Storm and Sanitary Analysis vs. Hydraflow Hydrographs

[Anonymous]

I used Storm and Sanitary Analysis 2016 (SSA) and Hydraflow Hydrographs Extension for AutoCAD Civil 3D 2016 to create a hydrograph using the SCS method.  For each program the drainage area (97.5 ac), CN (69), and time of concentration (4.7 min) inputs are the same.  The rainfall depth with a Type II distribution is 2.9" over a 24 hour time period and the peak shape factor is 484.

The peak flowrate calculated in SSA is 83.91 cfs and 109.67 cfs in Hydraflow Hydrographs.  Could someone help me understand why there is such a big difference in the peak flow between the two software programs using the same hydrologic method? 

Thanks

[BrianHailey]

I don't know what the difference is but I can see the difference on my end as well (in the 2018 versions). I'm getting less flow than you in Hydrographs though but almost exactly the same as you in SSA (off by 0.1cfs).

[BrianHailey]

Oh, and a time of concentration of less than 5 mintues for 100 acres seems really small to me, but I don't know the data...

[Timothy_Sean_Hulbert]

Greetings,

This can occur when the time the reporting and routing time are not set to small enough values. Can you try a reporting time of 60 seconds and a routing time of 5 seconds. This should improve your results. If not please share the SSA model. (you will need to change the extension to share here).

[Anonymous]

Timothy,

I am not sure changing the reporting time and routing do anything at all. i tried on my project and the results remain the same. I am recreating a project done in Pondpack to make a case at my workplace to switch to either SSA or Hydraflow. I did put the same data in both and on 1 year storm the results are similar but when i check the 100 year storm the differences are significant. The difference in Hydraflow seem to be the time interval under the hydrologic data area. If use the 3 minutes interval as Pondpack does the result is lower peak flow but 2 or 1 minute result in an significant increase. What should be the right interval ? SSA results are close to Pondpack but the reports in SSA are not as clean as Hydraflow. How can i get the same results on both SSA and Hydraflow? whats different on the equations that triggers different results. i am attaching the files for your review. Thank you in advance.

[Anonymous]

Here are the files. they didn't got attached, in the first try. Thanks.