Applies To Product(s): Bentley SewerGEMS, Bentley CivilStorm, Bentley StormCAD, Bentley SewerCAD Version(s): 08.11.XX.XX Environment: N/A Area: Original Author: Mark Pachlhofer, Bentley Technical Support Group Problem What is the difference between the Backwater Analysis and Capacity Analysis flow profile methods? Solution The default option for the Flow Profile Method is 'Backwater Analysis' and it is used most of the time when computing a system because it uses the gradual varied flow algorithms, which are more rigorous and generate solutions that more closely reflect reality. This analysis starts at the outfall and solves the network equation upstream. The 'Capacity Analysis' still uses a backwater approach, with the profile type for a pipe being primarily dependent on the pipe's full flow capacity and downstream hydraulic grade. It’s a more simplified approach and is only advantageous over the gradually varied flow analysis in terms of processing time. If you are dealing with a large network and you wish to arrive quickly at reasonable approximation then the capacity analysis is the way to go, otherwise, the backwater analysis is the best option. Note: see the help contents for more information on Gradually Varied Flow (GVF): Contents > Theory > Gravity Pipe Hydraulics > Gradually Varied Flow Analysis Contents > Theory > Gravity Pipe Hydraulics > Capacity Analysis (Approximate Profiles) Basically, the depth of flow can vary over the course of the length of pipe, based on the flow regime (how steep the pipe is, etc.). This can allow hydraulic jumps. This can all be accounted for with a 'Backwater Analysis', whereas with a 'Capacity Analysis', the program assumes the pipes are flowing steady, which is not nearly as accurate. See Also Why does the profile appear to be at odds with the results for capacity? Why is the HGL reset at the rim elevation of flooded structures?
↧