Dam Safety and Security

Dam safety concern in wake of Hurricane Matthew

Dams and other water-retaining infrastructure systems across the southeastern U.S. were tested after Hurricane Matthew slammed the Atlantic seaboard in October.

Flooding has perhaps been worst in North Carolina, where 15 were confirmed dead as of Oct. 11 and officials near Spring Lake evacuated the area downstream from Woodlake Dam.

Located on the Lower Little River, the dam impounds a 10,000 acre-feet reservoir and was rated as one of the state’s largest high-hazard dams last year.

State and county inspectors feared that a failure could cause up to 3 feet of additional flooding and had at one point declared a breach to be “imminent,” although officials later said the structure is stable and no further evacuations were planned.

North Carolina’s Lake Upchurch Dam was also reported as being near the overtopping level, while a number of smaller dams breached or were near breaching.

Elsewhere in the southeastern U.S., before the hurricane hit land the South Carolina’s Emergency Management Division warned dam owners and operators to lower their reservoir levels in anticipation of flooding.

Hurricane Matthew caused particular concern given the large number of dams within the state that failed during a period of historic rainfall last fall.

The S.C. governor’s office said it had concerns about 250 dams in the state, although more than half had been inspected as of Oct. 11. Still, reports indicate that at least seven in the Pee Dee and Midlands regions had failed, leading to flooding in the Little Pee Dee, Lumbar, Waccamaw and Black rivers.

California says Sweetwater Dam needs safety improvements

Officials from California’s Division of Safety of Dams say they are concerned by the reluctance of the Sweetwater Authority Board to perform dam safety repairs to Sweetwater Dam.

The dam, located 12 miles east of San Diego, is a 180-foot-high, 700-feet long masonry arch dam that was completed in 1888 as part of San Diego County’s irrigation system. The dam now impounds the 960-acre Sweetwater Reservoir and operates in conjunction with the upstream Loveland Dam for flood control and water supply.

State officials said California’s Sweetwater Dam poses a risk to those downstream should its owners choose not to correct a flawed spillway design.
State officials said California’s Sweetwater Dam poses a risk to those downstream should its owners choose not to correct a flawed spillway design.

While the dam was expanded to its current size after overtopping killed eight people in a flood in 1916, the state said its spillway is still susceptible to causing danger to those living downstream of the structure.

According to DSOD, the design of Sweetwater’s spillway is flawed, with the discharge needing to be focused more toward the structure’s center. While the dam itself is still sound, the fear is that flooding could cause parts to erode should corrections not be made.

Sweetwater Authority Board previously voted not to perform what is projected to total about million in repair work, although area sources have since reported the board will finance the project following a visit from the state.

U.S. Senate passes bill that includes measures for dam safety

A bill passed by the U.S. Senate contains measures that provides federal funding to rehabilitate high-hazard dams.

Included in the Water Resources Development Act of 2016 – officially Senate Bill 2848 – are amendments to the National Dam Safety Program Act and grant money for infrastructure maintenance and improvements.

Per Section 3004, the act “is amended to direct the Federal Emergency Management Agency to establish a program to provide technical, planning, design and construction assistance grants to nonfederal sponsors (subject to a nonfederal cost-sharing requirement of at least 35%) for rehabilitation of eligible high-hazard potential dams.”

As defined in the WRDA, “high-hazard” nonfederal dams includes those that are located in states with their own dam safety program; are classified as “high-hazard” by the state in which they are located; have an emergency action plan approved by an applicable state agency; and fail to meet minimum state dam safety standards, thus posing an “unacceptable risk” to the public.

Notable in Section 3004 are stipulations that grant money may not be used to perform rehabilitation work on federally-owned dams; to perform routine maintenance and operation; to modify dams to produce hydroelectric power; or to increase the storage capacities of reservoirs.

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