4/98
SED2D-WES Version 4.3 Beta
Note that the SA, SR, and ST cards constitute a cascading set of defaults. The SA card should precede the
SR and ST cards. If neither an SR nor ST card is present, the grain size on the SA card will be used at all nodes
for both transport and effective roughness. If SR cards are present, they override the roughness size on the SA card
at those nodes specified. The ST cards override the transport size on the SA card at every node specified on the ST
card.
Two characteristic length parameters are requested on the SA card. CLDE is the length factor for
deposition. The default is a value of 1, corresponding to an average settling depth equal to the water depth. For
fine sediments that are distributed throughout the water column, a value of 0.5 is recommended. For coarser
sediments in less turbulent flows, a smaller value is suggested. CLER is the length factor for erosion. The default
value of l0 is suggested, but more investigation is needed to find the best value.
Settling velocity (WC cards). Settling velocities are specified on the WC cards. This settling velocity is
g.
an effective fall velocity which goes up with grain size, goes down with increasing turbulence, goes up with
increasing aggregation (cohesive sediments), and goes up if a too large value of CLDE is used. The best starting
point for noncohesive sediments are fall velocities for spherical particles of equal diameters.
For data on
appropriate values for settling velocities see "Some Fundamentals of Particle Size Analysis," 1957, Committee on
Sedimentation, Interagency Committee on Water Resources. For cohesive sediments, the settling velocity of
particles can vary enormously with sediment type, salinity, turbulence, and other chemical and physical conditions.
Laboratory or field tests are needed to define effective settling velocities.
Cohesive sediment characteristics (CC and CI cards). Figure 1 illustrates the relation between the
h.
various critical shear stresses for cohesive sediments. These values must generally be determined by laboratory or
field experimentation, but published results for similar sediments can be used if caution is exercised. Values
specified on the CC card for critical shear stresses for erosion and the erosion rate constant are overridden by those
contained on the CI cards.
The CC card should precede the CI cards.
The CI cards are used to assign
characteristics to various types of cohesive sediment bed layers. These characteristics are assigned to existing bed
layers as specified on the CL cards and to new layers as they are deposited. Freshly deposited sediments are
assigned a type 1 designation and increase to higher numbered types as the thickness of sediment above them
increases. Data for the CI cards should come from laboratory tests on the sediments to be modeled.
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WORKING DRAFT
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