288 mason. SHORE-CONTROL PROBLEMS [Ch. 15 



geological knowledge of the materials present to be acted upon, might 

 well lead to quantitative descriptions of physiographic processes. 



Collaboration can probably be effected best by liaison between in- 

 dividuals and collaborative research. The field is too narrow and 

 the specialization required too high to permit a more general approach. 

 Some instances of combined application of engineering and geological 

 knowledge, notably by W. C. Krumbein in the study of the details of 

 littoral movement, have led to highly useful concepts that explain 

 formerly complex situations. 



FUTURE RESEARCH 



In our present state of knowledge needed future research can be 

 specified only in general terms. It can be stated that wide opportuni- 

 ties exist for research, and any discussion of needed research will 

 certainly encompass only a part of the wide variety of problems that 

 may exist. 



One of the first problems to be studied as a concurrent geological- 

 engineering problem is that of the definition of physiographic units 

 for shore-study purposes. The problem involves, among others, de- 

 termination of material sources and the transportation sequence from 

 the source to the shore, with considerable attention to be devoted to 

 the volume and time scales of the phenomena; determination of the 

 limits of littoral transportation, both eolian and submarine; and con- 

 sideration of the energy situation. 



A second problem of prime importance in the study of many shore 

 processes is the relation between shore-material characteristics and the 

 dynamic processes of transportation to which the material has been 

 subjected. Shore studies are concerned with the behavior of a popula- 

 tion of particles in which the behavior of the population is conditioned 

 by, and may be chiefly dependent on, the characteristics of the in- 

 dividual particles. The possibility exists that modification of one 

 small fraction of the particles may change appreciably the behavior 

 characteristics of the population. For example, it is known that the 

 admixture of small amounts of clay in sand greatly increases the 

 velocity required to erode the sand. More adequate definition of the 

 erodibility and transportability of beach materials in terms of their 

 particle characteristics is required. Determination of the erosion sus- 

 ceptibility of beach materials when subjected to the oscillatory velocity 

 fields of wave action is a virgin territory, as is the problem of trans- 

 portation on the bottom or in suspension under the same conditions. 



