One of two refurbished lock gates is lowered into the canal at the Great Bridge Lock Feb. 20, 2014. The 72-ton set of aging lock gates were removed after 25 years and are being replaced with refurbished gates - part of a service plan to increase the lifespan of the Great Bridge locks. Each set of canal gates, which are managed and operated by the Norfolk District, is removed and refurbished on a rotational basis every 15 to 20 years.