Blakely Mountain Dam Monitoring System Completed.

Construction work is completed on the Government Contract issued by The Corps of Engineers on a new monitoring system to keep an eye on seepage at Blakeley Mountain Dam.

Construction of a 2 million dollar seepage collection system consisting of an impervious berm with 10 manholes, ditches, and a V-notch weir was completed in October 2009 to monitor flow through the dam.

Three manholes were equipped with turbidity meters to monitor soil particles movement through the system.

United States Army Core of Engineers will monitor the Lake Ouachita's Blakely Mountain Dam with installation of the new Equipment. U.S.

The Corps of Engineers installed the monitoring system to keep an eye on seepage at the Dam. The monitoring system is part of the analysis and response to the 2005 inspection within the overall dam safety program.

 In the wake of the regular 2005 inspection, engineers discovered that a layer of filter material had been installed incorrectly when the dam was originally built in 1953.

Filter material is designed to aid normal seepage under the dam. Without it, the seepage must be monitored more closely over time.

Buoy Placement for Dye Testing Locations below Blakely DamAll dams are designed to allow for controlled seepage. There are multiple layers of material in the core of the dam that allow a small amount of water to flow through the dam without moving any materials.
If material moves, over the long term; it would weaken the structure of the Dam.

 “The Dam has performed well over its 50 years of service and we believe at this time that it is functioning normally, however; we need to watch the seepage issue more closely as the Dam continues to age”, said Bob Fitzgerald, Dam Safety Officer for the Vicksburg District.

In order to install the monitoring system the Corps worked with Entergy to lower the level of Lake Hamilton during the normal winter drawdown of 2008 - 2009. This draw down required the maximum allowed drop in Lake Hamilton based on current permits to a total of 9 feet lower than normal pool.

 This will expose the piping system under Blakely Mountain Dam that allows seepage so the water can be channeled and the measuring system installed.

 For more information contact Frank Worley, Deputy, Public Affairs, (601) 631- 5053   Information courtesy of U.S. Army Corps of Engineers

Blakely Dam Powerhouse

In May 2006, as part of the dam safety program, a risk assessment screening was performed for Blakely Mountain Dam at Lake Ouachita. This screening determined the dam may be at risk for failure from seepage and piping due to construction methods and the apparent lack of an adequate seepage blanket.

This resulted in the dam being classified as Dam Safety Action Classification II (DSAC II).
Up date: Dam Safety Action Classification is now III (DSAC III).

The DSAC II dams are unsafe or potentially unsafe. Interim risk reduction measures are required to be implemented for dams with this classification. A seepage monitoring system has been designed to evaluate any deterioration of the core material.

 It will take a minimum of two years to determine the dam's condition and fully recommend risk reduction measures.

 Depending on that determination it could be numerous additional years to reclassify the dam from DSAC II to III or IV. Corps Dam Safety policies do not allow raising the flood pool at lakes with a dam classified as DSAC II or DSAC I.

 Since Blakely Dam cannot be reclassified to a higher DSAC classification in a timely fashion.
Members have requested a conservation pool reallocation at Lake Ouachita and are no longer seeking a flood pool reallocation.
Due to the urgent need for water supply in the Central Arkansas region and the timing of the DSAC determination at Lake Ouachita, this report still contains information about both Greers Ferry and Lake Ouachita, but only the Greers Ferry Lake storage reallocation will be pursued at this time. The Greers Ferry Lake and Lake Ouachita reallocations are two completely independent actions. The lakes have no environmental, economic, ecological, or hydraulic connections. The only reason the storage reallocations for both lakes are considered together in this report is because a November 2002 Planning Assistance to States (PAS) Study identified the best alternative for obtaining water for central Arkansas would be to purchase discretionary storage in Greers Ferry Lake and Lake Ouachita.

 

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