When was center hill lake built

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Center Hill Dam is founded in nearly flat lying limestone and shale of Ordovician age. In ascending order, the formations present at the dam site are the Carters, Hermitage, Cannon, Catheys, and Leipers of Ordovician age, the Chattanooga of Devonian and Mississippian, and the Fort Payne of Mississippian age. The contact between the Hermitage and Cannon formation is an unconformity with a significant amount of karst development.

The Catheys formation forms the upper portion of the foundation of the concrete dam and earth embankment see figure below. The Catheys is a finely crystalline to crystalline, hard, fossiliferous limestone. The contact between the Cannon and the Catheys is also an unconformity with localised karst development.

Limestone formations of the site geology, looking upstream: Top view — right rim, concrete and earthen main dam; Bottom view — left rim. Elevation msl is the spillway crest and elevation msl is the approximate stream bed. Down-cutting of the river through the rock layers has produced near vertical fracturing.

The joint patterns are roughly normal to each other and follow the general line of two arms of the bend of the river. The fractures and loose planes create an interconnected system of open features caused by millions of years of groundwater solutioning activity. The fractures and joints are filled or partially filled with soil or residual soil as shown in the middle photograph opposite.

Under the pressure of the reservoir head, typically ranging between ft m , internal erosion of the cavity infilling material has created a phenomenon known as piping. Typically, piping progresses from the downstream or outlet end and propagates upstream until an open conduit is completed.

As water erodes material from the karst features, the diameter of the opening conveying the water is ever increasing. This results in an increasing volume of water, a higher water velocity and higher erosive potential.

This severe progression of piping is most evident through the left rim. Along both the left and right abutments, piping is likely along both vertical joints and weak, horizontal bedding planes. Seepage through the main dam and saddle dam foundations is implicit from a combination of historic foundation data and current distress indicators such as abnormal piezometer levels, downstream wet spots and springs, cold zones at depth, and abnormal settlement.

Both the main dam embankment and the saddle dam are constructed of high quality, well-compacted clay. The main dam embankment lies on alluvial soils for much of the footprint. The designers believed conventional cutoff trench foundation treatment, supplemented with a single line grout curtain, would provide adequate seepage protection.

The 10ft 3m wide trench, however, was not deep or wide enough to sufficiently act as a long-term seepage barrier. The trench was designed with 1V:1H side slopes and is within primarily the Catheys and Cannon formations. The rock in these formations is soluble limestone riddled with fractures and vertical joints ranging in size from fractions of an inch to more than 50ft 15m. Stepped into the left abutment, slopes along the axis of the cutoff trench were near vertical and irregular see photo, below.

Main embankment left abutment cutoff trench. Note narrow, near vertical slopes and irregular sides. For the first 18 years after construction, no problems were detected with the embankment. In at Wolf Creek Dam, however, muddy flow in the tailrace was observed, followed by large active sinkholes on the downstream embankment. These projects were designed and built in similar geology with similar design philosophy.

The Wolf Creek piping crisis heightened concern with the similarly constructed Center Hill embankment. Prior to the Wolf Creek sinkhole, no instrumentation existed at either project.

Permanent piezometers were installed throughout the Center Hill embankment and switchyard in One study was temperature profiling from the bottom of the top of rock piezometers. Several zones of colder temperatures were found. Many solution channels crossed the core trench within the rock. District personnel concluded that a number of potentially serious conditions existed and an embankment grouting programme was performed along the axis of the embankment from Drilling was single line on 2.

Soft zones were found with drill water loss and connections between drill holes. Drill fluid losses and large grout takes required a contract modification to fill cavities. A total take of about 30,ft 3 m 3 of solids were placed in this programme. Early in the field investigations of the dam site, designers realised the thin reservoir rims on the left abutment might develop seepage through solution channels and joints in the Cannon and Catheys limestone formations.

Field investigations were performed on several springs. These investigations did not reveal immediate concerns; however, designers considered remedial work would be required in the future after impoundment. Cavities encountered in the exploratory borings were primarily in the purer limestone of the Cannon and Catheys formations, but were too intricate to be effectively treated.

In January , seepage developed through the left abutment and rim as the initial reservoir was filled. Maps of Center Hill Lake. Information about Center Hill Lake marinas. Information about Passes. Information about permits at Center Hill Lake. Points of Interest at Center Hill Lake.

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