Hydro Review

Dam Safety & Security

Multi-strand anchors to be installed at Dover Dam

Work is under way to bring Dover Dam on the Tuscarawas River in Ohio up to modern day safety standards and reduce the risk of failure.

Dover, owned by the U.S. Army Corps of Engineers, is a concrete gravity dam 66 feet tall and 842 feet wide. An analysis by the Corps' Huntington District indicated the 70-year-old dam was safe through pool elevations up to and including 907 feet. Because concerns about the possibility of a dam failure increase as pool elevation rises above this threshold, the Corps implemented an improvement program for the dam.

The first phase of the Dover Dam Safety Assurance project involves installing 36 multi-strand anchors in the spillway section to secure the dam to the bedrock. The anchors range from 19 to 48 strands and will be installed in holes ranging in diameter from 9 to 17 inches. Anchor length will vary from 103 to 153 feet.

Work on this phase began in October 2010 and is expected to take about two years to complete. In September 2010, the Corps awarded an $11.9 million contract to Brayman Construction Corp. of Saxonburg, Pa., for this work. Brayman also is working with the Corps on the Bluestone Dam Safety Assurance project in West Virginia.

Other work to be performed at the dam includes anchoring the stilling basin; installing training walls, a parapet wall on top of the dam, and a closure on the left descending abutment; and providing riverbank protection immediately downstream of the dam.

The total project cost is estimated at more than $60 million.

Reclamation moving forward on dam safety work at Echo Dam

The Bureau of Reclamation is preparing to begin excavation needed for a dam safety project at 4.5-MW Echo Dam on Utah's Weber River, 42 miles southeast of Ogden.

Work involves drilling and installing numerous dewatering and observation wells at Echo Dam to lower the groundwater table in the area immediately downstream of the dam to accommodate seismic retrofit work.

Echo Dam is a 158-foot-tall zoned earthfill structure that was constructed between 1927 and 1931 as part of the Weber River Project to help supply supplemental irrigation water to 109,000 acres west of the Wasatch Mountains. The dam is operated by the Weber River Water Users Association.

Work to lower the groundwater table will facilitate planned excavation downstream to replace potentially liquefiable materials in the dam foundation with stronger and denser material.

The dewatering work is to be performed 24 hours a day, seven days a week during excavation, expected to be complete by February 2013.

Rebuild of upper Taum Sauk reservoir receives award

The Taum Sauk Upper Reservoir Dam Restoration Project received the Engineer Society of Western Pennsylvania's Project of the Year Award in the civil category.

Rebuilding of the failed dike on the upper reservoir at the 440-MW Taum Sauk pumped-storage project included several innovative methods, including recycling flyash from a nearby waste pond for use in the concrete mixes and adapting the fundamentals of gravity dam design and the use of roller-compacted concrete (RCC) from a conventional shaped gravity dam to one of a symmetrical cross section with relatively low-strength RCC.

The mountaintop ring dam around the upper reservoir at Taum Sauk breached in December 2005. The project became fully functional again in May 2010. The finished dam is the largest RCC dam in the western hemisphere, Paul C. Rizzo Associates says.

Each year, the society recognizes an outstanding project that highlights the important contributions engineers make to society. The project chosen must represent technical innovation and commercial success and be a benefit to society.

This award was presented to Paul C. Rizzo Associates and AmerenUE at the society's annual awards banquet. Paul C. Rizzo Associates was the design engineer and quality control manager for the project. AmerenUE owns and operates the facility.

Corps awards contract for grout curtain at Wolf Creek

The U.S. Army Corps of Engineers has awarded The Judy Company Inc. of Kansas City., Kan., a $6.76 million contract for installation of two grout curtains as part of emergency dam safety repairs to 270-MW Wolf Creek dam and hydro project at Jamestown, Ky.

The Corps identified the earthfill and concrete gravity dam as being critically near failure or having extremely high life or economic risk. Money to repair the dam was included in economic stimulus appropriations approved by Congress. A 2008 assessment of equipment at nine Corps hydro plants on the Cumberland River in Tennessee and Kentucky, including Wolf Creek, found a need for up to $470 million in repairs.

The Corps awarded a $341.4 million construction contract for a 4,200-foot-long concrete seepage barrier at Wolf Creek to Treviicos Soletanche JV of Boston in 2008. The cutoff wall is the primary element of the seepage rehabilitation project. It is to be built deep into foundation rock beneath the 5,736-foot-long, 258-foot-tall dam to stop seepage. Work began in fall 2008; the contract performance period is four years.

The latest contract award involves installation of a grout curtain from the right end of the gallery to the base of the right abutment constituting a grout line about 1,500 feet long and 140 feet deep. Also included is a separate grout curtain in the power plant plaza adjacent to an existing diaphragm wall. The 600-foot-long plaza grout curtain requires drilling and installing casing through 70 feet of soil prior to constructing a 60-foot-deep grout curtain in rock.

DHS releases roadmap for secure control systems

The U.S. Department of Homeland Security (DHS) offers Dams Sector Roadmap to Secure Control Systems.

This 72-page document provides a beginning point and a template for action as industry and government work together to achieve a common objective for securing control systems within the dams sector, the report states.

The roadmap describes a plan and strategic vision for voluntarily improving cybersecurity of control systems in the dams sector. Many of the control systems used today were initially designed for operability and reliability during an era when security received low priority, the roadmap explains.

This roadmap brings together government agencies and dam owners and operators with a common set of goals and objectives. It provides milestones to focus specific efforts and activities for achieving the goals over the next ten years while addressing the most urgent challenges, longer-term needs, and practices for reducing cybersecurity risk to control systems. Challenges include developing mitigating solutions, defining longer-term needs, and articulating control system security guidelines and practices for improvement.

The five goals in the roadmap – each of which have near term (zero to two years), mid term (two to five years), and long term (five to ten years) milestones – are:

– Measure and assess security posture;

– Develop and integrate protective measures;

– Detect intrusion and implement response strategies;

– Sustain security improvements; and

– Secure by design.

The next step in following the steps outlined in the roadmap is to establish a working group with public and private representation across the dams sector.

DHS' Office of Infrastructure Protection and the National Cyber Security Division facilitated development of this roadmap.

– To access the roadmap, visit our hydro library at www.hydroworld.com/index/hydro-library.html and look under Dams & Civil Structures.

Concrete repairs needed at Trenton, Enders dams

The Bureau of Reclamation is preparing for concrete repairs to the Trenton and Enders dams in Nebraska.

Trenton and Enders dams are part of the Frenchman-Cambridge Division of the Pick-Sloan Missouri Basin Program. While they primarily provide water storage for irrigation along the Republican River, Trenton and Enders have been considered by a government study to be potential sites of hydropower projects of 15.4 MW and 6.8 MW.

Work at the 144-foot-tall earthfill Trenton Dam is to include concrete repairs on a spillway bridge, deck, beams, piers, and support pedestals; core drilling new deck drains on the spillway bridge main spans; repairing erosion damage on the dam's left embankment; and moving and replacing gutter drains on the left embankment.

Work at the 134-foot-tall earthfill Enders Dam is to include concrete repairs to the spillway floor and bridge; repairing bearing devices under the bridge beams; and installing sealant in expansion joints on the gate operating deck.

Spillway capacity being increased at Canton Lake Dam

The U.S. Army Corps of Engineers is working to install an auxiliary spillway at Canton Lake Dam on the North Canadian River in Oklahoma.

Canton Dam – a 68-foot-tall, 15,140-foot-long earth-filled embankment – includes a 778-foot-wide service spillway at the right abutment with 16 tainter gates. Corps hydraulic studies found the existing spillway is unable to discharge a probable maximum flood and the dam is likely to fail during a major flood.

To address the inadequate spillway capacity, the Corps has begun construction of an auxiliary spillway at the right abutment. Under the current contract, a 480-foot-wide auxiliary channel has been partially excavated. Fifty-foot-tall vertical diaphragm walls line the channel. The Corps chose a Fusegate system from Hydroplus Inc. for the new spillway.

The next phase of the work includes placement of a concrete weir about 35 feet deep and 70 feet long spanning the width of the channel. Other work includes a 40-foot-tall water intake monolith with a 47- by 15-foot base; 250 feet of 11-foot-diameter conduit; 30-foot-tall, 50-foot-wide Fusegates, diaphragm walls with anchors; and stop-log manufacture.

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