HOOK - A spit or narrow cape, turned landward at the outer end, resemb- 

 ling a hook in form, 



HYDRAULIC JUMP - In fluid flow, a change in flow conditions accompanied 

 by a stationary, abrupt turbulent rise in water level in the 

 direction of flow, A type of STATIONARY WAVE, 



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

 relief, bottom materials, coastal structures, etc, and 



(2) The description and study of sea, lakes, rivers, and 

 other waters, 



IMPERI>ffiAJ3LE GROIN - See under GROIN, 



INDIAN SPRING LOW WATER - The approximate level of the mean of lower low 

 waters at spring tides, used principally in the Indian Ocean and 

 along the east coast of Asia, Also INDIAN TIDE PLANE. 



INDIAN TIDE PLANE - The datum of INDIAN SPRING LOW WATER, 



INLET - A short, narrow waterway connecting a bay, lagoon, or similar 

 body of water with a large parent body of water. An arm of the 

 sea (or other body of water), that is long compared to its width, 

 and that may extend a considerable distance inland. See also 

 TIDAL. INI,ET„ 



INSHORE (Z01\IE) - In beach terminology, the zone of variable width extend 

 ing from the shore face through the breaker zone, (See Figure l) 



INSHORE CURRENT - Any current in or landward of the breaker zone, 



INSULAR SHELF - The zone surrounding an island extending from the line 

 of permanent immersion to the depth (usually about 100 fathoms) 

 where there is a marked or rather steep descent toward the great 

 depths , 



INTERNAL WAVES - Waves that occur within a fluid whose density changes 

 with depth, either abruptly at a sharp surface of discontinuity 

 (an interface) or gradually. Their amplitude is greatest at the 

 density discontinuity or, in the case of a gradual density change, 

 somewherein the interior of the fluid and not at the free upper 

 surface where the surface waves have their maximum amplitude, 



ISTHMUS - A narrow strip of land, bordered on both sides by water, 

 that connects two larger bodies of land. 



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