General

The San Angelo Project is in the immediate vicinity of the City of San Angelo in west-central Texas. Bureau of Reclamation development provides for the construction of Twin Buttes Dam and Reservoir, a headworks at Nasworthy Reservoir, and an irrigation and distribution system to serve a project area of about 15,000 acres. The project provides for the integrated operation of Twin Buttes Reservoir with the existing Nasworthy Reservoir to meet the municipal water requirements of San Angelo; and permits irrigation of the project lands and provides flood protection, recreation, and fish and wildlife benefits.

History

Early History

The Concho River area was first settled about 1870 by cattlemen who were followed by farmers. Although much of the area is still devoted to grazing, most of the land now cultivated was first broken and farmed between 1880 and 1910. The last of the State-owned lands went into private ownership soon after 1910.

Except for the city of San Angelo, the Concho River watershed is sparsely settled. The city owes its origin to the establishment in 1868 of a military post, Fort Concho, for protection against Indians. At the same time, the settlement which became San Angelo was developed across the river on the North Concho.

Investigations

In 1939, the Corps of Engineers reported favorably upon the construction of the O.C. Fisher Dam and Reservoir on the North Concho River for the primary purpose of flood control. Construction of the reservoir by the Corps of Engineers was authorized by the Congress in the Flood Control Act of August 18, 1941, and construction of the reservoir was completed in 1952. Subsequent to the 1939 report by the Corps of Engineers, the Bureau of Reclamation initiated investigations for developing an irrigation plan for using Concho River water in excess of the municipal and industrial needs of the area.

The Bureau of Reclamation completed a draft of a report on the North Concho Unit of the San Angelo Project in July 1946. This report set forth a plan for irrigating 12,000 acres of land. During the discussions of this plan with local interests and the Corps of Engineers in June and July 1946, the city of San Angelo requested that a portion of the conservation storage be reserved to furnish municipal and industrial wate to the city. The investigations by the Bureau of Reclamation were then directed primarily toward determining the amount needed by the city and the water supply that would remain available for irrigation use.

In September 1954, the San Angelo Water Supply Corporation, acting for the city, asked the Bureau of Reclamation to reopen the investigations of the water resources potential of the Concho River to recognize recent local developments.

These studies proposed a dam and reservoir on Middle and South Concho Rivers at the Twin Buttes site that could offer virtually full regulation of the South and Middle Concho watershed above Nasworthy Reservoir. The reservoir would yield, when operated jointly with the O.C. Fisher Reservoir, sufficient water to meet all foreseeable municipal requirements and would provide water to irrigate 10,000 acres of land. On the basis of these findings, the project was authorized for construction.

Authorization

The project was authorized by Public Law 85-152 on August 16, 1957 (71 Stat. 372).

Construction

Construction of Twin Buttes Dam was begun in 1960 and completed in 1963. Construction on the Main Canal and laterals was done at the same time; all facilities were completed in 1963.

Following completion of construction, severe drought conditions prevailed in the Twin Buttes Dam watershed until April through August 1971, when above normal rains broke the drought and brought substantial inflow to Twin Buttes Reservoir. Studies of seepage data resulted in a pilot grouting contract which was awarded in June 1976 and completed in March 1977. Subsequent to the grouting, a foundation cutoff wall was installed through a large section of the upstream toe of the dam, between 1996 and 1999.

BENEFITS

Irrigation

The San Angelo Project brings 15,000 acres of land under irrigation. Because of the severe drought conditions experienced following completion of construction, it was not possible to start irrigating until March 1972, when the development period began. Following the development period, bringing irrigation water to project lands increased the yield per acre and increased the variety of crops that can be grown. Principal crops are cotton, alfalfa, grain sorghum, oats, pasture, and grain.

Municipal and Industrial Water

San Angelo has grown rapidly since 1940 and is the most important population center in the Concho River Basin. The San Angelo Project assures an adequate water supply for the city until the year 2010, based on estimated population growth.

Flood Control

The North and South Concho Rivers, which join in the city of San Angelo, have produced numerous floods that resulted in extensive damage. The floods have occurred primarily as high peak, flash floods and have not been subject to forecast. Twin Buttes Reservoir provides flood control storage capacity of 454,370 acre-feet plus surcharge capacity of 446,950 acre-feet for regulation of floodflows. This flood storage, combined with spillway and outlet works capacities, is sufficient to protect against an inflow design flood having a peak of 725,000 cubic feet per second and a 3-day volume of 825,000 acre-feet.

Streamflow regulation provided by the project reduces agricultural losses in crops, livestock, and farm improvements, minimizes land damage, and protects recreation facilities. Damage to urban and suburban property is reduced or eliminated.<?p>

Recreation and Fish and Wildlife

The arid, relatively barren nature of the area limits recreation opportunities. Consequently, surface-water impoundments suitable for fish and wildlife and for recreational uses make an important contribution. Twin Buttes Reservoir also allows maintaining Nasworthy Reservoir at a relatively constant level, enhancing its recreation value.

Plan

Twin Buttes Dam and Reservoir is immediately upstream from the existing Nasworthy Reservoir, about 6 miles southwest of San Angelo. Twin Buttes Dam controls the flows of the South and Middle Concho Rivers and Spring Creek.

Irrigation water is released from Twin Buttes Reservoir into Nasworthy Reservoir, where it is diverted by project headworks into the 16-mile-long Main Canal. To assure the uninterrupted delivery of municipal water, irrigation releases are made from Twin Buttes Reservoir only when the water in storage exceeds 50,000 acre-feet. Water for municipal use is released as required from O. C. Fisher Lake or Twin Buttes Reservoir to flow down the river channels for diversion within the city limits.

Twin Buttes Dam and Reservoir

Twin Buttes Dam is a 134-foot-high zoned earthfill structure with a crest width of 30 feet and a crest length of over 8 miles. The embankment contains 21,407,330 cubic yards of material. An equalizing channel with a bottom width of 250 feet was excavated between the South Concho River and Spring Creek drainage areas. The outlet works for the dam, located near the left abutment, include an approach channel from the Middle Concho River. The spillway structure, on the left abutment, is an uncontrolled ogee weir 200 feet in width. A concrete chute section, 320 feet long, extends from the crest to a stilling basin. Water from the stilling basins of the spillway and outlet works discharges into a common channel.

Twin Buttes Reservoir has a total capacity of 640,568 acre-feet with a surface area of 23,508 acres. Active capacity of the reservoir is 632,214 acre-feet.

Headworks and Main Canal

The Main Canal headworks was constructed on the eastern edge of Lake Nasworthy. The headworks consist of a semicircular intake structure containing ten 4.5- by 5.5-foot intake openings with fish screens leading into a 5- by 6-foot concrete conduit, and an outlet transition connecting to the concrete-lined Main Canal. Flows are controlled by a 5-foot-square motor-driven slide gate mounted at the upstream end of the conduit.

The 15.9-mile-long Main Canal has an initial capacity of 165 cubic feet per second. The canal follows an easterly and northeasterly direction to the project lands east of San Angelo. A 39-mile system of concrete-lined laterals completes the distribution of irrigation water.

Overview

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Other

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