1	Low Impact Development and Stormwater Management
2	Contents of Presentation What Is Low Impact Development? Why Do We Need Low Impact Development What Are the Goals and Basic Principles of Low Impact Development Examples of Low Impact BMPs Low Impact Development Case Studies
3	Low Impact Development An innovative, environmental approach to land development and stormwater management
4	Why Do We Need Low Impact Development ? Protect and Improve Water Quality Watershed Hydrology Fish and Wildlife Reduce Infrastructure Costs Make Communities More Attractive
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8	Low Impact Development Objectives Reduce Effective Impervious Areas (the impervious areas that generates and contributes stormwater runoff to waterways) Maximize Treatment and Infiltration of Stormwater Maximize Evapotranspiration of Stormwater
9	Low Impact Development Planning Concepts Maintain/Improve Site Hydrology Think Small Control Stormwater at the Source Use Natural , Nonstructural Methods Create Multifunctional Environment Modified from Prince George County, Maryland
10	A. Maintain/Improve Site Hydrology Goal: Try to Mimic and Improve Existing Site Conditions Try to maintain predevelopment hydrology … peak flow … volume … time of concentration improve aesthetics provide recreational resources
11	A. Maintain/Improve Site Hydrology Identify Sensitive Areas streams/buffers steep slopes floodplains woodlands wetlands permeable soils
12	A. Maintain/Improve Site Hydrology Protect Natural Conditions retain/protect important natural features produce least hydrologic impact minimize site disturbance
13	A. Maintain/Improve Site Hydrology Evaluate Site Layout Alternatives to Reduce, Minimize and Disconnect Impervious Areas road layout and size cul-de-sacs cluster development drainage swales increased flow paths bioretention infiltration
14	B. Think small Small Areas: Micro-Subbasins Small Storm Events Small BMPs
15	Control Stormwater at Source Control Hydrologic Impacts at Source Distribute Controls Throughout Site use many small stormwater controls (BMPs – best management practices) Do not use one large detention basin to manage stormwater
16	Use Natural, Nonstructural Stormwater Management Methods Maximize Natural Features Swales Buffers Woodlands Slopes Minimize the Use of Storm Sewers and Large Detention Basins
17	E. Create Multifunctional Environment Design Multifunctional Systems Example: Bioretention System rain interception Wildlife habitat runoff storage filtration-pollutant removal infiltration-groundwater recharge aesthetics
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20	Using Site Design, Natural Features and Hydrology to Implement Low Impact Development Low Impact Development Site Planning Process
21	Low Impact Development Site Planning Process Step 1 Identify Institutional and Regulatory Constraints Step 2 Analyze Existing Site Conditions Step 3 Integrate Hydrology and Existing Site Conditions into Initial Design Step 4 Develop Preliminary Site Layout Plan and Stormwater Management Plan Step 5 Measure Soil Infiltration Rates Step 6 Revise Site Plan and Stormwater Management Plan Based on Results of Soils Testing Step 7 Compare Pre and Post Development Hydrology Step 8 Revise and Complete Low Impact Development Site Plan
22	Step 1 Identify Institutional and Regulatory Constraints Conventional Regulations & Regulators often inflexible restrict innovative development Need for Variances/Zoning Changes road width length of cul de sacs minimum lot setbacks cluster housing
23	Step 2 Analyze Existing Site Conditions Identify Areas to Protect and Integrate into Stormwater Management Plan Trees Wetlands Streams and ponds Steep slopes Good soils (A and B soils)
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25	Step 2 Analyze Existing Site Conditions Reduce Limits of Clearing and Grading save trees protect wetlands, ponds, and streams minimize soil compaction – protect and maintain existing soil conditions minimize construction easements and storage areas
26	Step 3 Integrate Hydrology into Initial Design Main Goal: Mimic Predevelopment Hydrology Runoff Volume Peak Flow Rate Time of Concentration Maximize Retention of Natural Features Slopes Vegetation Waterways Trees Minimize Storm Sewers and End-of-Pipe BMPs
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28	Step 4 Develop Preliminary Site Layout Plan and BMPs Place Houses & Roads on Poor Soils Treat and Infiltrate Runoff on Good Soils Minimize Directly Connected Impervious Areas Modify/Increase Drainage Flow Paths
29	Minimize Directly Connected Impervious Areas Disconnect Roof Drains Direct Flow from Impervious Areas to Vegetated Areas or Infiltration Areas Encourage Sheet Flow through Vegetated Areas Break Up Flow Directions From Large Paved Areas
30	Minimize Total Site Impervious Area Alternative Road Layouts Narrow Roads Reduced Sidewalks one side none Reduced On-Street Parking Smaller Rooftops-single vs. multifloor homes Smaller Driveways
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38	Modify/Increase Drainage Flow Paths Maximize Overland Sheet Flow Increase Flow Paths Maximize Use of Open Swale Systems Lengthen and Flatten Site and Lot Slopes Minimize Use of Storm Sewers
39	Step 5 Measure Soil Infiltration Rates At Proposed BMP Locations At Multiple Depths… Based on Type of BMP Proposed
40	Soils Testing Dig test pit with backhoe Identify soil characteristics Determine seasonal high groundwater level Measure soil infiltration rates with approved methodology Use Infiltrometer Do Not Use Percolation (perc) Test for Most BMPs
41	Infiltrometer Vs. Perc Test Use infiltrometers to measure downward infiltration of stormwater Do not use percolation tests to measure downward infiltration of stormwater Use percolation test if proposed BMP will incorporate lateral and vertical movement of stormwater (Example: infiltration trench) Some BMP manuals do not allow the use of percolation tests to measure stormwater infiltration
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45	Step 7 Compare Pre and Post Development Hydrology Quantify Pre and Post Development Hydrology Runoff Volume Peak Flow Rate Time of Concentration Determine Additional Level of Control Required
46	Step 7 Revise and Complete Low Impact Site Plan Use Trial and Error Iterative Process to Meet Stormwater Management Requirements If Necessary, Use Downstream/End-of-Treatment Control Techniques to Meet Requirements …Constructed Wetlands …Wet Ponds …Infiltration Basins …Naturalized Extended Detention Basins
47	Modified LID Planning Process Step 1 Develop Preliminary Site Layout Plan Step 3 Identify Potential BMP Locations Step 4 Perform Infiltration Testing BMP Locations BMP Depths Step 5 Integrate LID BMPs Into Site Plan Step 6 Compare Pre and Post Development Hydrology Step 7 Complete Low Impact Site Design
48	Low Impact Development Hydrologic Analysis
49	Hydrologic Design Approach Use Low Impact Design to Reduce runoff volume and peak flow Maintain/increase flow time (Tc) Use Low Impact BMPs to Infiltrate and evaporate stormwater runoff Treat stormwater runoff Use Detention/Retention to Meet final requirements
50	Stormwater Credits Can Be Used To Reduce Detention/Retention Needs Natural Area Conservation Disconnection of Rooftop Runoff Disconnection of Other Runoff Sheet Flow to Buffers Use of Open Channels Environmentally Sensitive Development
51	Low Impact Development Best Management Practices (BMPs) (Stormwater Controls)
52	Common Low Impact Development BMPs Disconnectivity Bioretention Infiltration Systems Open Swales Permeable and Porous Pavements
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55	Bioinfiltration Area – infiltrates stormwater
56	Biofiltration Area – filters stormwater
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72	Soil Amendment
73	Rain Barrels, Cisterns and Storage Tanks
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77	BMP Selection Criteria Goals Physical Constraints Regulatory Constraints Public Acceptance Costs Schedule
78	BMP Selection - Goals Peak Runoff Control Runoff Volume Control Water Quality Nutrients Bacteria Metals Flood Control
79	BMP Selection – Physical Constraints Available Land Soils Slopes Vegetation Wetlands Sensitive Areas
80	BMP Selection – Regulatory Constraints Ordinances Zoning Subdivision Stormwater Management Regulations and Regulators Design Criteria
81	BMP Selection – Public Acceptance Issues Health Issues Wetlands – West Nile disease Aesthetics Public Perception American Dream House
82	BMP Selection - Costs Construction Costs Maintenance Costs Loss of Income – Less units Increased Income – higher house prices
83	BMP Selection – Scheduling Issues Approvals & Permitting Public Acceptance Installation Constraints wetlands bioengineering
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91	Medium Density Residential Site
92	Medium Density Residential Site
93	Medium Density Residential Site
94	Medium Density Residential Site
95	Conventional Development
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97	Construction Cost Comparison
98	Florida Aquarium LID Retrofit
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107	Seattle Streets LID Program includes: Bioretention – Rain Gardens Natural Swales Narrow Streets
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112	F. X. Browne, Inc Low Impact Design Project LID Design Pennsylvania Age Qualified Community 209 Townhouses Clubhouse and Day Spa C and D Soils on Site Forested With Mild Slopes Intermittent Stream Runs Through Site Goal: Infiltrate 2-Year Storm
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114	F. X. Browne, Inc. Approach Identify Potential BMPs Locations Depths Perform Soil Testing Evaluate Soil Data & BMPs Develop Conceptual Plan Develop Final Plan
115	List of Potential BMPs Rooftop Disconnection Grass Swales Riparian Buffers Bioinfiltration Systems Infiltration Trenches Infiltration Basins Porous Pavement Constructed Wetlands
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118	Final F. X. Browne, Inc. Low Impact Development Plan Rooftop Disconnection (90% of houses) Riparian Buffers Along Stream 10 Bioinfiltration Systems 5 Infiltration Basins 2 Constructed Wetlands
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125	Low Impact Development Grass swales Bioretention systems – rain gardens Grassed cul-de-sac islands Lakes, ponds and wetlands Vegetated riparian buffers Natural prairie lawns Narrow streets Cluster development Lots of open space
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133	Other F. X. Browne, Inc. Low Impact Development – Conservation Design Projects
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138	Non-Structural Approaches to Stormwater Management
139	Environmental Ordinances Zoning Riparian Buffer Stormwater Management
140	Zoning Ordinance Setbacks and Yard Lines Cluster Housing Road Widths Cul de Sac Lengths Curb and Gutter Detention Requirements
141	Riparian Buffer Ordinance Benefits Water Quality Protection Stormwater Treatment & Infiltration Habitat Improvement Flood Control Recreation Aesthetics
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143	Stormwater Management Ordinance Meet Requirements of New DEP BMP Manual: Peak Rate Control Standard Volume Control Standard Water Quality Control Standard
144	Summary: Low Impact Development Low Impact Development is Feasible Low Impact Development is Needed to Meet NPDES Stormwater Requirements There is a need to: Work with Municipal Officials/Engineers Think “Outside of the Box” Be Creative Take Chances
145	Green Roofs
146	Types of Green Roofs Intensive (traditional roof garden) Minimum 1 foot soil depth 80-150 lbs/sf $25-40/sf Extensive (environmental roof) 1 to 5” of ‘soil’ 15-50 lbs/sf $15-25/sf
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153	Extensive Green Roofs Slopes to 30%...need grids for slopes >20% Best slope: 5 to 20% Saturated weight: 10 to 50 lbs/sf Alpine plants/succulents/low growing plants
154	Benefits of Green Roofs Reduce city “heat island” effect Reduce carbon dioxide impact Reduce summer air conditioning cost Reduce winter heat demand Potentially lengthen roof life 2 to 3 times Treat nitrogen pollution in rain Negate acid rain effect Help reduce volume and peak rates of stormwater Improve water quality of stormwater Improve aesthetics
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157	Vegetated Roof LID Fencing Academy of Philadelphia
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161	Conclusion Green roofs are an effective way to treat stormwater and reduce the volume of stormwater runoff Green roofs are cost effective over the typical life of a building Green roofs reduce heating and air conditioning costs Green roofs have many additional benefits including cleaning the air and producing oxygen