Spokane Valley-Rathdrum Prairie Aquifer Water Demand Forecasts Presented by: Mike Hermanson Water Resources Specialist Spokane County Utilities Spokane.

Spokane Valley-Rathdrum Prairie AquiferWater Demand Forecasts

Presented by:

Mike HermansonWater Resources Specialist

Spokane County Utilities

Spokane River Forum ConferenceMay 23, 2011

Background

• 2010 Spokane River Forum Water Demand Presentations

– Idaho Future Demand Study Draft Results presentation

– Spokane County Water Demand Model presentation of project goals, objectives, concepts.

Presentation Overview

• Spokane County Water Demand Model• Idaho Future Demand Study• Study Compatibility

Spokane County Water Demand Model

County Forecast

PublicSupply

Self Supply Residential

Self SupplyIndustry

Agricultural

CommercialIndustrial

UrbanIrrigation

Public-SupplyAgriculture

Single Family

Multi-Family

Non RevenueWater

Residence& Yard

SmallAgriculture

ThermoelectricPower

Golf Courses

Large Industry

Livestock

IrrigatedAcres

• Segregated by Water Use Sector– each subsector has a unique submodel, or way of calculating

water demand

Spokane County Water Demand Model• Segregated

Spatially– 487 separate

forecast units– A unique water

demand calculation is done for each forecast unit

• Segregated in monthly increments


0

100

200

300

400

500

600

700

2010

2040

CFS(

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SVRP Aquifer Monthly Water Demand 2010 & 2040

County Forecast

PublicSupply

Self Supply Residential

Self SupplyIndustry

Agricultural

CommercialIndustrial

UrbanIrrigation

Public-SupplyAgriculture

Single Family

Multi-Family

Non RevenueWater

Residence& Yard

SmallAgriculture

ThermoelectricPower

Golf Courses

Large Industry

Livestock

IrrigatedAcres

Each forecast unit can have different inputs into each sub model

• Disaggregated Model– In each forecast unit(487) there is a calculation for

each submodel (13) for each month 12– 75,972 water demand calculations per year

0

100

200

300

400

500

600

700

2010

2040

CFS(

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Water demand calculation for each month


• Developed and runs in Excel 2007

– Series of interconnected spreadsheets and formulas


• Single Family Residential Model– Collected 20 years of data from 15 Water Systems:

• monthly per connection water use from water systems, • weather data• demographic data

– Time Series-Cross Sectional Regression• How does water use vary due to variables that are fixed

such as home size.• How does water use vary due to variables that change with

time such as weather.


• Single Family Residential Model– Split into two models:

• Indoor water use model• Outdoor water use model that adds water to

indoor use May through October – Indoor model:

• Water use is a function of household income– Outdoor model

• Water use is a function of home value, temperature, precipitation, and lot size.


Variables Scenario 1 Scenario 2Household Income 30,000$ 80,000$ Assessed Value 144,000$ 252,179$ Average Max Temp

May 68 68June 75.13 72July 85.45 82August 83.06 85September 76.67 73October 60 52.26

Total PrecipMay 0.93 1June 1.18 2July 0.48 0.48August 0.74 1September 0.51 0.01October 2.33 2

Averag Lot Size > 0.6 acres 0 0City of Spokane Water Service 0 0

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecScenario 1 143 143 143 143 545 704 1022 936 752 403 143 143Scenario 2 226 226 226 226 1040 1201 1775 1952 1348 558 226 226

0

500

1000

1500

2000

2500

Jan

Feb

Mar

Apr

May Jun Jul

Aug

Sep

Oct

Nov Dec

Gal

lons

per

day

per

con

necti

onMonth

Single Family-Public Supply

Scenario 1

Scenario 2

Indoor model r2 = 0.55Outdoor model r2 = 0.74

Spokane County Water Demand ModelSingle Family Residential Model - Example

Sector Modeled Reported Relative % Difference

Total Production 41,895 41,530 0.88 %

Single Family Residential 15,920 15,617 1.92%

Multi Family Residential 3,996 4,102 -2.62%

Total Residential 19,916 19,719 0.99%

Commercial/Industrial 9,528 9,798 -2.79%

Total Non Residential 10,758 10,118 6.13%

Non Revenue 3,433 3,500 -1.92%

Annual Public Water System Use: Modeled vs. Reported

Reported in millions of gallons per year


• Impact of weather on water use

300

400

500

600

700

800

90019

98

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

Ann

ual A

vera

ge G

PD

SCWD#3 WSA 2

Actual

Modeled

300

400

500

600

700

800

900

2002

2003

2004

2005

2006

2007

2008

2009

Ann

ual A

vera

ge G

PD

City of Spokane

Actual

Modeled

300

400

500

600

700

800

900

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

Ann

ual A

vera

ge G

PD

SCWD#3 WSA 3

Actual

Modeled

300

400

500

600

700

800

900

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

Ann

ual A

vera

ge G

PD

Whitworth Water District

Actual

Modeled


• Demand from SVRP Aquifer from Spokane County


• Demand from SVRP Aquifer

Reported in billions of gallons per year

Year Water Demand

2010 53.86

2015 56.44

2020 59.70

2025 62.63

2030 65.71

2035 68.79

2040 71.87

Change 18.01

% Growth 33%


• Monthly Demand from SVRP Aquifer from Spokane County

0

100

200

300

400

500

600

700

2010

2040

CFS(

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156 CFS difference


• Conservation and Weather– Conservation efforts can be

masked by changes in weather


-

5

10

15

20

25

30

35

40

2010 2015 2020 2025 2030 2035 2040

2005 weather

2006 weather 5% conservation

20 year average weather

2006 weatherBillio

ns o

f Gal

lons

per

year

Forecast Year

Comparison of Conservation and Weather on Water Demand

-

5

10

15

20

25

30

35

40

2010 2015 2020 2025 2030 2035 2040

2005 weather

2006 weather 5% conservation

20 year average weather

2006 weatherBillio

ns o

f Gal

lons

per

year

Forecast Year

Comparison of Conservation and Weather on Water Demand

no conservation

no conservation

no conservation

Idaho Future Demand Study• Includes an estimate of current and future use by water use

sector on an annual basis:– Public Water Systems– Self Supplied Domestic– Self Supplied Commercial & Industrial– Agriculture

• Separates Irrigation and Non-Irrigation Use

• Evaluates consumptive vs. non consumptive use

• Range of population & employment growth scenarios

• Detailed analysis of conservation scenarios• Evaluation of potential climate change impacts

Idaho Future Demand Study

WA & ID Study Compatibility• Water Use by Sector

Water Use Sector WA IDPublic Water Systems 135,132 34,430

Self Supplied Domestic 411 8,800

Self Supplied Commercial/Industrial 20,988 4,220

Agriculture 5,555 24,700

Total 162,086 72,150

Values in annual acre feetValues are total use

• Aquifer Total Demand

WA & ID Demand

Idaho scenario – medium growth & no conservation

-

20

40

60

80

100

120

2010 2015 2020 2025 2030 2035 2040

Idaho Demand

Washington Demand

SVRP Aquifer Total Annual Water Demand Projections

• Additional Work that would enhance compatibility– Idaho:

• evaluate demand on a monthly basis– Washington:

• Utilize model to:– Develop alternate conservation scenarios– Develop alternate growth scenarios– Estimate consumptive/non consumptive use

WA & ID Demand

Spokane Valley-Rathdrum Prairie Aquifer Water Demand Forecasts Presented by: Mike Hermanson Water Resources Specialist Spokane County Utilities Spokane.

Documents

water demand slide

water demand calculations

water systems

year water demand calculation

water use sector

connection water use

monthly demand

sub model disaggregated