1 - Alaska Energy Data Inventory

C. Power Tunnel. The power tunnel is an ll-ft mod ifi ed horseshoe withan overall length of approximately 6,020 ft. Tunnel lining will berequired in those sections where faults or poor rock conditions are found.Tunnel lining will consist of concrete or shotcrete depending uponcircumstances but in no case will the tunnel diameter (lined section) beless than B.O ft with the exception of the gate structure. Typicalsections and details of the tunnel are shown on plate 4.D. Penstock. The penstock is a 6-ft diameter steel structure with anoverall length of 925 ft including transitions. A typical section of thepenstock is shown on plate 5.E. Rock Traps.(1) Primary Rock Trap - The rock trap at the entrance to thetunnel is part of the lake tap and is discussed ;n paragraph 1.05 of thisapp'end;x.(2) Secondary Rock Trapa - The secondary rock trap ;s located between sta 11+40 and sta12+00 and ;s shown on plate 20. The rock trap will be an 11 ft high and 20ft wide straight sided horseshoe with an additional 2 ft excavated beneaththe tunnel invert for sediment storage. The rock trap crown will match thealinement of the power tunnel crown so as not to trap air at the crown ofthe rock trap during tunnel filling for the lake tap. This 20 ft widesection may also serve the additional function of providing a constructionturnout either as-is or by widening it slightly.b The storage are .. located in the bottom of the rock trap has anapproximate volume of 44 Yd 3 • The cross-sectional area of the trapvaries from 190 ft2 to 230 ft2 (depending on sediment accumulation)resulting in a maximum velocity ranging from 2.7 to 2.3 ft/s with themaximum expected discharge of 51B ft 3 /s.Bl-5