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Elevation-Derived Hydrography READ Rules: Introduction


This document is a copy of the Elevation-Derived Hydrography READ Rules 2023 rev. A3 as found on the USGS National Geospatial Program Standards and Specifications website. For the latest version of the specification, please visit the site: Elevation-Derived Hydrography Data Acquisition Specification Rules 2023 rev. A2.


Elevation-Derived Hydrography 1.4

Revision History

Version 2023 rev. A3
  • Corrected FCodes for Connector, Connector: Culvert, Connector: Terrain Breech, and Underground Conduit to match Elevation-Derived Hydrography Data Acquisition Specification 2023 rev. A (A2) Table. 9 Feature type description, associated geometry, and use classification.
Version 2023 rev. A2
  • Corrected Canal/ditch and Dam/weir Attribute Information to match Elevation-Derived Hydrography Data Acquisition Specification 2023 rev. A (A2) Table. 9 Feature type description, associated geometry, and use classification.
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.
  • Add FlowClass field to line feature class attributes.
  • Add Limitation field to point, line, and polygon feature class attributes.
  • Changed name of sink/rise to sink feature.
  • 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 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 Area of Complex Channels (AOCCs) from EDH Specifications
  • Added Feature Types Canal/Ditch Polyline with EClass 3 and Canal/Ditch Polygons to correct missing Feature Types.
  • For clarity, replaced shortest axis measures with equivalent areal measurements for Ice Mass, Lake/Pond, Playa, and Reservoirs, as well as permanent islands in Sea/Ocean, Lake/Pond, Reservoirs, and Stream/River capture conditions.
  • For clarity, replaced minimum diameter measurements with equivalent diameter measures for Waterbodies, Reservoirs, and permanent islands in Sea/Ocean, Lake/Pond/, Reservoirs, and Stream/Rivers for breakline acquisition.
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.
  1. Four New EDH 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.

Note on Data Extraction Rules

Data Extraction Rules fall into three categories: capture conditions, attribute information, and source interpretation guidelines. The capture conditions explain the requirements for a feature to be collected, and other pertinent information about acquisition. The attribute information explains the definitions of the codes and attributes that must be applied to a feature if acquired, and the source interpretation guidelines give additional information for special circumstances to help determine whether a feature should be acquired or not. Not all features have source interpretation guidelines, and if this is the case, this will be indicated with “None.”