Environmental Engineering Reference
In-Depth Information
on navigational conditions, wave loads on adjacent structures, and recreation on
nearby beaches (e.g., surfing, swimming) might be expected (Michel et al., 2007).
Reduced wave action could alter bottom erosion and sediment transport and deposi-
tion (Largier et al., 2008).
Wave measurements at operating wave energy conversion projects have not yet
been made, and the data will be technology and project-size specific. The potential
reductions in wave heights are probably smaller than those for wind turbines due to
the low profiles of wave energy devices. For example, ASR, Ltd. (2007) predicted
that operation of wave energy conversion (WEC) devices at the proposed Wave Hub
(a wave power research facility off the coast of Cornwall, U.K.;
http://www.wavehub.
co.uk/)
would reduce wave height at shorelines 5 to 20 kilometers away by 3 to 6%.
Operation of six wave energy conversion buoys, a version of OPT's PowerBuoy
®
, in
Hawaii was not predicted to impact oceanographic conditions (Department of the
Navy, 2003). This conclusion was based on modeling analyses of wave height reduc-
tion due to both wave scattering and energy absorption. The proposed large spacing
of buoy cylinders (51.5 m apart, compared to a buoy diameter of 4.5 m) resulted in
predicted wave height reductions of 0.5% for a wave period (i.e., time between the
passage of consecutive wave crests past a fixed point) of 9 seconds and less than 0.3%
for a wave period of 15 seconds. Boehlert et al. (2008) summarized the changes in
wave heights that were predicted in various environmental assessments. Recognizing
that impacts will be technology and location specific, estimated wave height reduc-
tions range from 3 to 15%, with maximum effects closest to the installation and near
the shoreline. Millar et al. (2007) used a mathematical model to predict that operation
of the Wave Hub, with WECs covering an area 1 km by 3 km located 20 km from
shore, could decrease average wave heights by about 1 to 2 centimeters at the coast-
line. This represents an average decrease in wave height of 1%; a maximum decrease
in wave height of 3% was predicted to occur with a 90% energy transmitting wave
farm (Smith et al., 2007). Other estimates in other environmental settings predict
wave height reductions ranging from 3 to 13% (Nelson, 2008). Largier et al. (2008)
concluded that height and incident angle are the most important wave parameters for
determining the effects of reducing the energy supply to the coast.
DID YOU KNOW?
The PowerBuoy
®
, developed by Ocean Power Technologies (OPT), is one
of the most widely deployed WEC device designs in the world. A 10-buoy
test array of the PB150 PowerBuoy
®
has been proposed for deployment in
Reedsport, Oregon. The PB150 is a utility-scale 150-kilowatt buoy that—in
the initial design—contains hydraulic fluid, which is cycled as the buoy moves
up and down with the waves. The moving fluid or mechanical parts are used
to spin a generator, which produces electricity. The buoy is approximately 35
meters (115 feet) tall, of which approximately 9 meters (30 feet) project above
the water's surface), and is 11 meters (36 feet) in diameter. It is held in place by
a three-point mooring system (USDOE, 2012).
