Methodology of Sandy Beach Stabilization 
by Headland Breakwaters and its Application

Headland breakwaters have been used to protect reclaimed sandy beaches at the southeast coast of Singapore for nearly three decades. The stability of the bays and the maximum landward retreat or maximum indentation between the headland breakwaters are important design considerations for headland bay beaches. These factors also play a significant role in coastal zone management. A comprehensive study of the formation of static and dynamic stable sandy beaches between headland breakwaters has been made through a combination of theoretical, numerical, and experimental investigations including field monitoring.

Figure 1: Beach reclamation at the southeast coast of Singapore

Figure 2: Study area, southeast coast of Singapore


Figure 3: Equilibrium bay shape of Bay 21-22, by GENESIS


Figure 3: Dynamic shoreline changes of Bay 21-22, by GENESIS

Field surveys were conducted jointly with the Housing and Development Board on six consecutive bays between Breakwaters 18 to 24 at Bedok, southeast coast of Singapore (Figures 1 and 2 and Plate 1). By analysis it was found that when the dominant incoming wave crest was parallel to the control line joining the headland breakwaters, the bays presented parallel retreat and when the dominant wave crest had a certain angle with the control line, the bays formed were crenulated shaped. The maximum indentation and the breakwater indentation were both proportional to the angle between the control line and the dominant wave crest. The ratio of the breakwater indentation and the maximum indentation remained constant. These relationships could be used for design purposes and for stability analysis of headland bay beach areas. For crenulated bays, the up-coast berm had a sloping surface with grass cover representing a stable state. 

Plate 1 Crenulate shaped bay, southeast coast of Singapore


Plate 2 Experiments: monochromatic waves acting on sandy beach

The Shoreline change model GENESIS (US Corps of Engineers Model) was used to check the stability of the bays (Figure 3). Dynamic processes of beach development showed that the berm line retreat occurred mainly during the first and second year (Figure 4). The alongshore sediment transport rate resulting from beach erosion decreased with the beach development and diminished as the beach reached equilibrium. The breaking wave crest formed an angle with the initial reclaimed beach and the angle (between breaking wave crest and down-coast berm) became smaller with the beach development. The breaking wave crest became parallel to the down-coast berm when the beach reached equilibrium state.

An experimental study was carried out to investigate the dynamic processes of beach evolution and beach stability between headland breakwaters. The experimental study concentrated mainly on the effects of wave parameters, wave-induced currents, alongshore sediment transport, topographic changes, equilibrium bay shapes, stability and failure of the headland bay system (Plate 2). The results of the investigation have enhanced the understanding of the mechanism of near shore dynamic processes of beach evolution such as interactions among waves, current, sediment transport and bay shape and bed morphology. The experimental results are further validated by the well-proven empirical formulas for static equilibrium bay shape and simulations using the shoreline change model GENESIS.

A suite of numerical models comprising both in-house developed and other available models have been used to study the dynamic processes of beach evolution and formation of equilibrium bay between headland breakwaters. Numerical simulation by the wind-wave model MIKE21 showed that the wave breaker line is along the shoreline periphery of the four bays between Breakwaters 20-24 demonstrating that the bays are in equilibrium state. Simulations by GENESIS showed that the predicted equilibrium shorelines fit well with the surveyed shorelines. GENESIS also estimates dynamic profiles of bay development. Further an N-line sediment transport model has been modified and used to simulate the beach morphology changes in the vicinity of headland breakwaters at the southeast coast of Singapore.

Overall the research project has established a practical methodology with design guidelines for beach erosion control using the concept of sandy beach stabilization by headlands. This project has been carried out in joint collaboration with the Housing and Development Board and the Port of Singapore Authority and expert advice from Prof Y Tsuchiya (Emer.Prof at Kyoto University, and Professor Faculty of Urban Science, Meijo University - since expired), Prof T Yamashita (DPRI, Kyoto University, Japan), Mr Ho Wah Hin (PCE, HDB), Mr Law Kok Hwa (Sr Vice President, C&S Engrg Div., PSA) and Prof Cheong Hin-Fatt (Dean of School of Design and Environment). Research Engineers Sun Weidong, Budianto Ontowirjo and Graduate Assistant Chen Jian have been actively involved with the project.