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SENT BY:DPRA St -Paul, MN 4",4-12-99 ; 9t34AM ;
<br />612 227 5522 612 407 4131410
<br />(F •RvtOUS SUItY'Alr UUvnxwt,t
<br />that "a 20% reduction [in future impervious cover[
<br />1, .1 feasible and practical goal for Olympia and will
<br />1+,a require excepri anal changes in the Olympia com-
<br />munity.' The recommended reduction is equal to ap-
<br />+.+simarely 600 fewer acres of impervious coverage
<br />I,v rile year 2012. Planners wishing to see an example
<br />d' a comprehensive approach to reducing impervi-
<br />..ttsness would do well to read the Olympia ISRS
<br />Wl+orr. 14
<br />As with other natural resource protection efforts,
<br />,n+musucy and watershed -level planning approaches
<br />Itkv these are often the most effective way of achieving
<br />4ults• Addressing the issue at this scale provides an
<br />..vvrall perspective and rationale for the design and
<br />`ulatory tools described in the following sections.
<br />dire -level considerarions are then based not only on
<br />i Ire immediate impacts of a given development on the
<br />1„cal scream or pond, but also on the site's incremen-
<br />tal contribution to the pollution (or protection) of a
<br />Luger -scale water body or a4uifer. Review of site de-
<br />sign and stormwarer management plans, for instance,
<br />can be checked for consistency with goals for the ap-
<br />propriate watershed.,
<br />Providing this broad context has the added benefit
<br />,,rollowing for greater flexibility at the site level. Plan-
<br />ners can evaluate individual factors like a site's loca-
<br />tion within the watershed, irs land use, and the
<br />relative priority of the receiving stream as they relate
<br />to the overall plan, rather than applying a rigid and
<br />tmiform sec of requirements to all parcels -
<br />Site -level Planning
<br />Site planning is perhaps the leaso•exploved ap-
<br />proach to reducing water pollution. Kendig (1980)
<br />scares that "good design begins with an analysis of the
<br />natural and environmental assets and liabilities of a
<br />,site," and chat these factors should be the determi-
<br />nants of development patterns. Applying this prin-
<br />ciple co water resource protection. translates to
<br />maintaining the natural hydrologic function of a site,
<br />through retaining natural contours and vegetarion to
<br />the maximum extent possible. Consideration of im-
<br />pervious surface is a key element of this overall scrat-
<br />egy, extending to all sire -level considerations. These
<br />Include construction practices, design that reduces im-
<br />perviousness, and design, that. includes measures to
<br />mitigate the effects of the runoff frotrl impervious
<br />areas.
<br />Construction activity itself usually creates imper-
<br />vious surface, severely compacting earth with heavy
<br />machinery. Although erosion control practices may re-
<br />quire procedures for limiting Elie area of exposed soil
<br />and how long it remains exposed, chat requirement
<br />does not necessarily minimize the amount of com-
<br />pacred soil. Construction should be sequenced with
<br />this goal in mind, and it may be necessary lazer to
<br />loosen compacted areas and/or cover them with addi-
<br />cianal pervious materials (Crawl 1995).
<br />From construction, we move to reduction. For vir.
<br />tually all land uses, one of the best design -related op-
<br />portunities for reducing imperviousness is through
<br />the reduction of road widrhs. As has been seen, roads
<br />both constitute a major fraction of a community's im-
<br />pervious coverage, and tend to produce the most
<br />pollutant -laden runoff.
<br />The long-established concept of road hierarchies,
<br />which relates road size to the intensity of use, has
<br />many positive aspects beyond water quality, among
<br />them cost reductions and aesthetic
<br />are efits, Yet
<br />t article
<br />Southworch and Ben Joseph (1995),
<br />in on the history of residential srreec design, found that,
<br />for a variety of historical and institutional reasons,
<br />road hierarchies are often overlooked by local planners
<br />and commissions. The authors conclude that an over-
<br />errcphasis on traffic control has resulted in a "rigid,
<br />over -engineered approach ... deeply embedded in en-
<br />gineering and design practice." Simple math dictates
<br />that for a given length of subdivision road, reduction
<br />From a typical 32-foot to a 20-foot width results in a
<br />37,S% reduction in pavement, or over 63,000 square
<br />feet (about one and one-half acres) per linear mile. The
<br />Olympia study estimated that changing the width of
<br />local access roads from 32 to 20 feet would result in
<br />an overall 6% reduction in imperviousness for a given
<br />development sire in their region, that is, six acres less
<br />street pavement for a typical 100-acre subdivision
<br />(City of Olympia 1994b).
<br />Road surface reduction is a primary reason why
<br />clustering is the most pavement -stingy residential de-
<br />sign. Large -lot subdivisions, which have long been rec-
<br />ognized as being antithetical to most conservation
<br />goals (Arendt 1994a, t994b) generally create more im-
<br />pervious surface and greater water resource impacts
<br />than duster-srylc housing does, This is true even
<br />though the large lots may have less impervious cover-
<br />age per loc, because the attenuated design requires
<br />longer roads, driveways, and sidewalks, which make
<br />the overall subdivision parcel more impervious (figure
<br />5), Schueler (1994c) states that cluster development
<br />can reduce site imperviousness by 10-50%, depending.
<br />on lot size and the road network.
<br />In commercial and industrial zones, the focus of
<br />design-relared reductions in imperviousness shifts to
<br />parking areas, the largest component of impervious
<br />cover (table 1). Research has shown oversupply of
<br />parking co be the rule. Willson (1995), citing his re-
<br />search and that of many others, found that the
<br />"golden rule" of 4.0 parking spaces per 1,000 square
<br />APAI0UWgAL-5PR1Na 1996 251
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