Selection of temporary diversion tunnels and tunnel schemes for discharge of water

Abstract

The construction of hydrostations and hydraulic-engineering projects, which involves regulating the runoff of rivers for its multipurpose use, is associated with the need to divert the water arriving at the site during the construction period.During the construction period water is usually diverted through special temporary structures or through the incomplete main structures of the future hydrostation, or both.Diversion of water is affected by various factors and conditions, starting from natural ones --the character and adequacy of the river hydrographs, volume of river discharge during the years of construction, and others --and ending with the layout and types of planned main structures.Diversion structures are no less important than the main structures and their cost amounts to a substantial part of the cost of the main structures of the hydrostation. This is especially true for the construction of mountain and piedmont hydrostations being constructed on rock foundations (especially in narrow canyons), where the layouts and set of main structures are largely determined by the conditions of diverting the water and technology of construction, which is closely associated with the diversion scheme.Widely used at such hydrostations are temporary diversion tunnels, which in many cases are reconstructed later into service spillways --for permanent use as power or discharge channels during permanent operation of the hydrostation.In much the same way as streamflow regulation systems with discharge of water through permanent structure of the hydrostation, the water diversion system can be subjected to a technical and economic analysis for selecting its optimal parameters. The problem consists in selecting a rational scheme of use and parameters of diversion tunnels providing minimum expenditures on diverting the water under specified conditions of construction of the hydrostation.This problem is solved on the basis of technical and economic calculations (TEC), involving an examination of a number of variants of the characteristic parameters, from which should be taken those which on fulfilling all other requirements correspond to the condition of minimum cost.The performance of such technical and economic calculations by means of computers opens the way for obtaining a well-founded minimum cost of diverting water promoting an overall decrease in the construction cost of the hydrostation.To solve the indicated problem a special method can be proposed for determining the rational parameters of diversion tunnels, using the author's main principles and conditions affecting the rational parameters of temporary tunnels and also the principles of the standards for determining the cost effectiveness of capital investments and other materials.In the available literature the analysis of constructed diversion tunnels is aimed at improving and reducing the cost of structures and their operating conditions. In the standards and works on determining the cost effectiveness of investments there are no recommendations on selecting eco...