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Water: Green Infrastructure

Design and Implementation Resources

To provide the greatest benefit to water resources and the community, green infrastructure practices must be properly designed, constructed, and maintained.  This section is intended primarily for site designers and stormwater professionals seeking information on the design, construction, and maintenance of green infrastructure features.  This section provides access to design manuals and design tools, as well as resources addressing construction and operation and maintenance.  Common design challenges are also addressed, and a few resources for homeowners are provided.

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LID Design Manual
Design Manuals
Many states, counties, and non-profits have developed stormwater design manuals emphasizing green infrastructure approaches (also referred to as low impact development or environmental site design).  Here we provide links to a small sample of these design manuals selected from throughout the nation.  Each manual includes detailed design guidelines tailored to the local physical and regulatory landscape.  In general, each manual addresses planning and design approaches as well as structural stormwater controls. 
Arizona: Green Infrastructure for Southwestern Neighborhoods (PDF) (48 pp, 12.6MB, About PDF)
This manual is intended for both community leaders and professionals interested in applying green infrastructure in southwestern neighborhoods. The manual provides guidelines for retrofitting existing neighborhood streets, right-of-way and parking lots with green infrastructure practices. 

Georgia: Coastal Stormwater Supplement to the Georgia Stormwater Management Model (PDF) (542 pp, 13MB, About PDF)
The coastal supplement provides comprehensive guidance on an integrated, green infrastructure-based approach to natural resource protection, stormwater management, and site design.  Section 7 provides detailed information on site planning approaches, site design approaches, and green infrastructure practices, including information about applicability, design, installation, and maintenance.  

Florida: Low Impact Development Manual for Sarasota County (PDF) (85 pp, 5.1MB, About PDF)
This manual is primarily intended for professionals engaged in the planning, design, construction, operations, and maintenance of building and development projects in Sarasota County.  The manual provides technical guidance and design specifications for the three green infrastructure practices deemed most appropriate for Sarasota County. 

Maryland: Maryland Stormwater Design Manual 
The Maryland Stormwater Design Manual consists of two volumes. The first volume provides designers a general overview of how to size, design, select and locate best management practices (BMPs) at a new development site to comply with state stormwater performance standards. The second volume contains appendices with more detailed information on landscaping, BMP construction specifications, step-by-step BMP design examples, and other assorted design tools.  

Minnesota: State of Minnesota Stormwater Manual
The Minnesota Stormwater Manual also consists of two volumes. The first volume is dedicated to the physical and regulatory context of stormwater management in Minnesota.   The second volume provides technical and engineering guidance for stormwater professionals and regulators. 

New York: New York State Stormwater Management Design Manual (PDF) (642 pp, 13.4MB, About PDF)
This manual provides designers a general overview of how to select, locate, size, and design BMPs at a development site to comply with state stormwater performance standards. Chapter 5 provides complete definitions, design specifications, and computational methods for particular green infrastructure practices.  

Texas: San Antonio River Basin Low Impact Development Technical Guidance Manual (PDF) (407 pp, 18.4MB, About PDF)
This manual provides guidance to communities in the San Antonio River Basin on the selection, design, inspection and maintenance of green infrastructure practices. The overarching goal is to provide clear, unambiguous design guidance that is customized to the unique land formations and soil conditions in the San Antonio region.

Toronto: Credit Valley Conservation Low Impact Development Stormwater Management Planning and Design Guide (PDF) (300 pp, 12.1MB, About PDF)
This manual is intended for developers, consultants, municipalities and landowners interested in applying green infrastructure in the Toronto region.  Planning and design approaches are discussed, as well as green infrastructure stormwater controls. For each structural control discussed, the guide provides an overview, a design template, and a summary of maintenance and construction costs. 

The Credit Valley Conservation Landscape Design Guide for Low Impact Development (PDF) (98 pp, 4.8MB, About PDF) complements the Stormwater Management, Planning and Design Guide.  This appendix provides information for landscape architects and engineers on plant selection, planting, and landscape maintenance.   

Washington: Low Impact Development Technical Guidance Manual for Puget Sound (PDF) (256 pp, 7.7MB, About PDF)
This manual is intended for stormwater managers and site designers interested in applying green infrastructure in the Puget Sound region.  The manual provides detailed design guidelines for particular practices, as well as summaries of pollutant removal efficiencies, maintenance requirements, and cost.  

Design Tools
Many modeling tools are available to assist site designers in complying with local stormwater regulations and/or meeting voluntary performance standards.  See Modeling Tools for a more extensive discussion of modeling resources.   Here we list several spreadsheet tools and simple models that design professionals may find useful in selecting, sizing, and placing green infrastructure practices.  
Green Roof,
Downspout Disconnection,
Permeable Pavement,
Grass Channel,
Dry Swale,
Extended Detention Pond,
Sheetflow to Filter,
Wet Swale,
Constructed Wetland,
Wet Pond 
User Inputs:
Annual Precipitation, Land Cover Distribution, Soil Type Distribution, BMPs
Runoff Volume Reduction (ft3 /design storm), Phosphorus Load Reduction (lb/yr), Nitrogen Load Reduction (lb/yr)
Green Roofs,
Permeable Pavement,
Rain Gardens,
Retention Ponds,
Extended Detention Basins,
User Inputs:
Drainage Area, BMP Characteristics, Capital Costs, Maintenance Costs
Whole Life Costs, Present Value Graphs 
Extended detention,
Permeable pavement,
User Inputs:
Hourly Precipitation Record, Monthly Evaporation Rates, Land Use Distribution, BMPs, BMP Parameters
Runoff Volume, Pollutant Loads, Costs
Cost calculations based on WERF Whole Life Cost Model

Green Roof,
Planter Boxes,
Rain Gardens,
Native Vegetation,
Vegetation Filter Strips,
Amended Soil,
Reduced Street Width,
Permeable Pavement
User Inputs:
Annual or Event Precipitation, Land Cover Distribution, Soil Type, Runoff Reduction Goal, BMPs, BMP Parameters
Runoff Volume Reduction, Costs, Reduced Air Pollutants, Carbon Dioxide Sequestration, Value of Trees, Groundwater Recharge, Reduced Energy Use, Reduced Treatment Benefits

Rain Cisterns 
User Inputs:
Hourly or Daily Rainfall Record, BMP Parameters, Anticipated Usage, Water Cost, Sewer Cost, Cistern Cost
Runoff Volume Reduction, Usage Replaced, Payback Period

Design Challenges
Some site characteristics may limit the application of green infrastructure practices or require slight design modifications.  Here we review some of the most common design challenges cited by stormwater professionals and offer a few solutions. For a more extensive discussion of the challenges that may arise in implementing green infrastructure, see How Can I Overcome the Barriers to Green Infrastructure.

gi_greenarrow Clay or Glacial Till

Clay and glacial till often have low infiltration rates.  For sites dominated by these soils, engineers may therefore assume that infiltration based stormwater controls are not feasible.  While the design of green infrastructure practices for sites with clay soils may require greater care, many steps can be taken to design green infrastructure practices that meet water quality goals.
Measure soil infiltration rates:  By determining the infiltration rate of site soils before beginning the design of stormwater controls, designers can avert unwelcome and costly surprises.  Guidance materials generally recommend that the infiltration rate of native soils beneath infiltration practices be greater than 0.25 – 0.5 inches/hour. For a cautionary tale on the dangers of not incorporating measured infiltration rates into rain garden design, read about Seattle Public Utilities' experience with the Ballard Roadside Rain Garden pilot project (PDF) (10 pp, 318K, About PDF).
Amend soils beneath infiltration practices: Amending clay soils with compost or other organic matter can increase soil infiltration rates, while improving soil fertility and improving the ability of the soil to remove pollutants.  The Low Impact Development (LID) Center has developed a design specification for soil amended with compost.

Plant deep-rooted vegetation: Deep-rooted vegetation enhances soil infiltration rates by creating small conduits for water to infiltrate and increasing biological activity in the soil.  A 2010 report (PDF) (82 pp, 5.3MB, About PDF) by the U.S. Geologic Survey found that the median infiltration rate of a clay soil planted with prairie species (0.88 inches/hour) was more than three times the median infiltrate rate of a clay soil planted in turf (0.28 inches/hour).

Expand the storage layer and include an underdrain: Even when soil infiltration rates limit the volume of stormwater that can percolate into the groundwater, including a larger storage layer with an underdrain can significantly slow peak flows, protecting stream banks and potentially reducing combined sewer overflows.

Use practices that do not require infiltration: Rainwater harvesting, green roofs, vegetated swales, and practices designed for peak flow attenuation do not require soils with high infiltration rates.  These practices may be integrated into treatment drains to mitigate stormwater impacts. 

gi_greenarrow Poor Urban Soils

Many cities are interested in revitalizing urban areas by transforming vacant lots and other neglected spaces into green infrastructure assets. The poor condition of the soils on these lots, however, can be a significant impediment to green infrastructure. The soils are often severely compacted, lack sufficient organic matter, and can contain large amounts of construction debris, making them unsuitable as a growing medium.
Evaluate and recondition urban soils: Evaluate and recondition urban soils: Reconditioning methods for improving poor quality soils will vary depending on soil conditions and the intended use of the site. Sites intended for urban agriculture might require extensive reconditioning, whereas sites intended for recreation might require only moderate improvement. In 2011, EPA completed a report addressing the Evaluation of Urban Soils (26 pp, 3.2MB, About PDF). This report provides a concise, practical, and scientifically-based overview of the typical conditions of urban soils, and offers recommendations for how such soils can be rehabilitated or reconditioned to support green infrastructure or urban agriculture.

gi_greenarrow Brownfield Sites

A brownfield is a property where redevelopment or reuse may be complicated by the presence (or likely presence) of contamination. Many cities are interested in revitalizing urban areas by redeveloping vacant parcels and brownfield sites. Integrating green infrastructure into these sites can provide many environmental and community benefits. In planning infiltration-based stormwater management practices, however, care must be taken not to mobilize contaminants in the soil and increase the risk of groundwater contamination.
Perform site analysis and planning: In 2013, EPA released a decision tool on Implementing Stormwater Infiltration Practices at Vacant Parcels and Brownfield
 (15 pp, 774K, About PDF). This document guides decision-makers through six questions to determine whether infiltration or other stormwater management approaches are appropriate for a specific brownfield property.

gi_greenarrow Sediment Laden Stormwater

In arid regions, bare soils are more common and rates of erosion and sedimentation are relatively high. Fine sediments delivered by stormwater flows can clog infiltration practices and degrade their performance. Here we summarize a few strategies that stormwater professionals have applied to design and maintain effective green infrastructure practices in areas with high sediment loads.
Include a mulch layer: Mulch acts as a filter for the sediments carried in stormwater. By including a mulch layer above infiltration practices and replacing this layer when it is filled, the soil and gravel layers below can be protected from sedimentation.

Include a sediment trap: A sediment trap is a small depression bordered by a small berm that captures and collects sediment at the entrance to a bioretention area. Traps can be used at the inflow of many green infrastructure features to facilitate the removal of accumulated sediment and prevent the feature from becoming clogged.

Perform periodic maintenance: If a mulch layer or sediment trap is included, the accumulated sediment must be regularly removed to maintain the function of the stormwater management practice.

gi_greenarrow Cold Weather

Stormwater professionals frequently raise questions about the performance of green infrastructure practices in cold weather. Research by the University of New Hampshire Stormwater Center indicates that green infrastructure practices in their climate demonstrate excellent water quality treatment and peak flow reduction year round.

gi_greenarrow Limited Water Supply for Irrigation

Many stormwater professionals cite limited water resources as a barrier to green infrastructure in arid and semi arid regions. By following the principles of xeriscaping, however, green infrastructure practices can conserve water resources:
Create a plan: The first step in designing landscape features that can remain healthy and attractive with limited irrigation is to create a plan balancing water supply and demand. Annual water budgets will generally be appropriate for landscapes consisting of native plants at native densities, while monthly water budgets will be more effective for landscapes with exotic plants at higher plant densities.

Use low water use plants: Native and drought tolerant plants can drastically reduce, if not eliminate, the irrigation requirements of green infrastructure practices.

Use efficient irrigation systems: Irrigation systems will be most efficient when plants are grouped according to their water needs, and when the frequency and depth of irrigation is adjusted according to plant type, plant maturity, and season.

Consider soil amendments: Healthy soils are essential to retain soil moisture, sustain vegetation, and treat stormwater runoff. If site soils are poor, soils can be amended with organic material.

Use mulches: Organic mulch can increase water retention and pollutant removal while building soil structure and suppressing weeds. Note, however, that many desert trees and shrubs react poorly when their trunks come in contact with mulch.

Maintenance: All landscapes require maintenance, and xeriscaping is no exception.

gi_greenarrow Space Constraints

Many green infrastructure features require land area to allow stormwater to infiltrate into the soil. This can pose a challenge when space is limited, for instance in a retrofit project or in a right-of-way. Designers have developed many strategies, however, for overcoming this challenge:
Use features that serve multiple purposes: Swales and bioretention areas can be integrated into landscaped areas, medians, or parking strips. Similarly, permeable pavements provide volume reduction and water quality treatment without requiring any additional space.

Use features that fit into small spaces: Planter boxes and tree pits are examples of green infrastructure features that may be designed to fit into small spaces.

Subsurface storage or infiltration: Subsurface storage or infiltration tanks provide an alternative when space is too limited for any surface practices.
Edison Lot Construction
Many errors can be made in the implementation phase that severely compromise the performance and public acceptance of well-designed stormwater management practices.  In this section we collect resources on lessons learned from previous construction mistakes, as well as steps that can be taken to assure that practices are built as designed.

Designer's Guide for Low Impact Development Construction (PDF) (95 pp, 10MB, About PDF)
The designer's guide includes an overview of common LID construction errors, a discussion of how construction procedures and sequencing for LID sites differs from conventional sites, and recommendations for improving contracts, plans, and communication to avoid construction errors.

New York City High Performance Landscape Guidelines (PDF) (273 pp, 7.6MB, About PDF)
Part III of the landscape guidelines discusses how to anticipate potential construction problems and make construction practices more sustainable.  Though intended to inform the design and construction of public parks, many of the topics discussed are more broadly applicable.

Ballard Roadside Rain Gardens, Phase I  – Lessons Learned (PDF) (10 pp, 318K, About PDF) - This paper was prepared by Seattle Public Utilities to document several errors that were made in the design and construction of the Ballard Roadside Rain Gardens pilot project.  Three lessons that are discussed at length are: the importance of reviewing project goals and objectives with construction management staff; the importance of consulting with the geotechnical engineers throughout the design and construction process; and the importance of thorough and timely community outreach.

 Yard Maintenance Tools
Operation and Maintenance
Like all stormwater infrastructure, green infrastructure requires regular inspection and maintenance to assure that it is functioning properly.  Maintenance activities for green infrastructure practices generally require more labor and less heavy equipment than maintenance activities for gray infrastructure. The following materials offer guidance on what to look for in inspecting green infrastructure practice, and how frequently to conduct maintenance activities.
Green Stormwater Operations and Maintenance Manual (PDF) (48 pp, 1.4MB, About PDF)
This manual produced by Seattle Public Utilities provides a summary of routine maintenance activities for rain gardens, vegetated swales, and permeable pavements.  The charts included in the manual describe four levels of service from excellent effort (Service Level A) to poor effort (Service Level D).
Regular Inspection and Maintenance Guidance for Bioretention Systems/Tree Filters (PDF) (2 pp, 22K, About PDF)
This two-pager produced by the University of New Hampshire (UNH) Stormwater Center includes a list of inspection and maintenance activities for bioretention systems and tree filters and a checklist for inspection.
Regular Inspection and Maintenance Guidance for Porous Pavements (PDF) (2 pp, 20K, About PDF)
This 2-pager produced by the UNH Stormwater Center includes a list of inspection and maintenance activities for porous pavements and a checklist for inspection.

Homeowner Resources
Many state and local governments have produced guides for homeowners on installing rain barrels and rain gardens. Here we provide links to a small selection of these guides from different parts of the country.
New York: Guidance Manual for Homeowners (PDF) (8 pp, 4MB, About PDF)
This brief how-to manual developed by the Stormwater Coalition of Albany County guides homeowners through the process of siting, designing, and installing a rain garden or rain barrel on their property.
Oregon: Stormwater Management Facilities: Operation and Maintenance for Private Property Owners (PDF)  (22 pp, 295K, About PDF)
This document provides general guidelines to homeowners and homeowners associations on how to inspect and maintain stormwater management facilities. Topics addressed include sediment removal, vegetation management, and erosion. 
Wisconsin: Rain Gardens: A How-To Manual for Homeowners (PDF) (32 pp, 5MB, About PDF)
This manual provides homeowners and landscape professionals with the information needed to design and build rain gardens on residential lots.

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