A Process for Setting, Managing, and Monitoring Environmental Windows for Dredging Projects

TRB Special Report 262: A Process for Setting, Managing, and Monitoring Environmental Windows for Dredging Projects concludes that scientific information about risks to resources and technical options for reducing those risks was not being systematically incorporated into the dredging process. The process itself is complex and time-consuming because of the numerous federal and state agencies and interest groups involved. The committee recommended use of a broad-based decisionmaking process designed to engage stakeholders more effectively and to improve the scientific and technical basis for the decisions made.

Environmental windows are periods in which regulators have determined that the adverse impacts associated with dredging of waterways and disposal of the dredged materials can be reduced below critical thresholds, and dredging is therefore permitted. Conversely, seasonal restrictions are applied—dredging and disposal activities are prohibited —when the perceived increase in potential harm to aquatic resources is above critical thresholds. Since passage of the National Environmental Policy Act of 1969, resource agencies have requested environmental restrictions on dredging with increasing frequency. Today, more than 80 percent of federal contract dredging is subject to some type of restriction. At the request of the U.S. Army Corps of Engineers, TRB and the National Academies’ Ocean Studies Board convened a committee to address concerns about the decision-making process for setting environmental windows.

Windows are intuitively simple means of reducing risk to biological resources from stressors generated during dredging and disposal activities, including entrainment of fish eggs and larvae, resuspension of contaminated sediments, habitat loss, and collisions with marine animals. The use of windows as a management tool, however, can have significant cost implications for both the U.S. Army Corps of Engineers and the local sponsors of dredging projects, delay project deadlines, and increase risk to dredging personnel by shifting projects to periods of potentially inclement weather and sea states.