quantity and improve the quality of urban runoff.  These
impervious cover is a much better measure of the impact of
elements are:
urbanization than is population density.  He observed that
compact development;
two trends are evident in modern land-use planning.  First,
mixed uses;
the scale of most buildings, from residential dwellings to
short blocks; and
churches and malls, is increasing -- everything is larger now
respect for natural systems.
than it was 50 or 100 years ago.  And second, two-thirds of
all impervious cover is now “car habitat”:  roads, parking
The first three of these were originally articulated by the
lots, and driveways.  It is this “car habitat” that should
therefore be a principal focus of urban design.  The Center
distinguished urban planner Jane Jacobs; the last was
proposed by John Sewell and endorsed by other partici-
for Watershed Protection has reviewed more than 225
pants.  All are consistent with the principles of “new
research studies linking 26 urban stream indicators to
urbanism” now widely debated.  Yet Larry Bourne argued
impervious cover, and on the basis of these findings has
that many new urbanism communities have accommodated
developed a basic Impervious Cover Model.  The Impervious
Cover Model predicts that:
these principles while failing to address issues of access to
employment, and thus ignore traffic and related emissions.
watersheds with less than 10 percent impervious cover
The Center for Watershed Protection has developed a
should have the potential for good water quality; where
number of principles for the development of suburban and
that good quality is not realized, the cause may be
urban watersheds that incorporate these principles. (see
historic alteration rather than land-use.  Ten percent
Appendix I)
impervious cover is typical of rural to suburban
development with “estate” lots 0.5 to 1 hectare in size;
The Land Use Planning/Approval Process
watersheds with 10 to 25 percent impervious cover can
experience moderate degradation, but that degradation
The work group has long suspected that institutional
can be mitigated by careful site design and storm-water
arrangements are critical to managing the water quality
treatment practices.  Most suburban development is
impacts of urbanization, and indeed emphasized that point
typically within this range of impervious cover; and
in the SAB’s 1999-2001 Priorities Report, which stated:
watersheds with more than 25 percent impervious cover
typically cannot support designated beneficial uses and
This need for site-specific approaches may underlie much
exhibit degraded water quality. Active infill/redevelop-
of the management challenge of NPS [nonpoint source]
ment strategies will increase impervious cover in older
pollution. In particular, the current research suggests that
urban watersheds, thus potentially avoiding the
control of NPS [nonpoint source] pollution has been
development of greenfields.  The costs of such infill
hampered by:
however average roughly 10 times those of storm-water
insufficient persuasive evidence of the effectiveness of
treatment facilities constructed on a “greenfield” site.
best management practices;
lack of performance standards;
Mr. Schueler emphasized the need for upland reclamation
inadequate financial incentives for clean-up; and
and reforestation as part of an integrated “smart watershed”
inadequate institutional arrangements.
Current research further underscores the importance of
Several speakers noted that measures of vehicle distance
institutional arrangements.  Several key points were made.
traveled is very useful as a surrogate measure of vehicular
John Sewell reminded participants that Ontario’s current
emissions. Since increased road travel is a notable difference
system of land-use planning and urban design is not based
between traditional urban development and low-density
on the public good, but on what developers and investors
sprawl development, vehicle distance traveled is a poten-
can sell in the real estate market.  Although planning
tially important indicator for examining water quality
documents, such as official plans, reflect the good inten-
impacts from different urban forms.  It may also be the best
tions of the municipality, they are often too general and too
available estimate of the distribution of jobs and the labour
flexible to be a useful regulatory tool.  Too frequently,
official plans are amended to accommodate the demands of
a particular developer.
The Ideal Urban Form
On the U.S. side, much of land-use planning decisions are
Although participants agreed that no particular urban form
not based on comprehensive land-use plans (the equivalent
offered a “silver bullet” for the resolution of urban water
of the official plan) but on zoning regulations.  Zoning
quality impacts, there was considerable support for the
regulations carry the force of law, land-use plans do not.
notion that four elements of urban form can reduce the