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Delineation and Attribution Errors

Delineation and attribution errors are described in detail accompanied by visual representations with solutions provided.

Incorrect Outflow from a Dam

Hanging Artificial Paths

Roadside Ditches and Culverts Through Driveways

Ancillary Data Feature Capture

Dam Connector Length

User Defined Code

Missing Z Values

XYZ Value Does Not Match DEM 

Lake/Pond Boundary Misplacement

NHD Lake/Pond Not on DEM

Poor Delineation Quality

Culvert Placement

Waterbody Outlet Point

EDH Features Placed Through Structures

Lines Outside Channels

Missing Culvert

Number of Vertices

Artificial Paths Crossing Islands 

Artificial Path

Waterbody Boundary Does Not Match Surface Topography

Misattributed Drainageway

* See below for more information about the errors. Click the image for a larger view


Error: Incorrect outflow from a dam.
Incorrect Outflow From A Dam
In the example on the left, the area highlighted by the red box shows where the outflow from a dam is place in the wrong location, skirting around the edge of the dam.  In the example on the right, the area highlighted in the green box, shows a connector placed correctly through the dam feature.

Issue: Outflow of water from a dam should cross the dam. Not the emergency / overflow spillway.

Solution: Where a dam is located, a “connector” (EDH FCode 33400) should be added across the dam, and the stream should continue downstream through the obvious stream channel.




Error: Hanging artificial paths.
Hanging Artificial Paths
In the first example, there is an artificial path that is not connected to another drainage network feature outside of the waterbody.  This artificial path should be removed.  In the second image, the hanging artificial path has been corrected by adding the missing stream/river that connects.

Issue: Artificial paths with no connection to a stream/river outside the waterbody.

Solution: If a larger scale dataset is used to generate a smaller scale dataset, care should be taken to remove features that are no longer pertinent. For instance, if artificial path connections were included in a 1:5,000 scale dataset, but some of the connecting stream segments were pruned for the 1:24,000-scale dataset, the connecting artificial paths should be removed as well.












Error: Roadside ditches and culverts through driveways.
Feature Capture and Attribution error example 5
Example of extraneous canal features.

Issue: Automated processes may delineate roadside ditches and culverts through driveways as part of the stream network that are outside of the capture requirements.

Solution: QA linework and remove extraneous features that are automatically generated. See Elevation-derived Hydrography Acquisition Specifications for more information on canal density.




Error: Ancillary data feature capture.
Ancillary data feature capture
Ancillary data feature capture

Issue:   When DEM is inconclusive but, in order to maintain network connectivity, ancillary data sources may be used to determine feature placement.

Solution: Features captured based on information gathered from ancillary data must have ancillary data usage noted in the attribute table for the feature class.  The data source must be noted for reproducibility.



Error: Dam connector length.
Dam Connector Length
Image 1 is an example of a dam connector that is too long, ending past the edge of the dam.  Image 2 is an example of a correctly delineated dam connector, ending at the edge of the dam.

Issue: Connectors through dams or berms that extend too far in one or both directions across the obstruction.

Solution: If a connector feature is required through a dam or berm, it should only extend the distance across the dam structure, and no further (but be sure to connect low points on both sides).













Error: User defined code.
User Defined Code
Example of feature that may need a user-defined code because the FCode for the feature does not exist in the EDH schema.

Issue: Features were delineated for a special project and have no EDH FCode available in Elevation-derived Hydrography Acquisition Specifications.

Solution: All NHD FTypes may be used as codes, as well as other user defined codes.  These must be placed in the “UserCode” field for the feature class.





Error:  Missing Z values.
Missing Z values (Table)
In this example, the lack of z-values (elevation values) can be seen in the “edit sketch properties” in ArcMap.

Issue: Features do not contain Z value for vertices.

Solution: Assign z-values to vertices as data is created.






Error: XYZ Value does not match DEM.
XYZ Value does not match DEM (requires Graph)
Example showing the delineated stream location not matching the lowest point of the channel in profile, thus having X, Y, and Z coordinates that do not match the coordinates of the correct location on the DEM.

Issue: X, Y, and Z coordinates of the delineated stream do not match the lowest point of the channel in profile, thus having X, Y, and Z coordinates that do not match the coordinates of the correct location on the DEM.

Solution: Checks should be done to ensure drainage features are at the lowest point of the stream channel in profile.




Error: Lake/pond boundary misplacement.
Elevation derived hydrography breakline error example
Example of lake/pond boundary (blue line) not matching the shoreline on the DEM (orange line).

Issue: Waterbody boundary does not match shoreline.

Solution: If boundary is derived from a previously hydroflattened feature, it should match the hydroflattened boundary.






Error: NHD lake/pond not on DEM.
NHD lakepond not on DEM
Example of a lake/pond feature (A) with a water surface area less than 2-acres as compared to its banks, and (B) a pond with a 2-acre water surface area matching its banks.

Issue: If a previously collected lake/pond feature no longer has a 2-acre water surface area, as of date of lidar collection, it should not be collected. In the example, Pond B has a reduced amount of water as compared to the apparent boundary on the imagery (image1) and DEM (image 2). Although the banks have a 2-acre area, the water surface is less than 2-acres. Pond A was full to the 2-acre boundary at time of lidar collection and was delineated.

Solution: Collect waterbody features at the extent of water surface area.












Error: Poor delineation quality.
Poor delineation quality
Example of poor delineation quality. In the example, the upper tributary A has a jagged appearance and does not fit well in the channel. The lower streams B fit nicely in the channel and has a natural appearance that represents the stream well.

Issue: Lines should be delineated to match the bottom of the channel in profile, but must maintain a smooth, natural appears. 

Solution: Delineate features so they fit the DEM surface in X,Y, and Z dimensions, and so they maintain a smooth, natural appearance.








Error: Culvert placement.
Culvert Placement Error
The first example shows a culvert that is too short, not spanning the width of the culvert. The second example shows a culvert that spans the culvert from edge to edge.

Issue: Culvert does not match elevation surface.

Solution: If there is evidence for the location of a culvert under a road (i.e. concrete structures on either side of a road directing water to the pipe under the roadway), the culvert end nodes should match these locations.















Error: Waterbody outlet point.
Waterbody outlet point
Waterbody outlet point

Issue: Water should flow out of stream at the outlet as determined on the DEM. In this example, the outlet for the top waterbody is shown flowing from the northeastern portion of the lake, but the outlet should be from the southeast, highlighted by the red box. 

Solution:  Check to ensure automated drainage network methods find the appropriate outflow path from waterbody features. 




Error: EDH features placed through structures.
EDH features placed through structures
Example showing a stream delineated through a structure.

Issue: Care should be taken not to place EDH features through structures on the landscape. 

Solution: If the channel is not apparent on the elevation surface, check to ensure there is no structure before continuing to delineate the stream, placing a drainageway, connector, or other feature.





Error: Lines outside channels.
Elevation derived hydrography breakline error example
Example of stream/river features placed outside of their channels.

Issue: Lines fall outside of the elevation surface channel.

Solution:  Inspect linework and adjust the lines if they fall outside of the lowest point of the channel in profile.








Error: Missing culvert.
Missing culvert
Image 1 is an example of a stream/river crossing a road without a culvert, which is incorrect.  Image 2 is an example of a culvert placed to traverse the road.

Issue: Culverts should be added to continue stream flow under roadways. 

Solution: Culverts should be added to identify where streams flow under roadways. Don't stop stream segments at culvert locations; identify culverts so that flow path modeling will be more accurate.












Error: Number of Vertices.
Number of vertices 
Example of a high density of vertices. The raster pixels are 1 meter in size, and the vertices are falling less than 1 meter apart.

Issue: Vertices should be placed no closer than 1.5 meters apart. The figure shows a 1 meter lidar digital elevation model surface with a stream overlain with vertices closer than 1.5 meters apart, which is incorrect.

Solution: Reduce the number of vertices by generalization.






Error: Artificial paths crossing islands.
Artificial paths crossing islands
Artificial paths crossing islands

Issue: Artificial paths should take the shortest path from the inlet to the outflow from a waterbody.  Artificial paths should not cross island.  Point A in the example shows an artificial path crossing an island.

Solution: Delineate artificial path so that it takes the shortest path from the inlet to the outflow from a waterbody. Paths may be delineated to show flow around islands, but care must be taken not to form loops, where the direction of flow doubles back on itself.





Error: Artificial path.
Elevation derived hydrography conflation error example 2
Example showing a stream line going through a waterbody, where there should be an artificial path.

Issue: No artificial path inside a lake/pond.          

Solution: The segment that flows through the lake/pond should be coded as an artificial path, not stream/river. The flow of water through a waterbody should always be indicated with an artificial path that begins and ends at the end nodes of the connecting flowline segments, and is snapped to the waterbody boundary.    






Error: Waterbody boundary does not match surface topography.
Waterbody boundary does not match surface topography
Waterbody boundary does not match surface topography

Issue: Waterbody boundaries must match the apparent boundary on the surface, but must have a z-value that equals the hydroflattened surface of the DEM. In the example provided, the area within the red box highlights an example of where the waterbody boundary does not fit the boundary of the hydroflattened area.                            

Solution: Delineate the waterbody so it follows the edge of the hydroflattened surface, retaining the z-values of the hydroflattened surface. The waterbody boundary should not drift on the bank area.



Error: Misattributed Drainageway.
Mislabeled Drainageway
Example of drainageways misattributed at stream/river features.

Issue: Drainageways are locations where no definite channel can be found over a distance for a stream/river feature, but it is clear there is overland flow that connects downstream.  A drainageway is used to connect these features.                 

Solution: Split the stream/river feature and re-attribute the drainageway accordingly.