298 caldwell. SEDIMENTATION IN HARBORS [Ch. 16 



the short-comings of these various methods. It was pointed out that 

 rewarding contributions toward harbor improvement could probably 

 be made by investigations leading to the following: 



(1) A better definition of the relation between stream flow and the 

 movement of sand carried as bed load by the stream. This would in- 

 clude a definition of both the rate of sand movement and the path 

 of sand movement along the stream bed. Such information would 

 form the basis of a more rational design of dikes and training walls 

 as applied to harbor design, particularly of channel-type harbors. 



(2) A study of the capacity of flowing water to flush accumulated 

 silt and clay shoal material out of harbor areas before such materials 

 have had an opportunity to consolidate. This study would prove 

 valuable in the improvement of channel harbors subject to shoaling 

 by silt and clay deposit wherein currents, either fresh-water or tidal, 

 are periodically present to flush the harbor. 



(3) An evaluation of the factors governing the interchange of waters 

 between the main channel flow of a stream or estuary and the waters 

 of a contiguous off-channel harbor. This information would be particu- 

 larly valuable in the design of off-channel harbor improvements where 

 shoaling is due to silt and clay moving in from the parent stream. 



(4) A clearer understanding of the movement of littoral drift under 

 the impulsion of waves and alongshore currents. Such a study should 

 include an evaluation of the rate of drift in various depths under 

 various natural conditions. This information would be particularly 

 useful in the design and improvement of shore-line harbors. 



Other investigations that would be of value are mentioned in the 

 body of this chapter; however, the above four fields of investigation 

 are believed to be of particular promise. Improvements in the equip- 

 ment and technique of dredging would be of obvious value, but this 

 subject is somewhat outside the scope of this discussion. The large 

 yearly expenditures devoted to removal of shoaling in harbors in this 

 country alone would appear to justify considerable effort toward the 

 solution of the various sedimentation problems discussed herein. 



REFERENCES 



*Haferkorn, H. E. (1929). Sand -movement, beaches, and kindred subjects, a 

 bibliography: Engineer School Library, Office of Chief of Engineers, U. S. 

 Army. 



* Happ, S. C, Rittenhouse, and Dobson, G. C. (1940). Some principles of ac- 



* References marked with an asterisk contain fairly extensive bibliographies. 



