DeltaRCM’s model algorithm consists of a rule-basedflow routing scheme and a set of sediment transport rules. In each time step, water and sediment“parcels”enter the domain through afixed inlet channel and are routed by a weighted random walk. Weights are determined by the average downstream direction, the water surface gradient, and a depth-dependentflow resistance. The proportion of sediment parcels which are sand (fsand) can be specified; the remaining parcels are mud, and each has a different set of erosion and deposition rules. After routing the water parcels, the depth-averagedflowfield and then the water surface profile are updated, the sediment parcels are routed, and finally, the bed elevations are updated. A more detailed description of the model can be found in Liang, Voller, and Paola (2015), and an assessment of the hydrodynamics can be found in Liang, Geleynse, et al. (2015). Model deltas have also been extensively compared to observational, experimental, and numerical-model (Delft3D) data sets (Liang et al., 2016).

We develop and incorporate a simplified representation of emergent vegetation (e.g., marsh grasses) into the model. The vegetation is characterized by a rooting depth (droot), stem diameter (dstem), growth rate (r), and carrying capacity (K). We do not consider growth of individual plants, but rather a fractional cover of vegetation (representing biomass density) in each cell (fveg). Vegetation is established at the end of each time step in any cell with water depthh<0.5 m and the magnitude of bed elevation change in that time step Δη<0.01droot(i.e., the bed is essentially stable) atfveg= 0.05. We do not consider lateral propagation of vegetation, or growth of vegetation patches within a model cell. Vegetation establishes in a cell whenever model conditions become favorable—representing the assumption that the dispersion of seeds through the channel network would not limit growth over the time scales involved in delta evolution and that new land would be colonized effectively as soon as it becomes suitable. Once established, vegetation grows logistically up to the maximum density (fveg= 1). Both erosion and deposition cause mortality within a cell (Pasquale et al., 2014; Perona et al., 2012):fvegis reduced in each time step byΔη droot, assuming that there will always be a small number of small or weak plants that can easily be uprooted or buried. We do not consider organic sediment production, as we are interested specifically in the cohesive effects of vegetation.

Quoted from : Comparing the Cohesive Effects of Mud and Vegetation on Delta Evolution