Elevation-Derived Hydrography READ Rules: Sink

By NGP Standards and Specifications

The place at which a stream disappears into an underground conduit or an isolated depression where the network ends (Figure 66).

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Imagery and a map depicting sink features. — **Figure 66.** Sink features on the Santa Fe River, Florida, shown as examples of Sink hydrographic features. Source data are from the NHD (U.S. Geological Survey, 2020), which is used to provide examples of hydrographic feature types but may not have the same density and other characteristics of elevation-derived hydrography.

Delineation

The limit of Sink is the place at which a stream disappears underground.

Representation Rules

Delineate features as points, lines, or polygons based on their area or length along different axes (Table 31).

**Table 31.** Sink Representation Rules.
Kind of feature object	Area	Shortest Axis	Longest Axis
0-dimensional (point)	greater than 0	--	--
1-dimensional (line)	--	--	--
2-dimensional (polygon)	--	--	--

Special Conditions

None.

Data Extraction

Capture Conditions

If stream disappears,

then capture at the point of disappearance.

Attribute Information

FClass 1—Hydrography feature defined within the collection criteria of the elevation-derived hydrography specifications.
FCode 45000—Sink (the place at which a stream disappears into an under- ground conduit or reappears at the surface from an underground conduit, or an isolated depression where the network ends).
EClass 0— Not used to create elevation derivatives.

Source Interpretation Guidelines

A Sink feature shall be used at the lowest point of elevation in a Playa feature.