Beyond this: 



(g) The growth of n/a and X/a, with time, has been 

 found to be a function of (D/a)n. This function shows 

 ripples to be mature when n > a/D (Figs. 19 and 20). 



(h) The variety of initial bed forms which converge 

 into final forms depending, essentially, only on a and T 

 has supported the conclusion that an equilibrium profile, 

 when unconfined, is independent of its history (Figs. 21, 22, 

 and 23). 



(i) When confined at its ends, an equilibrium profile 

 has been found to have various sizes and shapes determined 

 by its value of X/a, which is contained within definite 

 limits but is otherwise determined by the history of the 

 profile (Fig. 25) . 



(j) Both two- and three-dimensional final bed forms 

 were observed. Clear criteria for these forms were not 

 established, but a dependence on <)) and, possibly, on a/D 

 is apparent (Figs. 27, 28, and 29). Three dimensionality 

 was found enhanced by a reduction in D and by growth or 

 instability of the profile. 



In this study, more than usual, discussions have involved the find- 

 ings of earlier studies, and it is hoped that the attempts to relate and 

 interpret them (e.g.. Figs. 3, 4, 5, 30, and 32) have a value apart from 

 the new laboratory observations. More work is needed to improve pre- 

 diction of the rippled character of the seabed under given conditions of 

 flow. The design curves of Mogridge and Kamphuis (1972), useful as they 

 are, need modification at large values of a/D as shown by the field 

 observations of Inman (1957) and Dingier (1975) and as discussed in 

 Section VI I, 3. Conditions for two- and three-dimensional bed forms re- 

 main poorly defined (Sees. VI, 2, 3 and VII, 4). Despite these reservations, 

 the character of the seabed can even now be predicted well enough to 

 encourage studies of the bottom stress and of the amount of sand in sus- 

 pension, both of which depend on the bed forms. As described in Section 

 1,1, results of these studies find application in coastal engineering 

 problems of surface wave decay and of sand transport. 



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