Sheet Flow over a catch basin 1

[Whyhi2001]

I'm working as an intern this summer and I am designing a drainage catch flow basin system for a property. The city is worried that the grade on the property is to high and the water will just flow right over the catch basin. My question is does anyone know how to calculate sheet flow over these grates or velocity for different types of lids. I have found GPM for different lids but that's it. Any info would greatly apricated Thank you

 

[Heaviside1925]

OP,
I deleted my original post, not because it was incorrect, but I wanted to read up on how industry does it. Looks like there are online calculators (random one I found in the link):

https://www.ejco.com/am/en/resource-center/engineering-calculators

and the spec sheet I attached also provide drainage rate for their products.
Determine your flow rate: Peak Flow Rate (Q) = Catchment Area (A) x Rainfall Intensity (I) x Runoff Coefficient (C)
If you catch basin lid's flow rate is higher than your required flow rate, then no sheet flow, provided that your catch basin and drainage piping can handle the flow as well. I'm sure there are much more analytical ways of determining this and this method seems very conservative but it's simple.