Elevation-Derived Hydrography Data Acquisition Specifications: Introduction
Elevation-Derived Hydrography Data Acquisition Specifications
Introduction
This document is a copy of the Elevation-Derived Hydrography Data Acquisition Specifications 2024 rev. A2 as found on the US Geological Survey (USGS) National Geospatial Program (NGP) Standards and Specifications website. For the latest version of the specification, please visit the site: https://www.usgs.gov/ngp-standards-and-specifications/elevation-derived….
Elevation-derived hydrography is collected by the USGS 3D Hydrography Program (3DHP) to refresh the geospatial representation of the Nation’s surface waters. Elevation-derived hydrography data will replace the legacy National Hydrography Dataset (NHD) linework in the 3DHP dataset, creating an improved, spatially accurate, and three-dimensional network collected using these specifications. Data collected and accepted using the Elevation-Derived Hydrography Data Acquisition Specifications 2024 rev. A will be published as 3DHP data by the USGS.
This specification is primarily for lidar-derived hydrography data, but IfSAR-derived hydrography data specifications are listed when different from lidar-derived hydrography requirements.
Elevation-Derived Hydrography Data Acquisition Specification Versioning
Schema
This specification reflects information in Elevation-Derived Hydrography schema 1.5. Please see previous versions of the Elevation-Derived Hydrography Data Acquisition Specifications; Representation, Extraction, Attribution, and Delineation (READ) Rules; and guidelines for earlier schema versions.
Release Date
1/23/2025.
Elevation-Derived Hydrography Data Acquisition Specification Versioning
The USGS uses a calendar year-based versioning for Elevation-Derived Hydrography Data Acquisition Specifications. The revision represented by a letter indicates the version of the specification released within a calendar year that includes changes to the specification, such as additional, changed, or removed requirements. The number after the revision letter represents versions of the specification where corrections were made to the specification but are not updated requirements (Figure 1).

Guidelines
The USGS Hydrography Specification Review Board (HSRB) reviews proposals to add, change, or remove requirements for elevation-derived hydrography throughout the year. The upcoming draft specification is modified when a proposal is approved. Pending that specification’s release, the USGS may publish a guideline with updated requirements in the interim.
National Hydrography Dataset
All references to the NHD in these specifications refer to the USGS hydrography data acquired prior to 2023 using methods different from this specification. The NHD was produced to a 1:24,000-scale or larger and will generally appear to be less dense and detailed than the data collected according to these specifications.
Requirement Terminology
Individual requirements defined in this report use “shall” or “will” statements, which have a specific meaning in the context of a specification requirement:
- A “shall” statement means the requirement must be met.
- A “will” statement indicates the requirement is expected to be met wherever possible, but exceptions to implementation may exist.
Revision History
Version 2024 revision A2
- User-Defined Features with FCode=0 in Table 11 corrected so FClass=9.
Version 2024 rev. A
- Updated horizontal and vertical Coordinate Reference System (CRS)s for different regions.
- Ice Mass feature type (FCode: 37800) removed.
- Dam feature type (FCode: 34300) removed.
- Updated Sea/ocean island size criteria.
- Added Final Deliverable Project Area (FDPA) requirement to be submitted a single polygon or multipart polygon.
- Added User-defined feature attribute information to Table 8, Table 11, and Additional User-defined Features section.
- Added valid field combination to Connector: Indefinite Surface, FClass=1 and EClass=0 to Table 11.
- Added valid field combination to Connector, FClass=1 and EClass=0 to Table 11.
- Added a description and definition field to Table 10. Domain values for EClass feature attributes. Removed the Feature Attribute column. Clarified several definitions.
- Updated Delivered Products and Formats section, to include requiring spatial metadata and omitted NHD features to be delivered in geopackage format.
- Updated Table 9
- Removed requirement to use EClass=0 from FClass domain values 1 and 9.
- Made domain value 1 the default value.
- Updated Vertical Alignment section with requirements for overlapping polygons.
- Topology Changes
- Added line feature valency limit of five features to Topology Rules section.
- Change feature edge matching requirement from exactly to within 0.001 meters.
- Removed outdated Topology Rule that Connector: Culvert features may split other features but must use the same FCode.
- Added Topological Relationships Between Elevation-Derived Hydrographic features section.
- Added requirement to snap inlet and outlet features at FDPA.
- Guideline Integration
- Added Inclusion or Omission of National Hydrography Dataset (NHD) Waterbody Features version 2 guideline contents to Special Cases.
- Added the Connector through Infrastructure Areas version 2 guideline contents to Special Cases.
- Updated Table 11 to include the associated Connector feature type EClass=0 and FClass=2 combination.
- Clarified Connector feature type definition to accommodate usage in infrastructure areas.
- Updated EClass and FClass value combinations to incorporate new FlowClass attribute.
- Added subsurface stormwater system considerations.
- Added the Network Connectivity through Ice Masses version 1 guideline contents to Special Cases.
- Added the Sea/ocean version 3 guideline contents to the Sea/ocean READ Rules Delineation section.
- Added Delineation of Features within areas with Digital Elevation Model (DEM) Limitations version 3 guideline contents to the Positional Assessment section.
- Added Vertical Integration of Linear Features through Depressions version 4 guideline content to the Depression and Terrain Breach sections of Special Cases and Indefinite Surface Connector READ Rules. For Connector: Indefinite Surface features:
- Added FlowClass value (2) requirement.
- Changed EClass from 0 to 2. Updated Table 11.
- Added Low Relief Areas to Special Cases from the Guidance for Stream Channel Delineation and Capture Conditions in Alaska guideline.
- Updated Stream/river and Canal/ditch feature Special Conditions for lidar and IfSAR based collection and simplified thresholds for determining if the feature is captured as a line or polygon feature.
- Added X, Y, and Z Coordinate Precision version 5 guideline content to the horizontal and vertical alignment sections.
- Added additional contents from the Stream/river Special Condition- Complex Interlacing Channel version 3 guideline content to the Complex Interlacing Channels Special Case section.
- Added Elevation Source Spatial Metadata Requirements version 1 guideline content to the Delivered Products and Formats section and tables section.
- Added the Source Raster and Vector Data Requirements version 2 guideline content to the Coordinate Reference Section and Delivered Products and Formats section.
- Added the Hydrologically Enforced DEM version 1 and Hydrologically Conditioned DEM version 1 guideline contents to Appendix 2.
- Added the Waterbodies and Islands guideline contents.
- Artificial path features around Islands to the Artificial Path READ Rules.
- Island representation information to the Additional Elevation-Derived Hydrography Treatment and Elevation Specific Features.
- Updated Lake/pond Capture Conditions and Source Interpolation Guidelines with new size criteria.
- Added Elevation-Derived Hydrography Lines Crossing Ridges guideline content to Lines Crossing Ridges Special Case.
- Added and updated Geomorphic Indicator guideline contents to Appendix 3.
- Added Difference DEM instructions to Appendix 4.
- Added Raster Spatial Reference Requirements to Appendix 5.
- Special Cases
- Moved content from Connector: Indefinite Surface; Connector: Non-NHD Dataset; Canals and Ditches; and Drainageway Special Cases to Appendix 1.
- Renamed Stream/river Special Case Complex Interlacing Channels.
- Renamed Culvert Special Case to Bridge Locations.
- Clarifies that a Connector: Culvert feature is not required for a continuous water feature when a bridge is removed in Culvert Special Case.
- READ Rules
- Canal/ditch
- Removed outdated Source Interpretation Guidelines from Canal/ditch READ Rules.
- Change Canal/ditch in agricultural fields exception from User Defined Feature to Canal/ditch FCode with FlowClass=2.
- Removed transportation size threshold for determining whether to use a Pipeline or Connector: Culvert feature.
- Clarified that Connector: Culvert feature type must be underneath a transportation feature.
- Canal/ditch
- Administrative changes to document.
- Added “Data” to the title of this document.
- Added specification versioning, guideline, and requirements terminology information to the introduction.
- Removed Collection Concurrent with Elevation section.
- Removed NHD references from FCode description.
- Removed 3DEP Lidar Base Specification (LBS) Required Hydroflattening Collection section.
- Removed reference to NHD specifications and 3DEP LBS from the Positional Assessment section.
- Removed references to accuracy standards.
- Change Lake/pond feature definition to include features formally collected as Reservoir features.
- Removed reservoir information from Lake/pond Source Interpolation Guidelines.
- Added contents of Elevation-Derived Hydrography Representation, Extraction, Attribution, and Delineation (READ) Rules to Appendix 1.
- Added READ Rule explanations to Appendix 1.
- Changed international boundary source to US Census Bureau data.
Version 2023 rev. A2
- Corrected Indefinite Surface Connector channelized segment length special case to include a length for the contiguous United States and Alaska.
Version 2023 rev. A
- The Low Confidence Area features are removed from the elevation-derived hydrography feature types.
- The reservoir feature type is removed from the elevation-derived hydrography feature types.
- Stream/river special condition added for complex interlacing channels.
- Changed or added additional EClass Domain Codes.
- Updated the Feature Type Description, Associated Geometry, and Use Classification Table with new EClass and FClass combinations as needed. This resulted in changes to some feature attribution information in the Elevation-Derived Hydrography Representation, Extraction, Attribution, and Delineation (READ) Rules 2023 rev. A.
- Added FlowClass field to line feature class attributes.
- Add Limitation field to point, line, and polygon feature class attributes.
- Changed name of Sink/rise feature to sink.
- Removed references to the National Hydrography Dataset (NHD) and replaced with elevation-derived hydrography or 3D Hydrography Program (3DHP) where appropriate.
- Ice Mass, Pipeline, and Non-NHD Connector FClass changed from 1 to 2.
- Removed the Feature type description, associated geometry, and use classification table from the Elevation-Derived Hydrography READ Rules 2023 rev. A. and referred the reader to the Elevation-Derived Hydrography Data Acquisition Specifications 2023 rev. A.
- Reformatted tables and in some case separated information into new tables for easier understanding.
- Changed geoid model to require GEOID18 specifically, instead of most recent.
- Clarified that Sink features may overlap a Playa feature.
Version 2022 rev. A
- Removal of AOCCs from Elevation-Derived Hydrography Specifications and from Task Orders.
Version 2021 rev. A
- Drainageway Definition Updated
- Old Definition: A drainageway is a watercourse that conveys, or is likely to convey water but lacks a clearly defined channel or banks differentiating it from an ephemeral stream/river. Drainageways typically convey water for limited periods of time and do not carry perennial flow. Drainageways may follow natural topographic flow paths or constructed or human-made flow paths.
- New Definition: Drainageway features are flowlines delineated where terrain modelling indicates potential headwater drainage but no channel is detectable. The drainageway code must only be applied at the initiation of flowlines or confluence of other drainageway features. The drainageway code must not be applied downstream of other non-drainageway NHD flowlines or waterbody features.
- Four New Elevation-Derived Hydrography Connector FCodes added to Connector Type
- Culvert (FCode: 33401)—A subsurface feature connecting upstream and downstream hydrography features under a constructed feature (Exception: See READ Rules “Connector” for Dam Features). Typically constructed of formed concrete or corrugated metal and surrounded on all sides; top, and bottom by earth or soil. The hydrographic features defined by this specification are intended to be suitable for elevation surface treatments such as hydro-enforcement. Culvert features are used to maintain connectivity of hydrographic network features, while providing attribution allowing the culverts to be easily identified for elevation surface treatments such as hydro-enforcement.
- Indefinite Surface (FCode: 33404)—Indefinite Surface Connectors are used where evidence of channelization is not present in the digital elevation model surface but connectivity between an upstream and downstream channel is indicated by terrain modelling. Situations where Indefinite Surface Connectors may be used include low confidence areas in the DEM or heavy vegetative cover in which the channel cannot be resolved. Indefinite surface connector features may also be used to connect through areas having conservation treatments such as grassed waterways, which are designed to prevent soil erosion and the formation of channels. This FCode is recommended for use in situations where streams sink into the ground under low or normal flow conditions, but would flow over the surface during high flow or flood conditions and connect to downslope hydrographic features.
- Terrain Breach (FCode: 33405)—Used to breach terrain (or elevation) features that block the flow in a drainage network, such as a small rise in elevation, landslides, moraines, glacial till, or berms. This connector is used to breach flow blockages on the elevation surface; with no known manmade feature such as a pipeline or culvert connecting upstream and downstream flow. Do not use the Terrain Breach to represent underground flowpaths in known karst, permafrost or thermokarst terrain (See READ Rules for “Underground conduit”).
- Non-NHD Dataset (FCode: 33410)— Used to provide network connectivity to or through a polygon feature that is represented in an external dataset maintained by another agency such as the National Wetlands Inventory, the Randolph Glacier Inventory, or other datasets related to hydrography. This connector will be used to traverse areas with no obvious network connections. Linear and polygon features that represent Stream/river or Canal/ditch flowpaths through the non-NHD dataset areas will be mapped as separate elevation-derived hydrography features. This connector shall be used with a dataset recognized by the USGS for these purposes.
Version 2020 rev. A
- Underground Conduit FCode
- “Positional Accuracy Indefinite” (FCode 42002) — The underground conduit allows network connectivity through areas where there is some evidence the water flows underground in karst and thermokarst regions.
- UniqueID Field
- The UniqueID field is meant to be populated by the contractor prior to delivery of data to the USGS. Unique IDs allow communication with contractors by providing a tracking system for individual features.