Wilson Lock dewatering provides opportunity for inspection in dry conditionsView Source
Wilson Lock dewatering provides opportunity for inspection in dry conditions
Nashville District – 4.12.22
By Heather King
FLORENCE, Ala. (April 11, 2022) – Work crews recently drained more than 15 million gallons of water from Wilson Lock to provide maintenance personnel dry conditions to repair and rehabilitate the navigation lock to keep vessels moving up and down the Tennessee River.
Wilson Lock is located between Florence and Muscle Shoals in northern Alabama. At 110-feet high and 600-feet long, the main chamber is the highest single lift lock east of the Rocky Mountains. The main and auxiliary locks allow commercial and recreational traffic to flow up and down the river, while the 16-mile, 15,500-acre lake formed by the Tennessee Valley Authority dam provides beauty and tourism to the area. Declared a National Historic Landmark in 1966, Wilson Lock and Dam is a spectacular site.
A maintenance team from the Great Lakes and Ohio River Division Regional Rivers Repair Fleet arrived March 24th to coordinate with the Wilson Lock staff on the periodic maintenance project. To ensure the structural integrity of the lock, a periodic dewatering is required. In the dewatering process, all the water in the main lock chamber is pumped out, exposing the chamber and its components. Dewatering allows maintenance crews to access machinery and components of the lock which are normally inaccessible.
The dewatering process requires a complete shutdown of the main lock for a period of 30 days. Requiring commercial vessels to pass through the smaller auxiliary lock, the shutdown creates longer lockage times.
Volunteering to assist the team at Wilson, Guntersville Lockmaster Ryan Johnson said, “A 30-day shutdown is better than a six month or longer shutdown because of a catastrophic failure of the lock or its components.”
In preparing for the dewatering, and throughout the process, safety is key, in and around the site, which has significant potential safety hazards. Crews are using cranes and lifting devices to reach heights up to 125 feet! Other traditional personal protective equipment like hard hats, eye and hearing protection, harnesses for anything above six feet, and life jackets are also required.
“Everything at Wilson is twice as big and twice as heavy,” said Johnson.
Due to the sheer magnitude of Wilson Lock, dewatering and the subsequent inspection and maintenance require a great deal of preparation, coordination, and effort. The Tennessee Valley Authority has a crew of painters available to remove any lead-based paint from the gates, thus removing hazards for maintenance crews. The Middle Tennessee River maintenance teams conduct all the work on the valve systems, while Cumberland River mechanics and crane operators volunteer to assist maintenance operations.
Prior to the actual dewatering process, divers play a critical role. Josh Miles, Nashville District lock and dam equipment mechanic and surface supplied air diver (hard hat), explained the role divers play.
“About a week before the actual dewatering process starts, we [hard hat divers] must inspect and make any needed repairs to the lock’s equalizing valves, ensuring water can actually get pumped out once we seal the upper chamber off,” Miles said.
Hard hat divers not only inspect the chamber but lay the crucial foundation to prepare the chamber for dewatering.
“We assist the fleet in setting the bulkheads on the upstream and downstream side to block the flow of water into the chamber, so the water in the chamber can get pumped out,” Miles said.
“Historically, dewatering at Wilson lock takes place every three years. However, due to many issues, seven years have passed since the last one,” said Brian Brewer, assistant operations manager for the Middle, Tennessee River.
Lockmaster Clay Askew noted the impact of the seven-year dewatering lapse is predictable.
“Since the last dewatering in 2015, we anticipate some predictable findings like cavitation in the concrete around the bulkheads. Additionally, three of the four main filling and emptying valves are shifting, and we found some bad seals on the valves and machinery itself,” Askew said.
For a structure which became operational in 1959, these findings are normal. However, it is important to note these issues are only discoverable through the dewatering process. If the issues are not addressed, eventually this could mean the complete failure of the valves. The cavitation around the bulkheads, if not properly sealed, could prevent future dewaterings because the bulkheads, which prevent water flowing into the chamber, would not set securely in the bulkhead slots. If dewatering inspections cannot occur, utilizing the lock becomes a giant game of Russian Roulette.
The inspection will conclude the week of April 25, with the lock returning to complete functionality April 28, 2022.
(The public can obtain news, updates and information from the U.S. Army Corps of Engineers Nashville District on the district’s website at www.lrn.usace.army.mil, on Facebook at http://www.facebook.com/nashvillecorps and on Twitter at http://www.twitter.com/nashvillecorps.