Abstract

Major Enhancements for NHDPlus Version 2 Grids
Track: Water Resources
Authors: Richard Moore, Alan Rea, Craig Johnston

New ArcGIS geoprocessing tools and processes have been developed to produce NHDPlus Version 2 data including flow-direction, flow-accumulation, and catchment grids that are consistent with streamflow directions represented in the National Hydrography Dataset (NHD) and divides represented in the newly completed Watershed Boundary Dataset (WBD). The processes involve creating hydrologically conditioned digital elevation models (DEMs) and generating flow-direction grids from the modified DEMs. DEM modifications are based on ingredient datasets, including WBD, NHD flowlines, and NHD waterbodies. NHDPlus production tools use NHDPlus value-added attributes (VAAs) to enhance processing of the DEM. Hydrologic sequence numbers are used to direct flow (stair stepping downward in the DEM) in a manner consistent with the flow direction of the NHD flowlines. Where divergences are represented in the NHD, a separate VAA is used to direct the flow down the main path. Flow accumulation and catchment grids are subsequently generated from the improved flow-direction grids.