Introduction to Dams

Total storage capacity is the sum of sediment storage capacity, dead water capacity, water diversion capacity, and flood control capacity. Although effective storage capacity is another numerical value that indicates the scale of water storage capacity, the ranking is almost always expressed in terms of total storage capacity. The unit is expressed in m3 (cubic meters).

Selective water withdrawal refers to withdrawing water from a dam lake, which varies in temperature and turbidity depending on its depth, for different purposes. For example, water on the surface of a dam lake is warmed by the sun, so only this water is withdrawn and used for agricultural purposes, such as growing rice. Selective water intake is achieved by installing selective water intake facilities attached to the embankment or installed in the dam lake, which take in water from each layer and discharge it downstream.

The design flood level is the water level of the dam lake at the time of the maximum flood that can be expected to occur once every 200 years (or the maximum flood flow in the past) during the dam's existence. It is assumed that the gates are fully opened and is taken into account as the highest water level that can be expected as a natural phenomenon.

Water rights are the rights to use water from rivers and other sources. In the case of dams, they are divided into agricultural water, water supply water, and industrial water. Water rights can be broadly classified into two types: conventional water rights and permitted water rights. The former do not require notification if the water was taken before the River Law was enacted (before 1896) and is socially recognized, while the latter require permission from the river administrator (national or local government) based on the River Law.

A permanent flood discharge is a gate facility that allows water from a dam lake to flow downstream while regulating the flow. It is used for normal flood control, while an emergency flood discharge is used for floods that are too large to be discharged by the normal flood discharge. A permanent flood discharge is generally equipped with a gate, but there are also some that have no gate but a hole.