Spokane Valley-Rathdrum Prairie Aquifer Water Demand Forecasts Presented by: Mike Hermanson Water Resources Specialist Spokane County Utilities Spokane River Forum Conference May 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 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 Spokane County Water Demand Model

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 Water demand calculation for each month Spokane County Water Demand Model

Developed and runs in Excel 2007 –Series of interconnected spreadsheets and formulas Spokane County Water Demand Model

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. Spokane County Water Demand Model

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. Spokane County Water Demand Model

Indoor model r 2 = 0.55 Outdoor model r 2 = 0.74 Spokane County Water Demand Model Single Family Residential Model - Example

SectorModeledReportedRelative % Difference Total Production41,89541, % Single Family Residential15,92015, % Multi Family Residential3,9964, % Total Residential19,91619, % Commercial/Industrial9,5289, % Total Non Residential10,75810, % Non Revenue3,4333, % Annual Public Water System Use: Modeled vs. Reported Reported in millions of gallons per year Spokane County Water Demand Model

Impact of weather on water use Spokane County Water Demand Model

Demand from SVRP Aquifer from Spokane County Spokane County Water Demand Model

Demand from SVRP Aquifer Reported in billions of gallons per year YearWater Demand Change18.01 % Growth33% Spokane County Water Demand Model

Monthly Demand from SVRP Aquifer from Spokane County 156 CFS difference Spokane County Water Demand Model

Conservation and Weather –Conservation efforts can be masked by changes in weather Spokane County Water Demand Model 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 SectorWAID Public Water Systems135,13234,430 Self Supplied Domestic4118,800 Self Supplied Commercial/Industrial20,9884,220 Agriculture5,55524,700 Total162,08672,150 Values in annual acre feet Values are total use

Aquifer Total Demand WA & ID Demand Idaho scenario – medium growth & no conservation

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