Pipes at 0%
Pipes at 0%
(OP)
I am working with a very flat site (.5%) I am proposing a series of ponds to detain the water. Each pond will have the same initial water level. The ponds will be several hundred feet apart (>500'). So if my inlet starts at the initial water elevation then the outlet into the next pond will be a couple of feet below the water level if the pipe has a slope. Is there any reason to have a sloped pipe if it is outfalling in a submerged condition like this? Why not just keep the pipe on a 0% grade. I have seen this done before but wanted to get other's thoughts.





RE: Pipes at 0%
good luck
RE: Pipes at 0%
In practise, however, if your pipes do not have some slope to them, water will invariably pond inside your pipe once the need for joint storage has been eliminated. If your design is for your pond to hold water, and the pipes will be submerged at all times, then this shouldn't worry you.
I would suggest that you have a slope, however small, to keep the water moving during times of drought.
RE: Pipes at 0%
RE: Pipes at 0%
RE: Pipes at 0%
RE: Pipes at 0%
While the ponds may look better when all of the pipes are hidden, one should also consider maintenance. Here, due to feedback from inspectors, regulators frown upon submerged pipes because they are difficult to inspect and maintain.
RE: Pipes at 0%
What software program do you use to model your interconnected ponds? I use xpswmm but find it somewhat cumbersome to use.
RE: Pipes at 0%
http://www.streamnologies.com/
Once one gets used to the interface, it is very easy to use.
RE: Pipes at 0%
Sheet flow
n=.4 for woods
slope = .5%
2 year rain = 4.4 inches
Tc=44 minutes
Shallow concentrated flow
slope = .5%
surface description = unpaved
Tc = 2.2 minutes
The first seems excessivly large, the second seems too small. Any insight on time of concentration would be appreciated.
RE: Pipes at 0%
A good way to get a feel for some of this stuff is to observe runoff during significant rain events on different surfaces.
Shortening the sheet flow to 100' in your example would reduce Tc from 46 min to 35 min. Still, I am trying to imagine being in a extremely flat wooded area during a heavy rain and observing flow. Hopefully, you know the woods that you speak of better than I, but I have observed this type of area having likely sheet flows less than 50 feet.
RE: Pipes at 0%
RE: Pipes at 0%
RE: Pipes at 0%
50' of Sheet flow
n = .4
slope = .5%
2 year rain = 4.4"
Tc=18 min.
velocity = .05 fps
250' of shallow concentrated flow
slope = .5%
surface description = unpaved
Tc=3.7 min
velocity = 1.1 fps
Total Tc = 18 min. + 3.7 min = 21.7 min.
21.7 minutes sounds a lot more reasonable than 46 minutes which I had before. However it seems unreasonable that the velocity jumps from .05 fps to 1.1 fps. Perhaps my "n" value is too large.