There is always the time honored option of adding code to Extran to help it better simulate the hydraulic structure of interest.... The City of Seattle's Engineering Design Division once upon a time added code into Extran to simulate Leaping Weirs based on either depth at the node or the velocity in the upstream pipe. It works like an on-off switch. At low flows, all of the flow falls down into the weir/orifice opening and into the first downstream location. Once the set depth or velocity is exceeding, then all of the flow "leaps" over the weir to the other downstream location. The input parameters are fairly simple. Our notes shows that the City of Seattle's experience suggests that the depth control was more stable than using velocity control.
Back in 1992 we were able to obtain that code and place it into our Portland SWMM code (thanks to Steve Merrill of Brown & Caldwell), although we never have used it (turned out that Portland's "leaping weirs" were actually side spill weirs). If anyone is interested, I can send what I have. Otherwise, perhaps the modelers up in Seattle could chime in with their latest experience and any updates to the code....
Virgil C. Adderley, PE
virgila@bes.ci.portland.or.us
Linear Mode
