For high flows (flows that come into contact with the maximum low chord of the bridge deck), the program has two methods available to the user: the pressure and weir flow method and the energy-based method. The following examples are some typical cases where the various high flow methods might be used.
When the bridge deck is a small obstruction to the flow, and the bridge opening is not acting like a pressurized orifice, the energy based method should be used.
When the bridge deck and road embankment are a large obstruction to the flow, and a backwater is created due to the constriction of the flow, the pressure and weir method should be used.
When the bridge and/or road embankment is overtopped, and the water going over top of the bridge is not highly submerged by the downstream tailwater, the pressure and weir method should be used. The pressure and weir method will automatically switch to the energy method if the bridge becomes 95 percent submerged. The user can change the percent submergence at which the program will switch from the pressure and weir method to the energy method. This is accomplished from the Deck/Roadway editor in the Bridge/Culvert Data editor.
When the bridge is highly submerged, and flow over the road is not acting like weir flow, the energy-based method should be used.