3.2 OCEANOGRAPHY IN THE UNITED STATES 



The next slide. This shown the amount of wave runup on a shore 

 structure. We have seawalls, breakwaters of various types, and 

 whether or not they will be overtopped during a storm is quite critical 

 in their design. 



These curves show that we were able through a set of laboratory 

 tests to determine the relative height to which the water would run 

 up as related to the slope of the beach and to the character of the 

 wave which came, whether it was long, medium length, or a short 

 wave. 



The next slide is the "Shock Pressure Against a Vertical Seawall." 

 We developed some electronic instruments and had constructed for 

 us some shock pressure cells which would react very rapidly 



We set this test up and broke this wave against a vertical seawall 

 in the laboratory and this action which you see is the shock pressure 

 wliich took place in about around one-thousandth of a second. 



When we translated that into prototype conditions or full-scale 

 conditions, it indicated a pressure of around 14 tons per square foot 

 on the full scale of seawall. 



The next slide. This slide is the one that shows a little about this 

 survey accuracy. 



We took a section of shore about 2,000 feet long and we made a 

 very careful survey, using many profiles. Then we dropped back 

 and computed what error we would have arrived at, had we used only 

 one profile or two or three. 



From this we are able to determine the degree of accuracy or the 

 amount of error we can expect in our computation if we do not use 

 enough profiles in the particular survey. 



The next slide is a view of an experimental groin of Palm Beach, Fla., 

 which was a part of the test to find out how long this steel sheet piling 

 will last under various conditions. 



We set up control tests all the way from Tampa Bay clear up to 

 Portland, Maine, and measured the decrease in thickness of steel 

 piling used on various types of shore structm-es over a period of around 

 20 years and from this we are able to determine the expected life 

 under various use conditions. 



You see that this piling has already lost much of its effectiveness by 

 being rusted through and worn out near the waterline. 



The next slide is drawn from the same area. One of the gentlemen 

 is taking the measui-ement of the loss in thickness. This groin is 

 cut through almost completely at the sandline and, as far as the shore 

 structure is concerned, it has just about lost its usefulness and can be 

 thrown away. 



The next slide shows the conditions we found. We found from 

 our studies that you had a zone in which the structure was always 

 covered with water wliich did not corrode very rapidly. 



We had an alternate wet and dry zone in the tide zone wliicli had 

 corrosion and erosion, and an air zone where the salt spi-ay got on the 

 steel and we were able to determine the rate of loss of steel in these 

 areas in order to determine whether we shoidd use steel or concrete 

 and what expected life we would luxve. We also found (hat the rates 

 depended on the climate, the air temperature, or watei' temperature. 



Tlie steel goes away twice as fast in the southern wMtei- of the gulf 

 or South Atlantic as on the coast of Maine. 



Mr. Miller. Whv is that? Do you know? It is clieniical. 



