Oregon’s Wickiup dam could fail during a moderate earthquake, according to US Bureau of Reclamation (USBR) dam safety officials.

Bureau officials said that an earthquake with a magnitude of 5.0 on the Richter scale could cause a catastrophic failure of the two-mile long earthfill dam, due to liquefaction of saturated silt and volcanic ash strata in the dam foundation. The chances of such an earthquake occurring were estimated to be about 0.1%per year.

The dam on the Deschutes river, completed in 1949, holds up to 200,000 acre feet of water. The water is used primarily for irrigation in Jefferson County. According to USBR officials, a failure of the dam, located upstream of the towns of Sunriver and Bend, could endanger up to 10,000 residents. In February this year the USBR proposed a US$40M project to strengthen the dam.

Users of the reservoir are concerned about their share of the bill for the renovation project. Federal law requires those who use the water to pay 15% of the bill for earthquake related improvements. The North Unit Irrigation District, which serves farmers in Jefferson County with water from Wickiup, is looking at a US$6M bill for its share. USBR hopes to complete the rehabilitation by 2001.