Model Input

Figure D1. Illustration of placement processes

Model Input

Input data for the model are grouped into the following general areas:

(a) description of the disposal site, (b) description of site velocities, (c) controls

for input, execution, and output, (d) description of the dredged materials,

(e) description of the disposal operation, and (f) model coefficients.

Ambient conditions include current velocity, density stratification, and water

depths over a computational grid. The dredged material is assumed to consist of

a number of solid fractions, a fluid component, and conservative dissolved

contaminants. Each solid fraction has to have a volumetric concentration, a

specific gravity, a settling velocity, a void ratio for bottom deposition, critical

shear stress, and information on whether or not the fraction is cohesive and/or

strippable. For initial-mixing calculations, information on initial concentration,

background concentration, and water quality standards for the constituent to be

modeled has to be specified. The description of the disposal operation includes

the position of the disposal barge or hopper dredge on the grid; the barge or

hopper dredge velocity, dimensions, and draft; and volume of dredged material

to be dumped. Coefficients are required for the model to accurately specify

entrainment, settling, drag, dissipation, apparent mass, and density gradient

differences. These coefficients have default values that should be used unless

other site-specific information is available. Table D1 lists the necessary input

parameters with their corresponding units. Table D1 also lists the input param-

eters for determining the contaminant of concern to be modeled based on

dilution needs. More detailed descriptions and guidance for selection of values

for many of the parameters are provided directly on-line in the system.

Appendix D Short-Term Fate of Dredged Material Model