Growth of Crenulate Shaped Bays to Equilibrium

by Richard Silvester, (M.ASCE), Prof. Coastal Engrg.; Asian Inst. of Technol., Bangkok, Thailand,

Serial Information: Journal of the Waterways, Harbors and Coastal Engineering Division, 1970, Vol. 96, Issue 2, Pg. 275-287

Document Type: Journal Paper


The coastal outline between headlands assumes a specific shape which is related to the direction of the most predominant waves in the area. This half-heart or crenulate shape has been recognized previously and used to determine net longshore drift along land margins of the world. The curved section of such bays has been shown to follow a logarithmic curve. The present study indicates that in the development of a bay, from an initial straight coastline between two headlands, the constant in the spiral curve varies. It approaches a specific limiting value which is determined solely by the obliquity of the waves to the headland alignment. Thus scale of operation, either model or prototype, is not influential. By checking the spiral constant and wave approach angle of any bay, a test can be made of its state of equilibrium. A prediction is thus available for the erosion that could occur should upcoast sediment supply be impeded.

Subject Headings: Curvature | Bays | Equilibrium | Littoral drift | Ocean waves | Shores | Alignment | Scale models

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