LID Design Standards for Streets-Model Subdivision Regulation
Model Subdivision Regulations – LID Provisions, Tyringham, MA
Section 9. Design Standards and Required Improvements
Streets Location and Layout
Swales, drainage, and curbs: Curbs are generally not appropriate in Tyringham, where most roads and gravel and very few curbs exist, except in very limited circumstances where stormwater
will be confined to feed into a formalized underground drainage system. Streets designed without curbs, however, shall use Low Impact Development (LID) drainage systems to closely mimic
natural systems that meet the following standards:
All of the stormwater from a 1” NRCS design storm drains into the ground and does not leave the site. A 1” NRCS design storm is a storm with 1” of rain within a 24 hour period. More
than 80% of Western Massachusetts storms are at or below this level.
Water leaving the road enters grassed swales graded flat enough to avoid erosion and hold and treat water.
Measures to reduce runoff, improve groundwater recharge, and improve stormwater quality, such as rain barrels (barrels at the base of roof gutter leaders that store stormwater and provide
water for future lawn and garden use), Rain gardens (rain is captured and retained in depressions carefully planted with native vegetation and allowed to drain into the ground.)
Curbs are only appropriate in narrow defined areas without opportunity for grassed swales or in village center-type projects. In those areas curbs shall be Type 2 bituminous concrete
or cement concrete curbs or granite curbs Type SB (sloped)placed on the bituminous binder, if the road is paved, or granite curbs of the road is gravel. Curbs shall utilize a 6” reveal
(or 6” of curbing exposed above the street pavement). The installation of bituminous berm, granite curb, granite edging and granite curb corners shall conform to the relevant provisions
of the Standard Specifications. All catch basin frames shall have granite curb inlets (Type VB) shall be built against and shall be installed true to the horizontal and vertical alignment.