Tannery Dam impounds a 20-acre lake in the center of a 550-acre master-planned residential development in Denton County. Between 2012 and 2019, a number of dam safety deficiencies were identified and our H&H engineers were engaged to design safety improvements to bring the lake into compliance with the TCEQ Dam Safety Program on behalf of the dam’s owner.

Our professionals modeled the hydrology of the 1- square-mile watershed, evaluated the adequacy of the existing earthen spillway, and performed a dam breach analysis of the area between Tannery Lake and Lake Lewisville.

The dam was replaced, due to evidence of significant seepage through the existing dam embankment, using increased compaction requirements, imported clay material, and a bentonite slurry trench cutoff wall with sand filter blanket and chimney drain to reduce future seepage. Due to the size of the dam, our work included the design of a new, lowered earthen spillway, widened from 40 feet to 75 feet, with an outflow channel to allow passage of the 75% Probable Maximum Flood (PMF) flows. A widened 10-foot crest was raised to a uniform 578.5 feet.

Our professionals also provided Watershed Appropriations Permit services and Clean Water Act compliance utilizing accepted Nationwide Permits through the USACE.