Purpose: By integrated operation with the Nasworthy Reservoir, located immediately downstream on the Middle Concho River, and the San Angelo Reservoir, located on the North Concho River, to satisfy municipal water requirements for the city of San Angelo, to permit irrigation of project lands theretofore unirrigated, and to provide flood protection and recreational opportunities. Location: On the Middle Concho River, Spring Creek, and the South Concho River, about 9 miles (14.5 kilometers) southwest of the city of San Angelo in west-central Texas. Constructed: 1960-1963 Drainage area:, 472 square miles (6, 402 square kilometers) Annual runoff: Average (1916-1957): 88, 200 acre-feet (108, 800, 000 cubic meters) Minimum (1952): 7, 400 acre-feet (9, 128, 000 cubic meters) Reservoir (Twin Buttes) Surface area: 23, 508 acres at top of flood control pool, elevation 1969. 1 (9, 513 hectares at elevation 600.18 meters) Maximum water surface: Elevation 1985.0 (605.03 meters) Active capacity: 632, 214 acre-feet (779, 836, 000 cubic meters) Dam Function: The dam extends across three streams--Middle Concho River, Spring Creek, and South Concho River--and impounds their waters to form a common reservoir. A low saddle connects the Middle Concho River and Spring Creek portions of the reservoir, and a connecting channel has been excavated through a higher ridge between Spring Creek and South Concho River just upstream from the dam. Type: An essentially homogeneous, rolled earthfill embankment with some zoned portions and with slope protection consisting of 3 feet of riprap on the upstream face and a 10-foot blanket of caliche material on the downstream face. Volume: 21, 442, 000 cubic yards (16, 393, 000 cubic meters) Dimensions: Structural height: 134 feet (40.84 meters) Height above streambed: 130 feet (39.62 meters) Top width: 30 feet (9.14 meters) Maximum base width:. 780 feet (237.7 meters) Crest length: 42, 460 feet (12, 942 meters) Crest elevation: 1991.0 (606.86 meters) Spillway Location and type: Uncontrolled reinforced-concrete overflow spillway in left abutment of dam with a chute and stilling basin discharging into Middle Concho River. Crest width: 200.0 feet (60.96 meters) Crest elevation: 1969. 10 (600.18 meters), or top of flood control pool Capacity: 47, 300 second-feet at maximum water surface elevation, 1985.0 (1, 339.4 cubic meters per second at elevation 605.03 meters) Inlet channel: A curved channel excavated in the left abutment, having a bottom width of 200 feet (60.96 meters), side slopes of 2 to 1, and floor at elevation 1964.0 (598.63 meters) Inlet structure: A reinforced-concrete structure 200 feet wide and 70 feet long (60.96 by 21.34 meters), with flared inlet walls and an apron which extends 40 feet upstream into the inlet channel. Floor is at elevation 1964.00 (598.63 meters), and the uncontrolled ogee crest at elevation 1969.10 (600.18 meters). Spillway--Continued Chute and stilling basin: A vertical curving reinforced-concrete chute 200 feet wide and Outlet Works 354 feet long (60.96 by 107.90 meters); and a reinforcedconcrete stilling basin 200 feet wide and 96 feet long (60.96 by 29.26 meters), with walls 45.5 feet (13.87 meters) high and with chute blocks at the upstream end and a dentated sill at the downstream end. Floor of stilling basin is at elevation 1849.0 (563. 58 meters). Location and type: A three-barrel conduit type at the left abutment, with stilling basin discharging into an outlet channel that joins with the spillway outlet channel to carry the combined flows to the Middle Concho River. Sill elevation of intake structure: 1885.0 (574.55 meters) Capacity: 25,000 second-feet with reservoir water surface at top of conservation storage, elevation 1940. 2 (707.9 cubic meters per second at elevation 591.37 meters); 35, 700 second-feet with reservoir water surface at maximum elevation 1985.0 (1,010.9 cubic meters per second at elevation 605.03 meters); for conservation releases, 200 second-feet with reservoir water surface at elevation 1894.0 and 400 second-feet with reservoir water surface at elevation 1912.0 (5.66 cubic meters per second at elevation 577.29 meters and 11.33 cubic meters per second at elevation 582.78 meters). Approach channel: An excavated channel about 1, 900 feet long with bottom at elevation 1884, a bottom width of 100 feet, and 2 to 1 side slopes (579.12 Intake structure: A rectangular reinforced-concrete structure 96 feet wide, 46 feet long, and 51 feet high (29.26 by 14.02 by 15.54 meters), with three bellmouthed entrances, located near upstream toe of dam. Structure is protected by trashracks on three sides and the top. Control gates: Three 12- by 15-foot (3.658- by 4. 572-meter) fixed-wheel gates upstream from three 12- by 15-foot (3.658- by 4.572-meter) top-seal radial gates in gate chamber located near crest of dam. The radial gates are for regulation of flow and the fixed-wheel gates are for normal shutoff and emergency closure. A 2- by 2-foot (60.96- by 60.96-centimeter) auxiliary gate is provided as an integral part of each fixed-wheel gate for regulation of the small conservation releases. Control house: The controls for all gates are housed in a control structure located on the crest of the dam above the gate chamber. Conduit: A reinforced-concrete pressure portion consisting of three 15. 5-foot-diameter (4.72-meter) circular tubes extending from the intake to the gate chamber near the center of the dam; and a reinforced-concrete free-flow portion consisting of three 17- by 17-foot (5. 18- by 5. 18-meter) horseshoe-shaped tubes extending from the gate chamber to the chute which discharges into the stilling basin. Chute and stilling basin: A 180-foot-long (54.86-meter) vertical curving reinforced- Frontispiece. --Aerial view of left portion of Twin Buttes Dam showing completed spillway and outlet works. Water is backed into spillway and outlet channel from Lake Nasworthy. P825-523-1873. FOREWORD Technical records of design and construction are a series of publications which record the planning, design, construction, and initial operation of Bureau of Reclamation structures. This technical record of design and construction for Twin Buttes Dam is divided into three parts. Part I is devoted to general planning, historical information, a description of the features, a summary of costs, and geology. In part II there are three chapters covering the design of the various features and their components. Part III contains one chapter on contract administration and three chapters comprising a concise narration of construction operations and equipment installation. This technical record was prepared by the Technical and Foreign Services Branch of the Office of Chief Engineer in Denver, Colo., from final design reports submitted by the design branches, final construction reports and cost information submitted by the field offices, and various planning reports. Acknowledgment is gratefully made to the designers and field personnel for their contributions to this work. There are occasional references to proprietary materials or products in this technical record. These must not be construed in any way as an endorsement, as the Bureau cannot endorse proprietary products or processes of manufacturers or the services of commercial firms for advertising, publicity, sales, or other purposes. |