Rockinghorse Lane Landslide-WO #015

During the winter of 1996, the region was hit with torrential rains and widespread flooding.  Due to the saturated ground conditions, the region also suffered a significant increase in landslide activity.  Lake Oswego was not immune to the flooding or the increase in landslides.

Since then, the City has exercised more scrutiny of development activity occurring in areas that exhibited slope movements during the 1996 event and is taking a closer look at one slide in particular.  This landslide is located at the east end of Rockinghorse Lane, straddling private property in Lake Oswego and extending into Tryon Creek State Park, within the City of Portland.  Early in 2005, City engineering staff solicited proposals from qualified consulting geotechnical engineering firms to provide an engineering analysis of the slide area and to make recommendations for alternatives to improve surface water drainage in the area. 

The consultant’s scope of services included drilling through the slide material into deeper, undisturbed soil layers, gathering soil samples for laboratory analysis and the installation of sensitive instrumentation.  The instruments will provide information regarding the level of groundwater activity and whether the old slide mass is still moving.  As engineers gain a better understanding of the slide area, decisions can be made on how to move forward with area drainage system improvements. 

In May of 2005, Landslide Technologies and their sub-contractor, Crux Boring, mobilized to the site and began boring test holes and retrieving soil samples.  Three borings were extended to depths exceeding 70 feet.  Instrumentation was installed and baseline monitoring points were established.  Periodic monitoring is expected to take place over the next three to five years during the winter and spring rainy seasons.   

Affected Streets

Rockinghorse Lane

Funded by

Funding for this project is provided from the fees that are generated from the surface water utility. 

If you have any questions regarding this project, please contact project manager, Rob Amsberry direct at 503.635.0268 or click here to send him an e-mail.