Rhode Island Stormwater Design and Installations Standards Manual - - PowerPoint PPT Presentation

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Rhode Island Stormwater Design and Installations Standards Manual - - PowerPoint PPT Presentation

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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.

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Horsley W itten Group, I nc. Horsley W itten Group, I nc.

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

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Community Planning LID Site Design Larger Conventional BMPs LID BMPs Receiving Waters

Low Impact Development (LID)

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Low Impact Development (LID)

S ite Design

Traditional

LID

BMPs

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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.
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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)

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Roads on ridge lines

  • r upland areas

Vegetated drainage swales Natural drainageways preserved Houses located on “brow” of ridge Undisturbed vegetation

  • n slopes

Roads on ridge lines

  • r upland areas

Vegetated drainage swales Natural drainageways preserved Houses located on “brow” of ridge Undisturbed vegetation

  • n slopes
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Site Layout and Buildings Fit to Terrain Site Layout and Buildings Fit to Terrain Site Fingerprinting Used to Reduce Clearing and Grading Site Fingerprinting Used to Reduce Clearing and Grading Development Located in Less Sensitive Areas Development Located in Less Sensitive Areas

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Buffers and Stormwater

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Reduce the Impacts

Reduction of Impervious Cover

  • Roadway Reduction;
  • S

idewalk Reduction;

  • Driveway Reduction;
  • Cul-de-sac Reduction;
  • Building Footprint Reduction; and
  • Parking Reduction.
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Which of these is not LID?

A B C D

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Which of these is not LID?

A B C D

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Which is not considered LID?

A B C D

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Which of these is not LID?

A C D B

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Which of these is not LID?

A B

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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)

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Rain Gardens

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Impervious Cover Disconnection Impervious Cover Disconnection

Mild vegetated slopes Adj acent to small parking lots and roadways Mild vegetated slopes Adj acent to small parking lots and roadways

Sour c e: City of Por tland, OR Sour c e: City of Por tland, OR

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Which is not considered LID?

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Source: http://www.rdrop.com/users/krishna/rainwatr.htm

Rain Barrels and Cisterns

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Green/blue Roofs

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Green/blue Roofs

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Stream Restoration

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Stream Daylighting

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Horsley W itten Group, I nc. Horsley W itten Group, I nc. Center for Watershed Protection

Reforestation

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Street Trees

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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 Rev and WQv storage requirements.

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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.
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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).

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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);

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Credit Restrictions

(Continued)

  • Lots > 6,000 ft2 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
  • wner/applicant
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Stormwater Credit (Recharge; Rev)

  • Two Methods:

– Percent Volume – storage provided based

  • n volume required for Rev and/ or WQv

– Percent Area (Rea) – 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)

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____

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Traditional controls

  • Goal: Get the water out
  • f here as fast as

possible;

  • Collect and store in big,

“ hole in ground” off-site;

  • Pipe discharge to a

stream or wetland;

  • Limited water quality

treatment and infiltration;

  • S

tormwater is a waste product. LID controls

  • Goal: Reduce the amount of

surface runoff by reducing impervious cover and preserving natural areas;

  • Rely on small, distributed on-

site practices;

  • Infiltrate or reuse as much as

possible; filter before discharge;

  • S
  • urce controls to minimize

pollution;

  • S

tormwater is a resource.

LID Summary

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Summary (cont’d)

  • S

ite fingerprinting

– Preserve natural areas – Retain key pervious areas

  • Residential

– Narrow streets – Alternative turnarounds – S mart sidewalks – S hared driveways – Reduced setbacks – Open section roads – Downspout disconnection

  • Non-residential

– Pervious spillover parking – Maximum parking ratios – S hared parking – Reduced stall dimensions

Traditional Design

LID

  • Mass clearing and

grading

– Loss of trees – Compaction of native soils

  • Residential

– Wide streets and cul-de-sacs – S idewalks to nowhere – Lots of turf – Curb and gutter – Ponds

  • Non-residential

– Big parking lots – Minimum parking ratios – Large stall dimensions

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LID Strategies and Associated Methods

Appendix A Checklist

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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
  • ils

− Natural pre-development hydrology maintained − Post-development Tc = pre-development Tc. − Travel time is approximately constant − Flow velocity kept as low as possible − S

  • il compaction has been minimized

− Grading (cut and fill quantities) minimized

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Reduce the Impacts

Reduction of Roadway Area

  • Lengths and widths minimized

Reduction of S

idewalk Area

  • One side of the street
  • Pedestrian pathways integrated into site design

Reduction of Driveway Area

  • S

hared driveways

  • Alternative paving surfaces
  • Narrower widths
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Reduce the Impacts

(continued)

Reduction of Cul-de-S

ac Area

− Eliminate the use of large radii bulbs, fully paved − Alternative turn- arounds − Grid design

Reduction of Building Footprint

− Less sprawling building footprints − Multi-story commercial buildings − Mixed use development

Reduction of Parking Lot Area

− Parking ratio evaluated (maximum and minimum) − S

ize of spaces/ stalls

− S

hared parking

− S

tructured parking

− Alternative paving surfaces for overflow parking

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Manage the Impacts

Disconnecting Impervious Area

− Impervious surfaces disconnected to qualified

pervious areas

Mitigation Runoff

− Roof runoff directed to a lower impact practice − A green roof has been designed to reduce runoff

S

tream Restoration

− Natural channel design/ stream channels restored

Reforestation

− Trees planted or conserved − Low maintenance landscaping and native vegetation