Generalities on static equilibrium bays: Fid-Bau Portal

Generalities on static equilibrium bays

Hsu, J.R.C. / Silvester, R. / Xia, Y.M.

AbstractPrevious methods of determining the curved waterlines of bays which form on the coasts around the world have involved the logarithmic spiral. This has been applied to unstable bays which could erode back to a limit termed “static equilibrium” for which the constant in the spiral could be related to the obliquity of the wave crests to the control line, joining the upcoast headland to the downcoast extremity of the bay. It is shown that this applies mainly to the shadow zone behind the upcoast headland and not to the full bay periphery and does not have a fixed centre. A new method is proposed utilising arcs from the point of wave diffraction to the shoreline, whose lengths and angles to the wave crest line are related to those of the control line. Data and curves are presented for the static equilibrium shape by which the stability can be tested. They thus predict the waterline for the case of no sediment supply either from littoral drift or rivers debouching into the bay. An indentation ratio can also be derived to test stability.