SWMM vs TR-55 for Runoff

[geosavvy]

Using the same rainfall events and identical subcatchments, the peak flow rate (at the outlet) is much smaller in SWMM than TR-55. Does anyone have any experience comparing the output of these two programs/methods?

Basically, it appears to me that SWMM uses one of three methods to determine how much rainfall infiltrates the ground. Then it uses one of three theoretical methods to route the runoff to the outlet and develop a hydrograph.

The infiltration methods offered by SWMM are: Horton, Green Ampt, and Curve Number

The routing methods offered by SWMM are: Steady Flow, Kinematic Wave, and Dynamic Wave

No matter which combination of these option I select, the peak flow generated is much less than what TR-55 generates using the "unit hydrograph" method to estimate peak flow rate.

Is TR-55 really that conservative? Or am I likely not setting up the model correctly?

Thanks in advance for the feedback.

 

[blueoak]

You are running two distinct models with probably different runoff and hyetograph selections. Depending on your assumptions for each I like a about 10% agreement.