Sonar scans Ohio River bottom

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By Phyllis McLaughlin

The Trimble Banner


Quietly, the Milton-Madison Bridge project is continuing as teams work to collect information that may help engineers determine the best of three possible sites for a new span across the Ohio River.

Sonar exploration of the river bottom was conducted on Thursday, July 2. From a small silver-colored boat, hydrographer Pat Hahs of Mainstream Divers used side-scan sonar equipment to map out debris, archeological artifacts and anything else lying at the bottom of the river.

Using a computer and a global positioning system (GPS) to guide him, Hahs steered the boat up and down the river along an invisible grid starting about 1,500 feet west of the bridge and stretching just over a mile  upriver. The sonar, which looks something like a small torpedo, scans about a 180-degree swath to the left and right as the boat progresses, sending back amazingly clear, images of the river bottom to Hahs’ laptop computer.

Images created from the scans will be studied back at the office, Hahs said, where he will measure the size of anything found on the river bottom and determine what the objects are and how far they are below the surface.

The technology, he said, is similar to that used by search-and-rescue teams to locate bodies or sunken vehicles.

Hahs said Thursday that his report should be completed within a week or two.

In the meantime, the cultural resources team from Wilbur Smith Associates has begun conducting a survey of possibly historic structures on both sides of the river in the areas where a new bridge might be constructed. Wilbur Smith is the engineering consulting firm from Lexington, Ky., hired to lead the bridge project.

In addition to sifting through old records and land surveys, team members are going door to door to talk to homeowners, take photographs and document structures to identify those that are at least 50 years old.