vvEPA
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-041 Apr. 1981
Project Summary
Integrated Control of
Combined Sewer Regulators
Using Weather Radar
M. B. McPherson
In this study, the possibility of
reducing the extent of overflows from
combined sewer systems was studied.
In general, when no in-line or other in-
system storage is used, integrated
regulator operation has no advantage
over local automatic-dynamic regula-
tor control unless (1) expected flow-
rates to the interceptors are estimated
before they occur, and (2) an
operational bias is introduced that
either minimizes overflows from only
some of the regulators on an intercep-
tor or favors the timing of overflows
from all of the outlets, such as after
the initial storm period. A review of
the capabilities of digital recording
weather radar indicates it has the best
potential for estimating rainfall
needed for flowrate predictions. Other
possible uses for such radars in metro-
politan areas were considered, partic-
ularly their use as part of urban flood
warning systems. The possibility of
inducing in-line storage in collector
sewers to gain greater flexibility with
integrated regulator operation was
also considered.
This Project Summary was develop-
ed by EPA's Municipal Environmental
Research Laboratory, Cincinnati, OH,
to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report
ordering information at back).
Introduction
Large construction projects involving
extensive new storage, transport, and
treatment facilities are often proposed
for combined sewer overflow pollution
control. The purpose of this study was to
explore the technical feasibility of less
costly measures that might prove ade-
quate with less stringent abatement
requirements or as a first step.
To what extent can overflows from
conventional combined sewer systems
that typically divert some stormwater
via regulators to interceptor sewers be
.reduced? The real-time, integrated
operation of all interceptor dynamic
regulators from a central computer was
postulated as a way to increase effi-
ciency When no in-line storage in
collector sewers or other in-system
storage is available, integrated opera-
tion can only have an advantage over
independently operated regulators
when flowrates to an interceptor can be
estimated in advance of their occur-
rence. Recently developed special
weather radar with storm tracking and
rainfall measurement and prediction
capabilities made exploration of the
integrated operation hypothesis
particularly timely. Because using radar
only with the integrated control system
limits its attractiveness, other uses for
radar in metropolitan areas were con-
sidered, particularly its use for urban
flood warning systems.
Latitude in operating a combined
sewer system is determined by how
flexibly the system can be manipulated.
In general, only by adding new storage
capacity can the flexibility, and hence
operational latitude, of a conventional
system be increased. Altogether, new
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off-line storage is very costly. There
have been a few instances where in-
line storage has been induced in exist-
ing collector and outfall sewers by
installing adjustable dams or gates in
them at relatively modest cost. The
potential for exploiting m-lmestorageto
gain greater flexibility with integrated
dynamic regulator operation was con-
sidered.
Conclusions
Integrated Regulator
Operation
To minimize overflows, automatic-
dynamic combined sewer system regu-
lators are operated under a local control
mode whereby each regulator is actu-
ated only in response to the stage of
flow in the interceptor in its immediate
vicinity. Using automatic dynamic regu-
lators is a substantial system improve-
ment over the more commonly used
perpendicular weirs, side weirs, and
other "static" regulators that are non-
responsive to flow conditions In
Montreal (Quebec, Canada) where no
in-line or other m-system storage is
available, the feasibility of integrating
the operation of all dynamic regulators
on a conventional interceptor system by
the use of a centralized automatic
control scheme was explored. No
advantage over local automatic-
dynamic regulator control accrues from
this centralized control unless flowrates
can be predicted adequately in advance
The minimum necessary lead time
equals the flow travel time between the
regulators furthest upstream and down-
stream among those to be operated
collectively.
Even if flowrate prediction is used, the
diversion of flows by the regulators
must be programmed to minimize
overflows at one or more particular
regulator, or at some time period over
the duration of storm event (e.g , during
the "first flush"), or both. That is, use of
a weighting function is also required.
Even if both flowrate prediction and a
weighting function are used, the total
volume of overflows for an event will not
be changed That is, even though
overflows are precluded or reduced at
designated outlets or for designated
time periods, or both, the total volume of
overflows for an event will remain
unchanged. When a pollutant charac-
teristic that diminishes in concentration
over time is considered, however, using
integrated regulator operation will
possibly reduce emissions at desig-
nated outfalls.
Preliminary tests indicate that a storm
moving across the tributary catchments
of an interceptor in the direction of flow
can increase the volume of overflows
over the amount for a stationary storm.
Although not tested, it is expected that
storm movement in the opposite
direction would dimmish the volume of
overflows over that for a stationary storm.
storm.
As would be expected, reductions in
overflows anticipated via integrated
regulator operation may be highly
system specific. The potential for over-
flow reduction in the Montreal case
appears to be marginal for a "first flush"
pollutant reduction but very promising
for pollution reductions at designated
outfalls.
In-Line Storage
In-line storage, viewed as a particu-
larly attractive means for reducing com-
bined sewer overflows, exploits the
"unused" volume in interceptors and
trunk sewers. Such temporary storage
can be induced by manipulating existing
or added flow-control devices or both
In-line storage has been a control com-
ponent of some central dispatching
systems designed for supervisory
operation.
Cursory comparison of potentially
useable in-line storage in Montreal and
Milwaukee (Wisconsin) with that
already exploited in Seattle (Washing-
ton) revealed two important departures.
The volume of useable in-line storage
inherent in the Seattle combined sewer
system is generous compared with that
potentially exploitable in Montreal and
Milwaukee. Most combined sewer
systems are in the northeast and mid-
west where rainfall intensities and total
storm depths are generally higher than
in Seattle. As a result, the success in
exploiting m-lme storage in Seattle
should not be casually presumed to be
duplicative elsewhere.
Digital Recording Radars
Newly developed capabilities for
measuring and prediding rainfall by
digital recording radars show
considerable promise for effecting auto-
mated combined sewer system
operation and for enhancing metropol-
itan flood warning syslems. Meteorol-
ogists are cautious about the reliability
of radar measurements, but such
measurements soon may explain
important rainfall characteristics that
have implications in planning and
design of urban water resources facili-
ties Two rainfall prediction schemes
that permit estimating rainfall over
discrete catchments up to 2 to 3 hours in
advance are of singular importance to
combined sewer operations. These
include digital recording radar and tele-
metered ramgage networks The weather
radar has a range of about 125 miles
(200 km), using a telemetered ramgage
network covering that range is not
realistic,however. The digital recording
radar is a realistic means for providing
the rainfall prediction required for auto-
mation ol conventional combined sewer
systems with long interceptors in large
metropolitan areas
areas.
Metropolitan Flood Warning •
In the Denver (Colorado) area, a
metropolitan flash-flood warning
system is being installed on a basin-by-
basin accretion basis Adding rainfall
and runoff prediction capabilities to
existing real-time rainfall and stream-
stage observations appear to have at-
tractive advantages Rainfall forecasts
based on satellite imagery show consid-
erable promise in filling the prediction
time gap between twice-daily synoptic
forecasts and the 2- to 3-hour lead time
provided by digital recording radars,
both for flood warning and for combined
sewer system operation Developing
flash-flood warnings over the next few
years in the Denver area should not only
greatly strengthen that capability but
should also provide important insights
for automation of combined sewer
system operations
Recommendations
In terms of pollution impact on
receiving water, little is known about
the reliability of rainfall prediction—
from catchment hydrology to combined
sewer system dynamics Although it
will be some time before this analytical
chain can be adequately tested, much
exploratory work remains. It is to be
hoped that tentative plans will be imple-
mented to determine the extent to
which rainfall and runoff predictions
can enhance combined sewer
operation. Findings from the predictive
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capabilities of metropolitan flood warn-
ing systems should be examined care-
fully for their potential transfer to
combined sewer system applications.
Because many combined sewer
systems have "static" regulators that
are nonresponsive to flow conditions,
regulator improvement and manage-
ment should be considered the first step
of abatement programs for combined
sewer overflow pollution. Without
adding storage, there appear to be limits
to the extent that overflows can be
minimized from combined sewer
systems with automatic dynamic
regulators. Because adding in-system
storage reservoirs is expensive com-
pared with inducing storage m collector
sewers, ;t is important that the degree of
availability of the latter be sampled
nationally as soon as possible.
In the meanwhile, observing the qual-
itative movement and intensity of
storms with the use of an inexpensive
display device, such as that used m
Denver (wherever a suitable National
Weather Service radar scanning area
exists), might improve understanding of
individual combined sewer systems.
Comparing areal implications from
radar with data from the local ramgage
network, even if done after the fact,
would enhance such surveillance. This
modest commitment could be an
excellent precursor for later adoption of
a digital recording radar capability.
The full report was submitted m
fulfillment of Grant No R806702 by the
Urban Water Resources Research
Council, American Society of Civil
Engineers, under the sponsorship of the
U S Environmental Protection Agency.
M. B. McPherson, formerly with the Urban Water Resources Research Council,
American Society of Civil Engineers, New York, NY 10017, is now an urban
water management consultant, Marblehead, MA 01945.
Douglas C. Ammon is the EPA Project Officer (see below).
The complete report, entitled "Integrated Control of Combined Sewer Regula-
tions Using Weather Radar," (Order No. PB 81 -175 804; Cost: $9.50, subject
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:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
i US GOVERNMENT PRINTING OFFICE 1981 757-012/7070
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Environmental Protection
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