In order to achieve the goals and purposes of this chapter, the following three storm water management zones (Zones A, B and C) are hereby established. The Zones are shown on the map attached as Appendix A of original Ordinance 07-2002-10 and incorporated herein by reference.
(a) Zone A. Zone A represents areas which require the most protective storm water management regulations. The goal of this zone is to preserve the natural condition of water bodies included in it, in whole or in part Zone A has, in general, little impervious surface area and few storm water facilities. In this zone, when site conditions permit infiltration of storm water runoff shall be required, rather than the directed flow of storm water runoff into water bodies. This storm water management practice provides greater protection for surface water quality, and also assists in augmenting stream base flow, reduction of flash storm flows and prevention of stream bank erosion. Section 1043.43 of this chapter specifies design criteria for Zone A, in order that the volume and rate of storm water runoff are controlled at predevelopment levels.
(b) Zone B. Zone B represents developed areas that have significant impervious surfaces and storm water runoff facilities in place. The goal of Zone B is the control of storm water runoff in order to prevent further destabilizing of streams and other water bodies. In this zone, the use of detention ponds, the maintenance and enhancement of buffer strips and other measures to reduce directly connected impervious areas are specified in Section 1043.43 of this chapter for the achieving of the storm water management standards applicable to Zone B. The management practices for this zone are intended to maintain existing water quality and to alleviate adverse downstream impact on water bodies.
(c) Zone C. Zone C consists of highly urbanized areas, or areas where there has been significant modification of drainageways. The amount of impervious surface area in Zone C is generally greater than 25 percent. Among the measures required in Zone C, as stated in Section 1043.43 of this chapter, are the use of sediment basins, the maintenance and enhancement of buffer strips along water bodies and the reduction of impervious surface areas that are directly connected to water bodies. An important element of storm water management practice in Zone C is the control and prevention, of sedimentation, in order to reduce pollution of water bodies.
(Ord. 07-2002-10. Passed 7-2-02.)
(d) Storm Water Management Zones.
(1) In any single development site, up to three different detention volumes may be calculated to determine the staged outlet elevations:
A. Water quality control;
B. Bank erosion control; and
C. Flood control.
These volumes are not intended to be additive; the flood control volume shall include the water quality control and bank erosion control volumes.
(2) The default flood control volume shall be based on detaining the 25-year storm frequency so long as the downstream storm water conveyance has adequate capacity and includes an acceptable emergency overland floodway. If the design engineer determines the downstream conveyance system is not adequate or an acceptable emergency overland floodway does not exist, then the flood control volume shall be based on detaining the 100-year storm.
(3) The Planning Commission, as part of its ongoing Master Plan Work, shall designate the Storm Water Management Zones.
(e) Flood Plain Protection.
(1) Natural floodway filling or alteration shall not be allowed without review and approval by the City and compliance with the Floodplain Regulatory Authority found in Part 31, Water Resources Protection, of the Natural Resources and Environmental Protection Act, 1994 PA 451, as amended (NREPA) on watercourses with contributing drainage area of two square miles or greater. If a floodway has not been mapped, the applicant's consultant shall provide the floodway delineation to the City for approval.
(2) Natural floodway fringe filling or alteration shall not be allowed without review and approval by the City and compliance with the Floodplain Regulatory Authority found in Part 31, Water Resources Protection, of the Natural Resources and Environmental Protection Act, 1994 PA 451, as amended (NREPA) on watercourses with contributing drainage are of two square miles or greater. If a floodplain has not been mapped, the applicant's consultant shall provide the floodplain delineation including the floodway, to the City for approval.
(3) To provide for streambank stability, a buffer zone is to be established and called out on a recorded plat, an approved block grading plan, a site plan, or an improvement plan. This zone shall consist of existing natural tree and vegetation slope protection within a minimum of 25 feet from the ordinary high-water mark. This buffer zone shall be maintained as is, that is, no earth change or disturbance is to take place.
(4) Replacement of lost floodplain shall meet the following criteria:
A. Replacement of the loss of floodplain storage volume at a one to one ratio unless watershed conditions warrant a higher ratio. This applies to floodplain associated with rainfall events up to a 100-year frequency. The grading plan shall provide for an equivalent volume of storage for floodplains associated with more frequent events such as 10 and 25 year frequencies.
B. Storm water detention does not apply toward the replacement volume.
C. Floodplain storage volume shall be computed above the seasonal high ground water level only.
D. The inflow and outflow rates to the area shall be consistent with predevelopment rates.
E. Up to 50 percent of the floodplain mitigation storage volume may be used for snow storage.
F. The proximity of the floodplain mitigation area shall provide for an equivalent hydrologic impact to the receiving stream and adjacent parcels.
(Res. 07-2002-01R. Passed 7-2-02.)