Stormwater Outfall - Definition?? 2

[gt5879c]

I've come across a discrepancy in the definition of a Stormwater Outfall. GA Env. Protection Div. says its the outlet of any stormwater conveyance system. But people have told me ASCE defines it as the stormwater conveyance system itself - not just the outlet, like an outfall sewer. What is the correct definition?

 

[TerryScan]

A regulatory entity can make their own definitions for terms. If one is dealing with a Georgia EPD term...one would use their definition.

If one is dealing with NPDES in Georgia, their website (

http://www.gaswcc.org/level-1a/1a-4-npdes.pdf)

page 42 states:
"Outfall – the location where storm water leaves the site or enters the receiving stream"

 

[LHA]

Terry's right, use the reviewer's definition.

The discrepancy is not a contradiction, but a difference in scope. If the study/concern is erosion and velocity at the outlet, as with an E&S plan, the "outfall" is the Endwall and Energy Dissipation. If the study/concern is capcity and failure to get water out of an area, as with municipal engineering review, the "outfall" is all facilities downstream of an area.

Engineering is the practice of the art of science - Steve

 

[MissouriPE]

For our MS4 permit, the state of Missouri (or at least one of their employees) defined an outfall as anywhere a concentrated flow leaves our City limits. Not sure this was right, but that is what I mapped. Yikes if it is really supposed to be the end of every pipe dumping into a waterway. I could map that eventually, but ick!

 

[LHA]

Again, correct, but a matter of scope. For MS4 enforcement, the study/concern is the contribution to degradation of common waters. Each numicipality within an Urbanized Area (UA) must take care of its own. So the "outfall" is a point where concentrated flow leaves a municipal limits.

The ones that I've mapped, I've also done the end of every pipe dumping into a waterway. It looks like job security for the PE in MO!

Engineering is the practice of the art of science - Steve

 

[saruman26]

For analytical purposes within the scope of a project, whether it be a subdivision or municipal sewer improvements, outfall usually refers to the discharge point from a storm sewer network or SWM facility into a receiving watercourse.

Of specific concern in most cases is to ensure that the design meets the requirements for Adequate Outfall, which means that the receiving channel or sewer network has adequate capacity to convey the discharge from your project site. For example, a SWM basin discharging to a stream, or a private storm sewer discharging to a public storm sewer.