DEVELOPMENT OF A NEW UNDERWATER PILING NOISE MITIGATION SYSTEM - USING HYDRO SOUND DAMPERS (HSD)

The aim of the recently published climate control by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) is a reduction of the German greenhouse gas emissions down to 20 % in 2050, compared to the generated greenhouse gas in 1990. To reach the given target a huge growth in renewable energy is necessary. One of the most potential possibilities to produce renewable energy in Germany will be the installation of offshore wind turbines. During the installation of offshore wind foundations such as monopiles, tripods, tripiles and jackets, mostly large tubular steel piles are impact driven to final penetration depth. In the process of impact driving, considerable underwater sound emissions will appear. In recent times, peak sound pressure levels above 190 dB re 1 mu Pa have been measured at a distance of 750 m away from the installation ground. These peak sound pressure levels, produced during the installation of any kind of driven offshore foundation, is potentially harmful to marine life, in particular to marine mammals such as harbor porpoises, harbor seals or grey seals. To protect the marine life the German Federal Maritime and Hydrographic Agency (BSH) set the maximum allowed underwater sound pressure level to 160 dB (SEL) at a distance of 750 m away from pile driving. To reach the given target by the BSH a new underwater piling noise mitigation system using so called hydro sound dampers (HSD) is presently developed at the Institute for Soil Mechanics and Foundation Engineering at the Technische Universitat in Braunschweig (IGB-TUBS). After small scale tests in the so called 'large wave channel' in Hannover a full scale test was performed in the Baltic-Sea some weeks ago. The results of the measurements are very promising, as a reduction of 12 up to 20 dB could be generated. Besides existing noise mitigation systems one of the main advantage of the hydro sound dampers is, that the mitigation can be pre-adjusted to a predefined frequency range, as marine mammals are sensitive only for a certain sound frequency range. In this paper, the results of the small and large scale tests and some new research findings concerning the shape and the material of the hydro sound dampers will be presented.