Natural Stabilization

Dec. 18, 2008

When the natural banks of Fred Creek, a storm water runoff channel near the campus of Oral Roberts University (ORU), began eroding and becoming an issue for the city of Tulsa, Okla., the city needed to stabilize the streambanks while providing an attractive green area for jogging trails and parks.

Fred Creek has velocities of 12 to 15 ft per second along the nearly half-mile stretch of drainage slated for improvement. Along the drainage near the ORU campus, two to four bridge abutments were being undermined by erosion, along with footings for utility lines crossing the creek. Rip-rap had been placed in several isolated locations but was not proving successful in halting the erosion issue.

Considering the Options

Natural stone was considered in conceptual phases of the project but was quickly ruled out as too expensive. Instead, the engineers turned to large block precast retaining walls to provide an engineered yet attractive solution.

“We have found in the past on similar projects that the smaller retaining wall blocks just won’t handle the velocity of the water,” said Bill Robinson, P.E., project manager and at the time, engineer in storm water design for the city of Tulsa. “This is one of five projects that [have] either been done or are under construction in Tulsa right now using Redi-Rock or equal products.”

The city of Tulsa wanted the contours of the renovated channel to follow the natural slope of the existing channel. This would create a more natural look, plus provide a more hospitable environment for wildlife and a safer escape route in the event that a person might fall in.

“A strong selling point for Redi-Rock is its ability to offer creative solutions in storm water applications and the flexibility of the system to create different shapes that can match the natural lay of the land,” said Steve Browne of SI Precast, the Redi-Rock dealer in Tulsa.

A Natural Look

Redi-Rock’s 26.6-degree batter angle created by its 9-in. setback retaining wall series allowed the flood channel batter to approximate the natural channel of the creek.

“Appearance at this site was especially important because it goes right through an urban campus with walking trails,” said Mike Peters, landscape architect with Alaback Design Associates in Tulsa. “We needed a natural-looking material that’s also functional, which is where Redi-Rock fit in.”

Since construction of the retaining walls has been completed, Alaback has installed lighting throughout the project and used landscape plantings to give it a natural look. The firm has also worked to restore creek bed habitat, including landscape plantings along the creek bottom. Landscaping is still in progess.

Future Plans

This is Phase I of the project to improve the Fred Creek drainage. The 9-in. setback retaining walls stand 18 to 19 ft at the tallest point and encompass a total of 68,000 sq ft. The project contains both gravity and reinforced walls that are placed atop a concrete footing and buried, on average, 5 ft. The walls are limestone texture, with 15 percent of the face area composed of half-blocks to “break up” the look of the walls.

The second through sixth phases of the $15.25-million Fred Creek drainage improvements project are expected to require extensive retaining walls, rip-rap, landscaping and new bridge construction. SI Precast is currently supplying blocks for Phase II of the project.

Robinson, the project manager for the Fred Creek project, has since been promoted to lead engineer for storm water planning for the city of Tulsa. He has said the city will continue working with large block retaining walls for its erosion control needs.

About the Author

Jake Manthei