FREEBOARD - The additional height of a structure above design high water 

 level to prevent overflow. Also, at a given time, the vertical dis- 

 tance between the water level and the top of the structure. On a 

 ship, the distance from the waterline to main deck or gunwale. 



FRINGING REEF - A coral reef attached directly to an insular or conti- 

 nental shore. 



FRONT OF THE FETCH - In wave forecasting, the end of the generating area 

 toward which the wind is blowing. 



FROUDE NUMBER - The dimensionless ratio of the inertial force to the 

 force of gravity for a given fluid flow. It may be given as 

 Fr = V /Lg where V is a characteristic velocity, L is a charac- 

 teristic length, and g the acceleration of gravity; or as the 

 square root of this number. 



GENERATING AREA - In wave forecasting, the continuous area of water 



surface over which the wind blows in nearly a constant direction. 

 Sometimes used synonymously with FETCH LENGTH. Also FETCH. 



GENERATION OF WAVES - (1) The creation of waves by natural or mechanical 

 means. (2) The creation and growth of waves caused by a wind blowing 

 over a water surface for a certain period of time. The area involved 

 is called the GENERATING AREA or FETCH. 



GEOMETRIC MEAN DIAMETER - The diameter equivalent of the arithmetic mean 

 of the logarithmic frequency distribution. In the analysis of beach 

 sands, it is taken as that grain diameter determined graphically by 

 the intersection of a straight line through selected boundary sizes, 

 (generally points on the distribution curve where 16 and 84 percent 

 of the sample is coarser by weight) and a vertical line through the 

 median diameter of the sample. 



GEOMETRIC SHADOW - In wave diffraction theory, the area outlined by 



drawing straight lines paralleling the direction of wave approach 

 through the extremities of the protective structure. It differs 

 from the actual protected area to the extent that the diffraction 

 and refraction effects modify the wave pattern. 



GEOMORPHOLOGY - That branch of both physiography and geology which deals 

 with the form of the earth, the general configuration of its surface, 

 and the changes that take place in the evolution of landf orm . 



GRADIENT (GRADE) - See SLOPE. With reference to winds or currents, the 

 rate of increase or decrease in speed, usually in the vertical; or 

 the curve that represents this rate. 



GRAVEL - See SOIL CLASSIFICATION. 



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