Overview of MDFATE

Overview of MDFATE

MDFATE was developed to address dredged material placement site manage-

ment issues. By tracking the volume of material placed in an offshore disposal

site from multiple dredging operations, site managers can plan for maximum

utilization of the site. Multiple disposals that are point dumped during one spe-

cific operation can be simulated to determine if navigation obstructions would be

created. For site-use planning, MDFATE will ultimately allow site managers to

plan for additional disposal sites as sites reach capacity.

While STFATE simulates short-term processes (seconds to hours) and

LTFATE simulates long-term processes (days to months) of dredged material

mounding, MDFATE brackets these processes by modeling the accumulation of

material on the bottom resulting from multiple disposals.

MDFATE may be roughly categorized into three primary components: grid

generation, model execution, and postprocessing. The initial step in executing

MDFATE and the foundation of the model is grid generation. Subsequent to

grid generation, model execution consists of running the modified versions of

LTFATE and STFATE, which provide information to augment the grid. Post-

processing consists of various plotting routines to present model results.

Disposal site-grid generation is based on a user-specified horizontal control

(state plane or latitude-longitude) to create a horizontal grid. Presently,

MDFATE can accommodate a grid with 40,000 nodes, which will allow repre-

sentation of a disposal site up to approximately 22,000 by 22,000 ft (100-ft grid

interval). ODMDS corner points are specified by the user, and MDFATE

creates the horizontal grid based on desired grid intervals.

Vertical control is based on a user-specified datum. MDFATE can auto-

matically create a uniform flat or sloping bottom based on the datum of interest,

or MDFATE can overlay actual bathymetric data in ASCII form and apply it to

the horizontal grid by a multipoint polynomial interpolation.

Once grid generation is completed, MDFATE can simulate multiple (hun-

dreds) disposal events that can extend over 1 year. The disposal operation is

broken down into individual week-long episodes during which long-term

processes are simulated by the modified version of LTFATE. Within each week-

long episode, the modified version of STFATE is executed that simulates

dredged material dumped through the water column to bottom accumulation.

Cumulative results are generated for self-weight consolidation, sediment

transport by waves and currents, and mound avalanching.

The original version of STFATE simulates single disposal events (i.e., one

dump) to model water column concentrations of suspended solids and a conserv-

ative tracer (not done for MDFATE version). STFATE also generates a disposal

mound footprint identifying the extent of dredged material coverage for the

dump as well as mound volume and thickness. Water column currents can be

Appendix E MDFATE Model