Eastern Snake Plain Aquifer Model: Design and Use

1. Eastern Snake Plain Aquifer Model:Design and Use WIMS Conference – Sept. 14, 2006 Allan Wylie, Hydrologist Hydrology Section, IDWR Michael Ciscell - Sr. GIS Analyst Adjudication Bureau, IDWR

2. Outline • Location • Model Committee • Introduction to the Model • Model Inputs • Model Structure • Calibration Targets • How the Model is Used

3. Eastern Snake Hydrologic Modeling Committee • Comprised of professionals working on Idaho water issues on the eastern Snake Plain • Agency representative • IDWR, BOR, USGS, US Fish and Wildlife Service • Industry Representative • Idaho Power Co • Researchers • U of I, IWRRI • Consultants • Surface water users, ground water users, spring users

4. Eastern Snake Plain Aquifer

5. Model Inputs • Identify Budget Components • Hydrogeologic processes • Prior studies • Input from ESHMC

6. Formalize Representationof Budget Components • Guided by purpose of projectand natureof studyarea • Focus on components most likely to reduce model uncertainty

7. Assemble & Test Budget Assemble Sense Check Sense Check Test Calibration Balance Sense Check

8. Model Structure • Numerical model • Grid • Number of rows, number of columns, number of layers • River representation • Springs representation • Data • Water table elevation • Snake River • Compute ground water contribution to river or river contribution to ground water • Gains or losses • Irrigated lands/Consumptive Use • PODs w/Priority Date & Rate of Diversion

9. Grid • Rotation 31.4˚ counter clockwise • 104 rows • 209 columns • 1 mi by 1 mi • 1 layer

10. Snake River • 5 river reaches above Minidoka • Ashton to Rexburg • Heise to Shelly • Shelly to near Blackfoot • Near Blackfoot to Neeley • Neeley to Minidoka • Minidoka to Milner/Springs • Gains not statistically significant

11. Springs • 6 Spring reaches • Devils Washbowl – Buhl • Buhl – Thousand Springs • Thousand Springs • Thousand Springs – Malad • Malad • Malad – Bancroft • 45 drain cells

12. Calibration Targets • Water table elevation data • USGS data • IDWR data • Reach gain and loss data • IDWR reach gain and loss program • USGS gaging station data • Watermaster diversion data

13. Water Table Elevation • Steady State - • No change in magnitude or direction of ground water flow • Rarely occurs in nature, • important in modeling • Transient • Seasonal • Mass measurement • Trend

14. Steady State • May 1, 1982 to November 1, 2000 • All water table elevation observations averaged • 1008 observations

15. Snake River • Snake River reaches • Monthly gains and losses for five river reaches

16. Snake River • Ashton to Rexburg

17. Springs • Nine springs with significant time series

18. The Model • Steady state • 1008 water table elevation observations • 5 Snake River gain and loss observations • 6 spring observations • Transient • 12717 water table elevation observations • 725 Snake River gain and loss observations • 1526 spring discharge observations

19. How the Model Is Used • Curtailment scenario • Demonstrate that the model could be used to simulate a curtailment of ground water users • CREP • Used to simulate effect of taking land out of production • Managed recharge • Simulate effect of proposed recharge projects • Conversion • Simulate effects of converting land from ground water to surface water irrigation

20. A Curtailment Scenario • Uncertainty • Response functions • Model grid • Irrigated lands • Water rights data base

21. Uncertainty • Model is simulation • Model misfit • Standard error less than 20 ft • Water level change about 4000 ft • Measurement uncertainty • Largest is river gains

22. Response Function • If left alone all aquifer water will discharge into the Snake River • Water pumped from anywhere in the aquifer would discharge to the Snake River • Water pumped may have come from the Snake River • Response Function is % of impact of that cell on the respective river reach

23. Irrigated LandsIncluded in Each Grid Cell

24. Ground Water Points of Diversion

25. Grid Response for a Reach

26. Model Layers

27. Select Priority Date

28. PODs Affecting Reach

29. Other Uses • Managed Recharge • Simulate effect of proposed recharge projects • Project near Jerome is being worked • CREP • Used to simulate effect of taking land out of production • Applications being taken on Eastern Snake Plain • Conversion • Simulate effects of converting land from ground water to surface water irrigation

30. Questions? Allan.Wylie@idwr.idaho.gov Michael.Ciscell@idwr.idaho.gov