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Not in my backyard. The
NIMBY syndrome traditionally infects communities when it comes
time to build landfills, chemical plants, and even group homes.
NIMBY has a new victim in Fairfax County-stormwater management
ponds.
In 1989, the Fairfax County Board
of Supervisors adopted a plan for managing stormwater countywide.
The plan identified 134 sites for building regional ponds that
would control both the volume of runoff and the pollutants within
it-quantity and quality, respectively. Thirty-two of those ponds
would be wet and the rest would be dry.* Each regional pond
would control a much larger area (at least 100 acres) than most
on-site ponds.
 Regional
ponds elicit a strong reaction among their detractors and defenders.
Neighboring homeowners claim that the ponds will devalue their
property. Environmentalists argue that regional ponds don't
do enough to protect streams. But County stormwater management
staff asserts that regional ponds are an important tool in controlling
flooding and protecting streams.
A recent public uproar over
a proposed dry regional pond in the southwest section of the
Difficult Run watershed has led the County to reassess the regional
stormwater management plan. Regional Pond D-40 was to be built
on forested land that was dedicated by the developer to the
County as a condition of building the development. Since 1989,
the County has granted five detention waivers for 28 acres of
upstream sites in anticipation of D-40 construction, according
to County engineer Paul Shirey. "No water quality controls
have been provided in the entire 317-acre drainage area to D-40
since the planned pond exempted those sites," said Shirey.
Mathew Taylor is a resident of
the newest subdivision in the D-40 drainage area. He leads a
group calling itself "Citizens for Responsible Stormwater
Management." The group wants the community to play a role
in deciding the best method to control stormwater. Taylor proposed
that the County forgo this regional pond and in its place use
innovative techniques such as rain gardens, wetlands, and swales.
Taylor offered an easement on his property for the County to
build a small rain garden to detain stormwater before it reaches
the stream.
Even ardent advocates for rain
gardens concede that unless at least half of the homeowners
in the drainage area built and maintained a rain garden, Taylor's
solution wouldn't eliminate the need for a pond. And while rain
gardens remove pollutants from runoff, they do not provide flood
control. Furthermore, bioretention as a replacement for conventional
ponds should be integrated as soon as planning starts, not after
construction of homes is nearing completion.
- PRO: Regional ponds require less
clearing. One regional pond would perform the function
of an average of 10-20 on-site ponds. Average clearing for
a regional dry pond is approximately 0.4 acres compared to
7.5 acres to construct the equivalent in on-site ponds.
- CON: This "tree save"
argument is valid only if the land designated for on-site
ponds is preserved, not used for building more houses. Furthermore,
although limited clearing is done to make way for a regional
pond and its dam, remaining trees are threatened by standing
water in the pond. Often, lack of maintenance gradually
turns a dry regional pond into a shallow wet pond or marshland.
Plants not adapted to wet conditions die over a five to ten
year period following construction.
- PRO: Land developers recognize
that economies of scale available at a single regional
pond produce lower capital costs in comparison to the implementation
of many on-site ponds and are able to pass savings on to home
buyers.
- CON: Construction of regional
ponds makes it possible for developers to avoid considering
more environmentally friendly and effective stormwater management
and site design practices.
- PRO: Properly planned and located,
regional ponds are safer and more aesthetically pleasing than
on-site pond areas that are often cleared and graded for
construction.
- CON: Wet ponds have the potential
to look nice with sufficient landscaping. However, wet ponds
can be a safety hazard, especially in areas where small children
play. In Fairfax County, the majority of regional ponds
are dry and ugly.
- PRO: Regional ponds provide improved
downstream channel protection. These ponds are designed
to reduce outfall velocity and as a consequence control downstream
erosion. Reducing erosion reduces sediment and pollutant transport,
which also improves water quality.
- CON: Although regional ponds protect
the downstream channel, the portion of the stream between
the pond and the upstream development is exposed to stormwater
runoff without any quantity or quality control.
- PRO: Since there are fewer facilities
to maintain under a regional plan, the annual cost of maintenance
is significantly lower. Regional facilities can be designed
to ease maintenance activities.
- CON: There is a significant lapse
between the time that an on-site stormwater management waiver
is issued and the regional pond is built. During this
period the stream is exposed to uncontrolled stormwater runoff
from the development unless temporary on-site stormwater management,
a rarity, is provided.
If the County does not construct the regional
ponds identified in its stormwater management plan, what are
the alternatives? There is much information available on how
other states and Canada manage their stormwater. While many
areas still build regional ponds, it appears that the thinking
has shifted toward finding ways of controlling stormwater closer
to the site through alternatives such as low impact development.
Traditional management solutions call for moving stormwater
off site as quickly as possible. Low impact development adds
landscape features that keep water on site, thus enhancing groundwater
recharge and mimicking pre-development conditions.
- In 1992, the County created a funding mechanism for stormwater
management. Developers would contribute to the cost of stormwater
projects in the 30% of the County where upstream land was
still developable. These stormwater projects would include,
but not be limited to, regional ponds. In drainage areas where
regional ponds were planned, the County allowed developers
to contribute to a "pro rata share" program in exchange
for not having to build on-site ponds. What should the County
do with the pro rata shares it collected to pay for stormwater
management in areas where there is none because the regional
ponds were not built?
- What should the County do about future development as it
impacts stormwater?
- How should the County pay the bill for extensive stream
restoration and future stormwater management facility maintenance
if regional ponds are assumed to have lower maintenance costs?
- Should Fairfax County ask the voters to decide on a stormwater
utility fee? Prince William County, Virginia, and Montgomery
County, Maryland, have user fees based on the amount of impervious
surface a property has. Prince George's County, Maryland,
has a stormwater tax based on property value.
In the case of D-40, the Northern Virginia Soil and Water
Conservation District has offered recommendations to the County
staff. Urban Conservation Engineer Asad Rouhi is not a fan of
regional ponds. "I recognize, however, that by not building
this particular pond, stormwater from the developments in the
drainage area will continue to discharge into the stream without
any quality or quantity control," said Rouhi. "Therefore,
at the end of the day I believe this pond will be built."
To decrease the negative impact of the pond on the environment
and aesthetics of the neighborhood, Rouhi recommends exploring
the possibility of decreasing the storage capacity of the pond
and therefore the pond's footprint. This would require a complete
reassessment of the design criteria.
Regional ponds are designed to hold the difference between
pre-development and post-development runoff. However, certain
assumptions are made in those calculations. For regional ponds,
the pre-development runoff estimates are based on a drainage
area that is 100% wooded and, therefore, has minimal runoff.
Post-development runoff estimates are based on the runoff from
the densest development in the drainage area. These numbers
are the extremes and may not be applicable to the D-40 drainage
area, according to Rouhi.
"If the difference between the pre- and post-development
runoff is lower than previously estimated, the pond could be
built with a smaller storage capacity," said Rouhi. "Decreasing
the water detention time from a maximum of 48 hours to 36 or
even 24 hours would also decrease the pond's storage capacity
needs."
Don Demetrius, an engineer in the County's Stormwater Planning
Division, is reviewing the specifications for D-40. "We
are in agreement with Asad about reducing the size of the pond,"
Demetrius said, "but we differ on how to do it."
He explained that a regional pond must be designed to meet
three objectives: water quality control, flood control, and
protection against dam failure. Even if the pond were designed
with a smaller footprint that could meet the first two objectives,
the storage capacity required to protect the integrity of the
dam in an extreme rainfall would have to be nearly as large
as in the original design. Thus the footprint may not be noticeably
smaller.
"We need to take a good hard look at how we do these
regional ponds," said Demetrius. "Building wet ponds
may be the answer because they do a much better job of controlling
water quality and they look better." On the other hand,
wet ponds require a larger dam and storage capacity and therefore
more land clearing to build it. He also pointed out that wet
ponds require more maintenance.
Even as the debate goes on and D-40 is on hold, construction
of regional ponds continues. As more and more land is developed,
Fairfax County planners must take a creative, aggressive approach
to handling the increased runoff that is polluting and eroding
our streams. To that end, the County is convening a multi-agency
task force to develop a position on the role of regional ponds
and other stormwater management tools in the County's stormwater
management program. Stay tuned for more reports on this critical
issue.
If you have any comments about this story or regional ponds
in general, please e-mail the editor.
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