Arrowrock Dam Research Paper


Arrowrock Dam was completed in 1915 by the Bureau of Reclamation and during a period of time it was the highest dam in the world with 350 feet of height. In 1937 the height of the dam was increased for 5 feet and the downstream face of the dam was resurfaced. Arrowrock dam is said to be one of the three instream storages dams situated on the Boise River.

In this paper I will provide the description of the Arrowrock dam, as the essential division of Arrowrock Division, as well as reveal the significance of the dam and its economic impact in Idaho.

Arrowrock Dam Historical Review

During first years of its existence, Arrowrock dam had a great influence on the city of Boise and its citizens. With the construction of the Dam upstream few years later, the valley obtained a water surplus allowing for year around irrigation.

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The Arrowrock Dam consruction project changed the city of Boise and the Boise Valley by allowing many more and larger farms in the territories that were in the past could not afofr themselves enough water to dampen an average garden. In 1900, farm population of the valley was about 1,600, the inadequate water supply meant that the region had met its maximum population and a decline of the city inevitable. By 1920, the number of farms had increased almost in three times due to Boise Project and construction of the Arrowrock Dam, in particular. In 1930, the population of farms raised to 15,400 and by 1940, farms were already inhabited by 16,000 residents. At present moment, Boise Project related irrigation construction holds the responsibility for 276,000 irrigated acres in the Arrowrock division, which is in total 8,500 farms.

Due to the dramatic rise of irrigable property, Boise city grew toward the hinterlands and absorbed some smaller urban communities along with creating some new. The irrigable land abundance brought new citizens and influenced the development of the city and the surrounding valley. Nowadays it is very hard to imagine the Boise landscape without the irrigation impact. Irrigation permitted Boise to develop and grow in all directions and at elevations that were not previously accessible to any significant Boise River water amount. This is what Pat Takasugi, Director of the Idaho Department of Agriculture said on this regard, “If you look at the ground between here and Mountain Home, the rest of the valley would look like that without the [Boise] project.” Of course, urban communities were confined to definite areas with only the easiest access to water and little but were separated by the desert. In accordance with Boise Project Manager Paul Deveau, before irrigation on the Bench, “there were hardly any people here.” Between years 1880 and 1910, the population of Boise City raised from 1,899 to 17,358 a main part of that because of irrigation related development. Deveau attributes much of the growth and appearance of the total valley, as it is known to us, to the New York Canal.

Distant agricultural communities were not the only areas that experiencied growth. The Boise city reaped the rewards of having water that was available above the Bench with the development of commercial and residential districts in the south of the city. Few Boise area maps before around 1910 even depict inhabitants south of the Boise River presence, as well as on the Boise Bench. As it was shown on a map of year 1917 of Boise city by the Intermountain Map Company, just a few years after the completion of the Boise Project an the Arrowrock dam construction, different commercial, agricultural, and residential developments covered the Boise Bench. And even though it can be claimed that numerous factors influenced the development of the region, extensive irrigation opportunities laid the foundation for it.

Arrowrock Dam Long Term Economic Impact

Arrowrock dam is situated in the Pacific Northwest Region, in the state of Idaho, in the Boise County. It is concrete thick arch situated 13 miles east from Boise on the Boise River. The construction of the dam lasted 4 years from 1911 till 1915, and later it was modified in the period 1935-1937. Dam’s crest elevation is 3216 ft, top of parapet elevation is 3219.75 ft, structural height is 350 ft, hydraulic height is 257 ft, crest length is 1150 ft and width -15.5 ft, base width is 223 ft and concrete volume of the dam is 636 000 cu yd. Drainage area of Arrowrock dam is 2210 sq mi and maximum water surface is 3224.1 ft. The foundation of the dam is hard, steamy, has a wide zone of granite porphyry, capped in left abutment with 50-foot basaltic lava flow.

From the very beginning it played an outstanding role in people’s lives of Idaho, as it could store more then 200 000 acre feet of irrigation water hat could be supplied to 340 000 acres of farmland in he region, where the annual level of rainfall was just 11 inches.

Arrowrock dam and reservoir are operated for flood control and irrigation purposes along with other reservoirs of the Boise River. Generally speaking the water is being stored in Arrowrock reservoir during winter and spring period in accordance with forecasted flood control and runoff requirements. Starting with April, the water is being released for the irrigation purposes from Arrowrock dam and this process lasts until early September.

Arrowrock Dam can be fairly called the example of the construction with long-term economic impact in Idaho that lasts already almost for a century.

The Boise county land with an area almost 400 000 acres, had always been very dry and even desert land with the small exception of near river territories. Bureau of Reclamation provided facilities that turned the desert lands into productive agricultural area with numerous thriving towns and cities. The most part of sweet corn seed is grown in this area. Boise lands also produce large amount of pasture, sugar beets, potatoes, corn, grain, alfalfa seed and hay, apples, onions, etc. And as forage and hay crops support large number of beef and diary cattle, cattle breeding is also very spread and thriving.

Arrowrock Dam is situated near Boise National Forest Mountains. Arrowrock Reservoir and recreation management area are used by recreationists, as these facilities provide the variety of settings.
Besides the purposes of irrigation, Arrowrock Reservoir is extensively utilized for the purposes of windsurfing, canoeing, fishing and boating.

The vegetation that surrounds Arrowrock Dam is mainly sagebrush-steppe. There are riparian vegetation small pockets along the shoreline. Riparian vegetation can be especially noticed in the place where tributaries enter the reservoir. The territories around reservoir is predominantly inhabited by exotic annual weds and grasses.

Many riparian species that are no native to the region become naturalized along the Boise River. These species include black locust, silver maple, Siberian elm, Russian olive and box elder. Along the Boise River can be also found 150 species of birds, 37 species of mammals, and many species of amphibians and reptiles. Arrowrock Reservoir serves as an essential wintering and breeding ground for many waterfowl species. Canada geese and mallards are said to be year-round waterfowl residents.

During the last decade a small percentage of employment in the Boise region is associated with farming. The percentage of farm-related employment within individual counties is not more then 7-8%. Therefore, statistical data from Bureau of Economic Analysis indicates the decrease of farm-related incomes and work force.


In the conclusion I would like to summarize that Arrowrock Dam was constructed between 1911 and 1915 on the Boise River. In 20 years its height was increased for 5 feet in the process of the reconstruction from 1935 till 1937. Dam’s primary purpose was the irrigation of the nearest areas, as lack of water supply was the greatest problem of the region. The average level of precipitations was about 11 inches per year. After the construction of the Dam, the economical situation in the region significantly improved due to increase of water supply ad subsequent development of agricultural sector. The amount of inhabitants in the Boise region increased in almost fifteen times, which promoted economic prosperity of the area.

Speaking about Dam’s functioning, it is necessary to mention that the water is being stored in Arrowrock reservoir during winter and spring period in accordance with forecasted flood control and runoff requirements. Starting with April, the water is being released for the irrigation purposes from Arrowrock dam and this process lasts until early or middle September.

Arrowrock Dam has also a positive impact on the flora and fauna of the area, which found this place very favorable. Even though compared to the beginning of the century, nowadays farming is not so popular and do not bring much profits, the Arrowrock Dam continue to positively influence and supply the region with the most essential substance for living- water.

“Arrowrock Dam. General Statistics”. Reclamation. Managing Water in the West. March, 2 2009
“Affected Environment and Environmental Consequences”. Apr. 2004. March, 2 2009
Hester, Johnny. Reinventing Boise. “Changing Influences on Boise’s Growth Pattern as Exhibited Through Maps, 1863-1930”. March, 2 2009
Mitchell, Kelly A. “And the River Runs On…” Dec. 2004. March, 2 2009
Long, Roger, B. and Zhang, Jinghua. “Economic Causes of Non-Point Pollution in the Boise River”. University of Idaho. College of Agriculture. March, 2 2009



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