FIELD AND MODEL STUDY ON THE PROTECTION OF RECREATIONAL BEACH AGAINST WAVE ACTION

Norio Tanaka

Abstract


The heightening of a sea wall is often proposed for the purpose of decreasing the amount of wave-overtopping. In a recreation beach, however, the heightening of sea wall is undesirable from the view-point of environmental preservation and beach utilization. In this paper, instead of it, a proposal is made of the sea wall with a wide frontal step as well as the widening of beach by artificial nourishment. The frontal step is not only effective to decrease the amount of wave-overtopping, but also serves as a promenade for visitors. The widening of beach is known to serve to decrease wave-overtopping as well as to increase the utility for recreation. However, the protection of the nourished beach itself becomes sometimes a difficult problem. In this paper, the hydraulic characteristics of a wide frontal step and the effect of several protective measures for the nourished beach are described on the basis of model and field tests conducted for the improvement of Suma Beach. Suma Beach is a recreational beach situated west of Kobe Port as shown in Fig. 1. The shore-line is about 2 km long and runs from east to west (Fig.11). The beach profile, as shown in Fig.2, has the narrow backshore at about 3 m above L.W.L. and a small step at about 1.5 m below L.W.L. The beach slope is 1/10 in the foreshore, 1/25-1/30 between 2 and 5 m below L.W.L and 1/60-1/80 in the offshore beyond about 6 m below L.W.L. The waves are predominant from the direction of SSW so that the beach materials tend to move eastward along the shore.

Keywords


model study; beach protection; recreational beach; field study

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