Multilevel schemes for the layout of temporary and permanent spillways are presently used in the construction of high-head hydrodevelopments.Such schemes, corresponding to the technical level attained by Soviet gate construction, provides the release of considerable flows over a wide range of heads up to 100-130 m. The number of levels of spillway structures at high-head hydrodevelopments can be reduced by using high-head gates.This can effect a considerable economy, especially in the case of spillway tunnels, since the cost of each level amounts to 10-20 million rubles.At present designs have been developed for deep, mainly vertical-lift and radial gates which can operate satisfactorily under heads to 200 m for opening areas of up to 30 m 2. However, if the temporary discharges during construction are great, the spillway is built with a large number of openings, which adversely affects the hydraulics and leads to an increase in the spillway face, rock excavation, and capital expenditures. Therefore, the need for creating high-head gates covering openings greater than 30 m 2 at heads to 200-300 m is quite pressing.

The construction of submerged gates for large high-head hydroelectric stations involves the solution of complex and frequently contradictory engineering problems. Consequently, it is not always pnssible to achieve reliable performance of the gates, mounting structures and adjacent sections of the conduit, employing the optimum and most economic version. Consequently, on a number of hydroelectric stations under construction (Nurek, Toktogul, and others) economic single-stage conduit systems have not been employed for passing the construction discharges. The conversion to multistage conduit systems has inevitably resulted in a higher cost and longer time for constructing the hydroelectric station. A further study of the conditions of reliable operation and the use of existing types of gate, together with their improvement, is of great importance.At the present time submerged gates are classified according to the design features (plane, segment, etc.) material, and purpose, which does not completely reveal their operational possibilities, i.e., the effect of variation in head and discharge through the conduit on the performance of the gate material and its hydraulic conditions. The gap may be filled if the classification expresses also the conditions of gate operation in the conduit in accordance with four basic features: the hydraulics of the gate and its location in the conduit section, performance of the sealing sections, the lifting and lowering forces, and performance of the gate material (see Table 1). A gate described in the table as optimum as regards one feature is not always optimum in respect to other features.The hydraulic working conditions of the gate and its location in the conduit section (columns 2-9) govern both the design of the gate chamber and the adjacent sections of the. conduit, their physical volume, and cost of construction, in addition to the intensity of pulsation of the flow, the vibration load, and cavitation processes. It is interesting to examine three sections of the conduit, before the gate, in the gate area, and after the gate. For various types of gate, the flow may or may not change direction on each section. In the first case, the flow is less turbulent and the cost of constructing the conduit sections is lower.The performance of seals against the water pressure on the gate (columns 10 and 11) determinates the operating reliability of the thrust assernbly and of the gate as a whole. If the gate is balanced and operates as a closed system, then the hydrostatic pressure acting on it is not transmitted to the seals. In the case of unbalanced gates, the loads across the thrust-access assembly are transmitted completely onto the sealing structures. Consequently, balanced gates are more reliable and economical for this reason.The lifting and lowering forces of the mechanisms (columns 12 and 13) determine the head, the method by which it is absorbed by the gate (columm 10 and 11) and by the support structure. In the case of balanced gates the head and the supporting construction have n...

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The construction of high-head hydroelectric stations on large rivers involves the solution of the difficuk engineering-technical problem of passing construction discharges during the erection of the station and the filling of the reservoir. Under such conditions the construction discharges are, as a rule, diverted through tunnels drilled through the rock. The peculiar characteristic of the operation of such tunnels is the extremely high fluctuation of head and discharge. During the first stages of construction the river discharges are passed with relatively low head which makes it necessary to construct tunnels of large cross sectional areas. Later as the reservoir fills and the head increases the discharge capacity of the tunneis increases and there arises the necessity of regulating the discharges; for this purpose the conduits are equipped with main (regulating) and emergency-repair gates. In designing such gates planners encounter the serious difficulties which as yet do not make it possible to close with one gate a large opening when the head ranges from 100 to 300 m. The principal difficulties are the following:1. The design of an opening structure of the required width for a hydrostatic load amounting to thousands and tens of thousands of tons.