Weather Monitoring and Mapping
Technologies to keep an eye on the weather and the infrastructure
The United States’ aging underground infrastructure,
increasing development, federal mandates, and the relative
unpredictable temperament of nature mean stormwater program managers are
eyeing the best technologies on the market to help plan programs and
model storm systems in order to correctly size stormwater
infrastructure, such as pipes, drainage systems, and retention/detention
Working Across Jurisdictions
Clint Cantrell, P.E., is a vice president for Metcalf & Eddy in the
company’s wet-weather technical practice division. In helping create
stormwater programs, Metcalf & Eddy uses technologies such as the
EPA SWMM (Storm Water Management Model) model, and Wallingford
Software’s InfoWorks model, DHI’s MIKE URBAN model, and Vieux &
Associates’ radar-based rainfall data for hydraulic model simulations.
“Many of our ongoing projects involve developing plans to address
current capacity issues and capacity required to support future growth
and development,” says Cantrell. “At present, many of our clients are in
the process of addressing required reductions of combined and sanitary
sewer system overflows as required by the EPA.
“Many options exist to address these problems, including combined
sewer separation, storage, high-rate treatment, and reduction of inflow
and infiltration,” he adds. “Key to this is utilizing a sufficiently
detailed model that can support the development of accurate cost-benefit
comparisons between levels of control and resulting improvements in
Over the past 10 years, there have been significant advancements in
both monitoring and modeling technologies, Cantrell points out. “For
example, we regularly use Doppler-based radar rainfall data to
supplement ground-based rain gauges,” he says. “This gives us a much
better understanding of the true spatial distribution of storms we
monitor to calibrate our models.
“In terms of models, vast improvements have been made, which now
allow us to model these complex systems very closely to how they operate
in reality,” he says. “This includes advanced real-time control
systems, which can be used to modify how a collection system operates
dynamically to achieve optimal performance.”
Cantrell has been involved with many stormwater programs, ranging
from small areas (less than 1,000 acres) to very large areas
(countywide). Currently, Metcalf & Eddy is working on two systems
that involve multiple cities and counties. Annual rainfall totals for
the two areas range from 40 to 50 inches.
One project in which the firm was involved was for the City of
Dayton, OH, and the Montgomery County Integrated Wastewater Model and
Master Plan. The two utilities joined forces to create a joint
wastewater master plan for their connected wastewater collection
systems, which serve a population of 159,000 in Dayton per the 2005 US
Census and 844,000 residents in the greater Dayton metropolitan area.
“The county’s sewers flow into the city sewers at several locations,”
says Cantrell. “Our project has involved the development of an
integrated GIS [geographical information system] and model to represent
both sewer systems in a holistic manner—essentially ignoring political
“Using the model—which is in the final stages of calibration—we will
develop short- and long-term solutions to address ongoing problems and
capacity needs for future development. The model is one of the largest
in Ohio, with more than 12,000 manholes and pipes.”
The Metcalf & Eddy team is utilizing advanced radar rainfall data
to enhance the calibration accuracy. The model represents all complex
details of the collection system and accurately predicts what is going
on during dry- and wet-weather conditions, notes Cantrell.
Metcalf & Eddy is also assisting with the Sanitation District No.
1 (SD1) of Northern Kentucky Infrastructure Plan. SD1 currently
provides wastewater collection and treatment services for 90,000
“Recently, SD1 entered into a federal consent decree with the US
Environmental Protection Agency to address overflows within its combined
and separate sewer systems,” Cantrell explains. He says SD1 has taken a
unique approach to develop plans focusing on watershed issues to ensure
a high cost benefit for any capital investments made, a plan endorsed
by the EPA as a model for other utilities to follow.
“SD1 has previously developed models of its collection systems and
key receiving waters and is currently in the process of updating and
refining these models,” says Cantrell. “Once this effort is completed,
the agency will develop integrated watershed plans to address pollution
from both point and nonpoint sources.”
New CSO Policy
Sacramento, CA, owns and operates a combined sewer system (CSS) serving
7,500 acres in its downtown area, conveying both stormwater runoff and
sanitary sewage in the same pipelines. There is an additional 3,700
acres with separate drainage systems, but the separated sewer discharges
to the combined sewer system.
Sacramento is generally flat with elevations ranging from 10 feet in
the southwest corner of the city and between 20 and 30 feet going north
and east from the southwest low-lying area. The city receives about 18
inches of rainfall annually and is located at the confluence of the
Sacramento River and the American River.
Years ago, the downtown area frequently flooded, and in the late
1800s, a significant portion of the downtown ground and floor elevations
was raised 12 feet. Later, a system of levees was constructed to
prevent severe flooding from seasonal high flows in the Sacramento and
Photo: Clint Cantrell of Metcalf & Eddy
|Metcalf & Eddy helps its clients address the reductions of combined
and sanitary sewer system overflows as required by the EPA.
Due to the levee system, the CSS pipelines—which used
to discharge directly into the Sacramento River—now terminate at two
major pumping facilities known as Sump 1/1a and Sump 2, constructed in
1908 and 1914, respectively.
Today, Sacramento operates the CSS under a National Pollutant
Discharge Elimination System (NPDES) permit for controlling combined
system overflows (CSOs) to the river and the surcharging of combined
sewer outflows to streets, says Bruce Barboza, a senior engineer for the
City of Sacramento.
In 1995, Sacramento produced a long-term control plan (LTCP) that
consisted of combined system improvements to reduce CSOs to the
Sacramento River and CSS outflows to the city streets.
The LTCP consists of increasing the pumping and treatment capacities
of the existing system, constructing large relief sewer pipelines that
serve as in-line pipe storage of excess combined sewer, and constructing
several local and regional underground storage facilities designed to
fill before outflows reach the street, says Barboza.
Initially, all combined wastewater is sent to two sump pumps. In the
first-stage operation, dry-weather flows and runoff from small storm
events are sent to the Sacramento Regional Wastewater Treatment Plant
(SRWTP). Flows that exceed 60 million gallons per day start up the
In those operations, the flows are routed to Pioneer Reservoir for
storage (23 million gallons) and to the Combined Wastewater Treatment
Plant (CWTP) for primary treatment of flows up to 130 million gallons
per day to be discharged to the Sacramento River.
When this treatment plant is at capacity, Stage 3 operations are
started. In those operations, the city operates Pioneer Reservoir as a
primary treatment plant for discharging up to 250 million gallons per
day of treated flows to the Sacramento River. When these capacities are
exceeded and the capacities of the upstream pipeline system and storage
facilities are surpassed, untreated combined sewage is released to the
In April 1994, the USEPA issued its Combined Sewer Overflow Policy
for controlling discharges to the nation’s waters from combined sewer
systems. One of the cornerstones of the CSO policy is the requirement
for nine minimum controls (NMCs), which apply to every CSS nationwide,
Barboza points out.
The NMCs are defined as the minimum technology-based actions or
measures designed to reduce CSOs and their effects on receiving water
quality without extensive engineering studies or major construction.
This policy stipulates that at least 85% of the average annual CSS storm
flow be captured and receive primary treatment with disinfection prior
The results of a five-year monitoring effort and study (Effluent and
Receiving Water Quality and Toxicity Summary Report for 1991–1995) found
Sacramento was in compliance with this policy during the study period
and treated approximately 92% of the total CSS storm flow volume prior
to discharge, says Barboza.
This monitoring effort was completed prior to implementation of the
improvements detailed in the 1995 CSS Improvement and Rehabilitation
Plan, which significantly reduced the occurrence of CSOs.
The 1995 LTCP was based on modeling evaluations conducted with the
city’s Combined System SWMM Model, which is a modified version of the
EPA’s Storm Water Management Model, says Barboza. The city has added
other modeling features for measuring combined sewer outflow volumes to
the street and re-entrance of the outflows, among others, he says.
The goal of Sacramento’s efforts is to ensure that new development
within the CSS addresses its downstream impacts either by paying a
mitigation fee or by directly providing mitigation, says Barboza.
“Additionally, we are studying areas of the CSS on its perimeter that
can be removed from the system by diverting the sewage into regional
sewer interceptors,” he says. “For major development projects—as well as
general infill development identified in the General Plan—we develop
regional projects using the CSS SWMM Model that mitigate the impacts and
also provide continuous reduction in overall flooding.”
Many of the 1995 LTCP improvements have been completed, and others
are in design or under review as part of an ongoing process to improve
the CSS system and update the LTCP. “The overall goal is to mitigate the
occurrence of combined sewer outflows to the street for storm events at
or below the 10-year, six-hour storm [about 1.65 inches in six hours],”
says Barboza. “The combined system area is experiencing a lot of new
growth, which will increase the combined sewer outflows to the street if
not controlled and planned for.
“The future combined area sewer flows from the city’s 20-year
projected growth and land-use development plan have been superimposed
into the SWMM model. We are in the process of looking at future combined
system mitigation improvement projects that will now include these
added future sewer flows from growth projections.”
In carrying out its mission, Sacramento is implementing several types of technologies:
- GIS base mapping: “The original shed map for the combined system
SWMM model was never put into a GIS format,” says Barboza. “We are
currently inserting the SWMM model into the city’s GIS base maps, thus
greatly simplifying updates to the system and facilitating
- Model calibration: “The combined system SWMM model has never been
calibrated to actual storm events and measured flows,” says Barboza. “To
date, all model evaluations are based on the city’s 10-year, six-hour
theoretical design storm event. The model applies this storm uniformly
over the entire drainage basin—a conservative and unrealistic assumption
for such a large basin. “We are looking at the use of radar-adjusted
rainfall data that have been extracted from actual storms that can be
entered into the model according to real time and the spatial rainfall
differences for the individual sheds. Our practice with some of these
data sets does look promising. We still need to get a flow meter plan
developed for proper correlation.”
- OneRain’s gauge-adjusted radar rainfall data service has been used for the past two rainfall seasons.
In its mission to develop stormwater programs, CH2M Hill uses XP
Software “from the planning phase to design,” notes Gabor M. Vasarhelyi,
MSCE, P.Eng. P.E. “We use it for watershed management planning and for
conceptual to planning detail design on storm drainage systems,” he
says. “In one part of our project, we are using it for monitoring.
Essentially, we are using monitoring data and evaluating the first four
months of a low-impact development system.”
Among the many goals of the municipalities’ stormwater programs is
the expansion of the storm drain system as the city grows, the
separation of a combined sewer system, and mitigation of flooding
problems, among others. Vasarhelyi’s firm deals with all such goals.
“When you do master plans in the municipal context, the primary purpose
is essentially to evaluate the system for four months and then develop a
capital improvement program so they can decide which elements of the
stormwater management system need to be updated and when,” he says.
“From then, the software is used for supporting more detailed designs.”
Vasarhelyi remembers the days when he used slide rules for mapping.
“When engineers use the non-modeling techniques, they essentially need
to make an evaluation based on a much more limited set of data,” he
says. “Modeling programs ensure you can create a digital model of a
physical system in the ground and expose it to a number of different
potential conditions, which you can phase.
“You can evaluate it, and your recommendations are really much better
founded than any other ways or approaches. With automation, you can
define and develop an ultimate system.”
Maurico Herrera, a water resources engineer with CH2M Hill, says the
models have evolved more into a user-friendly format than in the past.
“Originally, they were DOS-based programs, and now they are
Windows-based,” he says. “They have a better range with GIS and are more
efficient because we can compile lots of data, put it in the model, and
analyze different scenarios a lot quicker now than when this program
The ability to illustrate numbers with aerial photographs is another
plus, Vasarhelyi says. “There is a picture behind the numbers, so the
engineer has a much better connection to the actual physical system
that’s on the ground,” he says. “That is a revolutionary change compared
to modeling techniques that use DOS techniques. You just had numbers
and tried to visualize the numbers. Now you can actually work with real
pictures of the land.”
CH2M Hill uses software to do flood mapping for urban developers to
analyze how development is going to impact certain streams and for
Other modalities are used for long-term forecasting for water
supplies and considering the potential impact of climate change on water
availability in the long run.
Modeling also is used to project the impact of mining impacts on
streams and how major highway projects will impact the drainage and
irrigation patterns of the land.
The two key technologies used by CH2M Hill include GIS for data
management and analysis and hydrologic, hydraulic, and water-quality
modeling for system evaluations, planning, and design.
The GIS systems used by CH2M Hill include ArcView GIS and analytical tools and 3D-Analyst and Spatial Analyst.
Of the hydrologic, hydraulic, and water-quality modeling tools, CH2M
Hill uses EPA SWMM5, xpswmm, PCSWMM (for which Herrera is an
instructor), DHI Mouse, UBC Watershed Model, HEC-RAS, and HEC-GeoRAS,
At HDR Engineering Inc., an architectural, engineering, and
consulting firm based in Omaha, NE, Suresh Hettiarachchi, an engineer
with the company, says his firm uses SWMM, HMS, and HEC-RAS in assisting
municipalities in dealing with stormwater programs.
As such, the firm assists municipalities in meeting
certain goals, such as expanding the storm drain system as the city
grows, separating a combined sewer system and mitigating flood programs,
and examining water-quality issues as they relate to the quantity of
“We are using GIS a lot more,” says Hettiarachchi. “Integration with
GIS is making things easier. We relate to the ‘real world’ well with it
and can easily manage data.”
Carol Brzozowski specializes in topics related to stormwater and technology.