Internal erosion had been observed at the dam in January 2009, prompting an operational limitation of the dam at the headwaters of the Green River. After thorough analysis and review of the problem, USACE determined that the most effective risk reduction measures would be to rehabilitate the existing drainage tunnel at the dam, add a branch to that tunnel through the area of highest concern to intercept seepage, and install additional vertical and horizontal drains to channel more water from the abutment into the tunnel. Once these measures are in place, USACE believes that the dam could be operated at full capacity.

Back in 2009, USACE constructed a grout curtain to reduce seepage and improved the drainage of the right abutment by installing drains that more effectively direct seepage into the drainage tunnel. Data collected from testing this spring have shown these measures to be effective in controlling seepage through the abutment. USACE was able to hold a pool of 1167 feet above sea level (48% of full) for more than two months without seeing any problems. This has provided additional confidence in the storage capacity of the dam for this coming flood season.

The reservoir at Howard Hanson Dam reached 1170 feet in elevation and was held at an elevation at or above 1167 feet May 9 through July 12, allowing engineers to test the interim seepage barrier with additional reservoir volume. During the conservation pool, USACE conducted in-depth investigations of the dam’s current effectiveness.

Funding of US$44M was approved for repairs to the dam as part of a $59B emergency supplemental spending bill approved in early July by US Congress.