPSAT-1 drag accelerations and the storm events. We find that the drag acceleration correlates strongly with the level of geomagnetic disturbance. This indicates that the trajectory of KOMPSAT-1 is significantly perturbed during extremely disturbed intervals because of atmospheric density increase. The main contributor to the density increase is Joule heating associated with the geomagnetic activity rather than the solar EUV radiation, as reported by previous studies. We suggest that understanding how the upper atmosphere responses to the geomagnetic-associated heating is important to predict space weather impacts on low earth-orbiting satellites.