Hydraulic Structures: Fourth Edition

If the basin is long, the wavelength can be large in relation to the depth of
water, and the shallow-water result for the period of oscillations can be
applied, i.e.

TnLn/cLn/(gd)1/2.

If the width of a harbour Lwis comparable to its length Lb, more complex
patterns of resonant oscillations may occur. The harbour may be assumed
as both ends closed. The period of oscillation is

Tnm (^2) gd  
0.5
wherenandmare various modes assuming values of 0, 1, 2,...

14.8 Wave diffraction

Waves impinging on a structure of finite length bend in the lee of the
structure due to radiation of wave energy. This is the process of diffrac-
tion: wave diffraction at a semi-infinite breakwater is shown in Fig. 14.12.

m^2



Lw^2

n^2



Lb^2

WAVE DIFFRACTION 593

Fig. 14.12 Diffraction of waves in the presence of a semi-infinite break-
water (Muir Wood and Fleming, 1969)