Models a point where flow leaves the pipe network and discharges to atmosphere. There are three choices for the Discharge Element Type:

• Orifice - represents an opening to atmosphere at a junction of two or more pipes or the end of a single pipe. The initial pressure is typically positive and there is usually an outflow from the system at time zero. If the pressure P is positive, then the outflow/demand is Q =
  
  Qi. summed over all the Branches, i. P varies quadratically with Q. When the pressure drops to zero, this element allows air to enter the pipeline freely on the assumption that the opening for the liquid is infinite for air. In this case, the air pocket respectively expands or contracts accordingly as the liquid flows away from or towards the node, but the air remains at the branch end point(s) located at the orifice.
• Valve - discharges water from the system at a pipe end open to atmospheric pressure. It is essentially an Orifice to Atmosphere with a variable diameter which could become zero; optionally, the valve can start the simulation in the closed position and proceed to open after a time delay. As long as the diameter is positive, either outflow for positive pressure or injection of air for zero pressure are possible. In the latter case, the rate of change of the air volume Xi in each branch is described by the relation dXi / dt = - Qi, with the total volume X being the summation over all branch volumes Xi. After the valve closes, it behaves like a Junction element (and as a dead end junction if there is only a single branch connected).
• Rating Curve - releases water from the system to atmosphere based on a customizable rating curve relating head and flow. Below a certain value of head, the discharge is zero; in stage-discharge relations, head is equivalent to level for which the discharge increases with increasing level.