Project Description

LACHEL & Associates, Inc. (LFA) was contracted to provide a detailed inspection of the dewatered Crater Lake Power Tunnel while it was shut down for maintenance in early September, 1995. The inspection team consisted of a geotechnical, structural and construction engineers, all specializing in underground facilities.

Scope of Services

Due to the rapid development of the Juneau-Douglas environs, the Crater Lake Phase development of the Snettisham Project was initiated in 1984. In concept, the Crater Lake Project included an approximately 8,000-ft-long power tunnel from the existing underground powerhouse up a 12% grade, with an underwater lake tap under approximately 200 ft of water into Crater Lake with a normal surface elevation of 1,019 ft above sea level, lying southwest of the existing powerhouse, and the installation of a third generator in the existing powerhouse with an installed capacity of 31 mw. The Crater Lake Project was developed in two phases, with the initial phase including the Crater Lake access tunnel, penstock tunnel, and approximately 6,800 ft of power tunnel. The second phase of the work, conducted between 1987 and 1990, included the excavation of approximately 1,000-ft-deep surge shaft, the gate shaft, gate shaft adit, installation of an approximately 600-ft-long steel penstock, 700 ft of power tunnel and the underwater lake tap. Crater Lake power was placed on line in 1990 and has operated according to design with no indications of any significant problems.

LACHEL & Associates, Inc. concluded that the access adit, penstock tunnel, and powerhouse tunnel up to the gate structure are in excellent condition with no observable problems or problems which appear to be imminent in the near future.

Client

Alaska Industrial Development and Economic Authority