Minimum street grades

[roberttx]

Hi,

Does anybody knows what are the minimum grades for proper drainage on streets with curb and gutter?

Thank you,
Roberttx

 

[RWF7437]

In Oregon, USA the generally accepted minimum grade is 0.40%. It may be different in your part of the world.

Good Luck

 

[cvg]

It depends somewhat on your climate. If you are in a rainy, wet climate - you would expect to see higher cross slopes and longitudinal slopes. In dryer areas, possibly flatter. Your street department will likely set this standard. Or they may set a standard for the spread on flow on the pavement. This may vary for the type of street also, as arterials and high speed roads necessarily require stricter designs for drainage.

 

[KRSServices]

In my experience, the slope has little to do with the topography rather, the catchment, rainfall intensity, storm event design and water retention in the street in a given event. The municipality usually provides the "minimum specifications", but check calculations are required to ensure the retention is in accordance with the municipality's wishes.

KRS Services

http://www.krs-services.com

 

[Maury]

In Illinois, the minimum slope for curb and gutter is 0.40%. Inlets are spaced to limit water encroachment to 3' on to the traffic lane (10-year storm frequency).

 

[wolfhnd]

Depends on the type of road. Low volume low speed roads may have 6' spread on the driving lane. Higher volume higher speed roads the water is retained in the gutter. If your in a river bottom where there is little slope to the land you may not be able to maintain any slope In which case you can vary the cross slope and all drop inlets will end up in sags. If you can't get grade on the road the storm sewer may have the same problem and you can use larger pipes than needed. I would recommend a lateral with small pipes out of the DI, large pipes will seldom clog but I see a lot of silted up DI's.

 

[PELS]

What part of the country are you located?

We have areas in Northern California that are as flat as a pancake with no nearby major rivers or drainage channels to outfall a storm drain system into. Some municipalities in these types of areas allow a street grade as flat as 0.25% (.0025). The concept behind this is to utilize the street section to carry water during the heavy storm events and have it slowly bleed into a detention pond (sometimes these are park areas). The lot pads are set at an elevation that is a minimum of one foot above the 100-year HGL so although the streets may get flooded, the lots and houses stay dry. The street system then becomes a conveyance system for storm waters during these infrequent storms.

 

[roberttx]

Hi,

I am in El Paso, Tx. The county states the minimum is 0.5, but I've seen even 0.17%. For a nice 2 fps, I calculated 0.25% as the righteous minimum, but my boss argues it's too hard to construct even to 0.35%, therefore, that's what I work with.

Roberttx.

 

[RJLDesign]

0.4% is the flattest a kerb machine can lay to. so you dont want your road flatter then 0.4% for a long distanse for your contractors are hand forming it. Plus if you go much flatter then 0.4% you get even flatter grades around your intersection kerb gradings.

I personnly do not design below 0.5% unless really struggling for grade

 

[bank]

The county's right. El Paso has a mountain in the middle of it and a good portion of the city is on some kind of slope (my legs can attest to it). It would be hard to find many areas where o.2% would be appropriate. Now Houston is at least 20 miles wide in most directions, and it's so flat that you'd be able to see from one side to the other if the horizon or the trees didn't get in the way. Local rules dictate a minimum longitudinal slope of 0.30%. That works pretty well, and most contractors don't seem to have a problem maintaining it.