Effects of Underwater Noise

Transcription

1 Effects of Underwater Noise Impact pile driving noise prediction Marten Nijhof, Christ de Jong, Bas Binnerts, Michael Ainslie

2 2 Wind energy agenda Dutch energy agreement for sustainable growth (2013): A wind energy production capacity of MW should available by A total of MW in wind energy needs to be commissioned between (in addition to existing parks and parks for which construction is in preparation). Commissioned in Generated power(mw) Total generated power (MW) Operational by Source: Ontwerp-Rijksstructuurvisie Windenergie op Zee

3 3 Existing and planned wind parks Wind park areas IJmuiden Ver Borssele Hollandse Kust Ten Noorden van de Waddeneilanden Existing wind parks Existing wind parks Construction in preparation Licenced parks Licence pending Shipping areas Shipping route Separation zone shipping area Clearways Avoided area Precaution area Anchoring area Deepwater route Oil and gas production Production platform Boarders Exclusive Economic Zone (EEZ) Dutch territorial zone (12 mile) Source: Ontwerp-Rijksstructuurvisie Windenergie op Zee

4 4 Overview Current policy in NL for wind farm construction: 1 wind farm at a time, only between 1 st July and 1 st of January, developer required to perform EIA. Measure of impact NL government is currently re-assessing its policy How to plan construction of multiple wind farms? What criteria to adopt for assessing cumulative impact of multiple wind farms?

5 5 Overview Recent developments; Focus on effects on population level Measure of impact A Protocol for Implementing the Interim Population Consequences of Disturbance (PCoD) Approach, Harwood et al., 2014 Disturbance Effects on the Harbour Porpoise Population in the North Sea (DEPONS) initiative. (based on Nabe-Nielsen et al., 2014) Monitoring Guidance for Underwater Noise in European Seas, TSG underwater noise - MSFD, 2014

6 6 Overview TNO develops SORIANT (Sound Risk Analysis Tool); a tool to support the Dutch Government in: computing and visualizing impact of pile driving activities on marine mammals formulating assessment criteria (and the development of legislation). act as a framework to incorporate newly available knowledge identifying knowledge gaps to update the research agenda. 110 db 150 db 190 db

7 7 Overview Example Problem Assessment metric and criteria Acoustic model Effects of depth and wind Prediction of region of avoidance Prediction of cumulative effects Improved acoustic model 110 db 150 db 190 db

8 8 Example problem: statement and approach Problem statement: At which distance of an offshore pile driving operation are seals and porpoises affected by impact pile driving noise? Pile location

9 9 Example problem: statement and approach Problem statement: At which distance of an offshore pile driving operation are seals and porpoises affected by impact pile driving noise? Affected implies here: 1. Avoidance behaviour: fleeing from the exposed area 2. Hearing threshold shift (TTS / PTS) Approach: 1. Calculate sound propagation in vicinity of operation (SEL) 2. Calculate noise exposure of animals (due to a single pile) 3. Determine distances at which SEL surpasses threshold for avoidance behaviour/tts/pts (cumulative effect)

10 10 Assessment metric: Sound Exposure Level duration T 90 [s] s o u n d p re s s u re (k P a ) pressure p(t) / kpa cumulative energy (relative) Distance = 1 km time [s] time t / s Sound Exposure Level (SEL 1 ): p 2 integrated over pulse duration T 90 Cumulative Sound Exposure Level (SEL cum ): sum of SEL 1 over multiple blows

11 11 Assessment metric: Sound Exposure Level SEL (1/3-octave bands) [db re 1 µpa 2 s] OWEZ (690 kj, 800 m) Q7 (800 kj, 981 m) seal porpoise k 2k 4k 8k 16k frequency [Hz]

12 12 Assessment criteria (SEL in db re 1 µpa 2 s) Avoidance behaviour TTS PTS Porpoise SEL 1 > 136 db [Kastelein 2013*] SEL cum > 164 db [Lucke et al 2009] SEL cum > 179 db [SEL cum (TTS)+15 db] Seal SEL 1,W > 145 db [Kastelein 2013*] SEL cum,w > 171 db [SEL cum (PTS)-15 db] SEL cum,w > 186 db [Southall et al 2007] Single strike: SEL 1, and cumulative: SEL cum M-weighted: SEL W, and unweighted: SEL Values established by government sponsored Workgroup * based on observations during playback of pile noise in SEAMARCO basins

13 13 Acoustic Model Propagation model provides propagation loss (PL) Source strength/source level (SL) of an equivalent (point) source Calculated using measurement data SL is scaled to impact energy of hammer. Equivalent source 0 10 Propagation Loss FEM measurement position Range [m]

14 14 Sound propagation in shallow water Weston s flux integral method Modelled acoustic phenomena: cut-off frequency shallow water Low frequencies do not propagate Effects due to sea surface: Lloyd s mirror Lower levels close to the surface Wind perturbs the water surface scattering (lower reflection) Absorption/reflection of sound by at the water/sediment interface, Absorption in seawater

15 15 Source strength Source characterisation description based on measurements at Prinses Amaliawindpark (PAWP/Q7) : Pile diameter of ca. 4 meter, hammer energy of 800 kj / blow Sound measurements at ca. 5 km distance SL E 215 to 221 db re 1 µpa 2 m 2 s Scaling of SL E for example case: hammer energy of ca kj / blow 10log 10 (1900/800) 4 db SL E 219 to 225 db re 1 µpa 2 m 2 s spectrum max. PAWP(Q7) data PAWP (Q7) Ainslie et al 2010 Aquatic Noise, Cork

16 16 Effects of wind on Sound Exposure Level Depth [m] 136 db* -126 db Wind 0 m/s SEL 1 db re 1 µpa 2 s Range [km] *avoidance behaviour threshold porpoise = 136 db Depth [m] 136 db* -126 db Range [km] Wind 7.5 m/s SEL 1 db re 1 µpa 2 s

17 17 Prediction of region of avoidance Porpoise 1 m below sea surface 1 m above sea bottom

18 18 Prediction of cumulative effects Realistic soft start pile driving scenario All animals are assumed to be located 1 m above the sea bottom All animals relocate to 1 m below the sea surface after two blows Animals swim away from the source if SEL SS SEL avoidance Animals swim in a straight line away from the source Constant swimming speeds (porpoise 3,4 m/s, seal 4,9 m/s) Constant swimming depth (1 m below sea surface) Animals stop swimming if SEL SS < SEL avoidance

19 19 Prediction of cumulative effects Porpoise bed surface SEL [db re 1 µpa 2 s] avoidance PTS SEL cum TTS SEL 1 (bottom) SEL 1 (surface) Range [km]

20 20 Improving the acoustic model Actual field radiated by a pile is highly directive (Mach cone) A vertical array of point sources can approximate a Mach Cone Propagation Loss of a point source is depth depended! Using an equivalent omnidirectional point source is likely a crude approximation Omni-directional point source Approximation of Mach cone using point sources Mach cone

21 21 Improved source model Finite Element model 0 Normal modes/flux model FEM Depth dependent pressure from Finite Element model Range [m] Equivalent source Propagation Loss model measurement position FE model

22 22 Summary SORIANT (Sound Risk Analysis Tool) is developed to: compute and visualize impact of pile driving activities on marine mammals formulation of assessment criteria and the development of legislation. act as a framework to incorporate newly available knowledge identifying knowledge gaps to update the research agenda. Future work: Improved acoustic models, assessment of impact on population

23 23 Effects of Underwater Noise Impact pile driving noise prediction Marten Nijhof, Christ de Jong, Bas Binnerts, Michael Ainslie