9.3 Underwater Ambient Noise
20. Underwater ambient noise levels are subject to substantial variability depending on a number of natural and anthropogenic factors. Natural factors such as sea-state, rain, surf noise in coastal waters, movement of seabed material and marine animal vocalisations all influence ambient noise levels. These often lead to a diurnal and seasonal variation in the natural ambient noise level in the oceans or regional seas and can cause significant location dependency. The contributions of anthropogenic noise sources to the ambient level are difficult to quantify, although recent studies have indicated that there has been a trend of increasing deep-ocean ambient noise as a result of shipping (McDonald et al. 2008; Andrew et al. 2011). In the North Sea for example, the contribution of shipping noise to ambient levels has been shown to be significant (Ainslie et al. 2009). The ambient noise level is also highly likely to depend on the distance to shipping lanes, fishing areas, dredging areas or other areas where potential noise sources are operating.
21.
Previous ambient noise measurements undertaken in UK coastal waters (Nedwell et al. 2007a; Theobald et al. 2010; Robinson et al. 2011) indicate the higher-end TOB spectral noise levels to be generally between around 95 and 120dB re 1 μPa2Hz-1 with these peak band levels occurring between frequencies of a few tens of hertz to a few hundred hertz, depending on location and time. Such spectral composition is fairly typical of coastal underwater noise, with higher noise levels at frequencies below a few hundred hertz and falling off at higher frequencies. The ambient noise level over the lower frequency range is largely dominated by shipping noise and may be expected to depend on the distance to ports, shipping lanes and areas of other surface vessel activity.
22. Another type of ambient noise evaluation in the UK entailed assessment of likely ambient noise contributions. This formed a part in the Strategic Environmental Assessment (SEA), however, the assessment was only undertaken for SEA area 6, which includes parts of the western UK coast (Harland et al. 2005).
23. Natural environmental contributors to the ambient noise level in and around East Anglia THREE, and the East Anglia Zone in general, will likely be from the wind (sea- state) with contributions from rain noise and biological noise. Noise generated by the interaction of wind with the sea surface is likely to be the dominant natural contributor to ambient noise around the East Anglia Zone, and will range from a few hertz to a few tens of kilohertz. This sea-state related ambient noise reported by Wenz (1962) is thought to be the result of bubble oscillations and impact from breaking waves at the sea surface (Medwin and Beaky 1989; Medwin and Daniel 1990). Rain can also contribute to ambient noise at several tens of kilohertz in the
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Appendix 9.1 Underwater Noise Modelling 6
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150