Converting concetrated flow to sheet flow 1

[kkoloj]

Does anyone use anything other than dispersion walls or rip-rap to convert concetrated flow to sheet flow? The owner of this project is also thinking about using a sump pump. It seems there are a lot of disadvantages with this option.

Any feedback would be greatly appreciated.

 

[LHA]

Post here, for more hits:
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Engineering is the practice of the art of science - Steve

 

[nutbutter]

You could use a level spreader. It's basically a shallow ditch that will take in a concentrated flow and release it over a wide lip, or spillway, to create sheet flow. Here's a PDF of the basic concept:

http://www.abe.msstate.edu/Tools/csd/NRCS-BMPs/pdf/water/erosion/levelspread.pdf

peace,
stoddardvilla

 

[proletariat]

Reviewers commonly complain about level spreaders not really being "level" and not dissipating the flow. I have used a concrete level spreader similar to a curb with a series of orifices in it that are designed to pass the xx year storm before the level spreader overtopps. If the orifices get clogged, or there is a major storm event, then the water goes over the top of the spreader in normal fashion.

 

[bltseattle]

Related to proletariat's comment, King County Washington has details in their drainage manual that show a saw-tooth configuration intended to prevent concentration of flow when the spreader is not completely level.
See:
ftp://dnr.metrokc.gov/wlr/dss/dm98_fig/422cflow.pdf
ftp://dnr.metrokc.gov/wlr/dss/dm98_fig/422dflow.pdf

 

[LHA]

Pretty good idea, King County. But why skimp on conrete and use wood? PT or not, it will be rotted to next to nothing within 20 years. Maybe sooner, with the near-constant dampness. I'm going to look into a variation on a job I am currently doing, but it won't be PT lumber.

And why so deep for the influent pipe, unless you are trying to pickup some infiltration, which is actually a good use of land.

20% inflow gradient? Man, that water will be moving. I think I'm going to back that down a lot.

25 feet on level 4" pipe, with one cleanout? Probably OK, w/ 6" pipe, or more frequent CO's.

Needs note spec'ing 25' from bldg foundation.

Why solid cover on inlet? I'm using a grate, for better dispersal and larger inflows.

I'm allowing square or v-notch overflows. Constructability will be a nightmare w/ concrete v-notches, if cast in place.

I would actually call out AASHTO #3 stone (or whatever you prefer). I've been bitten too often by the Contractor saying "that IS clean stone", while pointing at a pile of Suitable Backfill.

Call out AASHTO Class 2 geotextile. I've been bitten too often by the Contractor saying "that IS filter fabric", while pointing at a roll of some flimsy stuff of indeterminate tensile stress.

Engineering is the practice of the art of science - Steve

 

[bltseattle]

Good points, LHA, all of which take the drainage manual concept to a constructable detail.


There are a few other designs, some using concrete components instead of wood, in the WA State stormwater manual, see pages 4-16 to 4-21 of Volume V per the attached link.

http://www.ecy.wa.gov/biblio/0510033.html