Sep. 25—Tuttle Creek Dam is getting a facelift after flooding two years ago damaged the rock overlay along the north bank.
U.S. Army Corps of Engineers crews are trucking in limestone chunks weighing a ton or more from the Bayer Construction quarry near Zeandale to fill in a 100-foot section of the overlay where 2019 flood waters degraded the north embankment.
Workers are filling in a stretch of rock overlay 600 feet long, 60 feet wide and 12 feet deep along the north side of the dam close to the road on top of the structure to bring the rock layer back to a gradual incline. Right now, that incline has a sharp drop-off on the north face just a few feet from the edge of the road, marking where the flood damage begins.
Brian McNulty, Army Corps of Engineers operations project manager at Tuttle Creek, said the lake was inches away from capacity as flood waters kept washing against the north face for several months in 2019, eroding the rock. He said the first phase of repairs consist of "a big wedge" of locally sourced rock being laid in alternating layers.
Corps project engineer Kyle Street said the main focus is keeping the larger stones from rolling down the embankment as the excavator positions the one-ton rocks for maximum coverage. He said crews will first lay in what's called "bedding rock," or smaller stones 8 inches or less in diameter.
"That bedding material acts somewhat as a filter," McNulty said. "The core of the dam is not very far underneath the rock in the steep part of the embankment."
McNulty said the core of the dam is clay-based, and the rock layers protect that core as waves wash against the embankment. Over time, McNulty said strong waves will wash out loose rocks and reveal that clay core.
"The rock fill is good because it's harder to erode," McNulty said. "The 2019 flood damaged that fill, so we're re-establishing that armor on the thinnest part of the core of the dam."
McNulty said the long, narrow shape of Tuttle Creek Lake creates waves that can stretch nearly the entire length of the lake. With enough time and power, those waves will cause erosion.
"With the orientation of the lake and the way the wind was blowing, the waves were splashing along the north side of the dam," McNulty said. "The main concentration of waves was pretty much in the center of the dam."
Tuttle Creek experienced its second highest pool in its history on May 31, 2020, at 1,135.84 feet, or about 60.84 feet above normal. This was mere inches from the top of the spillway gates. The only time it's been higher was in 1993, when the Corps was forced to open the dam's emergency spillway gates to protect its integrity, causing flooding in neighborhoods and areas downstream.
McNulty said the first phase of construction should wrap up by the end of November, with the second phase possibly being completed in mid-March depending on project funding. Bank fishing and pedestrian traffic is not allowed along the dam face while construction crews work in the area. The east and west dam parking lots are also closed to traffic during construction.