Hydraflow and SSA different results

[Anonymous]

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.

[Hidden_Brain]

how far off are you? usually flows are higher with lower time intervals. perhaps try all of them with 6 min interval, assuming all your Tc are higher than that.

[Anonymous]

Just to give you an example., if you look at the files EDA-2D on H&H wit time interval set to 1 min. i am getting 39.33 cfs. on a 100 year storm. In SSA same data, same storm is just 33.46 cfs. It is a big difference.  What should be the ideal interval number? Which software is right?

[Kevin.Spear]

In an effort to be exhaustive, what are the results of a hand calculation? Have you compared to any other software? Which formula/method are you using in each?

[Anonymous]

The results for the same area EDA-2B on Pondpack are closer to SSA results for the 100 year storm. The method used in all is TR-20-TR-55. The time interval on SSA is the default (not sure where to modify it), Pondpack is using 5 min. for time intervals, H&H won't let me set it to 5 min. because it cannot be 50% greater than the time of concentration. If i set it to 3 min i get less than Pondpack. If i set it to 2 min. i get higher than Pondpack.

           SSA = 33.46 cfs  default

 Pondpack = 33.14 cfs  5 min. interval

          H&H = 39.33 cfs 1 min. interval

We like the reports in H&H but we cannot use it until we figure out what should be the time interval setting. Should. if my time of concentration is 5 minutes, what should be the time interval?

[Kevin.Spear]

If I’m hearing you correctly, it sounds like you want to know how to set the time interval to get accurate results? Well, that will change based on your area of study and the various Tc lengths involved. @Matt.Anderson gave a great summary in this post back in 2011.



https://forums.autodesk.com/t5/civil-3d-forum/hydraflow-hydrograph-time-increment/td-p/3228300

[Anonymous]

Thank you Kevin. Based on his finding it looks like for a 5 min. TC. the more conservative interval should between 2-3 mins.