U.S. Geological Survey Elevation-Hydrography Breakline Specifications

3D Elevation Program and National Geospatial Program Hydrography DatasetsThe U.S. Geological Survey (USGS) is developing hydrographic breakline specifications to support the integration of the

National Hydrography Dataset (NHD), Watershed Boundary Dataset (WBD), and 3D Elevation Program (3DEP). These programs contribute foundational data to The National Map and derived products, such as the US Topo digital map series.

What are Breaklines?Breaklines are vector features that are used to enforce or maintain linear features

on an elevation surface. Elevation data can be used with breaklines to make multi-ple elevation surface types; for example, breaklines defining hydrographic features can be used to impose different hydrologic treatments (flattening and enforcement) on DEMs.

Finding the Connection• The NHD has a long-established data dictionary by which all data, regardless of source, uses a single common attribute table structure and set of domain values.

• No such template has been developed for elevation breaklines; each delivered set of breaklines could have different attribute field definitions and attribute values.

• The variability has made it impractical to assemble multiple breakline data deliveries into a coherent, usable hydrographic dataset.

• Using the established NHD Data Dictionary as a starting point, attributes needed for elevation have been added, and topological differences have been identified.

Example Geospatial Products Generated from Lidar and Hydrographic Breaklines

The elevation-hydrography breaklines specifications will be published in the Lidar Base Specifications version 1.3. The anticipated public release date is 2016.

3D Elevation Program

The USGS National Geospatial Program is developing the 3DEP to provide high-quality ele-vation data for the Nation. 3DEP is primarily col-lecting light detection and ranging (lidar) data for the conterminous United States, Hawaii, and U.S. Territories.

Read more: http://nationalmap.gov/3DEP/.

National Geospatial Program

Hydrography Datasets

The NHD and WBD are used to portray surface water on The National Map.

The NHD represents the drainage network, includ-ing features such as riv-ers, streams, canals, lakes, ponds, coastline, dams, and streamgages.

The WBD represents drain-age basins as enclosed areas in eight size categories.

Read more: http://nhd.usgs.gov/index.html.

Examples of breaklines representing single- and double-line streams, ditches, culverts, bridges, and a waterbody.

Bare earth surface before hydroflattening or hydroenforcement.

Note the rough surface of the stream and waterbody.

Example of hydroflattening.

Note the smooth surface of the waterbody and double-line stream

Example of hydroenforcement.

Note the cut through the highway, allowing water flow to be correctly modeled on the surface.

Benefits of sharing breaklines include the following:

1. Improve agreement of the NHD and WBD with the 3DEP Bare Earth digital elevation model (DEM).

2. Enhance 3D cartographic products.3. Augment NHD data with high-accuracy elevation

data.4. Augment the 3DEP Bare Earth DEM with well-de-

fined hydrographic data.5. Allow production of additional types of DEM prod-

ucts, such as hydroenforced DEMs

1. Natural resources conservation 2. Water supply and quality3. River and stream resource management4. Coastal zone management5. Forest resources management6. Rangeland management7. Wildlife and habitat management8. Agriculture and precision farming9. Geologic resource assessment and hazard mitigation10. Resource mining11. Renewable energy resources12. Oil and gas resources13. Cultural resources preservation and management14. Flood risk management

Benefits of Sharing BreaklinesLimited breaklines are currently (2016) being collected for lidar data. Collecting breaklines with the goal of sharing

them across data themes and programs will maximize the potential benefits.

By Christy-Ann Archuleta, H. Karl Heidemann, Silvia Terziotti, and Kristina Yamamoto

U.S Department of the InteriorU.S. Geological Survey

15. Sea-level rise and subsidence16. Wildfire management, planning, and response17. Homeland security, law enforcement, and disaster

response18. Land navigation and safety19. Marine navigation and safety20. Aviation navigation and safety21. Infrastructure and construction management22. Urban and regional planning23. Health and human services24. Real estate, banking, mortgage, and insurance25. Education K–12 and beyond26. Recreation27. Telecommunications

The National Enhanced Elevation Assessment, completed in 2011, assessed elevation data needs, projected benefits, and application business uses for Federal and state agencies. This survey determined numerous hydrologic application busi-ness uses for elevation data:

PointsFeature topology Elevation description Eclass Etype SFType NHD description Fgroup Fcode

Always point Spot elevation (verified as high accuracy) 2 1001 1 na 0 00000na na 0 0000 0 Sink/rise (emergence or disappearance of a

drainage in karst landscape)1 45000

Point or Line Gate (connecting two singleline flows; marks a potential change in flow direction)

3 1003 tbd Gate 1 36900

Point, Line, or Polygon Dam/weir (connecting two singleline flows; marks a change in WSEL )

3 1004 tbd Dam/weir 1 34300

Point, Line, or Polygon Other topographic element 2 1303 tbd na 0 00000

LinesFeature topology Elevation description Eclass Etype SFType NHD description Fgroup Fcode

Point or Line Gate (crossing polygonal water features; marks a potential change in flow direction)

3 1003 tbd Gate 2 36900

Point, Line, or Polygon Dam/weir (crossing polygonal water features; marks a change in WSEL)

3 1004 tbd Dam/weir 2 34300

Line or Polygon Stream (narrow; 1D, depicted as singleline; in a braided area, the apparent "main channel")

1 1101 tbd Stream/river (1D) 3 46000

Line or Polygon Canal/ditch (narrow; depicted as singleline) 1 1102 tbd Canal/ditch (1D) 3 33600Line or Polygon Culvert (singleline, or centerline of polygonal culvert) 1 1103 tbd --> Stream/river 3 46000

--> IF canal/ditch 3 33600--> IF artificial path 3 55800

Line or Polygon Spillway (singleline, or centerline of polygonal spillway) 1 1104 tbd --> Stream/river 3 46000--> IF canal/ditch 3 33600--> IF artificial path 3 55800

Always Line Stream braid (narrow singleline streams; not the apparent "main channel)

1 1105 tbd Stream/river (1D) 3 46000

Always Line Centerline (any waterbody) 1 1201 tbd Artificial path 3 55800Always Line Link (singleline to centerline) 1 1202 tbd Artificial path 3 55800Always Line Elevation terminus line (that is, artificial "centerline" of a

boundary waterbody)1 1203 tbd na 0 00000

Always Line Flattener 1 1204 tbd na 0 00000Point, Line, or Polygon Other topographic element 2 1303 tbd na 0 00000

na na 0 0000 0 Bridge (water conveyance; very rare) 2 31800na na 0 0000 0 Connector 3 33400na na 0 0000 0 Sink/rise (emergence or disappearance of a

drainage in karst landscape)2 45000

PolygonsFeature topology Elevation description Eclass Etype SFType NHD description Fgroup FcodePoint, Line, or Polygon Dam/weir (large; also use centerline as centerline) 3 1004 tbd Dam/weir (large; also use artificial path as cen-

terline)4 34300

Line or Polygon Canal/ditch (wide, depicted as doubleline with centerline) 1 1102 tbd Canal/ditch (wide, depicted as doubleline with artificial path as centerline)

4 33600

Line or Polygon Spillway (large; also use spillway line as centerline) 1 1104 tbd Spillway (large; also use artificial path as cen-terline)

4 45500

Always Polygon Lake/pond (use centerline as centerline) 1 1106 tbd Lake/pond (ase artificial path as centerline) 5 39000Always Polygon River (wide, 2D, depicted as doubleline with centerline) 1 1107 tbd Stream/river (wide, depicted as doubleline

with artificial path as centerline)4 46000

If wide, and braided or with numerous islands, the centerline should follow the apparent "main channel"

tbd Area of complex channel (very complex wide 2D "river;" main channel identified with artifi-cial path centerline)

4 53700

Always Polygon Reservoir (use centerline as centerline) 1 1108 tbd Reservoir (use artificial path as centerline) 5 43600Always Polygon Estuary (true estuary; see definition below) 1 1109 tbd Estuary (true estuary) 5 49300Always Polygon Fjord 1 1109 tbd --> IF Sea/ocean 4 44500

tbd --> IF Stream/river 4 46000tbd --> IF Lake/pond 5 39000

Always Polygon Bay/inlet/sound 1 1110 tbd Sea/ocean 4 44500Always Polygon Boundary waterbody 1 1111 tbd --> IF Sea/ocean 4 44500

tbd --> IF Stream/river 4 46000tbd --> IF Lake/pond 5 39000

Always Polygon Bridge deck (any type) 3 1301 tbd --> IF Bridge (water conveyance; very rare) 4 31800tbd --> (else) 0 00000

Always Polygon Swamp/marsh area (reference area for elevation) 9 1401 tbd Swamp/marsh 5 46600Always Polygon Braided stream area (reference area for elevation) (This is

not the same as the NHD Code 53700)9 1402 tbd na 0 00000

Always Polygon Unusually inundated area (reference area for elevation) 9 1403 tbd na 0 00000Always Polygon Island/sandbar-intermittently/partially submerged 2 1404 tbd na 0 00000Always Polygon Low confidence area (predetermined) (reference area for

elevation)9 1501 tbd na 0 00000

Always Polygon Low confidence area (sparse bare-earth) (reference area for elevation)

9 1502 tbd na 0 00000

Line or Polygon Culvert (large; also use culvert line as centerline) (uncom-mon)

1 1103 tbd na 0 00000

Point, Line, or Polygon Other topographic element 2 1303 tbd na 0 00000

Definitions for elevation descriptors

Lake/pond Flat, level banksRiver Gradient banks, flowing waterReservoir Gradient banks, flowing waterFjord/estuary Gradient banks, flowing, tidalBay/inlet/sound Gradient banks, nonflowing, tidalElevation termi-

nusA line of single elevation to which all networks ultimately drain. Usually the conceptual equivalent of a sea/ocean or large

lake boundary waterbody “centerline” (River boundary waterbodies would have their own gradient centerline). This line is an abstration; it does not represent any real-world feature or elevation. It is used by some processes to support conflation of Z-values to other lines, and to support monotonic flow enforcement. It has no equivalent in the NHD.

Boundary water-body

Opposite bank not “mapped;” polygon closed arbitrarily. Most commonly an ocean or large lake (for example, Great Lakes), or a river that defines a project boundary.

Definitions for hydrology descriptors

Estuary A semienclosed coastal body of water which has a free connection with the open sea and within which sea water is measur-ably diluted with fresh water derived from land drainage. May be a named feature. An estuary is defined by the National Oceanic and Atmospheric Administration’s Coastal Aquatic Framework or local information concerning the extent of the mixed zone of fresh and salt water.Area of mixed fresh and salt water, typically 10–25PPM saline.”

Connector A known, but nonspecific, invisible connection between two nonadjacent network segments. May be a named feature. Un-known connection between two or more surface water features usually determined by dye-traces through groundwater sys-tems.

Artificial path A surrogate for general flow direction in NHDWaterbodies and NHDAreas. Artificial paths carry the name of the flowline feature. NHDArea, stream/rivers will have an artificial path that will carry the name of the river. Generalized flow direction, no specific entity other than to connect 1D flow external to the 2D flow.

Imaging & Geospatial Technology Forum2016

[1D, hydrography line; 2D, hydrography polygon; Etype, elevation type; Fgroup, feature group; Fcode, feature code; NHD, National Hydrography Dataset; SFType, surface feature type; na, not applicable; tbd, to be determined; WSEL, water surface elevation]