ev, A. V. Nechaev, and N. M. Chasovskikh UDC 626.823.92 Tunnel spillways are widely used at hydro developments with dams on rock foundations being constructed at confined sites. Their use usually makes it possible to have a broad front of earthworks thanks to diversion of the stream through underground conduits and also to reduce the cost of construction in cases when the construction of an open outlet is related to considerable difficulties. The expediency of constructing such spillways is substantiated by technical and economic calculations. A variant of a shaft tunnel spillway was adopted when designing the hydro development of the Alindzhachai reservoir in the Nakhichevan ASSR.The following variants of outlet works were examined: traditional shaft spillway with a vertical circular shaft; spillway with an inclined shaft.However, as is known, all shaft spillways have a number of substantial shortcomings, the principal ones of which are the uncertainty of operation of the shaft and the danger of cavitation during passage of the flow.