DAM REMOVAL ENGINEERING ISSUES & OPTIONS

Presented by:

James G. Mac Broom, P.E. Milone & Mac Broom, Inc.

October 2011

• Fish Passage

• Habitat Defragmentation

• Water Quality

• Dam Failure Hazards

• On-site Safety

• D/S Channel Degradation

• Hydrologic Modifications

• Sediment Transport Continuity

• Maintenance & Operational Costs

CLEAR GOALS and OBJECTIVES

DAM REMOVAL ISSUES

HYDROLOGY • WATERSHED HYDROLOGY • FLOODWATER STORAGE • IMPOUNDMENT DRAWDOWN • DOWNSTREAM IMPACT • WELL IMPACTS

FLUVIAL MORPHOLOGY • Data Collection • CHANNEL MORPHOLOGY/DESIGN (form, function,

process, materials) • CHANNEL EVOLUTION • SITE RESTORATION

ECOLOGY • ANADROMOUS / RESIDENT FISH • AQUATIC HABITAT • HABITAT FRAGMENTATION

• ECOLOGICAL RECOVERY

• VEGETATION

• WILDLIFE

• SPECIES OF SPECIAL CONCERN

HYDRAULICS • CHANNEL HYDRAULICS & SAFETY • FLOODPLAIN HYDRAULICS • SEDIMENT STABILITY/TRANSPORT • FISH PASSAGE • ICE JAMS

WATER QUALITY • CHEMICAL PROPERTIES • PHYSICAL PROPERTIES • (i.e. temperature, turbidity) • PUBLIC HEALTH

SOCIOECONOMIC • OWNERSHIP (Water Rights; Easements)

• CURRENT USES

• RECREATION

• PUBLIC SAFETY

• ECONOMIC ANALYSIS • ARCHEOLOGICAL/HISTORICAL • SENTIMENTAL VALUE

• AESTHETICS

CONSTRUCTION • SEASONAL CONSTRUCTION LIMITS

• CONSTRUCTION ACCESS

• CONSTRUCTION SEQUENCE

• SEDIMENT MANAGEMENT AND DISPOSAL

• WATER CONTROL

ENGINEERING • DATA COLLECTION

• TYPE & CONDITION OF DAM

• SITE LIMITATIONS (Utilities, Topo)

• UPSTREAM & DOWNSTREAM ISSUES

(bridges/structures, tributaries)

• PROJECT PERMITTING

• ALTERNATIVES ANALYSIS

DAM REMOVAL FALLACIES • All Dams Have A lot of Sediment

• All Impounded Sediments Will Erode

• Barren Mud Flats Last Forever

• River Dries Up

• All Upstream Channels Headcut

• All The Fish Die

• Dam Removal Allows Fish Passage

CONSTRUCTION BID DOCUMENTS 1. Planning and Analysis

• Site Planning • Sediment Probes • Sediment Testing • Hydrology • Hydraulic Analysis • Schematic Alternates

2. Preliminary Design • Access • Water Control • Initial Breach • Sediment Management • Demolition Plan • Restoration Plan

3. Final Design • Cross Sections • Custom Details • Easements • Utilities

4. Cost Estimates 5. Specifications 6. Permitting

• Local, State, Federal

STUDY PROCESS DAM MANAGEMENT ALTERNATIVES

DATA COLLECTION BASE DATA

NID FEMA

STATE AGENCIES DESIGN PLANS

HISTORY OWNERSHIP

AS - BUILT DATA USE

DAM SAFETY HAZARD CLASSIFICATION

PHYSICAL INSPECTION SPILLWAY CAPACITY SIZE CLASSIFICATION

OPERATIONAL HAZARDS STRUCTURAL / GEOTECH .

SITE DATA TOPOGRAPHY

WETLANDS RARE SPECIES HYDROLOGY

GEOLOGY HISTORIC VALUE

SEDIMENTS WATER QUALITY PUBLIC &

REGULATORY PARTICIPATION

IS DAM SAFE?

EMERGENCY REPAIRS OR DRAWDOWN

MARGINAL DAM

REPAIR OR REPLACE DAM

IDENTIFY ALTERNATIVES

ELIMINATE DAM AND IMPOUNDMENT RETAIN DAM AND IMPOUNDMENT PROVIDE FISH PASSAGE LOWER

CREST

FISH LADDER

D/S RAMP

U/S RAMP

HIGH LEVEL BY - PASS

CHANNEL

NO ACTION

OTHER

FULL REMOVAL

PARTIAL BREACH

LOW LEVEL BY - PASS

VERY SMALL OR LOW RISK DAM, SIMPLE

DECOMMISSION

LIMITED FEASIBILITY STUDY

SITE SPECIFIC TOPICS

PUBLIC & REGULATORY PARTICIPATION, SELECT

ALTERNATIVE

IMPLEMENTATION CONSTRUCTION PLANS

SPECIFICATIONS COST ESTIMATES

FUNDING EASEMENTS

REGULATORY PERMITS CONSTRUCTION ADMINISTRATION

SITE RESTORATION AS - BUILTS

OPERATIONAL PLAN EMERGENCY RESPONSE PLAN

DETAILED FEASIBILITY STUDY HYDRAULIC ANALYSIS

SEDIMENT TESTING SEDIMENT TRANSPORT

CHANNEL MORPHOLOGY U/S AND D/S IMPACTS WETLAND IMPACTS

LAND USE / AESTHETICS AQUATIC SPECIES

RECREATION LAND RIGHTS

WATER RIGHTS UTILITIES

ACCESS FINANCIAL IMPACTS

CONSTRUCTION METHODS SITE RESTORATION EROSION CONTROL

YES NO

YES

NO

For additional information, please contact:

James Mac Broom, P.E.

716 - 726 South Main Street Cheshire, Connecticut 06410 Telephone (203) 271 - 1773 Fax (203) 272 - 9733 E - Mail: jimm@miloneandmacbroom.com

STUDY PROCESS DAM MANAGEMENT

ALTERNATIVES

FISH PASSAGE OPTIONS

• Dam Removal, Thru Channel

• Full Flow By-Pass Channel • Partial Flow By-Pass

Cannel • Downstream Ramp • Upstream Ramp • Structural Fish Ladder

• Trap and Haul • Elevators

FISH POWER MECHANICAL POWER

IMPOUNDMENT MANAGEMENT SEDIMENT

• Natural Erosion

• Excavate Sediment

• Relocate Sediment

• Contain Sediment

• Combination

CHANNEL FORM

• Natural Formed Channel

• Create Regime Channel

• Armored Channel

• Grade Controls

• Alignment Controls

• Combination

SEDIMENT DEPOSITS IN RESERVOIRS

Modified from Morris, 1998

SEDIMENT ISSUES

• Sediment Quality & Quantity

• Sediment Stability

• Sediment Transport

• Stabilize, Remove or Natural Erosion

• Sediment Disposal

• Downstream Sediment Impacts

• Ecological Recovery Time

Watershed Hydrology

Ecological Assessment

Non-Alluvial Channels

Alluvial Channels

Collect Data

Set Goals & Objectives

Contact Agencies

Estimate

Scope

• Historic Search • Watershed Search • Site Investigation • Geomorphic Observations • Substrates • Hand Borings • Ex. Hydrology Data • Ex. WS Profiles • Sediment Quality • Sediment Quantity • Grain Size Analyses

Hydraulic Geometry

Classification (Optional)

Reference Reach

Regional Data

Regime Eq.

Planform Habitat Passage

Aesthetics Banks Access

Vegetation

Sediment Management

Design Development

Modified from Mac Broom 2003

Profile Analysis

Drawdown Test if Possible

Threshold Stability

and/or

Sediment Transport Equations

Moderate Projects

Advanced Sediment Transport Modeling

Complex Projects

1D Fixed Width

1D Variable

Width

2 &3D

Hydraulic Analysis

Simple Projects

DAM REMOVAL SEDIMENT ANALYSIS

KEY CHANNEL EVOLUTION FACTORS

Independent

• Hydrology

• Sediment Yield

• Pre-Dam Substrate

• Valley Slope

• Valley Width

• Bank Vegetation

Dependent

• Sediment Gradation

• Cohesive Strength

• Pool Thalweg

• Pool Aspect Ratio

• Delta Position, Slope

• Breach Size & Depth

HYDROLOGIC DATA Mean Monthly Flows

Peak Flood Flow Rates Water Surface Profiles Velocity & Shear Stress

CHANNEL EVOLUTION MODEL UPSTREAM OF DAMS

Source: Mac Broom, 2005

DATA COLLECTION

PHYSICAL SEDIMENT & IMPOUNDMENT DATA

Bathymetry Thickness Gradation

Watershed Yield Residence Time

BEDROCK OR NO SEDIMENT

SPOT DEPOSITS OR THIN VENEER

Stable No

Erosion

Stable Little

Erosion

Flow Returns To Pre-dam Channel

Follows Pre-dam Channel

DEFINED THALWEG IN POOL?

COARSE SEDIMENT

Steep Or Narrow

Wide

Degrades To Armor Bed Or Regime Slope

FINE SEDIMENT

Narrow

Wide

Degrades To Base Level And Regime Slope,

Or Pre-dam Strata

DELTA STEEP OR WEDGE

DEPOSIT

Narrow

Wide

Degrades To Armour Layer Or Equilibrium Slope

Low Sinuosity, Low W / D

Ratio

Variable Sinuosity,

High W / D Ratio

Limited, Gradual

D / S Transport

Variable, Gradual

D / S Transport

Low Sinuosity Incised Channel

Higher Sinuosity,

Lateral Cuts, Floodplain Formation

Potential Short-term Impacts

High Sediment Load. May Redeposit In Impoundment

Single Stem,

Headcuts, Then

Widens

Possible Anabranched

Headcuts Then

Widens

Examples:

YES NO

May Degrade Or Bificate

EXAMPLES: Good Hope Dam Great Works Dam

EXAMPLES: Edwards Dam Bushy Hill Dam Chase Brass Dam

EXAMPLES: Freight Street Dam Platts Mill Dam Lake Switzerland Dam Fort Covington Dam

EXAMPLES: Anaconda Dam Union City Dam Community Lake Dam

EXAMPLES: Lowell Dam Mad River Dam Baker Dam Carbonton Dam

EXAMPLES: Saw Mill Dam South Batavia Dam Bunnels Pond Town Brook Dams

EXAMPLES: Bunnels Pond Dam Norwalk Mill Pond Jones River Dam

EXAMPLES: Jenkins Dam Mackenzie Reservoir Lake Whitney

IMPOUND- MENT

CHARACTER

CHANNEL PROCESS

CHANNEL EVOLUTION

D/S IMPACT

None

SEDIMENT DEPOSIT

TYPE

BOTTOM OR UNIFORM SEDIMENT DISTRIBUTION

Minor Short-term Sediment

RIGID BOUNDARY

RIGID BOUNDARY

THRESHOLD BOUNDARY

REGIME OR HYD. GEOMETRY

SEDIMENT TRANSPORT

SEDIMENT TRANSPORT

THRESHOLD BOUNDARY

REGIME OR HYD. GEOMETRY

SEDIMENT PRESENT?

YES NO

Variable

Degrades To Armor Bed Or Pre-dam Slope

Follows Pre-dam Channel

Limited

EXAMPLES: Cuddebackville Dam Briggsville Dam

VARIABLE

IN-CHANNEL SEDIMENT

EXAMPLES

INITIAL STABILITY ANALYSIS

UPSTREAM CHANNEL PREDICTION • Historic Data on Pre Dam Conditions

• Reference Reaches- NCD

• Regime Equations

• Hydraulic Geometry Equations

• Slope – Discharge , Stream Power

• Hydraulic & Sediment Transport Methods

• Extremal Hypothesis

0 50 100 150 200

0.00025

0.00030

0.00035

0.00040

0.00045

Stability CurveQ = 2400 cfs

Total Sediment Concentration = 50 ppm

Base Width, ft

Slop

e

Legend

Stability Curve

Degradation

Aggradation

SEDIMENT MANAGEMENT OPTIONS

• Do Nothing – Allow Erosion • Create Stable Channel • Stabilize Sediment, Re-vegetate • Relocate Sediment Onsite • Partial Dredge and Remove “Hot Spots” • Isolate and Contain Fines, Contaminants • Divert Channel Around Impoundment • Full Dredge and Remove • Combination

Passive Natural Erosion

Create Stable Channel

Phased Partial Depth Removal, Slow Sediment

Release

Downstream Sediment Trap

Partial Width or Depth Breach,

Contain Sediment

Dredge Clean Sediment

Dredge Contaminated

Sediment

Remove Off-Site or Relocate On-Site

Step 1 – Perform Assessment and Design

Step 2 – Predict Erosion

--------------------------

Erosion-Prone Volume Annual Yield

Collect Impoundment Data Length, Width, Area, Volume Bathymetry Thalweg Location Sediment Gradation, Distribution, Thickness, Cohesion Utilities, Tributaries Grade and Bank Control Points, Bedrock, Debris, Ice

Collect Watershed and Channel Data Hydrology, Geology, Thermal Regime Sediment Yield Valley and Channel Slope and Sinuosity Bankfull Dimensions Contaminants (Current, Historic, Point, Nonpoint)

Additional Samples and

Testing Contain Sediment

Stabilize Dam Bypass Flow

Test Sediment Quality Regulatory Criteria

Health Criteria Ecological Criteria

Reduce D/S Sensitivity Floodplain reconnection Dikes Channelize Flood-proof Evacuate Relocate Species

Step 3 – Evaluate Downstream Sediment

Impacts

Predict Channel Morphology Historic Channel Reference Reach Physical Constraints in Corridor

Classify Impoundment Transport Process Deposition Form and Process

Downstream Data Infrastructure (Bridges, Dams Dikes, Intakes, Outfalls) Water Uses Aquatic Species Flood and Erosion Risks Deposition Zones

. SEDIMENT MANAGEMENT APPROACHES FOR DAM REMOVAL

Step 4 – Select Management Alternates

Acceptable Contaminated Sediment Erosion < Annual Yield

Erosion > Annual Yield

Grade Control Bank Stabilization

• Hydrology – Watershed and Climate Change?

• Sediment Supply Reach - Load and Gradation

• Flow Regime - Roughness, Velocity, Shear

• Bank Stability - Mass Failures or Slow Slumps?

• Cohesion - Rate of Erosion?

• Channel - Slope, Shape, and Size

• Transport Capacity - Compare with Supply and Erosion Rates

• Buried Subgrade - Armor or Bedrock Controls?

• Legacy Dams - Submerged in Pool?

• Choice of Algorithms

• Prediction Accuracy

SEDIMENT ANALYSIS UNCERTAINTY

• Urban Dams • Legacy Dams • Wide Impoundments • High River Flow Rates • Sediment Sensitive Rivers • Contaminated Sediments • Undocumented Dams • Infrastructure, Bridges, Utilities • Weak or Unprofessional Management Teams

DIFFICULT DAM REMOVALS

DESIGN DAMS FOR FUTURE REMOVAL

• Permanent Access Roads

• High Capacity Outlet Works

• Sediment Sluices or Bypasses

• Multiple Construction Joints

• Clear Downstream Hazard Areas

• Archive Design Plans

• Construction Photographs