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United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-097 Jan. 1984
f/EPA Project Summary
Hydro Brake Regulated Storage
System for Stormwater
Management
Timothy M. Matthews, Paul D. Pitts, Jr., and R. Charles Larlham
The City of Cleveland, Ohio, and the
EPA Great Lakes National Program
Office investigated the effectiveness of
using a proprietary device to control the
release of off-line storage of Stormwater.
The device, the Hydro Brake,* purportedly
permits discharge at a relatively constant
rate under varying head conditions. The
primary objective of this investigation
was to evaluate the ability of the Hydro
Brake to effectively regulate specific
design flows from storage structures to
such an extent that (1) sewers could be
protected from surcharging and creating
combined sewer overflow into receiving
waters and (2) basement and street
flooding could be minimized in upstream
residential areas.
Three underground storage tanks
were constructed using 1.2- to 1.4 m-
diameter pipes that were outfitted with
Hydro Brakes of different flow rates.
The 57- to 283-m3-capacity tanks were
filled with water from nearby fire hy-
drants, and their rates of discharge
were measured to establish discharge
curves for the Hydro Brakes. To eval-
uate these tests, the discharge curves of
equivalent-size orifices were com-
pared. Monitored Stormwater flows
were similarly evaluated. In addition, 1 -,
5-, and 10-year return-period storms
were identified from storm frequency
tables. Stormwater inlet and discharge
hydrographs and storage needs were
then calculated from the storm runoff
data and the observed discharge curves.
Homeowners were surveyed to evalu-
ate the effects of the Hydro Brake/sto-
"Mention of trade names or commercial products
does not constitute endorsement or recommendation
for use.
rage installations on street and base-
ment flooding.
It was demonstrated that the Hydro
Brakes did release storm flows to
combined sewers more slowly and at a
rate more nearly independent of head
than orifices of equivalent size. Also,
the use of the Hydro Brake-storage tank
system appeared to reduce the incidence
of street and basement flooding.
This Project Summary was developed
by EPA's Municipal Environmental
Research Laboratory. Cincinnati. OH.
and the EPA Great Lakes National
Program Office, Region V, Chicago. IL.
to announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Combined sewer overflow (CSO) is
designed into many urban sewer systems
as the primary method of relief when
flows exceed the capacity of the systems.
Although CSO provides hydraulic relief
for receiving sewers and sewage treat-
ment plants, it also carries pollutants to
streams and other water bodies. CSO
occurrences can be eliminated, or their
impacts attenuated, by a variety of
acceptable methods. These methods,
however, are not always effective in
relation to another set of problems often
associated with combined sewer sys-
tems—basement and roadway flooding.
Those CSO control techniques that
include flow retardation may actually
exacerbate flooding problems.
Investigations have been undertaken to
determine cost effective methods to
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abate CSO without making flooding
worse or to abate flooding and surcharging
without increasing CSO. Much of this
effort has concentrated on methods to
retain upstream stormwater without
worsening local flooding. One method
has been to store upstream stormwater
and release it to receiving sewers after
downstream stormwater has drained.
This approach avoids upstream flooding
by not allowing stormwater into sewers
until capacity is available, and avoids
downstream surcharging and CSO by
permitting downstream flow to be con-
veyed away before upstream flows can
arrive.
The City of Cleveland, Ohio, and the
EPA Great Lakes Demonstration Program
investigated the effectiveness of off-line
storage with release controlled by a
proprietary device, the Hydro Brake, that
purportedly permits discharge at a
relatively constant rate under varying
head conditions. The primary objective of
this investigation was to evaluate the
ability of the Hydro Brake to effectively
regulate specific design flows from
stormwater storage structures so that (1)
receiving sewers could be protected from
surcharging and creating CSO conditions.
and (2) basement and street flooding
could be minimized in upstream residen-
tial areas.
Description of Hydro Brake-
Storage Installations
The Hydro Brake is a proprietary flow
regulator device that purportedly acts as
an energy dissipator by imparting a vortex
pattern to the flow passing through the
device. This static device is said to
develop control energy from the physical
geometry of the head above the unit—as
resistance to flow increases with increas-
ing head, the rate of increase of the
discharge from the device is reduced.
This head-discharge relationship results
in a much "flatter" rating curve than does
the discharge from unrestricted openings
or orifices of the same size. The "horizon-
tal conical" Hydro Brake unit is constructed
as a frustum of a cone, having a sealed
lower base and an open upper base,
which is the discharge side of the device.
A schematic diagram of a Hydro Brake
regulator is shown in Figure 1. The
diameter of the upper base describes the
size of the unit. The cone is oriented
horizontally such that its axis defines the
effective direction of flow. The flow
Outlet
Orifice
(Typical 3.5 inch
Diameter}
Direction
of Flow
Inlet
Typical 5 inch
Figure 1. Schematic of hydro-brake regulator.
2
enters through a slot along the face of the
cone between the two bases. The
orientation of this entry slot and the
conical shape combine to produce the
spiral flow pattern inherent with the flow
regulating capability of the Hydro Brake.
At each of the three Hydro Brake
installations, a stormwater retention
structure is located at the low point of a
drainage area and a Hydro Brake regulator
device is installed at the effluent end of
each structure. Discharge is to the
existing combined sewers. Figure 2
depicts the W. 170th Street installation
which is typical of all three sites. To direct
runoff to these units, there was some
minor storm sewer construction and
plugging of catch basin leads in the
immediate vicinity of the Hydro Brake
structures. Catch basins in more remote
locations of each drainage area were
modified through installation of 0.05 cfs
(1.4 L/s) and .25 cfs (7.1 L/s) Hydro Brake
devices. When surface runoff rates
exceed these values, storm flows bypass
the catch basins, flow along the street
gutter system, and drain to the retention
structures.
The W. 170th Street Hydro Brake
control structure consists of one 48-in.-
diameter (1.2 m) round corrugated metal
pipe, 163 ft (50 m) long, sealed at both
ends to form a tank. The storage volume is
approximately 2,000 ft3 (57 m3), and the
tank is buried 7 ft (2.1 m) to the invert.
The Hydro Brake is located at the
discharge end of the tank and is inserted
in a 12-in. (0.30 m) pipe, which discharges
to the 21-in. (0.53 m) combined sewer.
Two Hydro Brakes having discharge
ratings of 2.0 and 1.25 cfs (57 and 35.4
L/s) were tested at the site.
The W. 177th Street Hydro Brake
control structure consists of two 156-ft-
long (47.5 m), 87- x 63-in. (2.2 x 1.6 m)
cross-section corrugated-metal arch
pipes, buried 8 ft(2.4 m)tothe invert, with
a total volume of 10,000 ft3 (283 m3). The
two tanks are joined together by a 24-in.
(0.61 m) pipe. The Hydro Brake unit is
inserted in the 12-in. (0.30 m) effluent
line from a connecting manhole and is
drained to the 18-in. (0.46 m) combined
sewer. Hydro Brakes with ratings of 1.5
and 0.25 cfs (42 and 7.1 L/s) were
evaluated at this installation.
The Puritas Avenue Hydro Brake
Control structure is a corrugated arch
pipe 170 ft (52 m) long with a cross
section of 95 x 67 in. (2.4 x 1.7 m). It is
buried 10 ft (3 m) to the invert. Total
volume is 5,800 ft3 (164 m3). At the
downstream end of the tank there is an
18-in (0.46 m) spiral corrugated pipe
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Legend
(Not to Scale)
Combined Sewer
Storm Sewer
Catch Basin
Direction of Flow
Hydrobrake Location
A
763'—48"(49.7m.—122cm.) Q
21" Combined Sewer
(53 cm.)
W. 170 St.
Plan View
W. 170 St.
Profile View
—~ir
Storage Tank
163'—48"(49.7 m.—122 cm.)
M
M
f 21" (53 cm.) Combined Sewer (j>
L— Hydrobrake Location
Figure 2. W. 170 St. installation.
leading to a manhole containing the
Hydro Brake unit. This manhole has an
invert approximately 3.3 ft (1 m) below
the invert of the tank. An 18-in. (0.46 m)
effluent line from the Hydro Brake
manhole discharges to the 42-in. (1.1 m)
brick combined sewer. The original
installation consisted of a 7.0 cfs (197
L/s) rated Hydro Brake. A new unit rated
at 1.0 cfs (28 L/s) was installed later in
the project.
Study Approach
The Hydro Brakes were calibrated by
filling the storage tanks with water from
nearby fire hydrants and measuring head
and flow to develop discharge curves.
Five storm events were monitored for
inflow, hydraulic head on the Hydro
Brakes, and discharge. Discrete and
composite water quality samples were
taken from the storage tanks and analyzed
for biochemical oxygen demand (BODs),
volatile suspended solids, and total
suspended solids. Composite samples
were analyzed for total organic carbon,
chemical oxygen demand, chlorides,
sulfates, copper, cadmium, chromium,
lead, and zinc. Sedimentation in the
storage tanks was observed, and discharge
curves were developed and analyzed for
each of the Hydro Brakes. In addition to
the hydraulic monitoring and water
quality analysis, observations of the
operating characteristics of the device
were made, homeowner interviews were
undertaken, performance of the devices
were evaluated using storm simulation
techniques, and similar installations in
other communities were comparatively
analyzed using data from published
reports. With this information, an analysis
of the efficacy and cost effectiveness of
the off-line storage/Hydro Brake system
as a CSO attuentuation and flooding
relief approach was prepared.
Findings
This study examined the performance
and design concept of the Hydro Brake
method of flow control for regulating peak
runoff rates from the temporary storm-
flow storage. This application was
evaluated in relation to its ability to
reduce combined sewer surcharge and to
minimize flooding problems. Study find-
ings include:
1. The Hydro Brake device does
regulate flow rates at relatively
constant levels once an effective
operating head has been developed.
Below the effective range of heads,
however,-the device behaves as an
orifice. Hydro Brake flow rates
above the effective operating head
are substantially lower than those
for an orifice or other clear opening
of the same size. The head-discharge
curves for the W. 170th Street
Hydro Brake and an equivalent size
orifice are shown in Figure 3.
2. The flow regulating capability of the
Hydro Brake combined with a
storage system reduces CSO peak
rates and total volumes by reducing
the stormwater inflow rate to the
sewers upstream of the control
point and by delaying the drainage
of storm runoff. The data presented
in Figure 4 shows the potential
effectiveness of the W. 170th
Street installation.
3. By reducing the peak flow in the
sewer system, combined overflow
pollutant loadings are reduced
because the first flush effect is
dampened.
4. Hydro-Brake-regulated storage
tanks are effective in alleviating
sewer surcharge and basement
flooding problems.
5. Reduction in peak flow by the
Hydro-Brake-regulated detention
system depends on the percentage
of total runoff that can be inter-
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3 —
2 —
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Rainfall Intensity
in./hr. (cm./hr.J
Inflow
Outflow
(6 in./15 cm. Hydrobrake)
6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96 102
Time (Minutes)
Figure 4. W. 170St. design storm hydrographs 10yr. return—1/2 hr. duration (). 37 in.-3.48
cm.).
The full report was submitted in fulfill-
ment of Grant No. G005370 by the City of
Cleveland, Ohio, under the sponsorship
of the U.S. Environmental Protection
Agency.
sewer capacity was made available
during the monitored storm events.
Comparative flow rate analyses of ordin-
ary orifices, similar in size to the Hydro
Brake devices, strongly suggest that the
Hydro Brakes were able to control flow
using larger outlets than would have
been possible with a standard orifice.
In addition, the Cleveland study indicates
that by making additional sewer capacity
available, basement flooding and street
flooding were reduced. The City of Euclid
reports similar results. With the use of
Hydro Brakes in catch basins and street
storage, the City of Euclid was able to
reduce catch basin surcharging and,
consequently, basement flooding caused
by back-up flows from those catch basins.
The method of storage appears to be
relatively unimportant. As suggested in
the study prepared for the Borough of
York, the uses and needs of the project
area should determine the type of storage
—street, roof, and parking lot or buried
off-line tank. Then the Hydro Brake is
designed to best serve the discharge rate
and chosen storage method.
Hydro Brakes, by retarding flow while
permitting a larger outlet, appear less
likely to become fouled by refuse than
would a smaller orifice of comparable
discharge rate. As demonstrated in
Cleveland, however. Hydro Brakes may
themselves become fouled in some
instances. In the W. 177th Street
installation (Cleveland), a styrofoam cup
wholly blocked the flow of stormwater. In
the Standard 5-B-7 installation (Rochester),
a piece of lath apparently interrupted the
vortex within the unit, and thereby
permitted stormwater flow to occur at a
rate equal to a 3.5-in. (8.9 cm) orifice.
Generally speaking, maintenance was
not a problem at most of the sites,
although the Napean Township catch
basin installations were subject to solids
depositions and regular clean-out was
necessary because of odors.
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Timothy M. Matthews, Paul D. Pitts, Jr., and R. Charles Larlham are with Snell
Environmental Group, Inc., Stow, OH44224; J. Christopher Kocsan is with the
City of Cleveland. Cleveland, OH 44114.
Ralph G. Christensen is the EPA Project Officer (see below).
Douglas C. Ammon is the EPA Technical Advisor (see below).
The complete report, entitled "Hydro Brake Regulated Storage System for
Storm water Management," (Order No. PB 84-110 378; Cost: $19.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Great Lakes Demonstration Program
Great Lakes National Program Office
U.S. Environmental Protection Agency
Region V
536 South Clark Street
Chicago, IL 60604
The EPA Technical Advisor can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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