TM 5-814-9
6-5. Cleanup time (K)
N(st)
=
total number of wash hoses at
the wash stations
The recommended design time to drain the prewash bath and
clean up the facility is one (1) hour.
Nt1
=
total number of flusher points in
additional trench drains at
6-6. Water usage factor (Uf)
preparation areas
The usage factor is the estimated percentage of time that water
will be flowing at maximum capacity for any component at the
Nud
=
total number of flusher points in
facility. This factor is used in determining the overflow rate into
u-drains at the bath(s)
the sediment basin. The range is between 20 and 90 percent.
Usage factors vary between component parts of a CVWF; a
C
=
coefficient of runoff
prewash bath will normally require the use of a different usage
factor than a wash station.
I
=
rainfall intensity for region
6-7. Storm water
A
=
area of rainfall for surface type
Rain that falls onto the pavement should be directed toward the
Nt2
=
total number of flusher points in
treatment system since this stormwater may contain residual
trench drains at the wash station
contaminants from the handstands. Stormwater runoff from
area
adjacent unpaved areas should be directed away from the wash
Nint
=
number of vehicle interior wash
facility. The treatment system should be large enough to treat
points at the wash stations
stormwater collected on the paved areas of the wash facility or
captured on the basins; but not necessarily concurrently with
Ny
=
number of yard hydrants in
water generated during a peak use period. Excess water
wash area
generated from a storm event can be treated during low use
periods. Stormwater flow is estimated by the Rational Method
Water demand calculations. Water demands
(2)
as discussed in TM 5-820-1. The area of each surface type must
in gpm (1pm) are calculated using the follow-
be estimated first. After the treatment system is sized, the
ing formulations.
computations used for each surface type should be compared
with those used for the estimate and appropriate adjustments
Demand
Formulation
made to sizing the basin.
1. Bath flush, each occurrence
Q1 = VB/D
6-8. Stormwater bypass
2. Bath water cannons, vehicle washing Q2 = NwcFwc
A stormwater bypass should be provided at the head end of the
3. Wash stations, vehicle washing
Q3 = NstFst
treatment system just before the sediment basin. Stormwater
diversion prior to treatment should be considered standard
4. Flushing, additional trench drains
Q4 = Nt1Ft1
practice only if the CVWF is in a shutdown mode and the wash
5. Flushing, bath u-drains
Q5 = NudFud
facility has been cleaned up. This diversion should be operated
after each day's shutdown and when it is expected that the
6. Flushing, wash station trench drains
Q6 = Nt2Ft2
facility will not be in use for long periods of time, such as over
7. Wash stations, interior washing
Q7 = NintFint
a winter season.
8. Yard hydrants, clean-up
Q8 = NyFy
6-9. Washwater demand
9. Stormwater runoff, paved areas
Q9 = CpIAp
The following section defines the washwater demand param-
eters and computations for use in sizing the various convey-
10. Stormwater, on basins
Q10 = CbIAb
ances, wash facilities and treatment facilities in a CVWF.
b.
Maximum Flow. The pipes, trench drains, and weirs
a.
Parameters.
at the facility must be designed to handle the
maximum (Qmax) flow rate expected at any given
Terminology
(1)
instant. The designer must consider all of the water
VB
=
volume of tracked bath(s)plus
and solids from each source expected at any instant.
volume of dual-purpose bath(s),
The maximum flow is usually expected to occur
filled to maximum operating
during cleaning operations when the bath is flushed,
depth, in gallons.
the trench flushers are on, and the wash station
hoses and water cannons are in full use. The usage
Nwc
=
total number of water cannon
factor adjustment is not applied, since this is the
nozzles at the bath
peak situation and all systems are operating. The
F(i)
=
design flow rate per demand
maximum flow rate is the greater of either the sum
location, in gpm (1pm)
of Q1 thru Q8, contributions or the sum of Q9 and Q10
stormwater.
i
=
demand location
6-2
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