The inspection of deep and long, water-filled tunnels at pumped storage hydroelectric stations has posed a challenge to the electric utility industry. Virginia Power and its partner, Allegheny Power System, faced this challenge at its Bath County Pumped Storage Station in western Virginia. <p>Bath County is the largest station of its kind in the world with a combined generating capacity of 2100 megawatts. The station consists of six pump/turbines and three large tunnels, each 28.5 feet in diameter and approximately two miles long, which link the upper and lower reservoirs. <p>After reviewing the alternatives of using divers, manned submersibles and dewatering of the tunnels, the owners decided to use a submersible remotely operated vehicle (ROV) for the inspection task. A study was performed which determined that the owners could save approximately $677,000 by performing the work in-house versus hiring a specialty contractor. <p>An ROV system was developed and equipped specifically for tunnel inspection work. Three video cameras, a stereo photo camera, dye release system, dual head sonar, and a 7000 foot umbilical provided the inspection capabilities. <p>The overall condition of the tunnels was very good, particularly in the upper and lower horizontal sections. The vertical flow shaft of the tunnel had two predominant longitudinal cracks with the east wall crack showing evidence of water egress. <p>The ROV system proved to be a very safe, economical, and reliable means of conducting inspections of this type. The vehicle successfully completed the 6100 foot excursion at a maximum depth of 1350 feet, representing the longest tunnel excursion performed to date. It is probable that inspections of this type will become the norm at hydroelectric stations as well as other facilities with similar tunnel systems requiring inspection. <p>This report will describe the background of the project, discuss the evaluation of inspection alternatives. and provide a complete description of the HYDROVER system and its development. A brief discussion of the results of the inspection of the first of the three tunnels will be presented. Although portions of the remaining two tunnels have now been inspected, these results are not within the scope of this paper. <p>Following the discussion of the system development and inspection results, conclusions will be presented regarding the viability and future role of this advanced underwater technology. / Master of Engineering