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- Table 51: Hazard Categories of Montana Dams by Ownership
- Table 52: Dam Failure Risk
- 4.5.2 Dam Failure History in Valley County
- 4.5.3 Presidential Declared Disasters for Dam Failure
- 4.5.5 Vulnerability in Valley County
- 4.5.6 Dam Failure and Climate Change
- 4.5.7 Relationship to Other Hazards
4.5 Dam FailureDam failure was not identified in the 2008 Valley CountyPre-Disaster Mitigation Plan. It was included as a hazard in the 2015 update. Analysis of dam failure is included in this plan update to take an in-depth look at what dam failure is, the history of dam failure within Valley County, and the potential they have to impact residents. A definition of dam failure is provided prior to taking a closer look at the effect dam failure has on Valley County in order to provide the reader with knowledge of the hazard. Dam failures is typically the sudden release of all or most of the water being impounded by the dam, this release most often violent, sudden, and uncontrolled. Dam failure may be caused by faulty design, construction, and operational inadequacies, intentional breaches, or a flood event larger than the design flood. Dam failures are usually associated with intense rainfall or prolonged flood conditions, but can occur during an earthquake. The greatest threat from dam failure is to people and property in areas immediately below the dam since flood discharges decrease as the flood wave moves downstream. According to FEMA, dams are classified into one of three categories, as outlined below: Low Hazard Potential - Dams where failure or misoperation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner’s property. Significant Hazard Potential - Dams where failure or misoperation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be located in areas with population and significant infrastructure. High Hazard Potential - Dams where failure/misoperation will probably cause loss of human life. Montana has approximately 3,651 dams with anormal capacity of 50-acre feet (Department of Natural Resources and Conservation, DNRC, 2013). Of these dams, 189 are considered “high-hazard dams", indicating there is potential for loss of life downstream. Table 51 summarizes the hazard categories of dams by ownership. Table 51: Hazard Categories of Montana Dams by Ownership
4.5.1 Dam Failure RiskThe overall probability that dam failure will occur each year in Valley County is highly likely and its relative impact is high and thus the overall risk for Valley County is high. The risk for dam failure is different for each of the cities based on dams and the dam hazard rating of dams near those cities. In assessing dam failure data for the 2015 update, data from 2009 to 2014 was used to determine the risk for each of the cities and the county as a whole. Cities of Glasgow, Fort Peck, and Nashua proximity to higher hazard dams is notable. The table provided below provides the name of each of the cities in the county, the probability that dam failure will have an impact on that jurisdiction, the impact potential, as well as the overall risk calculated by the determine probability and impact ratings. Table 52: Dam Failure Risk
4.5.2 Dam Failure History in Valley CountyAccording to the National Inventory of Dams database, Valley County has 191 dams, all but eight of which are considered low hazard. Table 53 shows the high and significant hazard dams in Valley County. Table 53: High and Significant Hazard Dams in Valley County
Source: US Army Corps of Engineers, 2008a The Fort Peck Dam is the highest of six major dams along the Missouri Riverand adjacent to the community of Fort Peck. At 21,026 feet (6,409 m) in length and over 250 feet (76 m) in height, it is the largest hydraulically filled dam in the United States. The Fort Peck Dam creates Fort Peck Lake, the fifth largest man-made lake in the U.S., more than 130 miles (210 km) long, 200 feet (61 m) deep, and it has a 1,520-mile (2,450 km) shoreline which is longer than the state of California's coastline. The dam and lake lie within the Charles M. Russell National Wildlife Refuge. The dam and the 134-mile-long (216 km) lake exist for the purposes of hydroelectric power generation, flood control, and water quality management. The dam presently has a capacity of to generate up to 185.25 megawatts between its five generating units which are divided into the western and eastern grids. Three of the five units, were completed in 1951 andare located in Powerhouse Number One. These generators have a capacity of 105 MW. The two remaining generating units, were completed in 1961, and are located in Powerhouse Number 2 with a nameplate capacity of 80 MW. Fort Peck Dam was a major project of the Public Works Administration, during the New Deal. Construction of Fort Peck Dam started in 1933, and at its peak in July 1936 employed 10,546 workers. The dam, named for a 19th-century trading post, was completed in 1940 and began generating electricity in July 1943. The town of Fort Peck, Montana, "the government town," was built for Army Corps of Engineers personnel and men in "positions of responsibility" and their families during the dam's construction. Many of the facilities that supported the dam's workers are still utilized today, including the recreation center and theater. In addition to Fort Peck, other towns developed and grew to house the numerous workers. Including among these towns were Wheeler and McCone City along with a dozen others. Many of the homes were that were constructed to house these workers were later moved to farms and towns around Montana. 4.5.3 Presidential Declared Disasters for Dam FailureThere have not been any reported presidential declared disasters related to dam failure for Valley County. 4.5.4 Mitigation Actions in the Past Five YearsAccording to the US Army Corps of Engineers website, more than 100 Missouri River Mainstemrepair projects have been identified. Projects include repairing spillway gates, outlet works, scour areas, work recreational facilities, roads and other flood control structures that were damaged during the 2011 Missouri River flood. The estimated cost of making these repairs totals $234 million. Six contracts were awarded in 2012 to repair damages at Fort Peck Dam. They included repairing the gates, the spillway slab, the plunge pool, the recreation area roads and drains, the spillway access road and associated drains, the rehabilitation of eight emergency gate controls, the repair of relief wells, and the horizontal outfall pipes. All repairs were scheduled to be completed by December 2015. Bank Stabilization along the Missouri River Ten contracts were awarded in 2012 to repair damages along the Missouri River. They include repair of bank stabilization, navigation structures, and other infrastructure. Contractors continue working on the river. The bank stabilization repairs to the navigation reach between Sioux City and Rulo are scheduled for completion in summer 2015. All other repairs are complete. Dam Safety Program The U.S. Army Corps of Engineers (USACE) operates and maintains approximately 700 dams nationwide and in Puerto Rico that provide significant, multiple benefits to the nation—its people, businesses, critical infrastructure and the environment. These benefits include flood risk management, navigation, water supply, hydropower, environmental stewardship, fish and wildlife conservation and recreation. USACE’s dams are part of the nation’s landscape, integral to many communities, and critical to watershed management. The dam safety professionals carry out a dam safety program to ensure these projects deliver their intended benefits while reducing risks to people, property, and the environment through continuous assessment, communication, and management. By comparison, there are more than 87,000 dams in the National Inventory of Dams (NID) that are federal, state, locally and privately operated, and maintained. The December 2015 System Wide Infrastructure Framework (SWIF) plan for the City of Glasgow Cherry Creek Left Bank and Milk River Left Bank Levee System stated encroachment issues have been an ongoing problem for many years in Valley County. The Glasgow-Cherry Creek Left Bank and Milk River Left BankLevee System is comprised of 2.32 miles of levee, two closures, 3 pumping locations and was initially constructed in 1928. The leveed area reduces flood risk to approximately 561 building structures and an estimated economic asset value of $183,711,986.10, including a fertilizer plan, beer distributing warehouses, a hospital, the Valley County Courthouse and Valley County Detention Center, the City of Glasgow offices and water treatment plan and maintenance facilities, the US Post Office, Social Security and VA services facilities, assisted living and senior living apartment complex, Nemont Communications, grain elevators, a feed plan, and a commercial recycling plan. The direct population at risk impacts 870 during the day time and 930 during the night but impacts a total community population of 3,319. As Valley County and participating jurisdictions remain at risk to dam failure, dam failure remains a focus of this iteration of the plan. This iteration of the plan will focus on coordination infusion of emergency actions plan, development, and education. 4.5.5 Vulnerability in Valley CountyThe 2013 Update to the State of Montana Multi-Hazard Mitigation Plan and Statewide Hazard Assessment stated that numerous factors contribute to determining dam vulnerability including design standards; construction, operation and maintenance; intense rainfall or prolonged flood conditions; and/or earthquakes. The vulnerability of property and population downstream of dams is related to construction in inundation areas. The Dam Safety Act required that owners of all high and significant hazard dams prepare Emergency Action Plans (EAP). The objectives of the EAP is to pre-plan the coordination of necessary actions by the dam owner and the responsible local and state emergency management officials; identify conditions which could lead to dam failure in order to initiate emergency measures that could prevent or minimize the loss of life or property; and, provide timely notification of a warning of a dam emergency and evacuation in the event of potential failure of the dam. 4.5.6 Dam Failure and Climate ChangeAccording to International Rivers, the future will bring extremes of drought and flood outside the historical record that will continue to worsen as the climate warms. Large dam developers do not currently take climate change into account in their plans. If they did, dams would need much greater capacities to safely pass high floods and projections of power generation for hydropower projects would have to allow for the probability of new extremes of drought. These factors would increase the costs and reduce the benefits from dams, thus making the alternatives even more attractive. Large hydropower projects are potentially highly vulnerable to changes in precipitation and streamflow. A 2011 World Bank report states: “Heavy reliance on hydropower creates significant vulnerability to climate change and is a feature that many low- and middle-income countries have in common.” The report summarizes the impacts on the hydropower sector as “reduced firm energy, increased variability, and increased uncertainty.” In order to increase the flexibility of the system and its resilience to more variable climatic conditions, the report recommends an adaptation response that “may require a policy decision to diversify away from hydropower.” 4.5.7 Relationship to Other HazardsDam or levee failures can have a greater environmental impact than that associated with a flood event. Large amounts of sediment from erosion would alter the landscape changing the ecosystem. Hazardous materials are carried away from flooded properties and distributed throughout the floodplain. Industrial and agricultural chemicals, agricultural wastes, other solid wastes, raw sewage, and common household chemicals comprise the majority of hazardous materials spread by flood waters. These run offs and floods could polluting the environment and contaminating the flooded areas, including a community’s water supply. The soil loss from erosion and scouring would be significantly greater due to a large amount of fast moving water affecting a small localized area. Download 4.32 Mb. Share with your friends:
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