Designing for a Deluge
By Jeff Boutwell
In this day and age of flat or declining budgets, it is a rare opportunity to basically start from scratch and rebuild a park from the ground up. This was the case for the U.S. Army Corps of Engineers at Waco Lake in Texas. This 9,000-acre flood-control project recently went through a seven-foot rise to its conservation pool evaluation at the request of the city of Waco. In order to become a regional water supplier to the area's growing population, the state of Texas required the city to increase the available water supply that it owned, hence increase the amount of water stored in Waco Lake. This increase flooded an additional 1,000 acres of park and wildlife habitat.
While the main purpose of the Waco Lake project is water conservation, new parks and recreation facilities would have to be designed and constructed as well. These facilities would not only have to meet a specified budget but also would have to meet the demands and expectations of campers, bikers, picnickers, boaters, swimmers, and fisherman.
"It was basically a once-in-a-career opportunity," says William Haferkamp, civil engineer technician in the Waco Lake office.
Planning for new facilities started in 1997 with the evaluation of the facilities and the development of cost estimates for their replacement. The cost of replacement came to $5.4 million out of a total project price tag of $31 million financed by the city of Waco.
The planning team then went about the process of developing plans for specific facilities and parks with the premise of not if they will be flooded but when. This team had considerable experience in watching park facilities be inundated and reacting to water and wave action. One of the team's primary goals was not only to design and construct facilities that would withstand getting wet and drying out with little damage but also to construct them to withstand wave action driven by the high winds common in Texas.
The location of facilities was one aspect of the design process. Two goals of the team had to be met: to give the users what they desired, to be as close to the water as possible, and to minimize repair work necessary after a flood event. This was accomplished by setting a minimum elevation that all facilities would be constructed above. Using existing flood frequency charts—estimating how often a lake reaches a certain elevation—all new facilities were constructed at least 12 feet above the old pool elevation. Everything below the new pool elevation in the parks, trees included, was bulldozed.
Construction materials and methods for the facilities was another focus of the team. Experience had shown that shade shelters constructed of wood warped after they were inundated. The roofing decks want to float when submerged due to their buoyancy, adding pressure to the joist and support post. This along with strong wave action is enough to pull 4-inch-by-4-inch posts, both steel and wood, concreted three feet in the ground completely free. Therefore, all new campsite and picnic shade shelters were constructed of 4-inch-by-4-inch-square steel tubing with welded joints. This enables the entire frame to act as one solid structure for added support and strength.
The roofing is 16-gauge sheet metal. This does not have any of the warping or buoyancy problems of wood and is relatively simple and inexpensive to replace or repair if damaged by wind or wave action. Construction costs were actually cheaper than that of wood framing and decking.
The design and the construction of restrooms were extremely important. The most expensive facilities in the parks, they have to be functional for the users and highly durable for maintenance and repair. Wood-frame construction of restrooms has the same problems previously mentioned. Rock or brick veneer exacerbate the damage by wave action due to it sloshing around between the veneer and the wood-frame walls, causing the veneer to collapse into the wood framing.
Quite by accident one day, the team found the solution rolling down Interstate 35 on the bed of a semi-tractor trailer: precast concrete, modular restrooms. Water has no effect on the structure, and the design team has taken great care in the placement of the structures to shield them from open water and long wind fetches with the use of grassed berms and stands of trees.
Construction on most of the new facilities was completed in October 2003. Since that time, there have been five occasions when floodwater covered portions of the new areas, once with an 11-foot rise. On all of these occasions, there were no structural damages to any of the new facilities.
"The team worked extremely hard to come up with designs and plans that would fit into the budget all the while providing the general public with quality facilities," Haferkamp says. "No one person could say that they did it all. It was a team effort."
Jeff Boutwell is a recreation specialist for the U.S. Army Corps of Engineers in Texas. He is a graduate of Texas A&M University with a B.S. in recreation and parks and has been with the Corps for 18 years. He can be reached at firstname.lastname@example.org.
For more information
Waco Lake: www.swf-wc.usace.army.mil/waco/