Hydrologic Unit Code (HUC) 10

The Watershed Boundary Dataset (WBD) is a comprehensive aggregated collection of hydrologic unit data consistent with the national criteria for delineation and resolution. It defines the areal extent of surface water drainage to a point except in coastal or lake front areas where there could be multiple outlets as stated by the "Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD)" “Standard” (http://pubs.usgs.gov/tm/11/a3/). Watershed boundaries are determined solely upon science-based hydrologic principles, not favoring any administrative boundaries or special projects, nor particular program or agency. This dataset represents the hydrologic unit boundaries to the 12-digit (6th level) for the entire United States. Some areas may also include additional subdivisions representing the 14- and 16-digit hydrologic unit (HU). At a minimum, the HUs are delineated at 1:24,000-scale in the conterminous United States, 1:25,000-scale in Hawaii, Pacific basin and the Caribbean, and 1:63,360-scale in Alaska, meeting the National Map Accuracy Standards (NMAS). Higher resolution boundaries are being developed where partners and data exist and will be incorporated back into the WBD. WBD data are delivered as a dataset of polygons and corresponding lines that define the boundary of the polygon. WBD polygon attributes include hydrologic unit codes (HUC), size (in the form of acres and square kilometers), name, downstream hydrologic unit code, type of watershed, non-contributing areas, and flow modifications. The HUC describes where the unit is in the country and the level of the unit. WBD line attributes contain the highest level of hydrologic unit for each boundary, line source information and flow modifications.流域边界数据集（Watershed Boundary Dataset，WBD）是一套符合国家流域划定与分辨率标准的综合聚合式水文单元数据集。其定义了地表水向某一点汇流的区域范围，但沿海或湖滨区域除外——此类区域存在多个出水口，相关规则遵循《国家流域边界数据集（WBD）联邦标准与规程》中的"标准"条款（http://pubs.usgs.gov/tm/11/a3/）。流域边界仅基于科学水文原则划定，不偏袒任何行政边界、特殊项目、特定方案或机构。本数据集覆盖美国全境的12位（第6级）水文单元边界，部分区域还包含代表14位、16位水文单元（Hydrologic Unit，HU）的额外细分。在最低精度要求上，美国本土的水文单元划定比例尺为1:24000，夏威夷、太平洋流域及加勒比地区为1:25000，阿拉斯加为1:63360，全部符合国家地图精度标准（National Map Accuracy Standards，NMAS）。目前相关团队正针对有合作方及可用数据的区域开发更高分辨率的边界数据，并将其整合回WBD中。WBD数据以多边形数据集及定义多边形边界的对应线要素形式交付。WBD多边形属性包含水文单元代码（Hydrologic Unit Code，HUC）、面积（以英亩与平方千米为单位）、名称、下游水文单元代码、流域类型、非贡献区以及径流修正项。HUC用于标识该单元在全国的位置与层级。WBD线要素属性包含每条边界对应的最高层级水文单元、线要素源信息以及径流修正项。