SC Dams and Reservoirs Safety
Inspection of Embankment Dams
John A. Poole, P.E. SCDHEC
Topics Covered
• History of the Dam Safety Program: – Time line of the program and important events
• Inspections Performed by the Department
History of the Dam Safety Program
Toccoa Falls
• Question: How could such a beautiful natural treasure turn deadly?
• Answer: ????
Toccoa Falls
• Question: How could such a beautiful natural treasure turn deadly?
• Answer: Kelly Barns Dam
Kelly Barns Dam
• 40-ft height • 20-ft top width • 400-ft length • 4.6 sq.mile DA
that is heavily wooded
Disaster Strikes on November 1977
• Note tree root penetration through dam embankment
• pipe, old low dam, silt layers
Impacts Down Stream
• Toccoa Falls College campus area located in flood plain
• Breach occurred at night and caught many by surprise
• Approximately 40 people died by drowning or being crushed by debris
Down Stream Damage
• Many students lived in mobile homes and light weight trailers surrounding the campus
• Note the vehicle, they were not warned in time to escape
Creation of the Dams Inventory
• After the disaster at Toccoa Falls, then president, Jimmy Carter issued a proclamation for the ACOE to perform a one time inspection of all high hazard dams.
• The South Carolina Land Resource Commission (SCLRC) was tasked to generate an inventory of high hazard dams for the ACOE to inspect.
ACOE Findings
• Almost all of the dams inspected in SC were classified as “unsafe” due to their conditions.
• The state was then responsible for follow up work to ensure the conditions of the dams were improved to a safe level.
Dam Safety Program Findings
• In addition to the dams identified by the ACOE, the Dam Safety Program identified an overwhelming number of very small dams that were in unsafe conditions.
• In 1980, the act was amended to exclude all “very small” (less than 25 feet high and impounded less than 50 acre feet) dams from regulation unless they are a direct threat to life by their failure.
Working Towards Safety
• The dam safety program began working with individual dam owners to get their unsafe dams corrected
• Detailed studies and more careful inspections removed a number of dams in the Corp's reports from the unsafe list
• Legal action had to be initiated against a number of dam owners
Routine Inspection Program
• In 1984, the Dam Safety Program started a routine re-inspection program for all high hazard and significant hazard dams
• Low hazard dams would not be inspected, but would be checked for reclassification
Routine Inspection Program • Current Inspection and classification schedule:
–2-yrs for High Hazard Inspections
–3-yrs for Significant Hazard Inspections
–5-yrs for Low Hazard Classifications
Computers
• In 1985, the first desktop Personal Computer was acquired for the purpose of keeping the inventory of regulated dams. This inventory is still maintained by DHEC.
Disaster Strikes SC • Klaus and Marco,
entered the state simultaneously in early October, 1990
• Storms stalled over the state and dumped unprecedented quantities of rainfall
• 17 regulated dams failed
Storm Path Increases Danger
General Assembly Restructures State Government
• In 1994, many of the small independent agencies were abolished, and their functions were transferred to larger agencies
• SCLRC duties were absorbed by DHEC
Inspections Performed by Regional Staff
http://www.scdhec.gov/environment/envserv/regions.htm
Central Office Functions
• Issuing permits for: – New dams – Altering existing dams – Modifying Control Structures of dams – Repairing extensive damage to dams – Removing dams
• Enforcement actions
http://www.scdhec.gov/environment/water/drsmainpage.htm
Permit Application Form
http://www.scdhec.gov/administration/library/d-2602.pdf
SC DAMS AND RESERVOIRS SAFETY ACT
SC LAW 49-11-110
http://www.scstatehouse.gov/code/t49c011.htm
What is the Purpose of the Act? • It is the purpose of this article to provide for the
certification and inspection of certain dams in South Carolina in the interest of public health, safety, and welfare in order to reduce the risk of failure of the dams, prevent injuries to persons and damage to property, and confer upon the department the regulatory authority to accomplish the purposes.
• Protect citizens health, safety, and welfare by creating a regulatory program to reduce the risk from failure of dams
What Authority is granted to DHEC
• Power to promulgate regulations • Require permits (Section 49-11-200) • Conduct inspections (Section 49-11-230) • Take enforcement actions (Section 49-11-
190)
Permits are required for the following: • New Dam Construction or • Existing Dam
– Alteration – Repair – Removal
• "Alteration" means any change to a dam or reservoir which affects the physical parameters and safety of the dam or reservoir which may include but is not limited to changing the height of a dam, increasing the normal pool or principal spillway elevation or changing the elevation or physical dimensions of an emergency spillway.
• "Repairs" means any work done on a dam which may affect the safety of the dam. This includes but is not limited to work requiring excavation into the embankment fill or foundation of a dam or work requiring removal or replacement of major structural components of a dam.
• "Removal" means the destruction or breaching of a dam or reservoir to the extent that no water or fluid can be impounded by the dam or reservoir
Other stakeholders to consider
• Neighboring property owners • Local city or county governments • Other state agencies • Other DHEC regulatory programs • Federal regulatory agencies • Consultant Engineers
Inspections
• The Department’s regional staff are responsible for most inspections performed by the agency (DHEC) on regulated dams.
• The types of inspections performed are: – Preliminary/Routine Inspections – Classification Inspections – Construction Inspections (BOW Staff)
Preliminary Inspections
• These are visual but technical inspections that may involve an evaluation of the dams ability to adequately and safely pass large storm events.
• A more thorough evaluation or “detailed inspection” may be required due to findings from these inspections.
• In addition to scheduled inspections, these are also performed on a as needed basis.
Seepage
Slope Protection
Beaching
Scarp
Vegetative Growth
Trees and Shrubs
Cracking
• Commonly observed cracking on dams: – Desiccation – Transverse – Longitudinal
Desiccation Cracks
Transverse Cracks
Longitudinal Cracks
Slides
Depressions and Sinkholes
Debris
Burrowing Animals
Surface Erosion
Importance of Maintenance
Classification Inspections
• These are not performed to determine the dams condition, instead they are used to determine the dam hazard classification.
• Performed by evaluating properties at risk below the dam.
Hazard Creep
Construction inspections
• This are performed at various mile stones during permitted work.
• They help assure compliance with permitted plans.
• A final construction inspection must be performed before a certificate of operation or completion can be issued.
Failure Mode Analysis
• This involves a brainstorming to determine the possibles ways a new or existing dam may fail.
• Often involves detailed evaluations of the dam site and plans.
• Most typical failure types involve: piping, overtopping, and sliding.
Piping Failure
Over Topping Failure
Slide Failure
Questions?
John Poole, P.E., State Dam Safety Engineer SC DHEC – Bureau of Water Dams and Reservoirs Safety Program 2600 Bull St. Columbia, SC 29201
Phone: (803) 898-4212 Email: [email protected]