Hongochi-Teibu Dam built in 1904 and located on the Nakashima river in Nagasaki City. It is a 116 m long and 26.85 m height masonry dam for the drinking water supply to Nagasaki City. Improvement works for flood control begun in 2008, as part of the Nagasaki Flood Damage Emergency Dam Project.

In order to improve the capacity of the dam, CTI selected to build a new tunnel spillway with an inlet and a stilling basin of vertical shaft types as construction method for this project, and so be able to preserve this beautiful and historic view of this 100 year old dam. CTI designed the spill way using the 3D-FEM, hydraulic model test with 1/15 scale.