Figure 1. Planview sketch for channel transport sections

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ERDC/CHL CHETN-IV-34

June 2001

Outer Wave

Breakers

Surf

Zone

Wave

Crest

2 3

Channel

Channel Section

Centerline

Figure 1. Planview sketch for channel transport sections

Transport at Channel: The transport rate qin at the updrift edge of the channel may be

calculated from the depth-averaged longshore current (current uniform through the water

column) and the suspended sediment concentration distribution according to the product,

qin = ∫ U aC ( z)dz = U a ∫ C ( z)dz

(1)

where Ua = depth-averaged velocity normal to the channel, C(z) = sediment concentration, z =

elevation from the surrounding (ambient) bed, and ha is the ambient depth adjacent to the

channel (Figure 2). The transport rate per unit length of channel may have to be divided into

sections as shown in Figure 1, according to the current, ambient depth, channel depth, and

presence of wave breaking.

Empirically, the sediment concentration profile in the surf zone has been found to decrease with

elevation from the bottom as an exponential shape,

C ( z) = Cb exp ( -λz / ha )

(2)

where Cb = concentration at the bed, and λ = dimensionless empirical suspended-sediment decay

coefficient (Kraus and Dean 1987). The transport rate of sediment suspended to a certain level zs

above the ambient bed adjacent to the channel is then found by integration to that elevation as:

U aCbha

[1 - exp(-λzs / ha )]

qin ( zs ) = U a ∫ Cb exp ( -λz / ha ) dz =

(3)