FREEBOARD. The additional height of a structure above design high water level 

 to prevent overflow. Also, at a given time, the vertical distance 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 continental 

 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 characteristic length, and g the 

 acceleration of gravity — or as the square root of this number. 



FULL. See RIDGE, BEACH. 



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. 



GENEilATION 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 inter- 

 section 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 a 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 landform. 



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. 



GRAVITY WAVE. A wave whose velocity of propagation is controlled primarily by 

 gravity. Water waves more than 2 inches long are considered gravity 

 waves. Waves longer than 1 inch and shorter than 2 inches are in an 

 indeterminate zone between CAPILLARY and GRAVITY WAVES. See RIPPLE. 



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