They have the destructive force of hundreds of runaway freight trains, rushing uncontrollably downstream all at once.
Fortunately, dam breaks are rare. The last full-blown failure to hit Utah came New Year's Day 1989. The Quail Creek Dam collapsed, propelling a 12-foot wall of water into St. George and racking up more than $11 million in damage to homes, roads, farms and utilities.
That catastrophe spurred the Legislature to beef up dam-safety laws with updated design standards, enhanced inspector training and stricter quake-resistant regulations.
Yet even now, after more than 18 years and millions of dollars in improvements, scores of Utah dams still fall short of minimum safety standards, a problem magnified by the age of the structures, their seismic vulnerability and the hazard-boosting effects of urban development in dam-flood zones across the state.
Since the reforms of 1990, State Dam Safety Engineer David Marble said 191 dams so far have received the detailed compliance review ordered by law. Of those, 51 meet minimum safety standards (31 of those after the dams were rehabilitated). Owners of another 31 dams lower their safety risks by altering storage levels or spill flows, instead of doing reconstruction.
The remaining 109 of these so-called high-hazard dams are either prioritized for review or under investigation. Yet no dam is in imminent danger of failing, Marble insisted.
"Whether a dam is safe or not is a tough question," he said at his office at the state Division of Water Rights, which includes a staff of three full-time and two part-time dam inspectors, seven regional offices and support crew.
"When we refer to minimum safety standards, this is not a low-safety standard," he said. "This is the state-of-the-industry practice to protect public safety."
Of 900 dams in Utah, more than 850 are big enough to be listed on the federal National Inventory of Dams. About 50 are federally run and include monumental dams such as Flaming Gorge and Jordanelle. The rest are state-regulated; the bulk of which are privately owned by water districts and irrigation companies.
Because even small dams can store millions of gallons of water, they are inherently dangerous. All the same, little public awareness goes to the issue of safety.
"We don't really hear a lot about it," said state Rep. Roger Barrus, a retired engineer from Centerville who sits on the House budget committee overseeing dam spending. "It's something that does not get as much attention as other areas."
The biggest risks:
Dam security and safety took on more urgent dimensions with the terrorist attacks of Sept. 11, 2001, followed by the levee failures that accompanied Hurricane Katrina in 2005 and the Midwestern floods earlier this month.
States reported more than 1,090 dam-safety incidents between 1999 and 2004, including 125 failures, according to the Stanford University-based National Performance of Dams Program. Marble said Utah had at most a handful of similar incidents yearly during the same time frame and no failures.
The most immediate threats come from severe weather and earthquakes, Marble said, so Utah's standards are geared toward countering those dangers. "We're designing for extreme events," he said.
Seismic risks are real, notably along faults beneath the urban Wasatch Front. The looming threat of a major quake is made worse by the number of older earthen dams and their vulnerability to liquefaction, in which the shaken terrain turns Jell-O-like and causes slumps, cracks or collapse.
The state uses computer modeling to map the potential effects of earthquakes on its dams. But because it almost always involves structural work, such as replacing original construction materials or adding new foundation layers, seismic renovation of dams is expensive.
Flooding is a recurring risk. With this year's record precipitation in some areas, inspectors are watching several dams already well above their storage capacities. The state also has recently ordered steps, such as draining or mandatory reconstruction on several dams, to keep structural problems from deteriorating into an all-out failure.
Inspectors also have pressured dam owners for years to improve emergency spillways, a program which paid off during heavy storms in January 2005, when spillway diversion helped avert potential failures at Enterprise, Gunlock and Baker Ash dams in southwestern Utah. Of nearly 30 state dam projects completed recently, at least a third involved spillway work.
The state has averaged about two major renovation projects a year as it whittles away at its list of deficient dams.
Construction is being completed this season on the Upper Enterprise -- 12 miles upstream of the Washington County town of Enterprise -- one of nearly a dozen state and federal dam-repair projects under way. Owners of a dam near Kaysville were ordered last year to lower water storage or breach the structure temporarily to repair a potentially dangerous leak.
Design studies are being done now for upcoming work on such notable dams as Miller Flat, Wide Hollow, DMAD, Mill Meadow and Gunnison Bend.
The 94-year-old Sevier Bridge Dam in Juab County has undergone several costly reconstructions and still has safety concerns, state inspectors say. Yet shutting it down would cripple farming across the region, said Kenneth Fowles, Consolidated Sevier Bridge Co. president.
"They have some real nitpicking things I don't see the need for, but I'm not an engineer," Fowles, a hay and grain farmer in Delta, said of the inspectors. "We just try to comply with whatever they order us to do."
After all, Fowles added, "If nobody was forcing safety, there wouldn't be any safety."
High hazard, low funding:
State engineers target their most intense inspection efforts on about 190 high-hazard dams, a designation based solely on the potential loss of life and economic damage a failure could cause. Most federal dams in Utah also are deemed high hazard and are subject to yearly inspections and a comprehensive examination every three years.
Bruce Barrett, area manager with the U.S. Bureau of Reclamation in Provo, said the federal agency takes much the same approach to its 40 or so high-hazard dams in Utah, following guidelines in the Dam Safety Act passed by Congress in 1978, after the 1976 failure of the Teton Dam in Idaho. In addition to inspections, some of the larger federal dams -- such as Flaming Gorge and Glen Canyon -- have dam tenders who monitor the structures continually.
This season, the massive Deer Creek, Scofield and A.V. Watkins (Willard) dams will get sizable shares of $71.5 million in federal dam improvements scheduled through 2009. Without continued spending on such projects, time will only increase the risks to Utah's dams.
Beyond the threats from a monster storm or a hefty quake, age is a primary indicator of a dam's likelihood of failure, and 305 of Utah's dams including 97 of its high-hazard ones are more than 50 years old, a typical life span in dam design.
Fifty-three high-hazard dams are more than 75 years old and 17 of them were built a century or more ago. The state's oldest functioning dam on the national registry, Silver Creek Estates in Summit County, was built in 1865 -- one of 10 Utah dams erected in the decade after the Civil War and still in use.
Risks rise with the proximity of population centers to dams. Utah's geography of sheer mountains abutting major cities puts large numbers of residents within breach-flood range of one or more of these dams. Even in rural regions, dams commonly are upstream from towns.
Development in the shadow of dams is the primary force -- here and across the nation -- making dams more hazardous, according to a 2004 study by the Federal Emergency Management Agency.
"We call it hazard creep," said Sarah Mayfield, a spokeswoman for the Association of State Dam Safety Officials.
Population growth, in turn, drives further demand for dam construction. Only three states -- California, Virginia and Wisconsin -- have laws requiring developers or urban planners to recognize hazard creep.
While Utah has no related statutes, Marble said dam owners frequently are reminded that "as this creep takes place . . . they are responsible for that increased hazard rating."
The price tag to fix seismic and structural problems of Utah's dams is staggering. In 1995, the figure was pegged at $60 million, "a crude estimate," Marble said, and one that has shot up since. A recent American Society of Civil Engineers study put Utah's dam-rehabilitation tab as high as $203 million.
State aid helps dam owners defray the cost of safety upgrades. Utah doles out about $4.3 million a year in grants and offers interest-free loans. What's more, lawmakers have tweaked safety laws to protect dam owners from the full brunt of lifting up old dams to meet modern standards.
Dams built for flood control are exempt from seismic standards. More important, state law prevents the state engineer from requiring nonemergency upgrades even on privately owned dams unless the state Board of Water Resources pays 80 percent of the cost.
A veteran member of the state Water Development Commission said making taxpayer cash available to private dam owners serves a wider public interest.
"Upkeep will take care of itself as long as the government in the state of Utah is making sure the dams are safe," said David Ure, a Kamas dairyman and former state legislator. "Those dam owners have a very valuable asset tied up in those dams. They will rise to the occasion of ensuring dam safety."