Rainwater Runoff Control Measures

In recent years, there has been a trend of localized heavy rainfall across the country, increasing the risk of flooding due to rainwater. To protect the lives and property of citizens and maintain urban functions, the city is promoting measures to control rainwater runoff along with the development of public sewerage for rainwater.
To suppress rainwater runoff, we are working with relevant divisions to preserve permeable areas such as green spaces and parks. Regarding rainwater drainage facilities (such as rainwater pipes), large-scale projects require significant costs and time for development. Additionally, due to the need to respond to recent localized heavy rains, we are promoting the installation of rainwater infiltration facilities and rainwater retention facilities, in addition to rainwater drainage facilities.

Rainwater Infiltration Facility

This is a facility for efficiently allowing rainwater to permeate the ground. Examples include rainwater infiltration pits and infiltration trenches.
By allowing rainwater to permeate underground, it becomes groundwater, which can be effectively utilized as a healthy water circulation resource.

Rainwater infiltration pit

Rain that falls on the roof is directed to the rainwater infiltration pit via gutters and other means.
One rainwater infiltration pit with a diameter of 25 centimeters has the capacity to infiltrate approximately one bathtub's worth of rainwater into the ground per hour.
The rainwater infiltration pit allows rainwater to permeate through holes in the bottom and sides, as shown in the photo below.

Infiltration Trench

In addition to rainwater infiltration pits, further infiltration effects can be achieved by installing infiltration trenches.
Although it is not visible in daily life, it can be constructed on the premises as shown in the photo below. Rainwater infiltrates through the perforated pipes and the gravel at the bottom.

Rainwater Storage Facility

This is a facility for temporarily storing rainwater to utilize it as a water resource or to delay the outflow of rainwater. Examples include storage tanks and retention basins.

Retention Tank

This is a facility that collects rainwater that falls on building roofs and other surfaces.
By installing a storage tank, rainwater can be temporarily stored and used as valuable water for home gardens, watering trees, and during disasters.

Retention Basin

A facility for temporarily storing rainwater from the entire watershed, which delays the outflow of rainwater to the downstream area, aiming to cut the peak outflow and reduce flooding damage.