Abstract
Many existing practical sand transport formulae for the coastal marine environment are restricted to a limited range of hydrodynamic and sand conditions. This paper presents a new practical formula for net sand transport induced by non-breaking waves and currents. The formula is especially developed for cross-shore sand transport under wave-dominated conditions and is based on the semi-unsteady, half wave-cycle concept, with bed shear stress as the main forcing parameter. Unsteady phase-lag effects between velocities and concentrations, which are especially important for rippled bed and fine sand sheet-flow conditions, are accounted for through parameterisations. Recently-recognised effects on the net transport rate related to flow acceleration skewness and progressive surface waves are also included. To account for the latter, the formula includes the effects of boundary layer streaming and advection effects which occur under real waves, but not in oscillatory tunnel flows. The formula is developed using a database of 226 net transport rate measurements from large-scale oscillatory flow tunnels and a large wave flume, covering a wide range of full-scale flow conditions and uniform and graded sands with median diameter ranging from 0.13mm to 0.54mm. Good overall agreement is obtained between observed and predicted net transport rates with 78% of the predictions falling within a factor 2 of the measurements. For several distinctly different conditions, the behaviour of the net transport with increasing flow strength agrees well with observations, indicating that the most important transport processes in both the rippled bed and sheet flow regime are well captured by the formula. However, for some flow conditions good quantitative agreement could only be obtained by introducing separate calibration parameters. The new formula has been validated against independent net transport rate data for oscillatory flow conditions and steady flow conditions.
Highlights
In recent years a substantial body of field- and laboratory-based research has been devoted to measuring sand transport processes induced by waves and currents, and predictive approaches for the net, wave-averaged sand transport have been developed
The formula is based on Dibajnia and Watanabe’s (1992) semi-unsteady half-cycle concept, which accounts for the transport contribution related to unsteady phase lag effects within the wave boundary layer, and has bed shear stress as the main forcing parameter
The formula is developed using a database of 226 net transport rate measurements from largescale oscillatory flow tunnels and a large wave flume, covering a wide range of full-scale flow conditions and uniform and graded sands with median diameter ranging from 0.13mm to 0.54mm
Summary
The representative half-cycle orbital velocity for the wave crest, uc,r , and for the wave trough, ut,r , is : uc,r. The representative combined wave-current velocity vectors for each half-cycle are : uc,r uc,rx , uc,ry uc,r uδ cos , uδ sin (12). The degree of velocity skewness is expressed through the velocity skewness parameter R uc /(uc ut ) ; the degree of acceleration skewness is expressed through uc /(uc ut ) , where uc and ut are the amplitudes of the horizontal flow acceleration in the crest and trough directions respectively. In the case of irregular wave conditions we adopt the representative wave approach, in which the input water particle kinematics are those for a regular wave with time-series based on u usig , T = Tp, R = Rsig and β = βsig, where usig is the significant orbital velocity amplitude, Tp is peak spectral period, Rsig and βsig are the significant values of velocity and accelerations skewness parameter respectively
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