Assistant Secretary of the Army for Civil Works announces Regulatory Guidance Letter 18-01

By U.S. ArmyOctober 2, 2018

Work to remove West Silver Wetland Dam to improve stream habitat at Fort McCoy
A crew with the Wisconsin Department of Natural Resources works to remove an old dam along Silver Creek on July 18, 2017, at Fort McCoy, Wis. The removal of the old dam, built in 1952, is aimed at improving stream flow and habitat. The project is coo... (Photo Credit: U.S. Army) VIEW ORIGINAL

WASHINGTON (Oct. 02, 2018) - The Assistant Secretary of the Army for Civil Works announced today the signing of the U.S. Army Corps of Engineers (USACE) Regulatory Guidance Letter (RGL) 18-01, (Determination of Compensatory Mitigation Credits for the Removal of Obsolete Dams and Other Structures from Rivers and Streams).

RGL 18-01 provides guidance to USACE district engineers on the factors they should consider when determining the amount of mitigation credit generated from the removal of obsolete dams or other structures to restore rivers and streams. The guidance was developed through collaboration with a number of agencies, including the Environmental Protection Agency, and reflects practice over the last two decades as well as emerging science.

"This guidance is substantial for our nation because it will facilitate the removal of obsolete structures that can present public safety hazards and will enable the restoration of vital stream functions," said Mr. R.D. James, the Assistant Secretary of the Army for Civil Works. "These functions include more natural river flows, increased connectivity within the stream network, and the re-establishment of migratory routes and habitats for aquatic organisms."

There are an estimated 1 to 2 million small dams in the United States. Many of these dams were built in the 19th century and have deteriorated, been abandoned, or otherwise no longer fulfill their intended purpose but continue to impair the structure, functions and dynamics of streams.

Dams and other obstructions adversely affect stream functions by altering the stream's hydrologic, sediment transport and nutrient cycling processes. Removing dams and other obstructions can, to a substantial degree, reverse the impacts of those structures on riverine systems and provide environmental benefits while concurrently addressing public safety concerns associated with aging infrastructure.

USACE has the authority to issue permits under Section 404 of the Clean Water Act and Sections 9 and 10 of the Rivers and Harbors Act of 1899. Under its regulations, USACE may require that these permits include compensatory mitigation to offset unavoidable impacts to waters of the United States. Compensatory mitigation can be provided through restoration activities that improve the physical, chemical and biological processes performed by rivers and streams with the goal of returning the natural/historic functions performed by those rivers and streams.

The removal of obsolete dams and other obsolete in-stream structures can be an effective approach to restoring river and stream structure, functions and dynamics. These restoration activities may be performed by mitigation banks and in-lieu fee programs to generate mitigation credits that can be sold or transferred to permittees to fulfill compensatory mitigation requirements in permits. Restoration activities can also be conducted as permittee-responsible mitigation.

RGL 18-01 guidance covers aspects of these restoration activities that are not explicitly addressed by the compensatory mitigation regulations. It includes considerations for quantifying mitigation credits and recommendations for the treatment of losses of wetland that may result from the removal of dams and other structures. The number of mitigation credits will be determined on a case-by-case basis after evaluating a mitigation proposal involving the removal of an obsolete dam or other structure and will vary by project site.

For more information on compensatory mitigation, please visit the USACE Regulatory webpage at

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