Prism 



Moveable 

 Guide 



Channel 

 Wall 



It 



Survey 

 Rod 



Figure 2-1 . Cross-section sketch of the survey rod and carriage 



The second concern, rod flexure, was addressed by mounting the rod in a 

 fixed guide, as shown in Figure 2-1 . The guide provided primary support of 

 the rod and allowed ready relocation of the rod to one of three cross-channel 

 positions on the carriage. Stainless steel roller bearings were placed on both 

 ends of the guide to allow smooth vertical motion. A second, moveable guide 

 was set to minimize the unsupported length of the rod, and, when raised in 

 shallow water, to minimize horizontal sway of the prism. The movable guide 

 provided additional rigidity to the rod as the tires moved over ripples and 

 steep offshore bars. Because the rod was nearly neutrally buoyant and the 

 rollers allowed easy vertical movement, an error called "floating of the 

 wheels," signifying lifting of the wheels off the bottom, could occur if some 

 downward force was not exerted by the operator. 



Chapter 2 Beach Profile Surveys and Sediment Sampling 



41 



