Preventing the Occurrence of Extensive Flood Damage in Kyoto Using a Dam's Flood Control

At the Katsura River of the Yodo River System in Kyoto Prefecture, a large-scale flood occurred and the Hiyoshi Dam experienced the greatest inflow recorded since operation but by using the dams flood control, the water volume released downstream was reduced by approximately 90 percent.

It is estimated that this flood control prevented the spread of damage to the Togetsukyo Bridge in the Arashiyama District in Kyoto City (near Togetsukyo) and also virtually halved the number of houses flooded.

In addition, near the Kamo River confluence in downstream Kyoto, the water level rose to the levee crest and there was overflow on the right bank side but thanks to the Hiyoshi Dam's flood control and flood fighting activities by flood control brigades and Japan Self-Defense Force, and others, a levee collapse was avoided. If the Hiyoshi Dam did not

Togetsukyo Bridge soaked in water up to the parapet

(Around September 16, 9:00 AM)

The water level reduction effect of the dam

Source) MLIT

exist, and the levee broke near the right cost side, approximately 13,000 housing unites would be inundated and damages amounting to approximately 1.2 trillion yen are estimated to have occurred.

Prevent Flooding Damages through Levee Development

The Itayanagi district on the right bank of Iwakigawa River in Aomori prefecture was an area without a levee but levee development and river channel dredging was started from 1999 and in March 2013 a levee with a total length of 8.1km was completed.

In the floods caused by Typhoon Man-yi, although the water level exceeded high water level, actions such as flood fighting activities prevented the levee from collapsing. Thanks to the levee's development, it is estimated that approximately 3,100 ha (approximately 5,900 units) were protected from flood damage.

The Itayanagi levee that protected the city from flooding

## (d) Inner Water Measures

To prevent flooding through inner water inundation and strive for the healthy development of cities, the improvement of facilities such as sewer pipes and drainage pump stations are being promoted. However, in recent years, the frequency of concentrated downpours that far exceed planned scales increased rainwater drainage due to the advancement of urbanization, the increased complexity of the urban landscape including the concentration of population and wealth as well as the increased use of underground spaces make the risk of damage due to inner water inundation even greater. For this reason, measures such as integrated projects for the reduction of sewer flooding damages and integrated projects for inner water emergency measures are being utilized with the cooperation of relevant parties including regional authorities and affected residents to carry out hard measures such as proactively implementing rainwater drainage reduction facilities; soft measures such as providing rainfall information, land use regulations, and creation of inner water hazard maps; and self-help initiatives such as the placement of water stops and sandbags as well as evacuation activities in combination for the promotion of integrated flood measures.