Dam Rehabilitation in the USA…History and Trends

Workshop on Water Security in BulgariaSofia, Bulgaria, September 18-19, 2017

Greg Paxson, P.E., D.WRE / gpaxson@schnabel-eng.com

Large Dam Construction

50 Years

Source: World Register of Dams

Source: National Inventory of Dams

Dam Safety in the United States

Source: National Inventory of Dams

Periods of Change… the Catalysts

Dam Safety Catalysts (1910 to 1930)

1911: Austin Dam Failure (88 Dead)

1913: Pennsylvania enacts first known

dam safety legislation

1928: St. Francis Dam Failure (600+ Dead)

1929: California enacts dam

safety legislation

Consideration of uplift pressures

More in-depth Geologic

Evaluations

The 1970s…

Teton (11) Canyon Lake (33+)

Laurel Run+ 5 (45)

Buffalo Creek (125)

Kelly Barnes (39)

1972

1977

Dam Safety Catalysts – The 1970s

Gilboa Dam, NY Photo from Achievements and Advancements in US Dam Engineering (ICOLD 2013)

Federal Guidelines & Inspection Program (1979)

Rehabilitation of Deficient Dams (1980s - today)

Teton Dam (1976)

Dam Rehabilitation

• Spillway Capacity• Spillway Integrity (lined & unlined)

• Seepage/Internal Erosion

• Stability• Embankment Slopes• Structures

• Seismic• Stability• Liquefaction

• Structural Deterioration

• Operational

Dam Safety Regulations and Standards

“Self Regulated” Federal Dams

Non Federal Hydropower Dams

The States

State Regulated Dam Rehabilitation Projects

Source: National Inventory of Dams and Association of State Dam Safety Officials

Federal Dam Rehabilitation

Source: National Inventory of Dams and FEMA

$312M

$5.3B

$1.8B

Dam Rehabilitation Strategies

Post-tensioned rock anchor stabilization

Roller Compacted Concrete (RCC) Embankment

Overtopping Protection

Cutoff Wall (Embankment and Foundation Seepage)

Labyrinth Spillway

Drains and Filters (Seepage)

Dam Rehabilitation Strategies

Sources: Bruce et al, 2013 (Anchors); Bruce et al, 2017 (Cutoff Walls), Hansen, Schnabel, 2016 (RCC); Schnabel, 2017 (Labyrinths)

Selected Projects

Bluestone Dam, WV Smith Lake Dam, VA

Wolf Creek Dam, KYLake Townsend Dam, NC

Five Phases (2000 – 2025+)• Stability thrust blocks• Penstock auxiliary spillway• 494 rock anchors (up to 61

strands, 82-m long)• New stilling basin• $500M+ US

Bluestone Dam

• Karst (limestone) foundation

• Concrete barrier wall up to 84-m deep

• $340M US

Wolf Creek Dam

• Provides 70% of water supply to Greensboro, NC

• Concrete deterioration from Alkali Silica Reactivity

• Inadequate spillway capacity

• Earthen auxiliary spillway

• Gated spillway operational issues

Lake Townsend Dam

Opportunistic Reservoir Expansion (Dam Raise)

Dam and Levee Safety Catalyst

• Hurricane Katrina and Transition to Risk informed approaches

Another Catalyst?

• The Oroville Incident

Acknowledgements

National Dam Safety Review Board &Interagency Committee on Dam Safety