Overview

Fort Cobb Dam is on Pond (Cobb) Creek about 5 miles north of Fort Cobb, and roughly 5 miles above the confluence of Cobb Creek with the Washita River. The dam is a zoned earthfill structure containing 3,520,000 cubic yards of embankment. The crest width is 30 feet, and the crest length is 9,900 feet. The structural height of the dam is 122 feet.

Fort Cobb Reservoir has a total capacity of 143,740 acre-feet and covers an area of 5,956 acres at top of flood pool level. The uncontrolled morning-glory spillway in the left abutment consists of a concrete intake structure, concrete conduit, and concrete chute and stilling basin.

The foundation materials consist of as much as 117 feet of alluvium over bedrock in the flood plain, and relatively thin deposits of residual and slope-wash soils over bedrock on the abutments. The bedrock is sandstone and siltstone of the Rush Springs Formation. The upstream cutoff trench was also intended to reduce foundation seepage. On the abutments, the upstream cutoff trench was excavated to sound bed-rock up to the normal water surface elevation at approximately station 30+00 and station 80+00 The downstream foundation trench was back-filled with a drainage blanket followed by impervious, compacted Zone 1 fill. The upstream cutoff trench was backfilled with impervious, compacted Zone 1 fill only.

The spillway and outlet works are located on the left and right abutments, respectively. Both structures are founded entirely on sound siltstone and sandstone bedrock.

General

Dimensions

Hydraulics & Hydrology