Outflow slots may be customized to represent flow management structures commonly found in a river basin. These currently include valves, weirs, gates, generators and pump back generators. These components may freely be added to the outflow slot in any combination. They are polled in order from top to bottom, each decrementing as much of the node's release as possible. Any remaining release is passed to the next facet in the list until the release is entirely handled.

The valve and gate are functionally identical. The differentiation is provided for future expansion and to allow the user visually to differentiate them in the graphic user interface.

The weir is uncontrolled. As long as there is water above both its intake and centerline elevations, it will flow water.

All facets have three elevation terms. The intake elevation term is the bottom lip of the inlet works for the facet. The center elevation is the centerline of a valve, generator or pump back generator. It is the lip of a weir or gate. The outlet elevation is only useful if the facet may be discharging under water, either because of tailwater effects or because the surface elevation of a downstream reservoir is against the face of the dam.

Each facet has an interpolation table which relates head difference across the structure to discharge. This table can be derived from whatever characteristic equations or empiracle data the modeler cares to use.

Facets are polled during the begin time step and the finish time step operations of the outflow slot.

• During begin time step, the facets calculate the head difference across the outlet works and calculate their maximum possible release. The summation of the maximum releases of each facet becomes a constraint on the total release from the outflow slot. This constraint may be overcome only if the total inflow plus storage causes the structure to overflow. In that case excess water is released.

• During finish time step, the total release is known. The facet first checks that the upstream elevation is above both its characteristic elevation and the elevation of its inlet works. If that be the case, the facet then computes its discharge by linear interpolation in its head / discharge table, the head being the independent variable.