Design Guide
Storage Settling Basin
|
Step
|
Description
|
Method/Design Parameter
|
Equation |
Variables |
Value
|
Units |
| 2.1 |
Select storage type (see
Section 3.2) |
Determine preferred storage
method: Integrated using containment wall or dedicated external
basin. |
|
Integrated |
|
|
| |
Dedicated External |
|
|
| 2.2 |
Develop integrated storage/settling
basin |
Use if runoff collection area is suitable
for development of a watertight basin and sufficient volume can
be generated using a containment wall around all or portion of
runoff containment area. |
|
|
|
|
| 2.2.1(a) |
Determine maximum storage
volume required |
Volume is equal to the
conservative maximum storage volume calculated in Step 1.4.1 (a)
or Step 1.4.1 (b). |
|
Vmax = maximum
storage volume |
|
m3 |
|
OR
|
| 2.2.1(b) |
Determine minimum storage
volume required |
Minimum storage volume
is calculated in Step 1.4.2(a) or Step 1.4.2(b) |
|
Vmin = minimum
storage volume |
|
m3 |
| 2.2.2 |
Establish containment wall height |
|
|
|
|
|
| 2.2.2.1 |
Establish containment
wall height assembly with consistent slope perpendicular to runoff
flow to low side |
Calculate containment
wall height using Equation 3.4. |
h=sqrt(2Vs/L) |
h = retaining wall height |
|
m |
| V = volume of storage |
|
m3 |
| s = floor slope in the direction of
flow |
|
m/m |
| L = runoff area length at right angles
to flow |
|
m |
| 2.2.2.2 |
Establish containment wall height
for runoff collection area that does not have one consistent slope
to a low side |
Methods available for calculating
a volume based on a predicted elevation (top of wall) are the
average end-area method, the planimeter method, and the average-depth
method, or the creation of a 3-dimensional computer- generated
terrain model. |
|
h = retaining wall height |
|
m |
| 2.2.3 |
Establish total containment wall
height |
Establish final height required to
accommodate runoff storage + 0.30 m for freeboard + 0.15 m for
emergency overflow. |
ht = h + 0.30 + 0.15 |
ht = total containment
wall height |
|
m |
| h = retaining wall height |
|
m |
| 2.2.4
|
Calculate discharge rate from runoff
collection area of integrated storage/settling basin with a holding
time (htm) ranging from 4 to 10 hours (see Section 3.3.1)
|
Storage volume is equal
to or greater than storage volume calculated in Step 2.2.1(a). |
qmax = Vmax/htm |
qmax = discharge rate
for maximum storage volume |
|
m3/s |
| Vmax = conservative maximum
storage volume |
|
m3 |
| htm = holding time |
|
s |
| Storage volume is less than storage
volume calculated in Step 2.2.1(a) but more than minimum storage
volume from 25-year/5-minute storm event over a 15-minute period
from Step 2.2.1(b). |
qo = qp[1.25
- (1500V/RA + 0.06)0.5] |
qo = rate of outflow when
pipe flows full |
|
m3/s |
| qp = peak flow = discharge
from runoff collection area |
|
m3/s |
| V = available storage volume |
|
ha-m |
| R = return period runoff
25-year/24-hour |
|
mm |
| A = runoff collection area |
|
ha |
|
2.3
|
Develop dedicated external storage/settling
basin |
|
|
|
|
|
|
2.3.1(a)
|
Determine maximum storage volume required |
Maximum storage volume is equal to
the storage volume calculated in Step 2.2.1(a). |
|
V = maximum storage volume |
|
m3 |
|
OR
|
| 2.3.1(b) |
Determine minimum storage volume required |
Minimum storage volume is equal to
storage volume calculated in Step 1.4.2(a) or Step 1.4.2(b) |
|
Vmin = minimum storage
volume |
|
m3 |
|
2.3.2
|
Establish storage volume of existing
facility |
|
|
|
|
|
|
2.3.2.1
|
Establish volume capacity
of existing storage facility
|
Method used will depend on design
of existing storage facility. Subtract freeboard height (0.3 m)
and emergency overflow height (0.15 m) before calculating maximum
storage volume. |
|
V = storage volume |
|
m3 |
| If volume capacity is
greater than minimum volume required, then existing storage facility
may be used to accommodate runoff water. |
|
If Yes, proceed to next step |
|
|
| |
If No, existing facility is not suitable
for development of external dedicated basin |
|
|
| 2.3.2.2 |
Establish operating parameters
for existing storage facility
|
Establish the following: |
|
|
|
|
|
|
|
|
m |
|
- elevation of maximum storage volume minus freeboard (0.3
m) and emergency overflow height (0.15 m)
|
|
|
m |
|
- elevation of minimum storage volume
|
|
|
m |
|
| 2.3.3 |
Establish new dedicated external basin |
|
|
|
|
|
| 2.3.3.1 |
Establish basin dimensions |
Select minimum basin depth of 1.45
m (1.0 m liquid depth plus 0.3 m freeboard plus 0.15 m spillway
depth). |
|
Minimum basin depth |
1.45 |
m |
| Establish the basin length
to width ratio of 3 to 1 to accommodate required minimum storage
volume. Limit width of basin to between 3 m to 6 m to accommodate
removal of solids using standard backhoe reach lengths. |
|
Basin width |
|
m |
| |
Basin length |
|
m |
| Calculate basin depth for live storage
from 2.3.1 (a) or 2.3.1 (b). |
Basin depth for live storage |
|
|
m |
| Total basin depth is minimum basin
depth plus basin depth for live storage. |
Total basin depth |
|
|
m |
| 2.3.4 |
Calculate discharge rate from external
storage/settling basin |
Storage volume available
is equal to or greater than storage volume calculated in Step
2.3.1(a). |
qmax = Vmax/htm |
qmax = discharge rate for
storage volume |
|
m3/s |
| vmax = external storage
volume |
|
m3 |
| htm = holding time |
|
s |
| Storage volume available
is less than storage volume calculated in Step 2.3.1(a) but more
than minimum storage volume from 25-year/5-minute storm event
over a 15-minute period from Step 2.3.1(b). |
qo=qp[1.25
-(1500V/RA + 0.06)0.5] |
qo = rrate
of outflow when pipe flows full |
|
m3/s |
| qp = peak inflow
= peak discharge from runoff collection area |
|
m3/s |
| V = available storage volume |
|
ha-m |
| R = return period runoff
25-year/24-hour |
|
mm |
| A = runoff collection area |
|
ha |
