stormwater management report - retained volume calculations

[lubos1984]

Hello Everyone,

I'm currently working on my first stormwater management report and am having trouble figuring out the equation for retained volume. I've attached some screenshots. As the intensity of the rainfall decreases there should be a period when the retained volume begins to decrease ?
Thanks![URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1620924354/tips/New_Bitmap_Image_hwk3bk.bmp[/url][URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1620924379/tips/New_Bitmap_Image_jtl7ff.bmp[/url]
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1620924391/tips/New_Bitmap_Image_2_eina7v.bmp[/url]

 

[1503-44]

Do you understand the units of measurement?

mm/h x area is a volume. It is not L/s, which is a flow rate.

You do not need flow rate to solve this problem.

Calculate the volume of runoff during one hour of each given rainfall intensity
in the predeveloped state and the volume in the post developed state.

Storage volume is the difference. It is the volume that you need to store, if you had one hour of a given rainfall intensity.
If it rained 15mm/h for 2 hours, you would need to store 2 x 88.64m3

See the attached spreadsheet




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