HR: 0800h
AN: H51D-0400    [Abstracts]
TI: Wave-Dominated Delta Evolution: New Insights From One-Line Numerical Simulations
AU: * Ashton, A D
EM: andrew.ashton@duke.edu
AF: Division of Earth and Ocean Sciences, Nicholas School of the Environment and Earth Sciences/ Center for Nonlinear and Complex Systems, Duke University, Box 90230, Durham, NC 27708 United States
AU: * Ashton, A D
EM: andrew.ashton@duke.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Rd, Woods Hole, MA 02543 United States
AU: * Ashton, A D
EM: andrew.ashton@duke.edu
AF: USGS Woods Hole, 384 Woods Hole Rd, Woods Hole, MA 02543 United States
AU: Murray, A
EM: abmurray@duke.edu
AF: Division of Earth and Ocean Sciences, Nicholas School of the Environment and Earth Sciences/ Center for Nonlinear and Complex Systems, Duke University, Box 90230, Durham, NC 27708 United States
AU: Giosan, L
EM: lgiosan@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Rd, Woods Hole, MA 02543 United States
AB: Traditionally, researchers have expected that alongshore sediment transport always flattens planform bumps along an otherwise straight, sandy shoreline. This thinking was extended to the evolution of wave-dominated deltas after Komar (1973) added a fixed sediment source to a numerical one-contour-line coastal evolution model and showed that waves approaching with near-normal incidence (with a small angle between wave crests and the coastal trend, `shore angle') spread the sediment delivered at a river mouth evenly along the delta's coast, leading to `classic' delta evolution. However, recent research has underscored that shoreline evolution is strongly dependant on wave approach angle, and that the ability for alongshore sediment transport to flatten a planform bump decreases as deep-water wave angle increases. Waves approaching from sufficiently oblique angles (`high-angle' waves) result in a shoreline instability. Using a one-contour-line numerical model that includes a simple parameterization of barrier overwash, we investigate how the distribution of high-angle waves affects the evolution of wave-dominated deltas. `Sandy' sediment (that remains within the nearshore zone) is added at a constant rate to the coast at a fixed alongshore location. Numerical simulations show that, for the same sediment supply and wave energy, deltas prograde faster and with a more pronounced aspect ratio if the proportion of high-angle waves is increased. An asymmetry in the wave climate increases the tendency towards shoreline instability on the downdrift delta wing; simulations exhibit overwashing spits that extend from the river mouth. Similar asymmetrical delta evolution occurs at various spatial scales on the wave-dominated deltas such as Brazos, Nile, or Danube. Other simulations with an initially high, then later reduced, sediment input rate resemble the basic form of the Ebro delta with lobes recurving towards the mainland that extend from both sides of the river mouth. Although other processes that may be important in the evolution of some deltas are not included in the numerical model, these preliminary modeling exercises demonstrate that wave-dominated deltas can respond to reshaping by gradients in alongshore sediment transport in more complex and interesting ways than previously thought.
DE: 1862 Sediment transport (4558)
DE: 4217 Coastal processes
DE: 4255 Numerical modeling (0545, 0560)
DE: 4485 Self-organization
DE: 4546 Nearshore processes
SC: Hydrology [H]
MN: Fall Meeting 2005