Learn about the importance of Water Projects proposed in Elmore County

"If we don't plan for the future, we are not going to have a future."
Bud Corbus
Elmore County Commissioner


The Mountain Home Plateau Aquifer, extending westward across southern Elmore County into Ada County, provides municipal supply to the City of Mountain Home and Mountain Home Air Force Base, along with irrigation, commercial, domestic and industrial supplies to farms, dairies, and other businesses in Elmore County.

In addition to groundwater from the aquifer, other water supplies on the Mountain Home Plateau are Snake River water pumped for irrigation of farms, Little Camas Reservoir water conveyed to the area by the Mountain Home Irrigation District from the South Fork Boise River watershed, and water from creeks that flow onto the Plateau from the Danskin Mountains and Bennett Hills.

Snake River at CJ Strike Reservoir


Groundwater levels in the Mountain Home Plateau Aquifer have been declining in portions of the County for more than 40 years, prompting declaration of the Cinder Cone Butte Critical Groundwater Area in 1981 and the Mountain Home Ground Water Management Area in 1982.

The water table has fallen 100 feet or more in some locations. The decline in aquifer water levels threatens the existing economy and for many years has been a severe constraint on economic growth. Without some sort of action, wells will continue to go dry and existing water uses will be curtailed.

Management and administration

Management and administration of groundwater on the Mountain Home Plateau is influenced by four designated areas.

The Cinder Cone Butte area was declared a CGWA on May 7, 1981 because of declining groundwater levels. New groundwater appropriations are not allowed in the Cinder Cone Butte CGWA. 

Cinder Cone Butte CGWA Hydrographs March 2016

1981 Order Establishing Cinder Cone Butte CGWA


Following the Cinder Cone Butte CGWA declaration, a study was conducted to evaluate the entire Mountain Home area. As a result of that study, the Mountain Home GWMA (which surrounds the Cinder Cone Butte area) was designated on November 9, 1982. The Mountain Home GWMA, located in Elmore and eastern Ada counties, was designated because of declining groundwater levels. The order states that the area is approaching critical, “although there appear to be subareas where new appropriations could be authorized without injuring existing water rights.  

1996 Order Establishing Mountain Home GWMA

1982 Order Creating Mountain Home GWMA

The Idaho Department of Water Resources created the Consolidated Hearing area in 2012 as part of a joint hearing to evaluate six pending water right applications for irrigation and planned communities.  The Consolidated Hearing area include a portion of the Mountain Home Ground Water Management Area and is located generally west of the Cinder Cone Butte Critical Ground Water Area.  The area extends in a southwesterly direction from Elmore County into Ada County.  Although this entire area does carry the statutory restrictions of a groundwater management area, it functions in a similar manner with respect to new uses of groundwater.

Final Order Regarding Water Sufficiency

The Snake River Basin Adjudication (SRBA) defined the water rights within the Snake River Basin, including groundwater rights from the Mountain Home Plateau Aquifer.  Following issuance of the SRBA unified decree, the Idaho Department of Water Resources created Water District 161 in 2016 to measure diversions and administer groundwater rights within the aquifer.   The Water District now requires measurement and recording of groundwater diversions.

Idaho Department of Water Resources – Water District #161 (Mountain Home Area GW)

Current Water Projects

Canyon Creek flows onto the Mountain Home Plateau from the Danskin Mountains, north and northwest of Mountain Home, where all flows are typically diverted by the Mountain Home Irrigation District for filling Mountain Home Reservoir and for direct irrigation use. 

During times of heavy runoff, typically in February, March, or early April, the creek flow exceeds the capacity of the Irrigation District system and water flows past the diversion eventually reaching the Snake River a few miles upstream of CJ Strike Dam. 

For many years, water has been diverted into gravel pits north of I84 near Mountain Home for recharge purposes.

Water infiltrates through the gravel to recharge the aquifer. The capacity of the gravel pit diversion facilities has been a limiting factor.

In the winter of 2018-19, Elmore County improved the recharge diversion facilities using funding from an Idaho Water Resource Board grant. 

Three diversions systems are utilized (Ireland, BLM/ITD, and Simplot), each with headgates and measurement weirs. 

The County conducts water quality monitoring under an IDEQ-approved monitoring plan.

2017 recharge activities (prior to improvements to diversion systems by the County) are documented in this IDWR Technical Report

2019 recharge activities (following 2018-19 improvements).

Mountain Home Air Force Base (MHAFB) obtains its water supply from deep wells. 

Due to declining aquifer water levels, the Air Force has determined that the water supply is unsustainable and must be replaced for MHAFB to remain viable.

The State of Idaho, in cooperation with the Air Force, is working toward a Snake River supply for the Base. Current plans call for the Idaho Water Resource Board fund and construct a pump station at CJ Strike Reservoir and a pipeline that will extend down Strike Dam Cutoff Road and State Highway.

The Air Force will fund and construct a water treatment plant at MHAFB. The State has purchased senior-priority Snake River water rights that will be modified for municipal use at MHAFB.

Mountain Home Air Force Base Sustainable Water Supply Project – Idaho Department of Water Resources   

Idaho Water Resource Board approves priorities for allocating $70M in major water infrastructure projects statewide | March 22, 2021

The Idaho Water Resource Board and the US Bureau of Reclamation are proposing a joint project to raise Anderson Ranch Dam by approximately 6 feet to create 29,000 feet of additional storage space.

Elmore County is seeking 10,000 acre feet of this space for future use in the vicinity of Mountain Home.

The project is currently undergoing environmental compliance (NEPA) reviews.

Idaho Water Resource Board and Bureau of Reclamation to work on project design as next step for 6-foot raise of Anderson Ranch Dam

Idaho Water Resource Board takes key steps toward raising Anderson Ranch Dam to create additional storage water

Idaho Water Resource Board approves priorities for allocating $70M in major water infrastructure projects statewide

March 5, 2021 update Boise River Feasibility Study and Anderson Ranch Dam Raise

Boise River Basin Feasibility Study (idaho.gov)

Elmore County, with cooperation from Mountain Home Irrigation District, is moving ahead with design and permitting of a pump station and pipeline from Anderson Ranch Reservoir to Little Camas Reservoir. 

The pump station will divert water authorized under the County’s 200 cfs water right permit 63-34348.

The pump station would also be available to pump stored water from Anderson Ranch Reservoir in the event that county receives storage space from the Anderson Ranch dam raise project. 

Water delivered into Little Camas Reservoir can be conveyed through the Mountain Home Irrigation District system to the Mountain Home area for aquifer recharge and supplemental irrigation purposes.

2020-05-01 application package

Order on Reconsideration; Amended Preliminary Order Approving Permit Upon Conditions in the Matter of Application for Permit 63-34348 in the Name of Elmore County, Board of County Commissioners | May 7, 2019 (idaho.gov)

Elmore County holds the following water rights.

61-7731.  Water right license 61-7731 authorizes diversion from Canyon Creek of 22.68 cfs and up to 962 acre feet annually for groundwater recharge.

61-12314.  Permit 61-12314 authorizes diversion of up to 200 cfs from Canyon Creek for ground water recharge.

63-34348. Permit 63-34348 authorizes diversion of up to 200 cfs from the South Fork Boise River for ground water recharge and supplemental irrigation.

02-10535.  Application 02-10535 seeks 20 cfs of Snake River water for municipal and ground water recharge purposes.



Anderson Ranch Reservoir