Environmental Effects Framework

Contacts:

All forms of power generation, including renewables, have environmental impacts and it is important to fully understand impacts for rationale cost-benefit analysis. Because tidal hydrokinetic energy is a new form of marine renewable energy, our understanding of potential environmental impacts is evolving. Environmental effects are the broad range of potentially measurable interactions between tidal energy devices and the marine environment. These may occur during device installation, operation, maintenance, decomissioning, or an accident. Boehlert and Gill (Oceanography 2010) talks about these interactions in terms of stressors from the devices (e.g., noise) and receptors in the marine environment (e.g., marine mammals). These stressors may be categorized as follows (Polagye et al. 2010):

  • Presence of device: static effects - stressors caused by the presence of the device and foundation, including new structures in the water column and disturbances during installation and/or removal.
  • Presence of device: dynamic effects - stressors caused by the operation of the device, including blade strike, entrainment, impingement, and the device wake.
  • Chemical effects - stressors due to contaminants from lubricants, paints, or coatings.
  • Acoustic effects - stressors from noise due to device operation and/or installation.
  • Electromagnetic effects - stressors from electromagnetic fields associated with the generator and power electronics on a device and/or power cable.
  • Energy removal - stressors, primarily on the far-field environment, which are a consequence of energy removal from tidal systems.
  • Cumulative effects - stressors arising from a combination of other stressors and/or multiple sites developed in the same geographically connected body of water.

Because each stressor and receptor has multiple elements (e.g., injury, behavioral change for a fish) there are literally thousands of potentially measurable interactions. And it is infeasible to attempt to monitor all of these during pilot projects. Prioritization based on the best possible information and expert opinion has been recommended as one path forward (Polagye et al. 2010). Using this prioriziation, monitoring (both before and after turbines are installed) is targeted at potential environmental impacts, those environmental effects which rise to the level deleterious ecological significance. If environmental impacts are identified, then these should be mitigated against.

NNMREC (UW and OSU), Pacific Northwest National Laboratory, NOAA Marine Fisheries, and Washington Sea Grant organized a workshop in March 2010 to develop a better understanding of the environmental effects of tidal energy and its potential environmental impacts. Further information may be found on the workshop website.

Energy Removal

Contacts:

Industry Challenge: A critical unknown for large-scale operation of in-stream turbines are estuary-scale environmental effects. Estuaries are ecologically sensitive areas facing a host of human pressures and in-stream turbines must be deployed in a manner that does not exacerbate existing problems or cause new ones. Energy extraction through tidal power generation may change the energetic characteristics of an estuary and impact flushing and water quality. Substantial energy extraction from an estuary may result in reduction of the tidal range, which may affect the extent and the character of sensitive near shore habitat areas such as tidal flats. Finally, altered flow patterns around the device themselves may affect migration patterns of marine creatures as well as patterns of sedimentation and the benthic habitat These unknowns are of utmost concerns to regulators, as well as the citizens of the community contemplating tidal power generation who need to evaluate trade-offs between substituting for non-renewables and preserving the regional environment.

Approach: The University of Washington has performed leading edge work on estuary-scale environmental effects from in-stream extraction (Polagye et al. 2008). The Center proposes to further leverage its oceanographic expertise to address broad environmental concerns, such as estuarine circulation, basic biological productivity, and dissolved oxygen (Edwards et al. 2007). The SUNTANS hydrodynamic model from Stanford University has been implemented for Puget Sound and is undergoing rigorous calibration and validation for its tidal response against existing observations. A means for tidal turbine representation in the SUNTANS code is being developed in parallel. This model will be used for assessment of flow modification and estuarine-scale changes in the natural energetics due to in-stream energy extraction. As pilot systems are implemented and data collected, the model will be further validated and refined. The validated model will then be used to assess potential impacts of commercial-scale arrays. The Center will work with scientists and regulators to establish at which point in the scale of implementation the estuarine-scale impact becomes relevant, and to relate this to ecosystem-level concerns such as biological productivity and dissolved oxygen levels in water. These will help inform regulatory decisions on appropriate types of monitoring and studies and allocation of scarce resources.

Outcomes and Impacts:

  • Research: Improved understanding of estuarine dynamics and implications for turbine operation.
  • Industry: Critical points for turbine impact on estuaries to determine reasonable deployment size.
  • Regulatory: Guidance on appropriate environmental monitoring at various phases of array build-out.

Dynamic Effects

Contacts:

NNMREC is developing an instrumentation package to monitor for blade strike during device operation. While monitoring at other projects has not detected blade strike to either fish or marine mammals, this is a persistent concern which needs to be addressed, as possible.

Researchers at NNMREC are also developing a suite of numerical models to investigate:

  • Changes to sediment transport in the wake of an operating device
  • Pressure changes that a marine animal would experience if swimming through the swept area of an operating device

Acoustic Effects

Contacts:

The installation, operation, maintenance, or removal of a device from the marine environment will create anthropogenic noise. Because marine mammals and some fish are senstive to loud noise, it is important to quantify the noise generated by operating devices and be able to make pre-installation predictions of the area ensonified by device operation.

These efforts are closely tied to site and device characterization activities.

Figure - Estimated M-weighted received sound pressure levels for mid frequency cetaceans (dB re 1uPa) in the vicinity two hydrokinetic turbines operating at rated power in northern Admiralty Inlet, Puget Sound, WA. Black line denotes the 120 dB re 1uPa isobel (NMFS harassment threshold). White lines denote 1000 m contours from the project center point.