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PAGE-290 <br />kept in undisturbed natural vegetation, buffer zones will receive sheetflow <br />runoff; i.e., runoff which flows slowly in a spread out pattern rather than <br />being concentrated in a swale, from adjoining development and achieve <br />reductions in pollution discharges. <br />Within the University Lake Watershed (ULW) District, an area of land or <br />buffer zone along perennial and intermittent streams shall be required to. <br />remain in its natural state, unless the area is subject to serious erosion, <br />in which case an erosion resistant vegetative cover shall be established and <br />maintained. Perennial streams are those streams shown in solid blue on the <br />USGS quadrangle maps for Orange County. Intermittent streams are those <br />streams shown by broken blue lines on the same maps. <br />6.25.5.1 Calculation of Buffer Zone Width <br />Width; i.e., distance from the stream bank to the edge of the buffer, is a <br />critical factor in determining the effectiveness of a buffer zone. An <br />equally important determinant in pollutant removal in a buffer zone is <br />travel time; i.e., the greater the time allowed for runoff to travel through <br />a buffer, the greater the opportunities for pollutant removal through <br />sedimentation, filtration, absorption, and seepage into the soil profile. <br />Monitoring studies of highway runoff have shown that pollutant removal in <br />grass swales is at a maximum after a 15-minute travel time. Based on this <br />standard, Table 6.25.5 was derived to provide a sliding scale for buffer <br />zone widths based on slope and vegetative cover. <br />TABLE 6.25.5 REQUIRED BUFFER ZONE WIDTHS <br />ALONG PERENNIAL AND INTERMITTENT STREAMS <br />IN UNIVERSITY LAKE WATERSHED <br /> SLOPE <br />2% TO 4.9% <br />5% TO 6.9% <br />7% TO 9.9% <br />10% TO 14.9% <br />15% OR GREATER <br />e <br />TYPE OF GROUNDCOVER <br />GRASS ,(,FT) WOODS L <br />100 50 <br />150 100 <br />150 100 <br />200 100 <br />250 150 <br />The required stream buffer zone shall start at the stream bank and be <br />measured away from the stream for a distance depending upon the slope and <br />the vegetative cover near the stream. The slope shall be calculated by <br />measuring a distance of 250 feet from the stream bank, determining the rise <br />in elevation in that distance, and dividing the rise in elevation by the <br />distance of 250 feet. Based on the resulting slope calculation and the type <br />of vegetative cover near the stream, the applicable buffer zone width may be <br />determined from Table 6.25.5. Slope shall be determined from the USGS <br />quadrangle maps for Orange County, by on-site measurements or by special <br />survey by a registered engineer or surveyor.