COHYST2010 Groundwater Model: Phase II Summary

1. COHYST2010 Groundwater Model:Phase II Summary April 15th-16th Lincoln, NE Nebraska Department of Natural Resources

2. COHYST 2010: Groundwater Model Objectives • Simulate groundwater system response to changes in pumping, recharge • Measured through water levels, baseflows • Couple with CROPSIM & STELLA models to build integrated water budget

3. COHYST 2010: Groundwater Model Context † Average 1985-2005, from COHYST 2010 Phase I water budget report FINAL Phase I Water Budget CalendarYr3252012.doc

4. COHYST 2010: Groundwater Model Fundamental Approach • Single layer • ½ mi x ½ mi grid cells • Transient – 255 Stress periods (Oct-84 to Dec-2005) • Vadose zone not considered

5. COHYST 2010: Groundwater Model Fundamental Approach Platte & tribs simulated with variable stage, routing, and integrated in-stream budget (STR) Bounding basins included

6. COHYST 2010: Groundwater Model Fundamental Approach • Pumping + Recharge from CROPSIM • Annual pattern same, magnitude varies • Monthly stress periods • Initial condition (uncertain) estimated from: • mapped water levels • STR elevations • point observations

7. COHYST 2010: Groundwater Model Fundamental Approach • Functional goals: • Low mass balance (solver) error • Manageable run time • Robust – avoid instabilities under changed stresses • Level of calibration commensurate with purposes

8. COHYST 2010: Groundwater Model Fundamental Approach:Calibration • Baseflow targets – uncertain in managed system • Reach-by-reach • Semi-quantitative match{annual, seasonal} • Head targets – some uncertainty • Quantitative history match: • absolute elevations • relative differences

9. COHYST 2010: Groundwater Model Fundamental Approach:Calibration • Inputs: • Aquifer properties, boundary condition assignments,pumping, recharge, Platte surface flows, “observed” data for history matching • Manipulations: • Adjust properties, assignments within reasoned hydrologic constraints to better match observed history • Outputs: • Water levels, baseflows, regional water budget terms

10. COHYST 2010: Groundwater Model: Structure

11. COHYST 2010: Groundwater Model: Structure Stream Package

12. COHYST 2010: Groundwater Model: Structure General Head Boundaries

13. COHYST 2010: Groundwater Model: Structure Drain, River Boundaries

14. COHYST 2010: Groundwater Model: Structure • Evapotranspiration (EVT) • riparian, shallow GW • Head dependent: defined everywhere, active only where water level near “surface” • Elevation assignments: • Extinction depth: 1*stddev(DEM) • Max elevation: DEM maximum

15. COHYST 2010: Groundwater Model: Structure • Evapotranspiration (EVT)

16. Final Zoned Hydraulic Conductivity • Hydraulic conductivity spatial distribution

17. COHYST 2010: Groundwater Model: Structure • Recharge (RCH) & Pumping (WEL) • From CROPSIM Outputs

18. COHYST 2010 - Groundwater Model Final Run (22a_17_21) Summary • Evaluation criteria: • Calibration/history-matching • Head & baseflow residuals, statistics • Time series comparison (qualitative) • Trend differences • Internal budget reasonable? • Purpose: • GW budget makes sense within integrated budget? • Model suitable for, capable of assessing impact of change in GW on contributions to streams? • Robust enough to accommodate widely variable input stresses?

19. COHYST 2010 - Groundwater Model Final Run (22a_17_21) Summary • Evaluation criteria: • Calibration/history-matching: GW Budget

20. COHYST 2010 - Groundwater Model Final Run (22a_17_21) Summary • Evaluation criteria: • Calibration/history-matching: Head Residuals

23. COHYST 2010 - Groundwater Model Final Run (22a_17_21) Summary • Evaluation criteria: • Calibration/history-matching: Head Residuals

24. COHYST 2010 - Groundwater Model Final Run (22a_17_21) Summary • Evaluation criteria: • Calibration/history-matching: Head Residuals

26. COHYST 2010 - Groundwater Model Final Run (22a_17_21) Summary • Evaluation criteria: • Calibration/history-matching: Baseflow Residuals, Qualitative comparisons

27. COHYST 2010 - Groundwater Model Final Run (22a_17_21) Summary • Evaluation criteria: Baseflows

28. Quantitative/ Qualitative Comparisons

29. Simulated Baseflow (blue) Baseflow Target (dark grey) Daily Gage flow (light grey)

30. Logarithmic Scale Simulated Baseflow (blue) Baseflow Target (dark grey) Daily Gage flow (light grey)

31. Comparison of Simulated Total Flows (STELLA and MODFLOW) Simulated baseflow & daily measured gage flow for reference

32. Logarithmic Scale Comparison of Simulated Total Flows (STELLA and MODFLOW) Simulated baseflow & daily measured gage flow for reference

33. COHYST 2010 - Groundwater Model Final Run (22a_17_21) Summary: OutbasinBaseflows

34. COHYST 2010 - Groundwater Model Final Run (22a_17_21) Summary: OutbasinBaseflows

35. COHYST 2010 - Groundwater Model Final Run (22a_17_21) Summary • Evaluation criteria: • Purpose: • Scenario robustness • tested in Nov/Dec 2012, throughout process • Able to translate GW to SW (or  baseflow) • Depletions testing – in progress • Hydrologic connection/Cycle Well/[28/40 or 10/50] – in progress • Integrated budget – addressed by Duane

36. COHYST 2010 - Groundwater ModelSuccesses & Limitations

37. COHYST 2010 - Phase II Groundwater ModelSuccesses & Limitations • Water levels: • overall good agreement between measured and simulated heads, especially in area of interest • Trends/changes match reasonably well • Seasonal and multi-year variation captured • Congruence between modeled & observed groundwater flow system

38. COHYST 2010 - Phase II Groundwater ModelSuccesses & Limitations • Baseflows: • Can simulate seasonal, multiyear variability • Generally match magnitude of gains on a reach-by-reach basis within uncertainty of targets • Demonstrate dynamic interchange of SW/GW • Congruence between modeled & observed interaction of groundwater & surface water • *Lower Platte reaches?