Technology Related Environmental Impacts
As the marine renewable energy sector matures and project developers move into permitting and implementing pilot and full scale technology deployments (specifically underwater turbine generating units), there is an increasing need for assessment of potential environmental effects. Currently, the Town of Edgartown, Massachusetts is poised to begin a pilot test of underwater tidal turbine technology in the near-shore waters of Martha’s Vineyard, specifically Muskeget Channel. Similarly, hydrokinetic pilot deployments are taking place in Maine and New York. CSP-SMAST scientists have been collecting a wide variety of data to characterize potential sites for hydrokinetic power generation throughout New England, with a key site in Muskeget Channel under study and development through the University of Massachusetts-Dartmouth Marine Renewable Energy Center (MREC) and in support of the Town of Edgartown. In addition to the physical measurements associated with energy generation potential, the CSP scientific team has been conducting studies related to the potential environmental effects of hydrokinetic turbine placement and operation. In addition to developing the baseline environmental/ecological condition of Muskeget Channel, specific studies focusing on on sediment transport, benthic animal communities, seagrasses, and changes in community structure associated with technology deployment are underway.
At present, understanding of the potential effects on the environment resulting from the operation of the turbines, specifically associated with the moving blades, remains little studied. Effects of blade strikes, shear stress, small scale turbulence, and exposure to cavitation on zooplankton is poorly understood in general and limited by the nearly complete lack of field data related to tidal energy generation. To determine the effects of tidal turbines on zooplankton plankton, ambient communities will be measured as they are carried by tidal currents into the turbines and after they emerge. Effect of the turbines will be gauged based upon direct observations of individuals for injury or mortality or changes in total numbers. Mortality will be evaluated based primarily on movement (motility or internal organs) and we will employ both microscopy and a new automated instrument for evaluating zooplankton viability developed under a NOAA grant (C. Taylor, WHOI).
This study is being completed in association with the UMASS Marine Renewable Energy Center (MREC). The investigation is currently planned to be conducted in Muskeget Channel where CSP scientists have already completed detailed surveys of the physical characteristics of a proposed site for tidal energy development, assuming a pilot tidal generating unit is installed and operational. Otherwise measurements must take place in Maine where an existing energy developer is undertaking field testing of its turbine generating technology. As necessary CSP scientists will mobilize to Maine to obtain and analyze the zooplankton samples. Should the study take place in Muskeget Channel, extensive research on ecosystem abundance and community structure of zooplankton populations in Nantucket Sound and Buzzards Bay conducted by SMAST scientists over the last decade will provide sufficient basis for evaluating the results of the Muskeget Channel study.
As the Town of Edgartown in Massachusetts moves towards permitting a pilot scale test of tidal generating technology, collection of data to answer questions pertaining to effects on the marine environment becomes critical. In that light, the CSP will be conducting field data collection on background acoustic characteristics of the Muskeget Channel tidal energy site. This study is being completed in association with the UMASS Marine Renewable Energy Center (MREC) which is in the process of establishing a marine renewable energy test bed in waters inclusive of Muskeget Channel. This study is being conducted in order to determine if the deployment of underwater tidal turbines would have any effect on increasing noise levels in this marine environment. In order to determine whether or not the deployment and operation of underwater turbines for tidal energy production in Muskeget Channel would augment underwater noise above naturally occurring sound levels, it is necessary to establish baseline sound levels in the area being considered for deployment of a pilot scale turbine generating unit.
Measurement of background noise levels in the high current velocity zone will be undertaken from a vessel using recording marine hydrophones. Recordings of underwater noise will be completed at multiple locations and at two different depths. Measurements of noise levels (acoustic signals) will be undertaken in the upper and lower portions of the water column where turbine generating units and mooring cables will be sited. Background noise levels will be measured on both the ebb and flood tides to ascertain any differences between the two conditions. Building on these initial instantaneous measures, it is envisioned that longer term mooring based deployments of acoustic measuring devices will be undertaken at a few locations to ascertain how underwater noises vary on a diurnal basis as that has been documented to occur in other marine environments.
Project – Environmental Effects of Sediment Transport Alteration and Impacts on Protected Species: Edgartown Tidal Energy Project
Research Element 1 – Bio-fouling and Sediment Transport as it Relates to Installation of Tidal Generation Technology
Sediment alteration investigations are being conducted where hard structures of differing shapes are placed on the sediments and resulting changes in the sediment grain size are determined over an annual cycle. These investigations are being undertaken in the area of Muskeget Channel currently being considered for future pilot scale deployments of tidal current generating units. Parallel measurements outside the zone of altered flow will be made to control seasonal changes in both sediment (and possibly infaunal community composition). In these studies single point current meters will be deployed to quantify boundary current velocities. These data coupled with the current velocity and bathymetry data from the site will be used to parameterize and validate a sediment transport model being developed by co-researchers from Woods Hole Oceanographic Institution. Sediment transport modeling will be undertaken in a collaborative manner between scientists from Woods Hole Oceanographic Institution and UMASS-SMAST.
In conjunction with ADCP surveying along one transect, a bottom mounted upward looking single point current meter has been deployed to capture near continuous current measurements through a portion of the water column. This instrument was deployed for a complete lunar cycle to characterize variations in the velocity field as a function of changing phases of the moon while also serving as a validation of velocity measurements obtained during the ADCP surveying for that specific transect. The overall objective is to capture the average, maximum and minimum velocities and flows for evaluating the number of locations that can be utilized for deployment of tidal generating units and how the current intensity fluctuates through a lunar cycle in order to better understand the ramifications on power generation.
In support of the ADCP surveying, measurement of tidal elevation have been made at multiple (2-3) locations within Muskeget Channel and surrounding waters to the north (Nantucket Sound) and to the south (Atlantic Ocean). TDR deployments along the main N –S axis from Muskeget Channel to Hawes Shoals were conducted to further refine estimates of tidal delays in stage through the permit area to support viability of hydrokinetic energy deployments within the FERC site and to be able to related measured velocities to variations in tidal stage.
Building on previous bathymetric surveying, additional detailed bathymetric surveying has been undertaken to complete a bathymetric map of the critical main channel portion of the Muskeget Channel. Survey lines were run at <50 m intervals, with continuous recording of depth (0.1 ft) and location (d-GPS). The completed bathymetric map will be produced as a project deliverable, for the purpose of supporting siting decisions and will be utilized in the proposed sediment transport modeling.