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Clean Water Act Guidance

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This information was developed to provide WSDOT staff and consultants with up-to-date information on how the Supreme court's decisions in the consolidated Rapanos v. United States and Carabell v. United States cases (hereafter called Rapanos) are affecting the permitting of transportation projects.


Clean Water Act Jurisdiction Following the Rapanos Decision  


In June 2007, the United States Army Corps of Engineers (Corps) and the Environmental Protection Agency (EPA) issued a joint memorandum (pdf, 1.1 mb) that clarifies Clean Water Act (CWA) jurisdiction following the Supreme Court’s decision in the Rapanos case. Guidance in the memorandum identifies situations where a developer may need to obtain a CWA Section 404 permit before completing work in wetlands, tributaries, or other waters of the United States.

The Rapanos decision did not change CWA jurisdiction for traditionally navigable waters (TNW) of the United States. These waters include rivers, waters used for interstate or foreign commerce, interstate wetlands, tributaries, and wetlands adjacent to TNWs. By definition, adjacent wetlands may have a continuous surface water connection to TNWs, but may also be separated from these waters by a berm or dike.

With the Rapanos decision, CWA jurisdiction may also be extended to waters that are not TNWs of the United States if either of the following two standards are met.

  1. The first standard, based on the plurality opinion written by Justice Scalia, extends regulatory jurisdiction to non-navigable tributaries of TNWs that are relatively permanent (tributaries flow year-round or have continuous flow at least seasonally; e.g., typically 3 months) and wetlands that directly abut (there is a surface connection) these waters.
  2. The second standard, based on the concurring opinion of Justice Kennedy, requires a case-by-case determination (“significant nexus” analysis) for non-relatively permanent tributaries and adjacent wetlands that have characteristics that may significantly affect TNWs.

Jurisdiction under Section 404 of the CWA and the Rapanos Ruling

With the Rapanos ruling, the following waters of the United States are jurisdictional under Section 404 of the CWA:

  • TNWs, including territorial seas 
  • Wetlands adjacent to TNWs
  • Relatively permanent waters that flow directly or indirectly into TNWs
  • Wetlands directly abutting relatively permanent waters that flow directly or indirectly into TNWs 
  • Impoundments of jurisdictional waters

Where there is a significant nexus, CWA jurisdiction may extend to the following waters:

  • Non-relatively permanent waters that flow directly or indirectly into TNWs 
  • Wetlands adjacent to but not directly abutting relatively permanent waters that flow directly or indirectly into TNWs 
  • Wetlands adjacent to non-relatively permanent waters that flow directly or indirectly into TNWs 
  • Isolated (interstate or intrastate) waters, including isolated wetlands

Regulatory jurisdiction does not extend to swales or erosional features (e.g., gullies, small washes with low volume, infrequent or short duration flow). Upland ditches (including roadside ditches) excavated wholly in and draining only uplands are generally not considered jurisdictional unless there is a surface water connection between an adjacent wetland and a TNW. This connection creates the potential for a significant nexus.

Implementing the Rapanos Guidance for WSDOT Projects  

Ditch Sections

Ditch sections pose unique problems under the Rapanos guidance when determining both relatively permanent flows and presence of a significant nexus.

The guidance states, “Upland ditches (including roadside ditches) that do not carry relatively permanent flow generally do not fall under the jurisdiction of the Corps.” The key factor in this statement is “generally.”

In most situations, it is not possible to document whether a ditch or channel within the project area has relatively permanent flows (continuous flows for at least three months). For WSDOT projects, the presence of an ordinary high water mark (OHWM) should be used as a baseline to establish the potential of relatively permanent flows and the need to contact the Corps for a jurisdictional determination under Standard 1 (non-navigable tributary). The OHWM can be determined by defined bed and banks, or other physical indicators of flow may include such as shelving, wracking, water staining, sediment sorting and scour.

Significant nexus (Standard 2 of the Rapanos decision) requires a hydrological (e.g., in terms of volume, duration, and frequency of flow) or ecological connection that has a substantial cumulative effect on the physical, chemical, or biological integrity of TNWs. Although regulatory agencies continue to use the presence of a reliable OHWM with a defined bed and bank as a jurisdictional criterion for specific tributaries, other factors must be considered. These factors include significance of the tributary and associated wetlands for downstream water quality, flood control, aquatic habitat, or other ecological services.

It is important to note that the presence of an OHWM within a ditch section does not necessarily mean there is a significant nexus. It does mean that further documentation should be gathered to establish the flows and connectivity to other waters.

In some situations, such as on a steep slope or in highly erodible soils, a scour mark may not represent relatively permanent flows. In these cases, other indicators should be used to verify the OHWM. If there is a break in the OHWM within a ditch line, it should be noted in the information provided to the Corps. The limits of CWA jurisdiction in non-tidal waters are determined as follows (CFR § 328.4(c)(1)): 

  1. In the absence of adjacent wetlands, the jurisdiction extends to the OHWM.
  2. When adjacent wetlands are present, the jurisdiction extends beyond the OHWM to the limit of the adjacent wetlands.
  3. When the water of the United States consists only of wetlands the jurisdiction extends to the limit of the wetland.

In order to maintain consistency with both the criteria for limits of CWA jurisdiction published in the Federal Register and the Corps’ guidance related to the Rapanos ruling, WSDOT will conduct field assessments of jurisdictional ditches in the following manner:

  • For ditches that drain waters of the United States (including wetlands), or that are in close proximity where overflows may enter the ditch, there is the potential of a significant nexus WSDOT does not make jurisdictional calls, but can recommend a jurisdictional determination. The Corps is responsible for the final decision.  Figure 1 (pdf, 18kb), Figure 2 (pdf, 24kb), Figure 3 (pdf, 19kb), and Figure 4 (pdf, 18kb). 
  • WSDOT staff will walk ditch lines upgradient from a TNW until there is no evidence of flowing water, no scour marks or OHWM or the ditch no longer connects to downstream wetlands or TNWs. The absence of these features suggests that water is infiltrating, evaporating, experiencing vegetative uptake, or being dispersed. Lack of a scour mark does not necessarily mean that flow is insufficient to create a connection with TNWs. Information on this break should be noted in the submittal package to the Corps..


Two terms, adjacent and abutting, are used in the Rapanos guidance to describe the location of a wetland with respect to other waters of the United States, including tributaries.

Adjacent: Adjacent means bordering, contiguous, or neighboring. Adjacent wetlands may have a continuous surface connection to TNWs, but may also be separated from these waters by man-made dikes or barriers, natural river berms, beach dunes, or similar features. By definition, a continuous surface water connection is not required to establish adjacency. 

Abutting: Wetlands that provide a continuous surface connection to relatively permanent waters that flow directly or indirectly into TNWs are abutting. The wetland boundary must interface with the OHWM of the tributary. If the wetland boundary does not abut the OHWM of the tributary, the wetland is adjacent. Abutting wetlands are not separated from tributaries by uplands, berms, dikes, or similar features. It is important to note, a continuous surface connection does not require surface water to be continuously present between the wetland and tributary.

Wetlands adjacent to non-navigable tributaries that are not relatively permanent or wetlands that do not directly abut a relatively permanent non-navigable tributary may be jurisdictional if the Corps determines they meet the significant nexus criterion (Figure 3 (pdf, 19kb). Information listed in points two and three below will aid in the evaluation of a significant nexus.

What Information Does the Corps Need to Make a Jurisdictional Determination?

In order for the Corps to make a jurisdictional determination (JD) they must fill out a JD work sheet. We are not required to fill out the form, but the Corps will need sufficient information to complete the applicable parts of the JD form.  

The Corps has provided a drawing (pdf, 64kb) that shows the relationship of water features to navigable waters and how they relate to the Rapanos requirements.

The following information should be included in the Corps submittal:

Plan sheets and/or aerial photographs that show the relationship between*

  • Ditches
  • Channels
  • Wetlands
  • Tributaries
  • Traditional navigable waters.

If possible, highlight and label the foot print of the project in red; wetlands, streams, TNWs, ditches with OHWMs and any other water feature in blue; and the roadway/structures in black. This will assist the Corps in understanding the relationship of ditches and other water bodies to TNWs

Providing the following information is not required, but may assist in the Corps in making a timely jurisdictional determination.

  1. Watershed and/or sub-basin characteristics
    • Volume, duration and frequency of flows (If known – check USGS)
    • Size of watershed
    • Average annual rainfall
    • Average annual winter snow pack
  2. Ecological characteristics
    • Ability of tributary and its adjacent wetlands to carry pollutants and/or floodwaters to TNWs.
    • Ability of tributary and its adjacent wetlands to provide aquatic habitat support
    • The ability for adjacent wetlands to trap and filter pollutants
    • The ability of adjacent wetlands to store floodwaters.
    • The ability of adjacent wetlands to improve water quality

* It is important to show the flow path between a water body (including wetlands and ditches) and navigable waters. This includes connectivity through culverts and pipes. For ditches that have a break in the OHWM indicators, make note of the break.

“WSDOT Rapanos Package” Examples   

Examples of project submittals to the Corps that address Rapanos:

Latest Rapanos Guidance Documents