(A) Definition. Three categories of steep slopes are defined herein for use in this chapter. These categories are based upon the relative degree of the steepness of the slope as follows:
(1) Slopes of 20% to 30% inclusive.
(2) Slopes greater than 30%.
(3) No land shall be considered a steep slope unless the steep slope area has at least a 20% vertical drop and has a minimum area of 5,000 square feet.
(B) Purpose. Steep slopes are particularly susceptible to damage resulting from site disruption, primarily related to soil erosion. Such damage is likely to spread to areas which were not originally disturbed. Such erosion reduces the productivity of the soil, results in exacerbated erosion downhill, and results in increased sedimentation in drainageways, wetlands, streams, ponds and lakes. Beyond adversely affecting the environmental functions of these resource areas, such sedimentation also increases flood hazards by reducing the flood water storage capacity of hydrological system components, thus elevating the flood level of the drainage system in effected areas. Beyond these threats to public safety, disruption of steep slopes also increases the likelihood of slippage and slumping - unstable soil movements which may threaten adjacent properties, buildings, and public facilities such as roads and utilities.
(C) Determination of presence.
(1) Steep slopes are to be determined by using the following sources and/or methods in the order indicated below. If the first source is considered inaccurate or inappropriate, as determined by the Zoning Administrator, the succeeding source shall be used:
(a) A topographic survey prepared by and certified by an Illinois registered land surveyor at the petitioner's expense at a contour interval of not less than two feet.
(b) Topographic maps on file with the city.
(c) U.S.G.S. 7.5 minute topographic quadrangle maps.
(2) The area of steep slopes (in square feet or acres) shall be measured and graphically delineated on a topographic drawing and on the Natural Resource Protection Plan. Such steep slope drawing shall graphically indicate those steep slope areas, by slope type, of the property pursuant to the
STEEP SLOPE definition set forth in this section.
(D) Protection standards. Steep slope areas shall be retained to the extent shown on Table 154.503.1. Protected portions of steep slopes shall remain in an undisturbed state except for the land uses permitted per the requirements of § 154.404.
(Ord. O-05-04, passed 4-11-05)