1. Slope-Floating Beach with Pontoons . 



The basic concept of this design by Chen and Wiegel (1969) was the dissi- 

 pation of wave energy by waves breaking on a sloping beach. They constructed 

 and tested a physical model (Fig. 200) consisting of a sloping beach 25 feet 

 long (prototype dimensions), with the seaward end attached to a rectangular 

 air chamber (pontoon) 2.5 by 2.5 feet to provide buoyancy. The lee side of 

 the sloping beach was connected to a 14-foot-high vertical wall by steel 

 frames; about 11 feet of the vertical wall was submerged. A lee-side floating 

 pontooon 4 by 5.5 feet was connected to the vertical wall by a steel frame. 

 The total width, W, of the structure was 43.5 feet prototype dimension. 

 Experiments were conducted in a two-dimensional wave flume 106 feet long by 1 

 foot wide by 3 feet deep, with a 1:12 scale ratio, model-to-prototype. 



LEE SIDE 

 PONTOON 



L_l 



STEEL 

 FRAMES 



-VERTICAL WALL 



-0.5 



MODEL 



1 



SEAWARD - 

 PONTOON 



PROTOTYPE 

 12 



PROTOTYPE LENGTH = 43.5 Ft 



Figure 200. Slope-floating beach with pontoons for reservoir 

 applications (after Chen and Wiegel, 1969). 



Chen and Wiegel (1969) observed that small-amplitude waves broke com- 

 pletely on the sloping beach. The limited length of the slope prevented 

 large-amplitude waves from breaking completely on the beach. For waves about 

 as long as the breakwater width, a substantial amount of wave energy was 

 dissipated in the breaking process. The top of the beach was designed to have 

 a cavity of 2.5 feet between the beach and the vertical wall; hence, when 

 large-amplitude waves partially broke on the beach, parts of the wave mass 

 overtopped the beach and dropped beside the vertical wall. Considerable air 

 entrainment and mixing occurred in this process. The periodic impact of the 

 wave runup created a pressure fluctuation under the beach, which in turn 

 caused a heaving motion of the water surface. A further observation was made 

 of the slope-floating beach with pontoons drifting freely in the waves. Chen 

 and Wiegel (1969) believed that the slow drift rate indicated a minimal 

 mooring problem. 



258 



