The glider released from the towplane at an altitude of about 11,200 feet above mean sea level (msl). The glider then entered an area of lift which increased the altitude to 14,500 msl. The pilot continued westbound encountering areas of lift and sink. The pilot reported that they were unable to find the area of lift again and the descent rate increased to over 1,000 feet per minute (fpm). The flight instructor on board took over control of the glider and turned back toward the east hoping to find the area of lift that they had encountered earlier in the flight. The flight instructor stated the lift did not materialize and they encountered sink rates of up to 1,600 fpm. The flight instructor located a field in which to land. The flight instructor maneuvered the glider to align with the field and avoid houses as the sink rate continued to be about 1,000 fpm. During the approach, the left wing contacted a powerline which spun the glider around 180 degrees prior to it coming to rest approximately 200 feet short of the intended landing area. The glider received substantial damage to the wings and fuselage.