BY-PASSING LITTORAL DRIFT AT A HARBOUR ENTRANCE 



FOREWORD 



The problem of maintaining coastal harbors at locations 

 where the rate of littoral drift is large is encountered often, 

 Employment of fixed dredging plant to by-pass littoral 

 accumulations across the harbor entrance has been considered 

 at several localities in this country . Because of the large 

 cost of initial installation and the lack of assured design 

 criteria, no major installation of the fixed type has been 

 attempted in the United States. In addition to the obvious 

 benefit to navigation which would be achieved by intercepting 

 littoral material before it can reach and form shoals in 

 navigation channels, by-passing of the material to the down- 

 drift shore would prevent costly erosion problems which 

 sometimes result from interference with littoral processes „ 



A relatively small fixed dredge has been employed 

 intermittently with some success at South Lake Worth Inlet, 

 Florida. Application of the by-passing principal by employ- 

 ment of a conventional floating dredge has been successfully 

 accomplished at Santa Barbara, California, where the zone of 

 littoral accumulation is suitable for that method, and is 

 now a routine biennial operation , 



The following article is abstracted from a pamphlet 

 titled "Draga Fija" (Fixed Dredge) published in November 1950 

 by "Junta Directiva de Puerto s Libres Mexicanos" (Translation 

 by William Ho Vesper of the Beach Erosion Board Staff), It 

 is understood that the Salina Cms installation described 

 therein has not been in operation sufficiently long to es- 

 tablish conclusively its adequacy and economic value. An 

 early difficulty encountered, and the remedial means employed, 

 is described in the following extract from a letter 8 May 

 1951, received from the Secretaria de Marina Mexico? 



"The fact that the arms of the dredge are not long 

 enough to open a channel in the beach that would permit the 

 free entrance of the sand to the dredge, the Office of 

 Mexican Free Ports has found it necessary to install a power 

 shovel to open this channel and bring the sand to the dredge. 

 The scoop is hung from a cable supported by two posts lo- 

 cated as shown on the attached plan This scoop is moved 

 by a motor and capstan. Before the installation of the 

 scoop it was thought necessary to bring the sand to the dredge 

 by some means but it was not thought that the scoop would 

 necessarily be the solution to the problem .' 



