Western Snake River Plain- Treasure Valley Ground Water

Conceptual Cross-Section (Regional Scale)

Ground Water Flow Systems
The Treasure Valley contains a complex system of shallow, intermediate, and deep aquifers. Shallow aquifers often supply water to rural domestic and some irrigation wells. Municipal, industrial, and some irrigation wells typically draw water from deeper aquifers. Intermediate aquifers, found in the transition from shallow to deep zones, supply water for domestic, irrigation, and municipal uses.

Shallow aquifers, present throughout the central portion of the Treasure Valley are often contained in the Snake River Group sediments. Depths of these aquifers are generally less than 250 feet below ground surface. Ground water in shallow aquifers generally originates at ground surface, in the form of precipitation, infiltration from irrigated areas, or infiltration from river and stream channels or canals (see “Aquifer Recharge”). Shallow aquifers can contain very localized flow systems such as from an irrigated field to the nearest drainage ditch, or extend tens of miles.

A deeper, regional aquifer system underlies shallower aquifers. The regional system extends throughout the valley, with ground water flowing in a generally westerly direction. Water enters the regional system at the basin margins or in the easternmost portions of the valley. Some of the tilted sedimentary zones underlying the geologic unconformity represent productive aquifer zones. Coarse-grained sediments overlying the unconformity may act as a manifold distributing water from the east Boise and/or peripheral areas into the underlying aquifer zones.

Estimated Recharge to Shallow Aquifers

Aquifer Water Balance

Aquifer Recharge
“Aquifer recharge” refers to the water that is entering the aquifer system. Recharge to the Treasure Valley aquifers was estimated on the basis of land use (Urban and Petrich, 1998) . Approximately 50 percent of the Treasure Valley land area is flood or sprinkler irrigated. Seepage from flood irrigation (including canal seepage) accounts for approximately 95 percent of recharge to shallow aquifers. Only a small portion of this water, however, enters deeper aquifers; most of the shallow aquifers discharge into river, canal, or ditch channels.

Infiltration from flood irrigation and canal seepage far exceeds recharge from precipitation or other sources (see “Water balance”). Ground water withdrawals for industrial, rural domestic, municipal, and irrigation uses are much less than the water that returns to ground surface as natural discharge. However, much of the withdrawals occur from deeper aquifer zones, while much of the discharge occurs from shallow aquifers.

References:
Urban, S.M. and Petrich, C.R., 1998. 1996 Water Budget for the Treasure Valley Aquifer System, Idaho Department of Water Resources Research Report.

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Original content compiled by Christian Petrich, Margie Wilkins, Tondee Clark, and Tony Morse.
Images provided by Idaho Department of Water Resources
Adaptation for the Digital Atlas of Idaho by Ean Harker- design/html, Kyle Raverty- content, 11-2002.
Information supplied by the Idaho Department of Water Resources; 1301 North Orchard Street Boise, Idaho 83706 (208) 327-7900.