How can I view how much rain was not converted to runoff?


 Applies To 
 Product(s):PondPack, SewerGEMS, CivilStorm
 Version(s):CONNECT Edition, V8i
 Area: Output and Reporting
 Original Author:Jesse Dringoli, Bentley Technical Support Group


Problem

How can I view how much rain was not converted to runoff? (how much "loss") Can I view the infiltration on a per catchment basis in a report?

Solution

The amount of that water that flows off the catchment and into your system depends on the SCS CN (curve number) that you enter, which is a function of the type of land and how porous it is, etc.

If you want to compare the rain depth to the depth of runoff, you can compare the rain depth value to the Cumulative Runoff Depth value, which you can see in the Unit Hydrograph Summary report in Report Builder. You can also get this value under the "Results" section of the properties of the catchment.


SewerGEMS or CivilStorm

Option 1 -  Using the SWMM solver with EPA SWMM Runoff Method Catchments

You may have noticed that EPA SWMM reports the infiltration for each catchment. This is because the only runoff method you can use for the catchments is the EPA SWMM Runoff method, which makes sense. In order to view those same results in SewerGEMS or CivilStorm make sure your catchments are set to use the EPA SWMM runoff method and make sure you are using the EPA SWMM explicit solver, which is set in the calculation option (Analysis > Calculation Options). Once you compute your model you will find the infiltration results in the 'Subcatchment Runoff Summary' section of the calculation summary (Analysis > Calculation Summary) are the same you would get in EPA SWMM. You can find the infiltration on a per catchment basis there.   

Option 2 - Creating a formula based user data extension 

The steps below are done using US units, but the same steps would apply for SI units. 

1) Double click the catchment to open the properties and change the Volume(Total Runoff) to use the acre-inches unit. If you’re unaware of how to change units for a field please refer to this topic.

2) Check your catchments to note if you are using ‘scaled area’ or a ‘user defined area’ and make sure whichever you are using is set to the unit  ‘acres’. Note: It’s easiest for this workaround to make sure all the catchments are set to either scaled area or user defined area, but you could have a mix of them if necessary.

3) Go to Tools > User Data Extensions and right click on the catchment label then choose ‘Add Field’.

4) Set the ‘Name’ to ‘Total-Runoff_Depth’ and the Label to ‘Total Runoff Depth’.

5) Change the category to wherever you’d like this new field to be stored in the properties list. The default is to have it stored under the ‘User Defined’ section.

6) Set the ‘Data Type’ field to ‘Real(Formula)’ and click the ellipsis button on the right side of the cell that will be revealed next to the ‘Formula’ field.

7) If you’re using scaled area for your catchments please use step 7a below. If you’re using user defined catchment areas use step 7b. If you’re using a combination of both you will need to repeat steps 3 - 7 to make 2 new fields. You’ll want to make sure to give these fields slightly different names and labels in step 4.

                a) Locate the field on the left side of the window called ‘Volume (Total Runoff) (ac-in)’ and double click on it to add it to the bottom portion of the formula window. Now click the division sign ‘/’ to add that to bottom window in the formula. Finally, locate the field on the left side of the window called ‘Scaled Area (acres)’ and double click on it to add it to the bottom portion of the formula window. Click the ‘OK’ button. Your formula should read as follows:

[StandardCatchmentResults_RunoffVolume; AcreInches] / [HMIGeometryScaledArea; Acres]

b) Locate the field on the left side of the window called ‘Volume (Total Runoff) (ac-in)’ and double click on it to add it to the bottom portion of the formula window. Now click the division sign ‘/’ to add that to bottom window in the formula. Finally, locate the field on the left side of the window called ‘Scaled Area (acres)’ and double click on it to add it to the bottom portion of the formula window. Click the ‘OK’ button. Your formula should read as follows:

[StandardCatchmentResults_RunoffVolume; AcreInches] / [Hydrologic_Area; Acres]

8) In the ‘Units’ section set the ‘Dimension’ to ‘Length’, set the ‘Storage Unit’ to ‘inches (in)’ and set the ‘Numeric Formatter’ to ‘Depth’. Finally, click the ‘OK’ button to close the user data extensions window.

9) Go to Components > Storm Data and note the increment your storms are setup with. I will be using 6 minutes  as an example. Also, note the Depth in inches that your storm is set to use. I will be using 5.83(in) for this example.  Close this window.

10) Go to Analysis > Calculation Options and double click on the calculation option used for this scenario. Set the SWMM Output Increment to be equal to the storm increment from step 9.

11) Compute your model and note the Total Runoff Depth being computed in the new user defined field you created. Take this fields value and subtract it from the depth in inches from step 9 to find your infiltration for each catchment area. If you’d like you can create another real formula user data extension using the total cumulative storm depth in inches from step 9 as a constant and subtract the user data extension field that you previously created. This will allow you to see the infiltration in the catchment properties or in the catchment flextable.