Design Guide
Conveyance Pipe
|
Step
|
Description
|
Method/Design Parameter
|
Equation |
Variables |
Value
|
Units |
| 4.1 |
Define target flow rate |
Target conveyance pipe flow rate
is 10% greater than storage/settling basin discharge rate from
Step 2.2.4 or 2.3.4. |
|
Orifice discharge rate from storage/
settling basin increased by 10%
|
|
m3/s |
| 4.2 |
Establish
minimum pipe/channel slope |
Establish
minimum pipe/channel slope based on Manning's Equation (Equation
3.9). |
A=Q/V
D=(4A/3.14)0.5
R = D/4
S = (Vn/R2/3)2
|
A = area of pipe/channel |
|
m2 |
| Q = flow rate |
|
|
| V = velocity of flow |
|
m/s |
| D = diameter of pipe |
|
m |
| R = hydraulic radius
= area of water flow in pipe/channel divided by the wetted perimeter
of pipe/channel; for circular pipe R = D/4 |
|
|
| S = minimum slope of
pipe/channel |
|
m/m |
n = Manning's
n, PVC Pipe (smooth inner walls)
|
0.009 |
|
| 0.03 |
|
| 4.3 |
Establish design variables
for evaluation of conveyance system |
Establish the inlet elevation of
the conveyance pipe/channel from the sump/drainpipe (gravity flow
with adjacent infiltration area). |
|
EINLET = Inlet elevation
of conveyance pipe (from sump) or conveyance channel (from drainpipe) |
|
m |
| Establish conveyance pipe/channel
run length from sump/drainpipe to top of infiltration area. |
|
L = length of conveyance pipe/channel
run |
|
m |
| Establish the elevation of the existing
grade at top end of the candidate infiltration area. |
|
EEXISGRADE = elevation
at existing grade (at top end of infiltration area) |
|
m |
| Calculate outlet elevation
of the conveyance pipe. |
|
EOUTLET = EINLET
- (S)(L) |
|
|
| EOUTLET = outlet elevation
of conveyance pipe |
|
m |
| S = minimum slope of conveyance pipe
(see Step 4.2) |
|
m/m |
| L = length of conveyance pipe run |
|
m |
| Compare conveyance pipe
outlet elevation with elevation of existing grade at top end of
infiltration area. See Step 4.4. |
|
EOUTLET = outlet elevation
of conveyance pipe |
|
|
EEXISGRADE
= elevation at existing grade at top end of infiltration area
(see Step 4.4)
|
|
|
| Calculate elevation change between
inlet elevation of conveyance pipe/channel from sump/drainpipe
and elevation of existing grade at top end of infiltration area. |
|
ECHANGE =
Einlet - Eexisgrade
ECHANGE = elevation change (represents lift for
pump system or drop for gravity system)
|
|
|
| 4.4 |
Determine gravity or pump
system |
If the existing grade at the top
end of the infiltration area is lower than the conveyance pipe
outlet elevation calculated, e.g., positive elevation change,
then gravity flow to the top end of the infiltration area is possible.
Rerun Manning's equation to ensure that slope between inlet elevation
of conveyance pipe and existing grade at the top of the infiltration
area generates a minimum pipe flow velocity of 0.6 m/s |
|
Gravity flow |
|
|
| If the existing grade
at the top of the infiltration area is higher than the conveyance
pipe outlet elevation calculated, e.g., negative elevation change,
then gravity flow to the top end of the infiltration area is not
possible. A pump will be required to transfer the runoff to the
top end of the infiltration area. |
|
Pumped Flow |
|
|
| 4.5 |
Determine target flow
rate |
Target conveyance pipe
flow rate is 10% greater than storage/settling basin discharge
rate. See Step 4.1. |
|
Orifice discharge rate from storage/
settling basin
|
|
m3/s |
| |
Target conveyance pipe flow rate
(10% greater than orifice discharge rate from storage/settling
basin) |
|
m3/s |
| 4.6 |
Determine total head losses
between pump inlet and distribution pipe discharge |
Determine head differential. |
|
Difference in elevation between sump/drainpipe
and existing grade at top end of infiltration area (see Step 4.3)
|
|
m |
|
To calculate pipe friction losses use Darcy -Weisbach Equation
(Equation 3.8) with f = 0.020 or another equivalent method.
|
Friction losses = f(L/D)(V2/2g) |
Friction losses due to pipe run,
including localized losses caused by pipe bends, valves, etc.
|
|
m |
| f = friction factor |
0.020 |
|
| L = conveyance pipe length |
|
m |
| D = conveyance pipe diameter |
|
m |
| V = velocity of flow |
|
m |
| g = acceleration due to gravity |
9.8 |
m/s2 |
| Add pressure head of 0.9 m at the
distribution pipe. |
|
Distribution pipe pressure head |
0.9 |
m |
| Determine total head losses. |
Total head losses = head differential
plus pipe friction losses plus distribution pipe pressure head |
|
|
m |
| 4.7 |
Select type and size of pump |
Select submersible sewage pump (preferably
screw-induced flow) with automatic controls, capable of moving
up to 24 mm solids. Obtain flow curves for selected pump and select
the most efficient pump that will accommodate target conveyance
pipe flow rate and head differential. |
|
Manufacturer
HP
|
|
|
| 4.8 |
Determine pipe size required |
The pipe size must be sufficient
to convey the target discharge rate output. Check that pipe velocity
does not exceed 1.5 m/s and friction losses are acceptable. |
|
Conveyance pipe diameter |
|
mm |
| 4.9 |
Determine requirements
for power and controls |
Calculate distance from
power source and effort required to power and automatically control
pump. |
|
Check pump requirements (110 V or
220 V, or other) |
|
|
| |
Contact consultant or electrical
contractor for recommendations |
|
|
