Measurement and prediction of wave‐generated suborbital ripples

Abstract

[1] Experiments in a large-scale wave flume using regular and irregular waves with periods between 4 s and 6 s and heights between 0.2 m and 1.55 m have examined the formation of wave-generated ripples using sediment beds composed of four grain sizes (D 50 = 0.349 mm, 0.329 mm, 0.220 mm, and 0.162 mm) in a water depth of approximately 4 m. Estimates of wave-generated ripple height,h, and wavelength, l, were obtained using zero down-crossing analyses of bed profiles measured by acoustic means along a 4-m transect normal to the ripple crests. Further information pertaining to l was obtained from bed images obtained using scanning sonar. The analyses reported here focus on the sequence bedforms that evolved in response to stepwise increases and decreases in wave height. Results show that ripples for the most part are suborbital in nature and do not conform well to empirical equations used frequently to predict h and l values in the field. On the basis of the present data, two new equations for prediction of h and l are obtained and their use in field situations where hydrodynamic and sedimentary conditions favor development of suborbital bedforms is recommended.

The dimensions of sand ripples in full-scale oscillatory flows

“…Therefore, in terms of predicting the dimensions of equilibrium ripples generated by full-scale oscillatory flows, the best data arguably come from controlled full-scale laboratory experiments in which there is a high level of certainty about the flow and sand properties and the equilibrium state of the bed. Such studies include the oscillatory flow tunnel experiments of Lofquist (1978), Ribberink and Al-Salem (1994) and O'Donoghue and Clubb (2001) and the full-scale wave flume experiments conducted by Thorne et al (2002) and Williams et al (2004).…”

Predicting bedforms and primary current stratification in cohesive mixtures of mud and sand

“…The most comprehensive predictor for current-generated, wavegenerated and combined-flow bedforms was proposed by Soulsby et al (2012). Other widely used bedform predictors were proposed by Haque & Mahmood (1985), Baas (1993), van Rijn (1993, Julien & Klaassen (1995), Raudkivi (1997) and Karim (1999) for unidirectional currents, and by Nielsen (1981), van Rijn (1993), Wiberg & Harris (1994), Malarkey & Davies (2003), Grasmeijer & Kleinhans (2004), Williams et al (2004Williams et al ( , 2005, Camenen & Larson (2006), Yan et al (2008), Camenen (2009), Pedocchi & Garcia (2009) and Nelson et al (2013) for oscillatory currents.…”

Predicting Movable Bed Roughness in Coastal Waters

“…The common method requires a prediction of ripple geometry and there is no lack of published empirical relationships from laboratory and field measurements relating ripple dimensions to flow and sediment characteristics (e.g., Miller and Komar 1980, Nielsen 1981, Grant and Madsen 1982, Kos'yan 1988, Wikramanayake and Madsen 1994, Wiberg and Harris 1994, Mogridge et al 1994, Faraci and Foti 2002, Williams et al 2004, O'Donoghue et al 2006. Each formula performs well against the data used in its formulation, as expected, but generally much less successfully under reasonably different conditions.…”

“…It is physically reasonable to expect the larger waves in a random wave train to have a greater effect on the ripple dimensions than the smaller waves, which suggests that a near-bottom velocity greater than the rms velocity is necessary to represent random waves. Faraci and Foti (2002) and Williams et al (2004) similarly found that a single relationship could be used to represent ripple geometry under both types of waves if the significant wave height was used for the random waves. Furthermore, representing random waves with the significant near-bottom velocity has been used to successfully consolidate data in other boundary layer processes, such as initiation of motion (Madsen 2002).…”