Unified View of Sediment Transport by Currents and Waves. I: Initiation of Motion, Bed Roughness, and Bed-Load Transport

Abstract

Attention is given to the properties of sediment beds over the full range of conditions ͑silts to gravel͒, in particular the effect of fine silt on the bed composition and on initiation of motion ͑critical conditions͒ is discussed. High-quality bed-load transport data sets are identified and analyzed, showing that the bed-load transport in the sand range is related to velocity to power 2.5. The bed-load transport is not much affected by particle size. The prediction of bed roughness is addressed and the prediction of bed-load transport in steady river flow is extended to coastal flow applying an intrawave approach. Simplified bed-load transport formulas are presented, which can be used to obtain a quick estimate of bed-load transport in river and coastal flows. It is shown that the sediment transport of fine silts to coarse sand can be described in a unified model framework using fairly simple expressions. The proposed model is fully predictive in the sense that only the basic hydrodynamic parameters ͑depth, current velocity, wave height, wave period, etc.͒ and the basic sediment characteristics ͑d 10 , d 50 , d 90 , water temperature, and salinity͒ need to be known. The prediction of the effective bed roughness is an integral part of the model.

Beach nourishment effects on sand porosity variability

“…USACE (2002) states that the porosity ranges from 25% to 50% in natural sand (2 -0.063 mm) and does not directly depend on grain size but that it is sensitive to the sediment grain shape, roughness angularity and sorting (Dickinson and Ward, 1994). According to Reis and Gama (2010), Soulsby (1991) and Van Rijn (2007), the porosity of a pure marine sand bed is around 35%. However, other recent studies Reed et al, 2010;Tang et al, 2002;Wheatcroft, 2002) have recorded a variety of marine sand porosities, obtained via different techniques, ranging from 36.6 to 43.6% for quartz sands comprised of up to 98% sand particles (a composition very similar to that of the beaches on the Gulf of Cadiz).…”

A large scale morphodynamic process-based model of the Gironde estuary

“…. According to van Rijn [2007], the total bed roughness can be decomposed into a grain roughness ' s k , a small-scale ripple roughness k r , a mega-ripple component k mr , and a dune roughness k d :…”

“…For waves and combined waves and currents, ripple dimensions can be calculated as a function of the wave parameters. Here such estimations have been implemented only in the case of the Dee estuary [see again based on the methodology of van Rijn [2007] which, for combined waves and currents, utilizes a wave-current mobility number (U²+U w 2 )/gd 50 wherein U w is the near-bed wave velocity amplitude.…”

“…Wave stirring in the near-bed layer can greatly enhance the turbulence intensity and this should be reflected, in turn, in the bed roughness k s . Van Rijn [2007] proposed a formulation that typically enhances the 'physical roughness' k s by a factor of between 2 and 5 times due to wave-current interaction. One conceptual uncertainty here, however, is whether the k s enhancement should be applied to some or all of the four component parts of k s involved in Eq.…”

Morphodynamical modelling of field-scale swash events

“…The critical Shields parameter for bedload motion is θ crb ≈ 3.6 × 10 −2 , following Soulsby (1997) and Van Rijn (2007). As the beach sediment is a medium grain size, the angle of repose of sediment φ = 33 • 235 is assumed.…”