THE US ARMY CORPS OF Engineers (USACE) has released two draft studies indicating solutions to the seismic upgrading of the 42m high Tuttle Creek dam on the Big Blue river, in the state of Kansas, US.

The dam impounds approximately 2.8Bm3 of water at full pool level. USACE found that silts and loose sands in the foundation materials beneath the dam could liquefy during an earthquake of 5.7 to 6.6 magnitude. The proposals suggest the stabilisation of the dam’s foundation without drawing the reservoir down during construction. Modifications will also be required on the dam’s 18 gates. The estimated project cost is US$195M.

Although USACE’s ideas represent its preferred alternative, it is only one of five that will be studied further.

The other options considered are: leave the dam in its current condition, restrict lake operations, stabilise the foundation with lake drawdown, or enlarge the dam’s embankment.

The dam, completed in 1959, consists of a rolled earth and rockfill embankment with a gated, concrete chute spillway on the left bank to the north of the left (east) abutment, and an outlet works with intake tower and gated twin conduits 6m in diameter near the right (west) abutment.