Eugene's natural disaster plans: preventative, permaculture perspectives

  • Eugene's Multi-Hazard Mitigation program
  • floods: don’t build hospitals in floodplains
  • storms: plant fruit trees, not firs, around homes
  • landslides: ban clearcuts and new road cuts
  • wildfires: fireworks and clearcuts increase risk
  • earthquakes and coastal tsunami: seismic retrofit bridges & buildings
  • volcanoes: plan to do without Calif. products if Mt. Shasta erupts
  • dam collapse:
    the Willamette Valley tsunami, we must strengthen -- or remove -- the dams
  • critical infrastructure: redundancy, relocalization and renewables needed
  • hazardous material: ban toxics, monitor train & truck shipments through region
  • terrorism: community cohesion is solution
  • Disaster Mitigation and Land Use:
    Eugene needs intelligent (urban) design
    Hospitals, Earthquakes, Floods, and Lahars
    Troubled Bridges Over Water: the I-5 bridge crisis
    West Eugene sprawl in floodplains: WEP, Target megastore, Royal Node subdivision
  • The Long Emergency: Peak Oil and Climate Collapse require paradigm shift
  • Katrina disaster shows the Federal government response: we are on our own

 

The Willamette Valley Tsunami: Dam Collapses from Flood or Earthquake

Perhaps the most serious disaster threat faced by the Eugene area is the potential for catastrophic failure of dams during a large flood or earthquake. The only disaster that would be worse is some sort of national or global cataclysm (nuclear war or pandemic), scenarios that would not be limited to our region.

If a 40 foot wall of water swept through the Eugene - Springfield area, the aftermath would resemble a mix of the inundation zones from the 2004 Indian Ocean tsunami and the impact of Hurricane Katrina upon the City of New Orleans. If the dam failures would caused by a large earthquake, it is likely that this would be the end of the Eugene metropolitan region. The combination of bridge collapses, destruction of many buildings and the sudden, severe flood from the dam failures would make the area "resemble Hiroshima" -- as one City Councilor has privately expressed.

At a minimum, emergency response and awareness of these threats are desperately needed. Inundation maps need to be made public so that citizens would know how far - and which directions - to flee in the event of disaster. The State of Oregon posts tsunami inundation maps for coastal communities on its website, and posts signs on Highway 101 to indicate the danger zones. There is no technical, legal, political, financial or security excuse to keep similar information secret from the taxpayers of Eugene, Springfield and nearby communities -- since this knowledge would be the most important factor for minimizing casualties should this event occur. How far away from the river people would have to go is unknown to the average person. Would vertical evacuation in downtown Eugene be sufficient (going to the top of a parking garage or one of the taller buildings)? Widespread awareness of these facts could spur regional and federal government actions to address the problems by either strengthening or removing the dangerous dams.

Hills Creek dam (photo from Army Corps of Engineers)

 

The City of Eugene "multi hazard mitigation" discusses the dangers of nine dams -- Cottage Grove, Dexter, Fall Creek, Dorena, Lookout Point, Blue River, Hills Creek, Cougar, Fern Ridge. Three of them had no seismic considerations when built (Cottage Grove, Dorena, Fern Ridge). The others had some seismic concerns in the design, but that was before the threat of the Cascadia Subduction Zone was fully understood. A large Valley earthquake (Richter 7?) or a Subduction Zone event off the coast (Richter 9) could breach some, if not all of the dams.

According to the Multi-Hazard report, a failure of Lookout Point (upstream of Dexter) would require the evacuation of over 250,000 people with damages in excess of $10 billion.

Rep. De Fazio was asked about this September 19, 2005 at his town hall meeting, and he didn't want to deal with it. He just said that removing the dams was not practical (due to "developed" low lying areas) and refused to discuss the need to strengthen them.

Lookout Point (the large dam just upstream from Dexter, visible from Highway 58) is the largest reservoir in the entire Willamette River system. It is also next to a (possibly inactive?) earthquake fault.

The report does not estimate the money that would be required to strengthen (or dismantle) these dangerous dams, but the price tag probably has lots of zeros in it. But the federal empire is too busy destroying other countries to worry about such matters (and Eugene didn't vote for the dictator anyway). One Trident submarine or a couple of days of the Iraq occupation would probably cover the full cost of the repairs, but Halliburton and Lockheed Martin would not be able to reap obscene profits, so there are no plans to fix them anytime soon.


www.eugeneweekly.com/2005/12/15/news.html

Back on Oct. 13 in this column we wrote about the nearly three dozen "high potential hazard" dams in Lane County, all but one upriver from Eugene and Springfield. Dam failure from a major earthquake could bring catastrophic flooding. This past week we got a delayed response from Randy Prince who has served on a state advisory committee looking at such risks. He tells us no seismic upgrades are happening to Oregon dams, and money is being diverted away from even evaluating these dams. "Inundation maps for a disaster are secret," he adds, and the secrecy is heightened since 9/11. He notes that geology professor Ray Weldon at City Club estimated a major earthquake risk of 2 to 5 percent, but that "applies to each building in our area, not the chance of having an earthquake in our area that causes damage. Poorly sited or under-designed facilities are the ones that will fail when the 100 percent certain big quake happens." Prince says he's worried about local hospitals building new facilities along rivers and within inundation zones. We share his concerns.


The enormous US dam problem no one is talking about
By Gaylord Shaw
Christian Science Monitor
January 3, 2006

DUNCAN, OKLA. - The landscape of America, at last count, is dotted with 79,272 large dams. Most of them safely deliver bountiful benefits - trillions of gallons of water for drinking, irrigation, and industrial use, plus flood control, recreation, hydroelectric power, and navigation.
That's the good news.
Here, in my opinion, is the bad news: Disaster lurks in thousands of those dams.
At least 3,500 of America's big dams are unsafe, according to inspection reports filed away in obscure nooks and crannies of government offices across the country. Thousands more dams also are unsafe, the American Society of Civil Engineers concluded this year, but no one knows for certain how many because few states have the funds for even cursory safety inspections.
Thus, every moment of every day, unsafe dams form a vast reservoir of danger throughout America. That's not an overstatement. I'm not a professional engineer, but I've spent nearly two-thirds of my 45-year career in journalism studying unsafe dams. I've done on-the-scene reporting on dam failures that killed 175 people and caused billions of dollars in property damage. I've interviewed scores of victims, dozens of state and federal engineers, inspectors, and officials, and examined records on hundreds of dams.
In my view, the cumulative hazard posed by unsafe dams is huge, but it remains largely unexplored by the media. When a dam fails - and records suggest dozens do each year - the events usually are viewed as local, transitory incidents rather than a symbol of a national problem.
Hurricane Katrina underscored the peril of depending on man-made structures for protection against disaster. Failure of the New Orleans' levee system during the storm this year contributed to prolonged flooding and 1,300 deaths.
Months later, as scenes of misery and dislocation lingered in the public mind, President Bush urgently asked Congress to approve $3 billion for the Army Corps of Engineers to begin rebuilding New Orleans' battered levees. The House of Representatives included that amount in a $29 billion hurricane recovery assistance package it passed three days later.
In concept and construction, levees are close cousins of dams. But while politicians flocked to support repair of New Orleans' levees, they've virtually ignored a proposed Dam Rehabilitation and Repair Act which has languished for nearly a year in a House subcommittee. The proposal would authorize the Federal Emergency Management Agency (FEMA) to disperse $350 million over four years to help states repair unsafe dams. Chances of Congress enacting such a repair program anytime soon are slim.
The $350 million program would be a down payment of less than 10 percent toward the estimated $36.2 billion total cost of repairing America's unsafe dams. It also is approximately one-eighth of the amount the president is seeking for repair of the New Orleans' levees.
This is not to suggest that the New Orleans' levees go unrepaired. But from New England to Hawaii more and more aging dams are experiencing problems, with little public awareness. A few large and small examples:

• Taunton, Mass., got national attention in October when a 173-year-old, 12-foot-tall wooden dam above its business district began to buckle. Stores and schools were closed for a week and townspeople headed for higher ground. The crisis eased when the water level behind the dam was lowered. The federal government is now paying 75 percent of the $189,410 cost of tearing down Whittenton Mills Dam and replacing it with a new one.
• In the placid Schoharie River Valley of upstate New York, a volunteer group calling itself Dam Concerned Citizens was formed last month to press for emergency repairs to 182-foot-tall Gilboa Dam, built 80 years ago to supply drinking water to New York City. The dam has been leaking for years. Now citizens have established their own website which distributes emergency notification plans and publicizes preselected evacuation routes for use should the dam fail (www.gilboadaminfo.com).
• Residents of Denver, Colo., population 2 million plus, were warned last month by the Corps of Engineers that serious safety problems have been detected at Cherry Creek Dam, a 141-foot-tall earthen structure. The dam was built 55 years ago on what was then windswept pastureland 10 miles south of Denver. Now the dam looms above Interstate 225, a cluster of office parks and swank homes, a nationally known golf course, and several schools.

Bruce Tschantz, professor emeritus at the University of Tennessee who 25 years ago helped establish the first Office of Dam Safety in the then-nascent FEMA, reached back into classical mythology to fetch a phrase - "the sword of Damocles" - to express his concern about the dangers posed by deficient dams perched above developed areas. (Damocles was a courtier at the court of Dionysius I in the 4th century BC. He was so gushing in his praise of the power and happiness of Dionysius that the tyrant, to illustrate the precariousness of rank and power, gave a banquet and had a sword suspended above the head of Damocles by a single hair.)
"We know what the problems are, we know where they are, and we know how to fix them," Dr. Tschantz said in a telephone interview. It's that next step - actually getting the money to fix them - where we're stalled."
Tschantz doesn't point fingers of blame. But it's clear to me that Congress and several presidents, including the current occupant of the White House, share culpability on the national level, and that too many state and local officials have grown weary of trying to find sources of financing to make dams safer.
Jimmy Carter was the last president to display serious and sustained interest in the issue. He had been in office less than a year when, in the early morning darkness of a Sunday in November 1977, a never-inspected dam in the mountains of his home state of Georgia collapsed and sent a wall of water crashing down upon the campus of Toccoa Falls Bible College - a campus he had visited several times.
The Kelly Barnes Dam on Toccoa Creek dated back to 1899, when a rock-and- timber structure was built across a fast-flowing mountain stream to impound water for a small hydroelectric plant. Later, Toccoa Falls Bible Institute chose the valley below as the site for its campus, took over the power plant and, in 1937, decided to construct an earthen embankment over the original dam, eventually raising the structure's height to 42 feet.
Twenty years later, in 1957, the school abandoned the power plant. For the next two decades, the dam was neglected, visited only by an occasional fisherman or hiker. Pine trees grew to maturity on its downstream slope, sending roots deep into the dam's core. Portions of the steep embankment vanished in a landslide, but there were no repairs, even though water seeped almost continuously from the base of the dam. Finally, the weakened 78-year-old dam collapsed during a rainy night in Georgia.
In the valley below, Eldon Elsberry and two friends were on patrol in the campus fire department's Jeep. When the wall of water hit, it overturned the vehicle. "One minute the water [in the creek] was inches deep, and the next I was swimming for my life," Mr. Elsberry said. "I saw the bank and made for it." He turned and saw one of his friends struggling in the water. "I reached for his hand. He went by so fast I couldn't touch him."
Experts later calculated that the water released by the dam's collapse weighed approximately the same as 7,500 locomotives. As the water crashed across the campus, it destroyed a dormitory and crushed a cluster of mobile homes where married students lived.
Later, in the mud and tangled debris, 39 bodies were found. Twenty were children. College officials said they never hired a private consulting engineer because they had no idea it had safety problems. The state of Georgia never inspected the dam because, at the time, there was no state law requiring such inspections. Few other states had dam safety laws then, either. Pennsylvania was one of the exceptions. Its tough law was spurred by memories of the 1889 collapse of South Fork Dam above Johnstown that killed 2,209 people. Yet even with the strong state law requiring regular safety inspections, another 55 people in the same community died in July 1977 after the failure of Laurel Run Dam, just a few miles from where South Fork Dam triggered the disaster 88 years earlier.
While all states except Alabama now have laws or regulations establishing dam safety programs, enforcement is spotty, largely because of the paucity of inspectors. In Texas, for example, there are only six state employees to inspect nearly 7,500 dams. One Texas official noted that with the current staff level "some dams would not be examined for three centuries."
Let's do the math. Two of my teenaged grandchildren live in Texas. If we count 30 years for each generation, that means all the dams in Texas will be inspected by the time my grandchildren's great-great-great-great-great-great-great-great-great-grandchildren ring in a new year in 2306. Reassuring, isn't it?

• Gaylord Shaw won a Pulitzer Prize for a series investigating the state of the nation's dams for the Los Angeles Times in 1978.


JUNE 1999:

ONE OF CENTRAL OREGON'S DAMS COULD COLLAPSE IN A MODERATE EARTHQUAKE, prompting federal officials to warn people immediately below Wickiup Reservoir to flee to higher ground at the first sign of ground movement. "If people can feel an earthquake in the area, it's probably going to be strong enough to do something to the dam," said Larry Wolf, dam safety expert with the U.S. Bureau of Reclamation in Boise.
It is the first time in the Northwest that the bureau has advised residents to evacuate as standard practice during an earthquake. "Certainly we don't want to create panic, but we want people to be aware," he said. The dam is about 20 miles [32 kilometers] south of Bend and much closer to a number of upscale developments, including Sunriver, which can be packed with 20,000 people on a summer day.
The bureau estimates that floodwaters could endanger roughly 10,000 people. However, Wolf said there would be time for most people to evacuate. The flooded area would roughly follow the channel of the Deschutes River, extending beyond the banks for more than a mile in some places, he said. Because the river channel flattens in some developed areas, floodwaters would take about 14 hours to reach Bend, he said. An earthquake with a magnitude of 5.0 on the Richter scale could cause a catastrophic failure of the 2-mile-long earthen dam. However, he said the chances of such an earthquake are estimated to be about one-tenth of 1 percent each year. Wolf characterized the risk as remote but real. P The Klamath Falls earthquakes in 1993 were pegged at magnitudes of 5.6 and 6.0, and the Scotts Mills earthquake earlier that year in the Willamette Valley hit 5.6.
Wolf said data collected at the dam in recent years indicated that the saturated silt and ash layers of earth beneath the dam could liquefy during an earthquake. The dam was completed in 1949 and holds up to 200,000 acre feet of water, or enough water to cover 200,000 acres to a depth of one foot. The water is used primarily for irrigation in Jefferson County. Wolf said reclamation engineers have suspected for years that Wickiup Dam was at risk. Those fears were confirmed with additional analysis and testing last year. In February, the bureau decided it needed to warn local authorities and the public about the situation and to undertake a $40 million renovation project.
Jim Mumford, who heads the bureau's dam safety division in Boise, said these are far more specific warnings than the bureau has ever issued to Pacific Northwest communities. For example, when the Ochoco Dam near Prineville was at some risk of failing several years ago, the bureau told residents to contact local emergency service officials if there was a problem with the dam. But with Wickiup, he said, there won't be time to await instructions from officials. "This is the first time where we're saying, 'Don't wait for notification. The earthquake is the notification,' " he said. The bureau also has designated escape routes, then posted fliers and sent brochures to area homeowners with maps of those routes. Larry Zakrajsek, who does risk analysis for the bureau, said the agency did not rush to warn people partly because the danger is small and the dam has functioned well for 50 years.
By Gordon Gregory, Correspondent, The Oregonian The Spring Break Quake of 1993, which rattled buildings across western Oregon and caused $30 million in damage, was a harbinger of an 8 or 9 magnitude quake that is in Oregon's future, geologist Donald Hull tells legislators. "It's been 299 years since the last such event," Hull said. "The window of vulnerability is open again." Hull, who is Oregon's chief state geologist, hopes the Legislature will set aside money for better mapping of earthquake hazard zones and for public safety campaigns to let people know what to do when the Big One hits.
The department has been able to retrofit about 60 bridges since the Spring Break quake, but ODOT estimates that at least 1,500 other bridges in western Oregon are in need of at least some earthquake strengthening. Frank Nelson, ODOT's bridge preservation engineer, said eight more bridge projects are planned, and that the department might be able to do an additional four if lawmakers approve a gas tax increase for road repairs. Those projects should at least be enough to keep Interstate 5 -- Oregon's main north-south lifeline -- open in the event of a major earthquake, Nelson said.
Scientific evidence shows that major offshore earthquakes occur off Oregon's coast once every 350 to 500 years. The last one, in 1700, drowned coastal forests and sent tsunami waves across the Pacific so powerful that they destroyed Japanese fishing villages. Such a quake would not only devastate Oregon coastal communities, but inland areas as well. "The Willamette Valley is a big trough full of loose soils, gravel, sands and silts," he said. "When earthquake waves travel through that kind of sediment, they get bigger; they amplify. I'm just praying it won't happen in my lifetime."
Senate President Brady Adams said lawmakers are aware that Oregon is due for another huge earthquake. "It's hard to define in a specific time frame what the risk is. Is it going to happen tomorrow, or 200 years from now?" the Grants Pass Republican said. "There's no question the threat of earthquakes is real, but we also know we have school funding and other needs that are before us today."
Hull said he can't argue with that logic, but still thinks the Legislature should consider increasing at least to a small degree its financial commitment to preparing the state for the Big One. "There's nothing else in our foreseeable future that's going to be as devastating," the state geologist said. "It's not going to do us any good to fund education programs if the school buildings end up falling on kids' heads."


from

Eugene's Multi-Hazard Mitigation Plan

This NID (National Inventory of Dams) potential hazard classification is solely a measure of the probable impacts if a dam fails. Thus, a dam classified as High Potential Hazard does not mean that the dam is unsafe or likely to fail. The level of risk (probability of failure) of a given dam is not even considered in this classification scheme. Rather, the High Potential Hazard classification simply means that there are people at risk downstream from the dam in the inundation area, if the dam were to fail. ...

Table 12.3
NID High Potential Hazard Dams
Lane County

County Dam Name River City NID Height (feet) NID Storage (acre feet)
Lane Cottage Grove Coast Fork Willamette River COTTAGE GROVE 103 50,000
Lane Dexter Middle Fork Willamette River EUGENE 117 29,900
Lane Fall Creek Fall Creek SPRINGFIELD 205 125,000
Lane Dorena Row River COTTAGE GROVE 154 131,000
Lane Lookout Point Middle Fork Willamette River EUGENE 276 477,700
Lane Blue River Dam Blue River SPRINGFIELD 312 89,000
Lane Hills Creek Middle Fork Willamette River OAKRIDGE 341 356,000
Lane Cougar South Fork McKenzie River SPRINGFIELD 519 219,000
Lane Fern Ridge Long Tom River EUGENE 49 121,000

Of these NID High Potential Hazard dams all except Fern Ridge are upstream from the Eugene/ Springfield Metro Area.

 

12.4 Dam Failure Hazard Assessment: Eugene/Springfield Metro Area

A 1987 report on Dam/Levee Failure by the Oregon Emergency Management Division lists 51 historical dam failures in Oregon from 1896 through the 1980s. As of the time of this report, no dam failure fatalities had been recorded in Oregon. However, the potential for dam failure fatalities certainly exists in Oregon, in Lane County and in the Eugene/Springfield Metro Area, albeit with a low probability of occurrence.

To evaluate the level of risk posed by the dams affecting the Eugene/Springfield Metro Area, we consider the nine dams in the NID high potential hazard classification where the potential impacts of failure, including life safety, are greatest. Much smaller dams in the significant and low potential hazard categories do not pose a life safety threat and the risk of property damage is minimal or low.

 

12.5.1 Flood Damage to Dams

All of the Corps dams were designed and built with specific flood capacities. Current dam designs are based on Standard Project Floods. Standard Project Floods, as defined in the Corps Engineer Manual 1110-2-1411 (March 1, 1965) are floods resulting from the Standard Project Storm. In turn, the Standard Project Storm is defined, somewhat imprecisely, as the most severe flood-producing rainfall-snowmelt, depth-area-duration event that is considered “reasonably characteristic” of the drainage basin. Discussions with Corps staff in the Portland District Office indicated that the Standard Project Flood is approximately a 500-year flood event.

The Corp dams’ discharge design levels include the combination of spillway discharge capacity and reservoir outlet pipe discharge capacity. For example, for the Hills Creek Dam, the Standard Project Flood is 64,500 cubic feet per second. The maximum controlled discharge capacity of the dam is 151,760 cubic feet per second, or nearly two and one-half times the Standard Project Flood discharge. These data are included on the Hills Creek Project, Emergency Response Flowchart7. At discharges beyond the maximum controlled discharge capacity of the dam, the dam would be overtopped, discharges would be uncontrolled, and there would be a high probability of damage to the dam, with some potential for dam failure. The large margin of safety in the discharge capacity of the dam suggests that the Hills Creek Dam likely has the capacity to withstand floods at least as large as a 1,000 year flood event without expected damage. The other Corps dams have similar margins of flood design safety.

12.5.2 Earthquake Damage to Dams

All of these dams were designed and built in the 1940s to 1960s. Seismic design considerations were thus significantly lower than current seismic design considerations. A summary tabulation of the seismic design basis and inspection history of these dams is given below in Table 12.5 (Corps of Engineers, Portland District Office, March, 2001).

Table 12.5
Seismic Design, Evaluation and Inspection Data
Corps of Engineers Dams

Dam Date of Last Seismic Evaluation
Seismic Design Basis
Date of Last Periodic Inspection
Original Current
Cottage Grove 1981 None 0.21 g 1997
Dexter 1981 0.10 g 0.21 g 1996
Fall Creek 1981 0.10 g 0.21 g 1999
Dorena 1981 none 0.21 g 1997
Lookout Point 1981 0.10 g 0.21 g 1999
Blue River 1994 0.10 g 0.24 g 1996
Hills Creek 2000 0.10 g 0.22 g 1999
Cougar 1994 0.10 g 0.24 g 1997
Fern Ridge 2001 none 0.35 g 2000

 

As shown in Table 12.6, the Corps has conducted at least preliminary seismic evaluations of all of these dams. However, some of these evaluations were conducted in the 1980s and thus do not reflect current understanding of the seismic hazard in Oregon or current state-of-the-art seismic evaluation engineering principles. The Corps has an ongoing regular inspection program and an ongoing seismic evaluation program. Presumably, updated seismic evaluations of these dams will be completed over the next few years.

Seismic considerations were completely absent in the design of two of these dams: Dorena and Fern Ridge. The others were explicitly designed or probably designed to ground shaking levels of 0.10 g, which is the maximum seismic design level for any of the Corps dams in western Oregon. In contrast, the current Corps seismic design levels for dams at these sites (i.e., if new dams were to be built today) would be 0.21 g to 0.24g for the dams in eastern Lane County and 0.35 g for Fern Ridge . Thus, current seismic design requirements are for levels of ground shaking about two times higher than the probable design levels for most of these dams and about three times higher for Fern Ridge.

Seismic evaluations of dam safety are a highly technical, highly specialized art. Separate evaluations must be done for each dam. The evaluation requires a detailed analysis of the design and construction of the dam, an analysis of the current condition of materials and components, geotechnical analysis of the foundation and site, and a site-specific seismic hazard analysis. For emergency planning purposes, a seismic evaluation should include the probabilities of failure for a scenario earthquake such as a large magnitude event on the Cascadia Subduction Zone.

12.5.3 Loss Estimates (Preliminary)

Detailed loss estimates for possible failures of these dams are beyond the scope of this mitigation plan. However, we note that in 1987 the Oregon Emergency Management Division estimated that a completely catastrophic failure of the Hills Creek Dam, an extremely unlikely event, could require the evacuation of over 250,000 people with damages in excess of $10 billion. Adjusting these 1987 estimates for inflation and for population growth suggests that damages could easily exceed $20 billion. Detailed casualty estimates have not been made for catastrophic dam failures affecting Lane County. However, given the large inundation areas, high water depths, and the logistical difficulties in evacuating 250,000 people to safe ground, it is not difficult to imagine that a truly catastrophic dam failure could potentially result in 1,000 or more deaths.

The probability of catastrophic failure of these dams is impossible to estimate with any accuracy, from present data. Most likely, the probability is less than 0.1% per year (less than once in 1,000 years, on average) and perhaps substantially less. However, the consequences of failure are so high that careful evaluation is certainly warranted.

The potential impacts of dam failures on the Eugene/Springfield Metro Area are summarized below in Table 12.6

Table 12.6
Potential Impacts of Dam Failures on the Eugene/Springfield Metro Area

Inventory Probable Impacts
Portion of Eugene/Springfield Metro Area affected Direct impacts limited to mapped inundation areas for dam failures, or to smaller areas for more likely partial failures
Buildings Heavy damage in inundation areas
Streets within Metro Area Damage and closures in inundation areas
Roads to/from Metro Area Damage and closures in inundation areas
Electric power Damage and loss of service in inundation areas
Other Utilities Damage and loss of service in inundation areas. Potential for major damage to water and wastewater treatment plants in extreme events
Casualties Potential for high casualties (deaths and injuries) in extremely unlikely major dam failures, depending on warning time available and effectiveness of evacuations

 

12.6 Mitigation Strategies

Possible dam failures affecting the Eugene/Springfield Metro Area are low probability events, but the potential casualties and economic consequences are extremely high. The combination of low probability but large consequences makes analysis of such situations difficult from both a technical and a public policy perspective. The evaluation is difficult technically because it requires detailed engineering analysis of each dam and careful probabilistic risk analysis. As always, communication with the public must be non-alarmist, but factual, realistic and informative.

Recommendations

1. Because of the age of these dams, the seismic design basis of all of the dams potentially affecting the Eugene/Springfield Metro Area is significantly below current seismic design requirements. Preliminary seismic evaluations have been done but without sufficient detail to evaluate the probabilities of dam failures. Because of the extreme consequences of potential failure of one or more of these dams, we recommend that detailed seismic evaluations be conducted for all of these dams. All of these dams are owned and operated by the U.S. Army Corps of Engineers. Therefore, pragmatically, the role of the Eugene/Springfield community would be primarily to strongly encourage the Corps of Engineers to complete these urgently required seismic evaluations as soon as possible.

2. A key step in mitigation planning for dam safety is emergency planning. Emergency planners in the Eugene/Springfield Metro Area should obtain copies of the inundation maps for each of the major dams to familiarize themselves with the areas of potential flooding. For emergency planning, the estimated flood depths and the time periods from dam failure are particularly important. Flood depths and flood times both vary markedly with distance downstream from the dam locations. For emergency planning, key elements include community emergency notification procedures and evacuation planning (routes and traffic control). Because of the very large numbers of potential evacuees, training seminars and scenario exercises are strongly recommended.

3. All of these dams have Emergency Action Plans. These plans should be reviewed to ensure that they are complete and up to date. Emergency planning officials in each county should be fully informed of the detailed consequences of the potential failure of each dam. Public notification and evacuation plans should be updated and tested. For some types of dam failures, for example, those due to extreme floods, there may be some warning time. Decision making procedures, protocols, and procedures for issuing watches, warnings, and evacuation notices should be reviewed and updated and coordinated among all responsible federal, state, and local agencies. [emphases added]