Design of a Dam Sediment Management System to Aid Water Quality Restoration of the Chesapeake Bay

Transcription

1 Conowingo Dam Design of a Dam Sediment Management System to Aid Water Quality Restoration of the Chesapeake Bay Presented By: Sheri Gravette Kevin Cazenas Said Masoud Rayhan Ain Sediment Plume from Transient Scouring Sponsors: Lower Susquehanna Riverkeeper West & Rhode Riverkeeper Faculty Advisor: George Donohue

2 Agenda Context Stakeholders Problem/Need Statement Design Alternatives Analysis and Design of Simulation Design of Experiment Results, Analysis & Recommendations 2

3 Chesapeake Bay and The Susquehanna River Chesapeake Bay is the largest estuary in the United States 3 largest tributaries of the Bay are the Susquehanna, Potomac and James rivers Provide more than 80% of the Bay s freshwater Susquehanna River is the Bay s largest tributary Provides nearly 50% of freshwater to the Bay Flows from NY to PA to MD Map of the Chesapeake Bay Watershed Source: The PA Dept. of Environmental Protection 3

4 Lower Susquehanna River and Conowingo Dam Conowingo Dam (est. 1928) southernmost Dam of the Lower Susquehanna Quality of water from the Lower Susquehanna is vital to the bay s health Traps sediment and nutrients from reaching the Chesapeake Bay Water quality is closely related to sediment deposition The river provides power for turbines in hydroelectric plants and clean water to people Conowingo Hydroelectric Station Mainly provides power to Philadelphia, PA A black start power source Provides 1.6 billion kwh annually Map of Conowingo Reservoir Source: US Army Corps of Engineers, (2013) 4

5 Lower Susquehanna River: Steady State vs. Transient State Current Steady State: river flow rate less than 30,000 cfs Sediment/nutrients enters Chesapeake Bay at low-moderate rate TMDL regulations are related to steady state Transient state: river flow rate higher than 300,000 cfs Major Scouring event: enhanced erosion of sediment due to: significantly increased flow rates constant interaction of water with the Dam Chesapeake Bay: Before and After Tropical Storm Lee Source: MODIS Rapid Response Team at NASA GSFC 5

6 Flow and Sediment Build-up in Conowingo Reservoir Rouse number defines a concentration profile of sediment Determines how sediment will be transported in flowing water Holtwood Dam Rouse Number: Z = ω s u ω s =Sediment fall velocity u =shear velocity Significant amount of suspended sediment is located directly behind the dam (areas away from turbines) Conowingo Dam Rouse Number for Medium Silt Particle at 30,000 cfs Source: S. Scott (2012) 6

7 Sediment Deposition (million tons) Percent Capacity Sediment Deposition at Conowingo Dam Sediment Deposition Expected Threshold 100% 90% 80% 70% Deposition potential expected sediment deposited over a given time 60% % 40% 30% 20% 10% 0% At maximum capacity all Susquehanna River sediment flow s through to the Chesapeake Bay during normal, steadystate flow Year Sediment Deposition in Conowingo Reservoir; Construction to 2008 with Gap Prediction Source of Data: Hirsch, R.M., (2012) 7

8 Chesapeake Bay Total Maximum Daily Load (TMDL) Established by US Environmental Protection Agency in conjunction with 1972 Clean Water Act Actively planned since 2000 Covers 64,000 square miles in NY, PA, DE, MD, WV, VA, and DC Sets limits for farmers, plants, dams, and other organizations that dump sediment/nutrients into dam Designed to fully restore Bay by : 60% of sediment/nutrient reduction must be met 8

9 Lower Susquehanna Contribution to TMDL Watershed limits to be attained by 2025 are as follows: 93,000 tons of nitrogen per year (46% of Chesapeake TMDL reduction) 1,900 tons of phosphorus per year (30% of Chesapeake TMDL reduction) 985,000 tons of sediment per year (30% of Chesapeake TMDL reduction) 9

10 Agenda Context Stakeholders Problem/Need Statement Design Alternatives Analysis and Design of Simulation Design of Experiment Results, Analysis & Recommendations 10

11 Primary Stakeholders Objective(s) Issue(s) Lower Susquehanna Riverkeeper and Stewards of the Lower Susquehanna, Inc. (SOLs) - Find alternative uses for the sediment stored behind Conowingo Dam - Highlight vulnerabilities in environmental law - Minimize effects of major scouring events to the Chesapeake Bay - Cost to remove sediment from Reservoir is high - Providing pressure on FERC to require more strict relicensing requirements for Conowingo Dam Hydropower Plant Chesapeake Waterkeepers- West & Rhode Riverkeeper - Protect and improve the health of the Chesapeake Bay and waterways in the region - Cost to remove sediment from Reservoir is high Maryland and Pennsylvania Residents (Lower Susquehanna Watershed) Exelon Generation owner of Conowingo Dam Federal Energy Regulatory Commission (FERC) - Maintain healthy waters for fishing and recreation - Improve water quality of the watershed - Receive allocated power from Hydroelectric Dam - Obtain relicensing of Conowingo Dam prior to its expiration in September Maintain profit - Aid consumers in obtaining reliable, efficient and sustainable energy services - Define regulations for energy providers - Cost to remove sediment from Reservoir is high - Value low cost for power production and better water quality - Sediment build up has no impact on energy production - Pressure to update dam regulations 11

12 Agenda Context Stakeholders Problem/Need Statement Design Alternatives Analysis and Design of Simulation Design of Experiment Results, Analysis & Recommendations 12

13 Problem Statement - Conowingo Reservoir has been retaining a majority of the sediment flowing down the Susquehanna River - Major scouring events in the Lower Susquehanna River perpetuate significant ecological damage to the Chesapeake Bay - This ecological damage is caused by increased deposition of sediment and nutrients in the Bay 13

14 Need Statement Need to create a system to reduce the environmental impact of transient scouring events Need is met by reducing the sediment and nutrients currently trapped behind Conowingo Dam Reduce to 1,900 tons phosphorus per year Reduction is to be done while maintaining energy production and aiding TMDL regulations 14

15 Mission Requirements MR.1 The system shall remove sediment from the reservoir such that the total sediment deposition does not exceed 180 million tons. MR.2 The system shall reduce sediment scouring potential. MR.3 The system shall allow for 1.6 billion kwh power production annually at Conowingo Hydroelectric Station. MR.4 The system shall facilitate Susquehanna watershed limits of 93,000 tons of nitrogen, 1,900 tons of phosphorus, and 985,000 tons of sediment per year by MR.5 The system shall facilitate submerged aquatic vegetation (SAV) growth in the Chesapeake Bay. 15

16 Agenda Context Stakeholders Problem/Need Statement Design Alternatives Analysis and Design of Simulation Design of Experiment Results, Analysis & Recommendations 16

17 Sediment Mitigation Alternatives 1. No Mitigation Techniques (Baseline) Sediment remains in reservoir 2. Hydraulic Dredging Sediment removed from waters Product made from sediment 3. Dredging & Artificial Island Initially: Sediment is dredged to make an artificial island Over time: Sediment is slowly forced through the dam into bay Conowingo Dam Source: D. DeKok (2008) 17

18 1. No Mitigation Techniques 2. Hydraulic Dredging 3. Dredging & Artificial Island WHAT Sediment will reach capacity by 2030 Major scouring events will have the largest impact HOW Normal Flow: < 30,000 cfs Major Scouring Event: > 300,000 cfs Normal Flow at Conowingo Dam Source: E. Malumuth (2012) 18

19 1. No Mitigation Techniques 2. Hydraulic Dredging 3. Dredging & Artificial Island WHAT Remove sediment mechanically Concentration on suspended sediment Product yield from sediment HOW Rotating cutter to agitate & stir up Pipeline pumps sediment to surface Collection for further treatment Hydraulic Dredging Process Source: C. Johnson 19

20 1. No Mitigation Techniques 2. Hydraulic Dredging 3. Dredging & Artificial Island WHAT Diamond-shaped structure to divert water is placed in front of the dam Larger sediment load through the dam (at steady-state); remaining amount is dredged HOW Diverter made of dredged sediment product Diverts water left & right increases flow velocity Decreases Rouse number near suspended sediment Sediment mixed into wash load Potentially decreases total dredging costs Potential Artificial Island Location at Conowingo Reservoir Source: Original graphic by S. Scott (2012) 20

21 Primary Alternatives 1. No Mitigation Techniques 2. Hydraulic Dredging 3. Dredging & Artificial Island Sub-Alternatives Quarry Low Temperature Washing Rotary Kiln Plasma Gas Arc Vitrification Quarry Direct transportation from reservoir to quarry No opportunity to offset cost No one-time investment cost Rock Quarry 21

22 Primary Alternatives 1. No Mitigation Techniques 2. Hydraulic Dredging 3. Dredging & Artificial Island Sub-Alternatives Quarry Low Temperature Washing Rotary Kiln Plasma Gas Arc Vitrification Low-Temperature Sediment Washing Non-thermal Decontamination Potential use as manufactured topsoil One-time cost: Approx. $25 million (BioGenesis) Process includes: Loose screening Dewatering Aeration Sediment washing/remediation Oxidation and cavitation Low Temperature Washing Facility Manufactured Topsoil 22

23 Primary Alternatives 1. No Mitigation Techniques 2. Hydraulic Dredging 3. Dredging & Artificial Island Sub-Alternatives Quarry Low Temperature Washing Rotary Kiln Plasma Gas Arc Vitrification Rotary Kiln (Lightweight Aggregate) Thermal decontamination process Process includes: debris removal Dewatering Pelletizing Extrusion of dredged material One-time investment cost: Approx. $ million (HarborRock) Rotary Kiln Operation 23

24 1. No Mitigation Techniques 2. Hydraulic Dredging 3. Dredging & Artificial Island Sub-Alternatives Primary Alternatives Sub-Alternatives Quarry Low Temperature Washing Rotary Kiln Plasma Gas Arc Vitrification Plasma Gas Arc Vitrification (Glass Aggregate) % Decontamination and incineration of all organic compounds Intense thermal decontamination process Output: vitrified glassed compound slag One-time cost: Approx. $430 million (Westinghouse Plasma) Glass Aggregate (Slag) 24

25 Primary Alternatives 1. No Mitigation Techniques 2. Hydraulic Dredging 3. Dredging & Artificial Island Sub-Alternatives Quarry Low Temperature Washing Rotary Kiln Plasma Gas Arc Vitrification Cost/Revenue ($ per cubic yard) Distribution (Triangular) Comparisons: Quarry, Topsoil, and Lightweight Aggregate Cost PDF (Triangular) Quarry $0 $100 $200 $ Cost/Revenue PDF (Triangular) Topsoil Revenue Cost $0 $50 $100 $150 $200 $250 $ Cost/Revenue PDF (Triangular) Lightweight Aggregate $0 $50 $100 $150 $200 $250 $300 Sources: LSRWA (Quarry); M. Lawler et al and D. Pettinelli (Topsoil); JCI/Upcycle Associates, LLC (LWA) 25

26 Primary Alternatives 1. No Mitigation Techniques 2. Hydraulic Dredging 3. Dredging & Artificial Island Sub-Alternatives Quarry Low Temperature Washing Rotary Kiln Plasma Gas Arc Vitrification Cost/Revenue ($ per cubic yard) Distribution (Triangular) Comparisons: Plasma Gas Arc Vitrification Cost/Revenue PDF (Triangular) Low Grade Tile $0 $50 $100 $150 $200 $250 $300 Revenue Cost Cost/Revenue PDF (Triangular) High Grade Tile $0 $50 $100 $150 $200 $250 $300 Revenue Cost Source: Westinghouse 26

27 Agenda Context Stakeholders Problem/Need Statement Design Alternatives Analysis and Design of Simulation Design of Experiment Results, Analysis & Recommendations 27

28 Problem Overall: Project & Modeling Scope Sediment build up at Conowingo Dam has been detrimental to the Chesapeake Bay s ecosystem health following major storms (transient events) Problem Addressed by Model: 1. Sediment removal 2. Associated cost of remediation due to deposition of sediment and nutrients to the Chesapeake Bay 3. Sediment processing, sediment product production 28

29 Sediment Management Model Decomposition Model Simulates Model Type Sediment Removal Model Sediment flow from upstream and sediment outflow at Conowingo Dam - Microsoft Excel Spreadsheet Ecological Impact Model Cost of remediation and recovery based on phosphorus deposition to the Chesapeake Bay and hypothetical waste treatment upgrade costs - Java - Microsoft Excel Spreadsheet Reuse-Business Model Sediment product production, cost and revenue generation - Microsoft Excel Spreadsheet (Crystal Ball) 29

30 Stochastic Sediment Management Model 30

31 Stochastic Sediment Removal Model Input Flow Rate ( ) Source: USGS 31

32 Sediment Removal Model Three Different Future Worlds DRY FUTURE - 400,000 cfs max: Average Flow: 38,908 Median Flow: 26,826 Standard Deviation: 38,855 Avg. days/yr. > 150kcfs: 7.4 SIMILAR FUTURE-700,000 cfs max: Average Flow: 43,464 Median Flow: 28,638 Standard Deviation: 46,335 Avg. days/yr. > 150kcfs: 13.3 Historical Data: Average Flow: 41,271 Median Flow: 28,100 Standard Deviation: 47,095 Avg. days/yr. > 150kcfs: 12 WET FUTURE - 1,000,000 cfs max: Average Flow: 43,975 Median Flow: 30,685 Standard Deviation: 46,570 Avg. days/yr. > 150kcfs:

33 1 mi. Sediment Removal Model Bathymetry and Gridding L = Length W = Width D = Depth W L = Surface Area (SA) W D = Cross-Sectional Area (A) W L D = Volume (V) Water flow Scaled x10 Vertically W L D Conowingo Dam Actual Proportions Velocity Profile at 700,000 cfs. Source: U.S. Army Corps. Of Engineers Reservoir Bathymetry Source: USGS 33

34 Daily Cross-Sectional Area Sediment Removal Model Continuity & Shear Est. Equations A n+1,i = A n,i L i V i V i 400 i=1 + SS i L i + DS SA i SA i 200 i=1 L i Initial Cross- Sectional Area Area Decrease: Redeposition i = 1,.., 400; n = 1,.., 7305 Area Increase: Scoured Sediment Area Increase: Dredged Sediment Daily Scoured Sediment SS i = Z i Rouse Number Z = w s κ 1 10 (v i) i = 1,.., Q = Z SA i SA i Correlations: Flow, Rouse, Scoured Sediment SS = (Q) Source: U.S. Corps. of Engineering Variable L W D A SA V Q v SS DS Z w s k Description Reservoir Length Reservoir Width Reservoir Depth Cross-Sectional Area Surface Area Volume Flow Rate Flow Rate Adjusted Velocity Scoured Sediment Dredged Sediment Rouse Number Particle Fall Velocity Von Kármán Constant 34

35 Sediment Removal Model Assumptions Flow rates follow same trend from past 46 years Seeded correlation distributions are lognormal Redeposition is a fixed rate (4,000,000 tons/yr.) Particle fall velocity is fixed throughout reservoir 35

36 Average Daily Sediment Scoured ( 6,800 tons/day) P daily = P avg (SS) P avg Above Average Daily Sediment Scoured ( > 6,800 tons/day) P daily = P major (SS) P major = SurrogateRemediation Expense (Waste Treatment Plant Renovations) R = LSRP TMDL P W cost Ecological Impact Model Equations P daily daily phosphorus in tons SS daily sediment scoured in tons P avg random number that denotes average percent of phosphorus per ton of sediment P major denotes percent of phosphorus per ton of sediment during major scouring LSRP TMDL Lower Susquehanna TMDL limit for phosphorus (1895 tons) W cost average expense of phosphorus waste treatment renovations per TMDL limits 36

37 Ecological Impact Model Assumptions Linear correlation between sediment scoured and phosphorus scoured Linear correlation between hypothetical waste treatment upgrade costs and phosphorus scoured Nitrogen scoured is negligible with relation to waste treatment plant upgrade costs 37

38 Average ANNUAL Pollution Loads (tons) Ecological Impact Model Surrogate Data Based on surrogate data on Chesapeake Tropical Storm-Lee Related Pollution Loads (tons) Bay watershed wastewater treatment plant upgrades: Average expense of waste treatment renovations based on P TMDL : W cost = $ 6,300 /ton of phosphorus Phosphorus (P s ) 2,600-3,300 10,600 Sediment (S s ) 890,000-2,500,000 19,000,000 Ratio (P s /S s ) Waste Treatment Plant Plant 1 Upgrade Plant Name or Costs Areas Served (millions) Lexington and Rockbridge County(VA) 15.2 Plant 2 Hopewell (VA) Plant 3 Hopewell (VA) - Current 62 Plant 4 Buena Vista (VA) 30 % range of average ton of phosphorus per ton sediment % of ton of phosphorus per ton sediment during major scouring 38

39 Business Reuse Model Equations Production Equation: R i a i = p i Net Cost Equation: T i = c i + M x rev i R i a i = amount of sediment needed to make one unit of product i R i = amount of sediment removed and used for product i p i = units of product i produced rev i = revenue per cubic yard of product i c i =cost to produce product I per cubic yard of sediment processed T i = total cost M x = mitigation cost for one cubic yard of sediment 39

40 Business Reuse Model Assumptions (20 year NPV) Sediment can be processed on time Cost/revenue distributions are the same for all amounts of sediment input Cost/revenue values all follow a triangular distribution across all alternatives Market values will stay the same (no inflation for cost and revenue) Time horizon (20 years) is not a variable Discount rate=5% One-time set up cost excluded (included in utility analysis) 40

41 Agenda Context Stakeholders Problem/Need Statement Design Alternatives Analysis and Design of Simulation Design of Experiment Results, Analysis & Recommendations 41

42 Sediment Removal Model Design of Experiment For three future worlds (x3) Inputs Outputs No Mitigation Flow Rate (per day) Reservoir Bathymetry (per day) Reservoir Velocity Profile (per day) Sediment Scoured (per day) Sediment Redeposited (per year) source: U.S. Corps. of Engineering Sediment Dredged (per year) (note: dredging evenly 5 miles upstream daily) Reservoir Bathymetry (per day) Scoured Sediment (per day) Q L i, W i, D i v i SS i 4,000,000 tons 0 cy. L i, W i, D i SS i L i, W i, D i v i SS i 1,000,000 cy. L i, W i, D i SS i Dredging Q L i, W i, D i v i SS i 4,000,000 tons 3,000,000 cy. L i, W i, D i SS i L i, W i, D i v i SS i 5,000,000 cy. L i, W i, D i SS i Dredging & Island (note: 2 5 million cy./yr. dredged before simulation start) Q L i, W i, D i v i SS i 0 cy. L i, W i, D i SS i L i, W i, D i v i SS i 1,000,000 cy. L i, W i, D i SS i 4,000,000 tons L i, W i, D i v i SS i 3,000,000 cy. L i, W i, D i SS i L i, W i, D i v i SS i 5,000,000 cy. L i, W i, D i SS i Inputs to Feedback 42

43 Ecological Impact Model - Design of Experiment For current world view (700,000 cfs max) Input Outputs Scoured Sediment (per day) Estimated Remediation Expense Scoured Phosphorus (per year) No Mitigation SS R P SS R P Dredging SS R P SS R P Dredging & Island (note: 2 5 million cy./yr. dredged before simulation start) SS R P SS R P SS R P SS R P 43

44 Business Reuse Model - Design of Experiment Inputs Outputs Product Alternative Sediment Dredged (per year) (note: dredging evenly 5 miles upstream daily) Dredging and Transportation Costs Cost to produce product Revenue Generated from product Net cost to produce product Amount of product produce d Lightweight Aggregate 1,000,000 cy. T i p i 3,000,000 cy. M x c i rev i T i p i 5,000,000 cy. T i p i 1,000,000 cy. T i p i 3,000,000 cy. M x c i rev i T i p i 5,000,000 cy. T i p i Plasma (highgrade) 1,000,000 cy. T i p i 3,000,000 cy. M x c i rev i T i p i 5,000,000 cy. T i p i 44

45 Sediment Management System Value Hierarchy Sediment Scour Potential (0.5) U i = 0. 5 Minimize Susquehanna Sediment Impact to Chesapeake Bay Ecological Impact (0.5) S i E min E i, S max E min E max i = 1, 8 U i =Utility of dredging alternative i S i =scour potential decrease percentage of dredging alternative i S 5 =scour potential decrease percentage of dredging 5 million cy per year (the best option) E 0 =normalized cost of remediation of no mitigation after a scouring event E i =normalized cost of remediation of dredging alternative i after a scouring event E 5 =normalized cost of remediation of dredging 5 million cy per year with artificial island(the best option) 45

46 Agenda Context Stakeholders Problem/Need Statement Design Alternatives Analysis and Design of Simulation Design of Experiment Results, Analysis & Recommendations 46

47 Sediment Removal Model Results Future Looks Like Past - 700,000 cfs 47

48 Total Percent Decrease in Scour Sediment Removal Model Results Future Looks Like Past - 700,000 cfs 50% Percent Decrease in Scour After 20 years (700,000 cfs. max) 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% no mitigation Island 1-million Island,1-million 3-million Island,3-million Island,5-million 5-million For every 1 million cy dredged: 2% drop in scour (initial) 0.41% decrease in scour (final with maximum dredging) 48

49 Net Present Value Net Present Value Business Reuse Model Results Marginal Cost Time Flow Comparison :Two Sub-Alternatives $1,000,000, $500,000, Plasma high-grade $1,000,000, $500,000, Lightweight Aggregate $- $- $(500,000,000.00) $(500,000,000.00) $(1,000,000,000.00) $(1,000,000,000.00) $(1,500,000,000.00) $(2,000,000,000.00) $(1,500,000,000.00) $(2,000,000,000.00) 1 million cy/year 3 million cy/year 5 million cy/year $(2,500,000,000.00) $(2,500,000,000.00) $(3,000,000,000.00) $(3,000,000,000.00) $(3,500,000,000.00) $(3,500,000,000.00) $(4,000,000,000.00) Year $(4,000,000,000.00) Year 49

50 Utility Utility vs. Cost Island, 5 million 5 million Island, 3 million 3 million Island, 1 million 1 million Island Plasma High- Grade Lightweight Aggregate Quarry No mitigation 0 -$1 $0 $1 $2 $3 $4 Cost (Billions, Net Present Value, discount factor=5%) 50

51 Utility Utility vs. Cost Island, 5 million 5 million Island, 3 million 3 million Island, 1 million Plasma High- Grade Lightweight Aggregate Quarry $1 $0 $1 $2 $3 $4 Cost (Billions, Net Present Value, discount factor=20%) 51

52 Recommendations Best Alternative: Dredge 5 million cy/year and process into high-grade arc. tile via plasma gas arc vitrification Contact specializing company to perform further analysis for Conowingo Reservoir Next Best Alternative after Plasma: Dredge 1 million cy/year and process into lightweight aggregate with construction of artificial island Rank Alternative 1 Plasma, 5 million 2 Plasma, 5 million with Island 3 Plasma, 3 million with Island 4 Plasma, 3 million Future Work Conduct additional cost benefit analysis with any additional cost data attained for ecosystem impact 5 Lightweight Aggregate, 1 million with Island Look into dredging dams/reservoirs further North on the Susquehanna River Dispersion of cost Sediment reduction prior to entrance into Conowingo Reservoir 52

53 Questions? 53