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HURRICANE WIND PATTERN or ISOVEL PATTERNS - An actual or graphical repre- 

 sentation of near-surface wind velocities covering the entire area 

 of a hurricane at a particular instant. Isovels are lines connecting 

 points of simultaneous equal wind velocities, usually referenced 30 

 feet above the surface, in knots or mph; wind directions at various 

 points are indicated by arrows or deflection angles on the isovel 

 charts. Isovel charts are usually prepared at each hour during a 

 hurricane, but for each half hour during critical periods. 



HYDRAULICALLY EQUIVALENT GRAINS - Sedimentary particles that settle at 

 the same rate under the same conditions. 



HYDROGRAPHY - (1) A configuration of an underwater surface including its 

 relief, bottom materials, coastal structures, etc. (2) The de- 

 scription and study of seas, lakes, rivers, and other waters. 



HYPOTHETICAL HURRICANE ("HYPO-HURRICANE") - A representation of a hurri- 

 cane, with specified characteristics, that is assumed to occur in 

 a particular study area, following a specified path and timing 

 sequence . 



TRANSPOSED - A hypo-hurricane based on the storm transposition 

 principle is assumed to have wind patterns and other charac- 

 teristics basically comparable to a specified hurricane of 

 record, but is transposed to follow a new path to serve as a 

 basis for computing a hurricane surge hydrograph that would 

 be expected at a selected point. Moderate adjustments in 

 timing or rate of forward movement may be made also, if these 

 are compatible with meteorological considerations and study 

 objectives . 



HYPO-HURRICANE BASED ON GENERALIZED PARAMETERS - Hypo-hurricane 

 estimates based on various logical combinations of hurricane 

 characteristics used in estimating hurricane surge magnitudes 

 corresponding to a range of probabilities and potentialities. 

 The Standard Project Hurricane (SPH) is most commonly used 

 for this purpose, but estimates corresponding to more severe 

 or less severe assumptions are important in some project 

 investigations . 



STANDARD PROJECT HURRICANE (SPH) - A hypothetical hurricane in- 

 tended to represent the most severe combination of hurricane 

 parameters that is reasonably characteristic of a specified 

 region, excluding extremely rare combinations. It is further 

 assumed that the SPH would approach a given project site from 

 such direction, and at such rate of movement as to produce 

 the highest hurricane surge hydrograph, considering pertinent 

 hydraulic characteristics of the area. Based on this concept, 

 and extensive meteorological studies and probability analyses, 

 a tabulation of "Standard Project Hurricane Index Character- 

 istics" mutually agreed upon by representatives of the U. S. 

 Weather Bureau and the Corps of Engineers, is available. 



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