Dam surveillance plans activated following seismic activity
Labor Day weekend is a time for family and friends to gather and travel to popular recreation locations. For most, the holiday is seen as a relaxing three-day vacation from the normal moving and shaking. However, several in the area couldn’t miss the shaking felt at 7 a.m. Saturday morning Sept. 3.
Oklahoma shook with a record 5.6 magnitude earthquake that morning reported in Pawnee with the rattle felt in several surrounding states, including several projects in the Kansas City District.
Though this was the first shake for many in the district, lake offices knew how to respond. Personnel reported to their Project Office to conduct initial inspections of the dam, including checking for abnormalities, shifts or cracks in both the exterior and interior of the dam, the spillway and the shoreline area. While the initial inspections last up to two hours, the staff knew this was an important part of their job.
“Each lake project has a dam surveillance plan and emergency action plan specific for that location,” said Scott Mensing, dam safety program manager. “Initial inspections typically last a few hours to determine if any damages occurred. Due to the size of this earthquake, each project felt the tremors.”
“My staff that lives near Smithville Lake felt the ground shake. As soon as the quake hit, they were in communication with me and reported immediately to the dam to begin inspections,” said Lora Vacca, operations project manager for Smithville, Longview and Blue Springs lakes in Missouri. “I had to contact the staff for Longview and Blue Springs lakes as they were not aware of the quake. Luckily, and similar to our other lake projects, they did not find any abnormalities, but they continued monitoring the dam throughout the day due to possible aftershocks. Fortunately the earthquake didn’t startle our recreation visitors that holiday weekend; the fishing, boating and camping continued.”
However, Tuttle Creek Lake is situated about 15 miles west of the Humboldt fault line, passing through eastern Kansas, which could make visitors a little more concerned.
“Everyone we came in contact with was real calm,” said Brian McNulty, operations project manager for Tuttle Creek Lake. “Some people out walking stopped to ask us what we were doing during our initial inspections, but no one seemed concerned and, to our knowledge, no visitors left the lake.”
While this kind of activity in Kansas is not a common occurrence, a seismic reinforcement project consisting of warning sirens and 351 concrete transverse shear walls in the underlying alluvium to stabilize the dam's foundation was completed in 2010.
“As a precaution, based on the earthquake's magnitude and our distant proximity to the reported epicenter, our staff conducted a dam inspection. The reporting confirmed that no damage occurred to the structures,” said McNulty. “Due to the reinforcement project, our staff has great knowledge of how an earthquake could affect the dam. And by chance, our monthly inspection of the strong motion accelographs [seismic instruments] were conducted the day before the earthquake, so we knew they were operational when the event happened.”
“Inspections include checking the dam crest, embankments, slopes, downstream tow and abutments for signs of erosion, cracking and settlement. Also included are the spillway and outlet works, stilling basin tower and bridges to look for differential movement, deflections or cracking,” said Mensing.
While this is not a common practice, staff at all 18 lake projects were proactive and their reporting and response to the district and public was successful.
“All projects reported back in a timely fashion and the dams did not experience any damage,” said Mensing. “Overall the district feels the reaction by the team was successful and the processes followed were correct. We learned a few lessons with this event and may update a few processes accordingly to ensure we are able to respond appropriately and quickly during the next earthquake.”