Rhode Island Stormwater Design and Installations Standards Manual Public Workshop LID S ite Planning and Design S trategies: How to Meet Minimum S tandard No. 1 January 13, 2011 Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Low Impact Development (LID) Larger Conventional Community Planning BMPs LID BMPs LID Site Design Receiving Waters Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Low Impact Development (LID) Traditional LID S ite Design BMPs Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Minimum Standard No. 1 LID Site Planning and Design Strategies • Must be used to the maximum extent practicable; • Reduce runoff; • Document compliance, and why elements not incorporated in Accordance with Checklist in Appendix A of Manual; • Define what mitigation is offered. Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Avoid the Impacts Preservation of Natural Features & Compact Development • Preservation of undisturbed areas; • Preservation of buffers, natural drainage systems; • Reduction of clearing and grading; • Locating sites in less sensitive areas; • Compact development; and • Working with natural conditions (landscape, hydrology, soils) Horsley W itten Group, I nc. Horsley W itten Group, I nc.
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Houses located on Houses located on Roads on ridge lines Roads on ridge lines “brow” of ridge “brow” of ridge or upland areas or upland areas Vegetated Vegetated Undisturbed Undisturbed drainage swales drainage swales vegetation vegetation on slopes on slopes Natural drainageways Natural drainageways preserved preserved Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Site Layout and Buildings Site Layout and Buildings Fit to Terrain Fit to Terrain Site Fingerprinting Site Fingerprinting Used to Reduce Used to Reduce Clearing and Grading Clearing and Grading Development Located in Development Located in Less Sensitive Areas Less Sensitive Areas Horsley W itten Group, I nc. Horsley W itten Group, I nc.
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Buffers and Stormwater Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Reduce the Impacts Reduction of Impervious Cover • Roadway Reduction; • S idewalk Reduction; • Driveway Reduction; • Cul-de-sac Reduction; • Building Footprint Reduction; and • Parking Reduction. Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Which of these is not LID? A B D C Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Which of these is not LID? A B C D Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Which is not considered LID? A B C D Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Which of these is not LID? B A C D Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Which of these is not LID? A B Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Manage the Impacts Source Controls/Structural Controls • Disconnection of Impervious surfaces; • Mitigation of runoff*; • S tream restoration; and • Reforestation. *Practices that rely on natural systems (e.g., bioretention, WVTS , infiltration, filtering) Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Rain Gardens Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Impervious Cover Disconnection Impervious Cover Disconnection Mild vegetated slopes Mild vegetated slopes Adj acent to small parking lots Adj acent to small parking lots and roadways and roadways Sour c e: City of Por tland, OR Horsley W itten Group, I nc. Horsley W itten Group, I nc. Sour c e: City of Por tland, OR
Which is not considered LID? Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Rain Barrels and Cisterns Horsley W itten Group, I nc. Horsley W itten Group, I nc. Source: http://www.rdrop.com/users/krishna/rainwatr.htm
Green/blue Roofs Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Green/blue Roofs Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Stream Restoration Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Stream Daylighting Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Reforestation Horsley W itten Group, I nc. Horsley W itten Group, I nc. Center for Watershed Protection
Street Trees Horsley W itten Group, I nc. Horsley W itten Group, I nc.
LID Stormwater Credits LID S ite Design Credit: Disconnect ed Rooft op Runoff Disconnect ed Non-Rooft op Runoff Credit can be used to reduce or eliminate Re v and WQ v storage requirements. Horsley W itten Group, I nc. Horsley W itten Group, I nc.
LID Stormwater Credits • S till need to meet other S tandards; • Must maintain engineering “ standard of care” and “ good drainage design;” • Direct runoff over qualifying pervious areas (QPAs); and • LUHPPL runoff not eligible for credit. Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Qualifying Pervious Areas (QPA) • Natural or landscaped vegetated areas; • Fully stabilized; • CNs based on “good hydrologic conditions;” • Must be shown on site plans; • Must have 4 inches of topsoil and located outside regulated wetlands and buffer zones; and • Excessively fertilized lawn areas are not QPAs (must be planted with low maintenance grasses adapted to NE). Horsley W itten Group, I nc. Horsley W itten Group, I nc.
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Credit Restrictions • Qualifying Pervious Area (QPA) located 10 ft from bldg foundation; • Every 1,000 sq ft of impervious area must have at least 75 linear feet pervious sheet flow and be longer than the contributing flow length; and • Can be no overlap for QPA (i.e., can’ t direct 2 different areas to the same QPA); Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Credit Restrictions (Continued) • Lots > 6,000 ft 2 for rooftops; • Slope of QPA < 5.0%; • QPAs located over A or B soils; • No construction traffic over QPA; • O&M Plan required; • QPA cannot be a wetland resource; and • QPA must be controlled by the owner/applicant Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Stormwater Credit (Recharge; Re v ) • Two Methods: – Percent Volume – storage provided based on volume required for Re v and/ or WQ v – Percent Area (Re a ) – required impervious area to drain to a QPA based on: Rea = (F)(I), where F = Recharge Factor based on soils (dimensionless) I = Impervious area (in acres or ft 2 ) Horsley W itten Group, I nc. Horsley W itten Group, I nc.
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LID Summary Traditional controls LID controls • Goal: Reduce the amount of • Goal: Get the water out surface runoff by reducing of here as fast as impervious cover and possible; preserving natural areas; • Collect and store in big, • Rely on small, distributed on- “ hole in ground” off-site; site practices; • Pipe discharge to a • Infiltrate or reuse as much as stream or wetland; possible; filter before • Limited water quality discharge; treatment and • S ource controls to minimize infiltration; pollution; • S tormwater is a waste • S tormwater is a resource. product. Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Summary (cont’d) LID Traditional Design • Mass clearing and • S ite fingerprinting – Preserve natural areas grading – Retain key pervious areas – Loss of trees • Residential – Compaction of native soils – Narrow streets • Residential – Alternative turnarounds – S mart sidewalks – Wide streets and cul-de-sacs – S hared driveways – S idewalks to nowhere – Reduced setbacks – Lots of turf – Open section roads – Curb and gutter – Downspout disconnection – Ponds • Non-residential • Non-residential – Pervious spillover parking – Maximum parking ratios – Big parking lots – S hared parking – Minimum parking ratios – Reduced stall dimensions – Large stall dimensions Horsley W itten Group, I nc. Horsley W itten Group, I nc.
LID Strategies and Associated Methods Appendix A Checklist Horsley W itten Group, I nc. Horsley W itten Group, I nc.
Avoid the Impacts (continued) � Locating S ites in Less S ensitive Areas − Conservation development process utilized, where allowed − Development located in areas with least hydrologic value − Development on steep slopes/ ridges avoided � Compact Development − Conservation development process utilized, where allowed − Reduced setbacks, frontages, and right-of-way widths � Natural Landscape Conditions, Hydrology and S oils − Natural pre-development hydrology maintained − Post-development Tc = pre-development Tc. − Travel time is approximately constant − Flow velocity kept as low as possible − S oil compaction has been minimized − Grading (cut and fill quantities) minimized Horsley W itten Group, I nc. Horsley W itten Group, I nc.
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