04-20-99 CCM - Laserfiche WebLink

Home Browse Search

SENT BY:DPRA St.Paul, MN 4-12-33 ; 9:32AM 612 227 612 407 41914 8 using surveying equipment (sometimes as basic as a tape measure) is the most accurate and appropriate method. On the neighborhood level, "windshield" sur- veys may be appropriate where it is less important to have exact numbers. For community- or regional -scale areas, land cover derived from aerial photographs pro- vide; perhaps the best compromise between accuracy and cose. Finally, for Ippliracions encompassing even larger areas, remotely -sensed satellite -based land cover can be a viable option. At present impervious esd- maces based on satellite data must be calculated by applying literature values of imperviousness co sarel- lice land cover categories. We are currently involved with a remote ;easing research project at the Univer- siry of Connecticut that is attempting to devise a method for directly estimating imperviousness from satellite images (Civco and Arnold 1994). It is important to nore that all of these methods of measurement are increasingly being digitized and presented in the form of computerized maps in a geo. graphic information system, or GIS. This trend even- tually will make the information easier to acquire, often at lower expense. Many communities have been w 26 e nn V p Y E R 100 90 so 70 60 50 40 30 20 l0 112 113 unable to afford GIS, and others have been disillu- sioned at its cost and complexity once they invested in ir. Evolution of the technology, however, is making GIS more accessible to local officials every day. The Components of Irmperviouaness To measure and use impervious coverage as a tool for prorecting water resources, it is necessary to know how imperviousness is distributed about the land- scape. On aseale of increasing refinement, impervious .coverage can be broken down by land use, by function within each land use, and by its relative impact on run- o1W, Each of these pieces of the puzzle can help to tar- get planning and/or regulatory approaches to reducing impervious coverage. As with measurement techniques, the extent to Which planners need derailed information on these components depends on the particular application.. The percentage of land covered by impervious sur- faces varies significantly with land use. The most fie- quently cited estimates come from a report by the Sail Conservation Service (1975) (figure 3). "Scrip' type 114 1/N AnWendal Lot Size (acres) 3. Avenge percenrige of impervious mvenge by land use Soil Conservation Service 1975 APAJoUMAL'SPWNG1996 747