Browsing by Author "Blenkinsopp, C. E."
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- Overwash experiment on a sandy barrierPublication . Matias, Ana; Masselink, G.; Kroon, A.; Blenkinsopp, C. E.; Turner, I. L.This paper uses results obtained from the large-scale BARDEX II experiment undertaken in the Delta flume to investigate the morphological response of a prototype sandy barrier to wave and tidal forcing during overwash conditions. Since overwash processes are known to control short-term barrier dynamics and long-term barrier migration, the development of a robust quantitative method to define the critical conditions leading to barrier overwash is important both for scientific and practical management purposes. The Overwash Potential (OP), defined as the difference between the wave runup and the barrier elevation is used to define the overwash threshold condition, and to predict the morphological outcome of a particular overwash event. When OP is negative, wave runup is lower than the barrier crest and insignificant morphological changes are noticed at the barrier crest. When OP is positive, overwash occurs because predicted runup elevation is higher than the barrier crest. When OP is close to zero, overtop is expected with limited intrusion of water across the top of the barrier crest. To make effective use of OP it is necessary to identify a reliable runup predictor. Twelve runup equations were tested for this purpose, and the results were compared with the ones obtained using data from BARDEX experiment on a gravel barrier. A most reliable approach for the determination of OP for sandy barrier was similar to gravel barrier overwash experiments, with runup predictions provided by the equation of Stockdon et al. [Stockdon, H.F., Holman, R.A., Howd, P.A.,Sallenger, A.H., 2006. Empirical parameterization of setup, swash, and runup. Coast. Eng., 53, 573-588]. This is striking, since different runup predictors would have been expected because beach slope, hydraulic conductivity, grain-size, amongst other factors, differ for both types of barriers. Nevertheless, the two main morphologic characteristics for the computation of OP are beach slope and the barrier crest elevation, both accounted for in the proposed equation. The use of OP values provides a practical means by which to identify potential coastal hazards associated with barrier overwash processes and is considered to have a range of practical coastal management applications.
- Wave runup and overwash on a prototype-scale sand barrierPublication . Blenkinsopp, C. E.; Matias, Ana; Howe, D.; Castelle, B.; Marieu, V.; Turner, I. L.Accurate methods to predict wave runup are of critical importance to coastal engineers. Extreme runup during storm conditions can present a danger to coastal infrastructure and lead to dune overtopping and erosion, overwash. of barrier beaches and is an essential design parameter for certain coastal protection works. This paper uses data obtained during the unique BARDEX II prototype-scale laboratory experiment on a reflective sand barrier to investigate wave runup and overwash. Runup measurements were acquired using ultrasonic altimeters, 2D scanning Lidar and camera systems under controlled wave and water level conditions. It was found that extreme runup (R-2%) scaled well with the deepwater Irribarren number where the beach slope was taken to be the beach face gradient. The lower limit of the swash zone, defined by the 2% wave rundown limit was also found to be a function of the Irribarren number and was consistently below the SWL in all tests. The high resolution free-surface measurements obtained using the ultrasonic altimeters and Lidar enabled an analysis of the dynamics of individual swash events. It was found that the vertical runup excursion of each swash correlated strongly with the height of the bore at collapse, and could be predicted based on the assumption of a conversion of potential to kinetic energy at bore collapse. (C) 2015 Elsevier B.V. All rights reserved.