Diverting Stormwater Sheet Flow
Diverting Stormwater Sheet Flow
(OP)
I have a property going through engineering at this time and we've hit a bit of a dilemma. To preface my problem, I'd first like to describe the property and situation as best I can. The property is rectangular in shape (with the narrow ends being the front/back of the property and the long ends being the side) and increases in elevation from Front to Back. Three buildings are proposed on the site. The first two buildings (beginning at the front of the property) are rectangular shaped (170’x70’), sitting one in front of the other, 30' apart with a cartway in between, and have the long sides facing toward the front/back of the property. The third building is similarly shaped (170’x80’), 30’ apart from the second building (cartway in between), and is proposed to be built at a later date. All buildings have 30’ cartways on every side of the building and all buildings are proposed as over-under buildings. Over-under as in each building is two stories and you can access the lower level on one side and the upper level on the other side of the building. So, preliminarily, two buildings will be built with a large parking lot being in place of the third building until it is time to construct the third building. We also have a curb and gutter stormwater system proposed. All stormwater will sheet flow away from the buildings and out to the curbs for collection. With that being said, the large parking lot (which is in place of the third building until it gets built) will have stormwater sheet flow across the 6-8% grade and flood out the second building. Once the third building is in place, we won’t have that problem. But in the meantime, we need to construct some type of barrier which diverts the stormwater out to the side cart-ways and to the curb gutters. We could place an 8” high curb there (constructed to be the length of the third building and built in place where the outside wall will be of the third building closest to the second building) which will divert stormwater around to the cartways, but that is too costly for our means.
We’d like to know the most cost effective way to divert the stormwater so that it does not flood out the second building. The water will be sheet flowing across that parking lot with some velocity, so the barrier has to be tall enough to stop and divert the water. Also, this will be a temporary solution until the third building is constructed, so whatever is built to divert the stormwater will be removed when the third building is built. Any ideas?
Let me know if you need a better description. Thank you.
We’d like to know the most cost effective way to divert the stormwater so that it does not flood out the second building. The water will be sheet flowing across that parking lot with some velocity, so the barrier has to be tall enough to stop and divert the water. Also, this will be a temporary solution until the third building is constructed, so whatever is built to divert the stormwater will be removed when the third building is built. Any ideas?
Let me know if you need a better description. Thank you.





RE: Diverting Stormwater Sheet Flow
RE: Diverting Stormwater Sheet Flow
RE: Diverting Stormwater Sheet Flow
RE: Diverting Stormwater Sheet Flow
Since you can afford for water to back up in your parking lot, you should be fine with an 18" pipe and for the cost of that, I'd say it's worth it to know you're not going to flood that second building.
RE: Diverting Stormwater Sheet Flow
Longer term I might price a curb using low strength concrete (about half the cost and easy to tear out than standard concrete).
I would check out the erosion control magazines for stormwater. They have a lot of ideas that you can reproduce cheaper if need be. Also Rain for Rent and some companies rent the materials.
RE: Diverting Stormwater Sheet Flow
To minimize the drainage issues, can you grade the lot so half flows to one side and half to the other? Or can you put a cross slope on the lot so that it flows toward the gutter system? How about grading / paving a swale at the end of the lot to convey the water?
I'm not sure what you can do to divert this water that is much cheaper than a curb, unless you really want to go cheap. You could try sand bags. Or just dump a small riprap berm (which could be salvaged and reused somewhere else later) Or maybe wood railroad ties, anchored down - which could also prevent cars from driving off the lot.
RE: Diverting Stormwater Sheet Flow
Maybe we'll look into low strength concrete as blueoak mentioned.
RE: Diverting Stormwater Sheet Flow
RE: Diverting Stormwater Sheet Flow
RE: Diverting Stormwater Sheet Flow
RE: Diverting Stormwater Sheet Flow
RE: Diverting Stormwater Sheet Flow
riprap if placed properly will divert most of the flow.
As far as cross grades, you will need to do something in order to move the water to one side of the lot or the other. With 1% grade, I calculated flow depth against the curb of about 3 - 4 inches and about 5 feet wide. This wouldn't interfere with parking at all.
I would not count on low strength concrete being half the cost of higher strength. But an extruded asphalt curb might be cheaper.
RE: Diverting Stormwater Sheet Flow
I think proletariat is right and asphalt is the way to go. I always forget flexible paving because I lack the expertise to do it well.
For the asphalt, could you just drop it without compaction or would that be too weak? I have seen really nice vertical curbs with asphalt.
RE: Diverting Stormwater Sheet Flow
RE: Diverting Stormwater Sheet Flow
For 5 cfs, I can't see how a seeded earthen berm with the cheapest geosynthetic reinforcement will not suffice. But, even if not, asphalt has got to be cheaper than PT lumber.
Engineering is the practice of the art of science - Steve
RE: Diverting Stormwater Sheet Flow
Where would this water go if you didn't put any barrier?
RE: Diverting Stormwater Sheet Flow
RE: Diverting Stormwater Sheet Flow
RE: Diverting Stormwater Sheet Flow