Irrigation Research Station, Poondi, Madras
The existing Periyar Irrigation Tunnel diverting the waters from the Periyar Basin to the Vaigai Basin for irrigation, is proposed to be lined with concrete and made uniform in cross-section, for purposes of hydro-electric power generation envisaged in the Periyar Hydro-electric Scheme projected by the Electricity Department of the Government of Madras. A new forebay will be created downstream of the exit end of the irrigation tunnel, thereby submerging the same by about 75 feet. Hydraulic model studies were initiated and completed for arriving at the discharge characteristics of the tunnel after the proposed improvements. Many other allied problems such as the location of control gate, effect of aeration of the tunnel by vertical shafts, modularity phenomena and maximum discharge capacity of the tunnel were also solved after exhaustive experimentation. A special Transference Equation derived for obtaining the discharge scale for a model of this type, whose flow features are controlled more by friction rather than by gravity, merits particular mention. At a result of these studies, much light has been thrown on a number of interesting flow phenomena pertaining to tunnels and it can be stated that the knowledge gained herein will prove much useful for designing similar tunnels elsewhere.
