My Favorite Dams - Morris Sheppard Dam


Morris Sheppard Dam

Brazos River, Texas
David W. Harris, PhD, PE, F.SEI, F.ASCE




Morris Sheppard Dam forms Possum Kingdom Lake.  The lake is located where the Brazos River cuts through the Palo Pinto Hills.   Construction was begun in 1936 and completed in 1941. The dam is 2,700 feet (820 m) long and 190 feet (58 m) high.  The construction is unique with buttressed arched wings on either side of the nine spillway gates rather than the usual filled concrete.  (Wikipedia)
The lake is located where the Brazos River cuts through the Palo Pinto Hills.[7] The canyon thus formed provided a favorable site for impoundment of the reservoir and accounts for the unusual depth of the lake and the resulting clarity of the water.  It was the first water supply reservoir constructed in the Brazos River basin. The lake has an area of approximately 17,000 acres (6,900 ha) with 310 miles (500 km) of shoreline. It holds 750,000 acre feet (930,000,000 m3) of water with 550,000 acre feet (680,000,000 m3) available for water supply. (Wikipedia)

The lake is home to Possum Kingdom State Park, a 1,530-acre (620 ha) state park governed by the Texas Parks and Wildlife Department. (Wikipedia)
So why is this dam in Texas, owned and operated by the Brazos River Authority one of my favorites?
Morris Sheppard Dam is a unique dam built using the Ambursen design as mentioned and shown above.  Large buttresses support deck panels making up the water barrier.  An iconic structure and interesting for any structural engineer.

In 1998, the U.S. Bureau of Reclamation, my employer for 38 years, studied the Morris Sheppard Dam events that caused a 4+ inch movement downstream. The Concrete Dams Analysis Group reported the following (Anderson et al., 1998):

During a Federal Energy Regulatory Commission (FERC) mandated inspection, it was discovered that the hollow spillway section of the dam had moved downstream on a slippage zone in the foundation. Metal survey points, installed twenty years earlier, had been placed on a straight axis along a catwalk positioned 90 feet (27.4 m) above normal tail water inside the structure. The survey line indicated a downstream bow, across the length of the spillway section, with a maximum displacement of 4-1/2 inches (114 mm). The reservoir was lowered and core borings were made. Piezometers indicated that the hydrostatic uplift pressure under the spillway base slab was equivalent to 65 percent of the lake head.

Observations confirmed cracks in the footings of the hollow spillway.

As a dams safety consultant I was selected as a member of the Consultant Review Board for Morris Sheppard Dam.  Structural integrity of dams and public safety is a professional priority from 35+ years of work in the field.  It was an honor to join the Board of experts.

And I guess as a graduate from Texas A&M University, and a Texas PE there will always be a place set aside in my heart for Texas.

 References:
Anderson, C., C. Mohorovic, L. Mogck, B.Cohen, G.Scott, 1998, Concrete Dams Case Histories of Failures and Nonfailures with Back Calculations, United States Bureau of Reclamation, DSO-98-05
 

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