Evaluation of regional groundwater flow by dredging the Hida River,

Gero district in Gifu Prefecture

Shoya KITAGAWA

Course of Architecture and Civil Engineering Gifu National College of Technology

Background of the study

River channel dredging

The Hida River cannot secure Design Height Water Discharge

Drawdown of the groundwater level was forecasted

GROUNDWATER FLOW ANALYSIS

Table of contentsIntroduction of the study domain 　　　　　

Method of analysis and analysis result 　　　　　　

Analysis example of the Koden district 　

・ Background of the study・ Summary of the Gero district 　・ Area division of the Gero district 　

Analysis example of the Mori district 　

・ Effect assessment of the dredging

Summary

Basin summary of the Hida River

in the Gero district

Gero, Gifu

Hida River

Koden district

Shogano district

Ogawa district

Mori district

Area of the analysis

Yunoshima district

①considering several set of coefficient of permeability affecting the field survey②considering an incline of the impermeable ground

Method of analysisQuasi-three dimensional analysis

Basic equation of the groundwater flow

　0,,

ry

zhhyxk

yx

zhhyxk

x

h: groundwater level measured on x-y plane (m)z: height of the impermeable ground(m)k: coefficient of permeability(m/s)r: water supply strength from the upper part(m/s)

Gero-ohashi bridge

Koden district

0352.0

353.0

354.0

355.0

356.0

357.0

358.0

359.0

360.0

0 2 4 6 8 10 12 14

Gro

un

d h

eigh

t（m

）

X direction

353.0 -354.0 354.0 -355.0 355.0 -356.0

Analysis condition (Koden district)

Range of the analysis

Boundary water level①Incline of the

impermeable ground

Neighborhood of the Hida River ： k=14.4×10-5(m/s)Flat plains ： k=7.73×10-5(m/s)

②The distribution situation of the coefficient of permeability

0

4

356

357

358

359

360

361

362

363

364

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Gro

un

dw

ater

leve

l h(m

)

X direction

356 -357 357 -358 358 -359 359 -360

Range of the analysis

The point that groundwater level is high

The point that groundwater level is low

From this direction

Distribution of the groundwater levelbefore dredging(Koden district)

0

4

356

357

358

359

360

361

362

363

364

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Gro

un

dw

ater

leve

l h(m

)

X direction

356 -357 357 -358 358 -359 359 -360

The Hida River

Distribution of contour line and current speed vector(Koden district)

Range of the analysis

Infiltration from the river to the bank inland

0

4

356

357

358

359

360

361

362

363

364

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Gro

un

dw

ater

leve

l h(m

)

X direction

356 -357 357 -358 358 -359 359 -360

Contour line(Gero district)

Gero bridge

Upper stream

Down stream

320

240

160

80

00 240 480 720 960 1200

X direction(m)-1.50 --1.00 -1.00 --0.50 -0.50 -0.00

1.0~1.5m

0.5~1.0m

Dis

tan

ce f

rom

the

rive

r(m

)

Range of the analysis

Distribution of the groundwater level drawdown when river water level

decreased 1.5m

About 240m

The Hida River

Influence of the dredging

Range of the analysis

Comparison after/before dredgingContour line of after dredging

Contour line of before dredging

Contour line, in the Koden district

Range of the analysis

Contour line, in the Koden district

Blue ： After dredgingBlack ： Before dredging

Contour line after and before dredging

Comparison after/before dredging

Mori district

0

3

6

9

345

350

355

360

365

370

375

0 2 4 68

10

Y direction

Gro

un

d h

eigh

t(m

)

X direction

370 -375

365 -370

360 -365

355 -360

350 -355

Analysis condition (Mori district)

Range of the analysis

Boundarywater level

②The distribution situation of the coefficient of permeability

① Incline of the impermeable ground

Mountain area ： k=3.56×10-4(m/s)Flat plains ： k=17.8×10-4(m/s)

0

3

6

9

345

350

355

360

365

370

375

0 1 2 3 4 5 6 7 8 9 10 11

Y direction

Gro

un

dw

ater

leve

l h(m

)

X direction

355 -360 360 -365 365 -370 370 -375

Range of the analysis

Groundwater level

Distribution of the groundwater levelbefore dredging(Mori district)

720

640

560

480

400

320

240

160

80

00 80 160 240 320 400 480 560 640 720 800 880

Dis

tan

ce fr

om th

e ri

ver(

m）

X direction(m)

-1.50--1.00 -1.00--0.50 -0.50-0.00

1.0~1.5m

0.5~1.0m

0~0.5m

Upper stream

Down stream

About 300m

Distribution of the groundwater level drawdown when river water level

decreased 1.5m

Influence of the dredging

Range of the analysis

320

240

160

80

00 240 480 720 960 1200

X direction(m)-1.50 --1.00 -1.00 --0.50 -0.50 -0.00

1.0~1.5m

0.5~1.0m

Dis

tan

ce f

rom

th

e ri

ver

(m)

720

640

560

480

400

320

240

160

80

00 80 160 240 320 400 480 560 640 720 800 880

Dis

tan

ce fr

om th

e ri

ver(

m）

X direction(m)

-1.50--1.00 -1.00--0.50 -0.50-0.00

1.0~1.5m

0.5~1.0m

0~0.5m

Comparison of influence of dredging

Kod

en d

istr

ict

Mor

i dis

tric

t

About 240m

About 300m

Summary

Groundwater of the Koden district

On the influence by dredging

・ Infiltration from the river to the bank inland is thought about near the Gero-ohashi bridge down stream.

・ The shape of groundwater flow does not change after dredging.・ Mori district is influenced considerably by dredging compared with Koden district.

Groundwater of the Mori district

・ Groundwater flow is not complicated compared with Koden district.

END