An existing nonstable bay can be prevented from indenting to its equili- 

 brium shape by the construction of one or more fixed points around its 

 periphery. Research should be conducted to minimize the cost of head- 

 lands which might start as offshore breakwaters, even mobile units. 



171. SILVESTER, R., and HO, S.K., "Use of Crenulate Shaped Bays to 

 Stabilize Coasts," Pvooeedings of the 12th Conference on Coastal 

 Engineering 3 American Society of Civil Engineers, Vol. 2, 1972, 

 pp. 1347-1365. 



Keywords: Artificial headlands, Crenulate-shaped bay, Design guidelines. 

 Gabions, Littoral transport, Recreation, Rubble mound. Sand 

 tracer study, Singapore, Structural dimensions. Wave diffrac- 

 tion. Wave refraction 



Crenulate-shaped bays are common on coastal margins of oceans, 

 inland seas, or lakes where sedimentary beaches exist between headlands. 

 They have a particular orientation to the swell or resultant wave energy 

 vector, such that the straight tangent section is downcoast and the curved 

 part upcoast . The latter is a logarithmic spiral at all stages of devel- 

 opment of the bay. When fully stable, i.e., no littoral drift occurring, 

 the constant of the logspiral equation has a specific relationship to the 

 approach angle of the waves to the headland alinement. In this condition 

 it is known that diffraction and refraction are involved when waves sculp- 

 ture the curved beach in the lee of the upcoast headland. A further ratio 

 to identify stable bays appears to be the ratio of indentation length to 

 clearance between headlands. The application of crenulate-shaped bays to 

 stabilization of a reclaimed shoreline suffering strong littoral drift on 

 Singapore Island is described. 



172. SILVESTER, R. , and HO, S.K., "New Approach to Coastal Defense, 

 Civil Engineering 3 Vol. 44, No. 9, Sept. 1974, pp. 66-69. Discus- 

 sions by G.A Soucie, "Cape Hatteras, a Real Problem?" Nov. 1975, 

 pp. 62-63; C.W. Nelson, "Destroy Barrier Dunes," Nov. 1975, pp. 63- 

 64. Reply by R. Silvester, Nov. 1975, p. 64. 



Keywords: Accretion, Aesthetics, Artificial headlands. Beach fill. 



Construction procedures, Crenulate-shaped bay. Design guide- 

 lines, Environmental concerns, Gabions, Littoral transport. 

 Recreation, Rubble mound. Sandbags, Ship hulls, Singapore, 

 Structural dimensions, Tombolo 



The standard structures for shore protection, seawalls and groins, 

 do not always perform as desired. They may fail to stop erosion of the 

 beach. Seawalls are sometimes undermined and fail. The concept of 

 "artificial headlands" appears generally to cost less and to perform 

 better. The idea was suggested by observation of natural headlands and 

 bays on the seacoasts of the world. 



173. SILVESTER, R., and LIM, T.K., "Application of Wave Diffraction 

 Data," Proceedings of the 11th Conference on Coastal Engineering^ 

 American Society of Civil Engineers, Vol. 1, 1968, pp, 248-270. 



58 



