How Much Do We Have Left? Coming to Terms With the Colorado River Water Availability Study Annual Colorado Water Worksh

1. How Much Do We Have Left?Coming to Terms With the Colorado River Water Availability StudyAnnual Colorado Water WorkshopJuly 21, 2010 Ben Harding – AMEC Earth and Environmental Erin Wilson – Leonard Rice Engineers

2. Colorado Decision Support System - Overview • Water Management System • Developed by CWCB and Division of Water Resources • Goal is to provide data/tools to assist in making informed decisions regarding historic and future use of water Legislative Authorization Initial CRDSS Development (Gunnison, Yampa, Colorado, San Juan, Dolores) SPDSS Development (South Platte, North Platte) Maintenance & Updates, Arkansas? RGDSS Development (Rio Grande) CRDSS(Enhancements and Extension) 1998 future 1992 1993 2001

3. Colorado Decision Support System User/Operator/Administrator Input Consumptive Use Model“StateCU” HydroBase DataManagementInterfaces Results for Decision Makers GIS Coverages Surface Water Model “StateMod”

4. Estimating Water Availability Consumptive Use ModelStateCU Surface Water Model StateMod Results for Decision Makers Alternate Temperature Alternate CIR Physical and Legal Water Availability Alternate Hydrology Alternate Precipitation

5. Findings - Temperature • Map shows Averageof the Five 2040 Projections • All Five Projections show Temperature Increases • Increases basin-wide by 3.3 to 3.7 deg F • Lower elevations show largest increase • Increase occurs each month of the year

6. Findings - Temperature

7. Findings - Temperature

8. Findings - Winter Precipitation (Nov-Mar) • Map shows Average of Five Projections • Increases basin-wide by 6 to 13 percent • Increases more in the northern part of the basin • Increases more at higher elevations • Shifts from snow to rain in the shoulder months

9. Findings - Summer Precipitation (Apr-Oct) • Decreases basin-wide by 4 to 10 percent • Wet projections show more precipitation in some summer months than dry projections • Decreases more in the southern part of the basin • Decreases less at higher elevations

10. Findings - Precipitation

11. Findings - Precipitation

12. Findings - Crop Irrigation Requirement • Map shows Average of Five Projections • Increases basin-wide 2.6 to 6.7 in/yr for pasture grass • Basin-wide CIR is 20% greater than historical • Growing season increases basin-wide by 15 to 22 days • Increases more at lower elevations

13. Findings - Crop Irrigation Requirement

14. Findings - Crop Irrigation Requirement

15. StateMod Model Components

16. Inflow Hydrology – Natural Flows • Historical Natural Flows Estimated by Removing the Effects of Man from Gaged Flows • Diversions • Reservoir Contents • Return Flows • Climate Projected Natural Flows 16

17. Physical Systems • Diversion Structures • Location on the River • Headgate and Canal Capacities • Return Flow Locations • Reservoirs • Location on River or Off-Channel • Location of Carrier Ditches • Storage Volume, Outlet Capacities, Account Size, Area/Capacity Tables • Instream Flow Reaches • Beginning/Ending of Reach 17

18. Water Demands • Irrigation Demands • Full Irrigation Water Requirements from StateCU (Historical, Based on Climate Projections) • Municipal and Industrial Demands • Current Use Levels • Trans-basin Demands • Current Diversions • Reservoir “Demands” • Reservoir Capacities or Operational Targets 18

19. Water Demands • CWCB Instream Flow Demands based on Water Rights • Reservoir and Trans-basin Bypass Requirements based on Operational Agreements • Endangered Species Flow Demands based on Flow Targets 19

20. Administrative Conditions • Water Rights (Direct, Storage, Instream Flow) • Reservoir and Carrier Operations • Policies and Agreements (Such as Minimum Bypasses, Fish Flows, etc) • Potential Colorado River Compact Obligations NOT Included in Phase I • Conditional Rights without Current Demands NOT included in Phase I 20

21. Model Operations • Based on Natural Inflow and Return Flows from Previous Time Steps • Identifies Most Senior Water Right • Estimates Diversion =min (Demand, Water Right, Headgate Capacity, Available Flow) • Adjusts Downstream Flows to Reflect Senior Diversions and Immediate Return Flows • Future Returns are Calculated • Repeated for Next Junior Water Right 21

22. Sequence of Results: Uncompahgre River at Delta and Gunnison River Basin

23. Natural Flow

24. Modeled Streamflow

25. Water Availability

26. Water Availability

27. Modeled Consumptive Use

28. Modeled Reservoir Storage

29. Modeled Reservoir Storage

30. Result Summary: West-Slope Basins

31. Water Availability

32. Modeled Consumptive Use

33. Modeled Reservoir Storage

34. Modeled Reservoir Storage

35. Water Availability

36. Water Availability

37. Modeled Consumptive Use

38. Modeled Reservoir Storage

39. Modeled Reservoir Storage

40. Water Availability

41. Water Availability 41 PRELIMINARY RESULTS – UNDER REVIEW Colorado River Water Availability Study – Phase I

42. Modeled Consumptive Use 42 PRELIMINARY RESULTS – UNDER REVIEW Colorado River Water Availability Study – Phase I

43. Modeled Reservoir Storage 43 PRELIMINARY RESULTS – UNDER REVIEW Colorado River Water Availability Study – Phase I

44. Modeled Reservoir Storage 44 PRELIMINARY RESULTS – UNDER REVIEW Colorado River Water Availability Study – Phase I

45. Result Summary – Natural Flow • Annual flow increases in some possible futures and decreases in others • Annual flow generally increases in parts of the Yampa River basin and at higher elevation watersheds • Annual flow generally decreases in southwestern watersheds and at lower elevations • Shifts toward earlier peak runoff • Flow decreases in late summer and early fall 45 PRELIMINARY RESULTS – UNDER REVIEW Colorado River Water Availability Study – Phase I

46. Result Summary – Modeled Streamflow • Annual modeled streamflow decreases basin-wide, except in the Yampa River basin, and higher elevation locations in the Upper Colorado River basin • Modeled Flow increases in April and May and decreases in later summer and fall months 46 PRELIMINARY RESULTS – UNDER REVIEW Colorado River Water Availability Study – Phase I

47. Result Summary – Water Available to • Meet Future Demands • Higher elevations generally have less annual flow available to meet future demands, as a percent of modeled streamflow • Available flow generally increases in April and May, corresponding to the shift in natural flow hydrographs 47 PRELIMINARY RESULTS – UNDER REVIEW Colorado River Water Availability Study – Phase I

48. Result Summary – Modeled Consumptive Use • Increases in Yampa, White, Upper Colorado, and Gunnison basins by 4 to 18 % • Decreases in the San Juan and Dolores basins by 8 % 48 PRELIMINARY RESULTS – UNDER REVIEW Colorado River Water Availability Study – Phase I

49. Result Summary – Use of Reservoirs • Reservoirs show increased use • Pool levels fluctuate more than historical • Shifts in Runoff Increases the Value and Need for Storage 49 PRELIMINARY RESULTS – UNDER REVIEW Colorado River Water Availability Study – Phase I