To Appear: Proceedings 28th Coastal Engineering Conference, World Scientific Press, 2002.
ANALYTICAL MODEL OF NAVIGATION CHANNEL INFILLING
BY CROSS-CHANNEL TRANSPORT
Nicholas C. Kraus1 and Magnus Larson2
Abstract: An analytic model is presented for estimating the time-evolution of
bank encroachment, sediment deposition, and bypassing of a channel of specified
initial cross section exposed to an active zone of longshore or other known cross-
channel sediment transport. It is applicable to channels in estuaries, bays, and
lakes by input of the rate of sediment transport (sand to gravel range) approaching
normal to the channel. The model can be applied to estimate necessary depth and
width of a channel to be newly dredged or the performance of a channel to be
deepened and widened. The model is based on the continuity equation governing
conservation of sediment volume, together with typically available or estimated
input transport rates in engineering applications. An analytical solution of the
linearized coupled differential equations has pedagogic value and gives insight into
the processes of channel infilling and bypassing. The analytic model can also
serve as an engineering screening tool. Numerical solution of the full nonlinear,
coupled equations allows extension to more complex situations.
Navigation channels issuing through inlet entrances intercept sediment moving
alongshore. Sediment transported to a navigation channel can reduce channel width by
accumulating on the sides (bank encroachment), and channel depth can be reduced through
deposition on the bottom (Fig. 1). Sediment can also pass over a channel by moving in
suspension, and material deposited in the channel can be re-suspended and transported out,
both processes contributing to bypassing. At inlets, the bypassing rate in the predominant
direction of transport to the down-drift beach enters in sediment budgets, whereas the gross
rate of longshore transport relates to channel dredging requirements. In the present
discussion, along-channel transport is omitted, as is bi-directional transport, although the
latter is readily accommodated in the present model framework. Numerical solutions can
accommodate these processes, whereas analytic solutions are sought here.
1) US Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory,
3909 Halls Ferry Road, Vicksburg, MS 39180-6199 USA.
2) Water Resources Engineering, Lund University, Box 118, S-221 00 Lund, Sweden.
Kraus and Larson