Impact of Climate Change on Water Supplies of Everett, Seattle, and Tacoma May 2008

Impact of Climate ChangeImpact of Climate Change

on Water Supplies ofon Water Supplies of

Everett, Seattle, and Everett, Seattle, and TacomaTacoma

May 2008May 2008

AWWA-PNWS Annual ConferenceAWWA-PNWS Annual Conference

Vancouver WAVancouver WA

Based on Work of Climate Change Technical Based on Work of Climate Change Technical CommitteeCommittee

of Central Puget Sound Regional Water Supply of Central Puget Sound Regional Water Supply Planning ProcessPlanning Process

Climate Change Models General Circulation Models Climate Change Models General Circulation Models (GCM)(GCM)

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Impact on TemperatureImpact on Temperature

Impact on Sultan StreamflowImpact on Sultan StreamflowDHSVM Historic and GCM 2000

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Everett’s Water Source Everett’s Water Source StorageStorage

Spada Spada Reservoir Reservoir (50 billion (50 billion gallons) with gallons) with Culmback Culmback Dam in the Dam in the forefrontforefront

Spada Reservoir Rule Spada Reservoir Rule CurvesCurves

Water Year – July 1 to July 1

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Everett’s Water Supply and Rights Everett’s Water Supply and Rights

Supply YieldSupply Yield

Firm Yield = Avg. Annual Withdrawal Available 98% of Firm Yield = Avg. Annual Withdrawal Available 98% of

YearsYears

Firm Yield of Sultan Source = Firm Yield of Sultan Source = With Existing Facilities (Storage and Pipelines)With Existing Facilities (Storage and Pipelines)

Water RightsWater Rights

Existing Water Rights on Sultan = 137.5 MGD (QExisting Water Rights on Sultan = 137.5 MGD (QAA))

Pending Water Right Application: Pending Water Right Application:

QQI I = 200 cfs; if Q= 200 cfs; if QA A = 100 CFS = = 100 CFS = 64.5 MGD64.5 MGD (Est. Q (Est. QAA))

200 MGD

202 MGD

Three ScenariosThree Scenarios

Three operational scenarios were evaluated:Three operational scenarios were evaluated:

Unconstrained Yield Unconstrained Yield (Storage: 153,000 AC-FT)(Storage: 153,000 AC-FT) Yield Constrained by Transmission Upstream Yield Constrained by Transmission Upstream

of Chaplain Reservoirof Chaplain Reservoir (Storage: 153,000 AC-FT) (Storage: 153,000 AC-FT)

Yield Constrained by Hydropower Operations Yield Constrained by Hydropower Operations and Spada Minimum Surface Elevation of and Spada Minimum Surface Elevation of 1,380 ft1,380 ft (Storage: 101,000 AC-FT) (Storage: 101,000 AC-FT)

Impact of Climate Change on Impact of Climate Change on Three ScenariosThree Scenarios

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Annual Water Right - Sultan River and Chaplain

Reservoir (137.5 mgd)

2028

2062

Comparison of Existing Conditions and Comparison of Existing Conditions and Projected DemandProjected Demand

Climate Change Impact: 6 - 13 % reduction by Yr 2100

20 Years on Existing Right; 50+ Years on New 20 Years on Existing Right; 50+ Years on New RightRight

Summary of Climate Impact on Summary of Climate Impact on Water SupplyWater Supply

No Impact on Existing Water Right – No Impact on Existing Water Right –

Good for next 20 yearsGood for next 20 years

Firm Yield would be Reduced 6 – 13% Firm Yield would be Reduced 6 – 13% by 2100by 2100

Modification of SPADA Rule Curves Modification of SPADA Rule Curves would probably offset some of this would probably offset some of this impact (To be determined in impact (To be determined in future studies)future studies)

Provides retail and Provides retail and wholesale water to 1.45 wholesale water to 1.45 million people in regionmillion people in region

Sources of supplySources of supply Cedar River WatershedCedar River Watershed South Fork Tolt RiverSouth Fork Tolt River WellfieldsWellfields

Firm yield 171 mgdFirm yield 171 mgd Based on past 76 yearsBased on past 76 years 98% reliability 98% reliability

Total Demand:Total Demand: 2007: 126 mgd2007: 126 mgd 2060: 159 mgd2060: 159 mgd

Seattle’s Regional Water Seattle’s Regional Water SystemSystem

Adaptation OptionsAdaptation Options SPU identified a series of intra-system SPU identified a series of intra-system

modifications and new supply options – modifications and new supply options – and grouped them into Tiers.and grouped them into Tiers.

Applied the effects on supply using Tier 1 Applied the effects on supply using Tier 1 intra-system modifications.intra-system modifications.

Where Tier 1 modifications did not restore Where Tier 1 modifications did not restore supply fully, identified the need for supply fully, identified the need for subsequent Tiers.subsequent Tiers.

Subsequent Tiers include, but not limited Subsequent Tiers include, but not limited to, options such as:to, options such as: Conservation programs after 2030 Conservation programs after 2030 Reclaimed waterReclaimed water Cedar dead storageCedar dead storage

Tier 1 Modifications - CedarTier 1 Modifications - Cedar

Refill to 1563’Refill to 1563’ Current practice but Current practice but

1560’ used for firm yield1560’ used for firm yield Adds 5966 AF or 12% Adds 5966 AF or 12%

more useable storagemore useable storage Modify Overflow Dike Modify Overflow Dike

to 1554’to 1554’ Current crest is at 1550’Current crest is at 1550’ Reduces seepage lossesReduces seepage losses New project under New project under

developmentdevelopment

1563'

1560'

1550'

1554'

Masonry Dam

Maximum Elevation Chester Morse Lake1570'

Overflow Dike

5966 Acre - Feet

<1532’ Dead Storage

Tier 1 Modifications - ToltTier 1 Modifications - Tolt

1765'

1710'

1690'

South Fork Tolt Reservoir

7517 Acre - Feet

1660’Lowest Intake Level

Draw down to Draw down to 1690’1690’ Currently 1710’ Currently 1710’

used for firm yieldused for firm yield Adds 7517 AF or Adds 7517 AF or

18% more useable 18% more useable storagestorage

Tier 1 Modifications – Lake Tier 1 Modifications – Lake YoungsYoungs

506' 506'502.4'

497.4'

Lake Youngs

3437 Acre - Feet Model 5’ of storageModel 5’ of storage Current practice but Current practice but

not modelednot modeled Adds 3437 AF of Adds 3437 AF of

useable storageuseable storage

ConclusionsConclusions Climate change would result in decrease in Climate change would result in decrease in

available supply if no change in operationsavailable supply if no change in operations Would need new source of supply some time after 2050, Would need new source of supply some time after 2050,

consistent with SPU’s 2007 Water System Planconsistent with SPU’s 2007 Water System Plan

SPU is addressing the potential impacts of climate SPU is addressing the potential impacts of climate by investing in:by investing in: Portfolio of Tier 1 intra-system modifications to enhance Portfolio of Tier 1 intra-system modifications to enhance

flexibility of the systemflexibility of the system Ongoing conservation programs through 2030Ongoing conservation programs through 2030 Ongoing research and collaboration with the water Ongoing research and collaboration with the water

industry industry

The Tier 1 modifications SPU is currently making The Tier 1 modifications SPU is currently making and investigating will mitigate modeled effects for and investigating will mitigate modeled effects for all but the largest reductions in supply in 2075 all but the largest reductions in supply in 2075 Use of CML below 1532’ (Dead Storage) could mitigate Use of CML below 1532’ (Dead Storage) could mitigate

the largest reductions – other options are also available the largest reductions – other options are also available for considerationfor consideration

Climate Change Climate Change ImpactsImpacts

on on Tacoma Water SupplyTacoma Water Supply

Current Supply & Demand Current Supply & Demand SummarySummary

2006 average daily demand was2006 average daily demand was In 2006, approximately 88% of supply was In 2006, approximately 88% of supply was

from the Green River and 12% was from in-from the Green River and 12% was from in-town wellstown wells

Annual well use has varied over the last 10 Annual well use has varied over the last 10 years from as low as 4% of total supply to years from as low as 4% of total supply to 19%19%

Overall system yield is approximately Overall system yield is approximately based on historical databased on historical data

105 MGD

61 MGD

Basic Effects of Climate Basic Effects of Climate Change on Tacoma’s SourcesChange on Tacoma’s Sources

As temperatures increase, snowpack As temperatures increase, snowpack decreasesdecreases

Surface sources see Surface sources see higherhigher late fall & winter late fall & winter flows, and flows, and lowerlower late spring & summer flows late spring & summer flows

Groundwater sources may be affected by Groundwater sources may be affected by changes in precipitation, but these effects changes in precipitation, but these effects are likely to be much less significant than are likely to be much less significant than changes to surface sources that are caused changes to surface sources that are caused by temperature riseby temperature rise

Average Summer Inflow Average Summer Inflow Upstream of Hanson DamUpstream of Hanson Dam

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Operational Adaptations Operational Adaptations to Climate Change Impactsto Climate Change Impacts

Operational adaptations would be made prior to Operational adaptations would be made prior to constructing new projects. Some examples constructing new projects. Some examples include:include:

Begin Hanson refill earlier to capture more late Begin Hanson refill earlier to capture more late winter & early spring runoffwinter & early spring runoff

Increase reliability of Hanson refill by using more Increase reliability of Hanson refill by using more wells in the spring and storing more river water wells in the spring and storing more river water which otherwise would be used in the springwhich otherwise would be used in the spring

Store any excess first diversion water in late Store any excess first diversion water in late winter or early spring, in addition to second winter or early spring, in addition to second diversion waterdiversion water

ConclusionsConclusions

Climate change is expected to cause higher Climate change is expected to cause higher fall and winter river flows and lower spring and fall and winter river flows and lower spring and summer river flows as snowpack decreasessummer river flows as snowpack decreases

Tacoma’s system yield is projected to decline Tacoma’s system yield is projected to decline in the range of 4 to 8% by 2075in the range of 4 to 8% by 2075

While operational adaptations should be While operational adaptations should be sufficient to counter the effects in the near sufficient to counter the effects in the near term, additional water projects would be term, additional water projects would be needed in the future to maintain current levels needed in the future to maintain current levels of water supplyof water supply

Summary of Climate Change Summary of Climate Change ImpactsImpactsEverett Seattle Tacoma

Existing

Yield 200 ** 171 105

Demand 85 126 61

Future *

Demand = Yield 2060+/-+/- 2050++ 2040+/-+/-

Range of Climate -6% to -13% to -4% to

Impact on Yield * -13% -25% -8%

*Without Adaptation Strategies** Existing Water Rights are 137.5 MGD (Average Annual Quantity)

ConclusionsConclusions

Climate Change Will Cause:Climate Change Will Cause:

Higher Fall and Winter FlowsHigher Fall and Winter Flows Lower Summer FlowsLower Summer Flows Higher TemperaturesHigher Temperatures Higher Snow Line, Less Snow PackHigher Snow Line, Less Snow Pack Lower Water Supply YieldLower Water Supply Yield Little Impact in Near Term -- 0-20 YearsLittle Impact in Near Term -- 0-20 Years Operational Changes to Offset Impacts Mid-term -- Operational Changes to Offset Impacts Mid-term --

20 – 40 Years20 – 40 Years Additional Water Actions (e.g. Projects, Reuse, Additional Water Actions (e.g. Projects, Reuse,

Higher Conservation) to Offset Impact in Long Higher Conservation) to Offset Impact in Long Term -- Term -- 40 – 75 Years40 – 75 Years

Questions?Questions?

Documents

Impact of Climate Change on Water Supplies of Everett, Seattle, and Tacoma May 2008