"Considering 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 Dyke"
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.