beach and foreshore. Drawbacks to the use of split-hull barges include the 

 necessity for favorable wind and wave climate during operation and the possi- 

 bility that storms may move the sediment offshore, where it can be lost to the 

 littoral processes. 



Side-aast dredging has been a successful means of maintaining and improv- 

 ing inlets where shallow depths and wave conditions make operation of a pipe- 

 line or hopper dredges hazardous (Long, 1967). However, the effectiveness 

 of side-cast dredging as a bypassing method is limited by the length of the 

 discharge pipe supporting boom. While it is possible to discharge in the 

 downdrift direction, generally the dredged material is placed too close to the 

 channel to be effectively bypassed. Reversals in the littoral current, and 

 even changes in the tidal flow, can cause the dredged material to move back 

 into the channel . 



VI. GROINS 



1. Types . 



As described in Chapter 5, Section VI, groins are mainly classified as to 

 permeability, height, and length. Groins built of common construction 

 materials can be made permeable or impermeable and high or low in profile. 

 The materials used are stone, concrete, timber, and steel. Asphalt and 

 sandfilled nylon bags have also been used to a limited extent. Various 

 structural types of groins built with different construction materials are 

 illustrated in Figures 6-54 to 6-59. 



^' Timb er Gro ins . A common type of timber groin is an impermeable 

 structure composed of sheet piles supported by wales and round piles. Some 

 permeable timber groins have been built by leaving spaces between the 

 sheeting. A typical timber groin is shown in Figure 6-54. The round timber 

 piles forming the primary structural support should be at least 30 centimeters 

 in diameter at the butt. Stringers or wales bolted to the round piles should 

 be at least 20 by 25 centimeters, preferably cut and drilled before being 

 pressure treated with creosote and coal-tar solution. The sheet piles are 

 usually either of the Wakefield, tongue-and-groove , or shiplap type, supported 

 in a vertical position between the wales and secured to the wales with 

 nails. All timbers and piles used for marine construction should be given the 

 maximum recommended pressure treatment of creosote and coal-tar solution. 

 Ayers and Stokes (1976) provide timber structure design guidance. 



b. Steel Groins . A typical design for a timber-steel sheet-pile groin 

 is shown in Figure 6-55. Steel sheet-pile groins have been constructed with 

 straight-web, arch-web, or Z piles. Some have been made permeable by cutting 

 openings in the piles. The interlock type of joint of steel sheet piles 

 provides a sandtight connection. The selection of the type of sheet piles 

 depends on the earth forces to be resisted. Where the differential loads are 

 small, straight web piles can be used. Where differential loads are great, 

 deep-web Z piles should be used. The timber-steel sheet-pile groins are 

 constructed with horizontal timber or steel wales along the top of the steel 

 sheet piles, and vertical round timber piles or brace piles are bolted to the 

 outside of the wales for added structural support. The round piles may not 

 always be required with the Z pile, but ordinarily are used with the flat or 



6-76 



