The Failure of the Lower Colorado River Dam at Austin, Texas

Abstract

The Austin Dam on the Lower Colorado River of Texas was originally constructed between 1890-93 three miles northwest of downtown Austin, Texas. The dam's spillway sill rose about 66 feet above the foundation and was 1,091 feet wide, intended to pass up to 250,000 cfs, the highest overflow volume of any dam in the world at that time. A masonry head-gate control structure 95 feet wide and rising 12 feet above the spillway sill was constructed against the left abutment. Four penstocks fed electric generators in a powerhouse while three penstocks conveyed domestic water to the City of Austin. In just seven years of operation the reservoir lost nearly half (48%) of its storage capacity because of siltation. In early April 1900 the dam was subject to a flood of about 220,000 cfs, which brought flows more than 11 feet deep over the dam, likely exacerbating erosion and undercutting of the downstream toe, along the Balcones fault zone. After approximately 7 hours of spillage about 500 lineal feet of the dam's overflow section experienced basal sliding, pushing 60 to 80 feet downstream, quickly draining the reservoir and destroying most of the powerhouse. The dam's spectacular failure pointed to the need for more thorough assessments of basin hydrology and geology, particularly foundation conditions, such as karst and fault features. The dam's rather poor pre-failure performance also pointed to the need for better assessments of reservoir sedimentation, channel bed scour, reinforcement of downstream flow transitions, seepage cutoff walls, and alleviation of hydraulic uplift.