Ask NOW: Manhole frames recessed for a reason

Dec. 4, 2012

Manhole frames, inlet grates recessed for a reason

Issue: A reader noticed that the storm sewer inlet grates and manhole frames on Bluemound and Brookfield roads seem to be recessed below the road and wants to know why this is.

Status: Jeff Chase, city engineer, explained that in general the city attempts to lay storm sewer inlet grates and manhole frames flush with the road surface. But, he explained, it is critical that they are not placed above the surface of the road because otherwise snowplows will crush them.

Because it is so important that the grates and frames do not get hit by snowplows, they are sometimes recessed between an eighth of an inch and a quarter of an inch. This still provides a smooth ride for cars but also means they do not obstruct snow plows, Chase said.

The reader also may have been noticing the recessed storm sewer inlet grates in the curbs, Chase added. These are recessed in order to help the grates take in water. Those recessions are created by gradually slanting the curb downward over a distance of 12 to 18 inches.

Brookfield NOW .com

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