CABY and WEAP: Modeling to Support the IRWMP Process

1. CABY and WEAP: Modeling to Support the IRWMP Process David R. Purkey, Ph.D. Natural Heritage Institute David N. Yates, Ph.D. National Center for Atmospheric Research

2. Why are we here? The U.S. EPA has agreed to provide modeling support for the CABY process though application of the WEAP model. WEAP was developed with EPA support to provide a framework for climate change assessments for water resources and aquatic ecosystems.

3. What we have done so far.

4. Let’s start with some slightly philosophical musing on modeling

5. “In principle, anything can be a model, and that what makes a thing amodel is the fact that it is regarded or used as a representation of something by the model users.”Paul TellerThe Twilight of the Perfect Model

6. Examples of Models • A map • A photograph • A recipe • The Dow Jones Industrial Average

7. Examples of Models • A map • A photograph • A recipe • The Dow Jones Industrial Average • A collection of computer logic assembled in a manner that describes how water moves through a watershed.

8. “The only PERFECT model of the world, perfect in every little detail, is, of course, the world itself.”Paul TellerThe Twilight of the Perfect Model

9. “All models are wrong, some models are useful.”George E.P. BoxRobustness in the Strategy of Scientific Model Building

10. Presentation Outline • Overview of various types of water model. • Why use models? • WEAP, what is can and cannot do for the CABY process. • An example of a WEAP application in the American River Watershed.

11. Types of Water Models • Hydrology, Rainfall/Runoff Models • Hydraulic, Biophysical Process Models • Planning, Water Resource Systems Models

12. Hydrology Model

13. Hydrology Model Critical questions: How does rainfall on a watershed translate into flow in a river?

14. Hydrology Model Critical questions: What pathways does water follow as it moves through a watershed?

15. Hydrology Model Critical questions: How does movement along these pathways impact the magnitude, timing, duration and frequency of river flows?

16. Hydraulics Model

17. Hydraulics Model Critical questions: How fast, how deep and what is the horizontal extent of water flowing in a particular section of river?

18. Hydraulics Model Critical questions: What is the interaction between the velocity, depth and horizontal extent of water flowing in a river and important services provided by the river (e.g. habitat, water temperature, sediment transport, etc.)?

19. Hydraulics Model Critical questions: How will the velocity, depth and horizontal extent of water flowing in a river channel, and the associated services provided by the river, change if flows are adjusted or the channel is modified?

20. Systems Model

21. Systems Model Critical questions: How should water be allocated to various uses in time of shortage?

22. Systems Model Critical questions: How should infrastructure in the system (e.g. dams, diversion works, etc) be operated to achieve maximum benefit?

23. Systems Model Critical questions: How can these operations be constrained to protect the services provided by the river?

24. Systems Model Critical questions: How will allocation, operations and operating constraints change if new management strategies are introduced into the system?

25. Why use models?

26. A Simple System

27. A Relatively Simple System

28. An Increasingly Complicated System

29. Starting to be Too Much

30. System Overload!

31. We need a collection of computer logic assembled in a manner that describes how water moves through this watershed.

32. We need a model!

33. The WEAP Interface

34. A Simple System

35. What are we assuming?

36. What are we assuming? • That we know how much water is flowing at the top of each river.

37. What are we assuming? • That we know how much water is flowing at the top of each river. • That we know how much water is flowing into or out of the river as it moves downstream.

38. What are we assuming? • That we know how much water is flowing at the top of each river. • That we know how much water is flowing into or out of the river as it moves downstream. • That we know what the water demands are with certainty.

39. What are we assuming? Basicly, that this system has been removed from it HYDROLOGIC context.

40. What do we do now?

41. ADD HYDROLOGY!

42. Hydrology Model Critical question: How does rainfall on a catchment translate into flow in a river? Critical question: What pathways does water follow as it moves through a catchment? Runoff? Infiltration? ET? Seepage? Critical question: How does movement along these pathways impact the magnitude, timing, duration and frequency of river flows?

43. Planning Model Critical question: How should water be allocated to various uses in time of shortage? Critical question: How can these operations be constrained to protect the services provided by the river? Critical question: How should infrastructure in the system (e.g. dams, diversion works, etc) be operated to achieve maximum benefit? Critical question: How will allocation, operations and operating constraints change if new management strategies are introduced into the system?

44. WEAP, with its integrated Hydrology Molude, provides a framework for answering both set of questions.

45. The WEAP 2-Bucket Hydrology Module Surface Runoff = f(Pe,z1,1/LAI)

46. One 2-Bucket Model Per Land Class

47. This last point leads to a stylized groundwater representation

48. WEAP Relevancy to CABY Goals, Objectives, and Strategies • Water Supply Working Group • Water Quality Working Group • Environmental and Habitat Protection

49. WEAP Relevancy to CABY Goals, Objectives, and Strategies • Water Supply Working Group • Water Quality Working Group • Environmental and Habitat Protection While a model cannot directly satisfy stated goals and objectives, it can be useful in assessing the potential effectiveness of individual strategies for meeting goals and objectives and in identifying potential synergies or tradeoffs between strategies

50. Objectives that WEAP could help assess • WQ Obj. 2 • WQ Obj. 3 • WQ Obj. 4 • WQ Obj. 5 • WQ Obj. 6 • EHP Obj. 1 • EHP Obj. 2 • EHP Obj. 3 • EHP Obj. 4 • EHP Obj. 5 • EHP Obj. 6 • WS Obj. 1 • WS Obj. 2 • WS Obj. 3 • WS Obj. 4 • WS Obj. 5 • WS Obj. 6 • WS Obj. 7 • WS Obj. 8