Improvements in diversion tunnel design

Conclusion

The operating experience gained with the diversion tunnels of the Charvak, Nurek, and Toktogul hydroelectric schemes confirmed their high efficiency under severe hydraulic conditions, involving the conveyance of high-velocity discharges carrying abrasive sediments. It should be noted that the actual operating periods of the tunnels significantly exceeded the design durations. The expediency of adopting a horseshoe cross-sectional shape for large diversion tunnels operating under pressure, was also verified. At the same time, the operating record of these large size unique tunnels, the first in construction practice, has demonstrated the possibility of reducing the materials required for their construction, thus enabling their construction time and cost to be reduced, as well as the labor input in building similar tunnels of large cross section.