SC Dams and Reservoirs Safety

Transcription

1 SC Dams and Reservoirs Safety Inspection of Embankment Dams John A. Poole, P.E. SCDHEC

2 Topics Covered History of the Dam Safety Program: Time line of the program and important events Inspections Performed by the Department

3 History of the Dam Safety Program

4 Toccoa Falls Question: How could such a beautiful natural treasure turn deadly? Answer:????

5 Toccoa Falls Question: How could such a beautiful natural treasure turn deadly? Answer: Kelly Barns Dam

6 Kelly Barns Dam 40-ft height 20-ft top width 400-ft length 4.6 sq.mile DA that is heavily wooded

7 Disaster Strikes on November 1977 Note tree root penetration through dam embankment pipe, old low dam, silt layers

8 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

9 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

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13 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.

14 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.

15 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.

16 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

17 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

18 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

19 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.

20 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

21 Storm Path Increases Danger

22 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

23 Inspections Performed by Regional Staff

24 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

25 Permit Application Form

26 SC DAMS AND RESERVOIRS SAFETY ACT SC LAW

27 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

28 What Authority is granted to DHEC Power to promulgate regulations Require permits (Section ) Conduct inspections (Section ) Take enforcement actions (Section )

29 Permits are required for the following: New Dam Construction or Existing Dam Alteration Repair Removal

30 "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

31 Other stakeholders to consider Neighboring property owners Local city or county governments Other state agencies Other DHEC regulatory programs Federal regulatory agencies Consultant Engineers

32 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)

33 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.

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43 Seepage

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57 Slope Protection

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59 Beaching

60 Scarp

61 Vegetative Growth

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63 Trees and Shrubs

64 Cracking Commonly observed cracking on dams: Desiccation Transverse Longitudinal

65 Desiccation Cracks

66 Transverse Cracks

67 Longitudinal Cracks

68 Slides

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71 Depressions and Sinkholes

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75 Debris

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77 Burrowing Animals

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80 Surface Erosion

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84 Importance of Maintenance

85 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.

86 Hazard Creep

87 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.

88 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.

89 Piping Failure

90 Over Topping Failure

91 Slide Failure

92 Questions? John Poole, P.E., State Dam Safety Engineer SC DHEC Bureau of Water Dams and Reservoirs Safety Program 2600 Bull St. Columbia, SC Phone: (803)