Applies To Product(s): Bentley StormCAD, Bentley SewerCAD, Bentley SewerGEMS Version(s): 08.11.0X.0X. Environment: N\A Area: Modeling Subarea: N\A Original Author: Bentley Technical Support Group Problem Known flow doesn't add up in downstream structure? Why? Solution Known flows are used to represent measured or metered" flow from the field and are not additive. For example, if you have a known flow of 10 cfs empty into an inlet with a Known Flow set to 5 cfs, the flow in the downstream pipe will not be 15 cfs - it will be 5 cfs, as it overwrites the upstream flow value. That means if the value of local , user defined known flow at a node is greater than 0, this local value will overwrite the upstream known flow, rather than adding directly to the upstream known load. If the local user-defined known flow is equal to 0, total known flow will be equal to the known flow in upstream pipes. Flow (Known) remains constant as they travel downstream and combine with other flows, similar to additional loads. If you wish for the flows to be additive use Additional Flows or pattern based loads (sanitary loads) instead of known Flows. The behavior of known flows is different for steady state & EPS modeling & its applicable to GVF- Convex solver & GVF- Rational solver. During a Steady State analysis known flows are not additive except at network junctions. The Known Flow component will remain constant until it encounters a downstream Known Flow of a different value. During an Extended Period Simulation known flows are treated as a constant inflow hydrograph and lumped in with other hydrographs entering at the same point. Known Flows are additive during Extended Period Simulations. To summarize, for a steady state simulation flows are being reset to the known flow values downstream of the pipe. In an extended period simulation known flows get to combine with flows downstream and do not reset flow values. The main purpose of Known Flows are to provide the user a way of "forcing" the flow in a pipe based on flows that were already calculated or measured externally, instead of the user having to figure out all of the node inflows necessary to generate those pipe flows.
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