Steep stormline terminating in manhole. Energy dissipation nozzle?
Steep stormline terminating in manhole. Energy dissipation nozzle?
(OP)
We have a very steep site and will be sending stormwater down a hill to a swale and wanted to utilize a manhole as an energy dissipator at the bottom. I've seen installations like this around the city, but have never designed something like this myself. The site does not have room to accommodate a full riprap energy dissipation outlet design, so I was told to utilize a manhole instead. Essentially the water will flow down into the manhole and then overflow into the swale.
It would be 18" line at 25% for ~16' down the hill, which looks to be about 19fps based on my runoff calcs. Would there be a need for some sort of energy dissipation nozzle within the manhole for that kind of velocity? Do those exist?
It would be 18" line at 25% for ~16' down the hill, which looks to be about 19fps based on my runoff calcs. Would there be a need for some sort of energy dissipation nozzle within the manhole for that kind of velocity? Do those exist?
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RE: Steep stormline terminating in manhole. Energy dissipation nozzle?
use a grated basin (bubbler), not a manhole. water will fill the basin and back up into the storm drain. a nozzle may plug with debris
RE: Steep stormline terminating in manhole. Energy dissipation nozzle?
I was planning on specifying an open grate lid for the manhole to allow for the overflow, but maybe a bubbler CB would be more common? I was struggling to find the max pipe size allowed for CBs. The city's detail shows a max pipe size of 12", so I went the MH route. I was wondering about the riprap in the base also. Does that interfere with cleaning operations?
RE: Steep stormline terminating in manhole. Energy dissipation nozzle?
the example had riprap and filter material in the bottom allowing the water to soak away after storms, otherwise it would stay full of water for days
RE: Steep stormline terminating in manhole. Energy dissipation nozzle?
Will the soils percolate? A geotechnical report should have some comments on percolation.
RE: Steep stormline terminating in manhole. Energy dissipation nozzle?
RE: Steep stormline terminating in manhole. Energy dissipation nozzle?
here is another option, although it might be overkill for your situation. it is relatively maintenance free
RE: Steep stormline terminating in manhole. Energy dissipation nozzle?
BTW, the reason they are called baffled outlets is that they are often confused.
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RE: Steep stormline terminating in manhole. Energy dissipation nozzle?
How would I go about calculating the velocity of my water exiting the catch basin? I'm assuming it's an instance of the energy equation, but I'm struggling to recall how to set up this type of analysis. If I'm going from an upstream 18" pipe (that would be closed conduit flow) to a 24" grate catch basin, I would imagine my velocity at the grate would be lower compared to the 18" pipe due to the increase in cross-sectional area. I'm not sure how it works going closed conduit to open channel though.
RE: Steep stormline terminating in manhole. Energy dissipation nozzle?
How about putting a deep manhole or structure at the upstream end and flattening the pipe?
With your concept you are trying to essentially design a level spreader, which would need to be massive for that velocity.
RE: Steep stormline terminating in manhole. Energy dissipation nozzle?
I'm looking at this again and I think that would actually work. Originally we had a sanitary line running deep below this, but that has since been relocated, so now there is room to drop the upstream manhole quite a bit. I can get that slope down to ~ 10% with a 10ft deep manhole. Cuts the slope roughly in half, so that would help the velocities significantly.
RE: Steep stormline terminating in manhole. Energy dissipation nozzle?