Environmentally Sensitive Development Credit

Environmentally Sensitive Development Credit

This credit applies to low density development designs that incorporate Better Site Design features. The credit exempts the site from water quality and recharge requirements, and can also incorporate reductions in required volumes for channel protection and flood control. Following are two sets of example language for an environmentally sensitive development credit.

Environmentally Sensitive Development: Summary
Goals	Preserve natural and recreational open space Encourage more compact development to reduce the total impervious cover created on site. Encourage the use of non-structural treatment measures to treat stormwater runoff on-site
Stormwater Management Objectives	Recharge	Met by Environmentally Sensitive Development
	Water Quality	Met by Environmentally Sensitive Development
	Channel Protection/ Flood Control	Achieved through other site design credits.

Example 1: Focuses on incorporating other site design credits to reduce the treatment volume.

A development may be exempt from recharge and water quality requirements if the following criteria are met:

Total impervious cover footprint shall be less than 15 % of the lot area.
Grass channels shall be used to convey runoff on at least 75% of the road length.
At least 25% of the site area is conserved by a protective easement or other mechanism such as a natural conservation area.
Stream buffers shall be incorporated into the site design on both perennial and intermittent streams.
Rooftops and other impervious surfaces are disconnected or implement green rooftops.

Example 2: Focuses on preserving open space

A development may be exempt from recharge and water quality requirements if the following criteria are met:

The total site imperviousness is less than 15%
The average lot size is no greater than � of the zoned lot size.
The total site area is no greater than 10 acres.
A minimum of 40% of the site area is preserved as open space
A minimum of 25% of the site area is preserved as natural conservation areas, protected by a permanent easement or similar measure.
At least 75% of the open space shall be continuous.
The site uses grass channels in the place of curb and gutter.

The specific criteria for an environmentally sensitive development will vary between communities. The manual writer needs to use caution to ensure that this credit does not create a loophole for stormwater treatment requirements, and that the measures described constitute effective treatment.

While channel protection and flood control requirements should not be waived, the following assumptions can be made to reduce the required volume:

The current curve number or runoff coefficient can be reduced, as documented in other stormwater credits.
The pre-developed curve number can reflects existing conditions. For agriculture, existing conditions shall be defined by the average curve number for a five-year crop rotation recommended by the Soil and Water Conservation office, and shall be no higher than the curve number for small grains.

Modifications to the pre-development curve number condition only apply in communities that require the assumption of a highly pervious land use, such as woods in good condition. The pre-developed curve number needs to be clearly defined to limit abuse of this credit.