NRCS Overview National Dam Safety Program Technical Workshop #19 February 22-23, 2012 Thomas Brown National Design, Construction, and Soil Mechanics Center (NDCSMC) Fort Worth, Texas
NRCS Dam Inventory Significant Hazard: 2,200 High Hazard: 2,050 Total: 4,250 May 2011
Filter/Drain Configuration Filter/Drain objectives Intercept, filter and safely discharge seepage Implementation of TR60 minimum requirements varies Between regions and states Dam size Function Site Conditions Historically have often constructed individual filter/drain elements Foundation Drain Filter Diaphragm around outlet conduit
Typical Filter Diaphragm Configuration NRC S NEH Part 628 Chapter 45 Filter Diaphragms FEMA
Filter/Drain Trends Same overall filter/drain objectives Continuous filter/drain system including chimney Comprehensive protection against expected and unexpected Seepage More unique rehabilitation filter/drain configurations to address individual circumstances of existing structures
Typical Chimney Drain Sloping chimney filter/drain Conduit FEMA
More accessible design Pipe Components Larger diameter pipe Gradual bends Manhole access points Pipes placed near toe to allow excavation if required FEMA P-675, FEMA 484 Solid wall HDPE or PVC Reclamation DSO-09-01, September 2009 Flow measurement/sediment capture features
Lost River 16 West Virginia Water Supply- Flood Control Completed? Height 90 feet Gannett Fleming Inc.
Typical Embankment Section
Drainage System Perspective Gannett Fleming Inc.
Blanket Drain Typical Section Fine Drainfill ASTM C33 Fine Aggregate Medium Drainfill ASTM #8 Coarse Drainfill ASTM # 57
Drain System Plan
Manhole Section Pipe bend detail
New Creek 14 West Virginia Water Supply- Flood Control Completed 1963 Height 110 feet
Excavation Plan Gannett Fleming Inc.
Typical Section
Fine Drainfill ASTM C33 Fine Aggregate Coarse Drainfill ASTM # 8 Blanket Drain Detail
Coarse Drainfill Placement in Blanket Drain
Welding HDPE Toe Drain
Placing Fill on Top of Blanket
Completion of Blanket Drain At Outlet
Construction of Chimney Drain and Berm
Toe Drain Access Manhole
Renwick Dam North Dakota Flood Control Recreation Completed 1962 Height 50 Feet
Approximate Foundation Drain Location
12 inch diameter asphalt coated CMP
Excavation for Foundation Drain Inspection
Excavation for Foundation Drain Inspection
Exposed Foundation Drain Pipe
Cleaning Pipe
Second Drain Investigation Excavation
Open Joint in Pipe
Pipe Repair
Modified Drain Outlet
Millsite Dam Utah Water supply Completed 1972 Height 115 ft.
Typical Section Zone I = -5 w/30-48% minus No. 200 Zone II = -5 w/19-43% minus No. 200 Zone III = +5 material Foundation: Silty/Clayey Sand&Gravel
Placing Zone III
Chimney Drain
Surface of Chimney Drain During Fill Construction
Conceptual Modified Section
Used extensively Geosynthetics Primarily used in rehabilitation Limitations Use as a filter When located within the dam embankment In applications where both filtration and flow are required
Embankment Rehabilitation in Arid Regions Dry Dams Short duration loading Extensive Cracking Primary failure concern is erosion verses piping Choke filters rather than filter/drains Intercept and reduce erosive flow and particle movement through embankment cracks Drainage is not a primary consideration
Transverse Crack in Embankment
Upstream Approach 16-OZ Geotextile URS
HDR Engineering Inc. Filter Placement
Centerline Approach 16-OZ Geotextile Ninyo & Moore
Trench Excavation
Filter Placement
Filter Placement
Spillway Drains A preponderance of NRCS dams have unlined spillways Increasingly, hardened spillways are being used Majority are over the dam embankment Drainage system is important aspect of design
Salado 15R TX Flood Detention Completed 2005
RCC Plan
Section Through RCC Steps Geotextile Coarse Drainfill
Drain Pipe Detail
Drainfill Placement
RCC Placement
Finished RCC Lift
Bear Creek 12 North Carolina Low Hazard Spillway Repair RCC Drop Structure
Drop Structure Plan
Drain Section
Drain Construction
Geocomposite Drain
Geocomposite Drain
RCC Placement