Shusuke Watanabe

Changes in Bathymetry and Longshore Sand Transport around Artificial Headland with Various Shapes and Scales

The bathymetric changes and changes in longshore sand transport passing through the tip of the headland were investigated using the contour-line-change model, while changing the shape and scale of the artificial headland. The maximum shoreline recession and eroded area downcoast of the headland, and rate of decrease in longshore sand transport were compared each other. It is concluded that the groin part of the headland must be extended first to reduce longshore sand transport off the artificial headland.

Prediction of 3-D Beach Changes using BG-Model after Beach Nourishment in Lake Kasumigaura

In Lake Kasumigaura, lakeshore vegetations and sandy beach have been devastated in recent years. To recover the sandy beach in Okisu Area in this lake, beach nourishment has been planned with coastal facilities to stabilize the beach, such as groins, detached breakwaters, artificial reefs and artificial headlands. To evaluate the effect of these facilities, BGmodel proposed by Serizawa et al.(2006) was applied for predicting the three dimensional topographic changes after the nourishment. It is concluded that the most appropriate method is to stabilize the beach using a headland.

DYNAMIC SIMILARITY OF BEACH CHANGES DUE TO LONGSHORE TRANSPORT AND VERIFICATION OF ITS APPROPRIATENESS

Dynamic similarity of beach changes due to longshore transport was investigated. A relation that longshore sand transport is proportional to hc5/2, where hc is a closure depth, is introduced to derive time scale of beach changes:[t2]/[t1] is given by [l2] 2/[l1] 2.[hcl] 3/2/[hc2] 3/2, where subscripts 1 and 2 show the prototype and model, and 1 is the length scale. Effectiveness of this relation is tested by using the data sets of beach changes measured near the Katakai fishing port as a prototype and those on Odaiba beach as a model beach. Considerably good agreement was obtained.

APPLICATION OF THE THEORETICAL SOLUTION OF SHORELINE CHANGE TO KUJUKURI COAST AND EVALUATION OF COEFFICIENT OF LITTORAL DRIFT

Theoretical solution of shoreline change was applied to the Kujukuri, Misawa and Fuji coasts, and the coefficient of littoral drift was evaluated and compared. Aerial photographs were read to investigate shoreline changes on the updrift side of Katakai fishery port on the Kujukuri coast, where southward littoral drift dominates. Observed shoreline changes were well explained by the theoretical solution. The same method was applied to the Misawa and Fuji coasts, and coefficient of littoral drift on each coast was compared.

FIELD OBSERVATION OF MANLY COAST IN THE VICINITY OF SYDNEY AND SOME NOTES ON COASTAL ENVIRONMENT

Field observation of the Manly Beach in the suburb of Sydney in Australia was carried out to investigate coastal zone environment. Coastal zone in this area has a much better environment compared with the Japanese coast, much of which is covered artificially by concrete blocks. One of the utilizations, which is new in Japan, is the natural pool built at the corner of the pocket beach. This is a good idea in order to create safe, natural recreational zone for swimming and it may be introduced in Japan. Improvement method in building gently sloping revetment is discussed.

BEACH CHANGES CAUSED BY CONSTRUCTION OF DETACHED BREAKWATERS NEAR THE END OF A POCKET BEACH

Beach changes triggered by the construction of detached breakwaters near the end of a pocket beach were investigated at the Tojo coast in Kamogawa City in Chiba Prefecture. This beach has an around 3.9km long stretch and is facing the Pacific Ocean. Shoreline changes were read from the aerial photographs and field observation was carried out. Sand accumulated behind detached breakwaters thanks to their wave dissipation effect. Simultaneously this caused beach erosion in the other area and countermeasures were needed to protect facilities. The cause is due to the lack of thinking on overall balance of sandy beach in a closed system of littoral drift. It is concluded that construction of offshore breakwaters in a pocket beach should be carefully done because of the impact to the surrounding coast.