Installing a 22 inch Type C Reg-U-Flo vortex valve into the control
structure at Eastern Mall Office Park, South Portland, Maine.
The natural ability of the ground
to control water is compromised
by the construction of
buildings, roads and parking
lots on previously undeveloped green
areas. The problems associated with
uncontrolled stormwater runoff are
becoming more apparent with increasing
urbanization and changing weather
patterns. In many towns and cities
around the world the frequency of
stormwater flooding, and the costs of
consequential damage associated with
urban flooding are rising rapidly.
Conventional solutions to stormwater
flooding have typically relied on
increasing the conveyance capacity of
the collection system. Large diameter
relief sewers and tunnels are constructed
to cope with increased peak flows,
which transfer excess flows further
down the watershed, where it is hoped
that sufficient hydraulic capacity
exists. Finding a point in the drainage
system with sufficient hydraulic
capacity is a challenge. In most urban
drainage networks there will always be
a hydraulic bottleneck, a point in the
system where the amount of flow
entering the system exceeds the
hydraulic capacity of the sewer.
Conventional approaches to solving
flooding problems that rely on increasing
capacity often transfer, rather than
solve, the problem downstream, are
very expensive to install, are disruptive
and are not sustainable.
In order to prevent flooding problems
from becoming worse, more and
more municipal planning and permitting
departments are requiring developers
to minimize the impact of
stormwater runoff on the environment
by controlling flows and removing pollutants
on site. Planning, permitting
and environmental regulations are
becoming more stringent.
Controlling, storing and treating
stormwater runoff from new developments
can add significantly to project
costs. New and more cost-effective
solutions are needed to meet regulatory
requirements. Sustainable Urban
Drainage Systems (SuDS) offer a
means of meeting the regulatory
requirements without adding to project
costs. SuDS are designed to protect or
enhance water quality and the environment
by dealing with stormwater
runoff close to where it falls as rain
(source control approach) thereby protecting
water resources from the
impacts of excess flow and the associated
pollutants.
Hydro International, a company
with over 25 years of experience in the
field of stormwater management, is a
proponent of SuDS. Through hydraulic
research and development programs
the company has designed a range of
innovative devices that can be used to
help meet permit requirements without
incurring significant costs.
Technologies, such as the Reg-U-Flo® vortex valve, have been designed
with this goal in mind. This valve is a
self activating flow control device that
can be installed in either a manhole or
catchbasin to restrict site runoff to the
predevelopment rate. It operates by
harnessing the energy inherent in the
flow field and avoiding the need for
moving parts or power. No moving
parts mean rquire little or no maintenance.
The design of the valve is simple,
consisting of an intake, a volute and an
outlet. Flow is directed tangentially
into a volute to form a vortex. High
peripheral velocities induce an airfilled
core with a resulting back pressure
that reduces the discharge. By
using the vortex to control the flow,
clear openings are up to 600% larger
than conventional flow control
devices, such as sharp edged orifice
plates. The larger opening size has two
major benefits. Firstly, the larger
openings mean the vortex valves are
less prone to blockage from the trash
and debris often found in urban runoff.
Secondly, the larger openings allow
consulting engineers to consider new
approaches when designing drainage
systems. For example, installing the
valves at points higher up in the
drainage network can lead to a reduction
in the size and cost of downstream
pipe work - inlet or source control.
Reg-U-Flo vortex valves have a
unique S-shaped head/discharge curve,
which has been devised from extensive
computational fluid dynamic modeling
(CFD) and both laboratory and field
testing. The head discharge curve comprises
two distinct phases. As the head
increases, a transition takes place from
the free flow (lower portion of the
curve) to vortex controlled flow (upper
portion of curve). This unique characteristic
can reduce on site storage volume
requirements by up to 30%, lowering
overall project costs by as much
as 50%.
There are currently over 14,000 of
these vortex valves in operation
around the world, controlling a wide
range of flow from 0.15 cfs (4 l/s) to
425 cfs (11,900 l/s).
An example of the effective use of
the Reg-U-Flo vortex valves can be
seen at an office park in South
Portland, Maine. The office park consists
of three separate one-story buildings
totaling 93,000 sq ft, surrounded
by paved parking for 424 cars (an additional
183,000 sq ft) for a total of 6.3
acres of impervious surface out of the
10 acre site. The stormwater permit
required that post development runoff
should not exceed predevelopment
runoff rates. The post-development
runoff rate was calculated to be 45 cfs (1260 l/s) almost double the predevelopment
rate of 23 cfs (644 l/s).
Accordingly, onsite detention was
required to maintain the hydrological
equilibrium. Several options were considered
by the consulting engineer for
meeting the permit discharge requirements,
ranging from sub surface discharge
to on site detention ponds and
underground storage tanks.
The option that was selected as the
most cost-effective final design solution,
consisted of a piped collection
system oversized to provide underground
storage of excess stormwater
for the 1 in 10 year storm, in conjunction
with a single Reg-U-Flo vortex
valve to control the maximum rate of
discharge to the receiving stream. The
difference in storm volumes for the 1
in 10 and 1 in 25 year storms would be
stored as surface storage on portions of
the parking areas. This option proved
to be the most cost-effective and
allowed the most efficient use of space
for this site.
A 22 inch (560mm) Type C Reg-U-Flo
vortex valve was installed in a control
chamber to restrict the flow offsite
to the predevelopment runoff rate.
Forty-eight inch (1200 mm) diameter
storage pipe was used to create sufficient
storage to contain a 1:10 year
storm event underground. The cost of
upsizing the pipe drainage system to
create additional storage capacity was
minimal, while the conventional
drainage system design would have
required 24-36 inch diameter pipe simply
to convey peak flows.
The site contractor estimated that
the installed cost of the pipe storage
system with parking lot ponding was
approximately 4% less than installing
a conventional pipe collection system
with the detention basin. By eliminating
the detention basin the owner
reduced maintenance on the site and
avoided the need for an unsightly security
fence as well as the unsightliness
of windblown trash that inevitably collects
in and around detention basins.
Importantly, by eliminating the
large detention basin that was originally
planned for the site, more land surface
was made available for an additional
building.
Stephen Hides is President of Hydro International.
Contact e-mail: gmerill@hil-tech.com
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