BACKGROUND

Definition of Seiche
Problems encountered in calculating Seiche

Definition of Seiche
According to the Coastal Engineering Manual, seiche is defined as "an oscillation of the free surface in bodies of fluid enclosed wholly or partially by boundaries". It is classified as long wave with period ranging from minutes to hours. Seiches are generated by changes in pressure level and the resultant wind condition over the surface of the water body. Amplitude of seiche depends on the initial disturbance, whereas period of seiche varies with water levels, lake geometry and the force system acting on the basin, like the coriolis force.

Problems encountered in calculating Seiche
Traditionally, seiches period can be calculated using the Merian’s formula to find dominate seiches in the lakes:

 

where	T	=	periods
	L	=	basin length
	H	=	uniform depth
	n	=	number of modes (1,2,3..)

However, the above equation is only applicable to rectangular basins with uniform depth (by using the mean depth and the length). In practice, most of the lakes are of complex geometry and it is hard to obtain one unique width of basin. In addition, seiches at modes take place together with the fundamental mode in the lakes at the same time. The above equation cannot provide the spatial variation of free modes of seiches which would help in evaluating coastal erosion and sediment resuspension. Thus we would need another method in computing seiches.