WARRENTON — A decade ago, the Port of Astoria worked with the Columbia River Estuary Study Taskforce to expand the wetlands in Vera Slough, a tidal inlet, into the northwest corner of the Astoria Regional Airport from Youngs Bay.

The plan, meant to offset the impact of repairs at Pier 1, worked as designed and created an additional 16 acres of wetlands just off the Airport Dike Trail, raising the average level of water entering the airport by 2 feet.

Now the Port, as it prepares to spend $5 million in state and federal funding on a runway overhaul, has to figure out whether the improved aquatic environment could be endangering the airport next door.

The Port has dealt with cracks in the cement slabs on the airport’s tarmac, uneven settling and depressions where the tarmac connects to vertical drains and buildings. Port commissioners have voiced concern that the water movement in and out of the airport could be ruining the foundation of the tarmac, just as the agency is investing millions in government grants this summer into a runway rehab.

The Port is contracting a hydrologist to determine how water moves in and out of the airport.

“The big takeaway in my mind is that there’s a big change in the drainage characteristics of the airport about 10 years ago,” Airport Manager Gary Kobes said.

Kobes said the information gathered by a hydrologist will be given to a geotechnical specialist to determine what effect, if any, the Vera Slough project has had on the tarmac. The director of CREST, Denise Löfman, will present to the Port Commission on Vera Slough at its meeting Tuesday.

The airport sits on a former alluvial plain, bordered to the north by Youngs Bay and to the east by the Lewis and Clark River.

A dike system, under the jurisdiction of the city of Warrenton, protects the reclaimed land from tidally influenced marshes outside. At four points along the dike are tide gates, designed to drain the inland areas when the water outside is lower, and to seal shut when the tide reaches the gate.

The 2005 Vera Slough project replaced an older tide gate at the northwestern corner of the airport with a newer model — dubbed “fish-friendly” by some — using a float to help regulate at what water levels the gate closes. The change protects against flooding but allows more movement for aquatic life between tidelands and drained areas.

If it is determined the newer tide gate has had a detrimental affect on the infrastructure at the airport, Kobes said the Port would have to talk to the U.S. Army Corps of Engineers, the U.S. Fish and Wildlife Service and other involved agencies to see about modifying the tide gate.

The airport was built through a federal grant in the mid-1930s on land deeded to the Port from Clatsop County. In 1942, the U.S. Navy leased the airport from the Port and used it as an auxiliary naval air station until it was returned to the Port in 1948.

While the runways and taxiways have been repaved at times, Kobes said the tarmac stretching along the Port’s buildings at the airport has not been redone since the Navy days. He added that part of the tarmac is scheduled for refurbishment in 2019, as funds become available through the Federal Aviation Administration.

Five to six years ago, he said, the U.S. Coast Guard rehabbed the slabs leading up to its helicopter hangar, injecting materials underneath to level them out and caulking in between to prevent debris from flying around when the rotor blades of MH-60 Jayhawks are whirling. He added that the Coast Guard, which still faces issues with the ramp, is planning further work on the ramps this summer.

Kobes said the issues with the tarmac have so far shown no indication of affecting the rehab of Runway 1331 this summer. The Port secured $480,000 from a state Department of Transportation grant, used as a local match on a $4.5 million grant from the Federal Aviation Administration funding the rehab of the northwest-southeast runway.

Kobes said he has seen no indication that the runways have been compromised by Vera Slough. “And at this point, I would say it’s a stretch to say that it’s impacted the ramps,” he said.

Löfman said the tide gates have been functioning properly for 10 years. “Right now, there’s just a lot of water out there,” she said, adding there have been higher tides all over the region.