Damming News From Washington State

Trax3001BBS writes "A 65-foot (20-meter) crack has been found in Wanapum Dam, one of the major dams along the Columbia River in southern Washington. Water levels are being lowered to both reduce water pressure and give the inspectors access to the area. 'Earlier this week, an engineer noticed a slight irregular "bowing" above the spillway gates near where cars can drive across the dam. When divers finally took a look under water they found a 2-inch-wide crack that stretched for 65 feet along the base of one of the dam's spillway piers.' The article goes on to say, 'Even if the dam doesn't fail, the significance of the damage is likely to require extensive repairs and that, too, could impact the entire Columbia River system. "All these dams coordinate to generate energy on a regional scope," Stedwick said. "If Wanapum is impacted, that has impacts on dams upstream as well as below." Upstream dams would be required to handle more water; there's only one lower dam (Priest Rapids). After that is the last free flowing section of the Columbia river. I've taken walks along that section, and I've seen it deviate (higher or lower) by amazing amount of water, so it can handle the changing flow rate. Making this situation more complex, a large group of people would like that particular dam removed, as well as the one above and below it (think of the fish!). On top of that, after the Priest Rapids dam (downstream from Wanapum Dam) is the Hanford Nuclear Reservation, once a site for Plutonium production. Either of these issues could generate a ton of attention. Personally, I'd like to give the engineer that noticed a slight irregular 'bowing' my congratulations."

Moisture inside the dam wall

[MichaelSmith]

I believe the biggest problem with cracked dam walls is that moisture gets into the interior of the wall and softens the material which is keeping it strong. Then the crack opens a little bit more, more water gets in and you have a nice exponential curve happening.

There was a rumour about this happening to the hume reservoir in Australia about 20 years ago.

William Mulholland didn't take action

[kriston]

William Mulholland didn't take action when the St. Francis Dam performed similarly, and after his inspection, killed up to 600 people twelve hours after his inspection.

"Think of the Fish"

[Oysterville]

That last free-flowing stretch of the Columbia River that the OP mentions is also the last stretch of Columbia River that maintains spawning habitat. It also accounts for a very large portion of the salmon that return through the Columbia River estuary every year. If removing this dam would open up more spawning habitat, this would not be a bad thing.

Re:Moisture inside the dam wall

[wiredlogic]

Water doesn't "soften" concrete. H2O is molecularly bound into its structure and is a necessary part of maintaining the strength of concrete. Water invading earthen dams, on the other hand, is a more serious problem.

Re:Moisture inside the dam wall

[Charliemopps]

The steel is bathed in moisture for decades without weakening. Concrete hardens and is stronger under water. Water cracks concrete via the thaw freeze cycle. Water enters the void, freezes, expands, widens the void. But a 60 foot long crack suggests something shifted under the damn.

Data centers

[gbnewby]

The data centers in Quincy are quite large. Microsoft has a major facility, which is undergoing expansion. So does Yahoo, Intuit, Dell, and Sabey. These are major components of the tax base for the town of Quincy and elsewhere in Grant County. The data centers are highly resilient to power loss, with on-site diesel generators, 24x7 staffing, and all the other protections you'd expect. But prolonged use of the generators, if it becomes necessary, could exceed the permitted run time and accompanying pollution the facilities are allowed. Most likely, power from the other dams the Grant County PUD operates (or elsewhere on the regional power grid) could be routed to the data centers.

There are some other huge electricity consumers in the county. It's the world headquarters of a company that makes photovoltaic components, and also several food processors (all those potatoes from eastern Washington gotta be processed and cooked!). Industrial users might be able to turn down their power usage if there is a regional shortage, but data centers tend to operate at fairly stable 24x7 consumption levels. Major companies like those listed above have redundant facilities, and can shunt processing to other centers if required.

Site selection for major electricity consumers, including data centers, is a fascinating topic. The State of Washington has had various tax incentives to help businesses to choose to build facilities there. Electricity costs are among the lowest in the nation (under 3 cents/kWh for industrial customers). Plus, it makes extensive use of renewable sources, particularly hydroelectric (i.e., dams) and wind energy. Oregon has a similar story to tell, with their own rivers, dams, tax breaks, etc., and is part of why Amazon elected to put a huge facility there.

Re:O.M.G

[Solandri]

You joke, but the worst power generation-related accident in history was the failure of a series of hydroelectric dams [wikipedia.org]. About 30x more deaths than estimated by the UN and WHO to have been caused by Chernobyl.

I don't mean to say coal and oil are safer - they kill far more when used as intended. But the fact that the fuel needs to be delivered to a combustion chamber means you can usually cut off the energy source, limiting the scope of a single accident. That's not the case with hydro - once the water gets moving, there's pretty much nothing anything man-made can do to stop it. All that energy is gonna be released. Likewise, nuclear rates high in risk because the energy density of the fuel is so high - a million times higher than petroleum. Solar and wind would appear to be low-risk, but that's an illusion generated by their low energy density. When you normalize for how many solar panels or wind turbines need to be installed and maintained to generate 1 GWh of electricity, they end up killing more people than nuclear.

Everything has risk. The question isn't how much risk there is per disaster. It's how much risk there is per unit of energy generated.

Re:Moisture inside the dam wall

[Solandri]

It has nothing to do with the moisture. It has to do with pressure. A dam represents a boundary layer between high pressure (behind the dam) and low pressure (air in front of the dam. An intact dam's structure distributes those stresses evenly throughout its structure, and transfers them into the mountains/hills at the sides of the dam. A crack shifts the stresses which would've been borne by the cracked section to the uncracked sections, and particularly at the corners of the cracks. The high stresses at the corners cause the crack to grow. Eventually the crack grows large enough that the stresses are more than the uncracked section can withstand, and the dam fails.

That's what the engineer noticed. The dam was bulging because the uncracked section was holding back so much more stress than its design load that it physically deformed. 65 feet is a damn big crack (no pun intended). That engineer deserves a ticker tape parade in his honor.

Re:Lower the river, obviously

[Jawnn]

If there is only one dam below Wanapum, this will be easy.

Not so much. The author of TFS is an idiot. He missed McNary, John Day, The Dalles, and Bonneville dams.