Developing an evaluation method for channel widening

－Towards a friendly river to fish and people －

Group 7

Clean up campaign in Kakogawa River with Wakamiya Elementary School students 1

キーワード

Contents

Keyword Motive and purpose

Evaluation method and its accuracy

Conclusion

Acknowledgements References

Ecosystem Flood prevention

Sustainability of cross sectional shape

2

Keyword

River channel widening dredging a river to prevent flooding

Channel widening

ユールストローム図…

M.L.I.T plan

the plan carried out by the ministry of land, infrastructure, transport and tourism

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Target area

downstream area of the Kakogawa River

First-class river

Kakogawa River basin

Target area

Hyogo Prefecture

Kakogawa city

Kakogawa River

4

Especially important for our lives and economy

National governments are tasked with the management for these rivers

・

・

Motive｜flooding Kato city Touryu Bridge

Target area

Hyogo Prefecture

Kakogawa city

Kakogawa River

Kato city

Channel widening is necessary

5

Motive

The number of fish decreased after channel widening

Habitat quality decreased

the number of the fish captured per one time of casting net

＜Hakuryo Junior&Senior High School Biology Club ＞

Red line: the year when conducted channel widening

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[year] Red line: channel widening

The

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Purpose

Existing evaluation

事前評価… 事後評価…生態系，持続性

Sustainability…lower the frequency of channel widening

Habitat suitability…estimate the effect on the ecosystem

Let’s evaluate beforehand!! ② Suggest a new widening plan

using new method

Merits of prior evaluation

Habitat suitability, Sustainability…after channel widening River flow…before channel widening

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Establishing a method to evaluate channel widening plans beforehand

Evaluation method

Calculating velocity and depth

Ecosystem diversity

Flood prevention

Sustainability of river channel

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Calculating velocity and depth

Tool:iRIC

Velocity(m/s)

Velocity distribution map （4.2㎞～6.8㎞ from river mouth）

Target area 3.8㎞～11.8㎞ from river mouth

Discharge 27[m3/s]

Time 30,000[s]

Calculation conditions

Average velocity: 0.4[m/s]

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EED[Eco-Environmental Diversity] Index to evaluate the diversity of habitat EED has a positive correlation with the number of species of fish reference：Hirohumi ito ,Research on practical application of fish habitat evaluation

in small-scale rivers ,2016-4

流速と水深についてEEDを算出

depth(m)

velo

city

(m/s

) ～0.2 0.2～0.6 0.6～

～0.2 a1 a2 a3

0.2～0.6 a4 a5 a6

0.6～1 a7 a8 a9

EED = 1－ 𝑎𝑖2

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𝑖=1

a:the relative proportion of each environment

Ecosystem diversity｜Evaluation method 10

Flood prevention

Calculate water surface elevation during flood discharge

Compare with government-run widening plan

過去最大の増水にも耐えられる流量で 計画高水流量を流すことができれば 河川の氾濫の危険性は低いといえる

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Sustainability of river channel cross section

Hjulström diagram

Grain size：35.6mm

Deposition：

Under 0.55m/s

Erosion：

Over 2.3m/s

Grain size[mm]

Flo

w s

pee

d[c

m/s

]

Transport

Erosion

Deposition

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Calculation results

Accuracy of iRIC calculation

Actual measurement

結果

Actual measurement Calculation

4.2km 0.52m 0.67m

5.0km 2.12m 2.24m

compare

Difference：about 0.10m

The calculation is accurate

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Field work measure actual water surface elevation

1km 4.6km sedimentation 0.223 > 0.208

erosion 0 ＝ 0

Accuracy of evaluation of sustainability

The change of cross sectional shape

compare

結果

Light green：deposition Orange：erosion

1km (H27 to H29)

4.6km

(H24 to H29)

Deposition 1km＞4.6km

Erosion

1km≅4.6km

This evaluation method is accurate.

1m

25ｍ

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（reality）

Evaluation results

（simulation）

Velocity and depth

Calculate them using iRIC

Observe it after digging

Ecosystem preservation

Evaluate it using EED beforehand

Evaluate the effectiveness of flood prevention using iRIC

Evaluate it using Hjulström curve beforehand

Observe it after digging

Before

New method

Sustainability of cross sectional shape Flood prevention

Conclusion｜ Evaluation method

Before

New method

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:

:

:

:

Conclusion

・河道掘削において、断面を事前に、簡単に、 定量的に評価する方法を開発し、その有効性を示した

・開発した断面の評価方法で、掘削案の改善ができる ことを示した

Development of a method to evaluate channel widening plans easily, quantitatively, and before widening begins

Confirm the accuracy of the evaluation method

・

・

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Future issues

・Make a better channel widening plan

・Examine the accuracy of our evaluation method in greater detail

・Consider interactions among various kinds of fish

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Acknowledgements This study was supported by these people.

M.L.I.T Himeji Office of River and National Highways

Associate Professor, Department of Civil Engineering, Graduate School of Engineering, Osaka University

Mr. Masayasu Irie

Mizuho Information & Research Institute, Inc

Mr. Keisuke Inoue

Civil Engineering Research Institute for Cold Region

Mr. Toshiki Iwasaki

Hakuryo Junior&Senior High School Biology Club

We’d like to acknowledge their great help.

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References

・Evaluation and monitoring project commission．“Re-evaluation for the Kakogawa River improvement ”．Kinki Regional Development Bureau． 2011-12．https://www.kkr.mlit.go.jp/plan/ippan/zigyohyoka/ol9a8v000000dn20-att/4.pdf. （referred on 2018-09-17）

・ M.L.I.T Himeji Office of River and National Highways “an outline of the Kakogawa River basin”．2008-07-16．https://www.kkr.mlit.go.jp/himeji/iin/kako_ryuiki/pdf_files/20080716siryou7_vol01.pdf

（referred on 2018-09-17）

・Kakogawa River basin council，“The second Kakogawa River basin council, document 6（the report of the progress of the project）”.

・Hirohumi ito ,Research on practical application of fish habitat evaluation in small-scale rivers ,2016-4

（In Japanese）

・事業評価監視委員会．“加古川直轄河川改修事業再評価 近畿地方整備局． 2011-12．https://www.kkr.mlit.go.jp/plan/ippan/zigyohyoka/ol9a8v000000dn20-att/4.pdf．

（参照日 2018-09-17）

・国土交通省姫路河川国道事務所 “加古川流域の概要”．2008-07-16．https://www.kkr.mlit.go.jp/himeji/iin/kako_ryuiki/pdf_files/20080716siryou7_vol01.pdf

（参照日 2018-09-17）

・加古川流域懇談会，“第二回加古川流域懇談会資料6 事業の進捗状況について”

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Thank you for listening !

Discussion with M.L.I.T Himeji Office of River and National HIghways

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Q&A

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New channel widening plan

Blue：government’s plan • Flat • Hard to inhabit for various

species

Orange：cross-section A • Various water velocities

Light blue：cross section B More differences in depth than government’s plan

B A

Water surface

1m

25ｍ

Government’s

plan

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Evaluation results

Government’s plan

New plan A New plan B

Ecosystem diversity 0.793 0.837 0.822

Flood prevention criterion +0.06ｍ -0.06ｍ

Sustainability 42％ 34％ 37％

A B

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Example Applications of iRIC

・Inundation Simulation of Oda River in 2018 West Japan Flood ・Debris flow simulation in West Japan Flood Disaster

of 2018 in Kumano, Hiroshima, Japan ・Inundation Simulation of Shozu River

in 2017 Flood in Kyushu, japan ・A lot of research on rivers

Reference:iRIC Website＜http://i-ric.org/ja/＞

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27.1

19.3

11.2

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8.4

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4.9

3.8

2.3 1.0 3.4 Tanakia limbata

Freshwater minnow

Goby

Skin carp

Sugomoroko

Pike gudgeon

Dusky tripletooth goby

Sweet fish

Black bass

Blugill

Others

Proportion of the caught fish in about 5 km from the river mouth[%]

25 25

Sweet fish

50㎝ Skin carp

reference： WEB fish illustrated book

reference：M.L.I.T Himeji office of River and National Highways

Freshwater minnow

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The number of fish

[year]

the number of fish captured per one time of casting net ＜Hakuryo junior-senior high school biology club ＞

Lower stream Midstream

The number of fish

[year]

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Simpson’s Diversity Index

Cross sectional shape 29

The water level at flood discharge

Erosion at flood discharge

Government’s plan

１ ２ ３ ４

Erosion(％) 66 69 69 67 67

deposition（left）erosion（right）distribution map

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Satellite photo downstream of the Kakogawa River

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Cross-section 1m

25ｍ

River flow 400m

Water surface

Relationship between flow velocity, water depth, and water surface elevation

Bottom of the river channel

Water surface elevation

Water depth

elevation

Accurate

Accurate measurement by Himeji Office of River and National HIghways

Water surface elevation is accurate Water depth is accurate

Relationship between flow velocity, water depth, and water surface elevation

Water surface elevation is accurate Water depth is accurate

Area

Discharge[m3/s]=Area[m²]×Flow velocity[m/s]

Water depth is accurate Flow velocity is accurate

How to calculate flow velocity and water depth

Import the elevation data and make a grid

River bottom elevation

River flow

Target area 3.8㎞～11.8㎞ from river mouth

Discharge 27[m3/s]

Time 30,000[s]

… …

How to calculate flow velocity and water depth

Set calculation conditions

How to calculate flow velocity and water depth

Run the simulation

Calculation result of water depth

River flow

Widening of the width of a river

There is a house near the river, and width is not widened

Raising a dike

The top of the dike becomes the way, and construction is difficult

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Widening of the width of a river

Raising a dike

Dredging the bottom of a river, widening of the width of a river and raising a dike would affect the river ecosystem.

a river

Heavy rain falls, and a river rises.

The flooding is generated.

a river(conducted channel widening)

Heavy rain falls, and a river rises. But much water can discharge and are hard to occur a flooding.

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Geospatial Information Authority of Japan has already measured .

measure

measure

How to measure the water surface elevation

We can get the elevation here.

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20172016201520142013201220112010

sweet fish freshwater minnow skin carp [year]

the number of the fish captured per one time of casting net ＜Hakuryo Junior&Senior High School Biology Club ＞