Nima Bayati, MSc Mohsen Ghaderi, PhD



Dams have one or two bottom outlet tunnels according to their usage and size. Owing to the prevailing drought conditions in the regions around Iran’s Rudbar dam project; it was necessary to start supplying water to downstream areas before the steel lining in the bottom outlet tunnel was entirely finished.

Therefore, the inlet of the bottom outlet tunnel was temporarily blocked by a steel gate 8.4 m wide × 11.5 m high, weighing 125 t. It took 6 months to complete the service and emergency bottom outlet tunnel, during which time water was continuously being supplied to areas downstream of the dam.

Now, it was time for the temporary gate to be pulled up from a depth of 75 m underwater, and let the bottom outlet tunnel be used as planned; to control the water level of the reservoir.

This paper describes the design, construction and installation of the temporary gate and recommends a solution for pulling up the gate from a depth of 75 m underwater, using buoyancy effects, with a lifting force of less than 2 t. The operation at the Rudbar project was the first of its kind in the world that was implemented successfully.


dams, barrages & reservoirs energy rehabilitation, reclamation & renovation