The total study area encompasses the Big Wood River, Little Wood River, and Camas Creek drainages in central Idaho totaling approximately 3,200 square miles. The primary focus of the study is on the water resources of the Big Wood River basin, which includes the Big Wood River and Camas Creek (approx. 2,000 square miles). However, approximately 40 square miles in the Little Wood River drainage are irrigated from the Big Wood River so that basin is included in the study area for the purpose of simulating irrigation although otherwise it is not studied in detail. The study area lies within portions of Blaine, Camas, Elmore, Gooding and Lincoln counties and the major population centers include Ketchum, Sun Valley, Hailey, Bellevue, Fairfield, and Gooding. Map of the Big Wood Basin study area

Land Use/Land Cover

Land Use/ Land Cover (LULC) data based on satellite imagery can be used to understand what land uses or vegetation types are present, such as forests, agriculture, impervious surfaces, or open water. In 2010, the land use/land cover of the study area consisted mainly of shrubland/grassland (71%), forest (14%), and agriculture (13%), with developed lands, barren areas, wetlands, and water/snow/ice comprising the remaining 2%.

About 34% of the land in the study area is privately owned while the rest is public. The majority of the public land is managed by the U.S. Bureau of Land Management (BLM) with the U.S. Forest Service and the State of Idaho managing the rest.

Map of 2010 land use/land cover in the study area. Data from USDA National Agricultural Statistics Service (2010) summarized with Envision model (Bolte, 2013). Map of 2010 Land Ownership/Management
LULC map Ownership map

Surface Water Resources

The major rivers within the study area are the Big Wood River, Little Wood River, and Camas Creek, but because the primary focus of this work is on the water resources of the Big Wood Basin, only the hydrology of the Big Wood River and Camas Creek were simulated in detail. The Little Wood drainage is included only to encompass approximately 40 square miles of agricultural lands that are irrigated from the Big Wood River system near the town of Richfield.

The Big Wood River (Hydrologic Unit Code 17040219) runs primarily from north to south, beginning near Galena Summit, running southeast through a narrow valley bordered by the Smoky, Boulder, and Pioneer mountains, and past the towns of Ketchum, Hailey, and Bellevue before entering a wider valley known locally as the Bellevue Triangle. It continues south along the western side of the Timmerman Hills where it is dammed to form Magic Reservoir. The Big Wood receives streamflow from numerous tributaries, the largest of which are shown in the figure below. Characteristics and flows of the tributaries in the northern portion of the basin are further discussed in Bartolino (2009). Many of these larger tributaries flow perennially but water generally only flows seasonally or in response to large precipitation events in the smaller tributary canyons (Bartolino, 2009).

Camas Creek (Hydrologic Unit Code 17040220) is the largest tributary to the Big Wood River, joining in Magic Reservoir. This river runs primarily from west to east through an approximately 10 mile-wide valley known as the Camas Prairie (Claire, 2005). The basin is bordered on the south by the Bennett Hills and on the north by the Soldier Mountains. Below Magic Reservoir, the Big Wood River flows south before heading west near the town of Shoshone. It joins the Little Wood River near the town of Gooding to form the Malad River, a tributary to the Snake River. Elevation in the Big Wood River catchment ranges from approximately 3,000 feet above sea level at the mouth of the Malad River to nearly 12,000 feet in the Pioneer Mountains in the northeast portion of the drainage (Buhidar, 2001).

Although several reservoirs are located in the study area, only Magic Reservoir is included in this study. Magic Reservoir is the largest of the reservoirs and is located on the main stem of the Big Wood River at the confluence of the Big Wood River and Camas Creek. Magic Reservoir is privately owned and is managed for irrigation, flood control, and power generation by the Big Wood Canal Company; however, meeting irrigation needs is the primary operating objective. The 112 foot tall earth and rock dam has the capacity to store 191,500 acre-feet of water. In an average water year, the reservoir fills in the spring due to snowmelt runoff, with maximum storage generally occurring in May (USDA NRCS, 1996). During the agricultural growing season, the stored water is released and routed through a series of canals below the reservoir to irrigate approximately 36,500 acres in the Big Wood and Little Wood river basins (Big Wood Canal Company, personal comm.).

Major rivers, tributaries, and reservoirs within the study area. Also shown are four USGS streamgages that were used as reference points for the hydrologic model. Data from NHDPlus V2 (U.S. Environmental Protection Agency and U.S. Geological Survey, 2012)
Surface Water map

Uses of Surface Water

The Idaho Department of Water Resources water rights database indicates that most surface water rights are allocated for irrigation, power generation, recreation, wildlife, aesthetic purposes, and stock water. Many other water uses are appropriated that comprise very small proportions of the total basin water (Idaho Department of Water Resources, 2009a; b). Note that some uses are consumptive while others are not and water rights may be allocated for different lengths of time within a year. Also of note, the State of Idaho holds three water rights on the Big Wood River for minimum flow requirements totaling 11 m3/s (Idaho Department of Water Resources, 2009a).

Groundwater Resources

At least two aquifer systems underlay the upper portion of the study area – the Wood River Valley Aquifer System and the Camas Prairie Aquifer. The scope of this project does not include groundwater but for more information on the Wood River Valley aquifer, see ongoing groundwater resource studies by the United States Geological Survey and the Idaho Department of Water Resources. The lower basin is underlain by the Snake River Plain Aquifer system; more information can be found in the Eastern Snake Plain Aquifer Comprehensive Aquifer Management Plan.


The climate within the study area is characterized as continental, with temperature and precipitation varying with elevation. The table below summarizes the average annual precipitation and temperature ranges for three elevation zones in the Big Wood River drainage based on Buhidar (2001).

Elevation RangeAverage Annual Precipitation (in)Average Temperature Range
Minimum (°F)Maximum (°F)
High (>5800 feet)20.42154
Mid (4000-5800 feet)13.42958
Low (<4000 feet)10.23664

Nearly 60% of the annual precipitation falls as snow during the months of November to March. The amount of snowfall ranges from less than 2 feet in the low elevations to 4 feet in the mid elevations to 12 feet in the high elevations. Average snow depth ranges from 6 inches to 10 feet depending on elevation (Buhidar, 2001).


The 2010 population was approximately 34,000 with about 61% residing in urban centers and 39% in rural areas (U.S. Census Bureau 2010). Although the population density is quite low (11 people per square mile; the Idaho average is 19 and the U.S. average is 88), the development is generally concentrated in a small area due to development restrictions such as land ownership and suitability

Town2010 Population2010 Housing Units
Sun Valley1,4062,597
Bellevue 2,287926
Wood River Valley Urban Centers Total14,34210,614

*2010 population values listed here for reference although these towns were not considered in depth for this study as they lie within the Little Wood Basin and this project focuses on the Big Wood Basin.


The economic base of the study area varies by county. In Blaine County, services provide the economic base (U.S. Department of Agriculture, Economic Research Service, 2004). The Wood River Valley is a tourism destination due to its proximity to outdoor pursuits including skiing and fishing, among others. The Sun Valley Ski Resort is a large draw to the area, averaging over 380,000 skier visits per year. Many residents of the area are part-time, which is reflected clearly in the classification of housing units. The 2010 Census indicates that 32% (4,766) of housing units in Blaine County are for “seasonal, recreational, or occasional use”. In Camas County, this value is 60% (207 units). By contrast, in Gooding and Lincoln Counties 1% (94) and 2% (45) of housing units are for occasional use, respectively (U.S. Census Bureau, 2010a).

Outside of Blaine County, all other counties in the study area are considered to be farming dependent (U.S. Department of Agriculture, Economic Research Service, 2004). Per the 2007 Census of Agriculture, the market value of agricultural products sold was over $600 million in Gooding County, over $100 million in Lincoln County, and over $10 million in Camas County. Despite not being characterized as a farming dependent county, in 2007 Blaine County produced a market value of over $26 million for agricultural products sold. All counties have both crop and animal operations (U.S. Department of Agriculture, 2007).

Another economic consideration is employment types by industry. In Gooding, over 25% of employment comes through the farm industry. The largest employment industry in Blaine County is accommodation and food service (14% of jobs) followed by construction and real estate, each at around 10% of jobs. In Lincoln County, farming and government each provide 23% of jobs. Likewise in Camas County, most jobs are in the farm or government sectors, with each representing about 16% of jobs (University of Idaho, 2013).


See Additional Resources for a list of references cited here.