Elevation-Derived Hydrography Data Acquisition Specifications: Collection Area Requirements

Collection Area

Collection Concurrent with Elevation

Collection Area from Existing Elevation Data

Collection Area

The collection area refers to the geographic extent where the elevation source exists and from which hydrography will be derived. Hydrographic features can be collected at the same time elevation source data are being processed or taken from an existing 3D Elevation Program (3DEP) collection, when available. Collection areas from multiple sources of elevation data should be inspected and tile and collection area boundaries shall edge-match seamlessly and without gap prior to deriving hydrography.

Collection Concurrent with Elevation

Features shall be collected within the same defined project area (DPA) as the source elevation data (figure 1).

• Hydrography will be delineated for the entire DPA.
• Parts of the DPA within a complete 10-digit hydrologic unit will have complete network connectivity.
• Areas outside a 10-digit hydrologic unit, but within the DPA, will be connected and network connectivity created where possible.
  • Linework will not be snapped to less accurate features outside of the DPA.
  • A complete set of features shall be captured up to the boundary, but topology and network connectivity may need to be corrected at a later date.
• If elevation-derived hydrography exists adjacent to the DPA, linework will be snapped and merged to create continuous features that do not stop at the DPA boundary (unless it is also a hydrologic unit boundary).

Collection from Existing Elevation Data

Hydrographic features will be collected within watersheds, as defined by the Watershed Boundary Dataset (WBD). A 10-digit hydrologic unit is the minimum unit size recommended for collection (figure 2).

• Features shall be collected within a minimum 10-digit hydrologic unit area. A buffered area around each 10-digit hydrologic unit will be used to review and delineate features.
• Features that flow from one 10-digit hydrologic unit area to another that contains light detection and ranging (lidar) derived hydrography shall be snapped and topology corrected between hydrologic units.
  • Linear features shall be merged based on the feature code (FCode).
  • Polygons shall be merged with the same FCode.
• If less accurate hydrologic features are the only ones that exist outside of a hydrologic unit, features will not be snapped or adjusted to match those adjacent features.