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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: pooleja@dhec.sc.gov