of seaweeds than without (Buzovkina et al. 1992). Seaweeds may raise the pH of
the water by 0.1–0.4 pH units (Robertson-Andersson et al. 2008). This variation
may have an influence on scale formation on steel structures and thereby induce or
change localized corrosion processes (Beech and Campbell 2008). Careful monitoring of scale formation and appropriate maintenance measures will help to keep
corrosion risks below critical levels.
Fish farms cause metal enrichment in the bottom of the sea, e.g. extreme high
concentrations of Zn, Cu and Cd in sediments and pore water (Dean et al. 2007;
Kalantzi et al. 2013; Loucks et al. 2012; Nordvarg and Johansson 2002). Such high
concentrations may also increase the corrosion risk of steel due to higher conductivity of the electrolyte and creation of galvanic effects. Additionally, oxygen
consumption because of biodegradation may create an anoxic or anaerobic environment that stimulates MIC by microorganisms such as sulfate reducing bacteria
(SRB; Kawahara et al. 2008). Increase of carbon oxides and nitric oxides can also
increase the corrosion of steels (Beech and Campbell 2008). On sites with substantial water currents, however, it is not very likely that these processes will have a
strong effect on corrosion of materials and constructions.
No literature data have been found on effects of mussel farms on environmental
parameters that can be associated with corrosion risks. A priori such risks cannot be
fully excluded, depending on type of materials used in mussel farms. If similar
phenomena occur as described above for fish farms, e.g. metal enrichment and/or
anoxic conditions in the near environment, then potential risks may exist but again
on locations with sufficient water currents these risks are probably low.
5.3 Mechanical Risks of Wind Farms Due to the Presence
of Offshore Aquaculture Constructions
Offshore wind farms are constructed and developed to withstand the forces of the
oceans. Wind and waves cause the highest loads on a wind turbine (tower and
foundation). The presence of an offshore aquaculture may pose an additional threat
to the wind farm. The research question is: What are the effects of aquaculture
constructions and activities on the (mechanical) safety of offshore wind turbines?
To grow seaweed or mussels, usually nets or ropes are used (e.g. submerged
longlines, cf. Buck et al. 2010; Lagerveld et al. 2014); fish farms usually apply
special cages or more or less rigid characteristics. Common materials for fish cage
construction are wood, steel and plastic (Burak Cakaloz 2011).
The next section discusses likely scenarios that may occur and could lead to
mechanical risks to the turbine foundation when offshore aquaculture is carried out
within or in close vicinity of an offshore wind farm. Because the risks can be
different depending on the type of foundation, three commonly used structures and
their properties are considered: monopile, jacket and gravity based (Fig. 5.2;
Table 5.1).
5 Technical Risks of Offshore Structures
121
the water by 0.1–0.4 pH units (Robertson-Andersson et al. 2008). This variation
may have an influence on scale formation on steel structures and thereby induce or
change localized corrosion processes (Beech and Campbell 2008). Careful monitoring of scale formation and appropriate maintenance measures will help to keep
corrosion risks below critical levels.
Fish farms cause metal enrichment in the bottom of the sea, e.g. extreme high
concentrations of Zn, Cu and Cd in sediments and pore water (Dean et al. 2007;
Kalantzi et al. 2013; Loucks et al. 2012; Nordvarg and Johansson 2002). Such high
concentrations may also increase the corrosion risk of steel due to higher conductivity of the electrolyte and creation of galvanic effects. Additionally, oxygen
consumption because of biodegradation may create an anoxic or anaerobic environment that stimulates MIC by microorganisms such as sulfate reducing bacteria
(SRB; Kawahara et al. 2008). Increase of carbon oxides and nitric oxides can also
increase the corrosion of steels (Beech and Campbell 2008). On sites with substantial water currents, however, it is not very likely that these processes will have a
strong effect on corrosion of materials and constructions.
No literature data have been found on effects of mussel farms on environmental
parameters that can be associated with corrosion risks. A priori such risks cannot be
fully excluded, depending on type of materials used in mussel farms. If similar
phenomena occur as described above for fish farms, e.g. metal enrichment and/or
anoxic conditions in the near environment, then potential risks may exist but again
on locations with sufficient water currents these risks are probably low.
5.3 Mechanical Risks of Wind Farms Due to the Presence
of Offshore Aquaculture Constructions
Offshore wind farms are constructed and developed to withstand the forces of the
oceans. Wind and waves cause the highest loads on a wind turbine (tower and
foundation). The presence of an offshore aquaculture may pose an additional threat
to the wind farm. The research question is: What are the effects of aquaculture
constructions and activities on the (mechanical) safety of offshore wind turbines?
To grow seaweed or mussels, usually nets or ropes are used (e.g. submerged
longlines, cf. Buck et al. 2010; Lagerveld et al. 2014); fish farms usually apply
special cages or more or less rigid characteristics. Common materials for fish cage
construction are wood, steel and plastic (Burak Cakaloz 2011).
The next section discusses likely scenarios that may occur and could lead to
mechanical risks to the turbine foundation when offshore aquaculture is carried out
within or in close vicinity of an offshore wind farm. Because the risks can be
different depending on the type of foundation, three commonly used structures and
their properties are considered: monopile, jacket and gravity based (Fig. 5.2;
Table 5.1).
5 Technical Risks of Offshore Structures
121