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 amodel 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 TellerThe Twilight of the Perfect Model

“All models are wrong, some models are useful.”

George E.P. BoxRobustness 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

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

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

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?

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

Smax

Rd z1

Interflow = f(z1,ks, 1-f)

Percolation = f(z1,ks,f)

Baseflow = f(z2,drainage_rate)

Et= f(z1,kc, , PET)

Pe = f(P, Snow Accum, Melt rate)

Plant Canopy

P

z2

L

u

Surface Runoff =f(Pe,z1,1/LAI)

One 2-Bucket Model Per Land Class

This last point leads to a stylized groundwater

representation

hd

lw Sy,Ks

Percolation

Pumping

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

ProtectionWhile 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 AnalysisHydrology Model

Sediment Transport Model

Water Quality Model

Hydraulics Model

Socio-Economic Model

Systems Model

Ecosystem Model