Noise of underwater explosions in the North Sea. A comparison of experimental data and model predictions.

E M Salomons,B Binnerts,K Betke,A M Von Benda-Beckmann

doi:10.1121/10.0003754

Abstract

An analysis is presented of sound measurements performed near two detonations of unexploded ordnance (UXO) in the North Sea, at distances ranging from 1.5 to 12 km. The charge masses of the detonations were 325 and 140 kg TNT equivalent. The objective of the measurements was to improve the accuracy of model predictions of the area where UXO detonations affect harbour porpoises in the North Sea. For the predictions, an explosion emission model is combined with a shallow-water propagation model. The prediction model was previously validated for distances up to 2 km. The measurements reported here allowed validation up to a distance of 12 km. The measured levels and spectra are well explained by the model calculations. The model results depend strongly on the sea sediment layering. The propagation of high-frequency components appears to be affected primarily by the silty top layer, while low-frequency components are affected also by deeper sandy layers. Measured and calculated noise levels are used to determine permanent-threshold-shift effect distances for harbour porpoises (Phocoena phocoena). Values ranging from 2 to 6 km are found for the two detonations.

Highlights

The bottom of the North Sea is covered with large amounts of unexploded ordnance (UXO), such as aerial bombs, ammunition, mines, and torpedoes from World War II
The UXO detonations are a problem for harbour porpoises (Phocoena phocoena), which are highly susceptible to underwater sound (Kastelein et al, 2012; Ketten, 2006; Southall et al, 2019)
Measurements of sound levels generated by large UXOs in shallow water have been analyzed to assess the potential effects on harbour porpoises, up to a distance of 12 km

Summary

Introduction

The bottom of the North Sea is covered with large amounts of unexploded ordnance (UXO), such as aerial bombs, ammunition, mines, and torpedoes from World War II. The detonation causes a strong underwater pressure wave with a shock front, which may severely affect marine life. The UXO detonations are a problem for harbour porpoises (Phocoena phocoena), which are highly susceptible to underwater sound (Kastelein et al, 2012; Ketten, 2006; Southall et al, 2019). The problem occurs in shallow-water environments such as the North Sea and the Baltic Sea. In the North Sea, the harbour porpoise is the most abundant marine mammal species, with some areas having densities as high as about one animal per square kilometer. In the Baltic area, the harbour porpoise is critically endangered, and the population in the Baltic proper is estimated at a few hundred animals at most (Benke et al, 2014; HELCOM, 2020). The protection of harbour porpoises against underwater explosions has been the topic of several studies (N€utzel, 2008; Ainslie et al, 2009; Camphuysen and Siemensma, 2011; Koschinski, 2011)

Results

Discussion

Conclusion