A
CITIZEN'S GUIDE TO LOW IMPACT DEVELOPMENT
Conservation
and Ecology News - special edition. If
you have any comments regarding
this article please direct them to the author
tholz@scaconsultinggroup.com
YOU
CAN'T TELL THE PLAYERS WITHOUT A PROGRAM: A
CITIZEN'S GUIDE TO LOW IMPACT
DEVELOPMENT
Thomas W. Holz, PE, SCA
Consulting Group Lacey, WA
On
the poor soils that predominate most of the Puget Sound Basin, even the lowest
levels of development impact watersheds and salmon streams. Researchers
have measured declines in stream health for disturbances of as little
as 3% of a watershed. When 10% of a
watershed is paved, stream habitat
is in deep trouble. When 20% of a
watershed is paved, many streams
can no longer sustain fish populations. Traditional
urban development
equates to much higher impervious surface levels -- far more than
enough to devastate a stream. Although
decades of data have documented
the destructiveness of traditional development, only in the last
four years has the extreme sensitivity of watersheds and streams become
widely known.
Recent
research has shown that stormwater ponds are largely ineffective in protecting
streams. Pond construction requires removal of nature's perfect
stormwater management system, the forest, soil, and centuries-old duff.
Then a hole is dug, often deep into impervious hardpan.
The pond then
might fill with groundwater thus making its capacity unavailable to detain
runoff. But storing groundwater or surface water, the pond behaves exactly
like an impervious surface in that most precipitation that hits it will
discharge to surface water. Common
sense tells us that removing forest
in order to create another (effectively) impervious surface is a peculiar
way to mitigate for pavement.
If
streams are that sensitive and our engineered nostrums are ineffective, how
can we hope to save endangered fish stocks if we continue to develop watersheds"? Many in the scientific community are skeptical about the compatibility
of ANY development and habitat preservation.
And they may be
right. One thing on which most
agree is that we must completely revise our
definition of development if habitat is to be saved.
Some
claim that "low impact development" standards will save habitat in harm's
way. Perhaps.
Unfortunately for the average citizen, many competing
proposals are being offered under the rubric of "low impact development". Some proposals are quite minimal. Some proposals appear to have
substance until the land-use types that will be exempted from the standard
are revealed.
Will
all proposals work equally well? Skepticism
is well founded, for we have
had decades of promises of stream protection that have not been fulfilled.
Is there a risk that we will adopt an inadequate set of development
standards for the Puget Sound Basin? And
will we then see rapid
decline in the few remaining shards of aquatic life and habitat as the
rest of the basin is built-out? Many
scientists fear the worst.
Because
development is occurring in Washington at the rate of 70,000 acres per
year, whatever standard we adopt represents, in many regions, our last chance
to protect remaining habitat. It is
therefore vital that citizens be
able to distinguish between "low impact" proposals.
A
CITIZEN'S GUIDE FOR JUDGING HOW LOW IS "LOW IMPACT"
What
are the characteristics of a healthy watershed that cannot be violated
if aquatic life is to survive development?
We have paid in the hard
currency of ruined streams to learn these principles:
1.
Leave 60% or more of the watershed forested and soils undisturbed.
2.
Do not collect and discharge runoff; minimize and isolate impervious
surfaces.
3.
Maintain wide buffers for streams and minimize crossings.
Indicators
That Development is Not "Low Impact"
These
three principles have major implications for urban design.
When reviewing
a development proposal advertised as "low impact", measure it against
the principles of a healthy watershed:
Is
more than 40% of the native forest to be removed?
If so the hydrologic cycle
will be too greatly disturbed, a violation of Principle 1.
Is
impervious surface clustered? Impervious
surface must be isolated. If large
areas of contiguous pavement are proposed, too much soil will be sealed
off. Dispersal of the runoff
to the forest is difficult (on some sites
impossible) and the remaining soil on the site cannot absorb the runoff.
Impervious surface in clusters of more than 3,000 square feet or so
should be nested in a forest buffer. If
runoff must sheet-flow over an impervious
surface more than 50 feet or so to reach native soils, the design
is probably a violation of Principle 2.
Is
the forest separated from the structures and in its own cluster?
In a low
impact design, the forest IS the stormwater management system.
Its purpose
is not just aesthetics, but to buffer structures and prevent runoff.
If the forest is in a separate reserve, it cannot efficiently perform
this service. If it is located
uphill from the cluster of development,
then it is useless for this function. Such
a design will almost
certainly fail and lead to nuisance flooding, runoff, and a violation
of Principle 2.
Are
the Roads Too Wide? If roads
are shown as two (or more) lanes, parking
both sides, sidewalks in the same right-of-way with the roads, planter
strips and street trees, the forest will be disturbed more than it can
tolerate. Runoff will accumulate in volumes too high for the remaining
soil to absorb, a violation of Principle 2.
One-way, one-lane roads
through the forest with walks in their own separate right-of-way are ideal.
Are
Ponds Proposed to Mitigate for Development?
Ponds do nearly as much damage
to hydrology as pavement. Construction
of a stormwater pond means that
forest was sacrificed to build another form of impervious surface. Many
ponds on poor soils will counter-productively collect groundwater and discharge
it to surface water. Once
stormwater is collected in a pond it usually
must be discharged to surface water, a violation of Principle 2.
Are
Roads Buried? If roads will have curbs, they will form a trench from which
runoff cannot escape. Runoff must
then be collected in quantities too
large to be infiltrated, a violation of Principle 2.
Is
a drainage collection system needed? If
runoff is to be collected (e.g.,
swales, pipes, gutters, catchbasins) the design is flawed (e.g., bad
road design, too much or too clustered impervious surface).
Runoff will
almost certainly exceed the infiltration capacity of poor soils.
It is
unlikely, once collected, that such volumes of runoff can be "dispersed-in-the-forest".
If a design has these flaws, the principles of a healthy watershed will be violated and the proposal will likely damage aquatic life and habitat. Such development is not "low impact" but high-impact development in disguise.
__________________________________________________________________
The
Conservation and Ecology News is a weekly electronic compilation of
environmental and conservation issues that relate to our local and global
communities and is distributed by:
The Como Watershed Group--"A non-profit society committed to the long-term
conservation
of the Como Creek watershed and the environmental health of our community."
Mailing
address:
2570 Burian Dr., Coquitlam BC V3K 5W9
Phone: (604) 939-0523. Fax: (604) 939-0571
e-mail: cwg@vcn.bc.ca
If you have any questions, comments or requests regarding the information contained within this newsletter, or would like to be removed from the list please contact CWG through one of the above.
*Disclaimer:
CWG provides the C&E News as a roundtable of information on the
environment.
The opinions expressed or information contained within the articles
are not necessarily those of CWG.