SUPER LEVEES ALONG THE ARAKAWA RIVER IN TOKYO: EVALUATION FROM THE

VIEWPOINT OF SPATIAL PLANNINGIN A LOW-LYING AREA

SIT

International Conference on Flood Resilience Experiences in Asia and Europe

Hitoshi Nakamura1, Takaaki Kato2, Yuto Shiozaki21Shibaura Institute of Technology, Japan, 2The University of Tokyo, Japan

5-7 September 2013Exeter United Kingdom

Abstract

The purpose of this study is to examine super leveesalong the lower reaches of the Arakawa River in Tokyoand consider the need for reevaluation of super leveesas upland evacuation areas in the event of a large-scale flood in a low-lying area.

SUPER LEVEES

A super levee is a high standard river embankmentwith a broad width which can withstand even ifoverflow (Stalenberg B. et al., 2008). It is about 30times as wide (about 200m to 300m) as it is high, sothat even if it is overtopped, the flowing water doesnot breach the levee because it flows slowly across itstop surface (Figure 1, Arakawa-Karyu River Office,2013).A high standard levee improvement project (a superlevee project) was started in 1987 along the six largerivers in Tokyo and Osaka, i.e., Tonegawa, Edogawa,Arakawa, Tamagawa, Yodogawa and Yamatogawa.Because a super levee project is often promoted inconjunction with an urban development project alongthe river, the creation zone will exist discontinuously inthe long time. After the super levee project wasdecided to be abandon by the national budgetscreening system in 2010, the Ministry of Land,Infrastructure and Transport reviewed its policydrastically in August 2011. According to this newpolicy, the creation zone for super levees is narroweddown to low-lying areas or densely built-up areas inlarge cities where serious human damage is likelier tooccur in a large-scale flood.

References• Super Levees Guidebook (2007). Arakawa-Karyu River Office, Ministry of Land, Infrastructure and Transport, Tokyo, Japan.• Stalenberg B. and Kikumori Y. (2008). Urban Flood Control on the Rivers of Tokyo Metropolitan. In Graaf, R. D. and Hooimeijer, F. (editors), Urban Water in Japan, Taylor & Francis

Group, London, UK, 119-141.• Arakawa-Karyu River Office, Ministry of Land, Infrastructure and Transport (2013). Activities of our Office: Super Levees. http://www.ktr.mlit.go.jp/arage/english/outline/01.html#1

(accessed 1 July 2013)

CITY PLANNING MASTER PLAN

An examination of the description of the city planningmaster plan of the local governments of 5 wards(Sumida-ku, Koto-ku, Adachi-ku, Katsushika-ku,Edogawa-ku) along the Arakawa River in the lowlandsof eastern Tokyo reveals that every local governmentspecifies the necessity of flood control measures.Although super levee project zones are specifiedthroughout all the lower reaches of the Arakawa River,they are not specified in the city planning master planmap for each ward. Only the Katsushika city masterplan shows generously “evacuation area from thecreation of uplands” in the urban safety developmentpolicy (Figure 2). Some areas along the Arakawa Riverare designated as planned upland evacuation areas,however, there are no urban planning regulationsabout super levees.

CONCLUSION

From the viewpoint of spatial planning such as theabove, it is important to reevaluate the need for superlevees as an upland evacuation area.A detailed analysis of possible evacuation spaces onthe super levee and evacuation routes to them is thenext research theme. And an appropriate cost-benefitanalysis of super levees as upland evacuation areasshould be further considered.

LOW-LYING AREA IN TOKYO

The population in low-lying areas (an area where theground is lower than the mean sea level) in Tokyo isabout 1.8 million. These low-lying areas have beenexposed to flood risks and the risks have beenincreasing due to climate change. Several tens ofthousands people cannot be assumed to be able toevacuate even if all tall buildings, including the privatebuildings, are assumed to be places of refuge.Therefore, in low-lying areas, the creation of a large-scale upland evacuation area is required.

The difficulty of consensus building, large-scalecompensation for removal, project prolongation, andeffects on the surroundings including sunshineexposure are disincentives for the project. Only in theHirai 7-chome district have inhabitants promoted theproject by themselves in cooperation with theEdogawa ward land readjustment project. Althoughthis project did not create an open space for refuge, itimplies the new feasibility of the project.

ALONG THE ARAKAWA RIVER

An interview survey of the Arakawa-Karyu River Officerevealed that in the lower reaches of the ArakawaRiver, super levee projects have been complete or inprogress at 15 sites; 8.75 km as of March 2012.Completed projects comprise 13 sites, approximately5.03 km, and projects in progress comprise 2 sites,approximately 3.72 km (Table 1, Figure 3).This accounts for about 15 % of the total length of58.2 km. As for the land use of these 15 super levees(Table 1), 8 projects include dwelling houses, 4projects include public parks, 8 projects include publicfacilities other than parks and 2 projects include otherland use such as commercial buildings.From the standpoint of securing an upland evacuationarea, it is desirable to create a public park or publicopen space on the site, but these cases comprise only4 out of 15. In specific circumstances, however, it ispossible to use public facilities, roads, private openspaces, commercial buildings and high-rise apartmentbuildings on the super levee site as small-scaledispersed evacuation spaces.

Figure 1. Super levee (Source: Arakawa-Karyu River Office, 2013)

Figure 2. “Urban safety development policy (flooding)” in the Katsushika city master plan

Figure 3. Super levees along the Arakawa River (Adapted from Arakawa-Karyu River Office, 2007)

Table 1. Super levees along the Arakawa River

Hirai 7‐chome District

Komatsugawa District Shikahama District

Odai 1‐chome District Shinden Distict

Kawaguchi DistictKita‐akabane District

Odai District

Super leveedistrict

Main land use

Length(m)

Area(ha)

Mean width(m)

Filling completion

yearDwellingPublicpark

Public facility

other than park

Ohters

1 Shinsuna X 1,140 18 158 2004

2 Komatsugawa X X X 2,380 23 97 in progress

3 Hirai X100 1.5 150 2003

4 Hirai 7-chome X

5 Senju X X 100 1 100 2000

6 Odai X 100 0.4 40 1991

7 Odai 1-chome X X X 670 12 179 2004

8 Miyagi X 300 1.6 53 2001

9 Shinden X X 1,360 27 199 2007

10 Shikahama X 300 10 333 1991

11 Kawaguchi X X X 1,340 11.5 86 in progress

12 Kita-akabane X 500 4.2 84 2003

13 Ukima provisional completion

14 Funado X 70 0.6 86 2006

15 Toda-koen X 150 2.8 187 2008

District Public facilities other than park + Others

1 Shinsuna Water station, Water treatment plant, Electric power transmission facility

2 Komatsugawa Junior high school, Pumping station

5 Senju Community (Lifelong learning) center

7 Odai 1-chome New transportation system station, Station square + Commercial buildings

9 Shinden Elementary school, Junior high school, Sewerage facility, Fire fighting center

11 Kawaguchi Elementary school, Junior high school, Kindergarten + Temple, Driving school

12 Kita-akabane Disaster prevention station (stockpile warehouse for food and materials)

14 Funado Recycling facility

Place of refuge for people requiring an aid

(Existing)   Evacuation area from(Plan)         the creation of uplands

Creation of uplands in built‐up areas along the riverCreation of uplands in built‐up areas along the riverPriority area for flood control measures

Orientation of safety evacuation areas