Evaluation of regional groundwater flow by dredging the

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 The Hida River cannot secure Design Height Water Discharge River channel dredging Drawdown of the groundwater level was forecasted

Table of contents Introduction of the study domain　　　　　 ・Background of the study ・Summary of the Gero district 　 ・Area division of the Gero district 　 Method of analysis and analysis result 　　　　　　 ・Effect assessment of the dredging Analysis example of the Koden district 　 Analysis example of the Mori district 　 Summary

Hida River Gero, Gifu Basin summary of the Hida River in the Gero district

Ogawa district Shogano district Mori district Yunoshima district Koden district Area of the analysis

Method of analysis Quasi-three dimensional analysis Basic equation of the groundwater flow 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) ①considering several set of coefficient of permeability affecting the field survey ②considering an incline of the impermeable ground

Gero-ohashi bridge Koden district

Analysis condition (Koden district) ①Incline of the impermeable ground Boundary water level Range of the analysis ②The distribution situation of the coefficient of permeability Neighborhood of the Hida River：k=14. 4× 10 -5(m/s) Flat plains：k=7. 73× 10 -5(m/s)

Distribution of the groundwater level before dredging(Koden district) The point that groundwater level is high From this direction The point that groundwater level is low Range of the analysis

Infiltration from the river to the bank inland The Hida River Distribution of contour line and current speed vector (Koden district) Range of the analysis

Down stream Gero bridge Upper stream Contour line (Gero district)

About 240 m The Hida River Influence of the dredging Distribution of the groundwater level drawdown when river water level decreased 1. 5 m Range of the analysis

Contour line, in the Koden district Comparison after/before dredging Contour line of after dredging Contour line of before dredging Range of the analysis

Contour line, in the Koden district Comparison after/before dredging Contour line after and before dredging Blue：After dredging Black：Before dredging Range of the analysis

Mori district

Analysis condition (Mori district) ① Incline of the impermeable ground Boundarywater level Range of the analysis ②The distribution situation of the coefficient of permeability Mountain area：k=3. 56× 10 -4(m/s) Flat plains：k=17. 8× 10 -4(m/s)

Distribution of the groundwater level before dredging(Mori district) Groundwater level Range of the analysis

About 300 m Range of the analysis Down stream Influence of the dredging Distribution of the groundwater level drawdown when river water level decreased 1. 5 m Upper stream

Koden district Mori district Comparison of influence of dredging About 240 m About 300 m

Summary Groundwater of the Koden district ・Infiltration from the river to the bank inland is thought about near the Gero-ohashi bridge down stream. Groundwater of the Mori district ・Groundwater flow is not complicated compared with Koden district. On the influence by dredging ・The shape of groundwater flow does not change after dredging. ・Mori district is influenced considerably by dredging compared with Koden district.

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