The Mill Creek Dam is an earth-fill dam 120-ft high, 3,050-ft long and 800-ft wide at its base. Its purpose is flood control and was last filled in 1996. Currently it is approximately 5-10% filled.
Some of the specific deficiencies noted by the Corps include:
- Gravel and silt materials in the dam possibly washing away
- Inadequate protection measures to prevent seepage
- Dam material not sufficiently compacted (dense)
- Gravels in dam’s foundation
- Lack of emergency spillway
- Inlet and outlet works not designed to withstand an earthquake
The Corps is implementing “interim risk mitigation measures” including increased monitoring and surveilance and coordination with local agencies for emergency alerts and flood control options while additional studies are conducted. Long-term planning will begin in 2010.
Story credit Seattle PI by way of ASCE Smart Brief.