Subject: Watershed Management #1
From: [email-masked] (Paul Cass)
Date: Sat, 26 Feb 1994 05:14:18 GMT
Newsgroups: sci.bio.ecology

The following article is part of a watershed seminar held at Oregon State
University in Spring, 1992.  The summary was written by Penny Cass and approved by the
speaker.  This article is part of a publication that can be ordered from the
Oregon Water Resources Research Institute, OSU, Strand Ag Hall 210,
Corvallis, OR 97331-2208 (503) 737-4023.  The article may be reprinted
without permission for educational purposes.  If used, Please send 2 copies
of your publication to OWRRI.

MANAGEMENT OF URBAN WATERSHEDS
Wayne Huber, OSU, Civil Engineering

     All watersheds obey the same physical, chemical and biological
principles.  The primary difference between urban and rural watersheds is
the larger amount of impervious surface -- rooftops and pavement -- within
city boundaries, and the city's hydraulically efficient drainage system. 
Natural watersheds slow the movement of water with vegetation, overland
flow, and infiltration, but the network of pipes, channels, and sewers in
urban areas rapidly moves the greater volume of runoff to receiving waters
(Figure 1).  Management of urban watersheds involves assessing the impact
of urban activities on runoff and receiving waters, and providing the impetus
and methods for control of water quantity and quality.  Computer models
can be helpful in making management decisions.  

URBAN RUNOFF PROBLEMS

     Historically, from the mid-1800s the major focus of urban watershed
management has been on drainage and prevention of flooding.  With roof
drains frequently connected directly to the sewers and impervious surfaces
preventing infiltration, civil engineers have to manage larger volumes of fast-
moving water.  

     Although management of water quantity is still a primary
engineering concern, attention is now directed to management of urban
water quality as well.  Storm water picks up many impurities as it moves
through the urban environment (Figure 2).  Oil and grease from parking lots
and roads, leaves, dust fall from industry, particulates from many sources,
nutrients from fertilizers, pollutants in snowmelt, zinc from automobile tires,
heavy metals and other toxics are all carried by storm water to natural
receiving waters, where water quality may be affected.  Thus, nonpoint
source runoff constitutes an important origin of pollutants, comparable to
traditional point source discharges from industry and sewage treatment
plants.  Both point and nonpoint sources must be considered for control of
water quality.  

     Major water quality problems in many older cities are caused by
combined sewer systems that carry both sewage and storm water runoff. 
Sanitary sewers are dry weather flow conveyances for sewage.  Where the
same pipes convey both storm water and sewage, combined sewer
overflows (CSOs) can occur after rainfall.  Heavy rains can produce a vol-
ume of water larger than the sewage treatment plant can handle, and sewage
is discharged directly into the receiving waters.  Portland has 43 combined
sewer overflow locations into the Willamette River and Columbia Slough
(Figure 3); Corvallis has five such discharge points into the Willamette River
(Figure 4).  

     Polluted storm water and sewage discharging from combined sewer
overflows affect aquatic ecosystems, cause bacterial problems such as
coliform in shellfish and closure of water contact recreation, and can affect
water supply, fishing, aesthetics, and navigation (through increased
sedimentation).  Water quality standards are violated more frequently, and
the cost of providing basic public services is increased.  

METHODS OF CONTROL

     Simple maintenance can help reduce adverse water quality effects. 
For example, drainage systems frequently have curb-side catch basins that
capture debris washed off city streets.  Cleaning these devices, which have
sometimes been in place for decades or longer, requires investment in
equipment and personnel but can help control quality problems.  

     Urban erosion from vacant lots, road construction, and building
projects needs to be controlled to prevent sediment from filling culverts and
reducing hydraulic capacity of drainage systems.  Eliminating improper
connections to storm drains from small industries (e.g., service stations) and
controlling infiltration into the sewers can prevent many pollutants from
ending up in receiving waters.  

     Some control methods focus on increasing infiltration through
trenches, basins, and porous pavement.  Increasing contact with the soil and
creating roadside swales, where water flows over vegetation, can also help
reduce the volume of storm water and often remove most of the particulates
suspended in the water.  Innovative compost filters are now being
implemented in the Portland area.  

     Storage of storm water and combined sewage is perhaps the single
most important method of control.  The water can be held in ponds so that it
has time to infiltrate into the soil.  Settling of solids from the water occurs
and is primarily a function of detention time, which increases with the
volume of storage provided.  On a larger scale for combined sewers, water
can be stored in tanks during the rainfall event, then pumped to the
treatment plant after the flow rate has returned to normal.  

     Storm water ponds can be integrated into new urban developments and,
if designed attractively, become an amenity.  Dry ponds are vegetated
storage areas that accommodate flooding during major storm events, while
wet ponds have a permanent pool of water and are more effective for
nutrient removal.  Constructed wetlands can be used to remove solids and
phosphorus.  

     Urban runoff control measures are often called Best Management
Practices (BMPs).  The best BMP approach forms a treatment train where
water is moved through a series of controls.  For example, water can be
taken from a parking lot, routed over a grassy swale, and moved eventually
into a pond.  Treatment trains are particularly effective for controlling the
"first flush" or dirtiest, initial portion of the runoff.  All structural BMPs must
be maintained to be effective.  

IMPETUS FOR CONTROL

     Control of water quality discharges from urban watersheds is spurred
by concerns such as human and aquatic health, aesthetics, and recreation. 
Impetus also comes from federal legislation: the Federal Water Pollution
Control Act of 1972, the Clean Water Act of 1977, and the Water Quality
Act of 1987.  The Clean Water Act established the National Pollutant
Discharge Elimination System (NPDES), which initially required permitting
for sewage treatment plant and industrial discharges and has now been
extended to storm water discharges.  

     Federal financial assistance for urban water quality control is no
longer available.  Local governments will have to pay for any future
improvements.  One source of revenue is a storm water utility that charges
local residents and businesses based upon the amount of impervious surface
(typically a standardized $3-5 per month for a residence).  Public relations
and educational campaigns that inform citizens that waste dumped in drains
ends up in rivers and that outline the costs of clean-up, constitute control
methods themselves and provide an impetus for public involvement.  

MODELING OPTIONS

     Models are used to analyze runoff management options and assist
engineers in decision making.  Data for these models come from studies such
as the EPA Nationwide Urban Runoff Program (NURP).  Eugene was one
of thirty NURP cities studied between 1978 and 1984.  The data from these
studies can be used to evaluate runoff problems and calibrate models that
predict storm water and combined sewer quantity and quality.  The models
can also be used to identify pollutants from various sources in the watershed. 

     For prediction of runoff quality, models sometimes use a build-
up/wash-off concept.  This conceptualizes the quality process as an
accumulation of pollutants during dry weather and subsequent wash-off of
pollutants during a storm event.  The output from the model is concentration
and mass as a function of time and location in the watershed.  

     Several urban watershed models exist.  The EPA Hydrological
Simulation Program - Fortran (HSPF) model is being used in the Tualatin
Basin near Portland to characterize urban and non-urban land-surface runoff. 
The EPA Storm Water Management Model (SWMM is being used in
Portland and many other cities for analysis of CSO and storm water
problems.  SWMM analyzes the various effects of urban control strategies,
including storage, infiltration, treatment, and hydraulic controls.  SWMM and
similar models can produce relatively accurate predictions of water quantity
(hydrographs) when good rainfall data are used as input.  However, quality
processes can only be simulated accurately when local calibration data are
available.  Still other models from EPA and elsewhere can be used to
evaluate receiving water impacts.  

SUMMARY

     Historical problems of drainage and flooding in urban areas are now
complicated by important considerations of water quality.  Protection of
receiving water quality is a federal and state requirement, but local
governments need to provide incentives and educate the public about water
quality concerns since the public has to foot the bill for controls.  Data and
models can provide guidance for decision makers.  Programs to evaluate
urban nonpoint source quality management should be integrated with overall
watershed management in order to provide for a comprehensive stewardship
of our receiving waters.  

REFERENCES:

Donigian, A.S., Jr. and W.C. Huber. 1991. Modeling of Nonpoint Source
Water Quality in Urban and Non-Urban Areas. EPA/600/3-91/039.

Roesner, L.A., B. Urbonas, and M.B. Sonnen (eds). 1988.  Design of Urban
Runoff Quality Controls. Proc. of Engineering Foundation Conference,
American Society of Civil Engineers. New York.

Schueler, T.R. 1987. Controlling Urban Runoff:  A Practical Manual for
Planning and Designing Urban BMPs. Metropolitan Information Center,
Metropolitan Washington Council of Governments, Washington D.D.

Torno, H.C. (ed). 1989. Urban Stormwater Quality Enhancement ~ Source
Control, Retrofitting, and Combined Sewer Technology, Proc of Engineering
Foundation Conference, American Society of Civil Engineers, New York.

Urbonas, B.R. and L.A. Roesner. 1993. Hydrologic Design for Urban Drainage
and Flood Control. Ch. 28 in Handbook of Hydrology, D.R. Maidment (ed).
McGraw-Hill, New York.

Urbonas, B.R. and P. Stahre. 1993. Stormwater Best Management Practices
and Detention for Water Quality, Drainage, and CSO Management. Prentice-
Hall, Englewood Cliffs, NJ.