Geoscience Reference
In-Depth Information
14.3 Methodology
As outlined before, the modelling of coastline changes requires data about surface
elevation, vertical crustal movement, and climatically driven sea level change. In
addition, on a local scale, erosion, transport, and accumulation play a major role.
These morphodynamic processes are controlled by sediment properties and driving
forces. They are simulated by the stratigraphic modelling software Sedsim, origi-
time as a function of the depositional environment.
The structure of the program is modular with distinct algorithms handling the
different physical processes which effect the sediment distribution. Sedsim is con-
trolled by a text file, with each of the separate processes having its own section
which can be selectively used. An orthogonal regular grid is used to describe the
surface and the cumulative deposition and erosion of sediments on that surface are
recorded at user-specified time intervals. Four types of user-specified siliciclastic
sediments are allowed as well as two carbonate types and two organic types.
Fluvial processes are controlled by a marker in cell technique, which flows
Lagrangian fluid elements over the imported digital elevation model (DEM) grid
surface, depositing or eroding sediment depending upon its current transport capac-
ity. Each fluid source is specified by location, initial velocity, volume, and initial
sediment composition, with fluvial, hypopycnal, hyperpycnal, and debris flows
capable of being modelled.
Vertical movements of the earths crust are controlled either by specifying the
tectonic movement of each surface point directly or with the ISOSTACY module
In addition to surface movement, sea level fluctuations are implemented via a simple
input file.
The influence of waves can be incorporated in a range of different waves depend-
ing upon the detail of data available for input. From a general wave direction and
height which lasts for the entire simulation, to a time-varying direction and height,
through to a complete wave field detailing the changes at each grid point. Wave
refraction into shallow water can also be selectively used. The module works by
calculating the sediment mobilized by wave impact on the coastline and determines
the amount of that sediment transported alongshore depending on the wave incident
angle, wave height, depth of mobile bed, and wave base.
Storm surges effects are included either by specifying known storm data includ-
ing the time, incident angle, wave height, and time duration or by creating synthetic
storms by listing the mean storm return time, direction, deviation in direction, wave
height, and storm duration. The storm module calculates the storm erosional impact
above storm wave base and moves the sediment offshore to below storm wave base
perpendicular to the coastline.
Sedsim also offers other modules for modelling slope failure through over-
steepening of sediments, the ability to grow organics and carbonates through a
system of fuzzy rules, compaction due to loading of overlying sediments, a cellular
automata-based aeolian module, as well as the ability to include contour currents
