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"The desert breathed and then went silent at the first mention of nightfall, a kind of quiet that comes only at the edge of the Earth."
Craig Childs, The Secret Knowledge of Water
The acoustical coolness of a canyon breeze. The roll of thunder dissolving into the falling rain it's unleashed. The cacophonous recital of machinery and vehicles and jets soaring overhead. It's all taken into account in the Soundscape Management Plan for Zion National Park.
The plan, adopted Sept. 17, has been in the works for more than three years, and is the first of its kind in a major national park. Its purpose is protecting attributes of sound and the lack of it for the benefit of wildlife and the nearly 3 million annual visitors to the southern Utah park.
Since 2007, the park has used portable, solar-powered monitoring stations to record sound as well as measure weather and wind speed. The devices monitor an area 24 hours a day, for up to 28 days at a time. That information was analyzed to map sound in the park.
Frank Turina, of Fort Collins, Colo., a planner with the natural sounds program for the National Park Service and project manager for the Zion document, said an area's soundscape is as valuable as air quality and watershed although, unlike those resources, it is intangible.
"Sound has an inherent value to the park that we want to preserve and protect for the future," Turina said in a telephone interview.
He said the new plan uses the science of acoustics to specify conditions under which park managers would need to act to protect and preserve the soundscape of Zion. That science gives the plan objectivity and credibility.
"It is a very interesting and new application of old science to protect natural areas in the park," he said. "This [project] is on the cutting edge."
One focus of the study was determining the length of time between human-caused sounds in the back country. Most of those sounds are made by commercial and private aircraft, including helicopters.
"We want longer periods between noise events in the back country," said Turina. "Now it's two to three minutes before you hear a human-caused sound, usually involving an overflight, and we want to expand that to a seven-minute period. If we meet that goal we will reassess the situation to see if a longer interval is warranted."
He said the plan can only work if the Park Service and the Federal Aviation Administration have a creative, cooperative approach to overflight problems. While the FAA isn't required to act because of the plan, the science adds weight to its suggestions.
According to Turina, human-caused sounds particularly affect wildlife. A change of only three decibels can have a drastic effect on whether predators can detect prey, he said.
To put that in perspective, conversation between people standing three feet from each other generates an average of about 60 decibels, while a car going 50 miles per hour generates about 70 decibels, Turina said. "The pain threshold is 110 to 120 decibels."
In the "front" area of the park, including entrance areas and locations of public facilities, the goal is to reduce noise through changing employee activities and technology.
That can range from something as simple as using rakes and brooms instead of leaf blowers, to using technology that reduces noise when replacing shuttles and park vehicles.
Kezia Nielsen, an environmental protection specialist who worked on the project, said the plan will enhance the visitor experience.
"Surveys have shown that 90 percent of people who visit the national parks want natural quiet and to be able to hear the sounds of nature," she said. "They cannot have that experience with human-caused sound."
Nielsen said monitoring stations around the park will be maintained to collect information for further analysis on night and daytime acoustics.
"It's amazing what you can hear when you take the time to listen," she said. "It's important for people who get out of the big cities to be able to hear nature, from the rustling of the wind to even insects moving through leaves."
Park superintendent Jock Whitworth is proud Zion is taking the lead in developing such a plan and hopes other parks follow. Discussions on the soundscape began in 2001 as part of the park's General Management Plan.
"We looked at the plan for years and decided [sound] is a natural resource to protect so we began gathering data," he said. "It's important to have and preserve those ambient sounds of water, wind, birds and other animals."
He said future decisions could affect overflights, loudspeaker restrictions and park maintenance, and even dealing with the rumble from "deep throated Harleys" that are often heard on the park's highways.
David Nimkin, southwest Utah regional director for the National Parks Conservation Association, said his group contributed positive comments on the plan during the public scoping process.
"What is significant about the plan is that it is the first in the country that elevates natural silence to a standard where it has an intrinsic value within parks that needs protection," said Nimkin.
The association also hopes the idea of a soundscape plan catches on with other national parks, especially Bryce Canyon National Park. Nimkin said air tours over that southern Utah park, including helicopters, can be intrusive to the natural experience at times.
He said Grand Canyon National Park has made great strides in regulating those tours and working with the FAA in reducing sound levels from aircraft.
"This [Zion] plan is one more step in helping park managers protect resources," Nimkin said. "It is one more element those managers are striving to manage that has been defined."
How to enjoy the sounds of nature
Close your eyes
Stop. Listen to what's around you. Do you hear more with your eyes closed?
Lift up a finger for each sound you hear. Use your left hand for natural sounds and your right hand for human-made sounds.
Walk and listen
Do you hear your footsteps? Do you hear your clothes rustle? Can you walk without making any sound?
What is the most beautiful sound you hear? What sound is the least appealing?
Listen to landscapes
How does the shape of the land affect the way sound travels to your ear? Where is the source of each sound? Are there any echoes? What is the closest sound you hear?
Walk in the wild
Walk as though a predator were after you. Walk as though you were a predator.
Chat like an animal
Listen for an animal. What sound does the animal make? Can you make its sound?
Source: Nature Sounds Society
Online Read more about soundscapes
O Read the soundscape management document prepared by the National Park Service.