Water Quality Modeling An OverviewAn Overview Quality/Planning/TMDL/Modeling... · • Models...
Transcript of Water Quality Modeling An OverviewAn Overview Quality/Planning/TMDL/Modeling... · • Models...
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Water Quality Modeling An OverviewAn Overview
Adugna Kebede, NC DWQModeling and TMDL UnitModeling and TMDL Unit
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What is a model?What is a model?
A d l i ll bj t ll b ilt t• A model is a small object usually built to scale, that represents another often larger objectlarger object.
A th ti l d l i id li d• A mathematical model is an idealized formulation that represents the response of a physical system to anresponse of a physical system to an external stimuli.
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What is a model?What is a model?
• A theoretical construct,• together with assignment of numerical
l t d l tvalues to model parameters, • incorporating some prior observations
drawn from field and laboratory datadrawn from field and laboratory data, • and relating external inputs or forcing
functions to system variable responsesfunctions to system variable responses
* Definition from: Thomann and Mueller, 1987
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Models
• Toys• Meteorologicalg• Economic• Health Risk• Health Risk• Climate
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What is a water quality model?What is a water quality model?
• A mathematical representation of pollutant fate, transport, and degradation within a water body
OR • A mathematical representation of the
movement of pollutants from land-basedmovement of pollutants from land based sources to a water body
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Model CalibrationModel Calibration
Calibration: The procedure of adjustment of parameter values of a j pmodel to reproduce the response of reality within the range of accuracy y g yconsistent with the intended application of the model.
Refsgaard, J,C. and H.J. Henriksen. 2003. Modeling guidelines – terminology and guiding principles, Advances in Water Resources 27, 71-82.
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Model ValidationModel Validation
Validation: Substantiation that a model within its domain of applicability pp ypossesses a satisfactory range of accuracy consistent with the intended yapplication of the model.
Refsgaard, J,C. and H.J. Henriksen. 2003. Modeling guidelines – terminology and guiding principles, Advances in Water Resources 27, 71-82.
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Don’t Mistake a Model for Reality!
• Models summarize data, provide one line of evidence, and provide an imperfect approximation of reality
• “All models are wrong; some models are useful” [George E. P. Box]
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Processes to consider in a model
http://www.kohalacenter.org/hisp/watershed.shtml
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Modeling System C tComponents
Environmental Factors: Precipitation, Temperature, Solar Radiation
Land River LakeDownstream
Receiving Water
Management Practices, Water Withdrawals, Waste Inputs
Water
From Jon Butcher, Tetra Tech, Inc
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How do you go from this?How do you go from this?
1
45
32
8
5
76
15 1312
11
10 9
14To this?
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To this?To this?Segment 1 Response to New Hope Creek Load Reduction
1
Segment 1 Response to New Hope Creek Load Reduction(average annual frequency of excursions)
10% 100% TP Load, 70% TN Load (30% TN reduction)
Existing condition
lPLo
ad
0.8
0.9
40.030 0
Percent of ChlorophyllExcursions
(Observations > 40 µg/l)
a
Existing condition
ofE
xist
ing
Tota
l
0 5
0.6
0.730.025.020.015.012.010.0
Frac
tion
o
0.3
0.4
0.58.06.0
100% TN Load, 40% TP Load (60% TP reduction)
Fraction of Existing Total N Load0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0.2
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Break it up!!!!Break it up!!!!
• Lake/reservoir broken into discrete
13
2areas or segments
• Spatial distribution f d t
45
2
6of data• Hydraulic barriers 10
89
76
• Water quality will be predicted in each segment
15 13
14
1211
segment 14
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The model sees thisThe model sees this…Major11 Major inflowOutflow
1
245689121314 1
15 7 31015
Major inflow
1245689121314
26 25 24 222829222223224
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Common Questions Regarding the Use of ModelsUse of Models
• Should they be used? Is a model necessary?• What are the primary waterbody characteristics?• What are the primary waterbody characteristics?• What are the concentration and response dynamics?• Which model should I use? - Model selectionWhich model should I use? Model selection• What are the trade-offs between using simple and
complex models?• Which features of the system should the modeling efforts
focus on?• How can modeling results be integrated into the overall• How can modeling results be integrated into the overall
assessment and planning framework?• How can complex model results be effectively transmitted
to the public?
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Models can be …• Emprical
Models are based on statistical relationship– Models are based on statistical relationship between parameters of interest and other variables (such as time)variables (such as time)
• Deterministic and MechanisticModels are developed using a combination– Models are developed using a combination of physics, chemistry, and statistical relationships. Also called process-basedrelationships. Also called process based or physically-based models.
• CombinationCombination
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Model Basisy = 0.8466xR2 = 0.7716
1,000
10,000
100,000
eom
ean
X f ( )1
10
100
1 10 100 1,000 10,000 100,000
FC geomean
EN
T g
e X = f (y)FC geomean
Empirical Formulations
Deterministic ModelsFormulations
(statistical relationships based on data)
Models(biological, chemical, physical processes)) p ys ca p ocesses)
Load = #/acre/yrLoad = #/acre/yrFrom Jon Butcher, Tetra Tech, Inc
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Models vary by typeModels vary by type…
• Receiving water models– These models predict what is happening in
the receiving waters, e.g., rivers, lakes, estuaries.
• Watershed loading models– These models predict what is happening
on “land” that results in an export of pollutant to the river, lake or estuary.
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Models vary by pollutantModels vary by pollutant…
• Suspended sediment/ Turbidity• Metals• Metals• Dissolved oxygen• Nutrients/Chlorophyll • Organic chemicals (SVOCs, persistent g ( , p
bioaccumulative chemicals)
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Models vary by waterbodyModels vary by waterbody…
• Rivers • Lakes• Estuaries• Tidal creeks and• Tidal creeks and
baysOcean• Ocean
• Groundwater
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Models vary in complexityModels vary in complexity…
• Simple – Long-term average representation of the system.
(Typically, an equation) Won’t vary in time or space.
• Moderately complex• Moderately complex– Average representation of the system (monthly,
annually). May vary in time or space.y) y y p• Complex
– Daily (or less than daily) representation of the y ( y) psystem. Varies in time and space.
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Level of Complexity -Landscape Models
• Export Coefficients• Export Coefficients– average annual unit area loads based
on landuse typeL di F ti• Loading Functions– simplified erosion and water quality
loading combined with basic representation of hydrologic processes
Increase representation of hydrologic processes • Dynamic Models
– mechanistic (process-based), time-variable representation of watershed
ed Com
p
variable representation of watershed processes, including hydrology, erosion, and water quality
plexity
From Jon Butcher, Tetra Tech, Inc
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Level of Complexity -R i i W t M d lReceiving Water Models
• Steady-state ModelsSteady state Models– fate and transport model that uses constant values
of input variables to predict constant results (under a representative condition)p )
• Quasi-dynamic Models– similar to steady-state formulations, but may include
diurnal representation
Increase diurnal representation• Dynamic Models
– mathematical formulation describing the physical behavior of a waterbody and its temporal variability
ed Com
p behavior of a waterbody and its temporal variability • Hydrodynamic - circulation, transport, temperature,
deposition• Water Quality - nutrients, toxics, pathogens,
plexity
temperature, etc.
From Jon Butcher, Tetra Tech, Inc
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The more complex the modelThe more complex the model
The more data youneed!!!
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General ways data is used in ymodeling
• Model Construction (development)• Initial conditions• Forcing functions and boundary
conditionsModel Calibration• Model Calibration
• Model Verification
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TMDLsTMDLs
• Should attain standards at all points in a listed segment or watershedB t i ti l t d l t TMDL• But, impractical to develop separate TMDLs for every stream segmentDetermine key “pressure points” where• Determine key “pressure points” where upstream control needs are most stringent
• Revise refine and nest management as• Revise, refine, and nest management as necessary
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TMDLsTMDLs
T i• To summarize:• TMDL = LC = WLAs + LAs + MOS
• Models are used in Linkage Analysis (Linking Sources to Targets)(Linking Sources to Targets)
• Models are used to determine Loading Capacity, and to separate the Wasteload yAllocations (point source) and Load Allocations (nonpoint source)
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Protocols for TMDL DevelopmentSuggested TMDL Components
• Problem Statement• Numeric TargetsNumeric Targets• Source Assessment• Linkage Analysis• Linkage Analysis• Allocations
M it i /E l ti Pl (f• Monitoring/Evaluation Plan (for phased approach)(I l t ti F ll th TMDL)• (Implementation: Follows the TMDL)
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Problem StatementProblem Statement
• Designated uses and impairment• Geographic setting and scaleg g• Potential sources• Potential control options• Potential control options• Temporal considerations
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Numeric TargetsNumeric Targets
• Select Indicators– Applicable numeric or narrative standard– Potential measures useful as indicators
when numeric standards are not available• Identify target values• Compare existing and target conditionsCo pa e e s g a d a ge co d o s
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Linking Sources to Water Quality
• Identify cause-and-effect relationships between selected water quality targets andbetween selected water quality targets and identified sources
• Determine level of analysis and method Determine level of analysis and method of linkage
• Assess linkages• Estimate total loading capacity or needed load
reductionUtili i l ti th d• Utilize simulation methods.=Establish overall assimilative capacity and load reduction neededcapacity and load reduction needed
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Linkage AnalysisLinkage Analysis …
D ib h li k d t• Describe how sources are linked to impairment of designated uses, e.g.– erosion of logging roads ->erosion of logging roads >– excess fine sediment load ->– increased embeddedness of substrate ->– poor spawning success of salmonids ->– failure to support designated coldwater fishery
• What components of the linkage can be• What components of the linkage can be measured and predicted to evaluate control options (indicators)?p ( )
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A Typical Point-Source Modeling Problem
• Steady-state• Low flow conditionsLow flow conditions
6.5
7.0
7.5
on (m
g/L)
5.0
5.5
6.0
O C
once
ntra
tio
3.5
4.0
4.5
Pre
dict
ed D
30 28 26 24 22 20 18 16 14 12 10 8 6 4 2River Mile
Minimum DOStandard
33
River Mile
From Jon Butcher, Tetra Tech, Inc
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A Typical ypWatershed-Scale
ProblemProblem
34From Jon Butcher, Tetra Tech, Inc
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Model Selection ProcessIdentify Decision NeedsIdentify Decision Needs
I
II Identify Land, Water, and Identify Land, Water, and Management FeaturesManagement Features
III Identify Special or Innovative Identify Special or Innovative AnalysesAnalyses
IV Evaluate Constraints and User Evaluate Constraints and User PreferencesPreferences
V Evaluate Candidate Models and Evaluate Candidate Models and SelectSelectSelectSelect
From Jon Butcher, Tetra Tech, Inc
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Model Selection Process• Indicators relevant to
Identify Decision NeedsIdentify Decision NeedsI
• Indicators relevant to management decision– Compliance with numeric
II Identify Land, Water, and Identify Land, Water, and Management FeaturesManagement Features
and narrative standards– Load of pollutant– Conc. of pollutant
III Identify Special or Innovative Identify Special or Innovative AnalysesAnalyses
– Secondary impacts
• Critical Condition vs. Continuous Simulation
IV
yy
Evaluate Practical Issues and Evaluate Practical Issues and User PreferencesUser Preferences
Continuous Simulation
V
User PreferencesUser Preferences
Evaluate Candidate Models and Evaluate Candidate Models and SelectSelectV SelectSelect
From Jon Butcher, Tetra Tech, Inc
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Model Selection Process• Waterbody type
Identify Decision NeedsIdentify Decision NeedsI
• Waterbody type– River– Lake
II Identify Land, Water, and Identify Land, Water, and Management FeaturesManagement Features
• Watershed Uses & Sources
Rural
III Identify Special or Innovative Identify Special or Innovative AnalysesAnalyses
– Rural– Urban– Forest
IV
yy
Evaluate Constraints and User Evaluate Constraints and User PreferencesPreferences
• Management Techniques– Stormwater ponds
V
PreferencesPreferences
Evaluate Candidate Models and Evaluate Candidate Models and SelectSelect
Stormwater ponds– Operations– Flow management
V SelectSelect
From Jon Butcher, Tetra Tech, Inc
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Model Selection Process• Special processes
Identify Decision NeedsIdentify Decision NeedsI
• Special processes that are not typically included in models
II Identify Land, Water, and Identify Land, Water, and Management FeaturesManagement Features
III Identify Special or Innovative Identify Special or Innovative AnalysesAnalyses
IV
yy
Evaluate Constraints and User Evaluate Constraints and User PreferencesPreferences
V
PreferencesPreferences
Evaluate Candidate Models and Evaluate Candidate Models and SelectSelectV SelectSelect
From Jon Butcher, Tetra Tech, Inc
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Model Selection Process Model Specific Features– Ease of use
Identify Decision NeedsIdentify Decision NeedsI
– Time to apply– Difficulty– Availability
II Identify Land, Water, and Identify Land, Water, and Management FeaturesManagement Features
y– Credibility– Data needs– Software capabilities
III Identify Special or Innovative Identify Special or Innovative AnalysesAnalyses
Software capabilities
User Specific Preferences– Trained staff
IV
yy
Evaluate Constraints and User Evaluate Constraints and User PreferencesPreferences
Trained staff– Available experts– Available data– Time/schedule
V
PreferencesPreferences
Evaluate Candidate Models and Evaluate Candidate Models and SelectSelect
Time/schedule– Resources/financial
considerationsV SelectSelect
From Jon Butcher, Tetra Tech, Inc
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Modeling Process
Modeling Approach Development
Modeling Process
Modeling Approach Development
Data Collection (historic, field monitoring)
Model Input Preparation and Configuration
Phase I Model Input Preparation and Configuration
Calibration
V lid tiPhase Validation
Verification
Phase II
Analysis of AlternativesPhase IIIIII
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Selecting a model frameworkg
M d l f k• Model framework– Data availability– Watershed characteristicsWatershed characteristics– EPA guidance (e.g., Nutrient TMDL Protocol)– Experience (personally and as a unit)– Schedule
• For nutrient response models, must select one of the following:one of the following:– EUTROMOD, BATHTUB, CE-QUAL-W2, EFDC,
WASP
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NRM: Frameworks differ byNRM: Frameworks differ by…
• Spatial variability:Spatial variability: – Models entire lake as one unit; No spatial
variability. (EUTROMOD)y ( )– Models different parts of the lake; some
spatial variability. (BATHTUB, CE-QUAL-p y (W2, WASP, EFDC)
• Temporal scale of outputp p– “Growing season” output only
(EUTROMOD, BATHTUB)( )
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Frameworks differ by ContFrameworks differ by… Cont.
• Temporal scale of output– Daily output (CE-QUAL-W2, EFDC, y (
WASP)• Ability to evaluate effect of water y
movement– Hydrodynamic components (CE-QUAL-y y p ( Q
W2, EFDC)• Complexity……Complexity……
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SummaryM d li i d t k t d i i• Modeling is undertaken to serve a decision need
• Simple and complex deterministic and• Simple and complex, deterministic and empirical models all have their roles in TMDL development
• Design the modeling process based on the problem (Questions to answer), Information Needs and data (resources) avialabilityNeeds, and data (resources) avialability
• Models are used to determine Loading Capacity, and to separate the WasteloadCapacity, and to separate the Wasteload Allocations (point source) and Load Allocations (nonpoint source) in the TMDL ProcessProcess
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Some Useful Websites for TMDLSome Useful Websites for TMDL Modeling
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Questions?Questions?
Adugna Kebede
NCDWQ M d li & TMDL U itNCDWQ – Modeling & TMDL Unit
1617 Mail Service Center
Raleigh, NC 27699-1617
(919) 733-5083 ext. 515