Abstract
Cape Wind Energy, LLC has proposed to build a wind turbine farm on Horseshoe Shoal in Nantucket Sound. This site has been evaluated in a previous study (Swanson and Isaji, 2005). An alternative site, 9 km (5.6 mi) southwest of Tucknernuck Island, is also being evaluated for the purposes of comparison and is the subject of this report. The project will consist of 130 wind turbine generators (WTG), an electric service platform (ESP) and a series of cables connecting the WTGs to the ESP and a pair of cables from the ESP to shore at Yarmouth. The cables are to be buried using a jetting technique whereby pressurized seawater is jetted below the seabed to fluidize the sediments along the cable route. The cable then sinks of its own weight through the fluidized sediments and is buried as the sediment returns to its pre jetted condition.
Questons have been raised during regulatory agency review concerning the environmental effects of the suspended sediment injected into the water column above the cable route during the jetting process. Specifically, questions concerning the concentration of suspended sediment and the subsequent deposition on the seabed as well as the spatial extent and duration that these processes last have been raised.
Cape Wind Energy, LLC contracted with Applied Science Associates, Inc. to perform a modeling study to estimate the resulting suspended sediment and deposition from the cable burial process for the cables connecting the WTGs to the ESP at the alternative site. The study used two models: HYDROMAP to calculate currents, and SSFATE to calculate suspended sediments in the water column and bottom deposition resulting from jetting operations.