Adaptation of a Risk-Based Framework for Evaluating Indirect Effects of Dredging on Sensitive Habitats near Federal Navigation Channels: An Application of the Framework to Coral Reefs at Honolulu Harbor, Hawai'i.

In major harbors and ports in the United States and its territories, the U.S. Army Corps of Engineers maintains Federal navigation channels in proximity to coral reefs (e.g., Honolulu Harbor, HI; Miami Harbor, FL; Apra Harbor, Guam) and other sensitive habitats. To effectively predict potential adverse impacts from dredging activities near these sensitive habitats, a holistic approach to improve understanding of the pressures on these habitats is needed to foster a more complete prediction of risk drivers. To achieve this, risk-based frameworks that account for the full range of natural and anthropogenic impacts need to be adapted and applied specifically for assessing and managing indirect dredging impacts on sensitive environments. In this paper we address this need by incorporating a Drivers-Pressures-Stressors-Condition-Response (DPSCR 4 ) conceptual framework to broaden a comprehensive conceptual model of the coupled human-ecological system. To help understand these complex interactions, DPSCR 4 was applied to evaluate dredging and other unrelated environmental pressures (e.g., terrestrial runoff) in a proof-of-concept dredging project in Honolulu Harbor, HI, USA, with a focus on the indirect effects of dredge plumes. Particle tracking models and risk-based tools were used to evaluate sediment resuspended during a hypothetical mechanical dredging activity near sensitive coral habitats. Stoplight indicators were developed to predict indirect sediment plume impacts on coral and then compared to exposure modeling results. The strengths and limitations of the approach are presented and the incorporation of the risk-framework into environmental management decisions is discussed.