Environmental Engineering Reference
In-Depth Information
structure (e.g., rotors, pilings, concrete anchor blocks) will cause scour, and this
sediment is likely to be deposited further downstream. On average, extraction of
kinetic energy from currents and waves is likely to increase sediment deposition in
the shadow of the project (Michel et al., 2007), the depth and areal extent of which
will depend on local topography, sediment types, and characteristics of the current
and the project. Subsequent deposition of sediments is likely to cause shoaling and
a shift to a finer sediment grain size on the lee side of wave energy arrays (Boehlert
et al., 2008). Scour and deposition should be considered in project development, but
many of the high-energy (high-velocity) river and nearshore marine sites that could
be utilized for electrical energy production are likely to have substrates with few or
no fine sediments. Changes in scour and deposition will alter the habitat for bottom-
dwelling plants and animals.
Loss of wave energy may lead to changes in longshore currents, reductions in
the width and energy of the surf zone, and changes in beach erosion and deposition
patterns. Millar et al. (2007) modeled the wave climate near the Wave Hub electri-
cal grid connection point off the north coast of Cornwall. The installation would be
located 20 km off the coast, in water depths of 50 to 60 m. Arrays of WECs con-
nected to the Wave Hub would occupy a 1 km × 3 km site. The mathematical model
predicted that an array of WECs would potentially affect the wave climate on the
nearby coast on the order of 1 to 2 cm. It is unknown whether such small reductions
in the average wave height would measurably alter sediment dynamics along the
shore, given the normal variations in waves due to wind and storms.
Water quality will be temporarily affected by increased suspended sediments
(turbidity) during installation and initial operation. Suspension of anoxic sediments
may result in a temporary and localized decline in the dissolved oxygen content of
the water, but dilution by oxygenated water current would minimize the impacts.
Water quality may also be compromised by the mobilization of buried contami-
nated sediments during both construction and operation of the projects. Excavation
to install the turbines, anchoring structures, and cables could release contaminants
adsorbed to sediments, posing a threat to water quality and aquatic organism. Effects
on aquatic biota may range from temporary degradation of water quality (e.g., a
decline in dissolved oxygen content) to biotoxicity and bioaccumulation of previ-
ously buried contaminants such as metals.
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Installation and operation of hydrokinetic and marine energy projects can directly
displace benthic (i.e., bottom-dwelling) plants and animals or change their habitats by
altering water flows, wave structures, or substrate composition. Many of the designs
will include a large anchoring system made of concrete or metal, mooring cables,
and electrical cables that lead from the offshore facility to the shoreline. Electrical
cables might simply be laid on the bottom, or they more likely will be anchored or
buried to prevent movement. Large bottom structures will alter water flow, which
may result in localized scour and/or deposition. Because these new structures will
affect bottom habitats, changes to the benthic community composition and species
interactions in the area defined by the project may be expected (Louse et al., 2008).
