DAM REMOVAL ENGINEERING ISSUES & OPTIONS

Transcription

1 DAM REMOVAL ENGINEERING ISSUES & OPTIONS Presented by: James G. Mac Broom, P.E. Milone & Mac Broom, Inc. October 2011

2 CLEAR GOALS and OBJECTIVES Fish Passage Habitat Defragmentation Water Quality Dam Failure Hazards On-site Safety D/S Channel Degradation Hydrologic Modifications Sediment Transport Continuity Maintenance & Operational Costs

3 DAM REMOVAL ISSUES SOCIOECONOMIC OWNERSHIP (Water Rights; Easements) CURRENT USES RECREATION PUBLIC SAFETY ECONOMIC ANALYSIS ARCHEOLOGICAL/HISTORICAL SENTIMENTAL VALUE AESTHETICS HYDROLOGY WATERSHED HYDROLOGY FLOODWATER STORAGE IMPOUNDMENT DRAWDOWN DOWNSTREAM IMPACT WELL IMPACTS WATER QUALITY CHEMICAL PROPERTIES PHYSICAL PROPERTIES (i.e. temperature, turbidity) PUBLIC HEALTH ENGINEERING DATA COLLECTION TYPE & CONDITION OF DAM SITE LIMITATIONS (Utilities, Topo) UPSTREAM & DOWNSTREAM ISSUES (bridges/structures, tributaries) PROJECT PERMITTING ALTERNATIVES ANALYSIS 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 FLUVIAL MORPHOLOGY Data Collection CHANNEL MORPHOLOGY/DESIGN (form, function, process, materials) CHANNEL EVOLUTION SITE RESTORATION CONSTRUCTION SEASONAL CONSTRUCTION LIMITS CONSTRUCTION ACCESS CONSTRUCTION SEQUENCE SEDIMENT MANAGEMENT AND DISPOSAL WATER CONTROL

4 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

5 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

6 STUDY PROCESS DAM MANAGEMENT ALTERNATIVES DATA COLLECTION BASE DATA NID FEMA STATE AGENCIES DESIGN PLANS HISTORY OWNERSHIP AS - BUILT DATA USE PUBLIC & REGULATORY PARTICIPATION RETAIN DAM AND IMPOUNDMENT PROVIDE FISH PASSAGE FISH LADDER D/S RAMP U/S RAMP LIMITED FEASIBILITY STUDY SITE SPECIFIC TOPICS HIGH LEVEL BY - PASS CHANNEL SITE DATA TOPOGRAPHY WETLANDS RARE SPECIES HYDROLOGY GEOLOGY HISTORIC VALUE SEDIMENTS WATER QUALITY LOWER CREST IDENTIFY ALTERNATIVES NO ACTION OTHER YES YES REPAIR OR REPLACE DAM DAM SAFETY HAZARD CLASSIFICATION PHYSICAL INSPECTION SPILLWAY CAPACITY SIZE CLASSIFICATION OPERATIONAL HAZARDS STRUCTURAL / GEOTECH. IS DAM SAFE? MARGINAL DAM EMERGENCY REPAIRS OR DRAWDOWN ELIMINATE DAM AND IMPOUNDMENT FULL REMOVAL NO PARTIAL BREACH VERY SMALL OR LOW RISK DAM, SIMPLE DECOMMISSION LOW LEVEL BY - PASS STUDY PROCESS DAM MANAGEMENT ALTERNATIVES IMPLEMENTATION CONSTRUCTION PLANS SPECIFICATIONS COST ESTIMATES FUNDING EASEMENTS REGULATORY PERMITS CONSTRUCTION ADMINISTRATION SITE RESTORATION AS - BUILTS OPERATIONAL PLAN EMERGENCY RESPONSE PLAN PUBLIC & REGULATORY PARTICIPATION, SELECT ALTERNATIVE For additional information, please contact: James Mac Broom, P.E South Main Street Cheshire, Connecticut Telephone (203) Fax (203) E - Mail: jimm@miloneandmacbroom.com NO 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

7 FISH PASSAGE OPTIONS FISH POWER Dam Removal, Thru Channel Full Flow By-Pass Channel Partial Flow By-Pass Cannel Downstream Ramp Upstream Ramp Structural Fish Ladder MECHANICAL POWER Trap and Haul Elevators

8 IMPOUNDMENT MANAGEMENT CHANNEL FORM Natural Formed Channel Create Regime Channel Armored Channel Grade Controls Alignment Controls SEDIMENT Natural Erosion Excavate Sediment Relocate Sediment Contain Sediment Combination Combination

9 SEDIMENT DEPOSITS IN RESERVOIRS Modified from Morris, 1998

10 SEDIMENT ISSUES Sediment Quality & Quantity Sediment Stability Sediment Transport Stabilize, Remove or Natural Erosion Sediment Disposal Downstream Sediment Impacts Ecological Recovery Time

11 DAM REMOVAL SEDIMENT ANALYSIS Set Goals & Objectives Contact Agencies Estimate Scope Collect Data Drawdown Test if Possible Profile Analysis Historic Search Watershed Search Site Investigation Geomorphic Observations Substrates Hand Borings Ex. Hydrology Data Ex. WS Profiles Sediment Quality Sediment Quantity Grain Size Analyses Non-Alluvial Channels Alluvial Channels Classification (Optional) Watershed Hydrology Hydraulic Geometry Reference Reach Regional Data Regime Eq. Ecological Assessment Hydraulic Analysis Complex Projects Moderate Projects Simple Projects Advanced Sediment Transport Modeling Threshold Stability and/or Sediment Transport Equations 1D Fixed Width 1D Variable Width 2 &3D Design Development Planform Habitat Passage Aesthetics Banks Access Vegetation Sediment Management Modified from Mac Broom 2003

12 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

13 HYDROLOGIC DATA Mean Monthly Flows Peak Flood Flow Rates Water Surface Profiles Velocity & Shear Stress DATA COLLECTION NO SEDIMENT PRESENT? YES PHYSICAL SEDIMENT & IMPOUNDMENT DATA Bathymetry Thickness Gradation Watershed Yield Residence Time CHANNEL EVOLUTION MODEL UPSTREAM OF DAMS Source: Mac Broom, 2005 YES DEFINED THALWEG IN POOL? NO BOTTOM OR UNIFORM SEDIMENT DISTRIBUTION BEDROCK OR NO SEDIMENT SPOT DEPOSITS OR THIN VENEER IN-CHANNEL SEDIMENT COARSE SEDIMENT FINE SEDIMENT DELTA STEEP OR WEDGE DEPOSIT SEDIMENT DEPOSIT TYPE Stable No Erosion Stable Little Erosion Variable Steep Or Narrow Wide Narrow Wide Narrow Wide IMPOUND- MENT CHARACTER Flow Returns To Pre-dam Channel Degrades To Armor Bed Or Pre-dam Slope Degrades To Armor Bed Or Regime Slope May Degrade Or Bificate Degrades To Base Level And Regime Slope, Or Pre-dam Strata Degrades To Armour Layer Or Equilibrium Slope CHANNEL PROCESS Follows Pre-dam Channel Follows Pre-dam Channel Low Sinuosity, Low W / D Ratio Variable Sinuosity, High W / D Ratio Low Sinuosity Incised Channel Higher Sinuosity, Lateral Cuts, Floodplain Formation Single Stem, Headcuts, Then Widens Possible Anabranched Headcuts Then Widens CHANNEL EVOLUTION None Examples: Minor Short-term Sediment Limited Limited, Gradual D / S Transport Variable, Gradual D / S Transport Potential Short-term Impacts High Sediment Load. May Redeposit In Impoundment D/S IMPACT EXAMPLES: Good Hope Dam Great Works Dam RIGID BOUNDARY EXAMPLES: Edwards Dam Bushy Hill Dam Chase Brass Dam RIGID BOUNDARY EXAMPLES: Cuddebackville Dam Briggsville Dam VARIABLE EXAMPLES: Freight Street Dam Platts Mill Dam Lake Switzerland Dam Fort Covington Dam THRESHOLD BOUNDARY EXAMPLES: Anaconda Dam Union City Dam Community Lake Dam THRESHOLD BOUNDARY EXAMPLES: Lowell Dam Mad River Dam Baker Dam Carbonton Dam REGIME OR HYD. GEOMETRY EXAMPLES: Saw Mill Dam South Batavia Dam Bunnels Pond Town Brook Dams REGIME OR HYD. GEOMETRY EXAMPLES: Bunnels Pond Dam Norwalk Mill Pond Jones River Dam SEDIMENT TRANSPORT EXAMPLES: Jenkins Dam Mackenzie Reservoir Lake Whitney SEDIMENT TRANSPORT EXAMPLES INITIAL STABILITY ANALYSIS

14 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 Stability Curve Q = 2400 cfs Total Sediment Concentration = 50 ppm Legend Stability Curve Slope Degradation Aggradation Base Width, ft

15 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

16 Predict Channel Morphology Historic Channel Reference Reach Physical Constraints in Corridor Step 1 Perform Assessment and Design Classify Impoundment Transport Process Deposition Form and Process Collect Watershed and Channel Data Hydrology, Geology, Thermal Regime Sediment Yield Valley and Channel Slope and Sinuosity Bankfull Dimensions Contaminants (Current, Historic, Point, Nonpoint) Test Sediment Quality Regulatory Criteria Health Criteria Ecological Criteria 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 Erosion < Annual Yield Downstream Data Infrastructure (Bridges, Dams Dikes, Intakes, Outfalls) Water Uses Aquatic Species Flood and Erosion Risks Deposition Zones Step 2 Predict Erosion Erosion-Prone Volume Annual Yield Erosion > Annual Yield Step 3 Evaluate Downstream Sediment Impacts Step 4 Select Management Alternates Acceptable Additional Samples and Testing Contaminated Sediment Contain Sediment Stabilize Dam Bypass Flow Reduce D/S Sensitivity Floodplain reconnection Dikes Channelize Flood-proof Evacuate Relocate Species Passive Natural Erosion Phased Partial Depth Removal, Slow Sediment Release Downstream Sediment Trap Create Stable Channel Partial Width or Depth Breach, Contain Sediment Dredge Clean Sediment Dredge Contaminated Sediment Grade Control Bank Stabilization Remove Off-Site or Relocate On-Site. SEDIMENT MANAGEMENT APPROACHES FOR DAM REMOVAL

17 SEDIMENT ANALYSIS UNCERTAINTY 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

18 DIFFICULT DAM REMOVALS 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

19 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