Design Guide
Distribution Pipe
|
Step
|
Description
|
Method/Design Parameter
|
Equation |
Variables |
Value
|
Units |
| 5.1 |
Determine distribution pipe (or distribution
channel) length |
Determine actual distance pipe or
distribution channel must distribute water from Step 6.7 (i.e.,
width of VFS). |
|
Distribution channel to be gravel
lined with geotextile fabric underneath |
|
m |
| 5.2 |
Select diameter
(or width and depth) of distribution pipe or channel required |
The distribution
pipe (distribution channel) dimensions must be sufficient to convey
the maximum siphon or pump output, or collection pipe orifice
discharge capacity (gravity system) determined by flow and pipe
velocity using Manning's Equation (Equation 3.9). |
D = 4[((Vn)/S0.5)1.5] |
Distribution channel
to be level on the downgradient side for even flow distribution
along the length of the distribution channel |
|
|
| D = diameter of pipe |
|
m |
| V = velocity of flow |
|
m/s |
| n = Manning's n |
0.009 |
|
| S = slope of pipe |
|
m/m |
| 5.3 |
Determine capacity of
orifice opening in distribution pipe |
Use Equation 3.7; assume
the head to be 0.90 m; assume C = 0.61. |
Q = (C)(A)(2gh)0.5 |
Q = orifice discharge capacity |
|
m3/s |
| C = orifice constant |
0.61 |
|
| A = orifice area |
|
m2 |
| g = acceleration due to gravity |
9.8 |
m/s2 |
| h = head on orifice |
|
m |
| 5.4 |
Determine number of orifices
to meet flow capacity being delivered |
Use a 1.25 target distribution
rate. Divide the target discharge rate for the distribution pipe
by the orifice discharge rate determined in Step 5.3. Consider
using a gated pipe with a minimum gate spacing of 0.6 m. |
No. of orifice = 1.25 × target
discharge rate/orifice discharge rate |
No. of orifices |
|
|
| Orifice spacing = distribution pipe
length/no. of orifices |
Orifice spacing (centres) |
|
m |
