Acoustic monitoring report, Denali National Park and Preserve – 2013

Betchkal, Davyd

In 2013, park staff deployed acoustic monitoring systems to 9 locations in Denali National Park and Preserve. The purpose of this effort was to inventory the ambient acoustic conditions and amount of non-natural sound in Denali National Park as called for in the 2006 Backcountry Management Plan. Data collected included sound pressure levels every second and continuous MP3 audio recordings throughout the sampling period. These data serve as a permanent record of existing acoustic conditions at these locations for the summer of 2013. Table i shows summarized results of 2013 monitoring, including ambient and natural ambient sound statistics in dBA (A-weighted decibels), average percentage of time audible, number of events per day, and the average maximum sound pressure level (SPL) for aircraft sound sources. Aircraft are specifically reported because they are the most prominent extrinsic sound occurring in Denali’s backcountry. (An extrinsic sound is defined as any sound not forming an essential part of the park purpose. Median ambient (L50) describes the acoustical environment as measured, including both natural and extrinsic sounds. Natural ambient (Lnat) estimates what the acoustical environment would be without the contribution of extrinsic sounds. Variation in anthropogenic noise were apparent upon analysis, typifying each location. The highest rates of air traffic were measured at Fang Mountain, where north-side flight routes culminate. It had an average of 31 aircraft noise events per day, and a maximum of 58 noise events per day. Similarly Carlson Creek (within the McGonagall Pass area) had an average of 29 events per day and a maximum of 61 noise events per day. In contrast, 6 events per day were detected at Birch Creek. This relatively-intact condition of solitude is shared by most nearby monitoring locations in the west-central portion of the park. The Fang Mountain location was originally sampled in 2011. Resampling sought to determine the effect of a Denali Aircraft Overflights Advisory Committee aviation best practice enacted during the spring of 2012. Data from Igloo Canyon were used to quantify the effects of hybrid bus technology on the Denali Park Road corridor. The hybrid engines tested were louder than 60% of the conventional diesel fleet. The hybrid systems were also determined to be louder than the expected range of means for a conventional diesel engine of the same volume.

Acoustic monitoring report, Denali National Park and Preserve – 2013

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