Arkabutla Dam Outlet Conduit Internal Erosion – a Case History

Arkabutla Dam is located near the town of Hernando, MS - about 20 miles south of Memphis, TN. The dam was put in service in 1943 and consists of an 85-foot tall, 9700-foot long rolled earth fill embankment across the Coldwater river, a tributary to the Yazoo river, which flows into the Mississippi river near Vicksburg, MS. Since its completion in 1943, there have been numerous problems with internal erosion of the poorly graded foundation sands into and through joints in the outlet works conduit and from the drains in the stilling basin. The problems came to a head in May of 2023, when a sinkhole was discovered near the downstream end of the outlet conduit, and the project’s emergency action plan was activated to warn the public of a possible failure situation developing at the dam. This paper will provide a summary of USACE’s response to the emergency, including a review of the data from recent instrument installations and other observations which support the progression of the internal erosion failure mode along the outlet works of the dam.