Investigating the Colorado River Simulation Model James Prairie Bureau of Reclamation

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

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

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

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

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

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

USGS gauge (Colorado River near Glenwood Springs, CO) Historic flow from Historic salt from Case Study Area

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)

Existing Salt Model Over-Prediction

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

Statistical Nonparametric Model for Natural Salt Estimation Based on calculated natural flow and natural salt mass from water year 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

Local Regression alpha = 0.3 or 27 neighbors X Y

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

Nonparametric Salt Model and USGS Salt Model

Natural Salt Mass from Nonparametric Salt Model and USGS Salt Model

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

Comparison with Observed Historic Salt

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)

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

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

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

Recomputing natural flow from 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

Determining Natural Flow

After Natural Flow Is Calculated Extend new natural salt model throughout the 21 upper basin natural flow gauges Check natural flow and salt relationship ; 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

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

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

Drainage Area Colorado River Basin 241,000 mi 2 Upper Basin 110,000 mi 2 Case Study 4,558 mi 2