Trends Spring 2016 - Page 3

Ayres did a great job of taking on the project. Their willingness to jump in at a time when we thought we were facing a really substantial cost increase was so important. been out of operation for more than 20 years. But in the early 1980s, Dakota County officials restored the dam’s electrical-generating capacity. “The facility was gutted and kind of put back in the most simple, basic, cheapest way possible,” Petersen said. But that proved to be merely a stopgap measure. In May 2011, Ayres submitted its proposal for how Dakota County could satisfy an order from the Federal Energy Regulatory Commission to upgrade the capacity of the Byllesby Dam to deal with problems of water “overtopping” the dam at times of peak river flow. According to FERC’s modern safety standards, Byllesby Dam is classified as a “high-hazard dam.” Pete Haug, Ayres’ project manager for the dam project, explains the “high- hazard” classification means that, with the City of Cannon Falls lying just a mile downstream, “there is a very good chance people will die if the dam fails.” While the dam has never experienced such a catastrophic failure, “the safety standards are so much higher now than when the dam was built” in 1910, Haug says. To bring the dam up to today’s standards, the Ayres team planned and supervised the resurfacing of the original concrete dam, which is 60 feet high and more than 1,100 feet long. The biggest improvement involved adding two 65-foot-wide by 14-foot-tall hydraulically operated floodgates to a spillway created just to the south of the dam. Multiple systems were put in place to control the rate of river flow through the floodgates; now water can pass through at a rate of 37,500 cubic feet per second when the gates are fully open. “We added 80 percent more flood capacity to the dam,” Haug said. “That’s an incredible increase.” The project was completed between May 2013 and July 2014. During that time, construction crews contended with extreme weather conditions, ranging from 99-degree heat that summer to -24-degree cold and 70 inches of snow that winter. “This was a unique project for the County,” Petersen said, explaining that its sheer size and complicated nature required a broad range of expertise that was well beyond the scope of County staff. All challenges met From creating engineering design – Josh Petersen, Senior Resources Engineer, Dakota County Environmental Resources TRENDS │3