Water, water, everywhere … in Kanagawa Prefecture

Before visiting water source forests of Kanagawa Prefecture, let me tell you how the supply coordination goes for our community’s potable water. Very roughly speaking, we have 2 kinds of water utility corporations. One is Kanagawa Water Supply Authority 神奈川県内広域水道企業団 who supplies water for 93% of us in Kanagawa. Another is smaller water authorities that provide water mainly from local underground water and springs to the mountainous west of the prefecture, and the city of Odawara. These two entities cover 99.9% of the population. Historically speaking, the area for Kanagawa Water Supply Authority includes the City of Yokohama where the oldest modern water supply network was established in Japan. (More to Yokohama’s system in my later post.) Yokohama has the second largest population in Japan, and composes the megalopolis Tokyo area together with the cities of Kawasaki and Sagamihara.  All the 3 cities are covered by the Authority.

The municipalities and water supply in Kanagawa Prefecture

When Japan had a go-go economic growth, the population growth in those cities and the rest of the eastern Kanagawa was very fast. It was a serious problem for the prefecture 50 years ago how to secure large enough water supply for rapidly growing cities. Between 1961 and 1966, the prefectural government of Kanagawa, cities of Yokohama, Kawasaki, and Yokosuka built Shiroyama Dam 城山ダム in the north of Shiroyama 城山 (that’s the place we visited in my post on October 20^th). It created Tsukui Lake 津久井湖 providing water and electricity to the east of the prefecture. Though, it was not enough. In 1969, the local offices decided to have one entity for permanently pooling the public fund to build and maintain larger water supply system covering 2/3 of Kanagawa. The Kanagawa Water Supply Authority was born.  With this money, in 1978 they completed the construction of Miho Dam 三保ダム surrounded by deep West Tanzawa Mountains 西丹沢, and in 2000 Miyagase Dam 宮ケ瀬ダム in the north of Mt. Oyama 大山. Kanagawa has 2416 km² occupying only 0.64% of Japanese land, where 74.9% of us live in a megalopolis Tokyo. Nonetheless, regarding water sources, we have 4 large dams surrounded by deep mountain forests (; that is, the aforementioned 3 dams and Sagami Dam 相模ダム to which I return in my later post). In contrast, Tokyo of 2191 km² has only 1 dam, Ogouchi Dam 小河内ダム, as water sources within their domain. We in Kanagawa seldom have water shortage. Tokyo had drought alert this summer, an annual event. Projecting decreasing population for decades to come, water management of Kanagawa is sitting pretty these days.

Shiroyama Dam.
We can visit this structure in 5 minutes’ walk
from Tsukuiko Shiroyama Park 神奈川県立津久井城山公園we visited 2 weeks ago.

Tsukui Lake created by Shiroyama Dam.
It’s one of the water reservoirs for Kanagawa Prefecture.
Could you see a peak with a tower?
It’s on the border between Kanagawa and Tokyo.
Mt. Takao 高尾山 is beyond that point.

Miyagase Lake created by Miyagase Dam

On the north shore of Miyagase Lake,
there is a picnic park.
The view of the lake from the park’s rambling promenade
is refreshing for sure.
Driving or biking is a popular option to go there,
but there also is a commuter bus service, Hashi-07 橋07,
by Kanachu Bus from the north exit of JR/Keio Hashimoto Station.
The destination is the terminal stop for the service
at Toriihara-Fureai-no-Ie 鳥居原ふれあいの館.
(Time table, here.)

The park has a farmers’ market where we can find fresh produce
daily harvested in the mountainous northern Kanagawa.
Lunch and craft souvenirs are available as well.

According to Dr. Keiko Izumi 泉圭子 of Iwate Prefectural University, Tokyo and Yokohama have a similar modern history for the development of water source. Even though, as early as 1926, Tokyo started to request sharing water with Kanagawa. No attempt by Tokyo has succeeded so far. Granted, Tokyo has a larger population in a smaller domain than we. Though, at least we have not had a governor as Mr. Ishihara who ordered to “annihilate all the coniferous trees in Tokyo to reduce hay fever problem.” I think we are paying at least the minimum dues in taxes and water tariffs to build and maintain dams and water source forests. It’s essential nurturing forests that can store rain water and release it naturally to rivers. Dams are a sort of the final step to maintain water reservoir, not the beginning. The other day, we Kanagawa forest instructor trainees had a seminar with Mr. Masashi Chokki 一寸木将資 of West Sagami Forestry Ltd. （有）西さがみ森林. His company undertakes works from the prefectural government for the forests in Odawara and Hakone area. He said “It’s a kind of occupational habit … whenever we have TV footage of floods, I cannot stop checking the form of trees floating in muddy streams. Are they processed logs probably stored in a lumberyard deep in the mountain? If so, it could be a sign they cut trees rather too much. Or, are they large trees uprooted? It would suggest the upstream mountain has been neglected for a long time … not sufficient undergrowth was there to prevent the massive landslides. In contrast, don’t you think we in Kanagawa so far have been spared from the disaster recently? I think we are doing our best for protecting our forest for water.” I agree.

The main watershed and water facilities in Kanagawa Prefecture

At Samukawa Water Intake Facility,
there is a small museum explaining
water distribution system of Kanagawa Prefecture.
They have a very interesting chronological table
listing requests from Tokyo for water to Kanagawa.
Hmmmmmmmmm …

Samukawa Water Intake Facility on Sagami River.
The water collected here is distributed
to the east of the prefecture, including Yokohama.
We can see water-source mountains of Tanzawa over there.

A Forest of Growing of Kanagawa Prefecture
where no-pollen cedars were planted 5 years ago.
This summer, we completed a final mowing
for baby coniferous trees.
Now they are tall enough and
have no threat of shadows cast by undergrowth.
They should be able to have lots of sunshine
to get bigger by themselves.
To reach to this stage,
forest volunteers of Kanagawa
have invested lots of man-power, and money
(; could you see at the bottom a protection mesh against deer?).
Here, the prefecture is planning
to create a “Forest of Centuries.”
In 400 years’ time this place may have
gigantic cedars with diversified lower trees
and underbrush
where lots of water is reserved for Sakawa River.

Er, well, I am not deserved for this self-congratulation at all, actually. Telling you the truth, before starting the forest instructor training, I did not recognize how deeply water supply of my home prefecture interconnects many forests. I was like, “Well, Yokohama hasn’t received any water from Western Tanzawa, have we? Then, taking care of forests near Miho Dam does not have much everyday meaning for our life!” WRONG. The water of Miho Dam is certainly used for Odawara, but thirsty Yokohama is daily receiving water from there too. The Authority pumps up water using lots of fossil fuel at Iizumi Water Intake Facility (ASL12m; we can see the facility from windows of Shinkansen bullet train just before Odawara Station) and sends it to Kosuzume Water Treatment Plant (ASL 58m) in the south of Yokohama, some 43km north. The prefecture has a huge aqueduct running from Odawara to Sagamihara with a diversion to the east, i.e. Yokohama, starting near Mt. Oyama. Maintaining good forests now in Hakone will pay dividends for Yokohama’s water bill in future. By the same token, it is not at all useless remembering the water levels of all 4 dams far from the downtown Yokohama. (We can check real-time water levels of all 4 dams here.) Each municipality in Kanagawa Prefecture has a complicated system of water pipes where computerized systems watches and predicts water flows 24/7. If a community would have a surge of water demand, the system adjusts the entire distribution, including the discharge from dams, in order to halt water outage as much as possible. (That’s why water outage occurs here when we have electricity outage. No-power means no-computer working.) So, taking care of the condition of all the dams and water source forests in Kanagawa has a very practical sense for people living in Yokohama.

This summer,
Lake Miyagase has experienced very low water level
due to erratic patterns of rain.
Even though, the prefecture did not have water problem.
When Miyagase has shortage,
2 underground aqueducts from another tributary of Sagami River,
i.e. Doshi River 道志川 (more to this very important river in my later post),
divert the water directly to Miyagase.

These days, I do not care much whether water stored underground in a particular forest could end up at my faucet. Even man-made water system can have such a complicated connection. No one knows how natural water moves beneath the thick leaf-litter of rich forest. Besides, for water of Kanagawa Prefecture, the ultimate source is Mt. Fuji. Sagami River originates from Oshino-Hakkai 忍野八海. Sakawa River starts from the east of Mt. Fuji. Between there and my bathroom, there are lots of forests. In deep mountains, I really felt it nonsense to identify the water source for particular me, this tiny creature. It’s much more fun to thank God for pure water from beautiful Mt. Fuji 24/7. It would be a privilege on earth where many people face serious disputes for scarce water … Any way, let’s visit water source forests in Kanagawa from next week!

Kanagawa Water Source Authority

1194 Yasashi-cho, Asahi-ku, Yokohama, 241-8525

Phone: 045-363-1111