Alaska Airport Runway Expansion
Coastal Engineering Support Services
Sitka Airport (SIT) is a state-owned airport providing year-round service for commercial, private, and military aircraft. The airport’s single paved runway (11-29) is set at elevation 26 ft MSL, built on a reclaimed island in Sitka Sound. Due to its exposure and relative short length, the Federal Aviation Administration (FAA) required that the airport’s runway safety area (RSA) be expanded.
In 2010 and 2011, Lally was requested to support engineering efforts carried out by MACTEC Engineering & Consulting relating to site data acquisition, coastal engineering and construction. Lally performed field reconnaissance in winter 2010/2011 to oversee a marine geophysical survey, inspect the conditions of the existing Runway 1129 embankment fill and breakwater, and investigate potential sources of quarry stone and other fill materials for the runway improvements project.
The marine geophysical survey, conducted by a subcontract marine surveyor, consisted of seismic reflection survey and single beam, dual-frequency bathymetric survey within and around the offshore fill boundary of the proposed runway extension. Recommendations made by Lally to run additional cross track survey lines and integrate a heave/pitch/roll (motion) compensator to remove long period swell from the bathymetric data were made and improved survey data quality and utility.
Lally met with Alaska Department of Transportation (ADOT) managers for access to the runway, inspected breakwater conditions, and acquired local knowledge on storm activity, wave runup and overtopping impacting runway operations. Recommendations were made for further data needs and hindcast data in order to determine optimal breakwater parameters, including crest height, width, armor slope, and stone sizing to reduce wave runup and overtopping onto the runway during storm events. Further effort in Sitka was made investigating potential sources of armor stone and filter stone, and staging areas for direct loading of barges to avoid traffic through town to the airport.
The project was issued for construction by FAA and completed in 2013. In total over 1,200,000 tons of armor stone, filter stone, and crushed gravel were imported from both local and Canadian sources for the project.
Services Provided
Marine Geophysical Survey Oversight
Airport Breakwater Inspection
Coastal Processes Assessment
Construction Planning
Location
Sitka, Alaska