NHDPlus v2.1 and Alaska Beta NHDPlus

This dataset contains upstream watershed drainage areas for catchments comprising Catchment Fabric HUC12 units. The dataset is incomplete for Alaska.本数据集包含由集水区结构（Catchment Fabric）与12位水文单元代码（HUC12）单元构成的集水区的上游流域排水区域。该数据集在阿拉斯加州境内的数据存在缺失。