NRCS Overview - Association of State Dam Safety Officials

NRCS Overview - Association of State Dam Safety Officials

NRCS Overview

National Dam Safety Program

Technical Workshop #19

February 22-23, 2012

Thomas Brown

National Design, Construction, and Soil Mechanics Center


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


NEH Part 628

Chapter 45




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




• 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


• Height 110


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 –


• Completed


• 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


• 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


• Primarily used in rehabilitation

• Limitations

– Use as a filter

– When located within the dam embankment

– In applications where both filtration and flow are


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


Crack in


Upstream Approach

16-OZ Geotextile


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


• Increasingly, hardened spillways are being


• Majority are over the dam embankment

• Drainage system is important aspect of design

• Salado 15R

• TX

• Flood


• Completed


RCC Plan

Section Through RCC Steps


Coarse Drainfill

Drain Pipe Detail

Drainfill Placement

RCC Placement

Finished RCC Lift

• Bear Creek 12

• North Carolina

• Low Hazard

• Spillway Repair

• RCC Drop


Drop Structure Plan

Drain Section

Drain Construction

Geocomposite Drain

Geocomposite Drain

RCC Placement

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