We measured the infiltration capacity of the grass.

On October 19, 2022, we conducted an experiment to measure the infiltration capacity of turf in Kikuyo Town, Kumamoto Prefecture. The measurement we conducted was a double ring infiltration test.

It is a simple device that uses two cylindrical iron tubes to measure the speed at which water seeps into the ground. (The photo shows the state immediately after the measurement. A piece of grass is cut out and a ground infiltration experiment is being conducted.)

By recording the numbers on the ruler at regular intervals and calculating, you can find out how much water will penetrate per hour. It took about 40 minutes to complete the test per location.

(The photo shows the penetration being measured. It took until the evening.)

The turfgrass we measured had water infiltration of between 60mm and 100mm per hour, with a large degree of variability.

With permission from the landowner, we compared the state of the land after removing the grass with the state before removing the grass, but it did not seem to necessarily increase the infiltration capacity. The world of infiltration is quite complicated.

Knowing this infiltration capacity provides one piece of information for determining how much rain an area will need to begin to flood when heavy rain falls.

At the Green Watershed Flood Control Laboratory, we investigate how long it takes for rain to run off from a particular location, and use this information to help plan watershed flood control.