storm pipe minimum slope???
storm pipe minimum slope???
(OP)
I'm pretty new to doing stormwater drainage plans. I recently was told that 0.5% slope for pipes only really drains when the pipe is a minimum length and using this slope doesn't work well for small sites. I am currently working with a very flat site and am having difficulties getting it to drain. I'm using a 1% on the asphalt (which I am also concerned about - but again the site is virtually flat).
Here are my questions:
1) Is there a minimum pipe length for a 0.5% slope? If so what?
2) Is there greater flooding danger using 0.5% assuming the pipe is sized correctly? Does oversizing the pipe help prevent this?
3) What are some other options to help drain a small (2 acres) flat site besides bringing in fill? Someone has mentioned slot drains to me, but I don't really know anything about those.
THANKS FOR YOUR HELP!!!!
Here are my questions:
1) Is there a minimum pipe length for a 0.5% slope? If so what?
2) Is there greater flooding danger using 0.5% assuming the pipe is sized correctly? Does oversizing the pipe help prevent this?
3) What are some other options to help drain a small (2 acres) flat site besides bringing in fill? Someone has mentioned slot drains to me, but I don't really know anything about those.
THANKS FOR YOUR HELP!!!!
RE: storm pipe minimum slope???
This is will help carry sediment through the pipe system. And when not possible to achieve this velocity try to at least avoid a drop in velocity in the pipe system.
RE: storm pipe minimum slope???
In terms of minimum slopes; yes, scour velocity should be maintained. Beyond that, pipe material also makes a difference. We used 1% minimum for CMP and 0.5% minimum for RCP and HDPE.
Other options to consider are eliptical pipes, which on a 2 acre site probably won't help much, and concrete channels. Curb cuts need to be very well maintained to remain effective. A little grass taking root will trap sediment over time and turn your parking lot into a dam.
RE: storm pipe minimum slope???
For RCP, a 3fps min. velocity for a pipe with an 0.013 manning's N yields minimum slopes of 0.32% for 15" dia., 0.17% for 24"dia., and 0.10%for 36"dia.
Using the steepest slope achievable keeps pipe sizes down.
RE: storm pipe minimum slope???
Dik
RE: storm pipe minimum slope???
RE: storm pipe minimum slope???
Dik
RE: storm pipe minimum slope???
RE: storm pipe minimum slope???
RE: storm pipe minimum slope???
RE: storm pipe minimum slope???
Lndsn,
I would consider keeping as much of your drainage above ground as possible. The use of concrete drains for parking areas and if you can discharge your roof drains to the surface often helps. Sometimes you have to adjust the location of buildings. However, depending on your area you may be able to better fit it with any required stormwater quality treatment and just add as small swale or basin at a corner of the site or at required vegetated areas. I like slot drains, but mostly interior. OUtside the plug, grow grass and can just be a pain. They are useful for pedestrian crossings though.
RE: storm pipe minimum slope???
1. The probability of the "ten year storm" occuring being equaled or exceeded in the next 10 years is 65%, not 1 %. The probability of that same storm being equaled or exceeded in the next 50 years is 99.5 %. This, it is more likely than not that the ten year storm will occur mote often than every ten years as suggested by earlier comments.
2. The velocity of flow in a circular pipe is the same full or half full. Therefor, you might expect to achieve self cleaning velocity ( 2.5 ft/sec) even if the flow is only half the design flow at least once a year 9depending on the weather patterns where you live, of course). This should provide more frequent "flushing" of the pipe than suggested in some earlier comments.
For very large pipes ( 27" and larger), I've seen slopes as flat as 0.001. These are not desirable but are theoretically possible. For smaller pipes the 0.50% slope suggested by others seems more reasonable.
Good luck
RE: storm pipe minimum slope???
Please do a web search for trech drains. There is a ot of good information on them.