To put together a hydrokinetic project, the exact conditions of the project site must be determined. This process includes collecting information on river flow, depths, and fish data. Some of this data can be obtained from public sources.
Mapping Streamflow and Depths
Federal agencies including the USGS, the EPA, and the U.S. Army Corps of Engineers maintain detailed historic precipitation and runoff databases that are useful in project planning. In particular, the USGS has daily streamflow statistics for 485 sites around Alaska. This information can be found on their website.
Unfortunately, the gauging stations where these data are collected are often widely distributed, particularly in rural areas of the state. Additionally, because the amount of power that can be generated is a function of the cube of the velocity of the water: Power(kW) = k(velocity)3 where k=constant, the exact location of a hydrokinetic device within the water column will have a large impact on how much power is ultimately generated. It is recommended that local measurements of depth and water flow be obtained.
The best tool for measuring river or tidal flow in a specific location over time is the Acoustic Doppler Current Profiler (ADCP), which maps velocities at all depths through the water column. ADCPs are often deployed from a survey boat or barge. The timing of these surveys is important, and long-term data create a more accurate picture of the total potential. However, data collected by an ADCP can be adjusted using daily historical averages and extremes. This greatly reduces the time required to determine optimal locations.
Equipment can be readily purchased to measure local streamflow, however processing data requires some expertise. Alternatively, there are several companies that can conduct local resource assessments for both tidal and in-stream applications, as well as complete a bathymetric map of the floor of the water body (river or tidal basin). This is useful not just in determining water depth, but also in predicting how the flow through the channel might change over time, due to silting and/or flood events. It is important to remember that installing a hydrokinetic device will in itself change the flow of a river and can result in sediment deposition over the course of time.
Since they are relatively consistent and predictable from year to year, obtaining data on current flow for tidal energy resources is easier than for river environments. Basic data on Alaska’s tidal energy resources can be obtained from the EPRI reports, ‘Knik Arm Tidal Energy Report’ and ‘Southeast Alaska Tidal Energy Study’ . In addition, there are data available from the Alaska Energy Authority on tidal energy resources in the Aleutians, Kodiak, Dillingham, and Bethel.
Directly or indirectly, any river or tidal turbine installation has the possibility of impacting fish, marine mammals, seabirds, and benthic fauna; however, these impacts are largely unknown. Direct impacts to aquatic organisms are primarily the result of contact with structures (such as turbines) placed in the immediate habitat. Such impacts may result in injury or mortality. Indirect impacts can include species displacement due to modified environmental factors that change migratory patterns such as a modified tidal stream that is relied upon for migration in and out of a bay or estuary.
One significant concern is potential impacts to Alaska’s fish, particularly salmon. It is generally thought that hydrokinetic devices will have limited impact on adult species migrating upriver to spawn. They tend to favor slow water along banks rather than fast currents where hydrokinetic devices would be sited, and they would be better able to maneuver around an upstream diversion, which they could sense from turbulence and pressure changes. There is potential to affect outmigrating smolts. They tend to prefer the faster flowing waters where devices would be placed, and they would have less time to react to turbulence or pressure changes.
In any case, environmental impacts will be site specific. Until more information is gathered, a site specific environmental survey should be conducted at any location considering hydrokinetic power generation. The Alaska Department of Fish and Game conducts fish monitoring programs throughout the State, and there are several private companies that conduct surveys.