In association with Swanson Environmental Associates and Power Engineers, IES was contracted by Mayflower Wind (MFW) to provide a sediment dispersion modeling assessment to evaluate potential impacts of the construction activities associated with an export cable installation for the MFW offshore wind farm. Mayflower Wind plans to add a second export transmission cable from the offshore wind farm to the former Brayton Point power station site in Sommerset, Mass. and wished to assess the potential impacts of the construction activities. The application included hydrodynamic modelling for current and tidal predictions along with sediment resuspension, transport, dispersion and deposition modelling. The results provided estimates of the maximum sediment concentrations in the water column as well as the deposition areal coverage and thickness of resettled sediments. The effort was performed in support of the development of the MFW’s offshore wind farm Construction and Operations Plan (COP) development.
A gas pipeline company, is proposing to expand its existing interstate natural gas pipeline system in Pennsylvania and New Jersey, and its existing offshore natural gas pipeline system in New Jersey and New York. The proposed project includes the installation of a 26-inch diameter pipeline to connect NJ to NY. The offshore portion of the pipeline will extend from Sayreville, NJ across Raritan Bay and Lower New York Bay to Rockaway, NY in the Atlantic Ocean.
The pipeline installation will require a range of dredging and burial techniques (e.g. clamshell dredging, jet trenching, and backfilling) each of which has the potential to produce seabed disturbances, suspended sediment plume formation, and smothering due to sedimentation. In addition, the dredging and burial activities are expected to cause the re-suspension of any contaminants that have deposited in the sediments over time. The sediments along the pipeline route have measured amounts of several metals and contaminants including mercury, silver, arsenic, nickel, lead, zinc, and PCBs.
The study included a detailed hydrodynamic calibration effort and a sediment transport and dispersion model application developed to assess potential environmental impacts of Project-related activities associated with seabed sediment disturbance and sediment resuspension. The modeling provided predictions of suspended sediment concentrations and deposition from a set of construction scenarios. The study also included an application of a contaminant transport model, and simulations, using the same calibrated hydrodynamic model output, to assess the potential maximum water column concentration of re-suspended contaminants, at the edge of a 500-ft dredging mixing zone at key locations along the route.
The Block Island Wind Farm was the first offshore wind farm to be built in US waters. As part of the permitting process, in the pre- Construction and Operations Plan (COP) period, the potential for impacts of resuspended sediments resulting from cable burial operations needed to be assessed. For this project, sediment dispersion modelling for the Block Island Wind Farm inter-array and export cable burial operations analysis for Deepwater Wind (DWW, now Orsted) was performed.
Model simulations of the circulation and transport, verified through current meter and tide gauge observations, were performed. The currents were used to develop model predicted sediment resuspension, water column concentrations and sediment deposition area coverage and thickness for the inter-array cable and export cable areas. Support for DWW with regulatory agencies and permit development was also provided.