SEDIMENT MOTION AT THE VICINITY OF A LITTORAL BARRIER 



by 

 Ning Chien 



This is a portion of a paper prepared by the author, at 

 that time a graduate student research engineer at the Univer- 

 sity of California, under a research contract between the 

 University of California (Institute of Engineering Research) 

 and the Beach Erosion Board. The paper in entirety appeared 

 under the same title in April 1955 as a Technical Report 

 Series 14, Issue 17, of the Institute of Engineering Research, 

 Wave Research Laboratory, College of Engineering, University 

 of California. 



INTRODUCTION 



This investigation is a continuation of the study made in 1952 

 (Chien and Li) on the effect of a littoral barrier on a sandy coast. The 

 littoral barrier is defined as any natural or man-made abrupt change in 

 shore alignment, such as prominent head- lands, projecting rock cliffs, 

 and coastal works like groins and jetties. 



From the 1952 study, it was found that when the normal littoral 

 drift is interrupted by the installation of a barrier, the rate of drift 

 around the barrier will be resumed when the impounding basin of the 

 barrier is filled by the sediment originating at the upcoast side. The 

 conclusion thus drawn is true for the particular experimental arrange- 

 ment employed in that study, and should by no means be considered as 

 general. Indeed, the existence of natural littoral barriers indicates that 

 there must exist certain means by which the sediment passes around the 

 barriers without the formation of a beach. The purpose of this study is 

 to investigate the possible mode of sediment transportation at the 

 vicinity of a littoral barrier in laboratory scale. 



This was achieved by reproducing a small reach of a natural barrier 

 in the laboratory at which the motions of water particles and sediment 

 was observed. In this way the means by which the sediment particles 

 pass around the barrier are not observed directly, but rather deduced 

 from their mode of transportation in front of the barrier. As will be 

 shown later, the experiment was conducted in a model basin of limited 

 size. The barrier was oriented at an angle with both the wave generator 

 and the side-walls. Any waves reflected from the barrier are reflected 

 again after reaching the flapper of the wave generator and side-walls, 

 resulting in a very complicated wave pattern in the basin. For a suc- 

 cessful operation of this type of experiment, it is imperative that the 

 barrier must not reflect the approaching waves excessively. A preliminary 

 study was therefore made to explore the possibilities in designing certain 



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