Coho Water Resources
Integrated Water Resource Management
Expert Witness Support to Oso Landslide Litigation
The catastrophic Oso landslide on the north bank of the Stillaguamish River, Washington, on March 23, 2014, resulted in the tragic deaths of 43 people. The landslide complex had been unstable throughout history, with well-documented slope failures from 1952 through 2006.
Coho Water Resources worked for the victims and survivors of the Oso Landslide case to provide expert services on groundwater-related issues. We analyzed and integrated large data sets of groundwater elevation, historical LiDAR coverages, air photos and infrared sensing to develop an understanding of the groundwater flow regime and its role in the landslide. Our resulting conceptual model included the roles of precipitation recharge, springs and seeps, complex glacial sedimentary structures, discontinuous strata, enhanced permeability due to fractures, and shifts in groundwater divides.
Coho clearly communicated technical findings that directly refuted the defendants’ assertions. The case was settled in October 2016 just before trial in favor of the victims and survivors.
