Civil Engineers Prep For Dam, Museum

Building a world-class museum to house a multi-million dollar collection of historically important American paintings is no easy feat.
But straddle the museum over a creek that drains 700 acres of surrounding land and you’ve got a hydrology engineer’s dream — or nightmare.
Once it’s constructed, the Crystal Bridges Museum of American Art will have cost about $55 million, but it will be able to withstand a 100-year flood, thanks in part to work by CEI Engineering Associates Inc. of Rogers.
The firm has designed safety measures 50 percent higher than Bentonville’s requirements and the Federal Emergency Management Agency’s specifications for flood protection.
“I understand it’s been designed to withstand a flood of Biblical proportions,” said Bob Workman, executive director for Crystal Bridges. “Part of the strategy is allowing a major flood event to pass through the project and I am confident that the appropriate safeguards are in place.”
The museum is a charitable gift of Alice Walton, daughter of Wal-Mart Stores Inc. founder Sam Walton. Much of the permanent collection will be anchored by donations from Walton and the Walton Family Foundation.
So far, the collection includes paintings by Charles Wilson Peale, Charles Bird King, Winslow Homer, Norman Rockwell and an 1849 painting called “Kindred Spirits” by Asher B. Durand, which Walton paid $35 million for in 2005. An exact value of the collection is still not known.
Civil engineering on the site has been in the works for about eight months, Workman said. Footings and foundation work on the building should start this summer, and the project is scheduled to be complete by late 2009.
Workman and the museum’s public relations firm, Mitchell Communications Group of Fayetteville, denied multiple requests to tour the site, but a site dedication took place on May 3.

Bridging Water
The creek, known as Town Branch, does not appear on many maps, but runs from downtown Bentonville into the valley where Crystal Bridges is under construction. Two springs, including Crystal Spring, feed the McKisic Creek tributary on the 105-acre property.
When it’s not raining, between 1 and 2 cubic feet of water pass through per second. With site work and blasting in full bore on the mostly rock and clay ravine, engineers said the creek has been temporarily diverted through a channel running beneath the project.
Once construction is completed, two ponds will be created by a pair of “duck bill weir” dams that also serve as bridges between the buildings. The channel underneath will not be filled to allow the ponds to be drained if needed.
With water surrounding the artwork, it would seem as if the developers are flirting with disaster. But even the worst natural disaster wouldn’t penetrate the complex, which sits on a seven-acre footprint.
Obviously, one of the main aims of the museum is to protect the collection from not only from the elements but also from bandits. So for security purposes, those working would not discuss minute details about the underbelly of the project. Suffice it to say, the facility will be watertight and airtight.
“We covered all aspects and checked, double-checked and triple-checked to make sure everything worked before we issued our design,” said CEI engineer Koh Siong Chai, who’s heading up the Crystal Bridges project.
CEI was chosen as the engineering firm because of its reputation and familiarity with Northwest Arkansas. It also was wise to hire a nearby firm, so engineers wouldn’t be thousands of miles away if any wrinkles came up during construction, Workman said.
“It’s a very challenging building and a very challenging site,” Workman said. “We chose the most challenging site on the 105 acres, no question about that.”
Every detail in the design by world-renowned Israeli architect Moshe Safdie is meant for the project to look like it was dropped into the natural surroundings.
Timber removed from the site is being milled in hopes it can be reused in some way. A huge pile of topsoil has also been excavated, but kept nearby to put back onto the site before it’s completed.
Besides the wood, the dirt and a few pieces of construction equipment near the job site office, not much can be seen from the perimeter of the property that has been owned by the Walton family for years.
Inside, the pad work is nearing completion and, officials said, it looks basically like any other job site with different levels of red clay and rock cut out of both sides of the valley.

100-Year Storm
When studying Crystal Bridges, CEI’s engineers found that about 700 acres of land drained through the valley at the site.
“That’s a pretty big piece of real estate to be draining through a piece of property to begin with,” said Dan Weese, CEI’s regional manager. “We had to look at the design several different times and figure out how we could do this and make it safe.”
Chai examined rainfall events for the location and concluded that six inches of rain was the highest average during a 24-hour period. It also was determined that a 16-inch rainfall during a 24-hour span likely would occur every 100 years, so in the interest of taking extra precaution, the project was design to handle a 24-inch rainfall within 24 hours.
Other buildings in the region are designed to withstand a 16-inch rainfall event to meet the City of Bentonville’s and FEMA’s standards.
“We were driving around the other day and there are a lot of structures in this area that are going to be under water before Crystal Bridges,” Weese said. “But we are talking about a catastrophic, never-before-seen-in-the-history-of-Earth type of storms.”
The firm isn’t only protecting valuable art. The 100,000-SF museum is expected to have 75 full-time employees and about 250,000 visitors annually. So if the Great Flood occurs on a busy weekend, there could be up to 1,000 people at the complex.
At one point in the design phase, an outside engineering firm was called in to determine if CEI was being overly conservative. The third-party determined CEI’s plan was solid as bedrock.
“Because of the threat to life and property in this structure, we felt that the highest level of protection needed to be provided,” Weese said. “If this was a simple dam, but the only thing downstream of it was farm ground instead of the people of Bella Vista, we wouldn’t have designed it with the same level of protection.”

Dam It Up
Typically, civil engineering work is the stuff that nobody sees once a building is completed. With Crystal Bridges, the tops of the two dams will always be visible.
The dams snake the span instead of a typical straight dam and have a saw-tooth-like top to help divert debris while allowing water to be raised and flow over the tops.
“People usually will build a linear dam,” Chai said. “But our design is truly unique. It creates the edge of the dam where water can spill over it and helps the water not rise too much.”
An aspect that has yet to be addressed is evaporation. With minimal water flowing naturally, the possibity of the ponds drying up exists. One way that could be averted is if nearby wells are drilled to bring in more water, but plans aren’t in the works.
Erosion of the concrete buildings is another factor CEI studied. Concrete near the center of the main structure is the most likely to experience wear and tear, but Weese said it’ll be “20 to 50 years” before even minor maintenance is needed.