Sampling the Sound of Grand Canyon’s Silence

Standing about ear high on tripods, microphones attached to sound level meters and computers are trying to capture the sound of quiet at the Grand Canyon.

When the chatter of hikers, rumble of idling cars and buzz of air traffic are removed, what does nature sound like around the landmark? Grand Canyon National Park officials hope to help answer that question with data now being collected.

The information will be used in computer models that will help determine how noisy the park would be without human intrusion and whether current regulations on tour flights adequately limit noise.

“We’re trying to get what the natural ambient levels are,” said Ken McMullen, overflights and natural soundscape manager for the park.

Although the data collection and the models that will be used to determine the ambient noise level are new, the effort to determine whether the park is as quiet as it should be goes back a generation.

Congress said in 1975 that natural quiet was a resource at the Grand Canyon -- the way that animals and vegetation were -- and therefore must be protected.

The determination came at a time when flights over the canyon were virtually unregulated.

Tour operators started flying passengers over the canyon in 1927 and even as tour flights grew in popularity, flight routes, altitude and traffic control were left to individual operators.

Environmental activists said more regulation was needed to preserve the Grand Canyon’s natural state. But little was done until a midair collision in 1986.

Twenty-five people, mostly foreign tourists, were killed when a helicopter and a sightseeing plane collided 2,000 feet above the canyon floor.

The National Parks Overflights Act was passed the following year. The law required that natural quiet be substantially restored to the park.

The problem, McMullen said, was that no one defined “substantial restoration” and no one knew what “natural quiet” sounded like at the canyon.

Tour operators immediately saw a threat to their business and chafed at what they saw as unfair regulations. What ensued was nearly two decades of fighting on all sides and over nearly every issue.

“Everybody seemed to want to fight. The environmental groups wanted to fight. The air tour operators wanted to fight,” said Steve Bassett, president of the U.S. Air Tour Assn. “Instead of figuring out how to do it, we just fought all the time.”

Flight corridors, altitude requirements and caps on the number of flights were established, but tour operators continued to object to many of the rules.

In 2003, about 83,000 air tour flights went over the canyon; current rules cap the total at 90,260 flights annually.

It remains unclear whether natural quiet has returned to the park.

What constituted substantial restoration of quiet remained unsettled until 1994. The standard was set at half or more of the park having no audible aircraft noise at least 75% of the day. That didn’t settle the issue though.

“Even what we meant by the ‘day’ was a contentious issue for many years,” McMullen said.

Officials finally defined “day” as 7 a.m. to 7 p.m., a standard that the air tour operators still don’t like.

But without knowing what decibel “natural quiet” is at the Grand Canyon, it’s impossible to say whether substantial restoration has occurred.

Canyon officials just began gathering data in April using microphones placed in the four major types of vegetation, away from developed areas of the park. They’ll be able to take out human noise if it’s accidentally picked up by the sensors.

The data measuring the sound of wind in trees and birds chirping can then be used to fill in a model that will determine what the decibel level of nature is estimated to be at the Grand Canyon. Collecting data everywhere in the park is far too costly, so modeling provides a close approximation.

Getting to this point hasn’t been easy. The topography at the Grand Canyon is unique. Many existing models used to determine ambient noise levels focus on big cities and airports, making them of limited value in more rural settings and prompting more challenges from the air tour community.

It took four years of study, until January 2003, for the National Park Service and Federal Aviation Administration to find a model that seemed valid for Grand Canyon conditions, McMullen said.

The data collection will continue over the year because sound levels are different with seasonal change.

By winter, Grand Canyon officials should have an assessment of how close they are to natural quiet in the summer and whether current regulations are adequate. By next year, they hope to have an assessment that covers the winter months as well, McMullen said.

“That would be a huge step,” he said.

It will not, however, be the end to the ongoing questions about quiet in the park.

Air tour operators still want changes to the regulations, and Bassett said he couldn’t say whether they would accept the results of the sound model that the park planned to use.

“We think it’s probably getting better,” he said. “I really do have some sense that they are going to try to get it right.”

But he said the industry was more interested in plans to sit down with the Park Service, FAA, environmentalists, tribes and other groups as part of a dispute resolution process that may finally end the fighting.

That process is just starting and will probably take a couple of years to complete. Bassett said everything -- including current limits -- was up for negotiation, but he and McMullen both said they hoped that the negotiations would keep the decisions out of costly and time-consuming litigation.

“It just seems like all the stars are starting to align, and we will get something done,” Bassett said.