Postprocessing

Postprocessing

Model output from MDFATE consists of two-dimensional (2-D) contour

plots and 3-D surface images. Output can be either viewed within MDFATE or

data exported to an external graphics package for plotting. MDFATE also

allows grid comparison where before/after scenarios can be examined to analyze

mounding and/or erosion of a dredged material mound. Generic mounds may

also be created to model long-term morphological behaviors.

Capping Option

A dredged material capping option was developed for inclusion in the

MDFATE model. It is based on a modification to STFATE that allows for the

slow release of material from a barge/hopper so it may spread evenly on the

bottom with a minimum amount of momentum. The capping option specifically

addresses the short-term processes that affect dredged material as it experiences

passive transport, diffusion, and settling of solids based on individual particle

fall speed. The capping option assumes the material will be placed along

multiple transects that are repeated and offset to achieve the desired cap

thickness.

The STFATE model and its associated grid domain is used as a kernel within

the MDFATE grid domain for every disposal/capping event. The capping

module uses STFATE with a grid limited to 25 by 25 square elements as

opposed to the standard 45 by 45 rectangular grid elements available in the

original version of STFATE. If the capping site is large, each load of cap

material may require partitioning to ensure its fit within the adapted STFATE

grid. Running the adapted STFATE grid as a kernel within the MDFATE grid

and possible material partitioning contributes to a higher level of complexity for

the capping module than for MDFATE alone. This complexity, therefore, leads

to increased execution time.

Two disposal methods can be simulated with the capping module. One

method is the slow release of cap material through the slightly cracked (1 to 2 ft)

split hull of a split hull barge/hopper dredge. The second method simulates

hydraulic pipeline discharge from a hopper dredge reversing its dredge pumps.

The simulation can be either for pumping in the direction of vessel transport or

counter to vessel transport as the vessel transects the disposal area.

Due to the DOS 640K memory limitations, the capping module must be run

independently of the LTFATE long-term processes simulation. If the user

desires to simulate both capping and long-term processes, the MDFATE capping

module must first be executed followed by the LTFATE portion of MDFATE.

Appendix E MDFATE Model