Research Achievements - Original paper -

Experimental study on the accumulation of cedar at the bridge

Ryo NISHIWAKI, Kazuya Watanabe, Noritoshi SAITO, Yuriko MATSUBAYASHI and Hitoshi TANAKA

APAC 2019 - Proceedings of the 10th International Conference on Asian and Pacific Coasts ( APAC 2019 - Proceedings of the 10th International Conference on Asian and Pacific Coasts )    953 - 958   2019.10

Research paper (journal)   International Co-author

DOI

EXPERIMENTAL STUDY ON ACCUMULATION OF CEDAR AT THE BRIDGE

NISHIWAKI Ryo, WATANABE Kazuya, SAITO Noritoshi, MATSUBAYASHI Yuriko, TANAKA Hitoshi

Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) ( Japan Society of Civil Engineers )  75 ( 5 ) I_255 - I_260   2019.09  [Refereed]

Research paper (journal)   Domestic Co-author

<p> This paper presents an experimental approach to investigate the accumulation process of cedar at the bridge. Recently, it is frequently confirmed damage resulting from driftwoods in Japan. For example, Typhoon No. 10 in August 2016 caused flooding of Omoto River. It was a possibility of similar disaster in Akita Prefecture which has a lot of cedars. The hydraulic model experiments were carried out using a bridge model at Omoto River. The scale was 1/180. It based on the width of Omoto River and the water channel. The cedar rod was used for driftwood model. In the experiment, we focused on the number of driftwood accumulation at the bridge and changed in the water level on the upstream and downstream sides of the bridge. At that time, several patterns were prepared regarding the length of the driftwood, the average length of the mixed driftwood, and the flow rate as comparison objects. In conclusion, the experiment shows that the longer the driftwood length the larger the amount accumulation at bridge. This tendency was also observed in the mixed driftwood experiment. However the length of driftwood were different, water level was not changed. And the time which was taken to stop the rise of water level did not change due to the difference of driftwood length. In the experiment of the flow late, the ratio of driftwood accumulation was increased with the increase of the flow rate. In addition, it was suggested that flow velocity related to driftwood accumulation.</p>

DOI

STUDY ON THE BEHAVIOUR OF SANDBAR IN A RIVER CHANNEL AT THE BABAME RIVER

FUJISAWA Naoya, WATANABE Kazuya, SAITO Noritoshi, UEKI Koutarou

Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) ( Japan Society of Civil Engineers )  75 ( 5 ) I_275 - I_280   2019.09  [Refereed]

Research paper (journal)   Domestic Co-author

<p> Local heavy rain was caused flood damage in July and August 2017, May 2018 in Akita prefecture. High water level was observed in Babame river. Recently, it was frequently happened flood damage resulting from local heavy rainfall in Japan. Babame River was the largest Class B rivers in Akita Prefecture. Left hand side bank was scouring due to this damage. It was important to grasp sandbar shape and channel condition. This study proposed to maintain channel using UAV (Unmanned Aerial Vehicle) to take aerial photographs. Because it was important that regularly grasping of actual condition in channel management. At the first, about 50 aerial photographs were taken along a river from ground to 150 m height. Then, aerial photographs were taken to overlap 80 % of the photographs horizontally and vertically. It was taken aerial photographs from September, 2017 to November, 2018. This study was chosen 5 times in case of low water level and high water level. Then, this aerial photographs captured SfM(Structure from Motion) technique. It evaluated quantitatively the relationship between the behavior of sandbar and water level. The behaviour of the sandbar formation grasped from the aerial photographs. Sandbar area, length, and width was measured in this area. In this study, evaluation of sandbar width was important to grasp constriction of the channel and erosion of sandbar in channel management.</p>

DOI

EFFECT OF WAVE PERIOD AND WAVE STEEPNESS ON WIND SPEED ESTIMATION METHODS OF CONSIDERED CHARACTERISTICS OF THE REGION

WATANABE Kazuya, MUROHASHI Kai, SAITO Noritoshi, TANABU Osamu

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering) ( Japan Society of Civil Engineers )  75 ( 2 ) I_319 - I_324   2019.06  [Refereed]

Research paper (journal)   Domestic Co-author

<p> In the ocean surface, there are currents generated by ocean winds. Therefore, ocean wind observation was important to understand the ocean currents. The examination about the technique to estimate ocean wind was performed for a long time by wave data. Various data were included in measured wave data. The swell that a period was big and wave steepness was small. The swell affects the estimation of the ocean wind in previous study.</p><p> In this study, ocean winds were estimated by obtained wave height and period from NOWPHAS and SMB method and Toba 3/2-power law. Therefore, wave steepness was lower than 0.02 and a wave with more than 8s of period was the factor that measured value was different from the estimate of ocean wind. The estimation of ocean wind was improved by excluding the wave of the condition mentioned above.</p>

DOI

NUMERICAL STUDY OF TSUNAMI PROPAGATION USING A TURBULENCE MODEL

KUTSUZAWA Yuki, TINH Nguyen Xuan, WATANABE Kazuya, TANAKA Hitoshi

Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering) ( Japan Society of Civil Engineers )  74 ( 2 ) I_163 - I_168   2018.11  [Refereed]

Research paper (journal)   Domestic Co-author

&nbsp;The 2011 Great Earthquake and Tsunami has caused huge morphological changes along the coastal areas in the Tohoku region. One of the key parameters causing these dramatical damages is the tsunami bottom shear stress acting on the sea bottom. In general, the tsunami wave is a longwave and the steady flow resistance method have been practically used in many tsunami numerical models to estimate the bottom shear stress by mean of using the depth-averaged velocity and friction coefficient (Method 1). However, the actual tsunami waves are unsteady flow conditions, so the application of Method 1 may inappropriate. Therefore, the EFDC vertical turbulent model is applied to take into account the effect of complex boundary layer development under unsteady tsunami condition (Method 2). In this study, these both methods are applied to calculate the tsunami bottom shear stress and compare between them. The shape of vertical velocity distribution results from the Method 2 are similar to the wave friction method. And bottom shear stresses by Method 2 are overall larger compared to the Method 1 under tsunami wave impacts.

DOI

STUDY ON RECOVERY PROCESS OF SEDIMENT DEPOSIT AND MECHANISM IN THE FORMATION OF RIVER MOUTH TERRACE

WATANABE Kazuya, Dinh Van Duy, NOGUCHI Kazuya, TANAKA Hitoshi

Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering) ( Japan Society of Civil Engineers )  74 ( 2 ) I_787 - I_792   2018.11  [Refereed]

Research paper (journal)   Domestic Co-author

&nbsp;The river mouth topography was changed under the influence of external force on a continuous basis. It was performed numerical computation to grasp the topographical change. When it was simulated the shoreline change including around the river mouth, it was given the constant value as boundary condition at the river mouth which was quantity of sediment yield from river. The sediment yields from river were supplied at the time of a flood accidentally. River mouth terrace was formed of the sediment yields. Then, the sands were transported and returned to around the river mouth and beach slowly over time. However, two physical processes of "river mouth terrace formation" and "transported and returned to around the river mouth and beach" were not expressed in the numerical simulation definitely.<br>&nbsp;In this study, it was monitored the details in the recurrence process of the sand by UAV for Omono River mouth where river mouth sandbar was flashed. In July 22th 2017, heavy rainy disaster occurred and the flash of the river-mouth sandbar was confirmed in Omono river in Akita prefecture. The topography change of the tip of the sandbar became similar to the previous study. According to the previous study, the Omono river projection of the sandbar is divided into four patterns. In detail, (1) Both sides do not have a projection (2) There is a projection only in the right bank (3) There is a projection only in the left bank (4) there is a projection on both sides. Then, it was able to confirm the sandbar recovery process of 4 patterns from a photograph of UAV.<br>&nbsp;In addition, the characteristic topography seen in the UAV observation was inspected from detailed laboratory experimental data. As a result, similar to the observed topography was reproduced by the laboratory experiment.

DOI

High-resolution tsunami-bedload coupled computation in AMR environment

Yasunori Watanabe, Yuta Mitobe, Hitoshi Tanaka, Kazuya Watanabe

Proceedings of the Coastal Engineering Conference ( Proceedings of the Coastal Engineering Conference )  36 ( 2018 )   2018.10  [Refereed]

Research paper (journal)   Domestic Co-author

Numerical experiments on effect of river mouth morphology on tsunami behavior in rivers

Yuta Mitobe, Hitoshi Tanaka, Kazuya Watanabe, Neetu Tiwari and Yasunori Watanabe

Coastal Engineering Journal ( Coastal Engineering Journal )  60 ( 4 ) 516 - 531   2018.10  [Refereed]

Research paper (journal)   Domestic Co-author

DOI

Study on recovery process of river-mouth sandbar using UAV in Omono river

Noguchi, K. and Watanabe, K.

Proceedings of 8th International Conference on Fluid Mechanics     2018.09  [Refereed]

Research paper (journal)   Domestic Co-author

EXAMINATION OF OCEAN WIND ESTIMATING TECHNIQUE USING SMB METHOD AND TOBA 3/2-POWER LAW

Watanabe, K.

Proceedings of 8th International Conference on Fluid Mechanics,     2018.09  [Refereed]

Research paper (journal)   Single author

Numerical study on tsunami-induced bottom shear stress

Yuki Kutsuzawa, Nguyen Xuan Tinh, Kazuya Watanabe, Hitoshi Tanaka

Proceedings of 8th International Conference on Fluid Mechanics     2018.09  [Refereed]

Research paper (journal)   Domestic Co-author

ANALYSIS OF TSUNAMI CHARACTERISTICS ALONG RIVERS BASED ON OBSERVED AND SIMULAETD TSUNAMI DATA

MITOBE Yuta, TANAKA Hitoshi, WATANABE Kazuya

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering) ( Japan Society of Civil Engineers )  74 ( 2 ) I_228 - I_233   2018.06  [Refereed]

Research paper (journal)   Domestic Co-author

&nbsp;Characteristics of tsunami running up into rivers were discussed through analysis of observed tsunami profiles and numerical simulation. Tsunami form of the 2011 Great East Japan Earthquake Tsunami along Kitakami River, which was observed at Fukuchi Station (8.6 km from the river mouth) was compared with tsunami profiles observed along the coast and also on the ocean. River run-up of the 2011 tsunami along Kitakami River was simulated with Shallow-Water Equation model for more understanding on the characteristics of the observed tsunami form along the river.<br>&nbsp;On the ocean and also along the coast, the first wave was the highest, while the maximum water level at Fukuchi Station was recorded during the third wave. The wave height of the first wave rapidly got smaller with running up along the river due to the overflow of river embankments. On the other hand, the following waves ran up with the raised water level by the first wave to have less reduction of the wave height, resulting in the higher water level in upstream area than the first wave.<br>&nbsp;Due to the centrifugal force, the water level along the outer side of the curve of the river got higher to cause higher load and more overflow against the river embankment. Theoretical formula to calculate water surface slope based on the balance between pressure gradient and the centrifugal force shows good agreement with the simulated water surface slope around the breaching point of the river embankment of Kitakami River.

DOI

Investigation of the River Mouth Topography Change by the Response Characteristics of River Discharge and Ocean Waves at Yoneshiro River

Watanabe K.

Journal of Coastal Research ( Journal of Coastal Research )  85   61 - 65   2018.05  [Refereed]

Research paper (journal)   Domestic Co-author

DOI

A QUANTITATIVE EXPERIMENT ON THE DENSITY OF TSUNAMI INUNDATION WATER AND ITS INFLUENCE ON THE TSUNAMI RUN-UP DISTANCE AND DEPOSIT

MATSUTOMI Hideo, KONNO Fumiko, ATOMURA Koki, KONDO Kota, KAMATAKI Takanobu, WATANABE Kazuya

Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering) ( Japan Society of Civil Engineers )  73 ( 2 ) I_373 - I_378   2017.11  [Refereed]

Research paper (journal)   Domestic Co-author

&nbsp;For the advancement of the tsunami load and scale evaluations, the dependency of the density of the tsunami inundation water on the hydraulic quantities, and the dependencies of the tsunami run-up distance, deposit distance, deposit thickness on the density of the tsunami inundation water are examined through a devised hydraulic experiment. Within the experimental range of this study, it is veryfied that the density of the tsunami inundation water depends on Froude number of the incident tsunami and the sediment grain size, and the relative tsunami run-up distance (=the run-up distance of the inundation water with the sediment/the run-up distance of the inundation water without the sediment), ratio of the tsunami deposit distance to the tsunami run-up distance, ratio of the mean tsunami deposit thickness to the tsunami deposit distance depend on the density of the tsunami inundation water, and then four empirical expressions for those dependencies are proposed.

DOI

Examination of Historical Tsunami Height and Run-up Calculated by Numerical Simulation around the Kitakami River mouth

Watanabe, K. , Yamanaka, T.

Proceedings of the Vietnam-Japan Workshop on Estuaries, Coasts, and Rivers 2017     2017.09  [Refereed]

Research paper (journal)   Domestic Co-author

BEHAVIOR ANALYSIS OF THE FLOATING TYPE TSUNAMI EVACUATION SHELTER ON A BUILDING AND INVESTIGATION ABOUT THE FLOW VELOCITY AND WAVE FORCE

WATANABE Kazuya, TONO Yuki

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering) ( Japan Society of Civil Engineers )  73 ( 2 ) I_204 - I_209   2017.06  [Refereed]

Research paper (journal)   Domestic Co-author

&nbsp;After the East Japan great earthquake disaster occurred, it came to be predicted that the tsunami which was considerably huger than a previous assumption. It was pay attention to the hybrid refuge technique that was used together with the floating type tsunami evacuation shelter in addition to conventional high place refuge. The behavior of the shelter is divided into 3 patterns in previous study.<br>&nbsp;In this study, data was put in order by the Froude number and the wave force was measured to act on a shelter. Then it was performed an evaluation for the refuge using the shelter. Therefore, Pattern 1 was stable from photointerpretation and behavior analysis, and patterns two or three was unstable. However, Pattern 1 was shown great value from wave force, it was thought the risk that a shelter was destroyed. In addition, pattern two or three shows a relatively small value. From these reason, examination of the most suitable setting position will be important in the future.

DOI

EXAMINATION ABOUT THE BEHAVIOR OF THE FLOATING TYPE TSUNAMI EVACUATION SHELTER WHEN THE TSUNAMI BECOMES MAXIMUM WAVE HEIGHT AFTER THE SECOND WAVE

WATANABE Kazuya, Fuji Ryuya

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering) ( Japan Society of Civil Engineers )  73 ( 2 ) I_210 - I_215   2017.06  [Refereed]

Research paper (journal)   Domestic Co-author

&nbsp;There was the refuge technique that was hybrid which combined Floating Type Tsunami Evacuation Shelter with conventional high place refuge as technique to plan the improvement of the survival rate from a tsunami. Basic motion of Floating Type Tsunami Evacuation Shelter properties at having installed it on low land and a building are clarified in the previous study. However, there are many studies for the first wave of the tsunami. Therefore there is a possibility that it was not intend for the maximum tsunami wave height<br>&nbsp;In this study, it was performed experiments with the behavior of the Floating Type Tsunami Evacuation Shelter when the tsunami becomes maximum wave height after the second wave. Then, it was investigated the behavior of the Floating Type Tsunami Evacuation Shelter and examination about the wave height. As a result, it was able to classify the behavior of the shelter in 6 patterns. It was revealed that a change of the still water depth of the water greatly affected the behavior of the shelter. Because even the same condition might show different behavior, it will be necessary to perform wave height, speed, wave force and the analysis in future.

DOI

A new approach to numerical modeling of tsunami considering unsteady boundary layer development

Hitoshi Tanaka, Yuta Mitobe, Neetu Tiwari, Kazuya Watanabe and Yasunori Watanabe

Proceedings of The 3rd International Conference on Coastal Zone Engineering and Management in the Middle East (Arabian Coast 2016)     2016.11  [Refereed]  [Invited]

Research paper (journal)   Domestic Co-author

Examination about the formation of river mouth sandbar by the influence of river discharge and ocean waves at yoneshiro river mouth

Watanabe, K. and Miura, Y.

Proceedings of the Vietnam-Japan Workshop on Estuaries, Coasts, and Rivers 2016     2016.09  [Refereed]

Research paper (journal)   Domestic Co-author

Investigation of Saline Water Intrusion and Tidal Discharge for Different Type of River Mouths at the Sea of Japan Side

Watanabe, K.

Proceedings of the 3rd symposium on Two-phase modelling for Sediment dynamics in geophysical flows     2016.09  [Refereed]

Research paper (journal)   Single author