Topics Disaster Investigation and Utilization ofResults by the River Department
SUGIHARA Naoki, Research Coordinator for Integrated Water Disaster Management
River Department
HATTORI Atsushi, Head; FUKUSHIMA Masaki, Senior Researcher; MORI Hirotoshi, SeniorResearcher; FUKUHARA Naoki, Researcher
River Division, River Department
Keyword: disaster investigation
1. Introduction
The River Department of NILIM conducts disaster
investigations upon request for technical support fromriver administrators, and gives advice on emergency
measures, restoration methods considering the cause ofdisaster, subsequent river channel design, andinfrastructure design. This year, we dispatched personnel
to the river areas listed in the table below wherelarge-scale flooding or heavy rains caused damage toriver management infrastructure.
2. New findings obtained from this year's
investigations and countermeasures
In the Arakawa River of the Arakawa River Systemthat flows through Metropolitan Tokyo and Saitama
Prefecture, the cumulative rainfall reached a 10-year-highin early April during as a result of an hourly rainfall ofapprox. 25 mm/hr. As a result, slope slides occurredalong river levees soon after completion and caused
damage, including the outflow of sediment to themunicipal road, buildings, etc. Also, in the Shonai Riverof the Shonai River System in Aichi Prefecture, aconcentrated rainfall of approx. 89 mm/hr caused slope
slides along the levee soon after completion and sediment
outflowed to the municipal road.
The on-site investigation found that the main causes ofdamage were localized infiltration of rainwater into asteep slope where the topsoil was different from the levee
body in terms of construction time and material, and aparticularly weak slope since the river levee had recently
been constructed.
In response to the findings above, we organizedmatters to consider in "design," "construction planning,""construction" and "after completion" into a method forpreventing recurrence. This included considerations of agentle slope, water drainage to avoid a concentration of
rainwater and management of cover soil by compacting it
similar to the levee body. This method was disseminatedto the river administrators of the MLIT.
3. Utilization of investigation results
Investigation results and findings are organized as areport promptly after an investigation and are shared withriver administrators of the MLIT via a database ofdamage information.
In addition, findings areaccumulated in the same database and used as a basis for
updating technical criteria and guidelines, and areconsequently utilized for preventing the recurrence ofdisaster, upgrading design, management, etc.

Table: Main Rivers in 2013 Disaster Investigations
Date ofdisaster

Date ofinvestigation

Number ofdamagedlocations

Municipalities

River system / River
nameDamage form

Apr. 7

Apr. 83

Adachi-ku, Tokyo
Kawaguchi-shi, Saitama
Toda-shi, Saitama

Arakawa River System /Arakawa River

Slope slide in river leveeJul. 8Aug. 6

1

Yuzawa-shi, Akita

Jul. 13

Jul. 31

3

Yurihonjo-shi, Akita

Jul. 29

Aug. 12Jan. 17

1

Komatsu-shi, Ishikawa

Sep. 4

Sep. 101

Kanie-cho, Aichi

Sep. 16

Sep. 24
Nov. 19

1

Fukuchiyama-shi, Kyoto

Nov. 20

1
1

Ichikawa-shi, Chiba

Nov. 4
Nov. 13

Omonogawa River
Cave-in of flood channel, subsidence ofbed protection, etc.
System / Omono River
Koyoshi River System /Slope slide in river levee, sand boilingfrom foundation groundKoyoshi River
Kakehashi River System Slope slide in river levee, sand boilingfrom foundation ground/ Kakehashi River
Shonai River System /Slope slide in river levee
Shonai River
Yura River System / Yura Collapse of river levee, water leakage
from foundation groundRiverTone River System / Edo
Slope slide in river levee
River* Red cells: Damage caused by rainfall