Infratech Civil

Product:  Autodesk SSA  |   Subject: Storm and Sanitary Analysis

In this exercise, we will learn about stormwater SWMM and TR-55 design.

SWMM Method for detention design

In this section, we will work on the detention system. One of the main differences between a detention and a peak flow model is that the detention is analyzed over a longer period of time, typically 24-hours or more. This requires a time series hydrograph with a specified distribution model, instead of IDF curves. Even though an IDF curve can be used with the Modified Rational method, for example, usually it is not the recommended model by agencies. More commonly accepted methods for detention are the SWMM or TR-55. Let’s design the system with SWMM or TR-55.

Now, let’s see how to design a rain gage for extended detention, using SWMM or TR-55.

1. Open the file 05.02-DETENTION-SWMM-TR-55.spf or continue to work from the one saved in the previous chapter.
2. In the new file, double-click on Project Options in the data tree.
3. In the new window, change the Hydrology Method from Rational to SWMM or SCS TR-55.

4. We will not change the Time of Concentration (TOC) method. We can take advantage of the work we have already done in the storm sewers section. The same TR-55 TOC will be used.
5.  Then, click on OK.
6. Notice the IDF Curves option has now changed to Rain Gages.