the Waterfront Renovation of City Core of Tokyo Vol.2"
Date： 22, June. 2006 (Thu) 18:30-21:00
Place: Meeting Room B, Boissonade Tower 25F, Ichigaya Campus, Hosei University
"Comfortable Environment Development of
Koto including Affection for Water Park"
Kiyomi Sakaguchi (Former Manager of Engineering, Koto City Office,
Association for Bering Familiar with Waterfront of Koto)
Koto City is referred to as Koto Delta, with three sides enclosed
by water. The area has been suffered from flood damages and land subsidence
caused by groundwater utilization by factories. The river maintenance
has been implemented for both planned rivers for maintenance project
within Koto City, and unplanned rivers.
We decided to address the unplanned rivers because of petitions and
staffs' involvement. Because these rivers were commissioned rivers,
the maintenance work was financed by Tokyo and the surrounding areas
were developed based on park project of Koto City. The whole area has
been controlled by Koto City. The maintenance plan for rivers within
the Koto City drawn up in the latter half of the 40th year of Showa,
was changed for speeding up; the modified plan decided to lower the
water level of the Joto area for 1m, and unplanned rivers were upgraded
to planned rivers.
There have been various cases of waterfront maintenance in Koto; e.g.,
width of the Yoko-Jukken River was widened from 10 ken to 40m, while
plants were grown on the revetment. The basic concept for Koto City
at the time included green and water network concept, to promote the
greening. The banks of the rivers within Koto were not originally appropriate
for plants because of high salt content; however unused industrial
water was utilized to reduce the salt content for fostering the environment.
In Furuishiba, stones were used for maintenance works.
In the 60th year of Showa, Koto City started the navigation of Japan's
first water bus. The ships were specially manufactured for navigating
rivers with low bridge beams within Koto. The landscape seen from ships
was well received by boarding guests; however, the water bus system
was abolished after about 10 years because of economic viability and
poor water quality. I wish that water buses could continue in service
to attract interests from inhabitants including the water quality issues.
For the Onagi River, line of pine trees were planted based on the
Gohon-matsu drawn in a picture of Hiroshige Ando. However, the River
Bureau pointed out that the plants would damage its functions of a
bank; therefore we visited the Ministry of Construction for negotiation
and received the permission. In the process of planting, based on the
requests from inhabitants, we planted cherry blossoms in the middle
of the line. We can view cherry blossoms in full bloom every spring,
and the river banks are used as the stage of "Sakura Festival" held
by inhabitants. Lastly, other examples of promenade include Shiokaze
no Sanpomichi (promenade of sea breeze) along Shiohama Canal in the
port area, promenade of floating pier over Sendai Horikawa, crossing
promenade in Nakanoshima under Aioi Bridge, etc.
"Tide Walls of the Sumida River and Super
Kinji Ishikawa (Supreme Advisor, Tokura Corporation; Head Director,
A! Anshin Anzen Machizukuri Association)
The surrounding area of Okawa was a wetland; in fact it has been said
that when Yoritomo Minamoto hit Kamakura from Shimosa through Okawa,
many local samurais supported the army on ships. Ieyasu Tokugawa who
had moved to Edo built a reclaimed land on the wetland using waste
soil from construction of canals and the Kanada River; he also moved
the Tone River eastward to transform the wetland into safe residential
areas or commercial areas.
The river engineering work dramatically reduced the number of floods,
and the need for maintenance works. Actually, for 300 years until the
Meiji Era, the major renovation works for river were not implemented.
The severe flood damages occurred in the 40th and 43rd years of Meiji,
resulted to the construction of Arakawa discharge channel for moving
the Arakawa eastward to Katsushika and the direction of the Edo River.
By the channel construction, cross-section area of the Okawa (Sumida)
became wide enough to protect the river from floods. The renovation
of the river was no more needed. Although the Kanda River and the Shakujii
River diverted from the Sumida does not sufficient cross section area,
and are often suffered from flood damages, the flowing capacity of
the Sumida is enough to receive doubled flood flow by the development
of surrounding areas of the tributary streams.
The piping up of industrial water started at the beginning of Showa
along with the industrialization of Sumida and Koto, caused the land
subsidence in the area with soft foundation. The high tide water sometimes
flew over the dykes of the Sumida.
The dykes of Sumida could not stand for this new issue. In the 9th
year of Showa, Tokyo city established 10 years' plan against high tide.
Although the engineering works proceeded up to 80%, the intensification
of the World War II made this plan terminated.
In the 24th year of Showa, the high tide caused by KITTY ruined the
lower areas. In response to the damages, the fist protection project
from high tide of Tokyo started and completed after 8 years in the
32nd year of Showa. The industrial areas surrounding the river were
flourished through military procurement of the Korean War. At the same
time the needs for industrial water aggravated the land subsidence,
with maximum sinkage of 15cm a year. Isewan Typhoon (Vera) attacked
Nagoya with similar low land, caused the death of over 5000 and gave
nationwide recognition of the danger of high tide. To protect Shitamachi
(low city) of Tokyo against such damages, the plan for responding Isewan-type
typhoons was immediately prepared and carried out; as a result, the
razor-shaped concrete dikes were finally constructed.
The high tide wall like a prison was required to address the issue
of land sinking of 4m. For the construction of super dyke, it was required
to fill the sunken part and heighten the ground. Therefore, the super
dyke can reproduce the low, safe and refined Bokutei of Edo.