SUMMARY
East Branch Dam is
owned and operated by the Pittsburgh District, U.S. Army Corps of
Engineers. As part of a risk management approach to improving
public safety, the Corps has classified East Branch Dam as Dam Safety
Action Class (DSAC) II. East Branch Dam is considered to have
unconfirmed (potentially unsafe) issues which merit further study and
analysis, largely because it has a history of seepage related problems,
including a serious episode in 1957 that required lowering the lake
until repairs could be made. There have been no observed changes
in seepage conditions or performance of the dam in the time since
repairs were completed. The dam functioned safely during the
record pool event in 1972 resulting from Hurricane Agnes. As a
result of the DSAC II classification, the Pittsburgh District has
implemented Interim Risk Reduction Measures to reduce the risk to the
public. These measures include increased monitoring, 24/7
staffing, updating emergency operation plans, reducing the water level
in the reservoir to relieve pressure on the dam and stockpiling
emergency materials on site.
These and other short-term actions allow us to operate the dam to meet
our public safety objective while we further investigate our concerns
and pursue long-term repairs, if necessary. As we take steps to
reduce risk to public safety, we recognize that recreation, water
supply, hydropower and the environment may be impacted. The
Pittsburgh District staff will continue to work with our stakeholders
and the public to keep them informed of the dam safety issues related to
East Branch Dam.
DAM SAFETY PROGRAM
The U.S. Army Corps
of Engineers’ Dam Safety Program is critical to addressing our nation’s
aging infrastructure, reducing the risks of flood and storm damage and
making sure Corps owned and operated dams are operated safely and
minimize risk to the public.
The Corps owns and operates 610 dams that serve a variety of purposes
including navigation, flood damage reduction, water supply, irrigation,
hydropower, recreation, environmental enhancement and combinations of
these purposes. The Pittsburgh District owns and operates 16 flood
damage reduction dams and 23 navigation locks and dams. As part of
our responsibility in managing these dams, the Corps has a comprehensive
Dam Safety Program that has public safety as its primary objective.
Corps dams are routinely inspected and continually evaluated for safety
in accordance with the Federal Guidelines for Dam Safety issued in 1979.
Risk management changes are being implemented in the Dam Safety Program
to allow prioritization of work at the national level, thereby providing
a standard strategy for the continued safety and security of our
projects and the affected public. Dam safety risk has two
components: probability of dam failure and consequences if failure
were to occur.
In 2005, 2006 and 2007 the Corps of Engineers performed Screening
Portfolio Risk Analysis that considered performance and consequence of
failure (risk-informed screening) to prioritize approximately one-third
of Corps-owned and operated dams nationwide that were perceived to have
the highest risk. All 16 Pittsburgh District flood damage
reduction dams and four of our 23 navigation dams were screened as of
2007. The Corps of Engineers goal is to screen the remainder of
the portfolio by the end of Fiscal Year 2009.
The Corps of Engineers instituted a Dam Safety Action Classification
System intended to provide consistent and systematic guidelines for
appropriate actions to address the dam safety issues and deficiencies.
Corps dams are placed into five Dam Safety Action Classes (DSAC) based
on their individual dam safety risk considered as probability of failure
and potential failure consequences. DSAC I is the rating assigned
for the highest risk dams, and DSAC V are dams which are considered safe
and in compliance with current criteria. Consequences considered
include lives lost, economic, environmental and other impacts.
The Corps of Engineers has identified six DSAC I flood damage reduction
projects based on the risk analysis screenings to date. None of
Pittsburgh District’s flood damage reduction dams were identified as
DSAC I, and one flood damage reduction dam, East Branch Dam, was
identified as DSAC II.
EAST BRANCH DAM
East Branch Dam is
located on the East Branch Clarion River in Elk County, Pennsylvania.
Construction began in June 1948 and was completed in October 1952.
Impoundment of water began in November 1950 with full operation in June
1952. Normal summer pool is elevation 1670. The pool of
record is elevation 1685.6, reached on June 24, 1972 as a result of
Hurricane Agnes. This pool level was .6 feet above the spillway
crest elevation and was the only time the spillway carried flow.
The dam functioned safely during this event.
The dam is a rolled earth fill embankment with outlet works located at
the right abutment and an emergency spillway located in the left
abutment. The embankment is 1,725 feet long and has a height of
184 feet. The width is 20 feet at the top of the dam with a
maximum width of 1,115 feet at the base. The project purposes are
reduction of flood stages on the Clarion River, water conservation,
water quality, supplementary low-flow, recreation and conservation of
fish and wildlife.
The dam experienced a serious seepage related incident in 1957. In
May, muddy water appeared at the toe of the dam near the right abutment.
The pool was drawn down a total of 110 feet in three stages and
exploratory drilling was conducted. The exploratory drilling
revealed internal erosion that created a cavity in the impervious core
of the embankment. Repairs consisting of drilling and grouting
sealed the cavity and surrounding area. Grouting was completed in
November 1957. There have been no observed changes in seepage
conditions or performance of the dam in the time since repairs were
completed; however, the repair is now more than 50 years old.
East Branch Dam is inspected and monitored closely. The dam is
instrumented to monitor seepage, piezometric levels (internal seepage
pressure) and horizontal and vertical movements of the dam crest.
The dam is staffed seven days a week, 24-hours a day and is regularly
inspected by project staff as well as engineers from the Pittsburgh
District Office. Project staff inspects the dam daily during
normal operating conditions and more frequently during high pool levels.
Engineers inspect the dam at least annually, with more intensive team
inspections every five years through the Dam Safety Program.
East Branch Dam was screened in 2006 as part of the Screening Portfolio
Risk Analysis process. As a result of the screening assessment,
the dam was classified as DSAC II. East Branch Dam is considered
to have unconfirmed (potentially unsafe) issues which merit further
study and analysis.
EAST BRANCH DAM SAFETY STUDY
East Branch Dam has been given priority funding to implement Interim
Risk Reduction Measures and study alternatives for long-term remedial
measures, if needed. The steps following initial classification
and leading to approval of long-term remediation are considered a Dam
Safety Study.
Step 1. The first
step in the East Branch Dam Safety Study is to prepare an Interim Risk
Reduction Measures Plan and implement the proposed measures.
Interim risk reduction measures are not long-term solutions, they are
designed to minimize risk to public safety in the short-term while
pursuing long-term permanent fixes. They are an important step to
minimize the probability of failure and/or consequence until a permanent
fix can be implemented or investigations have determined that a
potential failure mode is not probable. It is the most responsible
way to manage a project’s risk to public safety. As we take action
to reduce risk to public safety, which is our first priority, we
recognize that other project benefits, such as recreation, water supply
and water quality may be impacted.
The Pittsburgh District has implemented, or will implement, the
following Interim Risk Reduction Measures for East Branch Dam:
-
Operate at a reduced operating pool
level
-
Update the existing dam safety
emergency action plan
-
Conduct emergency exercises
-
Provide 24/7 staffing
-
Update inundation mapping
-
Enhance inspection and monitoring
-
Pre-position contracts and stockpile
materials
-
Improve reliability of the outlet
gates and machinery
-
Perform a more detailed risk
assessment
A key interim risk reduction measure is
to operate East Branch Dam at a reduced pool level. This action
will both reduce the probability of failure due to internal erosion and
reduce potential consequences if a failure were to occur.
Step 2. Preliminary
Dam Safety Studies are the next step in evaluation of dam safety issues.
These studies include a more in-depth review of available data and a
more detailed risk analysis of all potential failure modes in order to
better define and confirm the dam safety issues. The Dam Safety
Action Classification will be reviewed and modified as appropriate.
The Interim Risk Reduction Measures will be reviewed and modified based
on the detailed risk analysis.
Step 3. Dam Safety
Modification Studies will follow if justified by the confirmed dam
safety issues. Modification studies include additional data
gathering, studies and detailed engineering analyses. A full range
of alternatives are evaluated with detailed cost estimates as well as
assessments of other impacts. Modification studies will lead to a
decision document with a comparison of alternatives and a recommended
plan.
CONCLUSION
Public safety is the number one priority of the U.S. Army Corps of
Engineers. The primary objective of our Dam Safety Program is to
maintain public safety by making sure the dams we own and operate are
safe and risks to the public are minimized.
An integral part of the Corps of Engineers Dam Safety Program is its
risk-informed screening process, Screening Portfolio Risk Analysis. The
Corps is focusing on projects with the most compelling dam safety issues
first, as identified by this risk-informed screening process.
Screening Portfolio Risk Analysis screened dams are classified based
upon confirmed or unconfirmed dam safety issues, the combination of life
or economic consequences should failure occur and the probability of
failure. This enables the Corps to prioritize dam safety actions
to correct deficiencies, which includes interim risk reduction measures
to be undertaken while further investigations are conducted and/or
remedial actions are implemented.
East Branch Dam has a history of seepage related problems, including a
serious episode in 1957 that required draining the lake until repairs
could be made. There have been no observed changes in seepage
conditions or performance of the dam in the time since repairs were
completed. The dam functioned safely during the record pool event
in 1972.
Our screening and classification of East Branch Dam identified this
project as having unconfirmed (potentially unsafe) issues which merit
further analysis and evaluation. We are taking a number of interim
risk reduction measures in order to reduce the probability and
consequences of dam failure while long term remedial measures are
pursued. As a key interim risk reduction measure the dam will be
operated at a reduced pool level.
Interim risk reduction measures are not long term solutions. They
are designed to buy down or minimize risk to public safety in the
short-term while pursuing long-term permanent modifications to a dam.
They are an important step to minimize the probability of failure and/or
consequence until a permanent fix can be implemented or investigations
have determined that a potential failure mode is not probable.
East Branch Dam has received priority for further studies to better
define and confirm the dam safety issues. Through this process, the
Corps will determine whether or not the dam is in need of repairs and
evaluate alternatives for permanent repair. The process of
evaluation is expected to take about two years. We will continue
to work with our stakeholders to keep them informed of the dam safety
issues related to East Branch Dam.
The Pittsburgh District operates and maintains East Branch Dam in such a
way as to minimize risk to the public. East Branch Dam is inspected and
monitored closely. The dam is staffed seven days a week, 24 hours
per day and is regularly inspected by project staff as well as engineers
from the Pittsburgh District Office.
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