Protecting natural soundscapes with an adequate margin of safety

Abstract

The natural ambient sound environment in park-like settings not only provides a masker for inappropriate sounds, but also affords different acoustic experiences to the park visitor due to its dynamic nature. At a single location, for example, the absence of wind and water movement may offer periodic opportunities to experience an environment completely devoid of audible sound. At the same location wind blowing gently through nearby conifers may offer a feeling of tranquility. In late spring the sound of water in a nearby stream may provide yet another experience. Each circumstance generates a different ambient sound environment, both for soundscape enjoyment as well as masking inappropriate sources (usually human activity). This dual role creates challenges in soundscape management and planning and makes difficult the use of a single ambient descriptor to protect a sites multiple non-concurrent soundscape resources. This paper examines soundscape impairment from a damage risk perspective by assuming independent, quasi-random arrivals of various soundscapes and human activity. Actual data from three western U.S. parks are used to establish reasonable parameter values for the analysis. The paper develops impairment risk with an adequate margin of safety in line with philosophies of the EPA Levels Document of 1974.