Department of Environment FUKUI National College of Technology UENO TAKUYA Fluctuation of The Takasu River Mouth in The Sanrihama Beach

The Relationship between the fluctuation of the river mouth and longshore sediment transport rate Discuss seasonal feature of fluctuation of the Takasu River Backhoe excavationRiver mouth close again After 4 days Purpose of this study The purpose of this study is to analyze,

the Sanrihama Beach the Takasu River Fukui off the Port Takasu off the Port the Sanrihama Beach length of the beach 4km Located in the northern part of Fukui Prefecture the Takasu River length of the river 4.84km basin area 14.46km 2 Flowing in the middle of the Sanrihama Beach Target sites of this study of this study Oceanographic Meter

1.The quantification of the observed data 2.The relationship between longshore sediment transport rate and drift length 3.Discussion of the results Content of this study

The quantification of the observed data

① The observed river mouth location was quantified as the drift length Drift length is the distance from the center line of concrete revetment to the river mouth Longshore sediment transport rate is sand move along a shoreline ② Longshore sediment transport rate was calculated from the wave observation data (NOWPHAS) NW wave sand （－ ） （＋ ） Ｎ Ｗ land sea shoreline negative northeast concrete revetment sea land positive southwest

The relationship between longshore sediment transport rate and drift length

Drift length and longshore sediment transport rate do not cause significant stretching from June to October. vary greatly from December to January. show maximum at the beginning of February. tend to occur from August to November. River mouth closure

Orientation of the longshore sediment transport rate was equal, but drift length was different direction. their trend of variation were similar the trend of variation of the two did not match

On the contrary to 2010 Orientation of the longshore sediment transport rate and drift length were different direction the trend of variation of the two did not match

Discussion of the results

The stretch was not affected by the wave diffraction due to the offshore breakwaters. A Part of the Takasu River Mouth Waves From The West Offshore Breakwaters Diffraction 2009, The drift length stretched to the southwest direction affected by the diffracted wave. Drift length

Number of days by wave directions in winter exceeding to the southwest direction Wave direction Number of days West 9104 West-northwest1093 Total 19 7 Longshore sediment transport rate exceeding to the northeast direction. 2009, 2010 Longshore sediment transport rate was

From the result of observation for about three years, in the Takasu River, I.Drift length from June to October → → does not cause significant stretching II.From August to November → → river mouth closure tends to occur III.Drift length and total longshore sediment transport rate → → are maximum at the beginning of February Conclusion

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