The main interest of the report lies in the results. When the long- 

 shore transport rate reaches a maximum value (a = 45°) , the shoreline 

 tends to form a cusp; i.e., a cape as shown in Fig. 11. 



Also of interest is Grijm's (1964) mathematical formulation for 

 different forms of river deltas for which he finds two possible solu- 

 tions, one with an angle of wave incidence everywhere less than 45°, and 

 another with the angle of incidence greater than 45°. The shoreline 

 curvature also depends upon the angle a as shown on Fig. 11. The 

 problem remains indefinite since it is unknown which solution is valid. 



The formulation of Grijm does not lend conveniently to numerical 

 adaptation. 



Bakker' and Edelman (1964) also studied the form of river deltas, but 

 instead of using f(a) = sin 2a , as Grijm, they used the linear approxi- 

 mation as given by Pelnard-Considere; i.e., f(a) S k tana for 

 o < tana < 1.23 . They also investigated the case of large angle of 

 approach using the function: 



fret) = — — for 1.23 < tana < <» . 

 tana 



Bakker and Edelman's (1964) solutions are similar to that of Grijm; 

 however, they also found a periodic solution as Larras (1957) did: 



y = exp 



^dQ 

 da 



1 ^'t . 



cos kx . (23) 



Equation (23) represents a sinusoidal shoreline for which the ampli- 

 tude of tne undulations decreases with time if -r-^ is positive (i.e., 



do 

 for small angles of wave incidence), but increases when -r-^ is negative 



(i.e., for large angle of wave incidence). The shoreline is thus un- 

 stable and the amplitude of the undulations increases. It can be 

 deduced that Grijm's solution for large angles of incidence is not 

 naturally found, since they are unstable and will be destroyed as small 

 perturbations trigger large deviations. 



Bakker (1968a) implies that Grijm did not discover this instability 

 because he confined himself to solutions growing linearily with t in 

 all directions, while the exponential solution in t also exists. 

 Komar (1973) also applies a numerical scheme based on the Pelnard- 

 Considere approximation to the problem of delta growth. He found shore- 

 line shapes identical to Grijm in the case of a small angle of approach. 



From these investigations, it is remembered that the Pelnard- 

 Considere approach is very powerful to predict shoreline evolution under 

 small angle of incidence. But under large angle of incidence, instabili- 

 ty of the shoreline makes it very difficult. Furthermore, the 



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