SKCT. 5] 



621 



Certain particulars of the behavior of surges in gulfs and semi-enclosed seas 

 are discussed on pages 626-640, dealing with the dynamics of such surges. 

 Here we confine ourselves to giving two illustrations in Figs. 7 and 8. 



Fig. 7 shows three synoptic charts of the sea-surface disturbance heights 

 caused by the disastrous storm surge of 31 January and 1 February, 1953, in 

 the North Sea (after P. Oroen, see Koninklijk Nederlands Meteorologisch 



Fig. 8. The "twin" surges of the North Sea in December, 1954, as recorded at the Hook of 

 Holland; the dashed line represents the equilibrium effect. 



Instituut, 1960). These charts show, among other things, a counterclockwise 

 turning of the main direction of the lines of equal disturbance height, which is 

 caused by the Coriolis force. 



Fig. 8 shows the "twin" surges of the North Sea in December, 1954, as 

 recorded at the Hook of Holland. This was a case of resonance. Further details 

 are discussed on page 637. 



3. Dynamics and Forecasting 



A. Fundamental Theory 



The mathematical theory of surges starts with the hydrodynamical equations 

 of motion. For the horizontal acceleration components these are : 



'dUx 



dt 

 du 



dUx 

 dx 



cu, 

 dy 



dUa 



8z 



du 



y CUu 



_ + „,_ + „,_ + „,_ 



dp dq drxx , ^ryx drzx 

 dp 8q drxy dryy drzy 



where /=2cu sin 9 = Coriolis parameter, g = potential of astronomical tide 

 forces, Txx, ryx, etc. = components of turbulent stress tensor, while the other 

 symbols have their usual meaning. 



Although lateral stresses may be of importance for the currents associated 

 with surges (especially in narrow sea areas), stress components other than tzx 



