Hydrodynamic and Water Quality Modeling Basics

Transcription

1 Hydrodynamic and Water Quality Modeling Basics Jim Bowen, UNC Charlotte LCFRP Advisory Board/Tech. Comm. Meeting, November 27, 2007 Wilmington, NC

2 Objectives of Presentation Introduction to Numerical Water Quality Models Introduction to Model Used - Environmental Fluid Dynamics Code (EFDC) Description of LCFR Application

3 A Numerical Model Example - The Monty Hall Problem Letter to Marilyn vos Savant (Sept. 9, 1990) "Suppose you're on a game show, and you're given the choice of three doors. Behind one door is a car, the others, goats. You pick a door, say #1, and the host, who knows what's behind the doors, opens another door, say #3, which has a goat. He says to you: 'Do you want to pick door #2?' Is it to your advantage to switch your choice of doors?" Craig F. Whitaker, Columbia, Maryland

4 Marilyn s Response You should switch because door #2 has a 2/3 chance of winning whereas door #1 has only a 1/3 chance of winning.

5 Marilyn s Response You should switch because door #2 has a 2/3 chance of winning whereas door #1 has only a 1/3 chance of winning. Thousands responded, (including many College Math professors) Marilyn is wrong the doors are equally likely to win

6 The Debate Rages at Work Yes, Marilyn is right, your odds are better if you switch No, Marilyn is wrong, 2 doors, 1 car, each door has a 50% chance of winning

7 The Debate Rages at Work Yes, Marilyn is right, your odds are better if you switch No, Marilyn is wrong, 2 doors, 1 car, each door has a 50% chance of winning My response - I m not sure, but I could easily write a computer program to simulate this problem

8 The Monty Hall Simulator, p1

9 The Monty Hall Simulator, p2

10 The Monty Hall Simulator, p2 About 50 lines of computer code Took about 45 minutes to write

11 The Monty Hall Simulator, The Results, Don t Switch >> lmad How many trials? (1-9,999): 999 What is your strategy? k = keep your door s = switch your door f = flip a coin, since the choices are equally likely Choose a letter: k You won the prize 34% of the time

12 The Monty Hall Simulator, The Results, Switch >> lmad How many trials? (1-9,999): 999 What is your strategy? k = keep your door s = switch your door f = flip a coin, since the choices are equally likely Choose a letter: s You won the prize 68% of the time

13 A Numerical SimulationModel Computer program that simulates the behavior of the system being studied Based on a conceptual model of how the system operates Computer code written to implement the conceptual model description Scenario testing used to answer questions of interest about system

14 What is a Water Quality Model? Models are Numerical Calculations Used to Estimate Anthropogenic Impact A Typical Modeling Problem Given: 1. Amount of Point and Nonpoint Source Inputs 2. Water Body Characteristics Find: 1. Water Quality of the Receiving Body

15 What is a Model? (continued) Given: 1. Amount of Point and Nonpoint Source Inputs 2. Water Body Characteristics Find: 1. Water Quality of the Receiving Body

16 What is a Model? (continued) Given: 1. Amount of Point and Nonpoint Source Inputs 2. Water Body Characteristics Find: 1. Water Quality of the Receiving Body Empirical Models

17 What is a Model? (continued) Given: 1. Amount of Point and Nonpoint Source Inputs 2. Water Body Characteristics Find: 1. Water Quality of the Receiving Body Empirical Models Mechanistic Models

18 What is a Model? (continued) Given: 1. Amount of Point and Nonpoint Source Inputs 2. Water Body Characteristics Find: 1. Water Quality of the Receiving Body Neuse, LCFR models Mechanistic Models

19 Steps in Creating a Mechanistic Model Code 1. Decide on What to Model 2. Create Conceptual Model(s) 3. Make Necessary Simplifying Assumptions 4. Write Governing Equations 5. Devise Numerical Solution Schemes 6. Implement Above in Computer Program

20 Steps in Applying a Mechanistic Model 1. Decide on What to Model 2. Decide on Questions to be Answered 3. Choose Model 4. Collect Data for Inputs, Calibration 5. Create Input Files 6. Create Initial Test Application 7. Perform Qualitative Reality Check Calibration & Debugging

21 Steps in Applying a Mechanistic Model, continued 8. Perform quantitative calibration & model verification 9. Design model scenario testing procedure (endpoints, scenarios, etc.) 10. Perform scenario tests 11. Assess model reliability 12. Document results

22 Mechanistic Model Basis: Conservation Equations Inflow State Variable Outflow Sources Sinks Water Volume

23 Mechanistic Model Basis: Conservation Equations Momentum Conservation (for Water Velocities) Energy Conservation (for Temperature) Mass Conservation (for WQ Constituents) Inflow State Variable Outflow Sources Sinks Water Volume

24 Mechanistic Model Basis: Conservation Equations Momentum Conservation (for Water Velocities) Energy Conservation (for Temperature) Mass Conservation (for WQ Constituents) Inflow State Variable Outflow Sources Sinks Water Volume

25 4. Governing Equations Based on Conservation Equations Momentum Conservation (for Water Velocities) Energy Conservation (for Temperature) Mass Conservation (for WQ Constituents) Inflow State Variable Outflow Sources Sinks Water Volume

26 Mechanistic Model Basis: Conservation Equations Change in Variable/Time = Inflow Rate - Outflow Rate +/- Sources & Sinks Inflow State Variable Outflow Sources Sinks Water Volume

27 Governing Equation 1. Momentum Balance Atmosphere Inflow/Outflow Water Column Sediment Convection Bottom Friction Wind Mixing Gravity Turbulent Diffusion

28 Governing Equation 2. Atmosphere Heat Balance Conduction Solar Radiation Inflow/Outflow Evaporation Water Column Turbulent Transport Conduction Sediment

29 Example of Mass Conservation: Dissolved Oxygen DO Inflow Reaeration Single Segment DO & BOD Consumption SOD DO Outflow

30 Example of Mass Conservation : Dissolved Oxygen Inflow DO Inflow Reaeration Single Segment DO & BOD Consumption SOD DO Outflow

31 Example of Mass Conservation: Dissolved Oxygen Inflow DO Inflow Reaeration Single Segment Outflow DO & BOD Consumption SOD DO Outflow

32 Example of Mass Conservation: Dissolved Oxygen Source Inflow DO Inflow Reaeration Single Segment Outflow DO & BOD Consumption SOD DO Outflow

33 Example of Mass Conservation: Dissolved Oxygen Source Inflow DO Inflow Reaeration Single Segment Outflow Sinks DO & BOD Consumption SOD DO Outflow

34 Governing Eq. 3: DO Conceptual Model BOD Sources NECF & Black R. BOD Load decaying phytopl. Cape Fear BOD Load Muni & Ind. BOD Load Sediment

35 Governing Eq. 3: DO Conceptual Model Cape Fear BOD Load BOD Sources, DO Sources & Sinks NECF & Black R. BOD Load Muni & Ind. BOD Load MCFR Inflows Sediment decaying phytopl. Input of NECF & Black R. Low DO Water Surface Reaeration Phytoplank. BOD Productivity Consumption Ocean Inflows Sediment O 2 Demand

36 Governing Eq. 3: DO Conceptual Model Cape Fear BOD Load BOD Sources, DO Sources & Sinks NECF & Black R. BOD Load Muni & Ind. BOD Load MCFR Inflows Sediment decaying phytopl. Input of NECF & Black R. Low DO Water Surface Reaeration Phytoplank. BOD Productivity Consumption Ocean Inflows Sediment O 2 Demand

37 EFDC, the big picture Hydrologic Conditions River Flows, Temp s, Conc s Tides Time EFDC Software Adjustable Parameters: (e.g. BOD decay, SOD, reaeration) Air temps, precip, wind, cloudiness Met Data Time Estuary Physical Characteristics: e.g. length, width, depth, roughness State Variables nutrients DO, organic C Time

38 Next Part of Presentation: More Info on EFDC Go to Very Short Intro to EFDC.ppt

39 Description of Model Application Flow boundary condition upstream Elevation boundary condition downstream 17 lateral point sources Extra lateral point sources add water from marshes

40 Description of Model Application Black River Flow Boundary Cond. NE Cape Fear Flow Boundary Cond. Cape Fear R. Flow Boundary Cond. Lower Cape Fear River Estuary Schematic Open Boundary Elevation Cond.

41 LCFR Grid Channel Cells in Blue Wetland Cells in White Marsh and Swamp Forest in Green, Purple

42 Data Source for Wetland Information

43 LCFR Grid Characteristics Off-channel storage locations based on wetland delineations 46 additional marsh cells added to original grid (1050 total cells, 8 vertical layers) Additional off-channel storage added to each basin (Cape Fear, Black, NECF) Significant amount of marsh area added to middle and lower estuary

44 LCFR EFDC Application: Other Input Files Meteorological forcings (from NWS) Freshwater inflows (from USGS) Elevations at Estuary mouth (from NOAA) Quality, temperature of freshwater inflows, at estuary mouth (from LCFRP) Other discharges (from DWQ)

45 LCFR EFDC Application: Data Collected Data Collected from 8 sources COE, DWQ, IP, LCFRP, NOAA, NWS, USGS, Wilmington WWTP Over 800 MB of original data collected so far Original data archived and saved as read only files

46 LCFR Model - What Does it Simulate? Water Properties Temperature, salinities Circulation Flows, velocities, water surface elevations Nutrients Organic and Inorganic nitrogen, phosphorus Organic Matter BOD (dissolved, particulate), chlorophyll Other Dissolved Oxygen

47 Cape fear river check point 1: NC11 2: LC 3: ACME 4: B210 5: DP 6: IC 7: NAV 8: HB 9: NC_7 10: NCF6 11: BR 12: M61 13: M54 14: M42 15: M35 16: M23 17: M18

48 April - November 2004 Salinity, New

49 April - November 2004 Temp., New

50 LCFR Model Application - What Can You Do With It? Model simulates behavior of estuary Pose scenarios - use model to estimate impacts e.g. climate impacts (how does WQ change w/ reduced inflows) e.g. management scenarios (how does WQ change w/ reduced wastewater inputs)

51 LCFR Model - What are we Working on Now? Hydrodynamic model calibrated Plan to finish WQ model calibration in December Run scenarios in January More in next talk

52 Information Available Online See LCFR website for more info This presentation is available Google Earth files available for download Grid and wetland data from presentation Monitoring stations, point sources Final EFDC grid information NOAA bathymetry Hydrodynamic model animations