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Full Equations (FEQ) Model for the Solution of the Full, Dynamic Equations of Motion for One-Dimensional Unsteady Flow in Open Channels and Through Control Structures

U.S. GEOLOGICAL SURVEY WATER-RESOURCES INVESTIGATIONS REPORT 96-4240

8. BOUNDARY AND INITIAL CONDITIONS


Simulation of unsteady flow in a stream segment (branch) requires information on the discharge and water-surface elevation at the boundaries of the segment throughout time and at all points in the system at some initial time, as described in section 5.3 " Nature of Shallow-Water Waves." For a network of open channels, the flow paths--branches, dummy branches, and level-pool reservoirs--are separated by special features such as junctions and hydraulic-control structures. Therefore, the system requires internal boundary conditions at the flow-path end nodes connected to special features, as well as external boundary conditions. Internal boundary conditions, which are typically determined from the hydraulic characteristics of the special features, are available for a wide variety of special features simulated in FEQ. This section details the internal and external boundary conditions and the initial conditions simulated in FEQ.

The special features in the stream system are considered small relative to the branches and level-pool reservoirs, so the storage and momentum content in the special features are negligible. Therefore, the equations of motion describing the hydraulic characteristics of flow through the special features that compose the internal boundary conditions are all steady-flow relations. For some special features--a long culvert is a simple example--this assumption is not valid. This culvert may have to be represented as a branch in the form of a storm sewer, not as a culvert, even though it has the physical form of a culvert. The concern in simulation of unsteady flow, however, is not on the physical form but on the effect that the feature has on the flows of interest.

8.1 Internal Boundary Conditions
8.2 External Boundary Conditions
8.3 Initial Conditions

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