# Model help:Avulsion

## Avulsion

This model illustrates the realistic looking deltas generated by a stochastic process.

## Model introduction

The model assumes that an avulsion happens every time step, the basin is flat-bottomed, and the grid scale is such that one cell is always filled by the river’s sediment with every time step. The model randomly generates angles from the distribution X, moves the mouth of the distributary by these angles around the coastline, and fills empty cells with sediment. A uniform distribution builds a symmetric and radial delta while the normal distribution creates a more lobe-like delta. These river-dominated delta morphologies would change with the inclusion of waves, tides, and other processes.

## Model parameters

Parameter Description Unit
Site prefix Site prefix for Input/Output files -
Case prefix Case prefix for Input/Output files -
Parameter Description Unit
Run duration simulation run time year
Standard deviation of avulsion angles degree
Minimum angle degree
Maximum angle degree
Number of rivers -
Bed load exponent exponent used in dividing sediment among branches -
Discharge exponent exponent used in dividing water among branches -
Parameter Description Unit
Number of grid rows number of rows in the computational grid -
Number of grid columns number of columns in the computational grid -
Spacing of grid rows spacing of rows in the computational grid m
Spacing of grid columns spacing of columns in the computational grid m
Row of hinge point -
Column of hinge point -
Parameter Description Unit
Output directory path to output files -
Interval between output files -
mean_bed_load_from_river file output file prefix for variable, in the format of NetCDF -
mean_water_discharge_from_river file output file prefix for variable, in the format of NetCDF -
Parameter Description Unit
Output directory path to output files -
Interval between output files -
Elevation file output file prefix for variable, elevation, in the format of NetCDF -
SedimentFlux file output file prefix for variable,sediment flux, in the format of NetCDF -
river_mouth_x_position file output file prefix for variable, river mouth x position, in the format of NetCDF -
river_mouth_y_position file output file prefix for variable, river mouth y position, in the format of NetCDF -
Parameter Description Unit
Model name name of the model -
Author name Name of the model author -

## Uses ports

This will be something that the CSDMS facility will add

## Provides ports

This will be something that the CSDMS facility will add

## Main equations

• Angular position of the distributary channel after n+1 avulsions
 $\displaystyle{ \Theta _{n+1} = \Theta _{n} + X_{n} }$ (1)

## Notes

In this model, the angular position of the distributary on the delta is the sum of angular jumps (Xn) that are generated from the distribution X. Regardless of the underlying physics, some probability distribution must represent this change in angle. The precise distribution will not be known, but observations of large deltas suggest that the probability of avulsing somewhere nearby is high, while the probability of larger avulsions is low (Milliman et al., 1987).

## Examples

An example run with input parameters, BLD files, as well as a figure / movie of the output

Follow the next steps to include images / movies of simulations: