Idaho Water IssuesIdaho Water IssuesBackground and ScienceBackground and ScienceFocus: Snake River Plain Focus: Snake River Plain

AquiferAquifer

Dr. Gary S. JohnsonDr. Donna M. Cosgrove

Mr. Bryce A. ContorDr. John Tracy

Idaho Water Resources Research Institute

University of Idaho

Topics for todayTopics for today

• Hydrology BasicsHydrology Basics

• Conjunctive Management ChallengesConjunctive Management Challenges

• Snake Plain ExampleSnake Plain Example

• Aquifer Management OpportunitiesAquifer Management Opportunities

The aquifer is a large, The aquifer is a large, leaky tankleaky tank

recharge varies dramatically

Output is more constantCharacteristics:

FlowRecharge and DischargeWater BudgetStorage

Aquifer Springs

Aquifer Flow

Aquifer Flow

Aquifer RechargeAquifer Recharge• Water entering the aquifer is called Water entering the aquifer is called

RechargeRecharge

• Common sources of recharge:Common sources of recharge:– Infiltrating precipitationInfiltrating precipitation– River or lake-bed seepageRiver or lake-bed seepage– Subsurface inflows from nearby aquifersSubsurface inflows from nearby aquifers– Seepage from human activitiesSeepage from human activities

•Storm drainsStorm drains

• IrrigationIrrigation

Aquifer DischargeAquifer Discharge• Water leaving the aquifer is called Water leaving the aquifer is called

DischargeDischarge

• Common sources of discharge:Common sources of discharge:– Spring dischargeSpring discharge– Seepage to rivers or lakesSeepage to rivers or lakes– Wetlands Wetlands – Subsurface outflows to adjacent aquifersSubsurface outflows to adjacent aquifers– Ground-water pumpingGround-water pumping

• Note that rivers can be a source of Note that rivers can be a source of recharge or dischargerecharge or discharge

Water BudgetWater Budget

• Since we cannot create or destroy Since we cannot create or destroy water, a basic law existswater, a basic law exists

• Inflow = Outflow +/- Change in Inflow = Outflow +/- Change in StorageStorage

• It is like a bank account, if we spend It is like a bank account, if we spend more money than we make, our more money than we make, our account balance goes downaccount balance goes down

Aquifer

Aquifer StorageAquifer Storage

• Aquifer storage is the volume of Aquifer storage is the volume of water stored in the aquiferwater stored in the aquifer

• We can detect increases in aquifer We can detect increases in aquifer storage by rising aquifer water levelsstorage by rising aquifer water levels

• Changes in storage impact Changes in storage impact connected surface waterconnected surface water

• Long term decreases in storage Long term decreases in storage indicate aquifer miningindicate aquifer mining

Jefferson County (5N 33E 13BDC3)

4520.00

4525.00

4530.00

4535.00

4540.00

4545.00

1/1/1970 1/1/1980 1/1/1990 1/1/2000

Wat

er L

evel

(ft

ab

v se

a le

vel)

Seasonal VariationLong-term Change

Well Water Levels

River/Aquifer River/Aquifer InterconnectionInterconnection• A gaining river or lake is said to be A gaining river or lake is said to be

‘hydraulically connected’‘hydraulically connected’– Springs and seeps discharge to rivers and lakesSprings and seeps discharge to rivers and lakes

• The gain is not at a constant rateThe gain is not at a constant rate– As aquifer elevation rises, the gain increasesAs aquifer elevation rises, the gain increases– As aquifer elevation declines, the gain decreasesAs aquifer elevation declines, the gain decreases

• If aquifer elevation is well below river If aquifer elevation is well below river elevation, river is a ‘losing’ reachelevation, river is a ‘losing’ reach

Discharge to River

PumpingRecharge

Conceptual Aquifer System

BASIC TRUTH: A gallon taken out of the aquifer represents a gallon that never makes it to the river

ISSUE: When, where depletion effects are felt

Conjunctive ManagementConjunctive Management

• Conjunctive Management is the Conjunctive Management is the simultaneous management of the simultaneous management of the surface-water resource and the surface-water resource and the interconnected ground-water interconnected ground-water resourceresource

• Not all aquifers are interconnected Not all aquifers are interconnected with rivers or lakeswith rivers or lakes

• The Snake Plain Aquifer is intimately The Snake Plain Aquifer is intimately interconnected with the riverinterconnected with the river

Why is Conjunctive Why is Conjunctive Management So Difficult?Management So Difficult?

• Water Law originally intended to Water Law originally intended to manage surface watermanage surface water– Effects are immediate, visible and down-Effects are immediate, visible and down-

stream onlystream only

• With ground-water, the effects exist With ground-water, the effects exist but are more difficult to identifybut are more difficult to identify– Effects are spatially distributedEffects are spatially distributed– Effects are spread out over timeEffects are spread out over time

Pocatello

IdahoFalls

Arco

TwinFalls

AmericanFalls

ThousandSprings

IMPACTS DONOT FOLLOWFLOW LINES

COMPLICATIONNO. 1

Pocatello

IdahoFalls

Arco

TwinFalls

AmericanFalls

ThousandSprings

TIMERIV

ER

IM

PAC

T

COMPLICATIONNO. 2:

TIME ATTENUATEDIMPACTS

How do we sort this out?How do we sort this out?

• Ground-water model can predict the Ground-water model can predict the timing and location of impactstiming and location of impacts– Identify arrival time of impactsIdentify arrival time of impacts– Identify arrival locationsIdentify arrival locations

• Ground-water model is a numerical Ground-water model is a numerical representation of a physical systemrepresentation of a physical system

• Example: Snake Plain Aquifer ModelExample: Snake Plain Aquifer Model

Some Snake Plain Some Snake Plain BackgroundBackground

Precipitation

Tributary Underflow

Evapotranspiration

SurfaceIrrigationSpring

Discharge

Major Sourcesof Recharge and

Discharge

-8

-6

-4

-2

0

2

4

6S

WIr

rig

ati

on

Tri

bu

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Infl

ow

Pre

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Str

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Riv

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Ga

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Ch

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Dis

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AF

/yr)

Snake Plain Aquifer Water Budget

Ground-water Pumping fromthe Eastern Snake Plain Aquifer

Ag Irrigation

Commercial, Industrialand Stockwater(including Dairy)

Municipal

Rural Domestic

Water Budget on Snake Water Budget on Snake PlainPlain• Approximately 6.5 million acre-feet (8,000 Approximately 6.5 million acre-feet (8,000

cfs) of water recharges the aquifer annuallycfs) of water recharges the aquifer annually

• Discharge to Thousand Springs reach is Discharge to Thousand Springs reach is 5,000 to 6,000 cfs5,000 to 6,000 cfs

• Discharge to American Falls reach is 2,500 Discharge to American Falls reach is 2,500 to 3,000 cfsto 3,000 cfs

• We are actually water-richWe are actually water-rich

History of Irrigation on Snake History of Irrigation on Snake PlainPlain

• Surface water irrigation started around 1890sSurface water irrigation started around 1890s– Water table rose 10s to 100s of feetWater table rose 10s to 100s of feet– New springs emergedNew springs emerged

• Earliest claims on spring flow in Thousand Earliest claims on spring flow in Thousand Springs started around 1920sSprings started around 1920s

• Ground-water pumping introduced in 1950sGround-water pumping introduced in 1950s– Rural electrificationRural electrification– Deep pump technologyDeep pump technology

• Water levels on Plain peaked in Water levels on Plain peaked in 1950s1950s

• Primarily declining since thenPrimarily declining since then– Impacts of ground-water pumpingImpacts of ground-water pumping– Conversion from flood irrigation to more Conversion from flood irrigation to more

efficient sprinkler systemsefficient sprinkler systems– Enlargement of irrigated areasEnlargement of irrigated areas– DroughtDrought

• The aquifer seems to be very The aquifer seems to be very responsive to droughtresponsive to drought

Spring Discharges and American Falls River Gains

0

1000

2000

3000

4000

5000

6000

7000

8000

1900 1920 1940 1960 1980 2000

cfs

KSprings AmFalls

Changes in diversions/timeChanges in diversions/time

Upper Snake Diversions (Does not include tributaries and side valleys)

0

2,000

4,000

6,000

8,000

10,000

12,000

1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

tho

usa

nd

acr

e fe

et

Changes in Ground Water Changes in Ground Water Irrigated Acres Over TimeIrrigated Acres Over Time

Ground-water Irrigation on Eastern Snake Plain Aquifer

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1940 1949 1959 1966 1979 1990 2006

year

acre

s USGS Data

Estimated Acres

1 million acres

~ 2 MAF/yr or 2,700 cfs

Model is Translation of Physical Model is Translation of Physical System to Numerical Model System to Numerical Model RepresentationRepresentation

Model

Recharge/Discharge

HydrologicProperties

Boundaries Aquifer Properties

StartingConditions

EndingWaterLevels

Spring DischargeRiver Gains and Losses

Snake Plain Model Snake Plain Model EnhancementEnhancement• Completed over past four yearsCompleted over past four years

– Appropriation from state, contribution Appropriation from state, contribution from Idaho Power, in-kind from USGSfrom Idaho Power, in-kind from USGS

• Collaborative processCollaborative process– Multi-agencyMulti-agency– Consultants for water usersConsultants for water users

• Model calibrated to 22 years of data, Model calibrated to 22 years of data, with 15,000 measured data pointswith 15,000 measured data points

Steady State Water TableSteady State Water Table

Comparison of Modeled to Comparison of Modeled to MeasuredMeasuredAquifer Water LevelsAquifer Water Levels

Future Snake Plain Future Snake Plain ChallengesChallenges• Continued changes in irrigation practicesContinued changes in irrigation practices

– Canal liningCanal lining– Continued conversion to sprinkler irrigationContinued conversion to sprinkler irrigation

• Land use changingLand use changing– Subdivisions taking over agricultural landSubdivisions taking over agricultural land– Industry moving inIndustry moving in– Dairies moving inDairies moving in

• Societal desires changingSocietal desires changing– Species protectionSpecies protection

• Potential for impacts of climate changesPotential for impacts of climate changes

Is this just an Eastern Idaho Is this just an Eastern Idaho Problem?Problem?

• Snake Plain may be ahead of other Snake Plain may be ahead of other basins in facing these challengesbasins in facing these challenges

• How we sort out the problems in the How we sort out the problems in the Snake Plain will have far-reaching Snake Plain will have far-reaching impacts throughout the stateimpacts throughout the state– Bear River DrainageBear River Drainage– Spokane Valley/Rathdrum Prairie AquiferSpokane Valley/Rathdrum Prairie Aquifer– Treasure Valley AquiferTreasure Valley Aquifer

Toolbox for Aquifer Toolbox for Aquifer ManagementManagement• Managed RechargeManaged Recharge

– Aquifer storage of excess spring run-off Aquifer storage of excess spring run-off in high water yearsin high water years

• Conservation Reserve ProgramConservation Reserve Program– Taking acres out of productionTaking acres out of production

• Ground-water BankingGround-water Banking

• Conversion of some ground-water Conversion of some ground-water irrigation back to surface irrigationirrigation back to surface irrigation

Toolbox for Aquifer Toolbox for Aquifer Management (cont’d)Management (cont’d)

• Partial or full curtailment of use Partial or full curtailment of use during low water yearsduring low water years

• Buy-out of some threatened water Buy-out of some threatened water rightsrights

SummarySummary• Spring discharge and aquifer water Spring discharge and aquifer water

levels are changing in response to:levels are changing in response to:– Man-induced effects: pumping and rechargeMan-induced effects: pumping and recharge– Weather variabilityWeather variability

• Demands exceed suppliesDemands exceed supplies• Some technical tools available to Some technical tools available to

minimize conflictminimize conflict• State in the position of balancing State in the position of balancing

prioritiespriorities

Protection ofSenior Rights

Full EconomicUse

More information?More information?Gary S. JohnsonGary S. Johnson

Idaho Water Resources Research InstituteIdaho Water Resources Research InstituteUniversity of IdahoUniversity of Idaho208-282-7985208-282-7985johnson@if.uidaho.edujohnson@if.uidaho.edu

Donna M. CosgroveDonna M. CosgroveIdaho Water Resources Research InstituteIdaho Water Resources Research InstituteUniversity of IdahoUniversity of Idaho208-282-7914208-282-7914cosgrove@if.uidaho.educosgrove@if.uidaho.edu

Bryce A. ContorBryce A. ContorIdaho Water Resources Research InstituteIdaho Water Resources Research InstituteUniversity of IdahoUniversity of Idaho208-282-7846208-282-7846contor@if.uidaho.educontor@if.uidaho.edu