Blakely Dam on Lake Ouachita is one of 694 dams, Nationwide and in Puerto Rico the U.S. Army Corps of Engineers (USACE) owns.
The average life expectancy of an earthen dam is 50 years, and 25% of the dams in the Army Corps of Engineers National Inventory of Dams. 52 percent have reached or exceeded the 50-year service lives for which they were designed. This number is projected to increase to 85% by the year 2020.
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). 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. This monitoring system is scheduled for implementation in 2009. Once the monitoring system is constructed, additional time will be required for monitoring purposes. 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.
Because USACE is responsible for making sure its dams do not present unacceptable risks to the public, USACE transitioned from a solely standards-based approach for its dam safety program to a dam safety portfolio risk management approach. A key mission of the USACE dam safety program is to achieve an equitable and reasonably low level of risk to the public from its dams.
The USACE dam safety program is managed from a risk-informed USACE-wide portfolio perspective applied to all features of all dams on a continuing basis. The urgency of actions, including funding, to reduce risks in the short term and in the long term is commensurate with the level of risk based on current knowledge.
USACE provides risk information to internal and external stakeholders. An informed and engaged public understands risk and can contribute to the evaluation of risk reduction options and can take some degree of responsibility for its safety.
There has been tremendous progress in the USACE Dam Safety Program in the past six years. The program has transitioned from testing new organizational policies, procedures, and organizational elements to operational and production mode. Many great ideas for different program elements have been put in place over the last few years including the implementation of a new comprehensive dam safety regulation that fully embraces and operationalizes USACE’s new risk-informed approach, as well as the establishment of production centers and an assortment of new management tools.
In 2005, the USACE started Screening for Portfolio Risk Analysis (SPRA). This analysis screened every one of the approximately 694 dams in the USACE inventory based on available information, to expeditiously identify and classify the highest risk dams requiring urgent and compelling action (Dam Safety Action Classification Classes I and II Dams).
This screening has yielded a clear but basic understanding of where the greatest risks and priorities are located. Completing SPRA has allowed USACE to develop a Portfolio Investment Plan for more than 300 dams within the portfolio determined to be “actionable,” or posing moderate to extremely high risks. The Dam Safety Action Classification System (DSAC) is intended to provide consistent and systematic guidelines for appropriate actions to address the dam safety issues and deficiencies of USACE dams.
U.S. Army Corps of Engineers (USACE) dams are placed into a Dam Safety Action Classification System (DSAC) class based on their individual dam safety risk considered as a combination of probability of failure and potential life safety, economic, environmental, or other consequences. The DSAC table presents different levels and urgencies of actions that are commensurate with the different classes of the safety status of USACE dams. These actions range from immediate recognition of an urgent and compelling situation requiring extraordinary and immediate action for unsafe dams through normal operations and dam safety activities for safe dams.
DSAC Class I (Very High Urgency) – Dams where progression toward failure is confirmed to be taking place under normal operations and the dam is almost certain to fail under normal operations within a time frame from immediately to within a few years without intervention; or, the combination of life or economic consequences with probability of failure is extremely high.
DSAC Class II (High Urgency) – Dams where failure could begin during normal operations or be initiated as the consequence of an event. The likelihood of failure from one of these occurrences, prior to remediation, is too high to assure public safety; or, the combination of life or economic consequences with probability of failure is very high.
DSAC Class III (Moderate Urgency) – Dams that have issues where the dam is significantly inadequate or the combination of life, economic, or environmental consequences with probability of failure is moderate to high.
DSAC Class IV (Low Urgency) – Dams are inadequate with low risk such that the combination of life, economic, or environmental consequences with a probability of failure is low and the dam may not meet all essential USACE engineering guidelines. DSAC Class V (Normal) – Dams considered adequately safe, meeting all essential agency guidelines and the residual risk is considered tolerable.
By Ben Sanders Striper Guide Lake Ouachita
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