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The Drainageway code must only be applied at the initiation of flowlines or confluence of other Drainageway features. The Drainageway feature code must not be applied downstream of other non-drainageway flowlines or waterbody features (see Topological Relationships Between Elevation-Derived Hydrographic Features).
When a high degree of uncertainty exists for headwater features, the Drainageway feature type (FCode: 46800) shall be used. This code indicates further investigation is necessary to determine if a hydrographic feature exists on the ground.
The limit of a drainageway is the topographic flowpath or the approximate overland flow path between two disconnected drainage network features. A drainageway may be determined by modelling techniques indicating potential headwater drainage, but no channel will be detectable on the elevation surface.
The Drainageway feature code must only be applied at the initiation of flowlines or confluence of other Drainageway features. The Drainageway feature code must not be applied downstream of other non-drainageway flowlines or waterbody features).
Representation Rules
Delineate features as points, lines, or polygons based on their area or length along different axes (Table 26).
Table 26. Drainageway Representation Rules.
Kind of feature object
Area
Shortest Axis
Longest Axis
0-dimensional (point)
--
--
--
1-dimensional (line)
--
greater than 0
--
2-dimensional (polygon)
--
--
--
Special Conditions
To accommodate variations in the shortest axis of drainageway:
FOR elevation-derived hydrography: If shortest axis of drainageway is
less than 20 feet (6 meters) regardless of distance, and is connected at the downstream end to a 2-dimensional (polygon) Stream/river,
then drainageway is represented as a 1-dimensional (line) basic feature object.
If shortest axis of drainageway is greater than or equal to 50 feet (15 meters) and does not meet drainageway criteria, collect as appropriate feature for capture conditions (Stream/ river, playa, and others as needed).
Data Extraction
Capture Conditions
Drainageway features have no clearly defined capture conditions. Modelling techniques (such as flow models, elevation surface models, and logistic regression models) expose features and, therefore, require further investigation to determine their status and classification as hydrographic features.
Attribute Information
FClass 1—Hydrography feature defined within the collection criteria of the elevation-derived hydrography specifications. FCode 46800—Drainageway (flowlines delineated where terrain modelling indicates potential headwater drainage, but no channel is detectable). EClass 2— Linear feature that follows elevation surface.