Some of the boulders weigh up to 15,000 pounds each. According to Luther Aadland, a dam modification expert for the Minnesota Department of Natural Resources in Fergus Falls, the boulders are being placed in 11 rows extending about 300 feet downstream from the dam. The first two rows below the dam are partial, Aadland says, while other nine rows will extend across the full width of the river. Aadland says each row is designed to drop about 1 foot in terms of water surface. When finished, the rows of boulders will reduce the vertical drop of the river below the dam to 5 percent, a slope that's very similar to a natural set of rapids.
Heavy work Getting the rocks into place is no small feat.
By Tuesday morning, the two partial rows were in place on the Minnesota side and work had begun on placing the first full row. Aadland said the farthest-downstream boulders probably won't be placed until spring flows recede. At the same time, the boulders will eliminate the dangerous roller currents associated with lowhead dams. Eddies and riffles between the veins of boulders will accommodate fish passage and create ideal spawning habitat for species such as walleyes and sturgeon, Aadland said. While the rows of massive boulders might be impressive, they're just one part of the project.