Hydrography 3
Hydrography 3 : The description, study, and mapping of the waters of the Earth's surface (the seas, lakes and rivers), including their forms and physical features. A member of the hierarchical system for identifying and subdividing river-basin units within the United States. Hydrologic units are used for the collection and organization of hydrologic data. The levels of the hierarchy, listed in order of largest to smallest in area, are: region, subregion, accounting unit, and subbasin. Each hydrologic unit is identified uniquely with a hydrologic unit code. (1) region - Mid-Atlantic region; (2) subbasin - The fourth level of subdivision of hydrologic units. A subbasin represents the geographic area of part or all of a surface drainage basin, a combination of drainage basins, or a distinct hydrologic feature. Subbasins are uniquely identified with eight-digit hydrologic unit codes. (3) subregion - Upper Chesapeake. (4) accounting unit - Upper Chesapeake. Delaware, Maryland,Virginia, and Pennsylvania. (5) subbasin - Chester-Sassafras. Delaware, Maryland, Pennsylvania
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