Stormwater Solutions for Green Infrastructure

As our cities and towns grow and develop, we modify our streams, wetlands and hillsides with roads, houses and buildings that cannot absorb rainfall and snowmelt like undeveloped areas. As the rain falls and snow melts on these surfaces, the water runs off and picks up sediment and pollutants and carries them straight to our streams. This runoff can increase flooding, damage streambanks and fish habitat, and pollute streams, lakes and estuaries.

This project provides education and technical assistance on green infrastructure (GI) practices that address these stormwater impacts.  You will find resources and guidance to help you through each step from selecting the most appropriate green infrastructure Best Management Practice (BMP) for your site, to construction and long-term maintenance.  The resources on this site can be used by everyone from municipalities to private landowners across Oregon and beyond.

Learn About Green Infrastructure

In undeveloped areas, very little rainwater or snowmelt runs off the land like it does in cities. Trees, plants and soil capture much of the precipitation, and some of it evaporates back into the air. Most of the precipitation that doesn’t evaporate or get captured by vegetation soaks into the ground where soil and microbes remove pollutants naturally. The water slowly recharges streams, wetlands and groundwater. Very little runs off, except in very large storms.

This natural hydrologic cycle is radically changed when land is developed in the way it has been for decades. Typical development clears the land of vegetation and covers it with hard surfaces such as roads, parking lots and rooftops. Construction compacts soils, so that even landscaped areas can generate unnaturally high runoff volumes. Storm drains are installed to get water out of the way by sending it into local streams or injecting it underground without treatment. Development dramatically increases runoff volumes which, even when controlled by detention basins, causes flooding, damages fish and wildlife habitat, and delivers urban pollutants such as oils and pesticides to local waterways. The decreased infiltration results in less cool, clean groundwater to recharge streams in the dry summer months.

We use the term Green Infrastructure (GI) to mean a combination of practices that conserve natural resource areas and use existing natural site features with distributed, small-scale stormwater management practices to capture and treat runoff with vegetation and soil similar to a well-vegetated undeveloped landscape. Examples of such practices include street trees, stormwater planters, rain gardens, porous pavement, vegetated roofs, and soil amendments.

GI practices may be incorporated into existing as well as newly built developments in a community. They increase groundwater supplies and reduce the negative water quality impacts to streams and fish habitat, flooding, and in many cases the cost of stormwater treatment and infrastructure. They are aesthetically pleasing and have been shown to increase real estate values.

Flooding is the most visible effect of our land use development patterns. Among other things, green infrastructure can improve public safety, reduce flood damage, and make communities more resilient.

What Does Green Infrastructure Look Like?

More likely than not, you have probably walked right by innovative green infrastructure practices.  Green infrastructure practices naturally blend in with their surroundings and provide site beautification. 

 

Case Studies

These case studies provide an overview of green infrastructure projects, including timeframes and costs, in different regions in Oregon.

Planning for Green Infrastructure

The GI site design process builds on the traditional approach to site design. It begins with analysis of the site, and incorporates steps to involve local decision makers early in the process. The process has been consolidated into nine basic steps*:

  1. Form an integrated project team and engage stakeholders
  2. Inventory and evaluate the site
  3. Integrate municipal, county, state, and federal requirements
  4. Develop initial concept design using nonstructural BMPs
  5. Organize pre-submission meeting and site visit with local decision makers
  6. Incorporate revisions to development concept
  7. Apply structural BMP selection process
  8. Apply necessary green infrastructure facility calculators
  9. Develop the preliminary site plan

 * Adapted from the Southeast Michigan Low Impact Development Manual.

Gather Your Team

The composition of a green infrastructure project team can greatly impact the ability to achieve project goals and long-term facility viability. Practitioners working in the field of green infrastructure can range from water quality technicians to engineers to passionate landowners. Here are some of the professionals who may be part of a green infrastructure project team:

  • Arborist – An arborist should be consulted when protecting mature trees and native forest remnants from construction, or when a site is challenging for tree selection.
  • Architect – If working on new development, the architect will be influential in determining the footprint of built infrastructure and impervious surfaces.
  • Contractor – As the main professionals performing the work, all contractors should be to actively engaged in project meetings to ensure transparent communication between the office and the field.
  • Engineer – Engineers, whether they be geotechnical, mechanical or electrical, are the technical experts on the project, ensuring facilities are designed properly and function as intended.
  • Landowner – The landowner, likely a key decision-maker, is an asset for many green infrastructure projects because of their knowledge of previous site use and challenges.
  • Landscape Architect – Landscape architects are knowledgeable about plant selection and placement. They should be consulted when considering design, aesthetics, and maintenance.
  • Maintenance Worker – Professionals who will maintain the facility post-construction can offer insight on maintenance feasibility and should be consulted at the beginning of the design process.
  • Natural Resource Professional – Depending on the project, a wetland scientist, hydrologist, biologist, or another science professional may need to be consulted.
  • Planner – Depending on the scope of the project, the planner can serve a key role in identifying ideal landscapes for green infrastructure practices. They are also familiar with appropriate policies and procedures.
  • Project Manager – Acting as the lead coordinator, the Project Manager can bring expertise from various backgrounds and should be role with project unknowns as the project develops.

Many of these professionals will not need to be fully engaged throughout the duration of the project; however, it is important to maintain clear and constant communication as projects often evolve over time. At the onset, invite all members of the project team to meet and agree on project goals, construction sequencing, and preferred methods of communication.

Site Planning Checklist

The Site Planning Checklist includes a list of over 300 environmental, social, and financial considerations that might direct decision-making about the best practices that might be implemented. While the list is a bit daunting, it is a useful tool in understanding the opportunities and constraints of your site.  You may not need to consider every item on this list on every site, the checklist is a good reminder of many environmental, economical, social and policy/planning factors that should be considered when planning green infrastructure projects.

See the Planning Checklist resources to help you find correct information about the most critical factors when planning your site. 

Checklist items are delineated by a set of 7 steps critical to the master planning phase of sustainable sites:

  1. Consider on-site natural resources
  2. Consider on-site infrastructure/built environment
  3. Consider off-site natural resources
  4. Consider off-site infrastructure/built environment
  5. Consider municipal, state, and federal guidelines/laws
  6. Consider the programmatic requirements
  7. Gather possible investigative reports and other information from design team members

Within each of the first 6 steps, the checklist reminds you to look for and log information as it relates to water resources, land forms, air quality, soils, livability, micro- and macroclimate, vegetation, renewable energy, cultural resources, staging and storage considerations, utilities, local suppliers & services, regulations, fire hazards, zoning, and stakeholder process. For step 7, we recommend reports that might apply to your project and include a checklist of items that may influence the design of sustainable sites and should be included in the report.

Understand Site Constraints

Floodplains

  • Do not place GI BMPs in a 100-year floodplain or they may be washed out in the next big storm.
  • To find if your property is within a 100-year floodplain, consult the Oregon Explorer map viewer (works ONLY with Internet Explorer web browser).  To find the floodplain layer, click “go to layers,” then click the plus sign and the checkbox next to "Hazards", click plus sign and check box under "Flood Hazard", then click the "Floodplain:  FEMA 100-yr".
  • Some agencies may not allow development in the 25-year floodplain. Contact your city or county's community development, public works, or engineering department to find out more.

Wetlands

  • Do not place GI BMPs in a low or seasonally wet area.
  • In Oregon, the Department of State Lands, Wetlands Program (503-986-5200) can help you identify if and where wetlands may be.
  • Wetlands may or may not be recognized and mapped as "jurisdictional." If a wetland has not been mapped, it may still fall under multiple jurisdictions. Fact sheets from the Department of State Lands on how to start to identify wetlands is available. 
  • You can also look up your site on Oregon Explorer map viewer (works ONLY with Internet Explorer web browser.) To find the Wetland layer, click the plus sign and the checkbox next to "Habitats and Vegetation," then click the plus sign and checkbox next to "Wetland", then click both checkboxes next to "Wetlands in Oregon" and "Wetland Inventory Boundary." To find the hydric soils layer, scroll down to "Landscape and Geology" and click on the plus sign and checkbox next to it, click on plus sign and checkbox next to "Soils", then click on the checkbox next to "Wetland Soils."

Riparian Areas & Buffers

A riparian area can be simply defined as land adjacent to a waterway that either influences or is influenced by that waterway. A rule of thumb to define this width is that it is equal to the average height of the trees adjacent the stream, since this is the range of influence that fallen trees and leaf litter are likely to have. 

  • Do not place LID facilities in a riparian area or buffer.
  • Contact your city or county planning department to help you identify if and where these may be on your site.
  • Contact the Department of State Lands (503-986-5200) to see if they have jurisdiction if you do have a waterway on your site.

Habitat Areas

Numerous above and below ground animal species provide important hydrologic benefits to our watersheds. Your site may have sensitive uplands that provide important habitat to some of our more specialized native animal species. Generally, if your site looks like it's been impacted by development, then it's likely that your site is not located in a critical habitat area.

If your site is natural looking, with native plants (i.e. Oak Woodland), then it's possible that you may want to avoid disturbances, like installing a rain garden, in this area.

  • Do not place GI BMPs in a critical habitat area.
  • Contact your local county or city Planning Department to find out if and where these areas might be.
  • Professionals from various state agencies such as Oregon State University Extension Service or biologists at Oregon Department of Forestry or Department of State Lands may be available in your region.
  • Consult the Oregon Conservation Strategy to discover if there are areas targeted for conservation.
  • Consult the Oregon Explorer map viewer (work ONLY with Internet Explorer web browser). (To find the Habitat layers: Click the plus sign and the checkbox next to "Habitats and Vegetation", then click the plus sign and checkbox next to "Bays and Estuaries", then click both checkboxes next to "Estuaries" and "Estuarine Habitat". Scroll down to "NW Forest Plan" and click both the plus sign and the checkbox next to it, then click the checkboxes labeled "Northern Spotted Owl Habitat" and "Marbled Murrelet Zone".

Septic Systems

  • Do not place GI BMPs over a septic field or other infiltration septic system; this could ruin your septic system in a variety of ways.
  • Your city or county planning department may be able to help you locate this if you don't know where it is on the site.

Contaminated Soils & Groundwater

Soil & groundwater contamination can come from many different sources including lead paint and leaking underground storage tanks from current and past land uses.

  • Search the DEQ Facility Profiler by address. If your site is listed here, check the status of cleanup. A status of "CLEANUP_COMPLETED" means that the site has been brought up to current regulatory requirements for land quality and the suitability of this site for a rain garden is not constrained by this criteria.
  • Historic land uses can often be found through your city or county planning department.
  • Oregon has a number of Groundwater Management Areas, which are designated areas of groundwater contaminated by nitrate. For infiltration LID facilities, consult a professional to assist with rain garden design to ensure that denitrification occurs before infiltrating to prevent further groundwater contamination.

Landslides

Infiltration LID facilities should not be uphill of a known landslide area. For all steep areas, infiltration facilities should be set back a minimum of 100 feet from down-gradient slopes of 10% or greater. Add 10’ of setback for each additional percent slope up to  30%.

  • Consult the Oregon Explorer map viewer (works ONLY with Internet Explorer web browser). To find the landslide layers: Click the plus sign and the checkbox next to "Hazards", then click the plus sign and checkbox next to "Geological Hazards", then click both checkboxes next to "Coastal Erosion", "Landslide Areas" and "Historic Landslide Points".

Wellhead Protection Areas

A wellhead protection area is a designated area of land where a jurisdiction might draw groundwater to supply public drinking water.

  • If runoff is from vehicular areas such as parking lots, driveways, and roads, then contact the city or county planning department to assess whether your site is in a wellhead protection area (i.e. Portland's Columbia Slough Wellhead Protection Area).

Drinking Wells

Groundwater can move twice as fast horizontally as vertically, so infiltrating too close to private drinking wells can contaminate them. 

  • If runoff is from vehicular areas like parking lots, driveways, and roads, search for nearby wells by address using the DEQ Well Log Query.  Click on "Find T-R-S by Address" and enter the address. On the next page, navigate to the "Type of Log" pull down menu and choose "Water Well", then click "Search". The resulting table shows all the water wells within that T-R-S, which stands for Township, Range, and Section. In this table, look for wells with a "Completed Depth" greater than zero. Locate these wells in relation to your site and infiltrate no closer than 2 times the completed depth. For instance, for a completed depth of 200', an infiltration rain garden should be at least 400' away.

 

Select Your Green Infrastructure Site

The EPA defines a best management practice (BMP) as "a device, practice, or method for removing, reducing, retarding, or preventing targeted stormwater runoff constituents, pollutants, and contaminants from reaching receiving waters."[1]  Despite the widespread use of "best" to describe these practices, these practices are much more effective when used in conjunction with each other. There are over 200 BMPs that may or may not apply to a particular project. Different practices may be addressed during all or some of the project phases. For example, saving a tree requires careful site layout in the planning phase: a design that reduces cut and fill, shows tree protection, and is mindful of utility and other excavation cuts needed during construction; a general contractor who respects the tree protection zone outlined during the design phase and calls an arborist when roots must be cut; and maintenance practices that support the health of the tree through appropriate pruning, integrated pest management, and limiting compaction.

Best management practices can be divided into two overarching categories, Runoff Prevention and Runoff ReductionRunoff Prevention BMPs tend to be either good decisions that protect a site (i.e. limit compaction), restore a site (i.e. use a foundation system that won't impede subsurface flows) or temporary measures (i.e. employ sediment prevention and erosion control). These practices may also be associated with behavioral changes like using integrated pest management.

Runoff Reduction BMPs, on the other hand, are engineered or highly designed facilities that mitigate the damage created  by changing the land use from natural lands (pre-developed or pre-settlement) to any other use (post-developed). They tend to be expensive and not as effective for protecting water resources as runoff prevention practices.

Stormwater Management Hierarchy

The Stormwater Management Hierarchy can be illustrated as an inverted pyramid. At the top are practices that closely resemble the pre-development site hydrology, shown here in dark green. Runoff Prevention BMPs, in hierarchies 1 and 2, manage rain where it falls by primarily limiting the extent of impervious surface onto the site. As you move down the hierarchy, runoff becomes more managed than prevented through a variety of practices, though overall less of the site hydrology restored. 

Prevention vs. Reduction BMPS

Green Infrastructure PREVENTION BMPs are easier to plan, design, build, and maintain.  They are more cost effective on average.

Green Infrastructure REDUCTION BMPs are more challenging to plan, design, build, and maintain.  They are more expensive on average.

BMP Suitability Matrix and Guidelines

The BMP Suitability Matrix provides critical guidance in selecting BMPs for your site based on a variety of site conditions and contextual factors. The BMP Suitability Matrix User Guide provides detailed information about how to read and interpret the Suitability Matrix and gives descriptions of both green infrastructure Prevention and Reduction BMPs.

Additionally, information about Tree Protection and Planting (a runoff Prevention AND Reduction BMP) can be found here.

Design and Size your Green Infrastructure Best Management Practices

Design and placement of Green Infrastructure BMPs should be informed by the natural and built environment both on-and off-site, as well as client/stakeholder preferences for cost and long-term operations & maintenance considerations. Design is usually an iterative process when used to optimize water quality protection, stream bank erosion reduction, appropriate flow conveyance, and flood storm mitigation.

GI Implementation Forms and Tutorials

Tutorials

We highly recommend that you review the tutorial and print out a copy to keep close at hand as you work through the GI Implementation Form.

  • Start here. This tutorial introduces the GI Implementation Forms.
  • This Continued Tutorial manages additional Catchments in the new development site from the Introductory Tutorial. Contains examples of different BMP worksheets and ways to overcome challenging soil conditions.
  • This Continued Tutorial manages an example redevelopment of an office site in eastern Oregon. Contains examples of retrofit and pavement removal BMPs.

Forms

There are THREE different forms based on Storm Type (see below). PLEASE BE SURE TO DOWNLOAD THE CORRECT FORM FOR THE STORM TYPE THAT MATCHES YOUR SITE LOCATION.

Technical Notes

  • Worksheet cells are locked so calculated values cannot change.
  • YOU MUST ENABLE MACROS IN EXCEL to use this form. In the Security warning that appears below the toolbar, select "Allow" or "Options". You may also need to "Enable" both Macros and Links.  If the warning does not appear, you may have to go to Options --> Trust Center --> Trust Center Settings --> Macros to allow the macros to run.

About the GI Implementation Form

What this form DOES:

  1. Calculates the total area where stormwater is managed by BMPs in each catchment of the site and calculates the required size of each selected BMP.

 What this form DOES NOT DO:

  1. Select BMPs for the user.  The BMPs are listed in order of priority based on the Stormwater Hierarchy; however the user must select the types of BMPs themselves.
  2. Provide specific information about construction, maintenance and costs.  Most of this information is provided in the BMP fact sheets.  We recommend that you review these fact sheets, particularly to PHYSICAL SETTING section, to make sure that BMP is appropriate for your site.  You can also find information about what BMPs are appropriate under a variety of physical constraints in the BMP Suitability Matrix.
  3. Provide structural design information:  This form does not calculate load bearing capacity (mostly related to Porous Pavement).  You must work with a geotechnical engineer who can analyze the soil to determine its load bearing capacity.

Funding for GI Implementation Forms provided by the US Forest Service.

What Storm Type is Your Site In?

Patterns of rainfall are modeled as types, which in Oregon include Type IA, Type I, and Type II. Type IA is the most gentle, longest storm while Type II storms are shorter, most intense storms. Many landowners prefer to see their facilities designed to empty within 24 to 30 hours; however, depending on rainfall distribution, facilities should be empty in at least: 

  • Type IA: 30 hours
  • Type I: 72 hours
  • Type II: 72 hours

Adapted from USDA Soil Conservation Service, Sept. 1987.

Precipitation Maps

Precipitation maps are used by engineers and other hydrology modelers to assess the size of a particular frequency storm for the project location. Engineers model their site’s rainfall response to different size storms that are expressed in inches over a 24-hour period. Each frequency has a different application. Not all storms are used in every jurisdiction, so check with yours to see which storm sizes are significant. NOTE: the "6-month, 2-year, 10-year, 25-year and 50-year" terms refer to a frequency analysis and DO NOT mean that this size storm only returns once in that particular time period.  

Precipitation varies greatly in Oregon. Know your storm patterns (distribution) and which storms to use for what.

  • Typically, a jurisdiction will conduct a frequency analysis of storms and identify the size of storm that is equal or greater than 80 - 90% of the storms that occur. This size storm is referred to as the "water quality storm". LID facilities designed to infiltrate runoff from this size storm using design standards (based on current research) are assumed to meet EPA water quality requirements. The 6-month design storm has been found to be a conservative estimate for a "Water Quality Storm" in Oregon and could be used when a city or county has not identified a specific size "water quality" storm.
  • Channel Shaping Storm: Streams adjust to additional water (either via runoff or seepage) by readjusting their shape. Exceeding the duration, volume, or frequency of the pre-development 2-year flow will cause channel erosion. The frequency of this storm may vary from 18 months to 2.5 years, depending on the watershed, but in the absence of better information, this is a good surrogate. As a rule of thumb, using LID to completely reduce runoff from the 2-year storm tends to attenuate flows from the 25-year storm. Using this strategy, LID would replace a detention basin.
  • The size of this storm dictates conveyance design of pipes, swales, ditches, etc. Designers might model one of these storms to keep what most would consider "all" stormwater on site using LID or to attenuate flooding if using a detention basin. Depending on built and natural conditions, an agency may use the 10-year or the 25-year storm.
  • The size of this storm dictates conveyance design of pipes, swales, ditches, etc. Designers might model one of these storms to keep what most would consider "all" stormwater on site using LID or to attenuate flooding if using a detention basin. Depending on built and natural conditions, an agency may use the 10-year or the 25-year storm.
  • Conveyance or Flood Storm: The size of this storm dictates conveyance design of pipes and bridges for primary roads. Agencies may use this size storm or a 100-year storm depending on the importance of using the road/highway during major flood events.

Fact Sheets

Infiltration Testing: Low-impact development fact sheet. One of the first steps in siting a low-impact development facility is infiltration testing. Infiltration tests estimate the rate at which runoff will infiltrate, or pass through, native soil. An infiltration test, in essence, involves digging a hole, pouring in water, and measuring the drop in water level over time. This fact sheet provides guidance for conducting tests to site and design infiltration facilities.

These fact sheets offer an overview of the siting, design, construction, and operations & maintenance of common green infrastructure/low-impact development (LID) practices: Rain GardensStormwater PlantersPorous PavementDry WellsVegetated Filter StripsWater Quality Swales, Soakage TrenchesVegetated Roofs and Infiltration Testing.

Additional Notes

Choose the Right Rain Garden

We hope this tool raises your awareness of siting considerations that can lead to both a less costly and more environmentally friendly rain garden. This “Choose the Right Rain Garden” decision tree tool helps users arrive at and implement the rain garden configuration that best suits their site conditions. Additional information and tips are offered below each question and many pages have illustrative graphics to help you choose the answer that reflects your conditions.

While rain gardens alone will probably not fully protect or restore your watershed, the goal of this wizard is to help you avoid the most complicated and therefore most costly to build and maintain configuration, the lined filtration rain garden. Throughout Oregon, these facilities don’t mimic pre-developed hydrology; additional runoff volumes (aka hydromodification ) flowing in and out of a lined facility are likely to damage downstream waterways, impacting water quality, habitat, and availability. In addition, they cost more to build and maintain.

Build your Green Infrastructure Best Management Practices

Green Infrastructure practices must be implemented with care at each stage of the development. If a facility is properly planned and designed but improperly constructed, the facility is unlikely to perform as intended and many benefits of green infrastructure will be lost. The facility may even pollute the stormwater further instead of protect it. Construction considerations for specific green infrastructure practices are presented in the associated individual fact sheets (see "Design and Size".

Your contractor plays a crucial role in helping your protect water resources during the design phase. Preventing erosion and controlling sediment are some of the most important elements.

Healthy soil (left) has room for air, water, & soil animals that help protect long-term permeability. Compacted soils (right)  generate runoff and reduce plant health that can cause landowners to apply fertilizers & pesticides that pollute downstream waterways. Compost amendment during the construction phase can help restore long-term permeability of soils disturbed during construction.

Native Plants & Noxious Weeds

Native plants are essential to healthy watersheds. They provide unique ecosystem services and products in our region that other non-natives may not provide. Native plants are generally easier to establish, and require less water and fertilizers.  They evolved over geologic time periods with other plants and animals in our watersheds and support the insects, that feed the birds, that spread the seeds, that grow the forests, that manage stormwater.

The following two references have been made available to help you choose the "right plant for the right place" in your stormwater facility or other area to be planted.

The USDA Plants list is a database created by the USDA. It has been found to be very helpful in researching native plants and their characteristics to help you choose the appropriate plants for your site.

The Oregon Noxious Weeds is a database of invasive, harmful plants in which you should not use in Oregon.

Non-natives may also provide these services, but they may also become invasive, and there's often no way to know which path a plant will take until it has been introduced into a watershed. Some non-natives have taken up to 80 years to become invasive after overplanting (i.e. kudzu planted on the East coast for erosion control); some spread quickly from just a few specimens (i.e. scotch broom dominates the Pacific NW landscape and originated from three plants introduced in the late 1800's).

OSU Extension Catalog

Tree Protection on Construction and Development Sites

This publication is a guide for protecting, conserving, selecting, maintaining, removing, and replacing trees on development sites in the Pacific Northwest.

Generate Native Plants List

The USDA has excellent online guidance for finding plants native to your state and even your county. The following tutorial with screen shots will help you use their website to identify suitable plants for your project. You may want to visit a nearby native plant nursery to see what’s available. If no native plant nursery is nearby, you’ll have to cross-reference what’s available in your area with this database.

Always avoid invasive plants. Some of these, such as periwinkle (vinca minor or major), English ivy, and yellowflag iris may be sold at your local nursery. For more information, visit the Oregon Department of Agriculture Plant Division’s Noxious Weed Profiles.

Tutorial

  1. Go online to the USDA PLANTS Database. In the upper left hand corner click on “Advanced Search”.
  2. We’re going to pick and choose a few different items on the “Advanced Search and Download” web page. Not all search options need attention. For any of these scroll menus, you may have to click outside the box in white space to get your choice to “stick”. Start by scrolling down under “1. Distribution” to “County Distribution” and choose your county. Scroll down to Oregon: Marion.
  3. Scroll down under “2. Taxonomy” to “National Common Name” and click the checkbox to the right that says “Display”.
  4. Scroll down under “3. Ecology” to “Duration” and choose “Perennial”.
  5. Go to the next item under “3. Ecology” to “Native Status” and choose “—L48 Native”.
  6. Scroll down (or up) to the “Display Results” button and click on it.
  7. A list of all plants native to Marion County in Oregon with their common names is generated.
  8. To narrow the search to certain types of plant, like shrubs and trees, click on the “Back” button or back arrow of your internet browser. Selections that might be appropriate to plant in a rain garden or your landscape area are:
    1. Forb/herb  (flowering plants that aren’t grasses, sedges, & rushes)
    2. Graminoid (grasses, sedges, & rushes)
    3. Shrub
    4. Subshrub
    5. Tree
    6. Vine
  9. Scroll down to “3. Ecology” and “Growth Habit”.  For this example, choose “Forb/herb”. 
  10. Your previous choices should still be selected. Scroll to “Review Selections or Sort Report” button in the middle or bottom of the page and click this to see what criteria you’ve entered so far.
  11. After you click, you’ll see all your criteria listed.
  12. Now click the “Display Results” button at the bottom of this page.
  13. This list is narrowed to native, perennial flowering plants in Marion County in Oregon.
  14. To narrow your search to find plants appropriate for different moisture zones, navigate back twice to the original Advanced Search and Download Page and scroll to “4. Legal Status” and look for “National Wetland Indicator Status”. Click the back button on your browser twice to the “Advanced Search and Download” page. Scroll to “4. Legal Status” and under “National Wetland Indicator Status”. Choose “—FACW (Facultative Wetland)”, then scroll down and click on “—FAC+ (Facultative +)”. Planting zones reflect the areas where the garden will have the most and least water when flooded, as well as during the dry season. The graphic on the top illustrates the topographic zones of the rain garden, the graphic on the bottom illustrates zones of high and low soil moisture and the corresponding National Wetland Indicator Status. (Graphic: Robert Emanuel, OSU).
  15. Let’s review our choices by clicking on the “Review Selections or Sort Report” button.
  16. Click on the “Display Results” button at the bottom of this page.
  17. You’ll see all the flowering, native, perennial plants native to Marion County, CA that are appropriate for the wettest zones of a rain garden.

Green Infrastructure Maintenance

Proper operations & maintenance (O&M) of Green Infrastructure facilities in this final post-construction phase will dictate whether the long term benefits intended are realized. The decisions made by everyone on the project team play a role in how costly or easy is will be to maintain GI practices. The ability and preference of the maintenance staff and land owners should be considered when choosing which GI practices to implement. Low cost maintenance green infrastructure facilities and landscapes should always be considered first, since the owner's long-term costs can be much higher than the costs associated with the up-front planning, design, and construction costs. If a particular facility is required by a jurisdiction, the design team should engage in an educational effort to clarify the benefits of the facility and the maintenance requirements to the owner and staff.

Resources

  • Developed and reviewed by a wide variety of practitioners, this maintenance guide was developed to serve as a field guide for contractors and maintenance staff.
  • This list of pesticides have been identified by various regional experts as being a "serious threat to salmon and other aquatic life". Pesticides inside stormwater facilities should be avoided anyway, but for areas that drain to stormwater facilities and streams, if pesticides must be used, avoid ones that are on this list.

Share

Community engagement is often on the back burner for infrastructure projects, but having public support for green infrastructure can influence decision-makers and key stakeholders to invest in green infrastructure, ultimately driving projects into action. Effective community engagement goes beyond traditional information sharing and establishes a meaningful atmosphere that connects the public with the project. Many green infrastructure facilities are associated with larger concepts, such as flood mitigation, stormwater management, or city beautification. Association with these topics presents an opportunity to speak to your audience about issues they are likely concerned about, and how green infrastructure BMPs can be part of the solution.

Developing a Community Engagement Plan with project partners is a great way to strategize the opportunities for engaging target audiences and addressing relevant perceptions. Effective community engagement plans -

  1. Define clear goals and objectives. Are you simply raising awareness or do you want to encourage action or change in behavior?
  2. Define who the target audiences are. Are they contractors, private landowners, youth?
  3. Identify possible partners to do outreach with. If you’re planning on reaching out to youth, consider partnering with a school or youth corps. Conversely, if you’d like to attract private businesses, connect with the chamber of commerce.
  4. Identify communication tools at your disposal. Do you have access to relevant websites, calendars, email lists, and continuing education resources?
  5. Evaluation. How will you measure and evaluate the community engagement activities you implement?  

Approaches to Community Engagement

Generally speaking, community engagement can be approached from three different angles dependent upon project goals and resources.

Passive. 

Passive education and outreach campaigns are developed to build baseline awareness of a concept without conversation to support the message. This is a great approach to take if the site is walked past on a daily basis. Examples of passive community engagement include interpretive signs, brochures, newspaper articles, internet articles, videos, and exhibits.

Active. 

Active education and outreach strategies include things like demonstration site tours, opening events, nature play, and field trips. These activities help build understanding of a process and allow audiences to experience the site firsthand. This in turn helps build acceptance. A key feature of the active education and outreach activities is that there are two-way conversations. Event organizers and leaders should be prepared to engage the audience and earn their support for their cause. Active education is often accompanied by interpretive signage.

Promotional. 

This approach builds awareness about ideas and causes. This is the public affairs version of your community outreach plan – it aims to inform the public. Promotional education and outreach can be subdivided into social media, broadcast media, and print and digital media (e.g. project website).

Green Infrastructure Resources

Organizations

On this page, you will find a list of organizations who promote, support, and fund green infrastructure projects.

Academic/Education

National

Nonprofit/Regional Alliance

Associations & Professional Societies

Research Institutions

State   

Federal

 

Resources for Experts

In this section we provide detailed information for engineers, public works professionals, landscape architects and others tasked with designing, building and maintaining green infrastructure best management practice facilities.

Fact Sheets: 

A series of low-impact development (LID) fact sheets to help raise awareness of functions and designs for common LID and Green Infrastructure practices: Rain GardensStormwater PlantersPorous PavementDry WellsVegetated Filter StripsWater Quality Swales, Soakage TrenchesVegetated Roofs and Infiltration Testing.

Standard Details

Provides standard details for green infrastructure best management practices

UICS

Provides information about underground injection control facilities authorization by Oregon Department of Environmental Quality (DEQ).

Oregon Rain Garden Guide:

A how-to guide to help you design and build a rain garden to treat the stormwater runoff from your own home or business. You don't have to be a landscape professional to use this guide. It provides the necessary information to safely build and maintain a rain garden, along with references for more detailed guidance for special conditions. It provides information specific to Oregon's conditions, including the rainfall and appropriate plants for your site.

Low Impact Development in Western Oregon: A practical guide for watershed health: 

This document will help your jurisdiction address MS4 and TMDL regulatory requirements for water quality during the “post-construction” phase. Once you adapt this to your jurisdiction, the resulting document will be one component of meeting your post-construction stormwater management goals.

Seattle Public Utility Design Checklists: 

Feasibility and design requirements for different BMPs from the City of Seattle, Washington.

Choose the right Rain Garden

Why Should I Use This Tool?

We hope this tool raises your awareness of siting considerations that can lead to both a less costly and more environmentally friendly rain garden. This “Choose the Right Rain Garden” decision tree (i.e. wizard) helps users arrive at and implement the rain garden configuration that best suits their site conditions. Additional information and tips are offered below each question and many pages have illustrative graphics to help you choose the answer that reflects your conditions.

Download a flow chart of the entire rain garden decision tree

While rain gardens alone will probably not fully protect or restore your watershed, the goal of this wizard is to help you avoid the most complicated and therefore most costly to build and maintain configuration, the lined filtration rain garden. Throughout Oregon, these facilities don’t mimic pre-developed hydrology; additional runoff volumes (aka hydromodification ) flowing in and out of a lined facility are likely to damage downstream waterways, impacting water quality, habitat, and availability. In addition, they cost more to build and maintain.

What if I Don’t Understand or Know the Answer to a Question?

We recognize that you may not have answers to all the questions, but only questions truly relevant to water quality and cost have been asked. If you need more information, footnotes below each question provide important general information. Clicking on the symbol will provide you with detailed information including step by step guidance, agency contacts, or online resources, as applicable. You may also want to experiment now, first answering conservatively, to see what configurations the decision tree takes you to.

Begin the Choose the Right Rain Garden decision tree  >>

 


Sensitive Areas: Question 1

Are EITHER of the following conditions true?

Rain garden will be located:

  • in floodplains1 or other sensitive areas such as wetlands2, riparian areas and buffers3, & habitat4
  • over septic systems5

Yes     |     No

 

If any of the above conditions are true, answer Yes. If all of the above statements are false (preferred), answer No. Answering yes means that this location is unsuitable for a rain garden. A lack of information from any one of the following sources does not necessarily mean that your site is without any sensitive areas. The ultimate decision will fall to those with jurisdiction, so be sure to contact any agencies mentioned for assistance if in doubt. 

1Use the 100-year floodplain area as a minimum. The 25-year floodplain may also be appropriate depending on the development standards and regulatory environment in your jurisdiction.

2 Wetlands may or may not be recognized and mapped as "jurisdictional". If a wetland has not been mapped, it may still fall under multiple jurisdictions. Rain gardens in wet or seasonally wet areas could cause damage to your property.

A riparian area can be simply defined as land adjacent to a waterway that either influences or is influenced by that waterway.

4Numerous animal species provide important hydrologic benefits to our watersheds. There may be sensitive uplands that provide important habitat to some of our specialized native animal species.

5Avoid installing rain gardens over a septic field or other infiltration septic system; this could ruin your septic system in a variety of ways.

 


Sensitive Areas: Question 2

Are ANY of the following conditions true?

Rain garden will be located:

  • in contaminated soils or groundwater1
  • so that it will drain or overflow to a known landslide area2
  • for runoff from vehicular areas, in wellhead protection areas3
  • for runoff from vehicular areas, within a horizontal distance of 2x the depth of any nearby wells4

Yes      |      No     

 

If any of the above conditions are true, answer Yes. If all of the above statements are false (preferred), answer No. Answering yes leads to Filtration facilities, which prevent infiltration with a liner or are located in native soils infiltrating less than 0.5 inch/hour. While rain gardens alone will probably not fully protect or restore your watershed anyway -- evaporation generally plays an important role in healthy watersheds – lined filtration facilities in Oregon don’t mimic pre-developed hydrology. The additional runoff volumes (aka hydromodification) flowing in and out of a lined facility still cause damage to downstream waterways, impacting water quality, habitat, and availability. In addition, they cost more to build and maintain.

A lack of information from any one of the following sources does not necessarily mean that your site is without any sensitive areas. The ultimate decision will fall to those with jurisdiction, so be sure to contact any agencies mentioned for assistance if in doubt.


1 Infiltrating into areas of contaminated soils or groundwater can expand the area of contamination via transport through the soil.

2 Infiltration rain gardens should not be installed in known landslide hazard areas.

A wellhead protection area is a designated area of land where a jurisdiction might draw groundwater to supply public drinking water. Infiltration of runoff from vehicular areas is prohibited to protect public groundwater drinking supplies.  In some jurisdictions, infiltrating roof runoff may be acceptable.

4 If runoff is not from vehicular areas, but is instead from roof or landscape areas, then automatically answer "No" to this. Groundwater can move twice as fast horizontally as vertically, so infiltrating too close to private drinking wells can contaminate them.  Locate these wells in relation to your site and infiltrate runoff in a rain garden no closer than 2 times the completed depth. For instance, for a well with a completed depth of 200', an infiltration rain garden should be at least 400' away.

 


Setbacks: Vertical Separation

Are both conditions true? The distance from the bottom of the facility to the top of:

  • the seasonal high groundwater table is at least 3 feet1.

     AND

  • bedrock, fragipan2 (an impervious subsurface layer), or other impermeable material is at least 2 feet3.

Yes     |      No    

 

 

If all criteria are met answer “Yes” to this question. If only one of the criteria is met, answer “No”

1Do not rely on groundwater modeling or maps; these are usually done at too large a scale and don’t apply to the site scale practices such as a rain garden. To  look for bedrock or other impermeable subsurface layer that may impede infiltration, after infiltration testing has confirmed that soils are suitable for infiltration (additional info is included in this wizard and the fact sheet “Infiltration Testing”), dig a hole 2 feet of depth from the bottom of the proposed rain garden. If the soil is pretty consistent all the way down, then you don’t have a fragipan or bedrock problem.  Now look for a seasonal high groundwater table by digging a hole to an additional one foot of depth. If the hole doesn’t fill up with water, then groundwater levels are sufficiently deep. Ideally, this will be done during the rainy season.

2A fragipan is an impermeable soil layer. In Oregon, volcanic activity is often the source of this condition; ash deposited long ago has been compacted by additional soil deposited on top of it over time.

3Vertical separation is the distance between the bottom of the rain garden ponding area and the top of a subgrade layer in question (i.e. bedrock, groundwater, or fragipan2) The soil is nature’s pipe that conveys water downhill to seep out to streams; adequate vertical separation provides enough voids and depth for that conveyance beneath infiltration facilities.

 


Setbacks: Horizontal Separation

Are all the following conditions true? Infiltration facility will be:

  • 10’ from a footing or foundation or the top of a wall AND
  • 10’ from underground tanks AND
  • 5’ from the property line1 AND
  • 100’ from down gradient slopes equal to or exceeding 10% plus 5’ of setback for each additional percent up to 30%2 AND
  • 5’ from underground pipes3 AND
  • 0’ from slabs footings or pavement4 AND
  • 0’ from pier or post footings5 or the bottom of a site (not building) wall

Yes     |     No    

 

 

All criteria must be met to answer “Yes” or if any one of these statements is false, but location has been approved by a geotechnical engineer, then answer Yes. Without adequate horizontal separation, infiltration facilities have the potential to flood basements, overturn walls, or otherwise damage other infrastructure.

1 Five feet from the property line assumes that the zoning requirements for your property require a minimum 5’ setback. If that’s the case, then this will provide the 10’ distance needed to prevent flooding.

2 Avoid installing infiltration facilities near slopes exceeding 30%.

3 Call 811 to locate utilities on private property. Infiltrating too close to pipes could polluted stormwater could contaminate the contents of the pipe. In addition, many pipes are installed on a bed of gravel, which provides a shortcut for infiltrating water that could cause damage to structures and pavements.

4 A vertical liner extending at least 6” deeper than the pavement section (including any base rock) should be installed so infiltrating water doesn’t undercut and cause a structural failure of the pavement.

5 Also known as an LID Foundation, which include any foundation types that don’t block the flow of groundwater the way conventional basements do.

 


    Slow Soils: Question 1

    Is the infiltration rate of native undisturbed soils less than 12 inches/hour?

    Yes     |     No    

     

    The infiltration rate of the native soils should be discovered with an infiltration test in the field at a depth equal to where water will infiltrate when an infiltration facility is completed. For a simple infiltration testing method suitable for homeowners and others, see “Step 3: Assess Soil” section in the Oregon Rain Garden Guide. For more detailed information on testing methods, see “Infiltration Testing”, a fact sheet geared to jurisdictional staff and experienced designers. Do not rely on the NRCS soils data or any other mapping of hydraulic conductivity.

     


    Slow Soils: Question 2

    Rain garden sized to drain in time for next storm?

    Yes    |     No    

     

    Whether or not a facility will empty out and be ready for the next storm is a function of the storm distribution (i.e. Type IA, Type I, and Type II). Type IA is the most gentle, longest storm while Type II storms are the shorter, most intense storms. In general, jurisdictions within the Type IA distribution in Oregon require facilities to be empty in 30 hours. 

    To determine the answer to this question, you or your designer probably need to model the rain garden. You can use popular engineering modeling software such as EPA SWMM or HydroCAD or OSU’s open-source Excel calculator. Video tutorials are available at this link.

     


    Slow Soils: Question 3

    Are native soils suitable for plants?

    Yes     |     No    

     

    In general, native soils will be suitable for native plants since they evolved together, even if your native soils are clayey and you find soil guidance that says a plant needs well-drained soils. In the experience of many, clays are acceptable as long as the seasonal and/or year-round groundwater table isn’t too high. Having said this, there are some exceptions. Sometimes past construction has already disturbed or replaced soils with structural (rocky) fill. Compost amendment and mycorrhizal treatment of any soil can be beneficial for plant establishment.

     


    Structure Protection

    Are both these statements true?

    1.  In a large storm or in the case of a clogging failure, when water flows over the berm and/or low point of the facility, it will NOT damage any structures downhill

         AND

    2.  In a large storm or in the case of a clogging failure, water will NOT back up to flood nearby uphill structures.

    Yes     |     No    

     

    Even when horizontal setback and vertical separation criteria are met, a rain garden could be placed in such a way that damage to a house or other structure is possible. “A” in the graphic above illustrates the first question of whether water may flow downhill to damage a structure. “B” illustrates how finish grades could cause water to back up against a structure and cause damage.

     

    Both conditions must be true to answer Yes. If only one condition is met, answer No.

    Answer No if your site looks like either of the two graphics in A or B or if your LID facilities will drain over a public sidewalk. A No response means you need an area drain or similar overflow structure, which costs more to construct and maintain, so, consider alternative locations where both criteria can be met, although this may not be possible to avoid. Stormwater facilities that might drain over public sidewalks will always need an area drain.

    The way a site slopes (retrofit) or the way it will be sloped (development or redevelopment where sites will be re-graded) will impact the answer to this question. For instance, a rain garden located behind a house where the house is downhill of the rain garden  -- even if the rain garden is located 10’ from the house and meets other setback requirements – may flow down the slope and into the house during a large storm. In this and other possible cases, the answer is “No”.

     


    Final Step - Site is Unsuitable

    Floodplains, wetlands, riparian and buffer areas, habitat areas and septic systems are not suitable locations for any rain garden configuration. Consider using alternatives to rain gardens to manage stormwater.

     


    Final Step - LID 1.04 Lined filtration rain garden

    RAIN GARDEN DOWNLOADS

    • Fact Sheet: Includes general information on infiltration vs filtration type facilities, siting, design (storm size, routing, vegetation, mulch, etc.), construction, maintenance, cost considerations, & pollutant removal, & avoiding a UIC (Underground Injection Control).
    • Designer's Checklist: This is a designer and plans reviewer checklist from Seattle Public Utilities. (Their term for LID is "Natural Drainage Systems (NDS)" and their term for rain gardens is "Bioretention". This checklist should only be used by experienced designers. Not all guidance may be required to be met for the jurisdiction you're working in.
    • Rain Garden Sizing Calculator(s): Download an Excel sheet or use our online calculator (SBUH Type IA storm distribution only).
    • Finding Native Plants
    • Maintenance
    • Details as follows:
    Standard Detail # Detail Title
    (Click links in this column to preview a JPG of the detail now.)
    Detail formats available for download Additional sustainability & design considerations for modifying details Provides on-site water quality treatment? Provides regional water quality treatment?* Provides runoff reduction/ peak flow attenuation? For use in clay soils?** Is this a UIC***
    (Under-ground Injection Control)?
    LID 1.04 Lined Filtration Rain Garden DWG PDF JPG PDF Y N N Y N
    Download additional details including flow chart & abbreviations

     

     


    Protect Groundwater Resources

    To ensure adequate water quality treatment, healthy soil infiltrating not too fast and not too slow is needed for a depth of 18”. When the infiltration rate of your native soil exceeds 12 inches/hour, groundwater resources may be at risk, so native soils should be amended or replaced for a depth of 18”. Amending soils to drain slower can be tricky and potentially expensive. Many designers send a sample of the native soil to a laboratory and request a “recipe” of what to mix in and in what quantities. A more cost-effective approach to lab testing is to replace the first 18” of native soil with an engineered soil mix. (See “Amended Planting Soil for specifications on materials, mixing and placement.)

     

    Next »

     

    Amended Planting Soil Specifications

    Amended planting soil (aka engineered soil, 3-way mix, bioretention soil mix) is a mix of loamy soil, gravelly sand, and compost. There are a number of landscape material suppliers in Oregon that can provide you with a suitable amended planting soil (aka 3-way mix, bioretention soil mix). If your supplier has a mix that meets the City of Portland’s requirements, this mix will be equivalent to the mix that meets the specifications below. If your supplier does not have a mix that meets the City of Portland’s requirements, share the following specifications with your supplier to see if they have an equivalent product.

    Compost

    Care should be taken to ensure that compost is clean and free of weeds, pollutants, or other deleterious materials that may impact plant health and water quality.

    Organic compost should have the following properties:

    • Weed seed and pollutant free.
    • 100% should pass a 1/2-inch screen.
    • pH between 5.5 and 7.0. If the pH isn't quite right, it may be lowered by adding iron sulfate and sulfur or raised by adding lime or recycled, ground gypsum board.
    • Carbon nitrogen ratio of 35:1.
    • Organic matter content between 40 and 50 percent.
    • Fully composed. Earthy is good. Avoid compost that smells like ammonia.

    Organic compost may consist of the following:

    • Mushroom Compost. The used bedding material from commercial mushroom production.
    • US Compost Council Seal of Testing Assured (STA) compost. Find a participating supplier near you. The STA program is no guarantee of quality, only that the compost has been tested and those test results are available for the designer’s review.

    Organic compost may NOT be:

    • Composted Yard Debris. Excessive pollutants, mostly herbicides, pesticides, and fertilizers, have historically been found in these materials. “Cides” can kill beneficial soil life, reduce stormwater benefits, and increase maintenance.
    • Peat Moss. Peat moss is extracted from wetlands; this has negative impacts on the watershed from which the peat moss was removed.

    Gravelly Sand

    Gravelly sand should be free of organic material, contaminants, and hazardous materials, and should conform to the following gradation, which you can compare against the gradation provided by your quarry’s material:

    U.S. Sieve Size Percent Passing
    2-inch 100
    3/4-inch 70-100
    1/4-inch 50-80
    No. 40 15-40
    No. 200 0-3

    Mixing

    Mix soil and amendments to a homogeneous (i.e. all the same) consistency. Do not mix compost, sand, and native soil in the rain or wet conditions. Even in dry weather, soils and amendments themselves should not be overly wet.

    Storage

    Store stockpiles of organic soil mix in a manner that prevents them from becoming wet from rain, stormwater runoff, or other sources of water, or contaminated by fine soil or other undesirable materials. All stockpiles of mixed soil material should be protected and covered.

    Placement

    Place amended soil mix in thickness (i.e. lifts) between 9 and 12 inches in loose thickness. Spray water over the entire lift to accelerate settlement. After all lifts have been placed, grade soil to finish grades as specified on the plans and spray a final time to ensure that soil will not slump to an unacceptable finished grade after the first few rainfall events. Do not over compact soil mix with mechanical equipment after placement; following the construction steps above, soils have already been water compacted.

    Engineered Soil Mix

    Engineered Soil Mix (aka 3-way mix or bioretention soil mix) should have the following properties:

    • Free of contaminants & hazardous materials
    • 60% Loamy sand
    • 40% organic compost
    • Organic content matter from 8-10% by weight
    • Cation exchange capacity (CEC) greater than 5 milliequivalents/100 grams of dry soil
    • 2 – 5% mineral fines
    • Conform to the following gradation:
    U.S. Sieve Size Percent Passing
    3/8-inch 100
    #4 95-100
    #10 75-90
    #40 25-40
    #100 4-10
    #200 2-5
    • Minimum long-term hydraulic conductivity of 1 inch/hour per ASTM D2434 at 85% compaction per ASTM D2668
    • Meet specifications above for organic compost, mixing, storage, & placement.

    Post-Construction Facility Infiltration Testing

    To test a recently constructed or existing bioretention facility:

    1.  Wet the surface of the rain garden with a sprinkler or hose until saturated.

    • Small rain gardens or cells separated by check dams (<100 square-feet in surface) area can be tested full-scale.
    • Large rain gardens, vegetated filter strips and swales can utilize isolated falling head tests (minimum 2 per 100 square- feet of area). For how to perform a falling head test, see “The Oregon Rain Garden Guide" under Step 3: Assess Soil.

    2.  Fill the testing area to a depth of 4-inches and track the time it takes to completely draw down.

    3.  Repeat test 3 times. If the water in any of the tests fails to draw down in less than an hour (i.e. infiltration rate = 4 inches/hour), add compost and gravelly sand to the mix and re-till. (If the facility is existing, remove plants before tilling soil, set aside, mix and re-till, then replace plants.)

    4.  Repeat this procedure until favorable test results are achieved.

     


    Structure Protection

    Are both these statements true?

    1.  In a large storm or in the case of a clogging failure, when water flows over the berm and/or low point of the facility, it will NOT damage any structures downhill

           AND

      2.  In a large storm or in the case of a clogging failure, water will NOT back up to flood nearby uphill structures.

      Yes     |     No   

       

      Even when horizontal setback and vertical separation criteria are met, a rain garden could be placed in such a way that damage to a house or other structure is possible. “A” in the graphic above illustrates the first question of whether water may flow downhill to damage a structure. “B” illustrates how finish grades could cause water to back up against a structure and cause damage.

       

      Both conditions must be true to answer Yes. If only one condition is met, answer No.

      A No response means you need an area drain or similar overflow structure, which costs more to construct and maintain, so, consider alternative locations where both criteria can be met, although this may not be possible to avoid. Stormwater facilities that might drain over public sidewalks will always need an area drain.

      The way a site slopes (retrofit) or the way it will be sloped (development or redevelopment where sites will be re-graded) will impact the answer to this question. For instance, a rain garden located behind a house where the house is downhill of the rain garden  -- even if the rain garden is located 10’ from the house and meets other setback requirements – may flow down the slope and into the house during a large storm. In this and other possible cases, the answer is “No”.

       


      Final Step – LID 1.06 Infiltration Rain Garden with Planting Soil

      RAIN GARDEN DOWNLOADS

      • Fact Sheet: Includes general information on infiltration vs filtration type facilities, siting, design (storm size, routing, vegetation, mulch, etc.), construction, maintenance, cost considerations, & pollutant removal, & avoiding a UIC (Underground Injection Control).
      • Designer's Checklist: This is a designer and plans reviewer checklist from Seattle Public Utilities. (Their term for LID is "Natural Drainage Systems (NDS)" and their term for rain gardens is "Bioretention". This checklist should only be used by experienced designers. Not all guidance may be required to be met for the jurisdiction you're working in.
      • Rain Garden Sizing Calculator(s): Download an Excel sheet or use our online calculator (SBUH Type IA storm distribution only).
      • Finding Native Plants
      • Maintenance
      • Details as follows:
      Standard Detail # Detail Title
      (Click links in this column to preview a JPG of the detail now.)
      Detail formats available for download Additional sustainability & design considerations for modifying details Provides on-site water quality treatment? Provides regional water quality treatment?* Provides runoff reduction/ peak flow attenuation? For use in clay soils?** Is this a UIC***
      (Under-ground Injection Control)?
      LID 1.06

      Infiltration Rain Garden with Planting Soil

      DWG PDF JPG PDF Y Y Y Y N
      Download additional details including flow chart & abbreviations

       


      Final Step - LID 1.03 Infiltration Rain Garden with Planting Soil and Overflow Structure

      RAIN GARDEN DOWNLOADS

      • Fact Sheet: Includes general information on infiltration vs filtration type facilities, siting, design (storm size, routing, vegetation, mulch, etc.), construction, maintenance, cost considerations, & pollutant removal, & avoiding a UIC (Underground Injection Control).
      • Designer's Checklist: This is a designer and plans reviewer checklist from Seattle Public Utilities. (Their term for LID is "Natural Drainage Systems (NDS)" and their term for rain gardens is "Bioretention". This checklist should only be used by experienced designers. Not all guidance may be required to be met for the jurisdiction you're working in.
      • Rain Garden Sizing Calculator(s): Download an Excel sheet or use our online calculator (SBUH Type IA storm distribution only).
      • Finding Native Plants
      • Maintenance
      • Details as follows:
      Standard Detail # Detail Title
      (Click links in this column to preview a JPG of the detail now.)
      Detail formats available for download Additional sustainability & design considerations for modifying details Provides on-site water quality treatment? Provides regional water quality treatment?* Provides runoff reduction/ peak flow attenuation? For use in clay soils?** Is this a UIC***
      (Under-ground Injection Control)?
      LID 1.03 Infiltration Rain Garden with Planting Soil and Overflow Structure DWG PDF JPG PDF Y Y Y Y N
      Download additional details including flow chart & abbreviations

       

      Slow Soils

      Is over-excavation to a soil with an adequate infiltration rate possible so that the rain garden can be sized to drain within 30 hours?

      Yes     |     No

       

      Many regions of the Willamette Valley, even though surface soils are clay, are underlain by a faster draining gravelly soil. The depth to this soil layer varies. Where this condition is present and excavation to this layer can be achieved in a cost effective fashion and area for a rain garden or stormwater planter is limited, you may choose to replace the slower draining surface soils with an engineered soil mix. This approach could significantly reduce the area needed to infiltrate the required design storm. The design infiltration rate should be based on the slowest infiltrating soil that runoff will pass through. In the example shown here, that would be the “Slower” rate of the engineered soil mix. This rate may be obtained from laboratory testing per guidance under heading “2.2 Phase Two” in the technical memorandum “Bioretention Soil Mix Review and Recommendations for Western Washington”, published January 2009.

       


      Final Step - LID 1.05 Filtration rain garden without an impermeable liner

      RAIN GARDEN DOWNLOADS

      • Fact Sheet: Includes general information on infiltration vs filtration type facilities, siting, design (storm size, routing, vegetation, mulch, etc.), construction, maintenance, cost considerations, & pollutant removal, & avoiding a UIC (Underground Injection Control).
      • Designer's Checklist: This is a designer and plans reviewer checklist from Seattle Public Utilities. (Their term for LID is "Natural Drainage Systems (NDS)" and their term for rain gardens is "Bioretention". This checklist should only be used by experienced designers. Not all guidance may be required to be met for the jurisdiction you're working in.
      • Rain Garden Sizing Calculator(s): Download an Excel sheet or use our online calculator (SBUH Type IA storm distribution only).
      • Finding Native Plants
      • Maintenance
      • Details as follows:
      Standard Detail # Detail Title
      (Click links in this column to preview a JPG of the detail now.)
      Detail formats available for download Additional sustainability & design considerations for modifying details Provides on-site water quality treatment? Provides regional water quality treatment?* Provides runoff reduction/ peak flow attenuation? For use in clay soils?** Is this a UIC***
      (Under-ground Injection Control)?
      LID 1.05 Unlined Filtration Rain Garden DWG PDF JPG PDF Y Maybe Maybe Y N
      Download additional details including flow chart & abbreviations

       

       


      Final Step - LID 1.02 Infiltration Rain Garden with Overflow Structure

      RAIN GARDEN DOWNLOADS

      • Fact Sheet: Includes general information on infiltration vs filtration type facilities, siting, design (storm size, routing, vegetation, mulch, etc.), construction, maintenance, cost considerations, & pollutant removal, & avoiding a UIC (Underground Injection Control).
      • Designer's Checklist: This is a designer and plans reviewer checklist from Seattle Public Utilities. (Their term for LID is "Natural Drainage Systems (NDS)" and their term for rain gardens is "Bioretention". This checklist should only be used by experienced designers. Not all guidance may be required to be met for the jurisdiction you're working in.
      • Rain Garden Sizing Calculator(s): Download an Excel sheet or use our online calculator (SBUH Type IA storm distribution only).
      • Finding Native Plants
      • Maintenance
      • Details as follows:
      Standard Detail # Detail Title
      (Click links in this column to preview a JPG of the detail now.)
      Detail formats available for download Additional sustainability & design considerations for modifying details Provides on-site water quality treatment? Provides regional water quality treatment?* Provides runoff reduction/ peak flow attenuation? For use in clay soils?** Is this a UIC***
      (Under-ground Injection Control)?
      LID 1.02 Simple Infiltration Rain Garden with Overflow Structure DWG PDF JPG PDF Y Y Y Y N
      Download additional details including flow chart & abbreviations

       

       


      Final Step - LID 1.01 Infiltration Rain Garden

      RAIN GARDEN DOWNLOADS

       

      • Fact Sheet: Includes general information on infiltration vs filtration type facilities, siting, design (storm size, routing, vegetation, mulch, etc.), construction, maintenance, cost considerations, & pollutant removal, & avoiding a UIC (Underground Injection Control).
      • Designer's Checklist: This is a designer and plans reviewer checklist from Seattle Public Utilities. (Their term for LID is "Natural Drainage Systems (NDS)" and their term for rain gardens is "Bioretention". This checklist should only be used by experienced designers. Not all guidance may be required to be met for the jurisdiction you're working in.
      • Rain Garden Sizing Calculator(s): Download an Excel sheet or use our online calculator (SBUH Type IA storm distribution only).
      • Finding Native Plants
      • Maintenance
      • Details as follows:
      Standard Detail # Detail Title
      (Click links in this column to preview a JPG of the detail now.)
      Detail formats available for download Additional sustainability & design considerations for modifying details Provides on-site water quality treatment? Provides regional water quality treatment?* Provides runoff reduction/ peak flow attenuation? For use in clay soils?** Is this a UIC***
      (Under-ground Injection Control)?
      LID 1.01 Simple Infiltration Rain Garden DWG PDF JPG PDF Y Y Y Y N
      Download additional details including flow chart & abbreviations

      Support for this project, content, and tools were made possible through the USDA Forest Service Western Competitive Grant Project.