Underwater noise generated by vehicle traffic in an underwater tunnel

Underwater noise measurements were made adjacent to the Monitor-Merrimac Memorial Bridge-Tunnel in the James River, VA during a field experiment in April of 2019. Anticipated sources of underwater noise included wind, waves and associated bubbles, flow noise, boat/ship traffic, industrial shipyard noise and traffic noise radiating from the underwater tunnel. During the field observations, winds, waves/surface conditions, underwater currents, water column structure and tunnel traffic were monitored by anemometers, high-frequency surface radar, ADCPs, echosounders and traffic sensors. The observed noise field exhibited high frequency and tidal-scale variability due to passing surface vessels and tidally driven currents in the estuary; most interestingly, the noise field exhibited variability on a diurnal time scale, closely correlated to the temporal distribution of vehicular traffic in the underwater tunnel. The tunnel traffic underwater noise amplitude varied by 1–5 dB at 10s to 100s of Hertz and exhibited a non-linear relationship to frequency.