I agree completely. There is this elaborate program that can do all this analysis using different methods and something as seemingly simple as using a DTM. As part of my thesis several years ago, I interacted with the DTM to using information to perform TR-55 analysis before all this stuff came out, and I am NO WHERE NEAR the level of programmer that is at Autodesk. Hopefully they look at these forums and get ideas of what they need to work on for the next realease. As far as Civil 3D itself, I do not know of any other inhancements that I would need other than what they have already made...other than this interaction with the DTM in SSA. It interacts nicely in C3D to find the catchments and flow paths (wish that was there when I was in my masters!) and everything. We will see...
Rich Bauer, MS, PE, SIT, M.ASCE
Engineering Department Manager
RB & Associates Consulting, Inc.
Web site www.rb-associates.net
i remember based on my testing on recent project work models that this feature does not "affect" results obtained by using the rational method as the computational method. it affects when using SCS TR-20 (and possibly TR-55) with structures (inlets).
the last time i faced this issue, i ended up using ponded area 100 sf as recommended by other folks here, and checked each structure/pipe for inflow/outflow mass balance (inflow from drainage area as CiA + bypass from upstream inlet = flow in the downstream pipe and so on). i will run some quick tests using the EPA SWMM computational engine and post back with results when i have time.
From what I am seeing, it does make a difference as far as the Flow Depth. Attached are the 2 "tests" I did. The ONLY difference in the 2 runs is the ponded area. I am using the rational method. The funny thing is that the gutter spread stays about the same but the depth doesn't. I am going to try TR-55 and see what happens.
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