An energetics bedload model for a plane sloping beach: Local transport

Abstract

Bagnold's energetics‐based sediment transport model for streams is used as a basis for the development of a model for the time‐varying transport of bedload over a plane sloping bed. The sediment transport vector is found to consist of two components: the velocity‐induced transport, directed parallel to the instantaneous velocity vector, and the gravity‐induced transport vector, directed downslope. The model is applied to the case of sediment transport within the surf zone for the separate cases of weak and strong longshore currents, relative to the wave (bore) oscillatory water velocity. The results suggest that Bagnold's oscillatory sediment transport model, which forms the basis for a number of longshore sediment transport models, is only correct for the special case of weak longshore currents and near‐normal incident waves. For an arbitrary strength longshore current v and a local incident wave angle α, the longshore transport rate is found to be proportional to 〈ũ3〉 sin α + 〈ũ2〉v(1 + sin2 α) + v3, where ũ; is the wave‐induced oscillatory water velocity. The model also predicts the onshore‐offshore sediment rate, 〈ix〉. For weak longshore currents and near‐normal incident waves, the predicted equilibrium beach slope is equal to tanϕ〈ũ3〉/〈|ũ;|3〉. Strong longshore currents and or significant local wave angle conditions, however, cause a change in this equilibrium beach slope.

Waves, Currents, Sediment Flux and Morphological Response in a Barred Nearshore System

“…Quite small asymmetries can therefore be more important than any net (Lagrangian type) steady drift, even where the latter may be quite high. The importance of this was clearly recognized by Inman and Bagnold (1963), Inman and Frautschy (1966) and Wells (1967) and most recently in the transport models proposed by Bowen (1980), Bailard (1981) and Bailard and Inman (1981). STORM EVENT 1980:05:31--1980 Figure 3 illustrates the temporal pattern of wind speed and direction and the angle of wave approach through the storm.…”

Near-shore sediment dynamics computation under the combined effects of waves and currents

“…Based on the pioneering works of Bagnold [10,11], the energetics approach was extended for alongshore and crossshore bed load sediment transport in a parallel development to Bowen [12], Bailard and Inman [13] and Bailard [14] extended this theory to account for suspended load. The resulting vector form of the total sediment transport rate kq st l is,…”

Prediction of Formation of Dynamically Stable Ebb Tidal Delta and Measures for Preventing Offshore Sand Loss

“…tanβ c is the equilibrium slope for which zero net cross-shore transport occurs when waves are incident from the direction normal to the slope. This represents the balance between the upslope flow asymmetry and the downslope component of gravity (Inman and Bagnold, 1963;Bailard and Inman, 1981). Regarding Eqs.…”

“…In the original equation by Bailard and Inman (1981), the coefficient G R in Eq. (8) is expressed in terms of the instantaneous velocity, the angle of repose of the sand and a friction factor, but in this study, sand transport due to currents is assumed to satisfy an equation with the same form as Eq.…”

“…(8), the same equation as that used by Serizawa et al (2008), was employed, which was derived by Bailard and Inman (1981) from the bed load transport formula of Bagnold (1963) by a linear approximation of the seabed slope.…”