Just above Knoxville, the mainstem Tennessee River begins at the confluence of the Holston and French Broad Rivers. Cherokee Dam is located at Holston River Mile 52.3 and Douglas Dam is located at French Broad River Mile 32.3. The Tennessee Valley Authority (TVA) initially constructed both Projects on a crash schedule to supply electricity for industrial needs leading up to and during World War 2. Cherokee Dam is a 175-foot-tall, 6,760-foot long composite structure consisting of north and south earth embankments, concrete gravity spillway with nine radial gates, intake/powerhouse, and nonoverflow sections. The Project also includes three earth saddle dams with a combined length of 1,770 feet and heights of 15, 30, and 85 feet. The Cherokee Project was completed on December 5, 1941 (one day before the attack on Pearl Harbor) after a construction period of 16 months and 5 days. The Douglas Project includes a 202-foot-tall, 1,705-foot-long concrete gravity main dam consisting of nonoverflow and intake/powerhouse sections, an 11-bay spillway with radial gates, and 10 earth saddle dams. The largest (Saddle Dam 1) is 102 feet tall and 1,920 feet long; the others vary from about 5 to 39 feet tall and from 20 to 650 feet in length. There is also an earth dike that protects the Town of Dandridge from inundation by the reservoir. Douglas was constructed in just 12 months and 17 days, with completion on February 19, 1943. Challenges during construction included karst conditions in the foundation at both sites. TVA recently completed semi-quantitative risk assessments of both Projects, and despite the rapid construction schedules only two potential failure modes related to karst were determined to be risk-driving. Both plot below tolerable risk guidelines, and only one is at a main dam (the other is at an ancillary structure). This presentation will cover the background and history of both Projects, including how karst features were treated during construction. It will also summarize the results of the risk assessments, and contrast how Cherokee and Douglas compare with TVA’s Boone Dam - which also has solution cavities in the foundation, but which required construction of a cutoff wall to mitigate high-risk karst -related failure modes.
