EVENT DETAIL

Topic: A Revisit to the 1980 Mt St. Helens Eruption from a Civil / Geotechnical Engineer’s Experience:  The Repair of the Yakima Tieton Irrigation District Feeder Canal

Register here.

This talk is about one of his early projects that happened in June of 1980, when a portion of a irrigation feeder canal was washed off a steep canyon hillside caused by the St. Helens ash that blanketed the area.  The runoff from a typical afternoon thunderstorm when mixed with the new 4 to 8 inches of SM type ash resulted in a slurry that carried stumps, trees & rocks into the canal and not through the culverts beneath, which were plugged by the ash.   This material ‘dammed’ the gravity flowing canal & backed up the water so it went over the edge in one critical place & eroded / undermined the natural hillside soils resulting in a huge landslide of the supported material that resulted in that portion of the canal dropping nearly 100 feet.  The canal water then poured out, eroding nearly all the soil down the bedrock, until shutdown at the headworks.  

Frank became involved 2 days after the failure of the canal and was part of the team that got the water running again in a total of 19 days. If not for the success of this team of engineers, contractors, and a helpful County government, approximately 26,000 acres of fruit trees would have been damaged or ruined.  This talk will set the stage of what was happening in 1980 related to the eruption and explain the engineering design and approach developed to speed up the solution.