Subwatersheds

The intent of defining Hydrologic Units (HU) within the Watershed Boundary Dataset is to establish a base-line drainage boundary framework, accounting for all land and surface areas. Hydrologic units are intended to be used as a tool for water-resource management and planning activities particularly for site-specific and localized studies requiring a level of detail provided by large-scale map information. The WBD complements the National Hydrography Dataset (NHD) and supports numerous programmatic missions and activities including: watershed management, rehabilitation and enhancement, aquatic species conservation strategies, flood plain management and flood prevention, water-quality initiatives and programs, dam safety programs, fire assessment and management, resource inventory and assessment, water data analysis and water census.在流域边界数据集（Watershed Boundary Dataset）中定义水文单元（Hydrologic Units, HU）的初衷，是建立一套基准排水边界框架，覆盖所有陆地与地表区域。水文单元旨在作为水资源管理与规划工作的实用工具，尤其适用于需要大比例尺地图所提供细节精度的特定场地与局域性研究。该流域边界数据集可与国家水文数据集（National Hydrography Dataset, NHD）形成互补，并支撑众多项目任务与相关工作，具体包括：流域管理、修复与提升、水生生物物种保护策略、洪泛区管理与防洪、水质相关举措与项目、大坝安全项目、火灾评估与管理、资源清查与评估、水文数据分析以及水资源普查。