General Restrictive Information for Green Infrastructure BMPs

Locate Restrictive Conditions

This page is intended to provide you with resources to help you identify conditions important when planning your site design and selecting green infrastructure BMPs. This is NOT intended to be a list of all the conditions that may affect the placement of GI BMPs; for these, refer individual Green Infrastructure BMP fact sheets.

Green Infrastructure and Important Site Constraints

Floodplains
Wetlands
Riparian Areas & Buffers
Habitat Areas
Septic Systems
Contaminated Soils & Groundwater
Landslides
Wellhead Protection Areas
Drinking Wells
Vertical Separation
Horizontal Setbacks

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, either recently (i.e. presence of a road, parking lot, fill/overburden, etc), 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. If you have a question:

  • 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", enter the address and click "Lookup". 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.
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