Mountain Home Plateau

Ground Water Conditions and Management Activities

Presented to the

Idaho Legislature Natural Resources Interim Committee

By Helen Harrington, IDWR

August 5, 2004

Welcome to the Western Snake

Plain• Lake and stream

sediments• Basalt appears as

interbeds and cap rock

• Subbasins• Boundary with

ESRP is in the vicinity of King Hill

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ADA

ELMORE

Boise

Glenns Ferry

Mountain Home

Mountain Home Ground Water Management Area

Cinder Cone Butte CriticalGround Water Area

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General Location

Regional Geology

• Alluvium & terrace gravels• Snake River Group• Idaho Group – primary aquifer• Idavada Volcanics• Idaho Batholith

Aquifers• Perched Aquifer

– Underlies approximately 38,000 acres around Mountain Home and Cinder Cone Butte area

– Depth to water ranges from 10 feet to several hundred feet below land surface

– Perched lenses of clay, silt, sand & gravel in the shallow alluvium

– Recharged from creeks, canals and seepage from Mountain Home Reservoir

– Perched water discharges to regional system – Supplies small domestic and irrigation uses

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E X T E N T O F P E R C H E DO R S H A L L O W G R O U N D W A T E R(Y O U N G , 1 9 7 6 )

Aquifers (cont.)

• Regional Aquifer– Depth to water generally greater than 250

feet– Well yields from 10 to 3500 gpm– Recharged from precipitation, streams,

perched aquifer, infiltration from irrigation– Discharges through well pumpage, springs

in Snake River canyon and underflow

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Map Scale (in m iles)

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WATER BALANCE

• An accounting of water availability– How much water comes in to the basin– How much water is used or leaves the

basin• Positive number –water available for

current and/or future needs• Negative number – use exceeds

recharge

CANYON CREEK AT OREGON TRAIL CROSSING

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ANNUAL DISCHARGE

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L E G E N DIR R IG A T IO N

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G R O U N D W A T E R U S E IN T H E M O U N T A IN H O M E G W M A

C U M U L A T I V E C F S B A S E D O N W A T E R R I G H T P R I O R I T Y D A T E

T O T A L : 4 7 1 cf s

T O T A L : 8 1 cf s

1982

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Township/RangeStudy BoundaryIrrigated Acres (1998)Supplemental AcresAcres Irrigated from Snake River

10 0 10 20 Miles

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Total Irrigated Acres: 46,328

Ground Water 28,815

Surface Water 17,513Snake River (15,451)

Surface&GW 5,681

IRRIGATED ACRES

WATER BALANCE (in acre-feet per year) Basin Inflow and Supply Supply/Use  

Canyon Creek yield 20,900Little Camas Creek (imported) 9,500Rattlesnake Creek yield 3,800Ditto Creek and adjacent areas 4,100Precipitation on rocky areas 4,400

Total 42,700  Consumptive Use and Loss 

Loss to Snake River 1,500Use by irrigated crops 69,600Use by Municipal and Air Base 2,500

  Total 73,600 Inflow Minus Use -30,900  

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Management Designations

CINDER CONE BUTTECRITICAL GROUND WATER AREAdesignated May 7, 1981

MOUNTAIN HOME GROUND WATER MANAGEMENT AREAdesignated November 9, 1982

Reasons for Designation

• Rapid agricultural development • Declines in ground water levels• Further information showed

declines over a larger area• Pending applications for

additional development of ground water

Administrative Restrictions

• Cinder Cone Butte CGWA– No new

appropriations

• Mountain Home GWMA– New

appropriations allowed if it is determined that sufficient supply is available and prior water rights will not be injuredException: Domestic uses and associated

domestic irrigation

Management Strategies

• Creation of advisory committee– Established by Director in 1996– Local representation, 10 members– Objectives:

• Develop recommendations for ground water management plan

• Develop ground water recharge program• Act as forum for data collection, review and

mediation• Act as forum for communication with community

Advisory Committee

• In 1999, a recharge project was initiated. – Source: Canyon Creek– Method: Infiltration through existing

gravel pits– Amount recharged: Approximately

1200-1500 acre feet– Impact: Undetectable change

Potential Sources for Managed Recharge

• Canal lining from Little Camas Reservoir• Canyon Creek

– Highly variable discharge– Primary source of water for Mountain Home

Irrigation District

• Snake River – Requires pumping and transport– Water availability

• Other local basins

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Information Needs

• Subsurface structures controlling water movement

• Ground water level information in specific locations

Thank You