1. Dave Clark and Michael Kasch
The Role of Water Quality Modeling in Watershed Management for the Clark Fork and Bitterroot Rivers
Missoula, Montana
April 1, 2005
Dave Clark and Michael Kasch

2. Introduction and Overview
Purpose: Nutrient Modeling for the Clark Fork and Bitterroot Rivers
Modeling Projects
Model Selection
Model Construction
QUAL2E Models
SWAT Model
Model Application
Project Status

3. Approach Purpose – Clean Water Act Sponsors Supporting projects
TMDL (Total Maximum Daily Load)
VNRP (Voluntary Nutrient Reduction Program)
Sponsors
Department of Environmental Quality (DEQ)
Tri-State Water Quality Council (TSWQC)
City of Missoula
Supporting projects
River and Watershed Models

4. Locations of Projects River Models Clark Fork River Bitterroot River
Warm Springs Creek to
Flathead River
Bitterroot River
Darby
Confluence with Clark Fork River
Watershed Model
Headwaters of Watershed to

5. Models

6. Model Selection
A model selection process was completed for the Clark Fork River with direction by TSWQC
Bitterroot River model selected to correspond with modeling on the Clark Fork River
Watershed model selected by DEQ
Models used to….
Assimilate monitoring data
Assess the river system
Prediction of response to drivers

7. Models River Model – QUAL2E (Enhanced Stream Water Quality Model)
Application funded by TSWQC & City of Missoula
Watershed Model – SWAT (Soil and Water Assessment Tool)
Application funded by DEQ
Public Domain Software
QUAL2E developed by EPA
SWAT developed by USDA-ARS

8. Model Capabilities
QUAL2E is a one-dimensional river model capable of steady flow simulations of multiple water quality parameters
QUAL2E complexity is low to moderate
Computer simulation time is minutes
SWAT is a watershed-scale hydrologic and water-quality model developed to predict the effects of alternative land use management operations on water, sediment, and chemical yields
SWAT complexity is high
Computer simulation time is hours (days)

9. QUAL2E - SWAT Models
Results from QUAL2E and SWAT may be entered into the other model
Model results may indicate key areas and land uses to focus on
SWAT
Ability to model non-point land use reductions
May be used to model development and land use conversion impacts

10. Model Parameters Model parameters may include: Flow Water temperature
Dissolved oxygen
Sediment
Nutrients (phosphorus and nitrogen forms)

11. Hydrology and Water Quality
Sources to the River
Upstream
Tributaries
Point sources (WWTPs)
Non-point sources
Irrigation drains/returns
Groundwater – including septic impacts
Withdrawals
Irrigation Canals
Locations along the River
Multiple water quality monitoring stations

12. Model Construction

13. Model Construction QUAL2E Grid based SWAT GIS based
Flow and water quality for headwater, tributaries, point sources, reaches
SWAT GIS based
Topography, land use, and soils
Management files
irrigation and agricultural practices, urban landscapes, groundwater

14. QUAL2E Model Grid 1-mile segments Clark Fork River Bitterroot River
39 Reaches
250 Segments
Bitterroot River
7 Reaches
84 Segments
Clark Fork River, Bitterroot River

15. SWAT Model GIS
DEM Land Use Soils

16. QUAL2E Model Dates
June, July, August – summer months selected for Clark Fork River Model to assess water quality during critical period
1992 and 1999 – selected for Clark Fork River Model
1992 low flow condition
1999 medium-high flow condition
1998 and 2001 – selected based on data availability (Bitterroot River)
1998 low flow condition
2001 average flow condition

17. SWAT Model Dates September 2000 through September 2003
Incorporate 2000 fire information into GIS land use data
Model 2004 and 2005 after model construction

18. Model Results and Refinement

19. Model Comparison
Compare results to monitoring data to test representation (calibration, validation, verification)
Check flow
Check conservative parameters (water temperature, sediment)
Check non-conservative parameters (dissolved oxygen nutrients)
Refine model construction
Adjust model coefficients

20. Results Clark Fork River August 1992 Total Nitrogen

21. Results Clark Fork River August 1992 Total Phosphorus

22. Results Bitterroot River August 1992 Total Nitrogen

23. Results Bitterroot River August 1992 Total Phosphorus

24. Model Application

25. Model Use Sensitivity Analysis Scenarios (What if’s)
Investigate drivers of water quality
Scenarios (What if’s)
Assess potential changes to water quality
Development
Land use management

26. Examples of Model Applications and Sensitivity Analyses
Model Scenarios – ONLY EXAMPLES
Reduce Tributary nutrient concentrations 50%
Non-point sources in watersheds
Reduce Point Source nutrient concentrations 50%
Set Point Source nutrient concentration to Clark Fork limits of TP = 1 mg/L and TN = 10 mg/L (about 64 to 74% TP reduction and 0 to 65% TN reduction)
Wastewater treatment plant changes
Increase all nutrient source concentrations 20%
Continued development and land use changes

27. Summary

28. Current Status Projects are ongoing No final results
Continuing to understand the watershed
Local knowledge important to model refinements
Point sources, WWTPs
Irrigation diversions and returns

29. Future Contact Will McDowell, TSWQC Michael Pipp or Kyle Flynn, DEQ
Michael Kasch or David Clark, HDR