Agenda - 04-02-1990 - Laserfiche WebLink

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PAGE2t a kept in undisturbed natural vegetation, buffer zones will receive sheetflow runoff; i.e. , runoff which flows slowly in a spread out pattern rather than being concentrated in a Swale, from adjoining development and achieve reductions in pollution discharges. Within the University Lake Watershed (ULW) District, an area of land or buffer zone along perennial and intermittent streams shall be required to remain in its natural state, unless the area is subject to serious erosion, in which case an erosion resistant vegetative cover shall be established and maintained. Perennial streams are those streams shown in solid blue on the USGS quadrangle maps for Orange County. Intermittent streams are those streams shown by broken blue lines on the same maps. 6.25.5.1 Calculation of Buffer Zone Width Width; i.e. , distance from the stream bank to the edge of the buffer, is a critical factor in determining the effectiveness of a buffer zone. An equally important determinant in pollutant removal in a buffer zone is travel time; i.e. , the greater the time allowed for runoff to travel through a buffer, the greater the opportunities for pollutant removal through sedimentation, filtration, absorption, and seepage into the soil profile. Monitoring studies of highway runoff have shown that pollutant removal in grass swales is at a maximum after a 15-minute travel time. Based on this standard, Table 6.25.5 was derived to provide a sliding scale for buffer zone widths based on slope and vegetative cover. TABLE 6.25.5 REQUIRED BUFFER.ZONE WIDTHS ALONG PERENNIAL AND INTERMITTENT STREAMS IN UNIVERSITY LAKE WATERSHED TYPE OF GROUNDCOVER SLOPE GRASS (FT) WOODS (FT) 2% TO 4.9% 100 50 5% TO 6.9% 150 100 7% TO 9.9% 150 100 10% TO 14.9% 200 100 15% OR GREATER 250 150 The required stream buffer zone shall start at the stream bank and be measured away from the stream for a distance depending upon the slope and the vegetative cover near the stream. The slope shall be calculated by measuring a distance of 250 feet from the stream bank, determining the rise in elevation in that distance, and dividing the rise in elevation by the distance of 250 feet. Based on the resulting slope calculation and the type of vegetative cover near the stream, the applicable buffer zone width may be determined from Table 6.25.5. Slope shall be determined from the USGS quadrangle maps for Orange County, by on-site measurements or by special survey by a registered engineer or surveyor. i..