Should We Trust?
by Lynn Stuter
News with Views.com, March 4, 2008
A recent report on krem.com caught my attention. That report concerns Dworshak Dam (Google Map Link) on the North Fork of the Clearwater River in Idaho, approximately 35 miles east of Lewiston, Idaho in what is considered central Idaho. The North Fork of the Clearwater River empties into the Clearwater River at Ahsahka (Ah-soc-a), just north of the town of Orofino. The Clearwater River empties into the Snake River at Lewiston, Idaho; the Snake River running, at that point, on the border between Idaho and Washington. The Snake River empties into the Columbia River at the Tri-Cities — the Pasco/Kennewick/Richland area of Washington. The Columbia River forms the border between Washington and Oregon and flows into the Pacific Ocean.
According to the news report on krem.com, Dworshak Dam is "potentially unsafe."
Before going further, a little about Dworshak Dam. The dam was put into service in June 1972. The dam stands 717 feet tall; is the third tallest dam in the United States, only exceeded in height by Hoover Dam in Nevada and Oroville Dam in California; and is the largest straight axis concrete dam in the Western Hemisphere, measuring 3287 feet across at the apex.
The reservoir behind Dworshak extends approximately 53 miles upstream. According to the Army Corp of Engineers Dworshak Dam holds back 3,468,000 acre-feet of water. To put that in perspective, one acre-foot equals 43,560 cubic feet of water which, in turn, equals 325,851.428 gallons of water. Doing the math, 4,368,000 acre-feet equates to 1,130,052,752,304 gallons of water being held back by Dworshak Dam. In terms of weight, one gallon of water weighs eight pounds. This equates to 9,040,422,018,432 lbs or 4,520,211,009.216 tons of water behind Dworshak Dam. It needs to be noted here that this weight is not the weight of the water pressing on the dam. It is, however, the standing weight of the water that would come out of Dworshak should it collapse. And, of course, moving mass weighs more and has greater destructive force than standing mass.
As the reservoir behind Dworshak Dam began to fill in 1972,
"vertical cracks striking upstream-down-stream occurred in the center of 9 monoliths of the concrete gravity structure. They extended from the base of dam to heights ranging to almost 400 feet and propagated downstream past the drainage gallery. Drain holes (1.5 inches in diameter) were drilled into the cracks from the galleries and angled to intersect the cracks at 5-foot vertical intervals along a line about 30 feet from the upstream face. These drain holes successfully reduced hydrostatic pressures in the cracks, resulting in the reduction of crack widths and arresting of the downstream propagation of the cracks." (Source)In 1980, the dam developed a ...
"236-ft. long crack on the reservoir side. 7700 gallons per minute of water was sprayed past the powerhouse down into the river. The cost to fix the leak exceeded $1 million. The U.S. Army Corps of Engineers drilled seventy holes into the dam to intercept the crack, relieving pressure on the dam. A plastic sheet was then lowered over the crack. This reduced the flow by half. Additional repairs including a patch made of sawdust, cement and volcanic ash further reduced the flow to an acceptable level." (Source)The last periodic inspection of Dworshak Dam was completed in June 2007. How in-depth that inspection was is not stated. In an undated report, issued subsequent to June 2007, by the U.S. Army Corps of Engineers, Walla Walla District, appearing on the krem.com website, the following is stated,
"While inspections and studies show that seepage and leakage water is passing through the dam's foundation and/or joint drains, the probability of failure at Dworshak Dam is relatively low. The current potential for failure is low because although we see increased seepage and uplift pressure readings, we are not seeing any additional signs of cracking and stress in the monoliths which would be the signs that the risk of failure is increasing."Further,
"In addition, we have completed an initial stability analysis and determined that the uplift values are not high enough to overturn a monolith. Given this amount, type, and level of inspections and evaluation, we believe Dworshak dam is in good shape."Please note that The U.S. Army Corp of Engineers does not state that they "know" Dworshak dam is in good shape, just that they "believe" Dworshak dam is in good shape. There is a big difference between "I know" and "I believe"; one is definitive, the other a subjective assessment.
What would happen if Dworshak Dam collapsed?
Dworshak Dam sits approximately 1.9 miles from the confluence of the North Fork of the Clearwater River and the Clearwater River. Were the dam to collapse or break, the reservoir of water behind that dam would obviously be unleashed and in a matter of seconds a raging torrent of water would be headed both up the Clearwater River and down the Clearwater River to Lewiston, Idaho and Clarkston, Washington. This fast-moving wall of water would be constrained by the canyon walls on either side of the Clearwater River.
At immediate risk would be the populated areas of Ahsahka and Riverside at the confluence of the North Fork of the Clearwater River and the Clearwater River, and Orofino, Idaho, which sits approximately four miles upriver from the confluence. These two communities and one town would have little to no warning. Eleven miles upstream sits the community of Greer; 25 miles upstream sits the town of Kamiah (Kam-e-i); 32 miles upstream sits the town of Kooskia (Koos-key); all sitting on the banks of the Clearwater River; all within the Clearwater Canyon.
The downriver rural populace along the Clearwater River would also be at risk as would Lewiston, Idaho and Clarkston, Washington, both of which sit on the banks of Clearwater River and Snake River, both within the Clearwater/Snake River canyons. The devastation and loss of life; the loss of infrastructure would be catastrophic.
Not only would the raging torrent destroy every road, bridge, railroad bridge and railroad track in its path, it would also collect up a growing volume of debris that would undoubtedly include any barges sitting at the Port of Wilma in Lewiston, any boats moored at marinas or sitting in yards and garages, railroad engines and cars, long haul trucks, fire trucks, farm equipment, motor homes and trailers, vehicles, household appliances and lumber from destroyed homes and outbuildings. At Lewiston, the torrent would gather the row on row of saw logs piled in the log yard on the property of Potlatch Forest Incorporated (PFI), sitting on the south bank of the Clearwater River just above the confluence of the Clearwater and Snake Rivers. The ever increasing volume of debris in the torrent would serve to increase the destructive power of the torrent as it raced downstream leaving a swath of destruction in its wake.
After hitting the Lewiston/Clarkston area, the raging torrent of debris filled water would head down the Snake River, constrained by canyon walls. Between Lewiston/Clarkston and the Tri-Cities (Kennewick, Richland, and Pasco), Washington, the deluge would hit four hydroelectric and lock dams on the Snake River; the locks on those dams are used to move barge traffic from the Pacific Ocean to the Port of Wilma at Lewiston, Idaho. The dams, in sequence, are Lower Granite, Monumental, Little Goose and Ice Harbor.
All together, these dams hold back approximately 1,108,865 acre-feet of water. This equates to approximately 361,325,243,709.22 gallons of water. It is doubtful that any of these dams is strong enough to withstand the type of debris filled torrent that would hit them suddenly and with force. By the time the torrent hit the Tri-Cities, the water volume would be approximately 1,491,377,996,013 gallons of water. That volume would be increased by debris contained therein.
At the Tri-Cities the Snake River flows into the Columbia River, making a sharp left to do so. Straight ahead lays Kennewick. The topography of the Tri-City area is relatively flat. A range of craggy hills runs from west to south to southeast bordering the Tri-Cities with a gap where the Columbia River cuts a channel through them. Coming out of the Snake River at the Tri-Cities, the deluge would wipe out Kennewick, Pasco and Burbank, probably Richland and West Richland. The natural path of the raging torrent would be to head southwest to the range of hills then back into the Columbia River, through the gap in the hills and on down the Columbia.
A report by KLEW TV out of Lewiston, Idaho, quoted the USACE, Walla Walla District, as saying:
"The Corps says, in the unlikely event of a failure at Dworshak, the impact would be ‘very high' and would extend all the way to McNary Dam."Would it stop there or would it continue on down the Columbia, taking out four more dams on its way to the Pacific Ocean: McNary, John Day, The Dalles and Bonneville? On this map, McNary Dam sits just above where US Highway 395 crosses the Columbia River at Umatilla, Oregon.
Would the power of this raging torrent of water be sufficiently dissipated by this point that the dams on the Columbia would contain it? What if they didn't? Once past McNary Dam, the water would be constrained by the Columbia River Gorge until it reached the Portland, Oregon and Vancouver, Washington area. Could these two densely populated cities be evacuated fast enough to mitigate loss of life? At the outside, it would probably take the water no more than five hours from the time it hit the Clearwater River until it was in the Portland/Vancouver area. Even if the call went out immediately to evacuate, would there be time enough to do so? Or would there be no call based on the above claim that the impact would go no further than McNary Dam?
The U.S. Army Corps of Engineers Interim Risk Reduction Measures at Dowrshak Dam report states that the Walla Walla District is implementing "several risk reduction measures:
When the I35 Bridge in Minneapolis, Minnesota collapsed, that wasn't supposed to happen either. But it did. After the fact, it came out that the government knew the bridge was structurally deficient (also here) at least two years before it collapsed.
Following the collapse of the I35 Bridge, the lack of attention to maintaining and repairing infrastructure, nation-wide, became a topic of news casts and newspaper articles across the nation.
Now maybe, just maybe, the raging torrent of water that would be unleashed were Dworshak Dam to collapse wouldn't cause the loss of life and destruction this writer believes it could. But what if it did? And maybe, just maybe, the energy generated by that raging torrent would dissipate long before reaching the Tri-Cities. But what if it didn't? Is "maybe" good enough? Is the "we believe" used in the USACE report on the dam good enough?
In the credibility department, the government has shown itself rather lacking. In the IRRM report for Dworshak Dam, the USACE states:
"Dworshak Dam received a DSAC IIrating primarily due to the consequences of failure rather than the potential for failure.We believe the public should be aware, but not concerned, because Dworshak Dam presents no immediate danger to people and property below the dam."
Unfortunately, this is, once again, what they "believe" to be the case, not what they know to be the case. Remember, they also believed the I35 Bridge wouldn't collapse; that the New Orleans levees wouldn't fail.
Some are making the claim that the concern about Dworshak Dam is being fueled by environmental extremists who want to see the dam removed.
If you lived in the path the raging torrent would take if that dam collapsed, would you want to stake your life on that being the case? We aren't talking a few people in the path of that deluge; we are talking about the populations of
And there's one sure thing about it, if Dworshak Dam collapsed, the "save the dams" movement would be a moot point.
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