At an increasing number of existing dams, the discharge function is being strengthened by improving or expanding the discharge system. Consideration is given to methods for improving existing discharge systems, expanding the discharge system by adding discharge pipelines inside the dam body or introducing overflow-type discharge systems, and constructing tunnel spillways in the right/left banks. Such structure-based countermeasures are, in some cases, combined with nonstructural countermeasures such as increasing the flood regulation capacity or changing the reservoir operation method. Work for increasing the discharge capacity is almost always executed while the reservoir is operating and it is often impossible to lower the reservoir level to the elevation where the equipment is to be expanded, so a cofferdam is built for underwater work.

It is also necessary to carry out large-scale excavation of the dam body, so each type of work must be accompanied by measures to guarantee safety and reliability. Advanced technological capabilities are essential to strengthen the discharge capacity of a dam in order to overcome technological challenges, such as the need to deal with tensile stress generated inside the dam body accompanying, large-scale excavation at the deeper elevation, to develop cofferdam methods ensuring safe excavation of the dam body while installing an overflow discharge system, and to overcome technological problems related to constructing a large-scale tunnel spillway. The Japan Dam Engineering Center has extensive knowledge on every step from planning to execution of projects to strengthen the discharge capacity of dams, and provides technological support to overcome problems faced at dams.