Spillway construction starts at California’s Folsom Dam
Federal, state, and local officials turned out for a ceremony marking the start of construction of an auxiliary spillway that will increase flood protection at 198.72-MW Folsom Dam on California’s American River.
The auxiliary spillway is being built as a joint federal project by the U.S. Department of Interior’s Bureau of Reclamation, the U.S. Army Corps of Engineers, the California Department of Water Resources, and the Sacramento Area Flood Control Agency.
The spillway is to address the hydrologic risk to Folsom Dam identified through Reclamation’s Safety of Dams program. It also is to achieve the Corps’ objective to double the flood protection for the city of Sacramento, to a 200-year flood.
In remarks to the ceremony, Interior Secretary Dirk Kempthorne said the project would protect a million people who live in the Sacramento area from the threat of a devastating flood.
Gov. Arnold Schwarzenegger, who advocates the construction of new dams for water storage, used the occasion to comment on a need to modernize California’s water infrastructure.
The auxiliary spillway will include an approach channel, control structure with six submerged tainter gates, a concrete-lined spillway chute, and a stilling basin to dissipate energy before water is discharged into the American River. Kiewit Pacific Co. of Concord, Calif., is construction contractor.
Governor proposes funding to repair Pennsylvania dams
Gov. Ed Rendell is pushing a multi-year plan to spend $12 million in the first year to repair seven state-owned high-hazard dams. The plan includes another $15 million for repairs and safety-related work at high-hazard dams owned by local governments in the state.
Rendell’s Rebuilding Pennsylvania proposal also includes provisions for repairing structurally deficient bridges.
“Rebuilding Pennsylvania will finally address every state-owned, unsafe, high-hazard dam, in an effort to keep surrounding homes and communities safe,” Rendell said.
The plan would direct $200 million to bridge repairs and include $13 million for flood control projects. In addition to the $12 million to repair state-owned dams, the plan includes $15 million in new general fund investments in local dam repairs, flood plain mapping, and infrastructure.
The governor said the department’s Dam Safety Program classified 24 state-owned high-hazard dams as unsafe. He said repair work to some of the dams is in the design or construction phase, or already eligible for funding through the state’s capital budget.
The $12 million would be used for seven of the 24 dams, in the first year of the program, a Department of Environmental Protection spokesman said. Estimates to repair the other 17 dams in the group total $37 million.
The $15 million in new general fund investments would support a state matching loan-grant program that could help cover 30 percent of the cost of repairing the 21 unsafe high-hazard dams owned by county or local governments. The Department of Environmental Protection, which regulates about 3,200 dams, would work with state agencies and municipalities that own the unsafe dams.
Corps selects fusegates for Canton Dam spillway
The U.S. Army Corps of Engineers plans to install 30-foot-tall labyrinth fusegates from Hydroplus Inc. at a new emergency spillway at Canton Dam. The dam is on the North Canadian River, about 75 miles northwest of Oklahoma City, Okla.
Fusegates are open “buckets” that tip in sequence, increasing spillway discharge capacity.
Six Hydroplus units installed several years ago to increase reservoir capacity at Terminus Dam in California’s San Joaquin Valley represented the first use of concrete fusegates in the U.S. The fusegates planned for Canton Dam are even larger.
The 68-foot-tall, 15,140-foot-long Canton Dam is an earth-filled embankment. It includes an existing 778-foot-wide service spillway at the right abutment with 16 tainter gates. Each gate is 40 feet wide and 25 feet tall.
Through hydraulic studies, the Corps determined the existing spillway is unable to discharge the new probable maximum flood. The dam is likely to fail during a major flood event.
To address the inadequate spillway capacity, the Corps will build an auxiliary spillway, also at the right abutment.
For the spillway control system, the Corps considered various alternatives, some involving tainter gates and others involving fuesgates. While the tainter gate option met project requirements, the Corps chose a fusegate alternative, citing lower project costs, minimum maintenance requirements, reliability in operation, and a longer life expectancy.
Nine fusegates, each 30 feet tall and 53 feet wide, will fit into the proposed 480-foot-wide spillway channel. Fusegates will be made of cast-in-place concrete and feature stainless steel inlet wells. Rubber seals will be installed between each fusegate, and between the fusegates and spillway sill.
Construction is scheduled for 2009.
Tennessee Valley Authority shores up Bear Creek Dam
The Tennessee Valley Authority (TVA) is rehabilitating its 68-foot-tall, 1,385-foot-long Bear Creek Dam. The earthen dam, in northwest Alabama, impounds water for flood control, recreation, and municipal water supply.
Water has leaked through the dam’s foundation since its completion in 1969. Following periods of heavy rainfall, the reservoir behind the dam can rise, and increase the risk of dam failure. To reduce that risk, TVA prepared an environmental impact statement (EIS) to evaluate alternatives for a long-term solution.
TVA released the EIS in August 2007 and a month later issued a record of decision stating it would build a roller-compacted concrete structure at the downstream toe of the dam and a cutoff-wall under the new structure to block water from passing beneath the dam.
Site preparation work began in September 2007, followed by dewatering and excavation activities. The rehabilitation work, scheduled for completion in June, could cost as much as $35 million, TVA said.
By rehabilitating the dam, TVA expects to operate the reservoir behind the structure at an elevation of 576 feet in the summer, which is the pool level called for in original designs. TVA also will incorporate new minimum flows downstream of the dam to improve habitat conditions for endangered species.
BC Hydro strengthens Ruskin in dam safety program
BC Hydro is conducting a C$145 million (US$144 million) seismic improvement program at the utility’s 105.6-MW Ruskin Dam in British Columbia, to be completed in 2010.
BC Hydro began lowering the level of Hayward Lake, the reservoir behind the 59.4-meter-tall dam, in October 2005. It said water levels behind the dam would remain low until a permanent seismic reinforcement is implemented.
The work to reinforce the dam is necessary, the utility said, as earthquake standards have increased since the dam was completed in 1930.
Investigations concluded the main body of the dam and gates were vulnerable in earthquake events.
Ruskin Dam impounds Hayward Lake Reservoir on the Stave River, downstream of 90-MW Stave Falls. The dam is located about 50 kilometers east of Vancouver.
Panels confirm Corps’ concerns for Isabella, Herbert Hoover
External peer review panels have confirmed the U.S. Army Corps of Engineers’ findings that Isabella Dam on California’s Kern River and Herbert Hoover Dike in south Florida are at high risk of failure.
Isabella Dam, built in 1953 as a flood control and water conservation structure, also controls flows released to Southern California Edison’s 12-MW Borel project.
The external panel’s Isabella Dam Consensus Report found the Corps’ Class I designation of “urgent and compelling” is appropriate for Isabella Dam for several reasons:
- – A possibility of piping along the outlet conduit of its auxiliary dam;
– Evidence the auxiliary dam’s drain blanket is not performing as intended;
– Studies finding the Kern Canyon Fault, under the auxiliary dam’s right abutment, is active;
– Evidence the upper 20 feet of the auxiliary dam’s foundation is loose and might be subject to loss of shear strength during seismic loading;
– Hydrologic studies that indicate the spillway to be inadequate; and
– Extremely high consequences of failure.
The panel recommended maintaining the current reservoir pool restriction of elevation 2,585.5 feet, 20 feet below normal pool. It called for other short-term risk reduction measures including: testing of new piezometers; evaluation and installation of devices to monitor the main and auxiliary dams and the Kern Canyon Fault; assessing underlying alluvium to determine its effect on seismic stability; updating the emergency action plan; and conducting emergency exercises.
The panel also recommended long-term risk reduction measures including completion of ongoing studies of major rehabilitation of the auxiliary dam and evaluation of overall earthquake performance of the main dam.
Herbert Hoover Dike is an earthen embankment system on the perimeter of Lake Okeechobee. Components of the system have been constructed intermittently since the early 1900s.
The system encircles almost all of the lake, which has a surface area of about 730 square miles. It consists of about 140 miles of earthen embankment with 57 water control structures.
The external panel’s Herbert Hoover Dike Consensus Report found the Corps’ Class I designation of “urgent and compelling” is appropriate for the project.
It cited piping at several locations and studies that conclude part of the dike would fail with sustained lake elevations above 21.5 feet, calculated as a once in 100-year occurrence.
It also said seepage volume and distress indicators in certain reaches at reservoir levels above 17 feet are cause for concern, as failure is considered very likely when operating at, or above, those levels for significant time.
The external panel said it supports the general design principles of a proposed $856 million rehabilitation program that would be completed in 2030. The program would feature a partial cutoff wall through the dike to prevent piping, the movement of material carried by seepage.
The Corps is responsible for lake management and the dikes in the system; the South Florida Water Management District owns and operates other structures in the system.
The U.S. Department of the Interior’s Bureau of Reclamation is using global positioning systems to monitor the condition of the 14 high- and significant-hazard dams in its Lower Colorado Region. The systems, provided by Orion Monitoring Systems Inc., record and graph any movement of the structures in real time in three dimensions.