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Drivers and Influencers of Water DemandCriteria for Selecting ‘Best’ Water Demand Forecasting Approach u What information is needed by planners and decision-makers?. Approach: water dema

Drivers and Influencers of Water Demand

Criteria for Selecting ‘Best’ Water Demand Forecasting Approach

u What information is needed by

planners and decision-makers?

u What type of models are needed to

provide this information?

u What is available?

u What is the quality?

u What models will the data support?

What are financial constraints?

Budget

Water Demand Forecast Approaches

Cost & Complexity

Trend

Extrapolation

Per Capita

Unit Use

Econometric

Trend Extrapolation

0

50

100

150

200

250

198

0

198

5

1990 1995 200

0 200

5 201

0 201

5

2020

Historical

Linear Trend

Pros:

required

Cons:

into the future

demands

in demographics, weather, or other factors

Approach:

Per Capita

Approach:

population to get per capita use

projected population to get future

demand

Pros:

population, to be accounted for

Cons:

follow population growth

such as price, income, types

of housing, employment trends, or other influencers of demand

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

800,000

1980 1983 1986 1989 1992 1995 1998 2001 2004

0 500,000 1,000,000 1,500,000 2,000,000 2,500,000 3,000,000 3,500,000 4,000,000 4,500,000

Water Demand

Population

Unit Use

Pros:

& drivers of water demand

to be accounted for

Cons:

weather, income, price and others are not incorporated

Approach:

single-family, multisingle-family,

non-residential)

appropriate drivers (e.g., housing

or employment) to get unit use

Example:

Single-family demand = 150 MGD

Single-family homes = 500,000

500,000 homes =

300 gallons/home/day

Approach:

water demands with factors that

influence those demands

elasticity is estimated

rates over time

Pros:

estimation of demand and its influencers

“explain” water use over time

results

Cons:

other methods

Elasticity Defined:

A statistical rate of change that

describes how a water use factor

influences demand A price

elasticity of -0.10 means that a

ten percent increasein real price

will result in a one percent

decreasein water demand

Example Elasticities

The following are elasticities estimated for water use factors from almost

200 statistical water demand equations in the United States

Marginal Price -0.050 to -0.250 -0.150 to -0.350

Income +0.200 to +0.500 +0.300 to +0.600

Household Size +0.400 to +0.600 +0.200 to +0.500

Housing Density -0.200 to -0.500 -0.400 to -0.800

Precipitation -0.010 to -0.150 -0.050 to -0.200

Temperature +0.300 to +0.600 +0.800 to +1.500

(Paredes, 1996).

Probabilistic Results from Econometric Forecasts

Bas elin

e Fo reca

st Bas elin

e Fo reca

st Ran ge d

ue t o hi

stor ical

we athe

r

Ran ge d

ue t o hi

stor ical

we athe

r

aphic

Rang e due

to de mogr

aphic

certa inty

grow th un

certa inty

Ra ng

e d ue

to cli

ma te

ch an ge

ge 75% 50% 95%

Ranges of Uncertainty: @Risk Model vs All High/All Low Assumptions

0

25

50

75

100

125

150

175

200

225

250

1995 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050 2055 2060

90th-95th 85th-90th 80th-85th 75th-80th 70th-75th 65th-70th 60th-65th 55th-60th 50th-55th 45th-50th 40th-45th 35th-40th 30th-35th 25th-30th 20th-25th 15th-20th 10th-15th 5th-10th

Zero-5th

Percentile

Actual

Demand

Firm Yield

Oal Forecast 5th Percentile Forecas t

All Low (≈0% probability)

All High (≈0% probability)

95th Percentile Forecast Draft Official Forecast

Growth in Population & Water

Consumption

0 200,000 400,000 600,000 800,000 1,000,000 1,200,000 1,400,000

0

30

60

90

120

150

180

210

Population

Total Consumption

Billed Consumption Non-Rev

Per capita Implications

Actual and Forecast Water Consumption Per Capita: Seattle & Non-CWA

With and Without Programmatic Conservation after 2005

0

20

40

60

80

100

120

140

160

180

GPD per Person WITHOUT Conservation

GPD per Person WITH Conservation

Actual GPD

per Person

Impact of All Forms of Conservation

on Past and Forecast Water Demand

0

25

50

75

100

125

150

175

200

225

250

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

Unattributed Savings Transitory Savings Conservation Programs Plumbing Code Rate Impacts System Operation Improvements

1990 Forecast with No Conservation

Actual Demand

2007 Forecast with Conservation

38

40

42

44

46

48

50

52

54

2004 TSP  Composite  Projection

2004  Financial  Forecast

Actual  Demand

Cascade average daily demand

(mgd)

Three-stage supply evaluation

Screening: Eliminates projects that are not feasible and do not warrant further investigation, using pass/fail criteria

Multi-Criteria Analysis: More refined analysis that evaluates projects using multiple ranking criteria

Detailed Evaluation

Detailed infrastructure and financial evaluation

of the highest ranked projects

10 Everett

-Sultan River

Supply

Expansion

Increase withdrawals from the Sultan River Basin (need further information on conveyance concept)

13 Lake

Sammamish

Develop supply from Lake Sammamish with Treatment Facility

14 Off-Stream

Storage

Impound water from tributaries in the high flow season and used to satisfy irrigation needs

18 OASIS –

Phases 1 & 2

Members utilize Lakehaven's ASR program water (directly, or via water swap between green river supply and ASR groundwater)

22 Water from

Puget Sound

Construct a desalination plant either alone or

in partnership with others Construct conveyance.

25 South

Treatment

Plant

Expand reclaimed water uses in Tukwila from South Plant.

30 Rainwater

Collection

Collect and store rainwater fo up to 7 Golf Courses

33 Regional

Unaccounted-for Water

Reduce transmission and storage losses from regional facilities

Rights Tech

Overview of Approach

life-cycle costs to utility, both capital and O&M

impacts of each alternative using value model

levelized unit costs

Value Modeling Overview

l Identify objectives or criteria important in selecting preferred alternative

l Define how these objectives will be measured and scored—can be simple 1-5 scale with endpoints

defined.

l Assign weights to the objectives

l Score each alternative, or package of alternatives, and document reasoning

l Determine single value score

l Test sensitivity of results to weights and scores

process

Acceptability

Public

Acceptability

(Stakeholders)

Public

Trust

30

Built

Environment

Natural

Environment

Environmental

Acceptability

of Construction

20

Timing Reliability Leads to Other Sources

Asset Reliability

20

Legal/

Regulatory

30

Ease of Source

Development

45

Natural Environment Secondary Impacts and Benefits/

Sustainability

Environmental Acceptability

25

System Robustness Operational Flexibility Security

Asset Reliability

25

Public Trust

25

Regulatory Compliance Source Compatibility

Public Health/WQ

15

Social (Lifestyles)

10

System Operation

55

Value Model

SPU Water Supply System Options

Value Model

Criteria and Weights

Value Model

Contributions to Value Score

0.0

0.2

0.4

0.6

0.8

0.0 0.2 0.4 0.6 0.8

Legal/Regulatory Env Acceptability Public Trust (Develop) Asset Reliability (Ops) Pub Health (WQ) Asset Reliability (Dev) Others

1.0 is best outcome, with positive consequences

0.0 is worst outcome, with negative impacts

Cedar Dead

Storage

Lake Youngs

Snoqualmie Aquifer

SFTolt 1695

SF Tolt 1660

NF Tolt Diversion Conservation

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Levelized Unit Cost (PVm$/PVmgd) a

a Calculated assuming all sources online in 2050 4 mgd conservation program begins in 2045 and phases

in over a 10-year period.

Low Value

Low Cost

High Value

Low Cost

Low Value High Cost

High Value High Cos t

SPU Water Supply Sources

Value-Cost Tradeoff

SPU Water Supply Sources

Value-Cost Tradeoff

Cedar Dead

Storage

Lake Youngs Drawdown

Snoqualmie Aquifer

SF Tolt 1695

SF Tolt 1660

North Fork Tolt Conservation*

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Levelized Unit Cost (PVm$/PVmgd) a

a Calculated assuming all sources online in 2050

Low Value

Low Cost

High Value

Low Cost

Low Value High Cost

High Value High Cost

Value: 0.478 - 0.500 Cost: $5.80 - $10.94

Reclaimed Water Projects

Preliminary Ranking of Supply Options

20%

20% 20% 13%

12%

10% 5%

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 Replacement Wells, No Treatment

Treatment for Inactive, Sustainable Wells

Within City Wells, No Treatment

Within City Wells, Treatment

Within City Wells, Treatment, Not Sustainable

Large Seawater Desalination

Small Seawater Desalination

Outside City Wells, No Treatment (Indian Spr)

Outside City Wells, No Treatment (N of River)

Surface Water Direct Use with Treatment

Surface Water with ASR Wells

Cost Supply Legal Institutional Environment Regulatory Permitting

Climate Change Planning

Washington Climate Impacts Group

Uncertainties