 Following the completion of the dam , the entrances to the two outer diversion tunnels were sealed at the opening and halfway through the tunnels with large concrete <unk> . The downstream halves of the tunnels following the inner <unk> are now the main bodies of the spillway tunnels . The inner diversion tunnels were <unk> at approximately one @-@ third of their length , beyond which they now carry steel pipes connecting the intake towers to the power plant and outlet works . The inner tunnels ' outlets are equipped with gates that can be closed to drain the tunnels for maintenance . 
