The Rough River Dam Safety Modification Phase II Project includes the construction of a new left abutment outlet works in order to facilitate cutoff wall construction. Completion of the new outlet works must require a new approach channel, control tower, service bridge, outlet conduit tunnel, stilling basin, and retreat channel along with commissioning of the new control tower. Completion of the cutoff wall requires abandonment of the existing right abutment outlet works, construction of a work platform, slurry control grouting, construction of a cutoff wall into the dam foundation and through the existing outlet conduit, abandonment of the existing control tower, backfilling the existing retreat channel, instrumentation installation/relocations, and relocation of Highway 79 back to the dam crest.
- Approach Channel: The approach channel is 945 feet long and 50 feet wide with 6V:1H side slopes. The excavation consists of a combination of underwater dredging, underwater intact rock excavation, and surface excavation in predominately hard bedrock.
- Control Tower: The control tower will be 177 feet tall and be composed of reinforced concrete having a footprint of 56 feet by 60 feet. The control tower will have two 6.25-feet x 14-feet service and emergency gates for primary flow conveyance. The tower will have a 150-feet long service bridge extending to the left abutment. A 600 feet long cohesive earth cofferdam founded on dentally treated bedrock will be required to protect the excavation up to the top of active storage for the reservoir. A double line grout curtain will be completed below the cofferdam and extend to surround the perimeter of the control tower pit excavation to minimize groundwater and seepage entering the excavation work area.
- Tunnel: The approximate 970 feet long tunnel will have a 14 feet inside diameter tunnel with a 12-inch abrasion resistant reinforced concrete liner. The tunnel heading shall be from the downstream portal. The upstream portal shall be constructed integral to the control tower. The portals and portions of the tunnel extending below the dam footprint shall be mechanically excavated.
- Stilling Basin: The stilling basin will be 115 feet long, 40 feet wide, and approximately 55 feet below the ground surface. The stilling basin excavation shall be staged to facilitate tunnel completion. The excavation will have a 15-foot horizontal bench, and rock fence located above the training walls. The bedrock excavation will continue downstream of the stilling basin and will be protected via a 2-foot thick concrete apron before transitioning to KYTC Class III Channel Lining at the intersection with the historic river channel.
- Abandonment of the Existing Control Tower: Once the new outlet works is operational and fully commissioned, the existing control tower and conduit will be abandoned by permanently sealing the existing service gates and filling the lower control tower and outlet conduit with balanced, stable, high mobility cement/bentonite grout or non-shrink concrete.
- Cutoff Wall: A new and complete 1,640 feet + long, 2 feet minimum thick, concrete cutoff wall through the embankment and into the foundation rock. Depth of the wall varies across the dam but can be as great as 200’ from the crest of the dam. Additional slurry control grouting will be required near the existing conduit. The cutoff wall will sever the existing conduit and extend through to the bedrock below. The work at the conduit area shall not proceed until the new outlet works is fully functioning and the existing outlet works has been suitably abandoned.
- Relocations: Highway 79 will be located back to the crest of the dam and dam restoration.
