Morris Sheppard Dam - A Project to Restore Dam Safety

Abstract Only - Morris Sheppard Dam impounds a 570,000 acre-foot lake on the Brazos River 100 miles west of Dallas, Texas. The dam is a 188-foot high flat slab buttress (Ambursen type) with a crest length of 2,740 feet. The 13,000 square mile drainage area is controlled by 9 roof-weir gates with a discharge capacity of 560,000 cfs. The dam is licensed to generate hydroelectric power by the Federal Energy Regulatory Commission. It also provides water for municipal, industrial and irrigation uses. The dam is owned and operated by the Brazos River Authority.
During a routine five-year inspection, it was discovered that the dam had moved about 4.5 inches since it was completed in 1941 and was continuing to move. The foundation uplift pressures were as high as 60 percent of reservoir head. The dam was not capable of passing the PMF as estimated on the basis of current criteria.
The paper describes the symptoms of movement discovered which resulted in a 13-foot lowering of the reservoir to temporarily improve its safety, the in­vestigation of the foundation requiring the cutting of 8-foot diameter holes through 24 9-foot thick buttresses, underwater exploration and mucking out of construction waste between the spillway buttresses, and construction of an in­ternal roadway for access to the foundation. A precision survey network was developed to measure movements and extensive instrumentation consisting of piezometers, inclinometers and extensometers installed to evaluate the founda­tion movement and uplift. The correction of stability with relief walls and added weight are discussed. A hydraulic model study was performed in order to design spillway modifications to prevent erosion damage. An emergency spillway will be provided to pass the PMF. A detailed structural analysis was made to evaluate overs tressing of the dam's components.
The total cost of correction will be about $20 million. Modifications to the dam should be complete by the end of 1989.