Session 1E Non-Structural BMPs 1 Chesapeake Bay Storm w ater - - PowerPoint PPT Presentation

Session 1E Non-Structural BMPs

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A d A d Agenda Agenda

• Site Design (self-crediting)
• Site Design (self crediting)
• Soil Amendments

Si l Di ti

• Simple Disconnection
• Sheet Flow
• Grass Channels

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Site Plan courtesy of

Key Resources on your disk y y

• October 2010 Webcast Archive: Disconnection
• Disconnection Webcast Resource Sheet

Disconnection Webcast Resource Sheet

• Filter Strip and Soil Amendments Presentation
• Relevant DCR Design Specifications:

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• No. 1 Disconnection

–

• No. 2 Sheet Flow

– No 4 Soil Amendments

• No. 4 Soil Amendments
• Urban Watershed Forestry Manual Part 2: Conserving and

Planting Trees at Development SitesThe Runoff Reduction Th P t ti Theory Presentation

• Urban Watershed Forestry Manual Part 3: Urban Tree

Planting Guide

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Non-Structural Practices Non Structural Practices

• Direct growth to identified

areas;

• Encourage infill and re-

development; areas;

• Protect sensitive aquatic

resources;

• Establish buffers along

development;

• Educate on material

disposal/recycling

• Spill Prevention/Clean Up
• Establish buffers along

stream and other waters;

• Maintain existing runoff

patterns and Tc;

• Spill Prevention/Clean Up
• Identify and eliminate illicit

discharges

• Promote street sweeping

patterns and Tc;

• Minimize impervious surfaces;
• Minimize disturbance of soils

and vegetation;

• Promote street sweeping
• Develop Public

Education/Participation programs and vegetation; programs

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Non Non-

• Structural Practices as part of the

Structural Practices as part of the Runoff Reduction Method Runoff Reduction Method

• 1. Minimization & Avoidance
• 1. Minimization & Avoidance
• 2. Reforestation
• 3. Soil compost amendments

p

• 4. Impervious disconnection
• 5. Sheet flow to Vegetated Filter and

g Conservation Areas (or Buffers)

• 6. Grass channels

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Sit D i Sit D i Thi t C id Thi t C id Site Design Site Design - Things to Consider Things to Consider

• Riparian Buffers
• Riparian Buffers
• Wetlands and Stream Channels
• Existing Woods
• Existing Woods
• Transitional buffers
• Soils Constraints (Texture, HSG, Perm.,

Bedrock, Water Table)

• Slope Constraints
• Access to Site
• Access to Site

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Example 14.98 acre development Example 14.98 acre development p p p p

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Identify Water Resources and Forested Areas Identify Water Resources and Forested Areas y

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Soils Investigation Soils Investigation g

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Determine Limits of Constraints Determine Limits of Constraints

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Typical Development Patterns Typical Development Patterns yp p yp p

14.98 Acres

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25 ½ acre lots

Alternative Development Alternative Development p

14.98 Acres

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25 ¼ acre lots

Eff t f T i l L t Eff t f T i l L t Effects of Typical Layout Effects of Typical Layout

Cl i f ti it (di t b d il )

• Clearing of entire site (disturbed soils)
• Significant Impacts to Wetlands and Stream

Channels Channels

• Impacts to designated Riparian corridors
• Increase in Impervious Cover
• Increase in Impervious Cover
• Directly Connected Drainage Systems

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LID Resources Report: LID Resources Report: Performance Standards

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Minimization & Avoidance Minimization & Avoidance

Design Goal: All /P t Si l L M i t Allow/Promote Simple, Low Maintenance Practices As Part of a Treatment Train Approach to Help Meet the Runoff Reduction Approach to Help Meet the Runoff Reduction Goal.

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Start By Reducing Clearing and

R d ff

y g g Preserving Highly Permeable Soils

• Reduces runoff

coefficient from pervious areas pervious areas

• Increases runoff

Increases runoff reduction rates for non-structural practices in poor soils

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Disturbed Soils Increase the Runoff Coefficient For Urban Turf

Runoff Coefficients for Use for Different Pervious Areas1 Hydrologic Undisturbed Disturbed Restored Restored

Coefficient For Urban Turf

y g Soil Group Soils 2 Soils 3 Soils 4 and Reforested

A

0 .0 2 0 .1 5 0 .0 5 0 .0 2

A B

0 .0 3 0 .2 0 0 .0 6 0 .0 3

C

0 0 4 0 2 2 0 1 0 0 0 4

C

0 .0 4 0 .2 2 0 .1 0 0 .0 4

D

0 .0 5 0 .2 5 0 .1 2 0 .0 5

1 Source: CWP and CSN (2008) and Pitt (2004) 2 Portions of a new development site, outside the limits of disturbance 3 Previously developed sites, and any site area inside the limits of disturbance 4 Pervious areas on the site restored per DCR BMP Spec 4

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We Have A Lot of Managed Turf in g the Bay!

For every acre of new impervious cover, we create 3 acres of managed turf 3 acres of managed turf cover. h h h d l What are the hydrologic implications?

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Disturbed Soils Are Not Very Pervious and Ineffective in Treating Stormwater and Ineffective in Treating Stormwater

• Top Soil is Stripped
• Soil Structure is Lost
• Subsoils are

Compacted Compacted

• Reduced Water

Holding Capacity Holding Capacity

• Low Infiltration Rate
• High Nutrient

g Concentrations

• Erosion & Runon to

I i C

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Impervious Cover

S il A d t S il A d t Soil Amendments Soil Amendments

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Soil Amendments Reduce the Runoff Coefficient For Urban Turf

Runoff Coefficients for Use for Different Pervious Areas1 Hydrologic Undisturbed Disturbed Restored Restored

Coefficient For Urban Turf

y g Soil Group Soils 2 Soils 3 Soils 4 and Reforested 5

A

0 .0 2 0 .1 5 0 .0 5 0 .0 2

A B

0 .0 3 0 .2 0 0 .0 6 0 .0 3

C

0 0 4 0 2 2 0 1 0 0 0 4

C

0 .0 4 0 .2 2 0 .1 0 0 .0 4

D

0 .0 5 0 .2 5 0 .1 2 0 .0 5

1 Source: CWP and CSN (2008) and Pitt (2004) 2 Portions of a new development site, outside the limits of disturbance 3 Previously developed sites, and any site area inside the limits of disturbance 4 Pervious areas on the site restored per DCR BMP Spec 4

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C t d I ti D th C t d I ti D th Compost and Incorporation Depths Compost and Incorporation Depths

Contributing I m pervious Cover to Soil Am endm ent Area Ratio 1 I C/ SA = 0 2 I C/ SA = 0 .5 I C/ SA = 0 .7 5 I C/ SA = 1 .0 3 Com post depth ( i ) 4 2 to 4 5 3 to 6 5 4 to 8 5 6 to 1 0 5 ( in) 4 to 3 to 6 to 8 6 to I ncorporation Depth ( in) 6 to 1 0 5 8 to 1 2 5 1 5 to 1 8 5 1 8 to 2 4 5 I ncorporation Method Rototiller Rototiller Subsoiler Subsoiler Method

Notes:

1 IC = contrib. impervious cover (sq. ft.) and SA = surface area of compost

amendment (sq. ft.)

2 For amendment of compacted lawns that do not receive off‐site runoff

For amendment of compacted lawns that do not receive off‐site runoff

3 In general, IC/SA ratios greater than 1 should be avoided 4 Average depth of compost added 5 Lower end for B soils, higher end for C/D soils

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Impervious Disconnection p

Simple Disconnection

Si l di ti Simple disconnection Compost amended flow path Rain garden (Urban Planter) Rain garden (Urban Planter) Infiltration Rainwater Harvesting

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Two Types of Disconnection

• Simple Disconnection: rooftops and/or on-lot

residential impervious surfaces are directed to res dent al mperv ous surfaces are d rected to pervious areas;

• Alternative disconnection: the use of

compensatory practices where the space p y p p required for simple disconnection may not be available, or enhanced performance is desired:

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Simple Disconnection Simple Disconnection

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Simple Disconnection Simple Disconnection

• Filter corridors from

the downspout to the street

• Level spreader to

distribute runoff over a ten foot width ten foot width

• Minimum and maximum
• Length;

Length;

• Width; and
• Slope criteria

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Summary of Stormwater Function Summary of Stormwater Function id d b Si l Di ti id d b Si l Di ti provided by Simple Disconnection provided by Simple Disconnection

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Si l Di ti D i C it i Si l Di ti D i C it i Simple Disconnection Design Criteria Simple Disconnection Design Criteria

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Simple Disconnection Simple Disconnection Simple Disconnection Simple Disconnection

Applications: Minimum lot sizes (e.g. 6,000 ft2)

• Minimum (and maximum)

dis ti l th

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disconnection length

• Maximum disconnection slope

Feedback Question #1: Feedback Question #1:

Wh t th b t t d t NSP

• What are the best ways to document NSPs

during Plan review?

• How should they be handled in ESC plans

during construction? during construction?

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Simple Disconnection Abuse Simple Disconnection Abuse Simple Disconnection Abuse Simple Disconnection Abuse

Application of a maximum impervious area per pp p p disconnection;

Commercial or mixed land-use applications can be h ll i d h ld id ili i d challenging, and should consider utilizing vegetated filter strips or conservation open space.

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Alternative Disconnection Alternative Disconnection Alternative Disconnection Alternative Disconnection

Utilized where the space required for simple disconnection may not be simple disconnection may not be available, or enhanced performance is desired or required desired or required.

• R i

t H sti & Cist s

• Rainwater Harvesting & Cisterns
• Micro-Infiltration (dry wells)

R i G d

• Rain Gardens
• Urban Planter

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Photo courtesy S. Schwartz & Cuyahoga Sustainability Network

Alternative Disconnection Alternative Disconnection Alternative Disconnection Alternative Disconnection

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Large Scale Disconnection: Large Scale Disconnection: d F l d F l Vegetated Filter Strips Vegetated Filter Strips

R E i i th Filt St i T Filt D i Re-Engineering the Filter Strip: Two Filter Designs

• Sheet Flow to

C d O

• Vegetated Filter Strip

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Conserved Open Space

Design Considerations for Vegetated Design Considerations for Vegetated Filt St i Filt St i Filter Strips Filter Strips

• Slope;
• Slope;
• Length (parallel and

perpendicular to flow) p p f )

• Contributing DA
• Sheet flow only
• Flow depth and velocity
• Vegetation
• Soils

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Reference: National Cooperative Highway Research Program (NCHRP) Project 25-25: Stormwater Treatment With Vegetated Buffers

C d O S C d O S Conserved Open Space Conserved Open Space

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Design Considerations for Conserved g Open Space

• Sheet Flow
• Boundary

Spreaders L l S d

• Level Spreaders

for concentrated flow

• Maximum slopes

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St B ff St B ff Stream Buffers Stream Buffers

• Designated during initial lot
• Designated during initial lot

recordation/subdivision;

• Protected with legal instrument

g m to prevent alteration of the land

• r vegetation;
• Width varies (35. ft to 150 ft.);
• Must establish sheet flow into

b ff buffer

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Summary of Stormwater Function Provided Summary of Stormwater Function Provided b C d O S d Fil S i b C d O S d Fil S i by Conserved Open Space and Filter Strips by Conserved Open Space and Filter Strips

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DESI GN FI LTER STRI P CONSERVED OPEN DESI GN CONSI DERATI ON FI LTER STRI P CONSERVED OPEN SPACE Slope

Ranges from 1% to 8% 1 Ranges from .5% to 6% 1

Slope

6% 1 First 10 feet < 2%

Sheet Flow

• Maximum flow length of 150 ft. from adjacent

g j pervious areas;

• Maximum flow length of 75 ft. from adjacent

impervious areas p

Concentrated Flow

Engineered Level Spreader

Boundary Spreader

• Gravel Diaphragm at
• Gravel Diaphragm at

Boundary Spreader

• Gravel Diaphragm at

Top

• Gravel Diaphragm at

Top

• Permeable Berm at

Bottom

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1: Allowable slope dependent on filter width.

Level Spreader Level Spreader p

Applicable to filter strips, buffers and

Henrico County, VA Level Spreader 30 to 40 ft in length; 50 ft width at level lip

buffers, and conserved open space with concentrated

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concentrated inflow.

Feedback No 2 Feedback No 2 Feedback No. 2 Feedback No. 2

What is the maintenance model to ensure NSP long term model to ensure NSP long term hydrologic function? What would an inspection be like?

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Grass Channels Grass Channels Grass Channels Grass Channels

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Grass Channel Grass Channel Grass Channel Grass Channel

Critical Design Parameter: Maximum “Design ” l fl l f 1 Storm” or Retention Volume flow velocity of 1 ft/s*

P f id l Edge of pavement drop Prefer trapezoidal channel geometry Edge of pavement drop w / flat “pre-treat area

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*Accepted methodology for computing small storm peak discharge

Summary of Stormwater Functions y Provided by Grass Channels

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Key Design Requirements Key Design Requirements

• Bottom width 4 to 8 feet.
• Side-slopes 3H:1V or flatter.
• The maximum total contributing drainage area 5

acres acres.

• The longitudinal slope less than 4%.
• The maximum flow velocity of the channel must be
• The maximum flow velocity of the channel must be

less than 1 foot per second during a 1-inch storm event.

• Flows non-erosive during the 2-year and 10-year

design storm events

• 10 year design flow is contained within the channel

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• 10-year design flow is contained within the channel

(minimum of 6 inches of freeboard).

Sheet Flow Edge

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Grass Channel Grass Channel

N Ed f d No Edge of pavement drop w / flat “pre-treat area

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Runoff must get into the channel!

Feedback No 3 Feedback No 3 Feedback No. 3 Feedback No. 3

What are measureable criteria What are measureable criteria at the site that would trigger NSP i t NSP maintenance or rehabilitation?

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Take-Home Points:

St t ith it d i t d i i

• Start with site design to reduce impervious

cover and volume associated with the Design Retention Volume Retention Volume

• Use disconnection and/or compost amendment

techniques as part of a rooftop to stream techniques as part of a rooftop to stream design approach

• Consider conservation areas stream buffers
• Consider conservation areas, stream buffers,

filter strips as an alternative to structural practices

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practices

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