using of scs method in civil storm on Geopak imported layout

Question

I have imported Geopak drainage file into civil storm package and applied SCS method . I have used time -depth curve for rainfall . In the catchment flexitable enertered curve number 75 , run-off method unit hydrograph, loss method SCS CN, SCS Unit hydrograph method . default curvilinear . 
 After applied computation ,observed few things that composite tc is not updating ,pipe sizes also not changing ? is any other options need to be modified ? please help me.

Jesse Dringoli · Answer

Hi Prasad, 
 Are you saying that the automated design feature could have selected a smaller pipe size and still be within the design constraints? If you manually select that smaller pipe size and compute Analysis, can you confirm that all design constraints are indeed met? 
 In that case, check to make sure the smaller size is available for design in the Conduit Catalog. Also, check the below article which explains how long travel times can sometimes cause this problem (if the problem is related to the capacity of the pipe): 
 Why is StormCAD over-designing the conduits during a design run on a system with very shallow slopes? 
 If this does not help, please provide a copy of your model.There are two options for sharing your model on Communities, whichever you choose please be sure to zip your files first. The first option is to attach the zip file containing your model to your reply on the forum using the Advanced Reply Editor (you'll find the link below and to the right of the reply box). If your data is confidential please use the instructions in the link below to send it via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley employees. Please be sure to reply on this thread with the name of the file after it has been uploaded. http://communities.bentley.com/help/w/be_communities_help/7079.be-communities-secure-file-upload

Jesse Dringoli · Answer

Prasad, 
 Unfortunately I do not see your file. Can you try uploading it again? Please be sure to zip the files first. In the meantime, here is some general information, based on your most recent replies: 
 If you would like to automatically size pipes based on design constraints, this must be done using the GVF-Rational numerical solver. This solver can be selected in the calculation options (under the Analysis menu) after which you can select "Design" for the "Calculation Type". You can then enter your design constraints under Components > Default Design Constraints and in the Design Alternative. However, automated design uses the Rational method, Q=CIA, which is a peak flow method. This requires the use of the Rational runoff method in your catchments, along with an IDF curve in your storm data. 
 You mentioned that you're using the SCS Method, which is a hydrograph method that cannot be used with rational- method-based automated design. So, this may be why you are not be seeing the desired result. More information can be found in our wiki, in the following article: 
 Troubleshooting Automated Design Results 
 Once you have configured the rational method for your catchments, selected the rational solver and Design calculation type and configured your default design constraints, you must configure the conduit catalog (under the Components menu) to include catalog classes with the pipe sizes you want to be available for design (by way of the "available for design" check box". For more on automated design, there are courses available on the LEARN server (Learn.Bentley.com) under Bentley StormCAD. 
 With automated design configured properly, if you want to limit the diameter of all pipes, you can either uncheck the "available for design" for larger sizes in the conduit catalog or use the "Limit Section Size?" option in the Section Size tab in the Design alternatve. 
 If you want to limit the size of specific pipes, check the box for "specify local pipe constraints" in the pipe properties or the table at the bottom of the Design alternative, then check the box for "limit section size" and enter the maximum rise (diameter). 
 If you would like to "fix" the diameter and/or inverts of a pipe (if you want the program to NOT design certain elements), uncheck the "design conduit" check box in the design alternative, or uncheck "design start invert" or "design stop invert". See more in this article in our wiki: 
 Automated design only on certain elements 
 Regarding your question on whether the manhole invert elevations are needed - if you intent to use automated design to size pipes and inverts, the manhole inverts do not necessarily need to be entered, as the automated design will enter them for you based on the design constraints. However you should provide some kind of boundary elevation for the Design to start from. This is usually the invert of the final outfall (choose "false" for "design structure elevation").

Jesse Dringoli · Answer

Hi Prasad, 
 Regarding the calculation options and peak flows - when using one of the dynamic numerical solvers, numerical instability can sometimes occur and you may notice a large Continuity Error in the calculation summary. This is typically the indicator that the results may not be accurate. More on Continuity Error here: 
 What is the continuity error and what's a good percentage for it? 
 There is a good help topic with assistance for adjusting the calculation options - "Troubleshooting Dynamic Wave Model Results". You can find additional guidance in the following article: 
 Troubleshooting unstable SewerGEMS and CivilStorm results using the implicit solver 
 Yes, the GVF-Rational or GVF-Convex solvers must be used to perform automated design (pipe sizing). You can then analyze the model using one of the dynamic solvers, but you'll need to use a hydrograph routing method such as the SCS Unit Hydrograph method.