Liberty-Chambers Navigation District Spillway Improvements

Liberty-Chambers Navigation District Spillway Improvements

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Planning, design and construction-phase services associated with reconstruction of a 150-foot wide overflow spillway for Lake Anahuac in Chambers County. Lake Anahuac is a source of fresh water for municipal, industrial and irrigation water users in Chambers and Liberty counties. The lake supplies water to a canal system with more than 100 miles of main canal and more than 300 miles of laterals.  The top-of-dam elevation is approximately 8 feet above mean sea level (msl), and the crest of the low-flow spillway is at elevation 4 feet msl. Located at the upper end of Trinity Bay, 4.5 miles of the earthen embankment and the low-flow spillway were destroyed by flood surges exceeding 20 feet during Hurricane Ike.

Conceptual design for the spillway included a reinforced concrete cap supported by rows of sheet pile driven to depths of 40 to 60 feet below sea level. Challenges included spillway foundation materials (reported by the District as “sugar sand”), energy dissipation as water flows over the spillway, toe scour at the upstream and downstream ends of the spillway, the saltwater environment, water management during construction, use of the spillway as a roadway to travel along the dam and hardening of the spillway to improve survivability in future hurricane events.