About 3:45 yesterday aftenoon a dump truck towing a backhoe with its boom extended up in the air dragged down power lines onto Highway 97 just south of the Deschutes Market-Tumalo Road interchange. The driver of the Central Oregon Irrigation District truck just kept on going north on 97.  One of the live wires struck the hood of car driven by 64-year-old Joseph Zimmer of Bend, causing him serious but non-life-threatening injuries. Sheriff's deputies caught up with the dump truck and driver about a half hour later near the Redmond Airport. Authorities say 55-year-old Stuart Keyte of Redmond was aware he hit the power lines with the excavator but left the scene anyway.  He was issued a felony criminal citation for leaving the scene.