Noda (1971, 1972) proposed a two-dimensional, coastal movable-bed, scale-model relationship with four basic scale ratios: (a) horizontal scale, (b) vertical scale, (c) sediment-size ratio, and (d) relative specific weight ratio. The model law was derived by empirically matching the distance from the stillwater level (SWL) intercept to the toe of the foreshore. This study was conducted to investigate the effects of the model sediment-size distribution and particle shape in movable-bed models and if possible further refine Nada's scale relationship. An experimental evaluation of the scale model relationship was also performed. The results showed that the effects of grain shape and size distribution are varied. In many cases there was little or no measurable effect; in others, particularly for smaller wave steepnesses, marked differences were apparent. These included multiple bars on profiles consisting of sediment with a bimodal sediment-size distribution and an unstable bar on profiles consisting of sediment with a very narrow unimodal size distribution or a spherical grain shape. Recommendations are made to avoid such sediments as possible model materials. The experiments showed that the initial profile slope influences the final stable profile shape. Under identical experimental conditions, the position of the longshore bar on the final stable profile varied between experiments, indicating that defining the "equilibrium profile" is not as straightforward as has been assumed. "Rocklite," a manufactured, lightweight ceramic sediment, was a potentially useful model material. The model evaluation tests were only partially successful. The slope of the foreshore was reproduced in scale, but the shape of the offshore and surf zones and the movement of the shoreline were not reproduced. Thee general results tend to confirm the difficulties of obtaining successful beach models in similitude.
Grain Shape and Size Distribution Effects in Coastal Models
Technical Paper ; TP 76-11
1976
17465873
Report
Elektronische Ressource
Englisch
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