Investigating the Colorado River Simulation Model

1. Investigating the Colorado River Simulation Model James Prairie Bureau of Reclamation

2. Motivation • Colorado River Basin • arid and semi-arid climates • irrigation demands for agriculture • Federal Water Pollution Control Act Amendments of 1972 • “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

4. 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

5. Seminar Outline • Motivation for research • Initial findings • Working with a case study • New salinity modeling techniques • Extending knowledge of our case study • Current Efforts • Recompute Natural flow • Verify entire Colorado River Simulation Model • Future Research

9. Research Objectives • Verify the data and calibrate the current model for both water quantity and water quality (total dissolved solids, or TDS) • Investigate the salinity methodologies currently used and improving them as necessary for future projection

10. Investigation of Colorado River Simulation Model • First developed in Fortran in 1970’s • Moved to RiverWare in 1990’s • Relies on Conservation of Mass for modeling • water quantity and, • water quality (TDS). • Monthly Time Step • Runs with operational rules to simulate operational policies in the Colorado River Basin

11. Initial Findings • Data and Methodological Inconsistency • Need to improve current model techniques • Stochastic stream flow simulation • Estimating natural salt • Adding uncertainty • Working with a case study • Detailed investigation of current methods • Development of new methods

12. Case Study Area • Historic flow from 1906 - 95 • Historic salt from 1941 - 95 USGS gauge 09072500 (Colorado River near Glenwood Springs, CO)

13. 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)

14. Existing Salt Model Over-Prediction

15. New Modeling Techniques • Found problems with the current method to estimate natural salt in the upper basin • Can we fix the problem? • Alternate methods the estimate natural salt with the available data

16. 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

17. Local Regression alpha = 0.3 or 27 neighbors Y X

18. e * y * x Residual Resampling y = y* + e* Y X

19. Nonparametric Salt Model and USGS Salt Model

20. Natural Salt Mass from Nonparametric Salt Model and USGS Salt Model

21. USGS Salt Model and New Salt Model with K-NN Resampling Comparison

22. Comparison with Observed Historic Salt

23. Key Case Study Findings • The new nonparametric salt model removed the over-prediction seen with the USGS salt model • Provides uncertainty estimates • Can capture any arbitrary relationship (linear or nonlinear)

24. Extending from Case Study • Applying case study results to entire model • Improved natural salt estimation model • Improved stochastic stream flow generation • Addition of uncertainty analysis • Ensure flexible framework

25. Current Efforts • Recomputing natural flow • Lack of base data • Undocumented procedure • Upper versus Lower Basin • Inconsistency across time periods • Inconsistent with future projection model

26. Natural Flow Development • Natural flow is a basic input for CRSS • Addressing Data Inconsistencies • Recomputing natural flow from 1971-95 Natural Flow = Historic Flow - Consumptive Uses and Losses +/- Reservoir Regulation • Addressing Methodological Inconsistencies • RiverWare model computes natural flow • Ensures consistency

27. Recomputing natural flow from 1971-95 • Data required for natural flow model • Historic USGS gauge data • 29 gauges • Historic main-stem reservoir outflow and pool elevations • 12 main-stem reservoirs • Historic off-stream reservoir change in storage • 22 off-stream reservoirs • Consumptive uses and losses • 9 categories

28. Determining Natural Flow

30. Extend new natural salt model throughout the 21 upper basin natural flow gauges Check natural flow and salt relationship 1941-1995; 1970-1995 Calculate natural flow for the lower basin Natural salt is back calculated as flow Verify entire basin for flow and the lower basin for salt Finally use more for a future projection Apr-Jul 2003 Aug-Sep 2003 Oct-Nov 2003 Dec 2003 After Natural Flow Is Calculated

31. Future Research • Explore salinity relationship over both space and time • Incorporate new stochastic flow generation methods • Investigate land use change and the impacts on salinity levels • Explore the relationship between basin area and both flow and salinity

32. Acknowledgements • Dr. Balaji Rajagopalan, Dr. Terry Fulp, Dr. 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

34. Drainage Area • Colorado River Basin • 241,000 mi2 • Upper Basin • 110,000 mi2 • Case Study • 4,558 mi2