Ebook Low Impact Development Handbook: Stormwater Management Strategies
Urban runoff pollution is commonly considered the nation’s number one water quality problem. Stormwater issues have increasingly become a key consideration in land use planning and development over the last several years in San Diego County. The San Diego Regional Water Quality Control Board (Board) first approved San Diego’s Municipal Stormwater Permit in 1990 (Order No. 90-42) and renewed the permit in 2001 (Order No. 2001-01), which required all jurisdictions to develop and implement a stormwater program. On January 24, 2007, the Board adopted the revised Municipal Stormwater Permit (Regional Water Quality Control Board (RWQCB) Order No. R9-2007-0001). The revised permit contains standards and requirements which are intended to further reduce the pollution that enters local streams, creeks, bays and beaches. San Diego County jurisdictions are mandated by the permit to regulate new and existing development and redevelopments (that add or increase impervious cover by 5,000 sq. ft.) to comply with stormwater requirements.
As part of the revised Municipal Stormwater Permit, San Diego jurisdictions must initially encourage developments to incorporate minimal Low Impact Development (LID) techniques into Priority Development Projects by January 2008. During this initial phase the LID Handbook will serve as the guidance structure for these LID techniques and the initial LID projects that will be monitored as LID standards and criteria are being developed in the region. San Diego jurisdictions will collectively establish feasibility and applicability criteria and develop specific LID requirements over the next couple years. Once these specific criteria and requirements have been established and accepted by the Board, the jurisdictions will have one year to incorporate the new LID requirements into their local codes and ordinances. Therefore, by the year 2010, the County and other local jurisdictions will each have an updated stormwater program with a comprehensive list of BMPs, including the new LID standards and criteria.
The Permit is a product of the federal Clean Water Act (CWA). The CWA passed in 1972 and was expanded to include stormwater regulation in 1990, making it illegal to discharge pollutants into waterways. The Board is responsible for ensuring that federal and state water regulations are implemented at the local level.
Stormwater runoff (also known as “urban runoff” in populated areas) is defined as rainwater that flows over land, roofs & pavements and then enters our stormwater infrastructure, i.e. our gutters and storm drains. It is important to note here, that all public storm drains in San Diego (west of the Tecate Divide) drain directly to our beaches without any wastewater treatment. As stormwater runoff flows over various structures and pavement, the water picks up and carries sediments and pollutants such as pesticides, fertilizers, oils, metals, bacteria, and animal feces down to our streams, lagoons, bays and beaches.
For the above reasons, on-site stormwater management has become one of the critical elements for preventing pollution from entering our storm drains. The County of San Diego is required to reduce the discharge of pollutants in urban runoff to the maximum extent practicable by requiring development to use stormwater best management practices (BMPs) and Low Impact Development techniques in new and redesigned developments.
LID uses decentralized, site-based planning and design strategies to manage the quantity and quality of stormwater runoff. LID attempts to reduce the amount of runoff by mimicking the natural hydrologic function of the site. LID focuses on minimizing impervious surfaces and promoting infiltration and evaporation of runoff before it can leave the location of origination. Using small, economical landscape features, LID techniques work as a system to filter, slow, evaporate, and infiltrate surface runoff at the source.
The LID Handbook is designed to assist public and private land developers with the selection of various design features. LID planning techniques include: minimizing paved areas, minimizing soil compaction, preservation of natural open space including trees and natural drainage channels, clustering of development on compacted soils, and locating open space areas to absorb overflows. In addition to planning, the LID Handbook discusses a broad range of LID Integrated Management Practices (IMPs) to help developers mimic the site’s natural hydrological function. IMPs may include directing runoff to natural and landscaped areas, man-made filtration devices such as small vegetated swales, rain gardens, and permeable pavements and pavers. Other basic principals include dividing and sectioning impervious surfaces (no large continuously paved areas), eliminating runoff pathways and re-dispersing runoff (no downspouts connected to stormdrains), and, where feasible, harvesting of rain water in rain barrels or cisterns and using runoff as an irrigation source. These LID techniques can be applied to areas of residential, commercial, industrial, and municipal development.
The LID Handbook has been initially designed to complement the existing County of San Diego Stormwater Standards Manual and the Landscape Water Conservation Design Manual. Once the County updates its local Standard Urban Stormwater Mitigation Plan (SUSMP) with revised BMPs, the LID Handbook will be incorporated into the updated Stormwater Standards Manual.
contents
Executive Summary
Section 1 Introduction
1.1. Purpose and Organization of the LID Handbook
1.2. Stormwater ManagementExecutive
1.2.1. Background
1.2.2. State and Federal Stormwater Regulations
1.2.3. Stormwater Management Plans and BMPs
1.3. Overview of Low Impact Development (LID)
1.3.1. Goals of Low Impact Development
1.3.2. Benefits of LID
1.3.3. Challenges and Limitations of LID Practices
1.3.4. LID and Stormwater Management Planning
1.3.5. LID and the Water Conservation in Landscaping Act4
1.3.6. LID and the Multiple Species Conservation Program
1.4. Summary of LID Considerations in San Diego
Section 2 Site Planning Practices
2.1. Site Assessment
2.2. Site Planning
2.2.1. Conserve Natural Areas, Soils, and Vegetation
2.2.2. Minimize Disturbances to Natural Drainages
2.2.3. Minimize and Disconnect Impervious Surfaces
2.2.4. Minimize Soil Compaction
2.2.5. Drain Runoff from Impervious Surfaces to Pervious Areas
2.3. LID Site Design Examples
2.3.1. Residential
- 2.3.1.1. Clustered Low-Density Residential Design
2.3.1.2. Single Residential Lot
2.3.1.3. Multi-Family Residential Site
2.3.1.4. Residential Hillside Site
2.3.1.5. Large Residential Flat Site
2.3.2. Commercial
- 2.3.2.1. Commercial Shopping Center
2.3.2.2. Commercial Office buildings
2.3.2.3. Commercial Restaurant
2.3.3. Industrial
- 2.3.3.1. Industrial Park
Section 3 Integrated Management Practices
3.1. Hydrologic Design
3.1.1. Infiltration
- 3.1.1.1. Infiltration Trench
3.1.1.2. Infiltration Basin
3.1.2. Retention and Detention
- 3.1.2.1. Extended Detention (dry) Ponds
3.1.3. Biofilters
- 3.1.3.1. Vegetated Swales / Rock Swales
3.1.3.2. Vegetated Filter Strips
3.1.3.3. Sand Filters
3.1.3.4. Bioretention
3.2. Permeable Pavement Design
3.2.1. Pervious Concrete
3.2.2. Permeable Asphalt Concrete (AC)
3.2.3. Permeable Pavers
- 3.2.3.1. Open Cell Unit Paver
3.2.3.2. Brick Pavers
3.2.3.3. Natural Stone Pavers
3.2.3.4. Concrete Unit Pavers
3.2.4. Subsurface Reservoir Bed
3.2.5. Granular materials
3.3. LID Road Design
3.3.1. Public Road Standards
3.3.2. Private Road Standards
3.3.3. Curb-Cuts
3.3.4. Rural Swale Systems
3.3.5. Concave Median
3.3.6. Cul-de-sac Design
3.4. LID Parking Lot Design
3.5. LID Driveway, Sidewalk, and Bike Path Design
3.6. LID Building Design
3.6.1. Dry-Well
3.6.2. Rain Water Harvesting
- 3.6.2.1. Cisterns & Rain Barrels
3.6.2.2. Large Scale Harvesting
3.6.3. Foundation Planting
3.6.4. Downspout to Swale
3.6.5. Vegetated Roofs
3.7. LID Landscaping Design
3.7.1. Soil Amendments
3.7.2. Street Trees
3.7.3. Plant Species Selection for Infiltration Areas
3.7.4. Landscape Maintenance for Stormwater Systems
Appendix 1 Glossary
Appendix 2 Bibliography
Appendix 3 San Diego LID Considerations
Appendix 4 Technical Fact Sheets
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