The USGS has released specifications for deriving hydrography from elevation data for use in updating the National Hydrography Dataset.
NHD derived from 3DEP Data
The 2016 Hydrography Requirements and Benefits Study documented a strong need for improved horizontal and vertical alignment of national hydrography data to elevation data. The National Hydrography Dataset (NHD) is the most up-to-date and geographically inclusive hydrography dataset for the Nation. Deriving NHD features from 3D Elevation Program (3DEP) data greatly enhances the vertical and horizontal spatial integration between the terrain and the stream network and provides the level of accuracy and detail required for local scale water resources applications while also supporting broader scale hydrologic modeling.
In support of this improvement, the USGS has developed new guidance for creating elevation-derived hydrographic features that are appropriate for ingestion into the NHD:
- Elevation-Derived Hydrography Acquisition Specifications describe requirements for the capture of hydrographic features from 3DEP products. The specifications provide a consistent data structure, definition of minimum set of features required, and horizontal and vertical positional assessments for alignment of features to the elevation surface.
- Elevation-Derived Hydrography Representation, Extraction, Attribution, and Delineation Rules (READ Rules) describe the parameters for the portrayal of hydrographic features as derived from elevation data, including the attributes, delineation instructions, and representation rules for the NHD.
Elevation-derived hydrography is created using algorithms that identify channels and depressions in elevation data that may carry surface flow. These features are processed into streamlines, lakes, and other hydrographic features, which may then be converted into NHD data. Hydrography developed using these specifications will be horizontally and vertically aligned with the 3DEP high-resolution bare-earth digital elevation model data. Density of delineated features will, at a minimum, match that of the NHD. The EDH will also be suitable for use with digital elevation models, as breaklines for hydro-flattening and for use in hydro-enforcement.
The NHD is a primary input to the NHDPlus High Resolution (NHDPlus HR), a scalable and openly accessible hydrography framework for the inland waters of the Nation. Updating the NHD and NHDPlus HR datasets with elevation-derived hydrographic features will support applications such as flood forecasting to move from the neighborhood to the street level by making the data more detailed, accurate, and precise. Deriving hydrography from elevation also helps to advance the future vision of the 3D National Terrain Model (3DNTM), an integrated elevation-hydrography surface from the peaks of the mountains to the depths of the oceans.
More information about the National Hydrography Dataset and related products and services is available at https://www.usgs.gov/core-science-systems/ngp/national-hydrography. For questions, please contact firstname.lastname@example.org