Problem

How can I model a user defined downstream tailwater condition, for example to model a downstream pipe that is assumed to be full?

Solution

There are multiple options to choose from for a boundary condition type of an outfall as follows.

1. Tidal Gate – Used to restrict backflow from entering system
2. Time-Elevation Curve – Used to describe elevation changes at boundary condition over time
3. Elevation (User Defined Tailwater) – To specify value of known tailwater at boundary (assumed hydraulic grade)
4. Elevation-Flow Curve - Used to define elevation changes at boundary condition over a range of flows.
5. Boundary Element – Can connect outfall to another element like pond
6. Cyclic Time-Elevation Curve – Used to describe the elevation changes at the boundary that repeat over time

Detailed information about each type can be found in help documentation under “Outfall-Boundary Condition “.

For this case of modeling a downstream pipe which is assumed full, use the boundary condition type "User defined tailwater". This will model an assumed water surface elevation at the outfall location.

To model a pipe which is full near the outfall, Set the Elevation (Use defined tailwater) to an elevation where the most downstream pipe is full (i.e. the elevation of the pipe’s upstream crown), which will replicate situation of pipe being full.

See Also

Modeling Outfall Flap Gates (Tidal Gates)