|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. Ground surface and bedrock surface profiles are shown on enclosure 1. Also shown on enclosure 1 are the profiles of the bottoms of the down-stream foundation trench and the upstream cutoff trench. These trenches were excavated through shallow weak layers in the flood plan alluvium from stations 49+00 to 64+00 to aid embankment stability 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.