THE NEWELL CREEK VILLAGE APARTMENT LANDSLIDE, OREGON CITY, OREGON, 2006

A study done by my students in 1992 of the Newell Canyon area near Oregon City, Oregon mapped over 60 landslides in the canyon. A proposed apartment complex had applied for a building permit for a site in the SE part of the canyon, near the headwaters. The geotechnical engineer who surveyed the site said that the site had no evidence of slope instability and no landslides were noted. Our report said that the site had the best landslide morphology found in the canyon with two slump surfaces being exposed. We presented our report to the city council in January, 1993. We recommended that the site not be built upon. Based on our report, the city council cut the size of the proposed apartment development from 250 to 125 units. In January of 2006 after a month of heavy rainfall of over 8 inches, the lower parts of the slide showed small landslides. Water and sewer lines were severed twice. A 10 feet high scarp developed at the base of the slide. Three small arcuate headscarps started to develop on the toes of the two ancient landslides at the site. One got be over 5 ft. high. Inclinometers were put into the ground to monitor movement. It seems that the whole lower slide has reactivated. Half of the apartments have been evacuated. Broken gutters have concentrated water on the slope leading to increased movement. This is a classic example of why one should not build on an old landslide for it has a high potential of reactivating and destroying structures that exist on it.