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SENT BY:DPRA St. Paul, MN 4-12-99 ; 9:33AM ; 612
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<br />levels of pollutants- The one unpaved surface moni-
<br />toyed, residential lawns, showed high levels of phos-
<br />yphotons presumably from lawn and garden fertilizers.
<br />tAs this study is augmented by Others over time, rch-
<br />able relationships between pollutant loads and spe-
<br />cific landscape components will undoubtedly emerge,
<br />Impervious cover can be further broken down into
<br />functional components, Schueler (1994a) and oth-
<br />ors point out the two major categories of impervious
<br />• aurface:'rooftops, and the transport system (roads,
<br />parking lots, driveways, sidewalks). In general, the
<br />transport system is the,dotninant component, rein-
<br />forcing the concept of an auiomobile-cenrric society.
<br />In the Olympia study, for instance, the transportation
<br />component ranged from 63% for single-family residen-
<br />t' tial development to 70% for commercial development
<br />i (City of Olympia 1995) (table 1).
<br />t One last refinement of the impervious component
<br />is its relationship in the landscape to surrounding
<br />d' areas, in the sense of how much of the rainfall onto a
<br />given surface is actually conveyed to a scream or
<br />smrmwacer eollectioa system. In general, the rooftop
<br />} component, which often drains to a lawn or Ocher per-
<br />mcable areas, has less impact than roadways, which
<br />typically channel runoff directly to the stormwarer
<br />tysccm- The Olympia study (1994b) calls this factor
<br />file effectiveness at producing runoff, and estimates im-
<br />pervious areas in low -density residential develop -
<br />Merits to be about 40% effective, while those in
<br />'.commercial/industrial areas are dose to 100% effec-
<br />rive. In theory.this.concept could be applied to all sur-
<br />Ki
<br />-faces-lawns themselves, for instance, can have a
<br />,::significant coefficient of runoff —but co our knowl-
<br />`:pdge this level of refinement has not beetl.researched,
<br />por is it generally, needed for most applications,
<br />perviousness in Planning: A
<br />.mework,-Some Examples
<br />3y considering the : distribution of impervious
<br />r by, Luid tie, fun;;don; and contribution to run-
<br />aerazegiaa,begin to emerge for the reduction of
<br />current and future levels oFimperviousness, We
<br />;est chat these saatelpes can be grouped into three
<br />categories: community or regional planning,
<br />hbothood and site planning, and regulation, Each
<br />gory presents, opportunities torevisit the rraesu quo
<br />t an eye to water resource protection- Following are
<br />e general concepts and specific examples,of such
<br />,hug ac.the Community or Regional,Lewl
<br />uiil use planning, even at the town level, need
<br />e based an traditional polirical boundaries. In-
<br />ereasingly, environmental and natural resource profes-
<br />sionals recommend planning based on the
<br />organization of natural systems (Environmental Pro-
<br />recrion Agency 1993c). Ecosystems as an organiza-
<br />tional unit have been suggested, but the functional
<br />definition of an ecosystem remains elusive.
<br />A more promising trend has, been toward using
<br />watersheds as planning units (Environmental Protec-
<br />donAgency 1993b). A watershed, or drainage basin, is
<br />an area that drains to a common body of water, be it
<br />a Like, river, scream, aquifer, or bay. Watersheds have
<br />an advantage in that they can be clearly defined as geo-
<br />graphic units. In addition, the watershed can be used
<br />as a system of organization ac any number of scales,
<br />from a major basin encompassing several states, to a
<br />regional basin involving several municipalities, to a
<br />local sub -basin on the neighborhood level.
<br />Thinking in, terms of watersheds is particularly ap-
<br />propriate for scormwacer management, which, after
<br />allis all about drainage. At the University of Connect-
<br />ieuc, we have developed a regional/community-level
<br />planning approach char provides an example of the
<br />use of both watersheds and impervious coverage, The
<br />Nonpoinc Education for Municipal Officials (NEMO)
<br />project was initiated in 1991 to assist communities in
<br />dealing with the complexities of polluted runoff man-
<br />agemenc (Arnold et aL 1993). The project, funded by
<br />the United Scares Department of Agriculture's Coop-
<br />erative State Research, Education and Extension Ser-
<br />vice, is run by an interdisciplinary tears chat includes
<br />water quality, natural resource planning, and com-
<br />purer technology expertise, NEMO uses geographic
<br />information system (GIS) technology as a cool to edu-
<br />cate local land -use decision -makers about the links be-
<br />tween their rown's land use and its water quality.
<br />Natural resource information an waterways and wa-
<br />tersheds is combined with satellite -derived, land -cover
<br />information, and then displayed on.colorful maps cre-
<br />ated with the GIS.
<br />At the heart of NEMO is an analysis of impervious
<br />cover, Literature values for the percentage of impervi-
<br />ous cover axe applied to satellite land -cover categories
<br />to come up with rough estimates for the current level
<br />of imperviousness within a rown or watershed. These
<br />values are averaged and displayed by local drainage ba-
<br />sin (average. area about one square mile) and carego-
<br />rized according to the protected/impacced/degraded
<br />scale of increasing impervious cover previously de-
<br />scribed and shown in figure 2. The current values are
<br />then contrasted with a zoning -based, build -out analy-
<br />sis of imperviousness, again displayed by local sub-
<br />basln (figure 4). The build -out allows town officials a
<br />look into the possible future of their town, not in con-
<br />ventional terms of population or lot coverage, buc in
<br />ppnjCWlLNLL'SPRING 1996 249
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