"Irrigation Channels and Paddy Fields in
Hino City as Fish Habitat and Their Future Prospects"
Kazuya Nishida (Laboratory of Water Resource Planning, United Graduate
School of Agricultural Science, Tokyo University of Agriculture and
Technology)
I have conducted researches on irrigation channels and paddy fields
of Hino and Hachioji as fish habitat, to consider the way of improvement.
Many kinds of fish including rare and endangered species can be found
in Hino Irrigation Channel because it takes water from Tamagawa (river).
The structure of aqueduct is mainly made up of two-sided concretes.
The channel of slow water flow with sand and mud, where submerged plants
grow, might provide the natural habitat for fish from paddy fields
(such as Juzukake-Haze (Gymnogobius cataneus). Though the area of earth
channel is small, the channel should be conserved because it functions
as the place for propagation and growth. Toyoda Irrigation Channel
is in similar situation with Hino Irrigation Channel. Hirayama Irrigation
Channel consists of three-sided concretes. Fish cannot pass winter
in the ditch, therefore it is assumed that fish cannot propagate in
surrounding paddy fields. Similar to Hirayama Irrigation Channel, Mukojima
Irrigation Channel is shallow with few submerged plants. However, in
the part of natural revetment, emerged plants can provide the fish
habitat. The research shows that paddy fields are very important for
propagation of fish.
I prepared several propositions. Because fish lack the place for passing
winter to obtain the stability as group of individuals, we should identify
the sites and environments for fish's wintering. It is necessary to
retain the place where water with enough depth could be kept during
winter. In order to intake or divide water during the period without
irrigation, weirs should be set in paddy fields and diverted channels.
Inhabitants can help to maintain the place where fish gather, such
as under bridges.
Paddy fields should be maintained and prepared for rice cropping as
the place for propagation of fish where fish come to grow and then
go. Surrounding areas of paddy fields should be retained for passing
winter. From the viewpoint as above, the way of maintenance should
be refined, as in Mukojima Irrigation Channel, or Yosomori Channel
where paddy fields and waterways have been improved in an integrated
manner.
The connection between irrigation channels and rivers should be retained
because carp, crucian, catfish run from rivers through intakes to channels
for egg lying. However in reality, it is difficult because of height
difference between waterways and rivers. Some waterways have channels
for fish, though its effect is not yet proved. Instead of water withdrawal
using pumps, weirs or natural withdrawal should be took into consideration.
From the viewpoint of the place for drainage, I think that it is sufficient
to keep a place for propagation several or some 10 meters from drainage
point.
*For further details, refer to the research report of 2006, "Water
Town, Hino-For Renovation of Irrigation Channels". |
|
|
[Fig.1 Fish Collected
in the Irrigation Channels in Hino] |
|
[Fig.2 Fish Distribution
in the Irrigation Channels in Hino and Negawa] |
|
[Fig.3 Fish (Wetherfish
and Kinbuna: Carassius auratus subsp) Distribution in Irrigation
Channels in Hino and Negawa during Summer Season] |
|
|
"Restoration of Water Circulation"
Yumiko Yamamoto (Study Group of Asakawa)
We works for restoring water circulation back to community planning
of Hino.
In "Hydrological Study on Conservation of Water Environment of
Hino Based on Observation of Sites", we tried to clarify the flow
of groundwater by measuring wells. We investigated various wells near
the Hino Station, on the table land of Chuo express way, near downstream
of Hodokubogawa, etc. (Fig.1).
We proposed wand at the confluence of Hodokubogawa and Tamagawa. In
relation to "Water Town and Water City Conference", its setting
was completed only during four months owing to the active supports from
specialists including Mr. Ogasa (an officer of Hino City). During several
yeas, the number of types of fish in the wand has become a little greater
than in the main river, Hodokubogawa.
We also conducted surveys on vegetation. Under the Arai Bridge, we checked
the vegetation within 10 meters square; there were 54 types of plants.
The community of Kitsunenokamisori (Lycoris saguinea) cannot be found
no more. We asked several times to conserve the community, though it
was lost because people cut the grass. Once soil, greens and organisms
were lost, it took long and is costly to take them back. Some of them
were never restored.
I think that significantly different three landforms of Hino are appealing;
hills, terraces, and alluvial areas. Furthermore, two large rivers flow
within Hino, and aqueducts, groundwater, spring waters and wells are
retained. We should utilize these resources. Large vertical interval
leads to an originality of landscape. I really feel that Hino is most
attractive and kaleidoscopic city in the suburbs of Tokyo. We have to
share such value. For this, One of my proposals is to make a map describing
various connections of resources, between terraces, hills, waters, and
greens. If citizens will participate with us, our activities will serve
role of conservation. By making a team, including researchers, officers
of city government, river administrator, members of JA, farmers, citizens,
NPO, teachers, etc., we will prepare systems, in order to establish a
place where we can try various things for you to experience.
We wish to people feel originalities of Hino, along with both nostalgia
and stylishness; at the same time we will aim to establish independence
of food, work, and city. In this period when farmlands have been dramatically
reduced, agriculture will end if we give up conservation. We hope to
keep Hino as attractive place. Originalities of land shape, farmlands
as working place, creatures in irrigation channels, etc. The last will
become a significant sales point of Hino.
Other issues include the closure of sewage plant of Kitano, along Yamadagawa
diverted from Asakawa. Though the water quality is poor, the discharged
volume from the plant into Asakawa during winter occupies 40%. Hachioji
City proposed the closure of the plant. I think it should be rejected;
however, if it should be approved, we will have to discuss the measures
to increase the water volume of Asakawa with specialists. We should work
with inhabitants around upper stream, where Kanto mountain areas and
hills exist. Because their subsoil flows are precious assets of Hino.
*For further details, refer to the research report of 2006, "Water
Town, Hino--For Renovation of Irrigation Channels". |
|
|
|
|
[Fig.1 Wells
for Measurement]
|
|
|
|
