Applies To Product(s): Bentley WaterGEMS,Bentley SewerGEMS, Bentley CivilStorm, Bentley StormCAD, Bentley PondPack, Bentley StormCAD, Bentley HAMMER, Bentley WaterCAD Version(s): 08.11.04.58 Environment: N/A Area: Modeling Subarea: Original Author: Mark Pachlhofer, Bentley Technical Support Group Problem Description I have a section of pipe that is made of two materials. Can I just average the pipe roughness to come up with a composite roughness? Solutions It may or may not be ok to combine the pipe roughness values to go with an average, but it certainly seems like there could be a case in which a good argument could be made for it. The best way to figure out what will work best for you is to try one and compare the results to your field data. Here are some ideas you can try that might help you out: 1) If you know where the pipe materials differ then try to add multiple pipes and use different roughnesses. For example if you know the first 1500 ft. of the pipe is shotcrete lined followed by 1500 ft. of partially rough cut D&B followed by another 1500 ft. of shotcrete lining then you might want to try making it 3 separate pipes each with their respective roughness values. Since I'm guessing it's not quite that simple here is a second suggestion 2) Use the roughness value that is the most conservative. This will assure that you design your system to handle the worst case scenario. 3) Try to model it a few different ways by taking advantage of creating some child scenarios and then compare the results to see the differences, if any. It would be a great use of the scenarios and probably wouldn't take that long.
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