HR: 0830h
AN: H51D-1112    [PDF]
TI: A 3D Ecomorphodynamic Model of Tidal Marsh Development
AU: * Kirwan, M L
EM: mlk13@duke.edu
AF: Duke University, Div. Earth and Ocean Sciences Duke University Box 90229, Durham, NC 27708 United States
AU: Murray, A B
EM: abmurray@duke.edu
AF: Duke University, Div. Earth and Ocean Sciences Duke University Box 90229, Durham, NC 27708 United States
AU: Morris, J T
EM: morris@biol.sc.edu
AF: University of South Carolina, Dept. of Biological Sciences University of South Carolina, Columbia, SC 29208 United States
AU: Pratson, L F
EM: lincoln.pratson@duke.edu
AF: Duke University, Div. Earth and Ocean Sciences Duke University Box 90229, Durham, NC 27708 United States
AB: Extensive loss of global marshlands has been attributed to a combination of sea level rise, subsidence, erosion, and reduced sediment supply. Field and laboratory measurements indicate that in many marshes, vertical accretion rates are in equilibrium with sea level rise. Because vertical accretion rates appear to keep pace with sea level rise even in areas of widespread lateral marsh loss, previous modeling efforts which have been restricted to zero and one dimensional models of vertical accretion are inadequate to characterize the response of marshes to environmental change. Furthermore, interactions between biological and physical processes, although recognized as essential components of marsh evolution, have been ignored in previous models, greatly limiting an understanding of marsh morphodynamics. We have developed a three dimensional model of tidal marsh development that integrates ecological relationships between marsh productivity, relative sea level, and sediment accretion with a spatially explicit, physical model of the geomorphological evolution of the marsh that is applicable to large spatial and temporal scales. The model consists of a cellular topographic surface initially flooded to high tide water depth. Parcels of water in each cell drain according to a parametrically represented water-surface elevation. Discharge is the cumulative volume of the parcels passing through divided by a typical period of high flow during a tidal cycle, 3 hrs. Velocities, based on Chezy-Manning equations and the cumulative discharge, are calculated in each cell. The local deposition rate is proportional to the local depth of the bed below high tide level, up to a threshold depth above which deposition is constant. The constant of proportionality between deposition rate and water depth is a function of biomass production and suspended sediment concentration. Local erosion rates are proportional to bed shear stress when a critical shear stress is exceeded. Bed shear stress is estimated by $\tau_{b} = \rho f_{c} v^{2}$, where v represents a typical velocity during the period of high flow during a tidal cycle. The model explicitly runs over a single ebb tide drainage. If flow fields are assumed to be similar during the flood tide, the results from the single ebb flow can be extrapolated in time steps ranging from days to years. With a constant sea level and sediment supply, the model has been used to build a marsh platform dissected by tidal creeks that is everywhere in steady state. Model experiments on geological time scales featuring variation in sea level and suspended sediment concentration will allow the simulation of marsh response to changing environmental conditions.
DE: 0400 Biogeosciences
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1890 Wetlands
SC: Hydrology [H]
MN: 2003 Fall Meeting