Stormwater Inlet Grate - Clogging Efficiencies

[BDAnderson]

Hello,

I'm curious to know how people determine anticipated stormwater inlet grate efficiencies resulting from grates clogging due to leaves and debris. I assume it is a function of longitudinal slope and inlet location (on a slope versus at a lowpoint).

Any ideas are appreciated!

Thanks,

Derek

 

[gbam]

In my area the DOT has set parameters describing the clogging for grated inlets as well as curb opening inlets. For instance, ongrade grates require a 50% efficiency and curb opening inlets 80%. I would recommend checking with your local DOT for design parameters.

 

[cvg]

while slope may technically have an impact on the amount of clogging of the grate, generally a grate clogging policy is set by the agency as indicated by gbam. sumped grate inlets have the lowest efficiency due to the tendency to clog and some agencies prohibit them.

 

[BDAnderson]

Thanks gbam and cvg. I'll take a look for any local regulations.

Derek

 

[bltseattle]

Here are other factors that fall under "engineering judgement", for consideration along with the regulatory requirements:

1. Are you in a "sump"/"sag" condition - if yes, use a higher factor than you would on a continuous grade.
2. You can also look at the tributary area for potential sources of clogging material. I use higher factors where big-leaf maples drop leaves on the street than when the vegetation is conifer, for example. Also, if you see trash/debris in the gutter or along the sidewalk like occurs in certain neighborhoods, that is a clue to apply a higher clogging factor.
3. Vaned grate inlets are generally less clog-prone than "flat" grates.