1. Groundwater Flux to the Upper Mississippi River – Approach and application to nutrient understanding

2. True confessions….  The “Upper Mississippi River” has a mix of geologic terrains and associated groundwater flow systems  This talk focuses on the unglaciated areas  However, approaches/insights gained are applicable to larger system  Work presented here was team effort

3. La Crosse Areas covered by Study Coon Valley Watershed Pool 8 of Mississippi River (Rick Hooper $) City of La Crosse La Crosse County

4. Present objectives  Characterize regional groundwater flow system  Quantify groundwater flow into Pool 8 and estimate importance for nitrate loading  Identify the area that contributes water to each municipal well  Investigate virus occurrence in municipal wells  Evaluate the effects of changing land use (primarily ag practices) on groundwater resources

5. Project Approach  Develop a simple regional groundwater flow model for greater La Crosse area  Cut out smaller models from regional model (Pool 8, La Crosse County, Coon Valley)  Perform project objectives on smaller models

6. La Crosse Area Projects Regional Model Pool 8 Model La Crosse County Model Coon Valley Model La Crosse Virus study

7. Advantages  Consistent base model helps ensure models agree with each other  Simple regional model allows for investigation of regional flow system not possible with smaller model  Leverage project funds because we aren’t reinventing the wheel

8. How groundwater models work:  Plumber’s Rule  Scotty’s Rule  Numerical equations representing real world entered into the computer  Allows us to quantify system and forms the basis for prediction  Data requirements can be large

9. Conceptual model Mississippi River Lemon Weir RiverLa Crosse River

10. Miss. River Regional Area Covered by the GFLOW AE Model La Crosse Black River La Crosse Kick- apoo Coon Root 175 miles Black River @ Neilsville simulated areas outside of watershed of interest

11. Potential Problems  Gaging station data sets may not overlap in time  Large basins have long-term gaging stations, but also may have confounding factors (e.g., dams)  Definition of baseflow = ?  Average baseflow may not be stationary in time

12. “Average baseflow” may not be stationary in time… Changes in Q 50 flows over time at Four Gaging Stations 0 200 400 600 800 1000 1200 Q 50 of Kickapoo and La Crosse River (cfs) 0 20 40 60 80 100 120 140 160 180 Black nr Galesville Root nr Houston Kickapoo @ La Farge LaCrosse @ Sparta 1938 to 1976 1992 to 2000 1997 to 2000 1938 to 2000 Q 50 of Black and Root River (cfs)

13. Results 1999 Q 50 baseflow 0 200 400 600 800 1000 1200 Q 50 Baseflow (cfs) Root River @ Houston Black @ Galesville La X @ SpartaKickapoo @ La Farge Coon @ Coon Valley MeasuredSimulated

14. R rates needed to match flux targets 5 6 7 8 9 10 11 12 Basin R rate (in/yr) 9.1 8.0 8.2 6.4 R_BlackR_LaxR_KickapooR_Coon Optimized R rates (1999 Q 50 targets, base=500) NE to SW

15. Okay, complete results 5 6 7 8 9 10 11 12 Basin R rate (in/yr) 11.7 R_Root 9.1 8.0 8.2 6.4 R_BlackR_LaxR_KickapooR_Coon Optimized R rates (1999 Q 50 targets, base=500) NE to SW

16. Digression: What is going on in the Root River?  Root River (using 1999 target) is higher than expected, with R rate higher than we’d expect to see in the NE parts of Wisconsin!  If we used the entire record (from 1909 until the present) the Root River has the lowest R rate of all basins  Upstream gage knocked out and not replaced  Suggests lack in our understanding,and a problem with our handling of the 1999 measured target  Need to monitor the tributaries if you want to simulate the larger system

17. Looking at the Pool as a whole under baseflow conditions… Source of Water to Pool 8 93.1% 6.4% 0.5% Pool 7 inflow Tributary inflow Direct GW discharge

18. Being that simulated streams at baseflow = “indirect gw dischg”… 93% 0% 7% Pool 7 inflow Surface water Groundwater (indirect and direct)

19. Not to say there is no event water… Estimated Total Flow using Sartz (1977) 91% 2% 7% Pool 7 Stormflow Baseflow

20. Geologic section Mississippi River Lemon Weir RiverLa Crosse River Eau Claire Confining Unit Hole in Confining Unit

21. Well Logs compiled by WGNHS

22. Top of Mt. Simon

23. Top of Eau Claire (blue=sh/slt or ss w/ much sh; green=ss w/ some sh) Northern part of Pool 8

24. Top of Bedrock or Land Surface

25. Add Fluvial Sediments

26. Add Surface Water features

27. Note how similar model is to conceptual model in cross section

28. Plan view Pool 8 model domain extracted from AE 2D model Pool 7 Pool 8 City of La Crosse Area of strong upward gradients (artesian wells) E-W cross section near Goose Island

29. 2D and 3D Regional Model Results 2D AE Source of Water to Pool 8 93.1% 6.4% 0.5% Pool 7 inflow Tributary inflow Groundwater 93.1% 6.5% 0.4% 3D FD Source of Water to Pool 8

30. Distribution of Flux from FD model **Preliminary Results River cell flux, ft 3 /d 2.7 – 0.05 0.05 – 0.02 0.02 – 0.007 0.007 – 0.005 0.005-0.004 0.004 – 0.003 0.003 – 0.0 Recharge 0 – 2.6 River Cell Flux (ft/d)

31. Nitrogen Data from BRD **Preliminary Results River cell flux, ft 3 /d 2.7 – 0.05 0.05 – 0.02 0.02 – 0.007 0.007 – 0.005 0.005-0.004 0.004 – 0.003 0.003 – 0.0 Recharge 0 – 2.6 River Cell Flux (ft/d) Max NO 3 = 16 mg/l as N Max NH 4 = 0.4 mg/l as N Max NO 3 = 13 mg/l as N Max NH 4 = 0.3 mg/l as N Max NO 3 = 6 mg/l as N Max NH 4 = 7 mg/l as N Max NO 3 = 3 mg/l as N Max NH 4 = 15 mg/l as N

32. Take Home Points  We have gw-sw modeling tools that can cover large areas (Mississippi Pool scale)  2D models performed well for:  Calculating boundaries for 3D inset models  Pool 8 water balance information  3D model performed well for:  representing best available knowledge  Time of travel, vertical gradients, distribution of flow into pool  Direct GW discharge to Pool 8 was small %  Distribution important for other research questions  Would be dominant if gw included discharge to tribs