Nurturing and protecting a water conservation forest for over a century.

First of all,where is this water conservation forest?

Drippy Drippy　The water conservation forest managed by the Tokyo Metropolitan Government Bureau of Waterworks is located upstream in the Tama River. It stretches some 20 kilometers north and south and 31 kilometers east and west, with an area of about 23,000 hectares. That comes to more than a third of Tokyo's 23 wards!
Little brother Brother　Is it really that vast!? Incredible!
Drippy Drippy　In fact, the Bureau of Waterworks has held and directly managed a water conservation forest for more than a century, and the mountains that were rough a century ago are now lush with greenery!
Map
What is its role?
Droplet Droplet　Plenty of the rain that falls in the forest accumulates in the spongy soil and flows slowly out to the rivers. In this way, the amount of water in the river is stabilized, preventing droughts or floods. This is why the forest is known as a “green dam.”  
Mom Mom　So the forest saves water, right!  
Droplet Droplet　And the dust and dirt that sticks to the water is removed as it moves through the soil, getting clean in the process. In this way the forest functions as a natural water filtering plant. And what's more, the tree roots firmly hold the soil, preventing the soil from flowing into the rivers.
Little sister Little sister　Great! It even has that kind of function!
Droplet Droplet　In addition, the trees also serve functions like absorbing carbon dioxide. Keeping the forest healthy is very important.

How is it managed?

Drippy Drippy　About half of the forest in the upstream area of the Tama River is a water conservation forest managed by the Bureau of Waterworks. The water conservation forest is systematically tended with planting, thinning, and pruning administered in order to cultivate a good forest.
Grandpa Grandpa　I had no idea the Bureau of Waterworks managed the forest!
Droplet Droplet　The other half is a private forest. Tending is not thorough in some of the private forest, and progressing forest decay is evident. As a result, the Bureau of Waterworks established the Tama River Water Resources Forest Team in 2002, and the private forest was restored through the tending of a great many volunteers. In addition, the private forest purchasing business is progressing to purchase the private forest and manage it properly as a water conservation forest.
Grandma Grandma　I want to go see this wonderful forest too!
Drippy Drippy　There are events sponsored by the Bureau of Waterworks, such as walks to experience the water conservation forest, so be sure to visit it!
forest
 

Toward a world-class water conservation forest.

　The Tokyo Metropolitan water conservation forest is the largest of the forests managed by water-supply corporations in Japan. The Tokyo Metropolitan Government Bureau of Waterworks has nurtured this forest over the course of more than a century as well as developing water source facilities such as the Ogouchi Dam.
　Ordinarily, continued usage of the dam would cause significant accumulation of sediment as a result of the driftwood and soil flowing from the forest into the river, in over fifty years of usage, the Ogouchi Dam has maintained		   an extremely low rate of sediment (the amount of sediment in proportion to the volume of water in the lake), at 3.2 percent.
　This is because the water conservation forest was kept robust and flourishing.
　In the past and going forward, we strive toward cultivating a world-class water conservation forest, with the motto of “potable delicious water obtained from rich forests.”
Kazuhiko Fujimura,
Senior director, Water Resources Administration Office
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