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SENT BY:DPRA St.Paul, MN ;-12-99 ; 9:30AM 612 227 5592 612 407 4191;#.3 <br />CRE.srr:lt L. AP-NOLD, JR. AND C. JAMF$ rMBONS <br />cation of impervious surface coverage as an urban <br />environmental indicator. <br />People, Pavement and Pollution <br />Impervious surfaces can be defined as any material <br />that prevents the infiltration of water into the soil. <br />While roads and rooftops are the most prevalent and <br />easily identi#ed types of impervious surface, other <br />types includ sidewalks, patios, bedrock ourerops, and <br />compacted soil. As development alters the natural <br />landscape, the percentage of the land covered by im- <br />pervious surfaces increases. <br />Roofs and roads have been around for a long time, <br />buc the ubiquitous and impervious pavement we take <br />for granted today is a relatively recent phenomenon. A <br />nationwide road census showed that in 1904, 93 per- <br />cent of the roads in America were unpaved (South - <br />worth and Ben -Joseph 1995). This changed with the <br />nr ewarw�xuhheN <br />he+ <br />rauoPP <br />9=T" �' 7a DEEP <br />n� Q O NIntTWhlaN <br />77 0°0 000 a °O <br />00 <br />0, <br />v. <br />NATURAL GROUND COVER <br />sn. EWO,T.N.N11.,,0. <br />VD% <br />KOO" <br />OOOa,o °�O u:u�naN <br />0 <br />0 G 0 0° <br />35-M % IMPERVIOUS SURFACE <br />early twentieth century ascendancy of the automobile <br />aver the railways, capped by the mid-century massive <br />construction of the interstate highway system, which <br />served to both stimulate and facilitate the growth of <br />suburbia. From that point on, imperviousness became <br />synonymous with human presence —to the point chat <br />studies have shown that an areas's population density <br />is correlated with its percentage of impervious cover • <br />(Srankowski 1972). <br />Impervious surfaces not only indicate urbaniza- <br />rion, bur also are major contributors to the environ. <br />mental impacts of urbanization. As the natural <br />landscape is paved over, a chain of events is initiated <br />that typically ends in degraded water resources. This <br />chain begins with alteracions in the hydrologic cycle, <br />the way that water is rransported and scored. <br />These changes, depicted in figure 1, have long <br />been understood by geologists and hydrologists. As <br />hex e1W'6TN wlP raw <br />10.20 % IMPERVIOUS SURFACE <br />...,-,.,FIGURE 1. Water eyde changes associated with urbanization <br />Source: Env;ronmend PmmrtiQn Agency 1993a <br />APAIGURNa-SPAING 096 <br />U° <br />DOO p D°U � <br />00 0 Q of Op0 <br />mn® <br />iwkTw <br />75-100 % IMPERVIOUS SURFACE <br />