Flow Velocity in RCP
Flow Velocity in RCP
(OP)
The minimum velocity of 2 fps - 3 fps shall be maintained as a self-cleaning velocity for storm drainage system.
In a County, the design criteria for flow velocity is 2 fts and 3 fps for full and half-full flow conditions, respectively.
Does this mean that we can assume full pipes with free outfall, e.g., Full Free Flow Velocity?
Most of the design cases, the actual flow velocity is much less than the above due to the HGLs of the exiting storm drainage system connected.
Is it OK to just assume full pipes with free outfall for the minimum velocity? Or the real velocity in the systems should be considered? I am confused.
Any information or advice would be highly appreciated!
In a County, the design criteria for flow velocity is 2 fts and 3 fps for full and half-full flow conditions, respectively.
Does this mean that we can assume full pipes with free outfall, e.g., Full Free Flow Velocity?
Most of the design cases, the actual flow velocity is much less than the above due to the HGLs of the exiting storm drainage system connected.
Is it OK to just assume full pipes with free outfall for the minimum velocity? Or the real velocity in the systems should be considered? I am confused.
Any information or advice would be highly appreciated!





RE: Flow Velocity in RCP
RE: Flow Velocity in RCP
for your situation, design for 1/2 full flow at a min 2% and you will be fine. yes, assume no tailwater conditions.
RE: Flow Velocity in RCP
RE: Flow Velocity in RCP
RE: Flow Velocity in RCP
I would be amazed at pressure flow design in a storm sewer calculations, where do you live and who is the reviewer?
RE: Flow Velocity in RCP
RE: Flow Velocity in RCP
RE: Flow Velocity in RCP
Culverts - should have capacity to convey the following:
A. 10-year storm without the headwater depth exceeding the diameter of the culvert.
B. 50-year storm without the headwater depth exceeding one (1) foot over the top of the culvert.
If you have not seen a storm drain that is occasionally surcharged, then you have never seen a storm greater than the 10-year storm.
Here is a reference document:
h
Assume flowing full in pipe at a design slope:
B. Design criteria and considerations
1. Design frequency--the return period of the design storm is 5 years for residential area.
2. Design flow depth--flowing full in pipe at a design slope, which generally is ground slope.
3. Design velocity
(a) The non-depositing (self-cleansing) velocity for silt and grit is vmin = 3 ft/s (0.9 m/s).
(b) The maximum velocity from scour consideration is vmax = 15 ft/s (5 m/s).
(c) The design velocity should satisfies vmin < vdesign < vmax.
4. Design slope
(a) Generally the ground surface slope.
(b) It may be adjusted to a larger slope than the surface grade from the non-depositing consideration.
(c) Minimize the design grade (slope) for minimum excavation, still meeting the criteria above.
http://
RE: Flow Velocity in RCP
A criterion that would better achieve the desired(?) performance would be something like "minimum 2 ft/sec at the 2-yr design flow", though I can't say I've ever seen that.
I would think a more