Article VIII: Performance and Design Standards

§ 388-43 Performance standards.

In order to achieve the goals and purposes of this chapter, the following three stormwater management zones (Zones A, B and C) are hereby established. The zones are shown on the map attached as Appendix A and made a part of this chapter.[1]

Zone A represents areas which require the most protective stormwater management regulations. Generally, lands in Zone A have less than 10% imperviousness. 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 stormwater facilities. In this zone, where site conditions do not permit infiltration of stormwater runoff, detention of stormwater runoff, with a restricted outlet, shall be required. This stormwater 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 388-44 specifies design criteria for Zone A, in order that the volume and rate of stormwater runoff are controlled at predevelopment levels.

Zone B represents developed areas that have significant impervious surfaces and stormwater runoff facilities in place. Generally, the lands in Zone B have from 10% to 25% imperviousness. The goal of Zone B is the control of stormwater 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 § 388-44 for the achieving of the stormwater 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.

Zone C consists of: (1) highly urbanized areas; (2) areas where there has been significant modification of drainageways; or (3) areas located in such proximity to water bodies that detention of stormwater runoff would be generally detrimental to such water bodies. The amount of impervious surface area in Zone C is generally greater than 25%. Among the measures required in Zone C, as stated in § 388-44, 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 stormwater management practice in Zone C is the control and prevention of sedimentation, in order to reduce pollution of water bodies.

[1]

Editor's Note: Appendix A is available from the Township offices.

§ 388-44 Design standards.

The design standards for stormwater runoff facilities for Zones A, B and C, as described in § 388-43, are the following:

	Zone A	Zone B	Zone C
Stormwater management standards	Use infiltration basins, infiltration trenches, extended detention basins, and/or constructed wetlands. Maintain and enhance buffer strips	Use detention ponds; maintain and enhance buffer strips, and reduce directly connected impervious area	Use sediment basins, maintain and enhance buffer strips, and reduce directly connected impervious area
Water quality control	Detain the first 0.5 inch of runoff from the contributing watershed, with detention per Zone B and infiltration where conditions permit, or provide equivalent treatment	Detain the first 0.5 inch of runoff from the contributing watershed for 24 hours or provide equivalent treatment, and infiltration when conditions permit	Provide sedimentation control within the drainage system, and infiltration when conditions permit
Bank erosion control	Rate of release shall be limited to 0.025 cfs/acre for a two-year storm event	Release rate of 0.13 cfs/acre per Kent County Drain Commissioner rules	Provide sedimentation control within the drainage system and infiltration when conditions permit
Flood control	Detention with infiltration when conditions permit; release rate of 0.13 cfs/acre per KCDC rules	Release rate of 0.13 cfs/acre per Kent County Drain Commissioner rules	Direct conveyance of stormwater runoff within the capacity of downstream system

§ 388-45 Resolution to implement performance and design standards.

The Township Board of the Township may adopt a resolution establishing more detailed design and performance standards for stormwater runoff facilities, consistent with the terms of this chapter, and in order to further implement its goals and purposes.