Water Quality Modeling in the Bear River Basin to Support Water Quality Trading

1. Water Quality Modeling in the Bear River Basin to Support Water Quality Trading Jeff Horsburgh David Stevens, Nancy Mesner, Terry Glover, Arthur Caplan Utah State University

2. USEPA Targeted Watersheds Grant • Develop an integrated, Internet-based Watershed Information System (WIS) • Investigate the feasibility of a water quality trading program • Develop a water quality model to support the water quality trading program

3. Why do we need a model to study the potential for trading? • Simulate the physical, chemical, and biological processes that affect pollutant concentrations • Consider spatial and temporal nature of pollutant loading • Calculate delivery ratios to • Determine the environmental equivalence of load reductions and potential trades

4. Background on Trading • Trading presumes that a TMDL has been completed • Assumes that pollutant loads and load reductions have already been allocated to the sources in the watershed

5. Why do we need a model? Producer X River Mile 15 Producer Y River Mile 5 Animal Producer Z River Mile 10 Point Source River Mile 1 Agricultural Diversion (50%) River Mile 7 Monitoring Location Receptor Point River Mile 0

6. Why do we need a model? Producer X River Mile 15 Total Phosphorus Load = 100 kg Producer X could only reduce loading at the receptor point by 40.5 kg even though his total loading is 100 kg! Delivery Ratio = 40.5/100 = 0.405 Loss to uptake/settling prior to diversion = 10% or 10 kg (90 kg left) Loss to uptake/settling prior to receptor point = 10% or 4.5 kg (40.5 kg left) Loss to Diversion = 50 % or 45 kg/yr (45 kg left) Monitoring Location Receptor Point River Mile 0

7. Why do we need a model? Producer Y can reduce loading at the receptor point by 90 kg if he eliminates his entire loading. Delivery Ratio = 90/100 = 0.9 Total Load = 100 kg Producer Y River Mile 5 Loss to uptake/settling prior to receptor point = 10% or 10 kg (90 kg left) Monitoring Location Receptor Point River Mile 0

8. What does this mean? • The point source’s cost per unit phosphorus reduction with Producer X would be higher than Producer Y • Producer X can only get credit for 40% of any load reduction that he creates • Producer Y can get credit for 90% • It would be more economical for the point source to trade with Producer Y • It is critical to have an estimate of the delivery ratios

9. Model and Trading Focus Area • Bear River from Oneida Narrows Reservoir to Cutler Reservoir • Cub River • Little Bear River • Spring Creek • Focus on areas with existing TMDLs

10. 303(d) Listed Water BodiesIn or near the Model Focus Area TP = Total Phosphorus, DO = Dissolved oxygen

11. TMDL – Existing TP Loads by Source Spring Creek Hyrum Reservoir

12. The Modeling Challenges • Large areas to be modeled • Relatively few data available to populate, calibrate, etc. • High spatial resolution needed to compare sources • Watershed scale models (HSPF, SWAT) cover just about everything, but you don’t get the spatial resolution that you need • Field scale models give you high resolution load estimates, but don’t tell you what happens downstream

13. Modeling Approach • One integrated modeling system made up of the following components: • Hydrologic modelcomponent (generates flows) • Watershed loading model component (generates constituent loads) • Stream response model component (simulates concentrations in the streams) • Accounting model component (accounts for diversions, interbasin transfers, local load reductions, etc.)

14. Model Segmentation • Subwatersheds • Primary unit of modeling • Loads are estimated at the subwatershed scale • Stream Reaches • Loads are routed through the existing stream network (from control point to control point) • One reach per subwatershed • Control Points • Breaks in the stream network at important locations • Calibration points • Diversion points • Major tributary confluences

15. Model Segmentation (cont.)

16. Hydrologic Model ComponentTOPNET/TOPMODEL • Estimation of the amount of flow generated within each subwatershed Source: Bandaragoda et al., 2004

17. Watershed Loading Component • Simulate the amount of loading generated within each subwatershed • Simulated loads will be based on: • Amount of flow generated in the subwatershed • Area of each land use within each subwatershed • Number and types of agricultural producers (e.g., number of animals, etc. – whatever info we can get!!!!!) • Point source data • Loads generated by the model will be compared to loads estimated in TMDL documents

18. Stream Response Component QUAL2K • Simulate the changes in TP concentration as water moves from control point to control point in the stream

19. Accounting Model Component • Superimposed over the other two components to account for withdrawals, transfers, etc.

20. Constituents to be Modeled • Total phosphorus is the focus • Other constituents that need to be simulated because they interact • Water temperature • Nitrogen concentrations • Algae • Dissolved Oxygen • BOD/organic matter • Inert/conservative tracer

21. What will the results look like? • Flows and concentrations at control points • Also along the length of modeled reaches if necessary • Tables of delivery ratios • Scenario specific

22. How will the trading study use the results? • Evaluate Potential Sellers • Seller A – • River Mile 10 • Delivery Ratio = 0.29 • Total Loading = 100 kg

23. How will the trading study use the results? • TMDL Load Allocation = 50 kg (TMDL Requires a 50 % reduction from nonpoint sources) • Additional Load Reduction via BMP = 25 kg • Total potential load reduction = 75 kg • Issue – there is no regulatory mechanism to force nonpoint sources to reduce loading? • Potential Parallel Paths • Path 1: Credits for Sale = (25)*(0.29) = 7.25 kg • Path 2: Credits for sale = (75)*(0.29) = 21.75 kg

24. Other Benefits Spatial • Evaluate potential trading scenarios to make sure that water quality standards are met under a variety of conditions Temporal

25. Water Quality Model Development Process • By component: • Coding (if required) • Verification of code and testing • Population – finding model inputs • Calibration – adjust model parameters so that results match data • Validation/Corroboration

26. Modeling Challenges RevisitedData Availability • Relatively few data available to populate, calibrate, etc. • Water quality data • Streamflow data • Diversion and water transfer data • Climate data • Stream hydraulic characteristics

27. Consider Total Phosphorus Little Bear River at Mendon Road Utah DWQ 4905000

28. Little Bear River at Mendon RoadAll Utah DWQ TP DataNo Streamflow Gage Available Total Phosphorus observations 241 observations from 1976 – 2004 (one outlier of 6 mg/L removed for plotting) Streamflow observations 162 observations from 1976 - 2004

29. Last 10 Years? • In the past 20 years or so, ~$5 Million has been spent in public cost share funds in this watershed to improve water quality • Data more than 10 years old are not representative of current conditions Total Phosphorus 99 observations from 1994 – 2004 59 % Reduction in available data Streamflow 72 observations from 1994 – 2004 56 % Reduction in available data

30. What if I want to characterize seasonal variability?

31. What about monthly variability?

32. What about interannual variability? Streamflow data from the only active USGS gage in the watershed show HUGE variability in flow from year to year! The average TP concentration during the dry years is 60 % higher than for the wet years

33. Simplified Conceptual ModelPhosphorus Loading How large are the bumps versus the baseline?

34. Simplified Loading Conceptual ModelWith Traditional Data

35. Modeling Challenges RevisitedSpatial Resolution • High spatial resolution needed to compare sources • Controls the spatial resolution of the model • Requires that we know the locations of sources with some certainty!

36. Why do we need a model? Producer X River Mile 15 Producer Y River Mile 5 Animal Producer Z River Mile 10 Point Source River Mile 1 Agricultural Diversion (50%) River Mile 7 Monitoring Location Receptor Point River Mile 0

37. Spatial Resolution • What we know: • Point source locations • Land use/land cover • Where we are struggling: • Locations of “Producers” or potential trading participants • Animal feeding operations • Actual farm units

38. Project Partners USU Project Collaborators: Nancy Mesner Terry Glover David Stevens Arthur Caplan United States EPA Gary Kleeman Bear River Commission Jack Barnett Water Quality Task Force Mitch Poulson Wyoming DEQ Jack Smith Idaho DEQ Lynn Van Every Utah DEQ Mike Allred

39. Contact Information Outreach and Education Nancy Mesner Nancy.mesner@usu.edu 435-797-2465 Modeling Jeff Horsburgh Jeff.horsburgh@usu.edu 435-797-2946 David Stevens David.stevens@usu.edu 435-797-3229