Long-Term Salinity Prediction with Uncertainty Analysis: Application for Colorado River Above Glenwood Springs, CO

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Long-Term Salinity Prediction with Uncertainty
AnalysisApplication for Colorado River Above
Glenwood Springs, CO

• James Roger Prairie
• Dept. of Civil, Architectural, and Environmental
  Engineering
• Masters Research Seminar
• Spring 2002

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Motivation

• Colorado River Basin
• arid and semi-arid climates
• irrigation demands for agriculture
• Law of the River
• Minute No. 242 of the International Boundary and
  Water Commission dated August 30, 1973
• Colorado River Basin Salinity Control Act of 1974
• Federal Water Pollution Control Act Amendments of
  1972

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Salinity Damages and Control Efforts

• Damages are presently, aprox. 330 million/year
• As of 1998 salinity control projects has removed
  an estimated 634 Ktons of salt from the river
• total expenditure through 1998 426 million
• Proposed projects will remove an additional 390
  Ktons
• projects additional expenditure 170 million
• Additional 453 Ktons of salinity controls needed
  by 2015

Data taken from Quality of Water, Progress Report
19, 1999 Progress Report 20,2001
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Existing Salt Model Over-Prediction
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Stochastic Simulation

• Simulate from the conditional probability
  function
• joint over the marginal densities

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Parametric PAR(1)

• Periodic Auto Regressive model (PAR)
• developed a lag(1) model
• Stochastic Analysis, Modeling, and Simulation
  (SAMS) (Salas, 1992)
• Data must fit a Gaussian distribution
• Expected to preserve
• mean, standard deviation, lag(1) correlation
• skew dependant on transformation
• gaussian probability density function

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Modified Nonparametric K-NN Natural Flow Model

• Improvement on traditional K-NN
• keeps modeling simple yet creates values not seen
  in the historic record
• perturbs the historic record within its
  representative neighborhood
• allows extrapolation beyond sample

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Residual Resampling
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Conditional PDF
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Low flow
Composites
High minus Low flow
High flow
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Statistical Nonparametric Model for Natural Salt
Estimation

• Based on calculated natural flow and natural salt
  mass from water year 1941-85
• calculated natural flow observed historic
  flow total depletions
• calculated natural salt observed historic
  salt - salt added from agriculture salt
  removed with exports
• Nonparametric regression (local regression)
• natural salt f (natural flow)
• Residual resampling

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Comparison with Observed Historic Salt
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Comparison With Calculated Natural Salt
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CRSS Simulation Model for Historic Validation
Natural flow 1906-95 Natural salt 1941-95
Constant salinity pickup 137,000 tons/year
Exports removed _at_ 100 mg/L
Compare results to observed historic for
validation
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Annual Model With Resampling

• Based on 1941-1995 natural flow
• 1941-1995 annual salt model
• Simulates 1941-1995

• Historic Flow and Concentration

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Modified and Existing CRSS Comparison Historic
Salt Mass

• Based on 1906-1995 natural flows
• 1941-1995 monthly salt models
• Simulates 1941-1995

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Policy AnalysisHistoric Simulation
gt 650,000 tons salt
gt 350 mg/L salt concentration
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Stochastic Planning Runs Projected Future Flow
and Salt Mass

• Passing gauge 09072500
• Based on 1906-1995 natural flows
• 1941-1995 monthly salt models
• Simulating 2002 to 2062

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Conclusion

• Developed a modeling framework for long-term
  salinity with uncertainty in the Colorado River
• modified nonparametric K-NN natural flow model
• statistical nonparametric natural salt model
• validation of historic record
• demonstrated future projection

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Future Work

• Extend the modified K-NN flow model to perform
  space-time dissaggregation to simulate flow and
  salt over the entire basin
• Move operational policy to an annual time step
• Further research into the relationship between
  salt loading and land use
• Continue work to incorporate climate information
  in streamflow generation

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Acknowledgements

• Balaji Rajagopalan, Terry Fulp, Edith Zagona for
  advising and support
• Upper Colorado Regional Office
• of the US Bureau of Reclamation,
• in particular Dave Trueman for funding and
  support
• CADSWES personnel for use of their
• knowledge and computing facilities

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Extra Slides Follow
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Conclusions

• developed and tested a new statistical
  nonparametric natural salt model
• discussed nonparametric techniques
• flexible and easy to implement
• can preserve any arbitrary distribution
• conditioning with additional data
• validation of historic record
• preservation of historic salinity violations

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Case Study

• Colorado River above USGS gauge 09072500
  (Colorado River near Glenwood Springs, CO)
• flow data available from water year 1906-1995
• salt data available from water year 1941-1995
• model at a monthly timestep to accommodate the
  reservoirs operating policy in the simulation
  model

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Motivation

• Generating synthetic natural flow
• future variability
• Index Sequential Method (ISM)
• cannot produce values or traces that had not
  occurred in the past
• limited variability among traces

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ENSO response in Colorado River Basin

• Published by Cayan and Webb, 1992
• A weak response seen over Upper Colorado River
  Basin

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Sea Surface Temperature
Correlation
Sea Level Pressure
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Residual Resampling
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Alpha 0.4 or k 18
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Model Validation Natural Flow

• 1941-1995 natural flow
• Utilizes subset of available record

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Model Validation Natural Flow

• 1906-1995 natural flow
• Utilizes entire available record

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Model Validation Natural Salt Mass

• 1941-1995 natural flow
• Utilizes subset of available record
• 1941-1995 monthly and annual salt model

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Model Validation Natural Salt Mass

• 1906-1995 natural flow
• 1941-1995 monthly salt models

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Annual model with no resampling

• 1906-1995 natural flow
• 1941-1995 annual salt model
• Historic Flow and Concentration

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Future Salt Mass
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Motivation

• Salinity Control Forum
• Federal Water Pollution Control Act Amendments of
  1972
• Numerical salinity criteria
• 723 mg/L below Hoover Dam
• 747 mg/L below Parker Dam
• 879 mg/L at Imperial Dam
• review standards on 3 year intervals
• Develop basin wide plan for salinity control

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Existing Colorado River Simulation System (CRSS)

• Includes three interconnected models
• salt regression model
• USGS salt model
• stochastic natural flow model
• index sequential method
• simulation model of entire Colorado River basin
• implemented in RiverWare

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Index Sequential Method

• Current stochastic hydrology model utilized by
  the USBR

Adapted from Ouarda, 1997
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Model Evaluation

• Natural flow 1906 to 1995
• Basic Statistics
• mean,standard deviation, autocorrelation,
  skewness
• Higher Order Statistics
• probability density function
• conditional probability
• Minimum and Maximum Flows

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USGS Salt Model

• 12 monthly regressions
• based on observed historic flow and salt mass
  from water year 1941 to 1983
• historic salt f (historic flow, several
  development variables)
• natural salt f (natural flow, development
  variables set to zero)

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Policy AnalysisHistoric Simulation

• gt 350 mg/L salt concentration

Incorporates total depletion as a function of
natural flow
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CRSS Simulation Model for Future Prediction

• Natural flows based on 1906-1995
• Natural salt model based on 1941-1995
• Projected depletions 2002-2062
• Constant Ag salt loading of 137,000 tons/year
• Constant salt removal with exports of 100
  mg/L/year

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Policy Analysis Future Projections
gt 750,000 tons salt
gt 600 mg/L salt concentration