LOCATION.--Lat 43° 35'39", long 115° 55'22"(Rev.)(NAD83), in SE1/4 NW1/4 SE1/4 sec.13, T.3 N., R.4 E., Elmore County, Arrowrock Dam quad., Hydrologic Unit 17050112, Boise National Forest, at Arrowrock Dam on Boise River, 14 mi east of Boise, and at mile 75.4.

DRAINAGE AREA.--2,216 mi², revised.

PERIOD OF RECORD.--October 1917 to September 1996 (discontinued). Published as "at Arrowrock", October 1917 to September 1962.

GAGE.--Water-stage recorder. Datum of gage is sea level, (levels by U.S. Bureau of Reclamation).

REMARKS.--Reservoir is formed by gravity-section concrete-arch dam, completed in 1915, and raised 5 ft in 1937; storage began in 1915. Controlled capacity, 286,600 acre-ft between elevation 2,940 ft and 3,216 ft at highest position of movable crest of spillway and 9.5 ft above sluice gate sill. Silt deposition at dam has raised the lower storage level and decreased the capacity of the reservoir. Prior to Oct. 1 1952, contents specified in publications of the U.S. Geological Survey were derived from original capacity table, and no silt corrections were made. Beginning Oct. 1 1952, contents were derived from revised table, which is the original table reduced by amounts varying from 347 acre-ft at elevation 2,974 ft to 5,000 acre-ft at elevation 3,085 ft and above. Water is used for irrigation in Boise Valley.

COOPERATION.--Gage readings and capacity table provided by U.S. Bureau of Reclamation.

EXTREMES FOR PERIOD OF RECORD.--Maximum contents observed, 301,200 acre-ft May 29, 1948, elevation, 3,219.1 ft; no useable contents during period in each of several years when sluice gates were open and natural flow was passing through reservoir.