9.6.1.4 Mitigation methods to reduce significance of environmental impact from construction phase
125. Mitigation strategies and measures which may reasonably be considered, in-line with JNCC guidance (JNCC 2010) include:
• •
Use of techniques to reduce noise output at the onset of piling using a soft- start;
Use of mitigation zones during construction activities through a Marine Mammal Mitigation Protocol;
126. The use of lower hammer blow energy during a soft-start procedure can reduce the risk of instantaneous onset of auditory injury. A soft-start can therefore be used to reduce the range over which instantaneous auditory injury may occur and, by deterring any animals in the vicinity to a safe distance before the full energy piling is reached, it can reduce the likelihood of instantaneous auditory injury occurring once higher piling energy is reached (assuming that animals flee from the noise source).
127. The estimated ranges for instantaneous onset of auditory injury for marine mammals (shown Table 9.6 to Table 9.9) indicate that harbour porpoise can be expected to be at risk of instantaneous onset of auditory injury at ranges less than about 1km even once the hammer strike energy reaches full hammer energy expected for East Anglia THREE. However, full hammer energy would not be used at the onset of piling. For hammer energies of 2,300kJ and below, which might be expected during the soft-start, the estimated ranges for potential onset of PTS do not exceed the 500m mitigation zone generally employed following JNCC (2010) guidance for pile driving and the animals will likely have moved far enough away from the sound source by the time full piling is employed.
128. A mitigation zone can be achieved by using either a passive or an active technique. Passive methods generally involve the use of MMOs and / or PAM whilst an active method could include the use of AMDs. A combination of the two may be the most effective strategy by actively seeking to repel animals to a safe distance and then monitoring to ensure this has been successful. However, it should be noted that the effectiveness of PAM may be reduced when using AMDs, but a combination of MMO and AMD compared to MMO and PAM may be more effective provided the animal is repelled by the sound and moves away. Given the sometimes limited effectiveness of vessel deployed PAM for this type of activity it may also be more effective to employ AMDs during conditions of reduced visibility.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Appendix 9.1 Underwater Noise Modelling 60
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