July 11, 2024
9th GEWEX-OSC 2024＠Sapporo

Experiment on a Levee Breach from Overtoppingat the World’s Largest Experimental Channel

世界最大規模の実験水路を活用した越水破堤実験
Chiyoda Experimental Channel
Total length : 1310m
Channel width : 30m
Maximum discharge : 170m3/s

Tomonori SHIMADA
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Presentation outline

Experimental
ChannelResearchPlan

Levee BreachExperiments

1. What is the Chiyoda Experimental Channel ?
千代田実験水路とは？
2. Research Plan for Experimental Channel
実験水路での研究計画
3. Introduction to Overtopping Levee Breach Experiments
越水破堤実験の紹介
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Experimental
ChannelAbout Chiyoda Experimental Channel

ResearchPlan

Levee BreachExperiments

The Chiyoda Experimental Channel
was constructed in 2007 using part ofthe Chiyoda New Channel that had
been built in the middle of the TokachiRiver as water-control measure.
治水対策として十勝川中流部に整備された千代田新水路の一部を活用して、千代田実験水路が2007年に完成

Phenomena that could not be clarified
in conventional model experiments orobserved in actual rivers can be
examined using the Chiyoda
Experimental Channel.
今まで縮尺模型では解明できなかった現象や実河川では観測が非常に困難であった現象などについて、この千代田実験水路を用いることで解明することが可能

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ExperimentalChannel

ResearchPlan

Chiyoda Experimental Channel Specifications
The channel was built using one of
the four gates of the diversion weir.

Levee BreachExperiments

Movie

実験水路は4門のゲートのうち1門を利用

The flow rate can be controlledusing a gate (Maximum discharge
170m3/s).
実験水路の上流端のゲートで流量をコントロールすることが可能（最大通水可能流量170m3/s）

It has a section with a channel widthof 30m, a length of 1300m, and ariver bed gradient of 1/500.
水路幅30m、長さ1300m、河床勾配1/500

4Experimental
ChannelResearch Plan for Experimental Channel

ResearchPlan

Levee BreachExperiments

The following areas of investigation were set in the form of long-term
experimental research plan as a collaborative effort involving theHokkaido Regional Development Bureau and the Civil Engineering
Research Institute for cold Region.
The plans support R&D to solve technical problems in the field andenable systematic and focused R&D associated with river technology.
現場における個々の技術的課題を解決するための技術開発、河川工学に係る体系的・重点的な技術開発のため、北海
道開発局と寒地土木研究所の共同研究により、以下のテーマを実験研究長期計画として設定

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Experimental
ChannelResearch Plan for Experimental Channel
Subject

Main long-term subject

1

Improvement of technology for assessing thefunctions of dike/protection workLevee BreachExperiments

Experiment examplesSubject 1

堤防・保護工の機能評価技術の向上

2

ResearchPlan

Examination of the levee
breach mechanism
破堤口拡幅機構の解明

Establishment of a tree management method
for water control and environmental protection
治水と環境を両立した樹林管理手法の確立

3

Improvement of soil/sand management
precision

Subject 4

アイスジャム河川の流れ

流域土砂管理の精度向上

4Flow in ice-jammed rivers

Improvement of river channel design
technology
河道設計技術の向上

5Clarification of changes in ecological systems
after flood disturbance
洪水氾濫後の生態系の変化の把握

6

Improvement of flood prevention technology
and awareness
水防技術・意識の向上

Subject 6

Flood drills, disasterprevention education forresidents
水防訓練、住民への防災教育

Experimental
ChannelResearchPlanLevee BreachExperiments

Study Background (Experiment on a Levee Breach)

Even today, with progress in river improvement, damage caused by levee
breaches still occurs frequently in many parts of Japan.
河川整備が進んでいる今日でも日本各地で破堤による被害が多発

There are concerns that floods with severe damage
will become frequent due to climate change.

Movie

今後、気候変動の影響により洪水被害が頻発化・激甚化することが懸念

Even though the damage caused by levee breaches
is devastating, the process of such breaches
Example of levee breach in the Kinu
initiated by overtopping is not well understood andRiver (September 2015)
elucidating the mechanism of levee breaches isSource:
Geospatial Information Authority of Japan website
important for establishing mitigation techniques.
(https://www.gsi.go.jp/BOUSAI/H27.taihuu18gou)
越水破堤のプロセスは良く分かっておらず、河川堤防の破堤機構の解明は、被害軽減技術の確立に向けて重要な課題
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Objective

ExperimentalChannelResearchPlanLevee BreachExperiments

Research on levee breach to date has mainly been based on model tests.
これまでの破堤に関する調査研究は、主に縮尺模型実験などを中心に行われてきた

Full-scale levee breach experiments can be performed in consideration ofside-overflow from levee placed longitudinally to the river channel flow as
seen with actual rivers.
千代田実験水路では実物大規模で、しかも実河川と同様に河道の流れに対して縦断的に配置された堤防からの横越流による破堤実験が可能

This allows examination of the levee breach process through collection ofchronological observation data on the levee and the amount of water flow
observed during levee breach.
破堤進行時の堤体および水理量の時系列の観測データを得ることにより、破堤進行過程を解明することが目的

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Experimental
ChannelResearchPlan

Overview of the experiment and ovsevation

Levee BreachExperiments

The basic dimensions of the levee are
3m(height), 3m(crown width), and theslope gradient is 1:2.
Overflow area

Levee
breachExperimental
channel

堤防の基本形状は高さ3m、天端幅3m、法面勾配2割

The following main items wereobserved:
Channel water level, Flow rate, Levee
breach shape(clarification of levee
breach conditions based on outflow
measured by acceleration sensors inthe levee) etc.
主な観測項目は、水路内水位、流量観測、破堤形状（堤防内に設置した加速度センサーの流出による堤体崩壊状態の計測）
9Situation of experiment

Experimental
ChannelResearchPlan

Levee BreachExperiments

Movie

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Experimental
ChannelResearchPlan

Levee BreachExperiments

Levee breach process estimation based on acceleration sensor records
Movie

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Conclusion
In previous studies, the process of width expansion in levee breach waspresumed according to only visual observation in scale-model experiments.
これまでの研究では、堤防決壊時の幅拡大過程は模型実験による目視観察のみで推定

This time, the use of acceleration sensors enabled the establishment of an
approach for measuring the process of levee breach for the invisible inside ofthe levee.
加速度センサーを用いることで、目に見えない堤防内部の堤防決壊過程を計測する手法を確立

The experiment revealed that it proceeds through four stages: (1) the start oflevee erosion due to overtopping, (2) the start of widening of a narrow erosion
trench across the levee body, (3) the acceleration of the widening of the breach,and (4) the deceleration of the widening of the breach.
この実験により越水から4つの段階（Step1:越水による堤体侵食→Step2:破堤口拡幅開始段階→Step3:破堤口拡幅加速段階→Step4:破堤口拡幅減速段階）を経て破堤が進行することを明らかにした12

Reference
The levee breach process can beclassified into four stages.

13

Reference
Summary of relationships linking levee breach extent and hydraulic flow (water depth, flow velocity, etc.)

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Reference
Summary of relationships linking levee breach extent and hydraulic flow (water depth, flow velocity, etc.)

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