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In the construction of high-head hydraulic developments, the discharge of water to the downstream slde is effected from different reservoir levels through multistage spillways. If the hydraulic development has an earth dam, then the spillway for each level, with the intake below the normal pool level (NFL), uses a tunnel. The upper level spillway may also be a tunnel. All these spillways are either connected to a single tunnel (Chirkey hydraulic development) or carried separately to the downstream side (Fig. 1).The total length of the tunnels of a multistage spillway system may be reduced if the lower tunnel portions of the different levels are connected into a single tunnel by means of a shaft. In this case it is necessary to ensure hydraulically favorable (impactless) conditions of joining of the flows at their confluence in the shaft.A design ensuring impactless entry of flow from horizontal or inclined tunnels into a shaft (proposed by S. M. Slisskii) was investigated at the Hydraulic Structures Department of the V. V. KulbyshevMoscow Civil Engineering Institute (MISI) and at the '~aznii~nergeti-ka" Laboratory. One of the alternatives was used at the high avalanche protection Medeo dam, a schematic of the spillway of which is shown in Fig. ic.For impactless jolnln E of the flow from the tunnel with the flow in the shaft, the following solutions have been proposed: i. Each tunnel-shaft junction is constructed in the form of a spiral chamber, from which the water enters the shaft by rotating around the shaft axis. Under the action of the centrifugal forces, the water spreads over the shaft walls, forming an air core, and moves downward alon E a spiral having an increasing pitch.In comparison wlth the radius of the upper portion, the shaft radius below the spiral chamber is made larger by an amount equal to the thickness of the water layer spread over the shaft walls. Since the stream diameters in the shaft above the spiral chamber and the air core below the spiral chamber are equal, impactless joining of the flows is ensured.The inlet part of the shaft in this case may be constructed in the form of a circular welt or of a splral chamber [1][2][3][4]. In the first case, translational and rotational flows are joined, and, in the second, flows rotating in one or different sides are joined.2. The tu~el (free-flow or pressure) is connected to the shaft in such a way that the external tunnel wall is tangent to the shaft wall (Fig. 2). The flow within the limits of the shaft spreads over its walls and moves downward along the spiral. In the shaft center, an air core remains, whichmay be filled with the flow coming from above. A spillway of this type may be called a tangential spillway.For study of the hydraulics of tangential spillways, the flow was fed to the shaft through both an inclined conduit (MISI model) and a horizontal conduit ("Kaznii~nergetlka" model). Depending on the presence or absence, in the shaft, of flow coming from above, the nature of its motion (translational or rotational), the type of motion (fr...

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