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

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.

What we have done so far.

Let’s start with some slightly philosophical musing on modeling

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

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

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.

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

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

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.

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

Hydrology Model

Critical questions: How does rainfall on a watershed translate into flow in a river?

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

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

Hydraulics Model

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

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.)?

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?

Systems Model

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

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

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

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

Why use models?

A Simple System

A Relatively Simple System

An Increasingly Complicated System

Starting to be Too Much

System Overload!

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

We need a model!

The WEAP Interface

A Simple System

What are we assuming?

1.That we know how much water is flowing at the top of each river.

What are we assuming? 1.That we know how much water is flowing at the top of each river. 2.That we know how much water is flowing into or out of the river as it moves downstream.

What are we assuming? 1.That we know how much water is flowing at the top of each river. 2.That we know how much water is flowing into or out of the river as it moves downstream. 3.That we know what the water demands are with certainty.

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

What do we do now?

ADD HYDROLOGY!

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?

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

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

The WEAP 2-Bucket Hydrology Module Surface Runoff = f(P e,z 1,1/LAI)

One 2-Bucket Model Per Land Class

This last point leads to a stylized groundwater representation

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

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

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

Examples of Strong Functionality WS Obj. 3: Optimize water use efficiency –Strategy 3a: M&I BMPs –Strategy 3b: Agricultural BMPs EHP Obj. 3: Manage rivers and tributaries to provide flow regimes that benefit native species and that support critical ecosystem functions –Strategy: Monitor and model river hydrology to determine natural flow regime and compare with existing management

Examples of Weaker Functionality WQ Obj. 3: Work collaboratively to restore the quality of state-designated, impaired water bodies (303(d)) –Identify challenges to management and possible actions for remediation. EHP Obj. 4: Improve water quality to restore and protect healthy aquatic ecosystems –Strategy: Purchase water rights from willing sellers and dedicate them to instream flows to improve water quality

The Web of Analysis Hydrology Model Sediment Transport Model Water Quality Model Hydraulics Model Socio-Economic Model Systems Model Ecosystem Model