Module 5c: Catchbasins in WinSLAMM

Problem Description

You are the stormwater engineer for a commercial site that must reduce its pollution load by 40 percent. The site is fully developed with silty soils. Determine the site’s pollution load if catchbasins were installed.

How much runoff and pollution does the site generate (Answers to be filled in throughout the example)?

  1. Runoff (cu ft): ______
  2. TSS (mg/L): ______
  3. TSS (lbs): ______
  4. Total Copper (lbs): ______
  5. Particulate Lead (lbs): ______

What is the percent reduction of TSS (lbs)? ______

Steps:

1)Save the file as another name and update the site description

2)Enter the catchbasin data

3)Run the model

4)View the output

5)Save the output

1) Save the file as another name and update the site description

Open Example 1a and save it as “Example 1c”.

Change the Site Description to reflect Catchbasins.

2) Enter the catchbasin data

You are going to add a catchbasin at the end of a drainage system.

Click on Land Use then Catchbasin or Drainage Control then Catchbasin

A diagram showing the Catchbasin input data can be found on the next page (page 3).

Go on to the next page.

Diagram of a catchbasin.

Enter the data for the catchbasin.

Enter in the following information.

1. Area served by catchbasins (acres) 7.39

2b. Number of catchbasins1.0

3. Ave. sump depth below outlet invert (ft)2.25

4. Depth of sediment0.0

5. Typical outlet pipe diameter (ft)0.5

6. Typical outlet pipeManning’s n0.013

7. Typical outlet pipe slope (ft/ft)0.020

8. Typical catchbasin sump surface area (sf)3.144ft diameter

9. Catchbasin Depth from Sump Bottom to str level3.25

10. Inflow Hydrograph peak to Ave. flow ratio3.8

11. Leakage rate through sump0.0

12. Critical particle size file nameNURP.cpz

Click Selectand pick “NURP.cpz” Then click OK

Select “Monthly”as the “Catchbasin Cleaning Frequency,”clickContinue.

3) Run the model

Click RunthenCalculate ModulethenSave File and Execute

4) View the output

i.Runoff (cu ft): 561,484 cu. ft.

ii.TSS (mg/L): 121.9 mg/L

iii.TSS (lbs): 4,269 lbs

iv.Total Copper (lbs): 0.6668 lbs

v.Particulate Lead (lbs):1.098 lbs

What is the percent reduction of TSS(%)? 2.76 %

Look through the output and determineif catchbasin fills up.

Change the Output Option so that you can see the results by rainfall. ClickView, then 3.Output Data Only for Each Rain

Click on Particulate Solids and Yield tab. Look at the Catch basin Volume % Full column. If this reaches 100% the catchbasin is full and will no longer trap sediment.

5) Save the output

Alternative Scenarios (if available time)

  1. Question: Based on the above results, the Catchbasin does not fill up. Change the cleaning frequency to determine how often the catchbasin could be cleaned so that it fills up once a year (if possible).

Answer: The catchbasin will not fill up even if it is only cleaned once per year.

  1. Question: How could you increase the catchbasin pollution removal efficiency?

Answer: A few options are to increase the sump depth, increase the number or catchbasins on site, or decrease the size of the outlet pipe.

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