This section provides a step-by-step process for designing a VFS
system. Engineers and other professionals should find this Design
Guide template very useful in designing VFS systems using either integrated
storage/settling basins or external storage/settling basins. The numbering
of the steps in the Design Guide matches the step numbers used in
the Case Studies found in Section 5 of the manual.
Design Guide
Runoff Collection Area
|
Step
|
Description
|
Method/Design Parameter
|
Equation |
Variables |
Value
|
Units |
|
|
Establish opportunity and constraint map for infiltration area
|
|
|
|
|
|
|
1.1
|
Establish extent of area contributing
runoff |
Identify on a map the drainage patterns
around proposed collection area; define all areas contributing
surface runoff to the collection area; eliminate all clean water
sources (e.g., roof drains), diverting clean flow and other waste
flow (e.g., milking centre washwater, etc.). |
|
|
|
|
|
1.2
|
Define and measure extent
of runoff collection area |
Measure the area contributing
water to the runoff collection area. |
|
A = runoff collection
area |
|
m2 |
|
1.3
|
Select runoff coefficient (see Section
3.1.3) |
Surface of runoff collection area
must be impervious. A concrete surface with a runoff coefficient
of 0.95 is assumed. Select runoff coefficient that describes the
imperviousness of the existing surface of the runoff collection
area. |
|
C = runoff coefficient |
0.95 |
NA |
|
1.4
|
Storage/settling volume and peak
discharge rate |
|
|
|
|
|
|
1.4.1(a)
|
Option 1 - Select
design-storm event (see Section 3.1.4) for calculating the runoff
storage/settling maximum basin volume requirements using the conservative
method |
Establish closest centre
to farmstead from Table 6.1 and determine maximum storage/settling
volume required |
|
Closest centre
|
|
|
| |
V = storage settling volume |
|
m3 |
| |
A = runoff area |
|
m2 |
|
OR
|
| 1.4.1(b) |
Option 2 - Conservative
maximum storage volume requirements based on a rainfall amount
for a 25-year/24-hour storm event
Use IDF Tables and Equation 3.1 to determine maximum storage
volume
|
Calculate maximum storage volume |
Vmax = CaA |
Vmax = maximum storage
volume |
|
m3 |
| |
|
C = runoff coefficient |
0.95 |
|
| |
|
a = rainfall amount 25-year/24-hour
storm event |
|
m |
| |
|
A = runoff area |
|
m2 |
|
1.4.2(a)
|
Option 1 - Minimum
storage volume based on peak discharge rate of a 25-year storm
return period for a 5-minute duration over a 15-minute period
holding time |
Establish closest centre
to farmstead from Table 6.2.
Establish peak discharge rate and minimum storage settling volume
required from Table 6.2.
|
|
Closest centre |
|
|
| |
Peak discharge rate |
|
m3/s |
| |
Minimum storage settling
volume required |
|
m3 |
|
OR
|
| 1.4.2(b) |
Option 2 - Use IDF Tables and Equation
3.2 and 3.3 to determine peak discharge rate and minimum storage/settling
volume required. Calculate minimum storage/settling volume |
Calculate peak discharge rate from
runoff collection area (Equation 3.2) |
qp= .0027CiA |
qp = peak discharge rate |
|
m3/s |
| C = runoff coefficient |
0.95 |
|
| i = rainfall rate 25-yr/5-min storm
event |
|
mm/h |
| A = runoff collection area |
|
ha |
| Calculate minimum storage
volume requirement with a minimum 15min (900s) holding time (Equation
3.3) |
Vmin= htm
x qp |
Vmin = minimum storage/settling
volume requirement |
|
m3 |
| qp = peak discharge |
|
m3/s |
| htm = min holding time |
900 |
s |
This site is maintained
by the Government of Ontario 
Queen's Printer for Ontario
