Beach changes triggered by the construction of detached breakwaters and harbor breakwaters were investigated through comparison of aerial photographs on the Yotsukura and Natsui coasts both located in a pocket beach of 11km long stretch facing the Pacific Ocean. Formation of wave calm zone behind these breakwaters induced severe beach erosion on the surrounding beaches as well as sand accumulation in the lee side of the structures. Further the construction of gently-sloping coastal revetment covered vast area of natural sandy beaches. Deep concern should be paid to the change in this coastal situation in order to preserve and recover natural coastal environment. key words: Beach erosion, gently-sloping coastal revetment, aerial photograph field observation

The obstruction effect of littoral drift by an artificial headland was investigated using the contour-line-change model, taking the Kujukuri coast as an example. Numerical simulation was carried out assuming the seabed slopes of 1/50 and 1/100, while changing the length and the shape of the headland. The rate of the obstruction effect of littoral drift by a headland was quantitatively evaluated. It is given by the function of time after the construction. Only the construction of the headland is difficult to form a statically stable beach, and sand bypassing or sand recycling is required to prevent further beach erosion.