clock menu more-arrow no yes

Filed under:


Atransient riding a train through Utah's arid West Desert in 1983 could not have dreamed that he would soon drown there in a flood. But the U.S. Army Corps of Engineers had warned three years earlier that someone would.

That's when it said the DMAD (Delta-Melville-Abraham-Deseret) Dam was unsafe because its spillway wasn't big enough to handle potential runoff. While no major modifications were made to the spillway, the report simply collected dust.Then in 1983, the DMAD Reservoir swelled rapidly with late spring runoff. The spillway buckled, the dam failed and floods scoured towns downstream causing millions of dollars in damage and cutting off the transient's train.

Nine witnesses said he tried to escape surrounding floods by swinging hand over hand across a telephone line. He lost his grip, fell and was swept under by the swirling waters. Police assume he drowned but never found his body or learned his name. He was soon as forgotten as the corps' report.

The DMAD was just one of 67 Utah "high hazard" dams a classification meaning someone would likely be killed if they fail that the corps declared unsafe during studies from 1977 to 1981, according to documents inspected by the Deseret News. Congress ordered those studies after the Teton Dam in Idaho collapsed in 1976, killing 11 people.

Almost all those dams still have not been upgraded, according to inspection reports in the state engineer's office. Many sit precariously upstream from the state's largest cities including Mountain Dell Dam above Salt Lake City and Logan First Dam above Logan.

Of the 101 "high hazard" dams the corps inspected in the state, just seven were considered safe. Besides the 67 dams declared unsafe, the corps said additional studies are needed to determine whether the other 27 dams it studied are safe. Congress never funded those recommended studies.

Richard B. Hall, the state dam safety engineer, said he thinks the corps used criteria that are a bit too strict. But he too still considers 27 of the 167 "high hazard" dams inspected by his office as unsafe, according to modern dam construction standards, and is unsure about 63 others.

In short, that means state and federal officials agree that at least half the state-inspected dams upstream from populated areas in Utah are either unsafe or they are unsure whether they are safe.

Besides those state-inspected dams, the U.S. Bureau of Reclamation built and inspects numerous other large dams in the state or near its borders. The 15 such dams evaluated so far in the bureau's "Safety Evaluation of Existing Dam" (SEED) program received mediocre or poor ratings.

Five were rated "fair," one was "fair to poor," eight were "conditionally poor" (meaning more study is needed to determine how safe they are) and one was "poor." However, the most questionable dams were evaluated in the program first, and safer dams have yet to be studied, said Wayne Wilson, engineer with the bureau's design and construction section.

To understand what danger dams may pose, an understanding is needed of three main characteristics that officials evaluate adequacy of spillways and outlets to handle potential runoff, or its hydrology; a dam's structural soundness and maintenance; and the ability of a dam to withstand earthquakes.

Hall said 90 percent of the dams deemed unsafe have spillways too small to handle potential runoff without overtopping the dam similar to the DMAD's problem. They are considered to be safe during normal operations in normal years, but runoff from heavy storms or snow pack could cause overtopping.

Water passing over the top of earthen dams may quickly erode its crest and downstream side, causing the dam to break apart. Water passing over a concrete dam may splash hard at its foundation, eating away dirt there and possibly causing the structure to tip over.

Hall said Utah has no laws that force existing dams to upgrade spillways to solve such potential hydrologic problems much like city building inspectors cannot force owners of older houses to install new plumbing and wiring to meet new, more stringent building codes.

About 10 percent of the dams are considered unsafe because of structural or maintenance problems such as broken outlets, sinkholes or seepage through the structure, Hall said.

If such problems are serious enough that they pre-sent immediate threat of a dam failure, the state may order the reservoir drained and the dam breached or repaired. But the process of ordering draining can drag on for years.

None of the dams have yet been classified as unsafe because of concern about how well they would hold up during earthquakes, although that is a main reason the Bureau of Reclamation gave many of its dams low ratings. Officials really don't know how dams would react in earthquakes.

Following are looks at potential problems with dams in each category of concern hydrology, structural problems and stability during earthquakes:

Hydrologic problems

Mountain Dell Dam is a large concrete structure sitting just off I-80 in Parleys Canyon, seven miles upstream from Salt Lake City. Officials admit now that it came within an hour in 1983 of overtopping, or having water spill over its crest.

That would have damaged or destroyed the Salt Lake City water treatment plant below it, and likely would have washed out much of the nearby freeway. Extended overtopping could have led to a dam failure that would have caused extensive flooding down Parleys Canyon and through much of Salt Lake City.

For that reason, he said, the city and its metropolitan water district had agreed with the state engineer that they should not fill the reservoir until after spring runoff. But in 1983, the runoff came so rapidly and abundantly that the reservoir filled anyway, even though the outlets and spillway were running nearly wide open.

"As I remember, it was a race to try to get up dikes along 13th South (to turn the street into a sandbagged river) to allow us to release as much water as we could to keep as much freeboard as possible at the dam," Hooton said.

He remembers that, at one point, projected runoff data made officials fear the dam would be overtopped no matter what they did. However, the weather cooled a bit and slowed the runoff allowing 13th South to be sandbagged and extra water to be drained by intentional flooding there.

Hooton and former Salt Lake County Flood Control Director Terry Holzworth, since promoted to director of Development Services, said the dam was within about an hour of being overtopped when city officials started flooding 13th South.

Holzworth said the street flooding could have been started earlier in dire emergency, but officials held off as long as they could.

Even though the dam was not overtopped, officials worried for a time that it still may have been damaged. With outlets running full blast, Hooton said the vibration and noise at the dam was tremendous. "You couldn't hear yourself think in the outlet house." He worried that could have caused cracks.

Later inspections pronounced the dam structurally sound, and even probably safe in case of an earthquake.

Officials say hydrologic problems with Mountain Dell's small spillway should soon be a thing of the past. The city, county and Army Corps of Engineers are building the new, larger $50 million Little Dell Dam upstream.

The new dam is designed to safely hold potential runoff in the area. Hooton said, when the new dam is complete, the older Mountain Dell reservoir will never intentionally be more than two-thirds full. That extra third of capacity at all times should allow the dam to handle any runoff safely.

But most of the other 27 to 65 dams with similar hydrologic problems depending on whether one looks at Army Corps of Engineers or state criteria have no immediate plans to upgrade their facilities.

An example is Logan First Dam just above Logan. Its spillway can pass only 1 percent of the potential maximum flood in the area. Corps of Engineer's criteria say a dam should pass 100 percent of that flood and considers it an emergency situation when a dam can pass only 50 percent of it, said John White, chief of civil design at the corps' Sacramento, Calif., office.

State inspection reports also say repairs have been needed for years for seepage and deteriorating concrete at the dam.

But Utah State University, which owns it, wrote state engineers that it can't afford repairs unless the Legislature comes up with more money.

Similar financial problems of other dam owners, such as small irrigation companies, was seen as the main hindrance to needed repairs in a recent dam safety progress report by the Federal Emergency Management Agency.

Utah, like most states, has no laws to force dam owners to use their scarce resources to upgrade inadequate spillways.

Montana, however, adopted such a law in 1985. It ordered owners of high-hazard dams to obtain construction permits to upgrade inadequate spillways by 1990, and finish construction by 1995.

Lawrence Siroky, assistant administrator with Montana's Water Resources Division, said many dam owners are hiring engineers to prepare construction plans. He said he likely won't know how well most dam owners will cooperate until the first 1990 deadline.

Hall said such a law may help in Utah. But before the Legislature considers it, he would rather see lawmakers appropriate money for high-tech equipment to allow inspectors to check out potential problems with outlets the pipes through dams that control how much water is released.

"A storm that produces 50 percent of the potential maximum flood happens once every 10,000 years which is a fairly remote possibility. But an outlet pipe breaking or becoming blocked is much more likely and can overtop a dam just as easily," he said.

He would like television equipment to allow underwater inspection of those outlet pipes, but that system costs an estimated $40,000.

Structural problems

In the 11 years since Utah created a formal Dam Safety Section in the state engineer's office, Hall said it has solved most serious structural and maintenance problems that could pose immediate threat of a dam failure.

To do that, he said, the office has many times had to threaten to have a reservoir drained unless repairs are made immediately. But that process sometimes takes time, and leaves residents downstream unprotected for weeks or months. In the case of Birch Creek Dam No. 1, it did that for years.

Birch Creek Dam No. 1 is just one example of many dams where recommended, or even ordered, improvements from the state are often ignored or not acted upon by owners.

Inspection reports in the state engineer's office show that on Oct. 13, 1981, the state ordered the Woodruff Irrigation Co. to restrict storage at the dam by leaving its outlet unblocked. The state noted that a large sinkhole in the earthen dam nine miles upstream from Woodruff, Rich County and earlier heavy seepage "raises considerable concern" about the dam's safety.

The state engineer said the dam had to be repaired before the 1982 spring runoff, or the dam would be breached so no storage could occur.

For whatever reasons, nothing happened for a year.

Files show that a year later on Oct. 22, 1982, the state engineer sent another letter saying inspectors had just "observed that no repairs had been done as required in the state engineer's order." Additionally, the outlet had been closed (against orders), and the reservoir storage was high enough that overflow was passing through the spillway.

"It is my duty to order the breaching of Birch Creek Dam No. 1 so that no storage may occur in 1983," the letter says. "Failure to abide by this order will result in our taking appropriate legal action," the state engineer warned.

The irrigation company wrote the next month that it planned to renovate and repair the dam to avoid breaching it. The state engineer's office said that would be fine, but asked that it be kept advised of plans.

The dam was not fixed by the next spring.

In fact, a letter from the state on July 26, 1983, said an inspection showed, "This reservoir was full and spilling, which is in direct violation of state engineer's restriction on storage in this structure. We must reiterate that this structure has been ordered breached to prevent storage."

It wasn't breached or repaired for years.

A letter from the state dated Oct. 16, 1985, said: "Our observations revealed the same problems that have existed for a number of years. . . . We have serious concerns relating to the stability of the dam. . . . We have no alternative other than to assume the dam and its appurtenant facilities are inadequate and the dam should be removed. . . . We feel we should give you one more opportunity to comply."

The Woodruff Irrigation Co. wrote back the next month saying it was trying to comply with ordered repairs, and complained that the reservoir had filled improperly because some unauthorized person had closed the dam's outlet gate.

Finally, a letter on April 15, 1986, from the state noted that some of the most major repairs had been made to the dam, such as filling sinkholes and adding needed riprap boulders to protect the dam against wave erosion.

But the letter noted that many ordered repairs had not been done, including clearing debris from the outlet channel and the intake, and removing brush. A letter two months later noted some but not all of those problems were resolved.

But a letter on July 15, 1986, said much needed work on the dam still remained. Another deadline of Oct. 1 was set for those repairs, or the state warned that another order to restrict storage there would be made.

The last inspector's work sheet in the file, dated Sept. 23, 1987, commended the irrigation company for removing much problematic vegetation. But said problems remained with seepage, more vegetation and rodents (roots from vegetation and rodent holes can cause seepage and potential failure of a dam).

Inspection records of other dams show most dam owners do comply with orders for major repairs, especially when their dams could either fail or be intentionally breached by the state.

But more minor repairs such as vegetation removal reappear year after year in inspection reports. In one case an old truck bed was being used as a bridge over a spillway; in another, a deteriorating spillway eroded to the point that the dam was considered in serious danger.

Seismic problems

More than four decades ago, in 1942, the state engineer sent the Legislature a report saying, "Many reservoir dams have been built without regard to proper precaution in their construction. At least 38 of these dams have failed."

He complained then that farmers built irrigation dams without proper engineering or materials. In 1942, such problems caused worry mostly about hydrologic or structural problems. Now it is causing concern about earthquakes.

The reason is simple. During an earthquake, many types of soil especially sands act as if they were a liquid. If an earthen dam acts that way in a major earthquake, the ground waves could cause buckling and distortions that could lead to a failure.

That is a special concern in Utah where scientists say a major earthquake is due. A 1980 bulletin of the Seismological Society of America says an earthquake measuring between 6.5 and 7.5 on the Richter scale is "due or past due somewhere along the Wasatch Fault."

Many of the older dams were likely built with "liquefiable " sandy materials that were near river beds where the dam was constructed. As Hall said, "If I were a farmer back then, I'd probably do the same thing. I wouldn't want to carry dirt in from a long way."

He said many dams were built by constructing an open slurry of water into which workers shoveled dirt. The mud mixture was then piled up into a dam. Records showcompaction of the dirt was sometimes accomplished by merely running horses over the dam, and ensuring their hooves sunk at least two inches.

Now heavy machinery is used, and compaction is measured with scientific precision.

No records at all were kept about the construction methods and materials of many older dams. Determining that information now would require expensive core drilling and other tests. Such studies were recommended by the Corps of Engineers for many dams, but were not funded by Congress.

Even if that information were available, the science of determining how dams will stand up during earthquakes is still in its infancy, Hall said. For example, officials still question what an earthquake would do to most federal dams in the state which are generally newer and have detailed data about their construction.

Of the 15 federally built dams that the Bureau of Reclamation evaluated in its SEED reports, 11 have high or moderate liquefaction potential.

But the report about East Canyon Dam near Morgan illustrates how tenuous those studies are. "Based on results obtained from the analyses used, one could not say the dam would be safe during the event (major earthquake). However, based on inherent limitations in the analysis, it would be premature to say the dam would be unsafe."

Hall expects that as seismology develops over the next several decades, better criteria for new dams will be developed as will ideas on how to make existing dams more safe.

Future outlook

Numerous suggestions have been made in federal and state studies on how to make dams more safe. The trouble is that they all require money and Congress and the Legislature have been trying to cut budgets, not add to them.

Sen. Fred Finlinson, R-Murray, chairman of the Legislature's Energy, Natural Resources and Agricultural Interim Committee, said anti-tax feeling would likely prevent lawmakers from funding more for dam safety anytime soon.

"If you asked people if they should raise their taxes so that every dam can pass a once-in-1,000-year storm, I suspect that would not pass a referendum this year. It may take a dam failure for something like that," he said.

Still, for the record, suggestions officials make to improve dam safety include providing money or tax incentives to help dam owners upgrade their facilities, passing laws requiring owners to bring dams up to code, passing funding for studies to better determine the materials and design of older dams to evaluate their safety, buying new equipment such as television systems that can inspect underwater outlets, and prepare more emergency action plans.

The Federal Emergency Management Agency has also recommended that states have better inspection programs. Utah is already one of 21 states with inspection programs that FEMA considers adequate.

But Hall said the program is still mainly concerned with rectifying maintenance problems that pose immediate threats for dam failure. He said his office is just beginning after 11 years to seriously address longer range hydrologic problems. And as staff and money is available, he wants to also better address seismolo-gic problems.

"Eventually, I guess we could work ourselves out of a job. That would be nice, but I doubt it will happen," Hall said.

Until it does and problems are resolved, official reports predict more people will die it's just a matter of when. In 1983, it was an unsuspecting transient riding a train near Delta. Depending on which dam fails next, reports say dozens or hundreds could die.