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Wetland Delineation and Assessment

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Hydric soil is one factor of wetlands.



Wetland Data Need

During Transportation Planning (pdf 312 kb) or Project Scoping (pdf 426 kb), it may be prudent to have field confirmation that wetlands are present or not in the potential project alternative alignments. Relying on the generalized information contained in the GIS Workbench may be insufficient to plan advance mitigation and the early stages of some projects. Please consult the WSDOT regional environmental office to determine whether a Wetland Inventory or Wetland Assessment report is appropriate. Spring and early summer are the ideal time of year for wetland field work. Early coordination with your environmental staff is important to get your work appropriately scheduled.

During the Construction phase (pdf 251 kb), at an early to mid-term point in the monitoring period, wetland mitigation sites are delineated to verify that the correct amount of compensation will be provided. A final wetland delineation is conducted at the end of the monitoring period to confirm the correct amount of mitigation has been provided.


Wetland Inventory

To perform a wetland inventory, a wetland biologist uses state and federal wetland delineation methods to determine if wetlands are present or absent in the given potential project impact area. If wetlands are present, the approximate locations are recorded but the boundaries are not surveyed. The WSDOT wetland biologist or qualified consultant prepares a memo that provides general information to assist planners to determine or compare project alternatives. This work can take from 20 hours for a small area with few wetlands to more than 60 hours for a large area. This estimate does not include survey work. (Procedure 300-a and Task 300-a) (pdf 41 kb).

Wetland Assessments

A Wetland Assessment includes detailed field evaluation of wetland boundaries (delineation), how easy the wetland would be to replace (rating), sometimes, what functions it performs, and buffer widths. A Wetland Assessment report:

Wetland Delineation

If approximate wetland locations are not sufficient, or more accuracy about the wetland boundaries is needed, a wetland delineation should be requested. This level of accuracy is appropriate at the beginning of the design and environmental review stage. This work can take from 80 hours for a small area with few wetlands to several months work by several delineators for a corridor.

If the project area expands into an area not evaluated by the wetland delineation field work, wetlands and buffers should be re-evaluated by a wetland expert to avoid unpermitted wetland activities or disturbance to the buffer of a nearby wetland.

To perform a wetland delineation, a wetland biologist follows the process outlined in Procedure 431-a and Task 431-a (pdf 47 kb), and:

  • Must be trained and have experience in wetland delineation.
  • Follows WSDOT Wetlands Guidance on Cultural Resources (pdf 9 kb) to determine if known or potential cultural resources are within the project area and works with cultural resources staff if historic sites are present or probable.
  • Fully completes data sheets (with clarifying comments as needed) so that a wetland reviewer can follow the thought-process and have enough information to concur with each decision.
  • Follows all WSDOT Delineation Guidance on specific delineation issues unique to roadways, and is encouraged to use other resources in the Delineation and Assessment Toolbox.

The Washington State Wetlands Identification and Delineation Manual (Ecology 1997), was repealed as of 14 March 2011. Check the wording of the local Critical Area Ordinance to see if it requires delineations using the state manual even if it has been repealed. If the wetland is isolated (pdf 45 kb), the Corps does not regulate it, but it is prudent to submit a Jurisdictional Determination form for their concurrence. Ecology regulates isolated wetlands, so a delineation report that includes isolated wetlands should be submitted to them.

Wetland Ratings

WSDOT uses the Department of Ecology’s Washington State Wetland Rating Systems to categorize wetlands based on their sensitivity to disturbance, significance, our ability to replace them, and the functions they provide. When determining which system to use, refer to the Boundary Between Eastern and Western Washington for the Wetland Rating System.

Note: In Oct. 2008, the Department of Ecology updated the above Rating System manuals with new WDFW priority habitat definitions. Use Version 2 of the ratings forms supplied by Ecology or the format-modified versions below. Annotated versions are also available from Ecology, but they do not include the WDFW priority habitat definitions.

WSDOT also applies any applicable county and city wetland rating systems defined in their Critical Areas Ordinances. Wetland Biologists must check local requirements. The Assessment toolbox contains additional ratings resources.

Wetland Functions

Executive Order EO 89-10, Protection of Wetlands, includes a no net loss goal that includes both area and function. A delineation provides the area of a wetland, and a functions assessment provides an evaluation of the functions the wetland provides. The Department of Ecology’s Washington State Wetland Rating System was developed to evaluate how difficult it would be to replace a wetland, and is required to determine the ratio to for replacement wetland area by many Critical Areas Ordinances. There are a number of full scale wetland functions assessment methods, but there are none that are both completely accepted in Washington, and practical for use in linear projects.

If a functions assessment is completed for the impacted wetland, it can be used to design replacement wetlands so that the same functions are provided. In order to evaluate if the mitigation site is providing the desired functions, the method used should be documented in the mitigation report so it can be used again at the end of the monitoring period.

Other Aquatic Habitats

Aquatic habitats or resources other than wetlands may be encountered on project sites and may also need to be assessed documented and permitted if impacted. Examples of other regulated aquatic habitats include:

Special training is required to delineate these habitats. For a list of staff available to regions to delineate other aquatic habitats, contact your Regional Environmental Coordinator, Regional Permit Coordinator, or Regional Biologist.

Wetland buffers

Buffers are defined by the Department of Ecology, but are regulated by local Critical Areas Ordinances. Ecology defines buffers in Wetlands in Washington State Volume 2: Guidance for Protecting and Managing Wetlands, (Appendix 8-C and Appendix 8-E). Ecology also provides guidance on buffer widths. Generally, buffers are:

  • the uplands [or wetlands] adjacent to an aquatic resource,
  • protect and maintain the functions and values of wetlands,
  • provide the terrestrial [or wetland] habitats for many species of wildlife,
  • can reduce impacts to the wetland from adjacent land uses.

How wide are wetland buffers?

WSDOT applies the corresponding buffer requirements from federal, state, and local governments to all wetlands identified within a project area based on each wetland's rating. Many local Critical Areas Ordinances have adopted the buffer widths suggested by Department of Ecology's guidance in Chapter 6.6 of Wetlands in Washington State.

How are buffers incorporated into the project?

Wetland biologists and consultants must follow WSDOT guidance on Delineating Wetlands and Buffers adjacent to road prisms (pdf 72 kb) and Buffers Across Roadways (pdf 19 kb). Wetland biologists inform the Project Design Team of:

  • The required buffer width of each delineated wetland within the project area
  • Any wetland buffers that extend into the project area, even though the wetland itself is located outside the project area and may not have been delineated.

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