Chapter 4 Integrating Site Design and Stormwater Management Frank X. Browne, Ph.D., P.E. F. X. Browne, Inc. .

Chapter 4Chapter 4Integrating Site Design Integrating Site Design

and Stormwater and Stormwater ManagementManagement

Frank X. Browne, Ph.D., Frank X. Browne, Ph.D., P.E.P.E.

F. X. Browne, Inc.F. X. Browne, Inc.

www.fxbrowne.comwww.fxbrowne.com

PresentationPresentation

Overview of Low Impact Overview of Low Impact Development ConceptsDevelopment Concepts

Discussion of Chapter 4Discussion of Chapter 4 Case StudiesCase Studies

Low Impact DevelopmentLow Impact Development

An innovative, ecosystem-An innovative, ecosystem-based approach to land based approach to land development and development and stormwater managementstormwater management

Why We Need Low Impact Why We Need Low Impact DevelopmentDevelopment

Protect and ImproveProtect and Improve Water QualityWater Quality Watershed HydrologyWatershed Hydrology Fish and WildlifeFish and Wildlife

Reduce Infrastructure CostsReduce Infrastructure Costs Make Communities More Make Communities More

AttractiveAttractive

Low Impact Development

Mimic Predevelopment Site Hydrology

Using Site Design Techniques that Store, Infiltrate, Evaporate and Detain

Stormwater Runoff

“The difficulty lies not in the new ideas,

but in escaping from the old ones.”

John Maynard Keynes, 1936

Conventional Low Impact

Functional Landscape DesignGood DrainageConventional

Low Impact Low Impact Development Development

ObjectivesObjectives

Reduce Effective Reduce Effective Impervious AreaImpervious Area

Infiltrate StormwaterInfiltrate Stormwater Maximize Maximize

EvapotranspirationEvapotranspiration

Low Impact Low Impact Development Planning Development Planning

ConceptsConcepts

A.A. Maintain/Improve Site HydrologyMaintain/Improve Site Hydrology

B.B. Think SmallThink Small

C.C. Control Stormwater at the SourceControl Stormwater at the Source

D.D. Use Natural , Nonstructural MethodsUse Natural , Nonstructural Methods

E.E. Create Multifunctional EnvironmentCreate Multifunctional Environment

Modified from Prince George County, MarylandModified from Prince George County, Maryland

Chapter 4Chapter 4

Integrating Site Design Integrating Site Design and Stormwater and Stormwater Management Management

SITE ANALYSIS

Background Site Factors

Site Factors Inventory

Site Factors Analysis

Background Site FactorsDescribe hydrologic context and other natural elements

Chapter 93 stream use designation Special Protection Waters (EV, HQ) Fishery/Aquatic Life Use (WWF, CWF, TSF)

Chapter 303d/impaired streams Aquatic biota sampling Sensitive downstream areas (water supply

source) Location of any know downstream flooding Any Special Areas?

Special Areas

Previously Mined AMD/AML areas Brownfields Source Water Protection areas Urban Areas Carbonate/Limestone Other

Site Factors Inventory

Describe the existing developed features of the site, if any

Describe important natural features of site

Describe the size and shape of the site

Special constraints/opportunities

Special site border conditions and adjacent uses

Describe the existing developed features of the site, if any

Existing structures/structures to be preserved

Existing cover/uses Existing impervious areas Existing public sewer and water Existing storm drainage systems Existing on-site water and

wastewater

Describe important natural features of site

Existing hydrology (drainage swales, intermittent, perennial)

Existing topography, contours, subbasins Soils on site – potential for infiltration Areas of vegetation (trees, scrub, etc) Special Value Areas Sensitive Areas PNDI areas or species

Special Value Areas

Wetlands, hydric soils Floodplains/alluvial soils High quality woodlands, other

woodlands and vegetation Riparian buffers Naturally vegetated

swales/drainageways

Sensitive Areas

Steep slopes Special geologic conditions

(limestone) Shallow bedrock (less than 2ft) High water table (less than 2ft)

Site Factors Analysis

Characterize site constraints Wetlands Bog turtle habitat Streams and ponds

Characterize site opportunities\ Good soils Woodlands Riparian buffers

Constraints and Opportunities

Avoid development on or near special and sensitive natural features

Place impervious areas on poor soils

Protect good soils – use for infiltration

Using the site opportunities

Has a Potential Development Area been defined?

Does the proposed layout fit the constraints and opportunities of the site?

MUNICIPAL INPUTSMUNICIPAL INPUTS Township Comprehensive Plan and

Zoning guidance

Township SLDO guidance and options

Township SLDO/stormwater requirements

Is useful interaction at sketch plan or even pre-sketch plan phases occurring?

Township Comprehensive Plan and Zoning guidance

Guidance in Comprehensive Plan?

Existing Zoning District? Total number of units allowed? Type of units? Density of units?

Any allowable options?

Township SLDO guidance and options

Performance standards for neo-traditional, village, hamlet planning?

Reduce building setbacks? Curbs required? Street width, parking requirements, other

impervious requirements? Cut requirements? Grading requirements? Landscaping requirements?

Township SLDO/stormwater requirements

Peak rate and design storms Total runoff volume Water quality provisions Methodology requirements Maintenance requirements

SITE DESIGN:SITE DESIGN:NON-STRUCTURAL BMPsNON-STRUCTURAL BMPs

Lot Concentration and Clustering Minimum Disturbance Impervious Coverage Reduction Disconnect/Distribute/

Decentralize Source Control

Lot Concentration and Clustering Reduce individual lot size Concentrate/cluster lots Configure lots to incorporate

natural site characteristics Orient structures to fit natural

topography Minimize site disturbance

Minimum Disturbance

Define disturbance zones for site Protect good soils Protect sensitive and special areas

Minimize total site compaction Maximize zones of open space and

greenways Consider re-forestation and re-

vegetation opportunities

Impervious Coverage Reduction Reduce road widths and lengths Use Cul-de-sacs with vegetated

islands Reduce driveway length and width Reduce parking ratios and sizes Evaluate shared parking Use porous surfaces where

applicable Design single-side sidewalks

Disconnect/Distribute/Decentralize Rooftop disconnection

Existing yard areas Existing vegetated areas/woods

Disconnection from storm sewers/street gutters Front/side yard opportunities Vegetated swales, rain gardens,

etc.

SITE DESIGN:STRUCTURAL BMPs

Volume/Peak Rate Using Infiltration

Volume/Peak Rate Reduction Using Other Methods

Runoff Quality/Peak Rate Reduction

Site Restoration Testing Protocols

Volume/Peak Rate Through Infiltration

Porous Pavement with Infiltration Beds Infiltration Basins Infiltration Trenches Rain Garden/Bioretention Dry Wells/Seepage Pits Vegetated Swales Vegetated Filter Strips Infiltration Berm/Retentive Grading

Volume/Peak Rate Reduction – Other Methods

Vegetated Rooftops (Green Roofs)

Capture & ReuseCisternsRain Barrels

Runoff Quality/Peak Rate Reduction Constructed wetland Wet pond/retention basin Dry extended detention basin

(Naturalized Basin) Water quality filters: Constructed

and Other Sand and sand/peat filters Multi-chamber catch basins and inlets

Site Restoration for Stormwater

Riparian Buffer RestorationLandscape RestorationSoil Amendment/Restoration

Streambank Restoration

Testing ProtocolsSoil Testing

Site Infiltration

STORMWATER METHODOLOGYAND CALCULATIONS

Iterative Process Occurring Throughout Planning and Design to Maximize Non-Structural Practices

Strive to Minimize Stormwater Runoff Strive to Achieve Standards of

Comprehensive Stormwater Management

DEVELOP COMPREHENSIVE STORMWATER

MANAGEMENT PLAN Has There Been Thorough Approach

To Use of Both Non-Structural and Structural BMPs? If not, what non-structurals and

structurals might be used? Should the building program be

modified?

What Related Benefits Are Being Achieved Through The Use of BMPs?

Case StudyCase Study

Stony Creek Farms Age Stony Creek Farms Age Qualified Residential Qualified Residential

DevelopmentDevelopment

Homsher Hill, LLCHomsher Hill, LLC

Worcester Township, PennsylvaniaWorcester Township, Pennsylvania

Proposed DevelopmentProposed Development

Age-Qualified CommunityAge-Qualified Community 209 Townhouses209 Townhouses ClubhouseClubhouse Day SpaDay Spa

Site ConditionsSite Conditions

ForestedForested C and D SoilsC and D Soils Mild SlopesMild Slopes Intermittent StreamIntermittent Stream Natural Stream BufferNatural Stream Buffer

GoalsGoals

Control 2-Year StormControl 2-Year StormPeak runoff ratesPeak runoff ratesRunoff volumeRunoff volumeWater qualityWater quality

Larger StormsLarger StormsControl peak runoff ratesControl peak runoff rates

ObjectivesObjectives

Reduce effective impervious areaReduce effective impervious area Maintain natural conditionsMaintain natural conditions Treat at sourceTreat at source Minimize storm sewersMinimize storm sewers Infiltrate and evaporate Infiltrate and evaporate

stormwaterstormwater

ApproachApproach Identify Potential BMPsIdentify Potential BMPs

LocationsLocationsDepthsDepths

Perform Soil TestingPerform Soil Testing Evaluate Soil Data & BMPsEvaluate Soil Data & BMPs Develop Conceptual PlanDevelop Conceptual Plan Develop Final PlanDevelop Final Plan

List of Potential BMPsList of Potential BMPs Rooftop DisconnectionRooftop Disconnection Grass SwalesGrass Swales Riparian BuffersRiparian Buffers Bioinfiltration SystemsBioinfiltration Systems Infiltration TrenchesInfiltration Trenches Infiltration BasinsInfiltration Basins Porous PavementPorous Pavement Constructed WetlandsConstructed Wetlands

Soil Test Locations

Infiltration Rates vs. Soil Horizon Type

0

5

10

15

20

25

A Bt Btx Bx Btx/C B/R C C/R

Soil Horizon increasing depth ----->

Infi

ltra

tio

n R

ate

(in

/hr)

< 1 FT 1 to 5 FT > 6 FT

Final Low Impact Final Low Impact Development PlanDevelopment Plan

Rooftop Disconnection (90%)Rooftop Disconnection (90%) Riparian BuffersRiparian Buffers Bioinfiltration Systems (10)Bioinfiltration Systems (10) Infiltration Basins (5)Infiltration Basins (5) Constructed Wetlands (2)Constructed Wetlands (2)

Stony Creek Farms Low Impact Development

2-year, 24-hr Frequency StormRouting through Basin #2

0

5

10

15

20

25

10 12 14 16 18 20

Time (hrs)

Flo

w (

cfs)

Pre-Dev Inflow Hydrograph

Post-Dev Inflow Hydrograph

Post-Dev Inflow Hydrographwith Infiltration BMPs

Post-Dev Routed OutflowHydrograph

25-year, 24-hr Frequency StormRouting through Basin #2

0

10

20

30

40

50

60

10 12 14 16 18 20

Time (hrs)

Flo

w (

cfs

)

Pre-Dev Inflow Hydrograph

Post-Dev Inflow Hydrograph

Post-Dev Inflow Hydrograph withInfiltration BMPs

Post-Dev Routed OutflowHydrograph

Case StudyCase Study

Bryn Eyre…the largest planned Bryn Eyre…the largest planned community in Pennsylvaniacommunity in Pennsylvania

Bryn EyreBryn Eyre Located on 5 square miles in Berks County, PALocated on 5 square miles in Berks County, PA Largest planned community currently being Largest planned community currently being

developed in the northeastdeveloped in the northeast Over 1500 acres of natural area preservation Over 1500 acres of natural area preservation

and open spaceand open space Project has a 25 year development schedule Project has a 25 year development schedule 5 million square feet of retail and commercial 5 million square feet of retail and commercial

spacespace 12,000 residential units12,000 residential units Three new schoolsThree new schools

Stormwater Management Stormwater Management ApproachApproach

Developed long-term, conceptual Developed long-term, conceptual stormwater management plan stormwater management plan for 5 square mile communityfor 5 square mile community

Developed detailed stormwater Developed detailed stormwater management plan for Phase 1management plan for Phase 1

Bryn Eyre BMPsBryn Eyre BMPs vegetated buffers and filter stripsvegetated buffers and filter strips bio-swalesbio-swales rain gardensrain gardens underground infiltration trenches and basinsunderground infiltration trenches and basins regionalized rooftop disconnectionregionalized rooftop disconnection dry wellsdry wells constructed wetlandsconstructed wetlands green roofsgreen roofs porous pavementporous pavement riparian buffer enhancementriparian buffer enhancement stream restorationstream restoration and naturalized extended detentionand naturalized extended detention bio-infiltration basinsbio-infiltration basins

Phase 1Phase 1 110 acres110 acres 459 residential units459 residential units

256 single family256 single family 203 town houses203 town houses

One bog turtleOne bog turtle

LID Approach – Phase 1LID Approach – Phase 1

Performed detailed site analysisPerformed detailed site analysis Performed over 50 soil infiltration tests Performed over 50 soil infiltration tests Identified sensitive areas…bog turtle Identified sensitive areas…bog turtle

habitathabitat Identified constraints and opportunitiesIdentified constraints and opportunities Used non-structural and structural BMPsUsed non-structural and structural BMPs Integrated site design & stormwater Integrated site design & stormwater

management…worked with plannermanagement…worked with planner

Phase 1 BMPs

19 Rain Gardens (7 water quality, 12 infiltration)

23 Bioswales ( 6 water quality, 17 infiltration)

17 Infiltration Trenches

4 Naturalized Basins (3 water quality, 1 infiltration)

Summary – Integrating Site Summary – Integrating Site Design and Stormwater Design and Stormwater

ManagementManagement Requires moreRequires more

Analysis…Modeling…DesignAnalysis…Modeling…Design Need to be creative, think outside of boxNeed to be creative, think outside of box Results are worth itResults are worth it

Better stormwater managementBetter stormwater management Less floodingLess flooding Less streambank erosionLess streambank erosion Improved water qualityImproved water quality Better aestheticsBetter aesthetics Less infrastructure costsLess infrastructure costs