Watershed Boundary Dataset HUC 8 SCTDD

Each drainage area is considered a Hydrologic Unit (HU) and is given a Hydrologic Unit Code (HUC) which serves as the unique identifier for the area. HUC 2s, 6s, 8s, 10s, & 12s, define the drainage Regions, Subregions, Basins, Subbasins, Watersheds and Subwatersheds, respectively, across the United States. Their boundaries are defined by hydrologic and topographic criteria that delineate an area of land upstream from a specific point on a river and are determined solely upon science based hydrologic principles, not favoring any administrative boundaries, special projects, or a particular program or agency. The Watershed Boundary Dataset is delineated and georeferenced to the USGS 1:24,000 scale topographic basemap. Hydrologic Units are delineated to nest in a multi-level, hierarchical drainage system with corresponding HUCs, so that as you move from small scale to large scale the HUC digits increase in increments of two. For example, the very largest HUCs have 2 digits, and thus are referred to as HUC 2s, and the very smallest HUCs have 12 digits, and thus are referred to as HUC 12s. Dataset Summary Phenomenon Mapped: Watersheds in the United States, as delineated by the Watershed Boundary Dataset (WBD) Geographic Extent: Upper and Lower Duck, Buffalo, and Elk Subbasins Projection: NAD 1983 Tennessee State Plane Update Frequency: Annual Visible Scale: Visible at all scales, however USGS recommends this dataset should not be used for scales of 1:24,000 or larger. Source: United States Geological Survey (WBD) Data Vintage: January 7, 2025 Data Accessed: April 7, 2026 Publication Date: April 11, 2026

每个流域均被视为水文单元（Hydrologic Unit, HU），并被分配水文单元代码（Hydrologic Unit Code, HUC）作为该区域的唯一标识符。美国境内的HUC 2级、6级、8级、10级与12级代码，分别对应流域大区、副大区、流域、副流域、汇水区与副汇水区。其边界依据水文与地形标准划定，勾勒出河流特定点位上游的陆地区域，且完全基于科学水文原则确定，不偏向任何行政边界、专项工程或特定项目与机构。本流域边界数据集（Watershed Boundary Dataset, WBD）的边界划定与地理配准均基于美国地质调查局（USGS）1:24000比例尺地形底图。水文单元以多级嵌套的分级排水系统进行划定，并匹配对应的HUC代码，即当尺度从精细转向宏观时，HUC代码的位数以2位为增量递增。例如，级别最高的HUC代码为2位，因此被称为HUC 2级；级别最低的HUC代码为12位，因此被称为HUC 12级。

数据集概况
制图对象：美国境内经流域边界数据集（WBD）划定的汇水区
地理覆盖范围：上达克、下达克、布法罗与埃尔克副流域
投影：NAD 1983田纳西州州平面坐标系
更新频率：每年一次
可视比例尺：全尺度可见，但美国地质调查局（USGS）建议本数据集不适用于1:24000及更大比例尺的应用场景
数据来源：美国地质调查局（USGS，WBD）
数据版本日期：2025年1月7日
数据获取日期：2026年4月7日
发布日期：2026年4月11日