Dam Safety

Dam Safety


Notable Dam Failures

Despite our best efforts to promote dam safety and assist owners in maintaining their dams in a safe manner, failures sometimes occur. 

Reasons for dam failures include:

  • Overtopping - 34% of all failures (nationally)
    • Inadequate Spillway Design
    • Debris Blockage of Spillway
    • Settlement of Dam Crest
  • Foundation Defects - 30% of all failures (nationally)
    • Differential Settlement
    • Sliding and Slope Instability
    • High Uplift Pressures
    • Uncontrolled Foundation Seepage
  • Piping and Seepage - 20% of all failures (nationally)
    • Internal Erosion Through Dam Caused by Seepage-"Piping"
    • Seepage and Erosion Along Hydraulic Structures Such as Outlet
    • Conduits or Spillways, or Leakage Through Animal Burrows
    • Cracks in Dam
  • Conduits and Valves - 10% of all failures (nationally)
    • Piping of Embankment Material Into Conduit Through Joints or Cracks
  • Other - 6% of all failures (nationally)

Notable Dam Failures and Incidents In Washington State

The following table and paragraphs describe some recent dam failures in Washington and the lessons learned.

Notable Dam Failures and Incidents In Washington State - a table that includes: project name, location, date of Failure, number of lives lost, nature of failure and damage.

Seminary Hill Reservoir, Centralia WA

Seminary Hill Reservoir failed in October 1991 due to a massive landslide beneath the embankment. 3.5 million gallons were released in less than 3 minutes flooding a residential area.


Chinook Water Supply Dam

The concrete overflow spillway had been modified to increase the storage of the reservoir, however this reduced the discharge capacity some 70 percent from the original design. The dam failed by overtopping during a flood in 1989.


Iowa Beef Processors Waste Lagoon

The Iowa Beef Processors Waste Lagoon failed when snowmelt in the area adjacent to the lagoon raised the water level to near the crest of the dam. Effluent flowed into animal holes near the crest and initiated an erosive breach. Over 270 acre feet of waste effluent were released downstream and washed out a railroad line causing a train to derail. The effluent was contained in another waste lagoon owned by a paper mill just upstream of the Columbia River narrowly averting an environmental disaster.

CSC Orchards, Frost Protection Pond

This failure occurred in July of 1995 due to erosive piping of the embankment materials along the outlet conduit. The reservoir was partially lined with a PVC liner, however, seepage passed beneath the liner and initiated the failure.


Olufson Dam

A 20 foot diameter sink hole appeared on the dam crest in December of 1996. A section of the drop inlet conduit running beneath the dam collapsed, resulting in embankment material being sluiced out through the break.