Launch Slideshow

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Bridging endangered habitat in Alaska's Cook Inlet

Bridging endangered habitat in Alaska's Cook Inlet

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    Not to be confused with “The Bridge to Nowhere” connecting the City of Ketchikan to its airport on Gravina Island, the 1.74-mile Knik Arm bridge cuts travel distance between Anchorage, Alaska's largest city, and its suburbs in Matanuska-Susitna Borough from 74 to 10 miles. The project also includes 19 miles of new roads. At press time, three consortiums were on the short list for a finance, design, build, operate, and maintain (FDBOM) contract. Construction could begin next year and is expected to be completed in 2016. Map: Knik Arm Bridge and Toll Authority

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    The Knik Arm Bridge and Toll Authority is required to detect the presence of a beluga whale subspecies for at least one season before beginning construction as well as during construction. Until the agency proved otherwise, the engineering community assumed acoustical monitoring was more effective than optical monitoring for locating the endangered species. Photos: (top) Knik Arm Bridge and Toll Authority; (inset) Rock Solid Products | iStockphoto.com

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    Early-morning traffic builds on the Glenn Highway as 10,000 daily commuters make their way from the suburbs into Anchorage, Alaska's largest urban center with nearly 300,000 residents of its own. In addition to providing an evacuation route during emergencies, the Knik Arm Bridge will relieve congestion by providing another route to and from these communities. Photo: Knik Arm Bridge and Toll Authority

 

The months that followed were filled with uncertainty. Could development still occur in this waterway? Could we identify construction techniques and adjust schedules to ensure the whales' lives weren't affected?

At this point the Federal Highway Administration (FHWA) entered into formal consultations with the service to answer fundamental questions about construction in marine environments. We worked closely with the service to identify what information and modifications would prove whales wouldn't be harmed and achieve a biological opinion of “no jeopardy.”

After three years of research and communication, a biological assessment explaining the impact of proposed alternate construction techniques and letter of authorization application were submitted. On Nov. 30, 2010, the service concluded that “the described action is not likely to jeopardize the continued existence of the Cook Inlet beluga whale, nor destroy or adversely modify its proposed critical habitat.” FHWA was free to issue us a build record of decision without requiring a new impact statement.

Confirming previous assumptions

Marine mammals use sound to communicate, capture prey, navigate, and avoid predators; and biologists don't want excessive noise levels — one of the greatest negative impacts of in-water construction — to alter a species' behavior.

Oscillators, which install pilings by drilling rather than hammering, have been used in similar projects because they're assumed to be quieter than pile-driving. But no quantitative evidence existed to back up the assumption. As a result, we funded research to collect the first in-water noise measurements of an oscillator system for drilled shaft bridge foundations. Sound was found to rapidly dissipate over a relatively short distance, indicating that oscillators do indeed minimize impacts to critical habitat (which includes the endangered species' prey).

As the first such measurements to be documented, the research provides baseline data for our project as well as projects globally where this method for drilling shafts can be used. We were asked to present the findings at the Society for Marine Mammalogy's biennial conference on biology in late 2011 and at the Alaska Marine Science Symposium in January.

We plan to curtail construction when belugas are most likely to be present, but our Marine Monitoring Program also needed an effective way of detecting them during nonpeak months. Detection is important because we're required to suspend drilling whenever a whale's present to avoid adversely affecting their behavior, which the service calls a “take.”

Initially, we — like virtually everyone involved in in-water construction — assumed that acoustical monitoring would provide the most accurate and earliest detection. But we discovered the opposite.

During a two-week “proof of concept” study in September 2011, we tested how well omnidirectional hydrophones made by Seattle-based Cetacean Research Technologies picked up the whales. Although promising, visually looking for them worked even better. Extremely high-powered (i.e., 25x150) “big eye” Fujinon MT150 binoculars with reticle spotted them up to six miles away. In fact, sometimes we saw a whale but picked up little or no vocalizations. Ultimately, the binoculars, the naked eye, a digital theodolite (a surveying instrument that measures both vertical and horizontal axes), and a rest station produced the best results.

Armed with this data, we added and refined conservation measures to minimize impacts by:

  • Not pile-driving from August to December, when whales are using the inlent; and limiting the activity from December through July, when they're less frequent.
  • Establishing a 2-square-mile safety zone and refining it based on sound measurements within the area. This allows us to take actual site conditions into account to ensure the animals are protected.
  • Monitoring the zone for whales before, during, and after pile-driving to hold a template in place to guide the oscillating drill. Monitoring will begin 30 minutes before initiating the “soft start” for pile-driving and continue as long as pile-driving is required. A soft start begins a process at less than full force, alerting wildlife to impending activity so there's time to leave an area before the process reaches full energy. Drilling won't begin unless and until observers have good visibility into the insonification zone, meaning we'll postpone the activity until fog lifts or light conditions improve.

Experienced marine mammal observers will look for whales both within and as they approach the safety zone in which noise levels could disturb the mammals. Monitoring sites will be established at a sufficient distance to give crews enough advance warning to shut down operations.

We'll avoid collateral impacts to the marine environment by not building permanent boat-launch facilities or providing direct access to tidelands during construction.

We're securing the final key permits, and hope to break ground next year. In the meantime, we continue collaborating with state and federal regulators to resolve environmental challenges while developing the infrastructure Alaska needs to prosper.

— McCarthy (shannon.mccarthy@alaska.gov) works in Government and Public Affairs for the Knik Arm Bridge and Toll Authority in Anchorage, Alaska.