Installation of an orifice gate at Center Hill Lake has been rescheduled for August 4 due to the need for a larger crane, according to the U.S. Army Corps of Engineers.
Originally scheduled for July 8, a small crane was scheduled to allow traffic to pass the dam along Highway 96 while the work was underway. However, the crane’s cables were not quite long enough to lower the gate down the upstream face of the concrete portion of the dam to its position near the base of the dam. The lowering of the gate has been rescheduled for Monday, August 4th, 2008 using a larger crane with longer cables. This crane will require full road closure from 9 a.m. until 2 p.m.
Work is continuing on the Corps of Engineers’ Center Hill Seepage remediation, a six-year, four-construction contract overall plan. The first of four large construction contracts to correct seepage problems at Center Hill Dam was not delayed by the altered schedule, but is in high production, working six days per week, two 10-hour shifts and has only halted for minor, temporary weather-related delays.
This contract will reduce seepage by a series of closely-spaced grout holes pumped into the earthen portion of the dam foundation and the left rim foundation, beginning in September and continuing for more than a year.
As part of environmental mitigation to continue a minimum flow into the Caney Fork River once the seepage is reduced, the overall seepage reduction plan includes manufacture and installation of an orifice gate. The orifice gate (photo 1) is a steel plate with open ports and will be placed over one of six 4 x 6-foot culverts called sluice gates, located at the base of the concrete portion of the dam. This orifice gate will provide an approximate 200 cubic foot per second minimum flow through the dam and will provide cold water releases and improve dissolved oxygen downstream to maintain the fishery once the seepage is cut off.
Tim Dunn, Resource Manager of Center Hill Lake, spoke with WJLE Friday morning about the project. "Earlier this year, in late February we awarded the first construction contract which is the first of several large contracts. It's a two year contract to grout the main earthen embankment of the dam and the left rim, which are the most critical parts of the dam to take care of first. So those are currently underway. If you come by the dam now you'll see the contractors well underway with clearing the left rim hillside and actually cutting through the hillside to facilitate the grouting or to get us in there where we can do the grouting much quicker and easier. They are also building a work platform on the upstream side of the earthen embankment and building a platform on the downstream side. So you can definitely see a lot of work going on around the dam now. We should be ready to start the actual grouting, which is drilling down into the ground underneath the dam, to inject a cement type mixture into the void later this summer, probably around September of this year."
"Also as part of the environmental mitigation, we are in the process of installing an orifice gate, which is a gate that goes on the sluice gate, which is an opening at the very bottom of the dam. We're in the process of installing it so that we can allow about a 200 cubic foot per second minimum flow of water to flow through the dam to offset the seepage that we're going to be blocking with the grouting work. What this will do is ensure that we have a continual flow of good cold water for the trout fishery down stream and it will also help water quality on downstream of the Caney Fork and into the Cumberland River system."
"We actually worked on it (orifice gate) earlier last week. We attempted to use a smaller crane so that we could keep the roadway over the dam open for the public to use. However the crane we used was not quite large enough to get down to the depths that we needed to get to so we have re-scheduled for early August. Actually on Monday, August 4th from 9:00 a.m. until 2:00 p.m. we're going to bring in a larger crane to set that gate. However, to use the larger crane we're going to have to close the roadway completely for about a five hour period so August 4th we recommend folks find an alternate route to cross the dam if they are down in this area. But that's just one part of the project. The other activities, the grouting and the clearing is going very well and progress is being made everyday."
"The actual rehabilitation of the dam is still well underway. There have been no changes to the plans or no disruptions to that. Just the mitigation of installing the gate has been delayed for about another three weeks or so until we can get a larger crane to set that, but that in no way hinders the actual rehabilitation of the dam project."
"We awarded the first contract in February. It's a two year contract and it was awarded for I believe $87-million. It's a very large construction contract. There will be other contracts. The total project cost is around $260-million and it will last about five years. Somewhere around 2012-2013 is when we will be finishing up the work."
"We have several risk reduction measures in place, one of those being maintaining the lake at a lower level. We're doing well with that. We're trying to target 630 as a maximum pool level and we're hoping to not go lower than the low 620's or 618 at the very lowest this winter. We're very dependant on rainfall so as long as we continue to get a few rains along we'll be doing fairly well with lake levels but if it turns off really dry we could see some really low levels this fall so again, we encourage folks to really be careful out there on the lake. It's still a very large lake, a very deep lake, but there are some areas that are shallower this time of year than what folks are accustomed to seeing so definitely use caution in those areas."
Travelers are encouraged to plan alternate routes during this time (August 4th). The closest alternate route to drive from one side of the dam to the other is to travel I-40 just north of the dam. From the east end of the dam, take HWY 96 to I-40, travel I-40 west for approximately 10 miles to exit #258. At exit #258, travel south on HWY 53 for approximately one mile before turning onto HWY 141, which leads to the west end of Center Hill Dam.
Additional information on the Center Hill Dam Seepage Rehabilitation Project may be found on the Nashville District website at http://www.lrn.usace.army.mil/CenterHill/.