Special Erosion and Sedimentation Prevention Requirements for Authorizations for Tier II Sites

Any development, enlargement or site alteration that is on a Tier II site and requires an authorization shall be subject to the provisions of this Section. The requirements of this Section shall supplement any other requirements set forth in Section 105-40 (SPECIAL REVIEW PROVISIONS) that also must be met.

Prior to construction, at least one of the erosion and sedimentation control measures described in paragraphs (a) through (e) of this Section shall be selected. A plan describing how the selected erosion and sedimentation control measure will be implemented and justifying its selection on the basis of the particular conditions of the site shall be prepared by a professional engineer or landscape architect and submitted to the City Planning Commission.

(a)        Benches and berms

These are level terraces or ledges constructed across sloping land to provide a relatively flat construction site or reduce the length and grade of the slope. Benches and berms reduce runoff and erosion hazards by slowing down the velocity of water and providing greater intake opportunity.

(b)        Diversion channels

These are earth channels with a supporting ridge on the lower side constructed across the slope lengths to break up concentration of runoff and move water to stable outlets at a non-erosive velocity.

(c)        Debris or sediment basins

These consist of a dam or embankment, a pipe outlet and an emergency spillway situated at the low corner of the site to provide a temporary means of trapping and storing sediment while releasing the water. They protect property below the installation from damage by excessive sedimentation and debris.

(d)        Retention ponds

These are impoundment-type ponds that temporarily store runoff water and release it at rates that minimize erosion and prevent flooding. They may be located above the site to trap water before it enters the area or within the site to protect properties below the site.

(e)        Grassed waterways or outlets

These are natural or excavated channels to dispose of excess runoff water from diversions, berms, benches and other areas at non-erosive velocities. Waterways or outlets are shaped or graded and established in suitable vegetation as needed, depending on the supplemental measure used to slow the velocity of runoff.