Behavior of Auxiliary Intake of Ramganga Dam at Low Levels

In June, 1975, when the auxiliary intake of Ramganga Dam was being run, its hemispherical trash-rack was lifted up, displaced from its seat, and subsequently sucked into the tunnel. Model studies were conducted to investigate the causes of the trash-rack displacement and of the auxiliary intake behavior at low reservoir levels. The studies indicated that the release of air-water spouts resulting from escape of locked air in the tunnel through the intake shaft at a reservoir level of El.970.46-ft could have lifted up and displaced the hemispherical trash-rack. In order to avoid air entry into the tunnel, a regulation curve for HB valve operation has been suggested to prevent recurrence of such a phenomenon in the future.