household size (i.e. number of individuals in each house-
concentrated water quality impacts in certain watershed
hold) over the past several decades.  Like population
locales such as urban centers. If development occurs in the
density, household density also has decreased and is an
low-density sprawling pattern that has been predominant
indicator of demographic shifts, but has limited application
since World War II, the impacts will be more due to
as an indicator of urbanization, or overall development
increased runoff from increased impervious surfaces across
density.  An effective measurement of urbanization should
the watershed, and deposition of air pollutants that come
measure the density of development, including commer-
from increased vehicular traffic associated with this urban
cial, industrial, warehousing, transportation corridor as
form. Because current development patterns are primarily
3.2
well as residential and other types of development.
sprawl, this population growth will likely be accompanied
by substantial land conversion from rural uses, such as
The Water Quality Impacts of Urbanization
agriculture, to urban and suburban uses.  Lower density
development means that the rate of land conversion
The consultants’ findings support numerous other studies
outpaces that of population increase. The rate of land
showing that urbanization changes surface water quality in
conversion is expected to be greatest on the U.S. side of the
fundamental ways.  Three principal sources exist:  treated
basin and may be 50 percent or more in some metropolitan
effluents and bypass from wastewater (sewage) treatment
areas.  With lower development density more roads and
plants; treated and untreated urban storm-water runoff ;
highways are necessary to connect the built environment,
and combined sewer overflows, carrying a mixture of
and more people are required to drive longer distances to
untreated sanitary sewage and storm water.  GHK’s results
get to and from home, jobs, shopping, etc.  Accordingly, the
confirm that sewage treatment plants can be important
projected population growth will include an increase in
sources of suspended solids, phosphorus and nitrogen,
daily vehicle distance traveled, which in some parts of the
metals, and a variety of chemicals used in pharmaceutical
basin is growing much faster than the rate of land conver-
and cosmetic preparations.  Storm water contributes
sion.  For example, Chicago’s population grew 9.6 percent
suspended solids, phosphorus and nitrogen (primarily
between 1982 and 1997, its urbanized area grew by 25.5
from animal excrement and lawn fertilizers), and metals,
percent and its vehicle distance traveled by 79 percent over
but in addition can be an important source of polynuclear
the same period.
aromatic hydrocarbons (PAHs) from vehicle exhaust and
other atmospheric sources, as well as microorganisms from
This development pattern is not, however, uniform across
animal excrement.  There is considerable variation in the
all Great Lakes city-regions.  Speaker Larry Bourne noted
degree to which these sources contribute to water quality
that 85 percent of Ontario’s population growth is occurring
impairments.  Factors influencing this contribution include
in the “Golden Horseshoe,” the northwestern portion of
the level and type of treatment practices (i.e. storm-water
Lake Ontario between Niagara and Port Hope.  In many
management) applied to a given stream, and the relative
parts of the basin, there has been a migration from rural to
contributions of industrial, commercial and residential
urban or suburban lands; at the same time, many U.S.
wastewaters to each stream in a particular region.
centres are experiencing migration from inner cities to
suburban lands.  In either case, the most pressing develop-
Notwithstanding differences from city to city and from
ment challenge therefore occurs at the urban fringe.
inner city to suburban regions, one fact was clear from
Patterns of urban development also vary from region to
these discussions:  the population of the Great Lakes basin
region.  GHK’s findings suggest that the Canadian city-
will continue to spread out faster than it increases over the
regions studied (Toronto, Collingwood, and Windsor)
next 20 years.  This sprawling development trend will mean
have exhibited more compact development than their U.S.
more sewage requiring treatment in urban and suburban
counterparts.  For instance, while the Toronto area
areas, more paved and roofed surfaces over which precipi-
population grew 13.8 percent between 1992 and 1999, its
tation will rapidly flow, and airborne pollutant loadings
urbanized land area grew by only 8 percent.  By contrast,
from increased vehicle distance traveled.  Although it is
the Milwaukee area population grew 6.5 percent between
unlikely that society can control the rate of growth, it can
1982 and 1997, its urbanized land area grew by 24.9
make choices about where urban development will occur,
percent over the same period.  Several factors may account
and how that development is configured.  Those decisions
for this contrast: differences in the way that urbanized land
will be taken under the current land-use planning and
is measured; differing land development (i.e. urban) forms
approval process in each jurisdiction.
in each city-region; the location and character of major
industrial complexes and the transportation corridors
Urban Impact on Water Quality
serving them; and different laws and regulations regarding
acceptable development patterns.
Tom Schueler presented persuasive evidence from the
Center for Watershed Protection demonstrating that
Various speakers commented on the dramatic reduction in
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