San Angelo Project

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. 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. Public Law 103-434, approved October 31, 1994 increased the irrigable acreage from 10,000 to 15,000 acres with no change in the quantity of water available. 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. 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. For specific information about recreational opportunities at Twin Buttes Reservoir click on the name below. http://www.recreation.gov/detail.cfm?ID=1171 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 (http://www.usbr.gov/dataweb/dams/tx00022.htm) has 454,370 acre feet of capacity assigned to flood control. and a surcharge capacity of 446,950 acre-feet for regulation of flood flows. This flood storage, combined with spillway and outlet works capacities, is sufficient to protect against the inflow design flood with a peak of 725,000 cubic feet per second and a 3-day volume of 825,000 acre-feet. The San Angelo Project has provided an accumulated $1,318,000 in flood control benefits from 1950 to 1999. 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. The San Angelo Project is a multipurpose project in the Concho River Basin of west-central Texas. In a region historically known for intermittent droughts and floods, the project provides protection against both weather extremes. The San Angelo Project supplies water for municipal and industrial use as well as irrigation agriculture. Project facilities also provide flood control. Since completion of the project, the region has prospered. The San Angelo Project is located in west-central Texas near the city of San Angelo. The project lies approximately 200 miles northwest of Austin and San Antonio and about the same distance southwest of Ft. Worth. The primary features of the project area are the Twin Buttes Dam and Reservoir, located six miles southwest of the city of San Angelo. The dam and reservoir capture and store the waters of the Middle Concho River, Spring Creek, and the South Concho River which are part of the Concho River Basin. Other features of the project include diversion headworks at Nasworthy Reservoir, constructed and operated by the city of San Angelo, and an irrigation and distribution system which serves about 12,000 acres of project land.(1) Operated in conjunction with nearby O.C. Fisher Dam and Lake, constructed by the U. S. Army Corps of Engineers, and Nasworthy Reservoir, Twin Buttes Reservoir and Dam strives to meet the municipal water needs of San Angelo, provide flood protection, and irrigate project lands. The Concho River Basin encompasses approximately 5,900 square miles including all or part of 14 counties.(2) The North and South Concho Rivers join within the city limits of San Angelo to form the Concho River. The Middle Concho and Spring Creek join the South Concho River a few miles upstream of the city. From San Angelo, the Concho River flows eastward and empties into the Colorado River of Texas. The project area has a semiarid climate with an annual average precipitation of about 21.5 inches, though this varies from year to year. The average temperatures range from 83.7 degrees in July to 46.3 degrees in January, but temperature extremes of 111 degrees and one degree have been recorded.(3)The growing season usually lasts from late March to early November. In 1629 and 1632, Franciscan missionaries from New Mexico traveled to the San Angelo area at the request of Jumano Indians. The missionaries stayed in the area for a couple of months baptizing the Jumano in the Concho River. Later, Spanish settlers returned periodically to hunt and trade with the Jumano and search for Concho pearls produced by freshwater mussels.(4) In 1684, Juan Domingo de Mendoza and his expedition camped at the confluence of the Concho. After the Mendoza party continued on their way, the region remained the exclusive domain of Native Americans until after the Civil War. Permanent settlement began in 1867, with the establishment of Fort Concho between the Middle and South Concho Rivers. The military post provided protection for settlers from Native American attacks. About the same time as the development of Fort Concho, the village of Santa Angela was founded along the banks of the North Concho. Santa Angela eventually became the town of San Angelo. In 1882, San Angelo became he county seat of Tom Green County when a flood washed away the former county seat of Ben Ficklin.(5) Ranchers first settled the Concho River region with farmers following close behind. Most of the region is used for grazing, but the land currently cultivated was first broken and farmed between 1880 and 1910. Except for the city of San Angelo, the Concho River watershed remains sparsely settled. To meet growing municipal needs, the city of San Angelo constructed Nasworthy Reservoir on the South Concho River below its confluence with the Middle Concho River in 1930. Held by a small earthfill dam, Nasworthy Reservoir provides 12,400 acre-feet of storage for municipal use. However, the continued growth of San Angelo necessitated the construction of additional water conservation works. In 1939, the U.S. Army Corps of Engineers reported favorably on the construction of O.C. Fisher Dam and Lake on the North Concho River for flood control. Congress authorized construction of the structures in the Flood Control Act of August 18, 1941. Subsequent to the Corps report, the Bureau of Reclamation began an investigation into the development of an irrigation plan for water which exceeded the municipal and industrial needs of the region. The study resulted in a request by Reclamation for a modification of the plan for O.C. Fisher Lake to included 80,400 acre feet of conservation storage.(6) The Corps made the modification to the reservoir plan. Construction was completed in 1952.(7) During June and July of 1946, the city of San Angelo expressed its desire to Reclamation that part of the conservation storage in O.C. Fisher Lake be reserved for municipal and industrial use. As a result of this request, Reclamation investigations focused on determining the amount of water needed by the city and the amount available for irrigation use. In July, Reclamation completed a draft report on the North Concho Unit of the San Angelo Project. The study concluded that 12,000 acres of land could be irrigated with water supplied by the conservation storage of the O.C. Fisher Lake. Additional water could be obtained from Nasworthy Reservoir with the addition of flash boards to the original structure. During this time the Upper Colorado River Authority purchased the right to 80,400 acre-feet of conservation storage in O.C. Fisher Lake. In November of 1949, representatives of the city of San Angelo, the Upper Colorado River Authority, and Reclamation reviewed the findings of Reclamation`s investigation. During the meeting the Authority requested the postponement of further Reclamation investigations until the city and the Authority reached an agreement concerning the use of the conservation storage in O.C. Fisher Lake. In January of 1953, the consulting firm of Forrest and Cotton, from Dallas, Texas, completed the report `The Surface Water Supply of the San Angelo Area.` The study concluded that sufficient water supplies existed in the North and South Concho Rivers to meet foreseeable municipal needs and irrigate a substantial amount of land. This report also recommended that the city and the Authority reach an agreement regarding where surplus stored waters could be used for irrigation and to permit the integration of the operations of O.C. Fisher Lake and Nasworthy Reservoir. Additionally, the report suggested enlargement of Nasworthy Reservoir to 85,000 acre feet. As a result of the study and previous Reclamation findings the Authority gave the city full and unrestricted use of the conservation storage previously purchased by the Authority.(8) However, San Angelo voters rejected the enlargement plan for Nasworthy Reservoir and called for a plan which would more fully meet the needs of the region. In September of 1954, the San Angelo Water Supply Corporation (SAWSC), acting on behalf of the city, asked Reclamation to reopen investigations. The resulting reconnaissance studies designed a plan which optimized the water resources of the Concho River Basin. The proposed project called for the creation of a dam and reservoir on the Middle and South Concho Rivers above Nasworthy Reservoir at the Twin Buttes site. The construction of a dam and reservoir at this site would maintain the surface of Nasworthy Reservoir at a constant level, store enough water to meet city municipal and industrial needs, and irrigate 10,000 acres. Reclamation estimated that the construction cost of the project could be repaid within a fifty-year period. The findings were presented to the city commission on October 22, 1954, and the commission advised Reclamation that they considered the project economically feasible. Detailed investigations of the project were initiated in December 1954 as part of the Texas Basins Project.(9) The Texas Basins Project was an investigation into the development of a statewide water plan through the construction and operation of an interbasin water supply works that Texas could use to supply water to meet anticipated urban and industrial growth as well as offset the predicted loss of most of the state`s ground water sources resulting from irrigation development.(10) The proposed project included a canal along the Gulf Coast, and distribution and drainage facilities extending from the Sabine River in the eastern part of the state to the Lower Rio Grande. The San Angelo Project superceded the San Angelo Unit, Colorado Division of the Texas Basins Project. The Texas Basins Project never developed beyond initial investigations. The SAWSC, which is responsible for municipal and industrial features of the project, entered into contracts with Reclamation for development of a multipurpose dam in October of 1955. In December of the following year farmers in the proposed project area created the Tom Green County Water and Improvement District No. 1(TGCWC & ID). TGCWC & ID is responsible for the agricultural aspects of the project. The San Angelo Project was authorized by Public Law 85-152 on August 16, 1957. The repayment contract executed on April 25, 1959, stipulated that the SAWSC would repay Reclamation $13,189,000 for the construction of Twin Buttes Dam and Reservoir. Executed June 18, 1959, the terms of the TGCWC & ID contract required the corporation to payback $4,000,000 in construction costs over a 40-year period exclusive of a ten-year development period which followed the first deliveries of water to project lands. During June of 1959, TGCWC& ID created a 10,000 acre irrigation district for the project and contracted with Reclamation for the construction of irrigation facilities. Passage and approval of the public works appropriation bill of $ 4,239,000 for the project came in August of 1959. In February of 1960, a definite plan for the project was approved and construction began in May. The development plan for the San Angelo Project called for construction of Twin Buttes Reservoir and Dam, and a diversion headworks at the south end of Nasworthy Dam, and an irrigation and distribution system. Working in conjunction with the existing O.C. Fisher Dam and Lake and Nasworthy Reservoir, Twin Buttes Dam and Reservoir would provide the water needed to meet anticipated growth in the region, provide flood control, and some recreational benefits. The construction of the Twin Buttes Dam necessitated the relocation of the Panhandle Railroad and the Santa Fe Railroads which crossed the axis of the damsite. Construction crews relocated the Santa Fe Railroad around the north end of the dam and the Panhandle line around the south end of the dam.(11) In addition to the railroad relocation, dam construction required the relocation of a portion of a road. Construction bids for Twin Buttes Dam opened on March 17, 1960. H.B. Zachry Company of San Antonio, Texas was awarded the contract on April 1, 1960, with the low bid of $11,836,428. Clearing operations of the damsite began on May 9, 1960, which required the grubbing of approximately 268 acres covered with vegetation. After chaining, piling, burning, and handpicking the site, construction crews then cleared topsoil and any remaining vegetation using a root plow and root rake to ensure the removal of all organic material. On June 7, 1960, stripping of the dam foundation began with the removal of all topsoil, plant life, and organic materials to a depth of six to eighteen inches.(12) In all, 313 acres were stripped. Excavation of the spillway and placement of material for the embankment began on June 22, 1960. That same day groundbreaking ceremonies for the project were held. The excavation of the cutoff trench in the dam`s foundation commenced on June 28, 1960. Positioned 100 feet upstream of the dam`s axis the trench extended across the river valley sections for 2.5 miles with an average depth of 25 feet. Of the 743,612 cubic yards of material excavated and used in dam construction.(13) Stripping of the spillway and outlet works sites areas also commenced in June. On July 9, 1960, installation of the embankment toe drains began. Installation of drains occurred in all areas of the dam foundation below elevation 1,930. The toe pipe drains consisted of 12 and 18-inch diameter perforated, asbestos-bounded, corrugated-metal pipe. Installed on both sides of the three streams, the outfall pipe was of same dimensions and material but not perforated. Excavation of materials began in borrow areas B, C, and D on July 15. Borrow areas B and D were located upstream from the damsite and borrow area C, located in the flood plain along the right side of the South Concho River, was the only downstream area utilized for the procurement of construction materials. The river basins of the three filling streams have two different levels of dead storage and are permanently separated by the hilly terrain, which required the construction of a 250-foot channel between the South Concho River and the Middle Concho and Spring Creek drainage area to equalize the surface level of Twin Buttes Reservoir. After releases either through the diversion works on the southern pool or the spillway on the northern pool, water transported through the channel to equalize the surface level of the Reservoir. Excavation of the equalizing channel began on August 4, 1960. The first concrete placements in the outlet works occurred on November 30, 1960, using concrete mixed from materials excavated in the project area.(14)Riprap bedding placement, using materials procured from under part of borrow area B and the stream bed of Spring Creek, began on December 21, 1960. Between elevation 1,960 and the crest of the upstream face of the dam embankment construction crews placed a three foot layer of riprap. A small amount of placement also occurred below elevation 1,875 on the downstream face of the dam next to structures in the approach outlet channels of the spillway, outlet works, and on the slopes of the embankment ramp for Knickerbocker Road. On the last day of the year the first concrete placements were laid in the spillway. Six days later grouting of the spillway began. The second day of February 1961, saw the first concrete placements in the equalizing channel. Completion of relocation of the Santa Fe and Panhandle rail lines occurred on the last day of February. While construction on the dam continued, Reclamation awarded the contract for clearing the reservoir site. Joe York and Son of Brackettville, Texas received the contact with the low bid of $89,000 in March 29, 1961. Clearing of the damsite began on April 17. Clearing crews encountered minor difficulties performing their duties because Reclamation gave the original owners of the land the right to keep all improvements until completion of the dam.(15) The preservation of fences and the presence of livestock in the area made clearing a cumbersome task. Construction at the damsite continued with completion of all grouting on April 8, 1961, and actual riprap placement started on April 25. Problems with the riprap subcontractor resulted in the cessation of placement activities on July 12. Construction did not resume until August 1, 1961, when H.B. Zachry assumed responsibility for riprap placement. Reclamation also awarded H.B. Zachry the contracts for the construction of the main canal on May 24, 1961, with a low bid of $1,487,994 and the irrigation distribution system on August 30, 1961, with a low bid of $985,173.50. Meanwhile, completion of the equalizing channel bridge and reopening of Knickerbocker Road occurred on June 9, 1961. On June 13, 1961, crews diverted Middle Concho River into Spring Creek and began work on the closure section across the Middle Concho River. Construction of the main canal commenced on June 20 and on September 28 work began on the irrigation distribution system. By the spring of 1962, contractors began wrapping up the clearing and construction operations of the project. On the last day of March, Joe York & Son finished clearing the reservoir site. On May 3 the final concrete placements were made in the spillway. On June 11, 1962, the work on the closure section of Spring Creek began, as did the closure section across the South Concho River on August 8. Construction continued on the project through the winter months of 1962 and by 1963 the project neared completion. Clearing and construction contractors of the project features encountered no major labor disputes or weather problems. All work on the dam was completed and accepted on February 13, 1963, with all project facilities completed later that year.(16) An earthfill structure, Twin Buttes Dam on the Middle Concho and South Concho Rivers is 8.2 miles long with a maximum height of 130 feet the Middle Concho River and 30 a foot wide crest. The total volume of the dam 21,442, 000 cubic yards.(17) The materials used in the construction of the structure were categorized into four different types. Zone 1 materials consisted of selected clay, silt, and sandfill which were used for the main portion of the dam. Materials classified as zone 2 materials consisted of sand, gravel and processed gravel and cobble fill. Construction of the drainage blanket portion of the dam used zone 2 materials. Materials designated as zone 3 materials included gravelly materials excavated during construction of the spillway and outlet works and were used in the dam`s foundation. Zone 4 materials consisted of caliche, a cement like type of soil, were used in the construction of the equalizing channel. Twin Buttes Reservoir has a controlled capacity of 632,220 acre-feet which includes 20,000 acre-feet for 100 years of sediment deposition and 50,000 acre-feet of conservation storage for municipal water supply. When the conservation storage level is less than 50,000 acre-feet, no water may be used for irrigation. A conservation storage capacity of 127,850 acre-feet is designated for joint use of irrigation, and municipal and industrial supply; and 454,370 acre-feet of capacity are reserved for flood control.(18) The irrigation facilities of the project include a headworks near the south end of Nasworthy Dam, feeding into a main irrigation canal with a distribution system composed of laterals, siphons, and culverts under the canal and bridges over it. The diversion at Nasworthy directs water flows into the main irrigation canal which travels northeast past San Angelo to the project lands. Lined with concrete the 15.9 mile long canal has a capacity of 165 cubic feet per second.(19) In all, the concrete-lined lateral distribution system totals 39 miles.

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 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. 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.

Contact

Title: Area Office Manager
Organization: Oklahoma-Texas Area Office
Address: 5316 HWY 290 W, Suite 110
City: Austin, TX 78735-8931
Phone: 512-899-4150

Contact

Title: Public Affairs Officer
Organization: Great Plains Region
Address: 2021 4th Avenue North
City: Billings, MT 59101
Fax: 406-247-7604
Phone: 406-247-7610

Contact

Organization: San Angelo Water Supply Corporation
Address: PO Box 1630
City: San Angelo, TX 76902
Phone: 915-655-9140

Contact

Organization: Tom Green County Water Control and Improvement District No 1
Address: PO Box 488
City: Veribest, TX 76886
Phone: 915-655-7601

Contact

Organization: San Angelo, City of
Address: PO Box 1751
City: San Angelo, TX 76902-1751
Phone: 915-657-4241

PROJECTS & FACILITIES

San Angelo Project

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