Subject: How to Use Two Control Curves in SWMM 5 to Simulate a Head Difference Rule
The SWMM 5 control rules for Real Time Control (RTC) do not allow the rule to be governed by the head across the orifice but does allow rules based on the depth, head and inflow at any node. If you have an Orifice in which you want the Orifice to be open when the head difference across the Orifice is either less than or greater than zero then and closed when the head difference is close to zero then you can use two Orifices (Figure 1) and two rules (Figure 2) to control the orifice setting for Orifice1 and Orifice2. In attached file the two rules have the settings set to two control curves. Orifice1 will start open and close gradually as the depth at Node UPNode increases, Orifice2 will start closed and gradually open when depth in Node DNode increases. Possible variations are to control Orifice1 based on the DNode and node UPNode to control Orifice2.
IF NODE UPNode Depth >= 0
THEN ORIFICE ORIFICE1 SETTING = Curve RuleOrf1
IF NODE DNode Depth >= 0
THEN ORIFICE ORIFICE2 SETTING = Curve RuleOrf2
Figure 1. Two Orifice Solution
Figure 2. Two Orifice solution to have control over the Orifice(s) at both the upstream and downstream nodes.