Kentucky 8, 10, and 12-digit Hydrologic Units

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” (https://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. Download Link: https://ky.box.com/s/bcrhmwev56q03xg28yrfyk7w4s8w8a44流域边界数据集（Watershed Boundary Dataset，WBD）是一套遵循美国国家汇水区划定与分辨率规范的综合聚合式水文单元数据集。其界定了地表径流汇聚至某一节点的区域范围，沿海或湖滨区域除外——此类区域存在多个出水口，符合《国家流域边界数据集（Watershed Boundary Dataset，WBD）联邦标准与规程》（下称"标准"）中的相关规定，标准文档链接：https://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、专项工程，亦不倾向于特定项目或机构。本数据集覆盖全美范围，提供12位编码（第六级）的水文单元边界；部分区域还包含代表14位、16位编码水文单元（Hydrologic Unit，HU）的额外细分边界。就最低精度要求而言，美国本土的水文单元以1:24000比例尺划定，夏威夷、太平洋流域及加勒比地区采用1:25000比例尺，阿拉斯加州则采用1:63360比例尺，所有精度均符合《国家地图精度标准》（National Map Accuracy Standards，NMAS）。目前正针对具备合作方与数据源的区域开发更高分辨率的边界数据，后续将整合至WBD中。WBD数据以多边形及其配套边界线数据集的形式提供，边界线用于定义多边形的范围。WBD多边形的属性字段包括水文单元编码（Hydrologic Unit Code，HUC）、面积（以英亩与平方千米为单位）、名称、下游水文单元编码、流域类型、非汇水区面积以及径流改造情况。HUC编码用于标识该水文单元在美国的位置以及所属级别。WBD边界线的属性字段包含每条边界对应的最高层级水文单元、线源信息以及径流改造情况。下载链接：https://ky.box.com/s/bcrhmwev56q03xg28yrfyk7w4s8w8a44