Nearly 150 people representing several surrounding counties gathered at Rough River State Resort Lodge on Tuesday night to hear an update on the upcoming Rough River Lake Dam project. Jeff Esterle, a geotechnical engineer and Dam Safety Program Manager for the U.S. Army Corps of Engineers, gave an hour-long presentation detailing the reasons behind the project and the timeline for its completion.
The Army Corps of Engineers conducted a Dam Safety Modification Report at Rough River in 2012, finishing the study in July of that year. The study's findings noted an “unacceptable risk due to foundation conditions that can be found when a dam is constructed on karst geology,” a dissolution of a layer of soluble bedrock, usually carbonite rock such as limestone.”
Simply put, the dam, which became operational in 1958, was erected on limestone bedrock, which can threaten the integrity of the dam if left un-rehabilitated. The Louisville District of the U.S. Army Corps of Engineers led a “routine five-year dam safety inspection” in June of last year, and Corps personnel additionally conducted “heightened surveillance during elevated reservoir pools,” to properly test the strain on the dam.
And while the dam is “currently operating as intended” and there is no immediate threat of dam failure, it has been recommended by the U.S. Corps of Engineers that a “major rehabilitation” take place at the dam “to ensure the structure’s integrity and lower the project’s risk.”
Diane Stratton, Rough River Lake Park Manager, stressed that the construction to take place, potentially over the next five years, is a preventative measure against future dam failure.
The remedial construction is to be completed in three stages (unless it is determined, at a later date, that the third stage of the proposed process is unnecessary). It begins with the construction of a new road, essentially moving Hwy 79 -- The project will begin at the top of the dam, and construction equipment of all sizes must have easy access to the work site. Something that would be impossible if the existing Hwy 79 remained open to traffic.
So in the interest of steady traffic flow and ready access to the work site by construction vehicles, it was determined to “move Hwy 79 to the lake side of the dam.”
Although moving Hwy 79 will begin in a few weeks, this phase of the project is not expected to be completed until 2015.
When the road has been moved, holes will be drilled into the top of the dam and grout injected into the limestone beneath. Thus strengthening the base -- or toe -- of the dam by “filling cracks, fissures and other openings in the bedrock that lies underneath the dam.”
The grout insertion phase is expected to be completed in 2016. At that time, the dam integrity will be studied, and officials will decide if it is necessary to install a “concrete cut-off wall” at the dam to further strengthen it, mitigating seepage.
If it is determined to construct a cut-off wall, the project isn’t expected to be completed until 2019.
Esterle and Stratton both stated that the Corps does not anticipate a prolonged drawdown of the reservoir pool and will utilize normal pool levels for the duration of the construction. It is possible, though, that at some point during the construction, it may be necessary to temporarily hold the lake below the normal recreation pool level. The summer pool level norm is 495 feet.
The (potential) five year project is expected to cost in the 150 million dollar range, with the initial road construction phase costing less than five million dollars.