DOCUMENT HISTORY AND STATUS Revision Date issued Author(s) Reviewed by Approved by Date approved Revision type A 20/6/13 C Bailey, M Yeates M Huber M Huber 21/6/13 Draft 0 21/6/13 C Bailey, M Yeates M Huber M Huber 21/6/13 Draft for client comments 1 28/6/13 C Bailey, M Yeates M Yeates M Yeates 28/6/13 Final 1.1 3/7/13 C Bailey, M Yeates M Yeates M Yeates 3/7/13 Revised Final 1.2 10/7/13 C Bailey, M Yeates M Yeates M Yeates 10/7/13 Revised Final 1.3 15/7/13 C Bailey, M Yeates M Yeates M Yeates 15/7/13 Revised Final ACRONYMS RELIANCE STATEMENT 1 2 Beneficial Reuse and Land Disposal of Dredge Material 2 Water Quality Monitoring Framework 3 Ocean Placement of Dredge Material and Long-term Sediment Migration 4 6 Purpose and Scope 7 What Does "Long-term" Mean? 8 9 15 Monitoring Methodologies and Parameters 19 Trigger Values and Management Responses 20 22 Bed Shear-stress Modelling 22 Identification of Alternative Sites for Dredge Material Placement at Sea 25 Sediment Plume and Migration Modelling 27 Sensitive Receptors Risk Assessment 33 41
The report aims to capture key messages and conclusions regarding dredge material management in the region that have resulted from the study. This report also identifies knowledge gaps and additional research that would further increase understanding of risks and potential management arrangements associated with dredge material placement in the World Heritage Area. What Does "Long-term" Mean? Consideration of time scale is essential at all levels of risk and impact assessment and environmental management. In this study, carried through to this report, "long-term" is applied on two different time scales, which may be thought of as strategic and technical: Strategic: The overall context of the study is aligned to the Strategic Assessment, i.e. the study has adopted a 25-year outlook. This 25-year perspective was adopted in consultation with the GBRMPA and port operators. The 25-year time frame has been used to develop outlooks for capital and maintenance dredging needs, and consequently the most relevant dredge material placement scenarios for investigation. SKM recognises that ports are expected to continue to operate on longer time scales of 50 years and beyond. It was not practical, however, to anticipate dredging requirements and other port-associated coastal developments on such a long time scale. Technical: The technical outputs of the study revolve around hydrodynamic modelling of the movement of dredge sediments. In this context, "long-term" refers to modelling over a period of 12 months from the commencement of the hypothetical placement scenario. This is the first study to incorporate the influence of large-scale currents to model dredge material movement over 12 months. Modelling dredge material movement on the 25-year strategic time scale is far beyond current technical capabilities.
Table 1. Summary of port-specific options for placement of dredge material on land. Disposal Option Port of Gladstone Rosslyn Bay State Boat Harbour Port of Hay Point Port of Abbot Point Port of Townsville Port of Cairns Land reclamation Creation of land in an area that is either permanently or partially submerged Y Mixture of clay, silt, sand, gravel N Y Rock only Y Sand Y Sand silt clay N Construction fill (supra-tidal) Material used for fill purposes above the spring high tide mark for load bearing purposes Y Mixture of clay, silt, sand, gravel N Y Rock only Y Sand N Y Mine rehabilitation Material used to fill disused/ closed mines N N N N N N Shore protection/Erosion control Material used for engineered purposes of hard structures, seawalls N N N N N N Beach nourishment Material used for replenishing beaches that are prone to erosion N N N Y Sand N N Construction material Material used to produce fill Y Gravel and N N Y N N