Sam Rayburn Labyrinth Spillway

An innovative labyrinth weir uncontrolled spillway was designed and constructed at Sam Rayburn Dam to correct serious erosion and hydraulic deficiencies. This was the first such spillway for the Corps of Engineers and the largest to date.

The project's existing uncontrolled broad-crested weir spillway channel had been excavated through highly erodible sands and sandstone. Protection from erosion consisted of an inverted "U" control sill that was 15 feet wide with 8-foot turned down edges. Subsurface investigations indicated that a large portion of the spillway channel was underlain by soft, clayey sandstone, dense wet clay, and unconsolidated saturated sands. About 1,300 feet downstream from the control weir the channel dropped off at a 3.3 percent gradient. Additionally, revised hydraulic criteria increased the required spillway capacity from 125,300 cfs to 227,500 cfs.

The Sam Rayburn Dam is a 120-foot high, 12,400-foot long earth and rockfill dam, located on the Angelina River, in Jasper County, Texas. It was originally constructed with a 2,200-foot-wide uncontrolled broad crested weir spillway. This Corps of Engineers dam was originally completed in 1965. The dam controls a drainage area of 3,449 square miles, impounds a normal pool of 114,500 surface acres with a volume of 2.9 million acre-feet of storage water.

Design investigations consisted of a detailed seismic refraction study of the entire spillway area, a pumping permeability test, 33 new subsurface borings, and extensive geotechnical testing. Extensive hydraulic analysis was done to optimize the labyrinth cycle dimensions.

The new project consists of a 290,000 square foot soil-cement slurry wall, a 640 foot wide uncontrolled labyrinth weir spillway with 16 cycles, a 1,225 foot long approach channel, a 4,622 foot long discharge channel, a concrete chute and stilling basin, two dams that tie the new spillway into the old spillway channel, a parapet wall along the crest of the dam to restore freeboard, and modifications of existing dikes in a low area along the left abutment.

Construction started in January 1994 with a contract bid price of $27,443,882. Work was essentially completed in December 1996 with a revised construction cost of $31,033,316. 10 pp.