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
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