formance of work shall be in accordance with the Federal SEC. 2. Construction authorized by this Act shall be for the SEC. 3. There is hereby authorized to be appropriated such sums as may be necessary to accomplish the purposes of this Act. All costs heretofore or hereafter incurred in the modification of dams to ensure their safety from failure shall be allocated among the authorized purposes served by the dams and related reservoirs in accordance with standard cost allocation procedures: Provided, however, That costs allocated to irrigation shall be reimbursable to the extent of the water users' ability to repay as determined by the Secretary of the Interior in the light of their outstanding repayment obliga tions. DEERFIELD DAM Deerfield Dam, a feature of the Rapid Valley project, South Dakota, was completed in 1947. It is located on Castle Creek, approximately 27 miles west of Rapid City. The dam is a 133-foot-high zoned earthfill structure. The dam crest is 35 feet wide and 825 feet long. An uncontrolled, concrete, side-channel-type spillway is located at the right abutment of the dam. The reservoir capacity is 16,000 acre-feet when the water level is at the spillway crest. Deerfield Dam was constructed to supply water to approximately 8,900 acres of supplemental-service land. If the maximum probable flood were to occur, the capacity of the spillway and outlet works would be exceeded, and approximately 23,000 cubic feet per second would flow over the dam crest. Rapid erosion of the earth embankment would result, and the peak flow below the dam would probably exceed 700,000 cubic feet per second. The seismic analysis of Deerfield Dam indicates that the dam is capable of withstanding safely the maximum credible earthquake event. The proposed corrective action includes raising the dam 16 feet and modifying the spillway. The estimated cost of the work is $1,092,000 (based on January 1977 price level). Deerfield Reservoir and the downstream Pactola Reservoir are operated on a pooled storage basis. Derfield Reservoir is filled each spring. The water elevation is held high during the summer months for recreation and is drawn down following the irrigation and recreation season. The evacuated reservoir space is reserved for winter inflow to prevent use of the outlet works and spillway during the coldest winter months. LAHONTAN DAM Lahontan Dam, a feature of Newlands project, Nevada, was completed in 1915. It is located on the Carson River, 18 miles west of Fallon, Nev. The dam is a 162-foot-high zoned earthfill structure; the crest is 20 feet wide and 5,400 feet long.. The active storage capacity of 295,000 acre-feet when the water level in the reservoir is at the spillway crest can be increased to approximately 314,000 acrefeet by the installation fo flashboards across the two spillways. The project is designed to irrigate approximately 73,000 acres of fullservice land, including approximately 4,900 acres of Indian land. Lahontan Dam is incapable of storing or safely passing the maximum probable flood. Flows from such a flood would damage the already deteriorated concrete in the spillway chutes, cause the right abutment of the dam to slough, and ultimately, failure of the dam. The resulting breach in the dam would permit an uncontrolled peak discharge of approximately 275,000 cubic feet per second. The maximum credible earthquake event would cause substantial damage to Lahontan Dam but would not cause it to fail. Corrective action includes the rehabilitation of the spillways and the outlet works and the construction of a concrete curtain wall in the dam crest. The estimated cost is $5,070,000 (based on January 1977 price level). Until the corrective work can be accomplished, the amount of storage during the snowmelt runoff season has been restricted. HYRUM DAM Hyrum Dam, a feature of the Hyrum project, Utah, was completed in 1935. It is located on Little Bear River at the southwest corner of the town of Hyrum, about 10 miles south of Logan, Utah. The dam is a 116-foot-high rolled earthfill structure; the crest is 35 feet wide and 540 feet long. The active storage capacity of the reservoir is approximately 15,000 acre-feet. Hyrum project contains approximately 6.800 acres of supplemental-service land. Porous material was used to construct the top 5 feet of the dam. Even if the reservoir were empty at the start of the maximum probable flood, the water level in the reservoir would rise sufficiently to permit the water to saturate and flow through the porous material. The flowing water would cause rapid breaching of the embankment and, ultimately, failure of the dam. The seismic analysis of the dam has not been completed. The proposed corrective action includes the construction of an auxiliary spillway at an estimated cost of $810,000 (based on January 1977 price level). Until the corrective action is completed, the spillway gates are kept completely open throughout the winter months, until runoff forecasts indicate that low frequency, high-volume snowmelt runoff is not likely to occur. STONY GORGE DAM Stony Gorge Dam, a feature of the Orland project, California, was completed in 1928. It is located on Stony Creek, approximately 40 miles southwest of Orland. The dam is a 139-foot-high concerte slab and buttress structure. The dam crest is 9.75 feet wide and 868 feet long. Flow in the spillway at the center of the dam is controlled by three crawler gates. The active storage in the reservoir is approxi mately 50,000 acre-feet. The Orland project contains approximately 19.600 acres of full-service land. If the maximum probable flood were to occur, the capacity of the spillway and outlet works would be exceeded and the water level in the reservoir would rise 4 or 5 feet higher than the crest. Overtopping the dam would result in the undermining of the buttresses and cause failure of the dam. The seismic analysis of Stony Gorge Dam indicates that no appreciable damage would result from the occurrence of the maximum credible earthquake event. The proposed corrective action includes the construction of an additional spillway and would cost an estimated $2,600,000 (based on January 1977 price level). Because Stony Gorge Ram can store or safely pass intermediatesize floods safely, no interim operating procedures have been mented. GIBSON DAM Gibson Dam, a feature of the Sun River project, Montana, was completed in 1927. It is located on the north fork of Sun River, 70 miles west of Great Falls. The dam is a 199-foot-high concrete arch structure. The 960-foot-long crest is 15 feet wide. A drop-inlet spillway is located near the left abutment. The active reservoir capacity is 105.000 acre-feet. The Sun River project contains approximately 91.000 acres of full-service irrigable land. If the maximum probable flood were to occur, the capacity of the spillway and outlet works would be exceeded, and the water level in the reservoir would rise 11 feet above the dam crest. Although the overflow would not cause the dam to fail, it would erode the abutments and weaken the dam. The seismic analysis indicates that the dam would not fail during the occurrence of the maximum earthquake event and that damage resulting from the event would not be major. The proposed corrective action includes the installation of aeration piers and protection of the left and right abutments by the installation of rockbolts. The estimated cost is $962,000 (based on January 1977 price level). To protect the dam from being overtopped by floods of less than a 100-year frequency, the reservoir storage is restricted until the snowmelt runoff recedes to less than 6,000 cubic feet per second. BLACK CANYON DAM Black Canyon Dam, a feature of the Payette division, Boise project, Idaho, was completed in 1924. It is located on Payette River, 5 miles northeast of Emmett, Idaho. The dam is a concrete gravity structure with a gated ogee spillway. The dam crest is 1,039 feet long. A powerpumping plant is located at the north end of the dam. The dam serves to divert water into the Black Canyon Canal. The Payette division contains approximately 60,000 acres of full-service land and approximately 54,000 acres of supplemental-service land. If the maximum probable flood were to occur, the dam would be overtopped by more than 3 feet, and the power-pumping plant build ing and penstocks, the utility building, the switchyard, and the new control building would be extensively damaged. No lives would be endangered. There is some concern about the capability of the dam to withstand the maximum credible earthquake event, and seismic studies have been initiated. The proposed corrctive action includes the construction of an auxiliary spillway. The estimated cost is $3,250,000 (based on January 1977 price level). The results of the seismic studies may indicate that additional corrective action is required. Because Black Canyon Dam is a diversion dam and the reservoir contains only limited storage, a change in operation would not eliminate the need for corrective action. ALTUS DAM Altus Dam and related earth dikes, features of the W. C. Austin project, Oklahoma, were completed in 1945. The dam is located on the north fork of Red River, approximately 18 miles north of Altus, Okla. The 110-foot-high concrete gravity dam is faced with granite masonry on both faces except for the downstream face of the overflow section. The crest is 10 feet wide and 1,112 feet long. The active storage capacity of the reservoir is 154,000 acre-feet. The W. C. Altus project furnishes water to approximately 47,000 acres of full-service land. If the maximum probable flood were to occur, the water level in the reservoir would rise approximately 12 feet above the crest of the dam, assuming that the existing dikes did not fail. The seismic analysis indicates that the dam and dikes would withstand safely the occurrence of the maximum credible earthquake. The proposed corrective action includes the lowering of the north dike, raising other dikes, and constructing one new dike. The estimated cost is $858,000 (based on January 1977 price level). To reduce the probability of serious freeboard encroachment at Altus Dam prior to the completion of corrective action, special arrangements for the receipt of precipitation and streamflow data have been made with the Weather Service and with the Corps of Engineers. We are cooperating with the corps in revising flood-control regulations for Altus Dam. THEODORE ROOSEVELT DAM Theodore Roosevelt Dam, a feature of the Salt River project, Arizona, was completed in 1911. The dam is located on the Salt River, approximately 30 miles northwest of Globe. The 280-foot-high rubblemasonry, thick-arch structure has two overfall spillways. Flows in the spillways are controlled by radial gates. The dam crest is 16 feet wide and 723 feet long. The active storage capacity of the reservoir is approximately 1,382,000 acre-feet. A powerplant is located at the base of the left abutment. The Salt River project contains approximately 263,000 acres of irrigable land, of which 238,000 acres are fullservice land. If the maximum probable flood were to occur, the water in the reservoir would rise approximately 2.5 feet above the top of the dam parapet and the dam would fail. The seismic analysis indicates that the dam is capable of withstanding the maximum credible earthquake event safely. The corrective action being considered at the present time includes raising the dam and modifying the spillway at an estimated cost of $1.209.000 (based on January 1977 price level). Under present operating restrictions, the normal water level in the reservoir has been reduced to protect against failure during intermediate floods. STEWART MOUNTAIN DAM Stewart Mountain Dam, a feature of the Salt River project, Arizona, was completed in 1930 and modified by the Bureau of Reclamation in 1936. It is located on the Salt River, approximately 41 miles northeast of Phoenix, Ariz. The dam, a thin-arch, concrete structure, has a concrete weir spillway at the left abutment. The dam crest is 8 feet wide and 1,260 feet long. The active capacity of the reservoir is approximately 70,000 acre-feet. A powerplant is located at the base of the right abutment. The Salt River project contains approximately 263,000 acres of irrigable land, of which approximately 238,000 acres are full-service land. In the event the maximum probable flood were to occur, Stewart Mountain Dam would not fail; the undermining effect of the highvelocity flows in the spillway, however, would cause severe damage to the right wall and floor slab of the spillway chute. A seismic analysis of Stewart Mountain Dam indicates that the dam could withstand the maximum credible earthquake event safely. The proposed corrective action includes raising the dam and modifying the spillway at a cost of $6,760,000 (based on January 1977 price level). To minimize damage to the spillway, discharges through the spillway should be restricted to a 105,000 cubic feet per second (approximately two-thirds of its capacity) until the corrective work has been completed. JACKSON LAKE DAM Jackson Lake Dam, a feature of the Minidoka project, Idaho-Wyoming, was completed in 1911 and was enlarged in 1916. It is located on the Snake River, near Moran, Wyo. The 78-foot-high dam is a concrete gravity structure with earth embankment wings. The crest is 20 feet wide and 4,920 feet long. The active capacity of the reservoir is approximately 847,000 acre-feet. The concrete overflow spillway is controlled by radial gates. Jackson Lake Dam is one of five Minidoka project dams. The project contains approximately 1,163,000 acres of irrigable land, of which 217,000 acres are full-service land. Jackson Lake Dam is capable of withstanding the maximum probable flood. The seismic studies are incomplete, however, the indications are that the earth embankments may require stabilization to enable them to withstand the maximum credible earthquake event. The concrete section of the dam has been stabilized and is capable of withstanding that event. |