Abstract
A facility, which lets flows in two steep non-pressure tunnels with different bed level confluent, and discharges the confluent flow into a conduit, is needed in Azusagawa-ugan district in Nagano Prefecture. However, it is impossible to apply existing confluent facilities to this district due to its unique field conditions. Therefore, a new confluent facility, which weakens a flow falling from a branch line tunnel by multistep, was proposed referring the multistep free fall type drop works constructed as a sewage facility, and was inspected by hydraulic model experiment. The assessment items for energy dissipation effect were the presence of the big fluctuation of water surface in a main line tunnel which occurred by a main line flow being obstructed by a branch line flow, and the presence of collision of a flow from the bottom step to a downstream wall in confluent facility.
