Safety study ahead for Eagle Mountain Dam in Texas
Tarrant Regional Water District (TRWD) is spending US$1 million during the next three years for a team from the University of Texas-Arlington to study if recent earthquakes in the area have had any impact on dam safety at Eagle Mountain Dam in Tarrant County, Texas.
A team of graduate students led by a veteran dam safety engineer from the university’s engineering department will primarily study the effect of three factors: “liquefaction, dynamic slope stability, and lateral spreading,” according to the water district.
Two Eagle Mountain dams and the lake they impound are located about 5 miles northwest of Fort Worth, on the West Fork Trinity River.
Two large embankment dams impound Eagle Mountain Lake. The main dam is 85 feet high by 4,400 feet long and the spillway dam (saddle dam) is 60 feet high by 3,480 feet long. The dams were completed in 1932 and began impounding water in 1934 for water supply, irrigation, flood control and recreational purposes. The facility is one of the largest raw-water suppliers in Texas, serving more than 1.7 million people in North Central Texas.
Since 2013, Azle and Reno – towns near the dams – have experienced several earthquakes, the highest magnitude measuring 4.0.
Reports indicate one TRWD dam safety engineer, Louie Verreault, said, “We hear these stories from southern California. They have a 6.0 earthquake, and suddenly, a dam failed. Well, we need to know what the impact is from the smaller ones.”
In 2007, TRWD asked Parsons Brinckerhoff Inc. to perform a seepage and stability assessment of both dams at Eagle Mountain Lake as part of a proactive management strategy for its existing infrastructure, according to the Association of State Dam Safety Officials.
Nine dams breached from 1,000-year rain event in South Carolina
After one of the highest rainfall levels ever recorded, in early October, from weather affected by Hurricane Joaquin, the South Carolina Emergency Management Division reported nine dams breached.
The breached, and/or failed, dams are:
– Aiken County: Corbett Lake;
– Fort Jackson: Semmes Lake Dam;
– Lee County: Clyburn Dam;
– Lexington County: Old Mill Pond, Gibson Pond Dam and Barr Lake Dam;
– Richland County: Upper Rocky Creek/North Lake Dam, Cary’s Lake Dam (Arcadia Lake Dam), and Beaver Dam/Boyd’s Pond No. 2/Wildwood Pond No. 2 were “intentionally breached for a controlled release.”
CNN reported the state experienced a “thousand-year rainfall,” meaning the amount of rainfall experienced in South Carolina has a 1-in-1,000 chance of happening in any given year.
Rain totals in the state included 24 inches in Mount Pleasant, about 20 inches in the Charleston metropolitan area and more than 18 inches in the Gills Creek watershed.
Global Diving and Salvage performing work in Lake Gregory
Divers from Global Diving and Salvage have begun work to replace two drainage valves in California’s Lake Gregory, according to Mountain News.
Diver work, installing two temporary plugs, hydroblasting and installing new 30-inch pipe are part of a $1.4 million contract awarded to Redlands-based Pro-Craft Construction by the San Bernardino County, Calif., Board of Supervisors on July 28.
Studies indicate a 30-foot thick section of the dam utilizes substandard materials and it was installed using improper construction techniques.
Lake Gregory is an artificial lake in the San Bernardino National Forest of the San Bernardino Mountains. The county owns the dam, and the lake and the surrounding area make up the Lake Gregory Regional Park.
In October, working from a barge anchored 40 feet from the shoreline, a two-member dive team began removing steel bar trash gate at the tunnel entrance designed to prevent large debris from entering the 4-foot-diameter tunnel, according to the Mountain News.
The dam was originally built by a private entity and has been in operation since Oct. 26, 1938. San Bernardino County Regional Parks Department took over ownership of the dam and Lake Gregory recreational facilities on Nov. 7, 1977 from the Crest Forest County Water District. An earthen dam, it did not incorporate drains, which are now standard in all dams.
The Division of Safety of Dams requires Lake Gregory Dam have an outlet valve system capable of discharging half of the water in the reservoir in seven days. Replacing the outlet valve will satisfy theses requirements enabling lowering the lake when necessary as a public safety precaution, according to local news reports.
The $12.8 million project should be complete by March 2017.
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