8 March 2019
Hooskanadan Landslide in Oregon – an update on the Highway 101 earthflow near to Brookings
Reports in the last few hours suggest that Highway 101 near to Brookings in Oregon might reopen on Saturday, following its closure as a result of the major Hooskanadan landslide. Tideway Contractors have focused on constructing an initial unpaved route across the landslide body, with ramps of suitable grade, to allow a single vehicle lane to be established in the first instance. The challenge has been that the landslide has continued to move during this process. Early in the reinstatement process the landslide was moving at an estimated 2 feet (60 cm) per hour, but during the week this was reported to have declined to 6 inches (15 cm) per hour.
This image, from 11 KCBY, shows the magnitude of the movement at Hooskanaden Creek, and the challenges in reinstating the road:-
The irony is of course that in emplacing fill on the landslide to create an appropriate grade, the contractors may have loaded the unstable portion of the slope, making movement slightly more likely. Unfortunately, in this type of situation it is the only realistic option, and it is an accepted management approach. The extent to which this has been necessary is better illustrated by this image, tweeted in the last few hours, showing the works from the other side:-
Regular correspondent funkenbeachin has pointed out to me some hydrograph data from Smith River, not far from the landslide, provided by the USGS. This seems to suggest a recent period of reasonably heavy rainfall, but conditions that are not particularly exceptional. There is no doubt that this slide will move again in the future, but the costs of permanent stabilisation are unlikely to be justifiable. The only realistic option is often to rebuild the road each time, and to accept the cost and inconvenience.