Bay Shape Research Articles

BEACH DEVELOPMENT BETWEEN HEADLAND BREAKWATERS IN A LOW WAVE ENERGY ENVIRONMENT, PASIR RIS, SINGAPORE

One of the function of the offshore breakwater is to protect the coast from wave action. By dissipating the wave energy along its entire length, the breakwater causes sediments in its lee to deposit and a shore salient is formed. If the offshore breakwater are placed in a series along a coast with a gentle offshore slope and a substantial littoral drift tombolo will form behind the breakwaters between which bays will be sculptured by waves to form stable shapes (1). These attached breakwater would thus form a series of artificial headlands. In nature, beaches between headlands are influenced by the position of the headlands. Where the headlands are closely spaced and a limited sediment supply exists, small pockets beaches are formed. Where the headlands are far apart and an adequate sediment supply exists, long and wide beaches are formed. Generally, between these two extremes most beaches between natural headlands take a shape that is related to the predominant wave approach; on the downcoast sector is a long and straight beach, while on the upcoast end is curbed beach. Silvester (2) in his model study established a relationship between the logarithmic spiral constant ( °^ ) and the angle of predominant wave approach ( & ). A quasi-permanent shape was reached when waves broke simultaneously around the model bay. As it is difficult to measure the curve sector in nature, Silvester and Ho (3) suggested the use of an indentation ratio to relate the bay's shape to wave approach.

ZETA BAYS, POCKET BEACHES AND HEADLAND CONTROL

The now familiar equilibrium shape of bay sculptured by waves between headlands can indicate to man the direction he could follow in stabilizing shorelines. The characteristics of these crenulate or zeta shapes are known and can be applied in design or defining limits of erosion. Some natural settings are discussed which introduce difficulties in identifying the correct bay shapes for applying these tools. The application of headland control to specific cases of instability is presented. The final requirement is emphasised of aiding Nature to protect the coastline by the formation of the offshore bar and its subsequent return to the beach without concurrent downcoast drift. The method currently receiving widespread support of placing offshore breakwaters in close proximity to each other is discounted as a viable protective alternative.