Spotlight on Franklin County Dam

Franklin County Dam is an earthen embankment 5,000 feet long with a maximum height of 73 feet. The subject dam impounds a pool having a surface area of 4,750 acres at normal pool elevation 378.0 feet for the purposes of County water supply and recreation. The dam is currently classified as a high-hazard structure by the Texas Commission on Environmental Quality (TCEQ), Dam Safety Program.

During implementation of another consultant’s plan for rehabilitation of the dam in 2010, an earthen buttress was installed against the downstream slope of the embankment. The buttress fill contained dispersive soils and resulted in erosion features known as “jugholes”. The jugholes limit the accessibility of mowers and so proper inspection and maintenance activities cannot be performed in the embankment’s current state. In addition to rendering the downstream slope extremely difficult to mow and maintain, the erosion features allow concentrated flow to occur during rain events and will continue to erode earthen materials if left unaddressed.
The condition of the dam recently came under scrutiny by the TCEQ. In 2019, Schnabel was approached to perform an archival review of available documentation for the dam, evaluate rehabilitation alternatives for the downstream slope, and assist Carollo Engineers (Carollo) and the Franklin County Water District (FCWD) in addressing dam safety concerns posed by TCEQ.

In 2020, Schnabel performed geologic investigations, including soil test borings, installation of piezometers, cone penetration testing, test pits, and laboratory testing. Information obtained from the geologic investigations was used to refine the preliminary rehabilitation alternatives. Schnabel presented the rehabilitation concepts to FCWD, Carollo and TCEQ and is now under contract with FCWD to provide detailed design services for the rehabilitation of the buttress. The measures will generally include a lime-treatment program of the dispersive soils in the buttress and the installation of a graded-aggregate filter drain between the original embankment materials and the buttress materials and into the foundation.