D-R-A-F-T
Conceptual Program Design
The program is based on the following conceptual model:
1.
Basic processes in sedimentation can be grouped into erosion,
entrainment, transportation, and deposition.
2.
Flowing water has the potential to erode, entrain, and transport
sediment whether or not sediment particles are present.
3.
Sediment on the streambed will remain immobile only as long as the
energy forces in the flow field remain less than the critical shear stress
threshold for erosion.
4.
Even when sand particles become mobile, there may be no net change
in the surface elevation of the bed. A net change would result only if
the rate of erosion was different from the rate of deposition - two
processes which go on continuously and independently.
5.
Cohesive sediments in transport will remain in suspension as long as
the bed shear stress exceeds the critical value for deposition. In
general, simultaneous deposition and erosion of cohesive sediments do
not occur.
6.
The structure of cohesive sediment beds changes with time and
7.
The major portion of sediment in transport can be characterized as
being transported in suspension, even that part of the total load that is
transported close to the bed.
The Derivation
The derivation of the basic finite element formulation is presented in Ariathurai
(1974) and Ariathurai , MacArthur, and Krone (1977) and is summarized below.
There are four major computations.
1.
2.
3.
4.
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