Risk Characterization from Sediment Released During Dredging Operations
Type:
Presented during:
WODCON XXII - Enhance the Harmony between Dredging and Ecology
Authors:
Joseph Z. Gailani, Tahirih C. Lackey, Burton Suedel, David B. King, Deborah S. Nelson, Sung-Chan Kim, John McManus, Robert H. Richmond, and Duncan B. Bryant
Abstract
"Dredging often occurs near sensitive habitat. Risk characterization is an integral part of dredging regulatory approval and sound dredging practice. This paper describes a risk characterization framework for evaluating risk associated with sediment released during dredging operations. Sediment release risk assessment is required to balance dredging project objectives, environmental concerns, and costs; however, no risk assessment framework for this specific need currently exists. To address this need, a risk assessment framework was developed that utilizes multiple sources of engineering and science-based information to assess and manage risk for navigation dredging projects where the environmental effects from sediments suspended during dredging are of concern. The framework includes five components: 1) problem formulation, 2) exposure assessment, 3) effects assessment, 4) risk characterization, and 5) risk management. The framework employs engineering and modeling data to estimate dredge plume exposure, and science-based data to assess effects on aquatic receptors. If unacceptable risks are predicted, these risks can be reduced by managing exposure through the use of engineering and/or operational controls. The framework is designed to assist risk practitioners in deciding how to combine multiple lines of evidence for predicting outcomes of the environmental effects inquiries posed by decision makers and stakeholders. The framework provides a systematic approach for characterizing the risk of dredging projects, thus providing a foundation for effective dredged material management decision making. A case study is used to demonstrate the framework. The case study involves risk associated with sediment released during a proposed channel deepening project near coral resources at Apra Harbor, Guam. The case study includes numerical modeling of sediment transport under two different dredging scenarios and comparison of modeled releases to coral effects data for suspended sediments and sedimentation. While the case study is associated with risk to coral, the same framework provides a robust method to evaluate risk to other sensitive species, such as fish larvae or submerged aquatic vegetation"
Keywords: Dredging, risk framework, coral, ecological dredging, sensitive habitat