Akio Kobayashi

Nihon University | Nichidai · Department of Oceanic Architecture and Engineering

On Kimigahama Beach, a pocket beach of 1070 m length and facing the Pacific Ocean in Chiba Prefecture, cuspate forelands were formed after the construction of two artificial reefs owing to their wave-sheltering effect. Then, significant amount of fine sand was transported inland from the cuspate forelands by wind. In this study, therefore, not only...

Coastal vegetation as one of the indices in evaluating coastal environment has an effect to stabilize the sand dune by preventing windblown sand. Thus, the conservation of coastal vegetation is important in the preservation of the coast. In this study, a model for predicting seaward boundary of the coastal vegetation was developed, including the ca...

Selecting the south and north coasts of Futtsu cuspate foreland with high and low incident waves, respectively, as the study sites, the relationship between the change in coastal vegetation zones and wave height was investigated. Although vegetations of several species were found on south and north coasts, the vegetation of high probability of occu...

On the Inage coast, beach nourishment was carried out in 2019 using white sand imported from western Australia for the reproduction of "white sandy beach". After the renewal work, white sand nourished on the beach surface was carried to the backshore by high waves associated with a typhoon and windblown sand due to strong wind, and the scenery of t...

Serizawa et al. predicted deformation of a circular island composed of sand using the BG model, taking the development of longshore sand transport owing to longshore variation in breaker height into account, after the calculation of the wave field using the energy balance equation. In this calculation, the calculation of wave field and beach change...

On a coast, which is composed of sediments with mixed grain sizes and is affected by strong winds, fine sand and medium-size sand are selectively transported to the back of the coast as windblown sand, leaving coarse sand and gravel on the foreshore. In this study, we proposed a model for predicting beach changes on coasts composed of sand of mixed...

Long-term shoreline changes of a cuspate foreland behind Okinoshima Island located in Tateyama Bay were investigated, and a beach survey was carried out using an RTK-GPS on May 2, 2018. Then, numerical simulation of the formation and deformation of a cuspate foreland between 1941 and 2012 was carried out using the BG model (a model for predicting 3...

A model for predicting 3-D beach changes in an extensive area including beach and backshore areas was developed, taking the effects due to both waves and windblown sand into account. In the calculation of beach changes, the BG model (a model for predicting beach changes based on Bagnold's concept) was employed, and a cellular automaton method was u...

On Ba Lang Beach in Nha Trang, Vietnam, the beach has been narrowed owing to land reclamation along the shoreline to construct a coastal road. The process of this artificial alteration was studied using satellite images, then the BG model (a model for predicting three-dimensional beach changes based on Bagnold’s concept) was used to investigate the...

The effect of the river-mouth current on sand movement around a river-mouth terrace was incorporated into the contour-line-change model to predict the dynamic equilibrium topography under the action of waves and current. Then, the river-mouth terrace topography, the velocity distribution of the river-mouth current, and the grain size distribution w...

The gently sloping revetment is stable when its toe is buried beneath a sandy beach. However, when the toe is exposed to waves as a result of beach erosion, fill material under the revetment is drawn out through the gap between the toe and the sandy beach, resulting in damage to the entire structure. Furthermore, when the toe of the revetment is ex...

In developing countries including Vietnam with rapid economic growth, the beach erosion has become severe. Various artificial facilities for economic development have been rapidly constructed on coasts, and once erosion occurs, stop-gap measures against erosion have been widely taken, resulting in further downcoast erosion. In this study, beach ero...

Morphology of sand dunes formed on the Hamamatsu-shinohara coast facing the Enshunada Sea was investigated by field observation. The development of sand dunes was numerically predicted using a model predicting the effect of both waves and windblown sand. In the field observation, development of sand dunes of a rhythmic shape similar to a sand spit...

When impermeable objects such as rocks or beach rocks are buried under the beach face, the return flow and seepage flow during wave run-up will change, causing the change in sand deposition and erosion of the foreshore. A two-dimensional movable bed experiment was carried out to investigate foreshore changes under the condition that rocks are burie...

On the Oiso-kitahama coast where westerly wind prevails in winter, field observation on the deposition around the multiple fences for preventing windblown sand were carried out in June and July, 2019. On this coast, 17 fences were built at an angle of 40° relative to the direction normal to the seawall with gradually increasing length of the fence....

Beach changes around a seawall (gently-sloping revetment) were investigated, when the seawall was constructed on a coast with seasonally-changing wave direction, taking Horikawa-hama Beach on the Kujukuri coast and Habushigaura Beach as examples. Beach changes around the seawall under these conditions were predicted using the BG model (a model for...

Morphology of sand dunes formed on the Maisaka and Hamamatsu-shinohara coasts facing Enshunada Sea was investigated by field observation. The development of sand dunes was numerically predicted using a model predicting the effect of both waves and windblown sand. In the field observation, development of sand dunes of a rhythmic shape similar to a s...

The longitudinal profile and cross-shore distribution of grain size composition of a sandy beach formed in the marginal areas of tidal flat and coral reefs were investigated, taking Sanbyakken sandbar facing Nakatsu tidal flat and the Nashiro coast in Itoman City located at the southwest end of Okinawa Island as the examples. Then, the change in lo...

On the east shore of Niijima Island located at the north part of Izushichito Islands, the Habushiura coast of 7 km length extends in the south-north direction. Typhoon 1919 landed the Kanto Plane on October 12, 2019, and high storm waves were incident to this coast, causing severe erosion while forming 12 m high scarp along the coastline. In this s...

A system examining the pattern of the shoreline changes around coastal structures was developed using a deep-learning method. First, shoreline changes around various coastal structures were predicted using the BG model given oblique wave incidence, while changing the shape and arrangement of the coastal structures. On the basis of the predicted sho...

The relationship between countermeasures against beach erosion and tsunami was investigated, taking the area around the artificial headland No. 12 on Horikawa Beach located in the north part of the Kujukuri coast as an example. On this beach, southwestward longshore sand transport prevails and HLs have been constructed from upcoast, resulting in th...

The formation of a blowout was predicted using a cellular automaton method, while changing the width and direction of a path crossing the coastal sand dune, and the appropriate direction of a path by which the formation of a blowout can be prevented was investigated. The example of a path to reach the shoreline on Sunayama Beach on Miyako Island wa...

Nagame-no-hama barrier island is located at the north end of Kami-koshiki Island in Kagoshima Prefecture and faces the East China Sea. This barrier island has 4.2 km length and is mainly composed of gravel, which was supplied from the sea cliffs at the north end of the island by storm waves in winter. The Tanoshiri Rock protrudes at the northwest e...

In Sanbyakken area bounded by the Nakatsu and Kakise Rivers flowing into the Nakatsu tidal flat, a sandbar of 600 m length extends with a salt marsh in the hinterland. Recently, large topographic changes have occurred around this sandbar. In particular, the river mouth closure is worried at the Kakise River mouth located at the south end of the san...

One of the causes of the beach erosion is due to the disruption of continuous longshore sand transport by artificial structures. In developing countries including Vietnam with a rapid economic growth, beach erosion that was experienced in Japan in the 1960s‒1970 is now occurring. Various artificial facilities for the economic development have been...

Field investigation on collapsing and scouring of the seawall on the Kenbutsu coast in Tateyama Bay was carried out, where a seawall was constructed at an excessively seaward location by land reclamation. Because of the protrusion of the seawall, severe wave overtopping has occurred. Although wave overtopping over the seawall was first confirmed on...

Futtsu cuspate foreland, which separates Tokyo Bay and Uraga Strait and extends westward, connected to Dai-ichi-kaiho Island in 1982. However, beach has been eroded in recent years, resulting in large shoreline recession. In this study, field observations were carried out at the tip of this cuspate foreland on July 16, 2017 and November 23, 2018 to...

When impermeable objects such as beach rocks are buried under the beach face, the return flow and seepage flow during wave run-up may change, causing the change in sand deposition and erosion of the foreshore. In this study, such examples were shown, taking the beaches on the Komesu coast in Okinawa and on Hithadhoo Island in Maldives as examples....

Long-term shoreline changes around a cuspate foreland behind Okinoshima Island located in Tateyama Bay were investigated, and beach survey was carried out using RTK-GPS on May 2, 2018. Then, numerical simulation of the formation and deformation of the cuspate foreland during 65 years was carried out using the BG model (a model for predicting 3-D be...

Under the condition in which data available for verification calculation are limited, a method to select optimum coefficient of sand transport in the BG model was considered, taking Kemigawa Beach as an example. Given the shoreline changes measured between 1990 and 1995 as the verification data, the difference between the predicted and measured sho...

A model for predicting 3-D beach changes in an extensive area including beach and backshore areas was developed, taking the effects due to both waves and windblown sand into account. In the calculation of beach changes, the BG model (a model for predicting beach changes based on Bagnold’s concept) was employed, and a cellular automaton method was u...

On a sand dune, a blowout is often formed owing to wind effect. The formation of a blowout was observed on November 25, 2016 at the Node coast facing the Pacific Ocean, where a blowout has been formed to leave a concave topography. Then, a model for predicting the formation of a blowout was developed using a cellular automaton method, in which two...

The mechanism by which the mouth of a small river is stably fixed in the wave-shelter zone behind an offshore reef composed of natural rocks was studied, taking a small river flowing into the Moriya coast together with two other small rivers as examples. The beach topography around the river mouth and the shape of the stream behind the reef were me...

When material dredged from a dam reservoir is used for beach nourishment, such an operation is often feared among fishermen, because fine components contained in the material are considered to damage the fishery in coastal sea. To study this issue from the scientific point of view, the characteristics of the materials dredged from the reservoir and...

On Hon Chong Beach north of Nha Trang in Vietnam, there existed a natural sandy beach until 2002, similarly to that on Nha Trang Beach. However, land reclamation was carried out along the coastline for the construction of a coastal road in 2003, and sandy beach was buried under the coastal road. In recent years, the recovery of sandy beach of Hon C...

On a coast with the predominance of windblown sand, generally the fences for preventing windblown sand are constructed. The effectiveness of such a measure against windblown sand has been confirmed at many coasts. However, practical numerical models for explaining the deposion process of windblown sand around a fence are limitted, in particular, in...

On the Ichinomiya coast located near the south end of Kujukuri Beach, beach nourishment using 8,800 m³ of sand was carried out in early July, 2017. To investigate the effect of the beach nourishment, field observations were carried out on May 27, 2017 before the nourishment, July 14, immediately after nourishment, July 22 and August 3, 1 and 3 week...

Artificial gravel can be produced from the mixture of coal ash, a small amount of cement, and water. Shell debris produced by smashing of the shell could be used as the beach nourishment material, similarly to natural gravel. However, there is no study on the movement of shell debris under waves. In this study, the difference in movement under wave...

On a sand dune, a blowout is often formed owing to wind effect. The formation of a blowout was observed on November 25, 2016 at the Node coast facing the Pacific Ocean, where a blowout has been formed to leave a concave topography. Then, a model for predicting the formation of a blowout was developed using a cellular automaton method, in which two...

The authors have studied the topographic changes and the changes in the vegetation zone on a marginal coast of a tidal flat, taking Banzu tidal flat left around the Obitsu River mouth in Tokyo Bay as an example. In this study, the exposure of a layer composed of cohesive material near the shoreline associated with erosion of the sand bar and the ch...

The controlling effect of longshore sand transport was investigated by the numerical simulation using the BG model, when various types of groins were installed on a coast composed of two grain size populations. It was found that groins of low-crown height and submerged-type groin are ineffective to control longshore sand transport, because coarse s...

The gently sloping revetment is stable when the toe of the revetment is buried beneath the sandy beach. However, when the toe of the revetment is exposed to waves as a result of beach erosion, fill material under the revetment is drawn out through the gap between the toe and sandy beach, resulting in the damage of the entire gently sloping revetmen...

Beach has been eroded at the Cai River mouth flowing north of Nha Trang, resulting in disappearance of all sandy beaches on both sides of the river mouth. The satellite images taken between 2002 and 2015 and the storm event occurred in 2008 were analyzed together with the field observation in 2015 and 2016. Most important cause of the beach erosion...

The controlling effect of longshore sand transport using groins (ordinary-type, groin of low-crown height, groin with an opening near the shoreline, submerged, slit-type groins) was investigated using the BG model (a three-dimensional model for predicting beach changes based on Bagnold' concept). When the landward end of the groin is located at the...

To study the possibility of the appropriateness of artificial gravel made of the coal ash for the material for beach nourishment, the movement of the natural and artificial gravel of the same grain size under waves were investigated using a two-dimensional wave channel experiment. It was found that the berm height was reduced with greater foreshore...

On the Moriya coast located in south part of Boso Peninsula, a small river flows into the sea, and the mouth of this river is stably fixed at a location behind the rocks located at the central part of this pocket beach. Because the wave-sheltering effect of the rocks were seemed to be the cause that the river mouth was fixed behind the rocks, field...

On April 18, 2015, field observation was carried out on the Kenbutsu coast in front of Katanagiri Shrine, which is located on the south shore of Tateyama Bay. A park was constructed by land reclamation in a shallow sea with reefs and narrow sandy beaches, and a seawall was built in front of the reclaimed land. Near the seawall surrounding the park,...

On Makuhari Beach located in Tokyo Bay, an artificial beach was built in front of the reclaimed land in 1979, and this beach was widely used for recreation. However, the beach had gradually been eroded. In 2009, a jetty was extended in the middle of the beach, and 12,000 m3 of gravel with the grain size of 4.2 mm was nourished on the beach between...

In general, foreshore and offshore tidal flat are separated with a break in slope, and a line connecting this break in slope and the shoreline obliquely intersect each other. No explanation of the mechanism was given in the previous studies. Field investigation was carried out on the Nako-funakata coast in Tateyama Bay with sandy beach and tidal fl...

The response of the beach composed of the mixture of gravel and sand to waves was experimentally investigated using two-dimensional wave channel. Gravel of the median diameter of 7.0 mm and sand of the diameter of 0.3 mm were mixed, while changing their contents, and a model beach of the slope of 1/5 was produced using the mixed material. The exper...

Three typhoons hit the Tojo-Maebara coast during summer in 2015, resulting in severe erosion. To investigate the cause of the beach erosion, field investigation regarding longitudinal profiles using a RTK and grain size distribution along the shoreline were carried out. The shoreline changes were also analyzed using aerial photographs. It is found...

Field observation was carried out on a land-tied island extending near Bip Island in Van Phong Bay in Vietnam. It was found that this land-tied island extended by the deposition of sand supplied by southward longshore sand transport along the west coast of Bip Island, and its amount was estimated to be 655 m³/yr on the basis of the investigation us...

The impact of the removal of a river mouth bar as a measure against river mouth closure to the surrounding coasts was investigated, taking the Hota coast as an example. Also, on this coast, landfilling was extensively carried out to build a coastal road along the coastline, resulting in the narrowing of the natural sandy beach. These anthropogenic...

In cooperation with Ho Chi Minh City University of Vietnam, beach changes on the coasts of Phan Rang City 270km east of Ho Chi Minh City were investigated. Beach changes associated with the elongation of a sand spit and sand accumulation owing to the blockage of longshore sand transport by a jetty were investigated using satellite images together w...

Two-dimensional movable-bed experiment was carried out using a wave flume to investigate the effect of the difference in content of gravel and sand to the changes in longitudinal profile. When gravel was used as the beach material, a model beach of 1/5 was produced and regular waves were incident to the beach, shoreward transport prevailed to form...

The relationship between beach topography and coastal vegetation was investigated by field investigations in the marginal area of Banzu tidal flat in Tokyo Bay. The longitudinal profiles, grain size distribution, and the distribution of coastal vegetation were measured across the barrier (sandy beach). When sandy beach is eroded, the shoreline shap...

The shape of the river mouth bar of the Song Ray River located 29 km ENE of Vung Tau and the shoreline morphology were studied using satellite images and site observation. It is found from the shoreline configuration that southwestward longshore sand transport prevails in this area, resulting in the elongation of river mouth bar of the left bank, a...

On the north shore of Lake Hinuma, Oyazawabana sand spit is formed owing to the wind waves from the east. Although this sand spit has been gradually eroded, beach was severely eroded by ground subsidence by 22 cm during the 2011 Great Earthquake together with the obstruction of longshore sand transport by a groin extended at the south end. In this...

We investigated the beach changes in shoreline area of the Hasaki coast with the boundary conditions as a pocket beach bounded by both reclaimed land of Kashima Port and Hasaki fishing port breakwater. In this area, southward longshore sand transport was predominant in the wave-shelter zone of the fishing port breakwater, whereas northward longshor...

The shoreline changes in the merginal area of the Banzu tidal flat were investigated by using aerial photographs and field investigations. The area immediately north of the Obitsu River mouth was eroded due to the spatial imbalance of longshore sand transport, and sand was transported to form a sand spit at the mouth of the north tributatry of the...

Topographic changes in the Co May River mouth located 9 km east of Vung Tau in Vietnam were investigated. Around this river mouth, the development of an asymmetric shoal in the east-west direction was observed, suggesting the predominance of southwestward longshore sand transport. Furthermore, sand was transported and deposited inside the mangrove...

The formation mechanism of a tombolo behind Oki Island in Tateyama Bay was investigated using aerial photographs together with beach survey data. This tombolo was formed on a shallow seabed, which was lifted by 1.6 m during the Kanto Earthquake occurred in 1923. Sand supplied from the Kanita River flowing into south of Oki Island was transported by...

Beach changes after the gravel nourishment were investigated on the Jinkoji and Akashi coasts in Ibaraki Prefecture. The formation of sand layer on the gravel bed due to shoreward sand transport of medium-size and fine sand under the calm wave conditions was observed and three-dimensional beach changes in response to the change in wave direction we...

Beach changes along a 7-km-coastline between the Minato River in Kazusaminato and Isone Point facing Uraga Strait were investigated using aerial photographs and by field observations. The relation between beach changes and the collaption of sea cliffs extending along the coastline were investigated. In particular, after the 2011 Great Earthquake, s...

Beach changes on the Hiari-ura coast facing the Pacific Ocean were investigated. This coast is located south of Taito Sea cliff and the sand supply from this coast is considered to be one of the supply sources to Kujukuri Beach, because the sand supply from the Isumi River flowing into this coast can be expected. The shoreline changes were studied...

Beach changes along the north shore of the Futtsu cuspate foreland were investigated using aerial photographs and field observation. In this area, sand has been supplied from the south shore of the cuspate foreland, while turning around the Futtsu cuspate foreland, and longshore sand transport with the order of magnitude of 3500 m³/yr occurred in 1...

Futtsu Point is a cuspate foreland separating Tokyo Bay and the Uraga Strait. On March 11, 2011, a tsunami generated by the Great East Japan Earthquake entered Tokyo Bay with approximately 2 m height, and flowed over this sand bar, dispersing the sand and leaving an isolated protruding sand bar. This resulted in the seawall at the foot of the sand...

Futtsu Point is a cuspate foreland separating Tokyo Bay and the Uraga Strait. On March 11, 2011, a tsunami generated by the Great East Japan Earthquake entered Tokyo Bay with approximately 2 m height, and flowed over this sand bar, dispersing the sand and leaving an isolated protruding sand bar. This resulted in the seawall at the foot of the sand...

Field measurements on the terrace topography, velocity distribution of the river currents as well as the grain size distributions were carried out at the mouth of the Yumizutani River flowing into Lake Biwa to investigate the formative mechanism of a river mouth terrace. On the basis of these field data, the action of river currents to sand movemen...

抄録 In beach nourishment using gravel, the macadam gravel is used so that the sharp-pointed shape of gravel is of concerned. In this study, the change in the shape of gravels due to wave abrasion was investigated. Gravel samples were collected from the Jinkoji and Akashi coasts in Ibaraki Prefecture, where beach nourishment using coarse materials ha...

抄録 The percolation effect of the foreshore composed of the combined layers of gravel and sand was investigated by a movable bed experiment using a wave tank. The grain size was selected to be d = 0.3, 1 and 3 mm. Under the condition that the grain size of upper layer is kept constant as d = 1 mm and the grain size of the lower layer is d = 0.3, 1 a...

抄録 A new model for predicting beach changes was developed using the cellular automaton method, taking sand transport under the ongoing and outgoing waves into account independently. The model was applied to predict sand deposition on the backshore with a steep foreshore slope on the Oiso coast. Furthermore, three-dimensional topographic changes wer...

抄録 Point Futtsu is the cuspate foreland separating Tokyo Bay and the Uraga Strait. In recent years, the shoreline around this cuspate foreland is considered to be stable, but large-scale seasonal variation may occur because wave direction at the tip of the cuspate foreland reverses seasonally. In the previous studies, however, such seasonal variati...