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National Hydrography Dataset (NHD) Data Dictionary Feature Classes

By NGP Standards and Specifications

The data dictionary for feature classes in the National Hydrography Dataset.

NHDFlowline : NHDFlowlines Consist Of Routes That Make Up A Linear Surface Water Drainage Network. Flowlines Have A Reach Code And A Measure, Allowing For The Establishment Of Upstream/Downstream Relationships. This Network Allows For Powerful Analysis And Modeling Capabilities.

Name Definition Type Allow Nulls Length Domain Default Value Comments
Enabled An indication of whether a feature can participate in a geometric network. Short Integer True   "Enabled" attribute values    
FCode Feature Code. Numeric value that encodes a set of characteristics for a type of feature. This five-digit code has two parts: the first three digits encode the feature type (FType); the last two digits encode values for a unique set of characteristics associated with the feature type. The set of characteristics may be single valued or multi-valued. Long Integer True       default value varies, depending on feature
FDate Date of last feature modification. Date False 8      
FlowDir Direction of flow relative to coordinate order. Long Integer False   HydroFlowDirections 0 Domain of values:With digitizedUninitialized
FType Feature Type. Numeric value that encodes a type of feature, represented as a three-digit code. For further refinement of the feature type classification, see FCode. Long Integer False       default value varies, depending on feature
GNIS_ID A permanent, unique number assigned by the Geographic Names Information System (GNIS) to a geographic feature name for the sole purpose of uniquely identifying that name application as a record in any information system database, dataset, file, or document Text True 10     GNIS_ID = "null" if no name is associated with the feature. Removed from WBD as of version 2.3 schema.
GNIS_Name The Geographic Names Information System (GNIS) assigned proper name, specific term, or expression by which a particular geographic entity is known. Text True 65      
InNetwork Identifies the subset of the NHDFlowline features that will be used/included in NHDPlus. Short Integer True   NoYesDomain  

InNetwork is an attribute that the user can set to define the subset of the NHDFlowline features that will be used/included in

NHDPlus. Yes = In network, Features included in the NHDPlus network.No = Out of network - Features not included in the

NHDPlus network.
LengthKM Length of linear feature. Value is computed when data are in Albers Equal Area projection. Double True       Computed
MainPath The main stream path that tributary streams converge to or diverge from. Long Integer True   MainPath    
NHDPlusID NHDPlus HR Unique identifier of a NHDFlowline feature. Found in NHDPlus HR Only. Double True       This field only exists when NHD feature classes are brought into NHDPlus HR.
OBJECTID Internal feature or event number. OBJECTID False        
Permanent_Identifier A 40-character globally unique ID (GUID) value that uniquely identifies the occurrence of each feature or event in The National Map. Text False 40      
ReachCode Unique identifier. The first eight digits are the WBD_HUC8. The next six digits are randomly assigned, sequential numbers that are unique within a HUC8. Text True 14     Required for all NHDFlowlines. NHDWaterbody and NHDPoint feature classes allow reach codes, but do not require them.
Resolution Source resolution. Long Integer False   Resolution   Currently NHD is available as separate resolutions.Domain values:Local > 1:12,000High 1:24,000/12,000Medium 1:100,000
Shape Feature geometry. Geometry True        
Shape_Length Length of the feature, which may differ from the field measured length due to differences in calculation. Units are map units. Double True       All features should have a positive integer value.
VisibilityFilter Allows for filtering of features for usage of vector data at approximate scales. Long Integer False   VisibilityFilter    
VPUID Vector Processing Unit Identifier. Found in NHDPlus HR only. Text True 8     This field only exists when NHD feature classes are brought into NHDPlus HR.
WBArea_Permanent_Identifier Permanent_Identifier of the waterbody through which the flowline flows. Text True 40      

SubTypes of NHDFlowline

SubType Description Definition
334 Connector Known, but unspecific, connection between two nonadjacent network segments.
336 CanalDitch Artificial open waterway constructed to transport water, to irrigate or drain land, to connect two or more bodies of water, or to serve as a waterway for watercraft.
420 Underground Conduit Underground passage of surface water.
428 Pipeline Closed conduit with pumps, valves, and control devices, for conveying fluids, gases, or finely divided solids.
460 StreamRiver Body of flowing water.
468 Drainageway A drainageway is a watercourse that conveys, or is likely to convey water but lacks a clearly defined channel or banks differentiating it from an ephemeral stream/river. Drainageways typically convey water for limited periods of time and do not carry perennial flow. Drainageways may follow natural topographic flow paths or constructed or human-made flow paths.
558 ArtificialPath Abstraction to facilitate hydrologic modeling through open water bodies and along coastal and Great Lakes shorelines and to act as a surrogate for lakes and other water bodies.
566 Coastline Line that follows the main outline of the land, including bays, but crosses rivers at their mouth. In the NHD, the outline of selected coastal islands are included as part of the coastline.

FEATURE CLASS

NHDArea : Areal Hydrographic Landmark Features.

Name Definition Type Allow Nulls Length Domain Default Value Comments
AreaSqKm Area of feature in square kilometers based on Albers Equal Area projection. Double True       Computed.
Elevation The vertical distance from a given datum. Double True   ElevationRange   Stage of the water elevation is encoded in the FCode.
FCode Feature Code. Numeric value that encodes a set of characteristics for a type of feature. This five-digit code has two parts: the first three digits encode the feature type (FType); the last two digits encode values for a unique set of characteristics associated with the feature type. The set of characteristics may be single valued or multi-valued. Long Integer True       default value varies, depending on feature
FDate Date of last feature modification. Date False 8      
FType Feature Type. Numeric value that encodes a type of feature, represented as a three-digit code. For further refinement of the feature type classification, see FCode. Long Integer False       default value varies, depending on feature
GNIS_ID A permanent, unique number assigned by the Geographic Names Information System (GNIS) to a geographic feature name for the sole purpose of uniquely identifying that name application as a record in any information system database, dataset, file, or document Text True 10     GNIS_ID = "null" if no name is associated with the feature. Removed from WBD as of version 2.3 schema.
GNIS_Name The Geographic Names Information System (GNIS) assigned proper name, specific term, or expression by which a particular geographic entity is known. Text True 65      
NHDPlusID NHDPlus HR Unique identifier of a NHDFlowline feature. Found in NHDPlus HR Only. Double True       This field only exists when NHD feature classes are brought into NHDPlus HR.
OBJECTID Internal feature or event number. OBJECTID False        
Permanent_Identifier A 40-character globally unique ID (GUID) value that uniquely identifies the occurrence of each feature or event in The National Map. Text False 40      
Resolution Source resolution. Long Integer False   Resolution   Currently NHD is available as separate resolutions. Domain values: Local > 1:12,000High 1:24,000/12,000Medium 1:100,000
Shape Feature geometry. Geometry True        
Shape_Area Area of feature in map units squared. Double True        
Shape_Length Length of the feature, which may differ from the field measured length due to differences in calculation. Units are map units. Double True       All features should have a positive integer value.
VisibilityFilter Allows for filtering of features for usage of vector data at approximate scales. Long Integer False   VisibilityFilter    
VPUID Vector Processing Unit Identifier. Found in NHDPlus HR only. Text True 8     This field only exists when NHD feature classes are brought into NHDPlus HR.

SubTypes of NHDArea

SubType Description Definition
307 Area to be Submerged Known extent of the intended lake that will be created behind a dam under construction.
312 BayInlet Water opening that is an opening into the sea/ocean into the land, or of an estuary, lake, or river into its shore.
318 Bridge Structure spanning and providing passage over a waterway, railroad, or other obstacle.
336 CanalDitch Artificial open waterway constructed to transport water, to irrigate or drain land, to connect two or more bodies of water, or to serve as a waterway for watercraft.
343 DamWeir Barrier constructed to control the flow or raise the level of water.
362 Flume Open, inclined, artificial channel constructed of wood, metal, or concrete; generally elevated.
364 Foreshore Part of a seashore between high-water and low-water marks.
398 Lock Chamber Enclosure on a waterway used to raise/lower vessels as they pass from one level to another.
403 Inundation Area Area of land subject to flooding.
431 Rapids Area of swift current in a stream or river, characterized by standing waves or by boulders and rocks.
445 SeaOcean Great body of salt water that covers much of the earth.
455 Spillway Constructed passage for surplus water to run over or around a dam.
460 StreamRiver Body of flowing water.
461 Submerged Stream Old river course inundated by an impounded water body.
484 Wash Usually dry portion of a stream bed that contains water only during or after a local rainstorm or heavy snowmelt.
485 Water IntakeOutflow Structure through which water enters or exits a conduit.
537 Area of Complex Channels Area where a stream or river flows in an intricate network of interlacing channels.
568 Levee A natural or manmade embankment along the edge of a stream/river, canal/ditch, or waterbody, that protects the surrounding land from flooding.

 

NHDWaterbody : Features Representing Areal NHD Hydrographic Waterbody Features. Some Waterbody Features Such As LakePond, Reservoir, And Estuary Must Have A Reachcode. SwampMarsh May Have A Reachcode. Ice Mass And Playa Do Not Have Reachcodes.

Name Definition Type Allow Nulls Length Domain Default Value Comments
AreaSqKm Area of feature in square kilometers based on Albers Equal Area projection. Double True       Computed.
Elevation The vertical distance from a given datum. Double True   ElevationRange   Stage of the water elevation is encoded in the FCode.
FCode Feature Code. Numeric value that encodes a set of characteristics for a type of feature. This five-digit code has two parts: the first three digits encode the feature type (FType); the last two digits encode values for a unique set of characteristics associated with the feature type. The set of characteristics may be single valued or multi-valued. Long Integer True       default value varies, depending on feature
FDate Date of last feature modification. Date False 8      
FType Feature Type. Numeric value that encodes a type of feature, represented as a three-digit code. For further refinement of the feature type classification, see FCode. Long Integer False       default value varies, depending on feature
GNIS_ID A permanent, unique number assigned by the Geographic Names Information System (GNIS) to a geographic feature name for the sole purpose of uniquely identifying that name application as a record in any information system database, dataset, file, or document Text True 10     GNIS_ID = "null" if no name is associated with the feature. Removed from WBD as of version 2.3 schema.
GNIS_Name The Geographic Names Information System (GNIS) assigned proper name, specific term, or expression by which a particular geographic entity is known. Text True 65      
NHDPlusID NHDPlus HR Unique identifier of a NHDFlowline feature. Found in NHDPlus HR Only. Double True       This field only exists when NHD feature classes are brought into NHDPlus HR.
OBJECTID Internal feature or event number. OBJECTID False        
Permanent_Identifier A 40-character globally unique ID (GUID) value that uniquely identifies the occurrence of each feature or event in The National Map. Text False 40      
ReachCode Unique identifier. The first eight digits are the WBD_HUC8. The next six digits are randomly assigned, sequential numbers that are unique within a HUC8. Text True 14     Required for all NHDFlowlines. NHDWaterbody and NHDPoint feature classes allow reach codes, but do not require them.
Resolution Source resolution. Long Integer False   Resolution   Currently NHD is available as separate resolutions.Domain values:Local > 1:12,000High 1:24,000/12,000Medium 1:100,000
Shape Feature geometry. Geometry True        
Shape_Area Area of feature in map units squared. Double True        
Shape_Length Length of the feature, which may differ from the field measured length due to differences in calculation. Units are map units. Double True       All features should have a positive integer value.
VisibilityFilter Allows for filtering of features for usage of vector data at approximate scales. Long Integer False   VisibilityFilter    
VPUID Vector Processing Unit Identifier. Found in NHDPlus HR only. Text True 8     This field only exists when NHD feature classes are brought into NHDPlus HR.

SubTypes of NHDWaterbody

SubType Description Definition
361 Playa Flat area at the lowest part of an undrained desert basin, generally devoid of vegetation.
378 Ice Mass Field of ice, formed in regions of perennial frost.
390 LakePond Standing body of water with a predominantly natural shoreline surrounded by land.
436 Reservoir Constructed basin formed to contain water or other liquids.
466 SwampMarsh Noncultivated, vegetated area that is inundated or saturated for a significant part of the year. The vegetation is adapted for life in saturated soil conditions.
493 Estuary Lower end of a river, or a semi-enclosed coastal body of water with access to the open ocean, which is affected by the tides and where fresh and salt water mix.

 

NHDLine : NHDLines Represent Linear NHD Hydrographic Landmark Features Used For Cartographic Representation.

Name Definition Type Allow Nulls Length Domain Default Value Comments
FCode Feature Code. Numeric value that encodes a set of characteristics for a type of feature. This five-digit code has two parts: the first three digits encode the feature type (FType); the last two digits encode values for a unique set of characteristics associated with the feature type. The set of characteristics may be single valued or multi-valued. Long Integer True       default value varies, depending on feature
FDate Date of last feature modification. Date False 8      
FType Feature Type. Numeric value that encodes a type of feature, represented as a three-digit code. For further refinement of the feature type classification, see FCode. Long Integer False       default value varies, depending on feature
GNIS_ID A permanent, unique number assigned by the Geographic Names Information System (GNIS) to a geographic feature name for the sole purpose of uniquely identifying that name application as a record in any information system database, dataset, file, or document Text True 10     GNIS_ID = "null" if no name is associated with the feature. Removed from WBD as of version 2.3 schema.
GNIS_Name The Geographic Names Information System (GNIS) assigned proper name, specific term, or expression by which a particular geographic entity is known. Text True 65      
LengthKM Length of linear feature. Value is computed when data are in Albers Equal Area projection. Double True       Computed
NHDPlusID NHDPlus HR Unique identifier of a NHDFlowline feature. Found in NHDPlus HR Only. Double True       This field only exists when NHD feature classes are brought into NHDPlus HR.
OBJECTID Internal feature or event number. OBJECTID False        
Permanent_Identifier A 40-character globally unique ID (GUID) value that uniquely identifies the occurrence of each feature or event in The National Map. Text False 40      
Resolution Source resolution. Long Integer False   Resolution   Currently NHD is available as separate resolutions.Domain values:Local > 1:12,000High 1:24,000/12,000Medium 1:100,000
Shape Feature geometry. Geometry True        
Shape_Length Length of the feature, which may differ from the field measured length due to differences in calculation. Units are map units. Double True       All features should have a positive integer value.
VisibilityFilter Allows for filtering of features for usage of vector data at approximate scales. Long Integer False   VisibilityFilter    
VPUID Vector Processing Unit Identifier. Found in NHDPlus HR only. Text True 8     This field only exists when NHD feature classes are brought into NHDPlus HR.

SubTypes of NHDLine

SubType Description Definition
318 Bridge Structure spanning and providing passage over a waterway, railroad, or other obstacle.
343 DamWeir Barrier constructed to control the flow or raise the level of water.
362 Flume Open, inclined, artificial channel constructed of wood, metal, or concrete; generally elevated.
369 Gate Structure that may be swung, drawn, or lowered, to block an entrance or passageway.
398 Lock Chamber Enclosure on a waterway used to raise/lower vessels as they pass from one level to another.
411 Nonearthen Shore Structure built of stone, concrete, or other building material, that borders a body of water.
434 Reef Chain of rocks or coral at, or near, the surface of water.
450 SinkRise Place at which a stream disappears underground or reappears at the surface in a karst area.
478 Tunnel Underground or underwater passage.
483 Wall Upright structure of masonry, wood, plaster, or other building material serving to enclose, divide, or protect an area.
487 Waterfall Vertical or near vertical descent of water over a step or ledge in the bed of a river.
503 Sounding Datum Line Line representing the tidal datum to which bathymetric contours are referenced.
568 Levee A natural or manmade embankment along the edge of a stream/river, canal/ditch, or waterbody, that protects the surrounding land from flooding.

NHDPoint : NHDPoints Contain Points Representing NHD Hydrographic Landmark Features.

Name Definition Type Allow Nulls Length Domain Default Value Comments
FCode Feature Code. Numeric value that encodes a set of characteristics for a type of feature. This five-digit code has two parts: the first three digits encode the feature type (FType); the last two digits encode values for a unique set of characteristics associated with the feature type. The set of characteristics may be single valued or multi-valued. Long Integer True       default value varies, depending on feature
FDate Date of last feature modification. Date False 8      
FType Feature Type. Numeric value that encodes a type of feature, represented as a three-digit code. For further refinement of the feature type classification, see FCode. Long Integer False       default value varies, depending on feature
GNIS_ID A permanent, unique number assigned by the Geographic Names Information System (GNIS) to a geographic feature name for the sole purpose of uniquely identifying that name application as a record in any information system database, dataset, file, or document Text True 10     GNIS_ID = "null" if no name is associated with the feature. Removed from WBD as of version 2.3 schema.
GNIS_Name The Geographic Names Information System (GNIS) assigned proper name, specific term, or expression by which a particular geographic entity is known. Text True 65      
NHDPlusID NHDPlus HR Unique identifier of a NHDFlowline feature. Found in NHDPlus HR Only. Double True       This field only exists when NHD feature classes are brought into NHDPlus HR.
OBJECTID Internal feature or event number. OBJECTID False        
Permanent_Identifier A 40-character globally unique ID (GUID) value that uniquely identifies the occurrence of each feature or event in The National Map. Text False 40      
ReachCode Unique identifier. The first eight digits are the WBD_HUC8. The next six digits are randomly assigned, sequential numbers that are unique within a HUC8. Text True 14     Required for all NHDFlowlines. NHDWaterbody and NHDPoint feature classes allow reach codes, but do not require them.
Resolution Source resolution. Long Integer False   Resolution   Currently NHD is available as separate resolutions.Domain values:Local > 1:12,000High 1:24,000/12,000Medium 1:100,000
Shape Feature geometry. Geometry True        
VPUID Vector Processing Unit Identifier. Found in NHDPlus HR only. Text True 8     This field only exists when NHD feature classes are brought into NHDPlus HR.

SubTypes of NHDPoint

SubType Description Definition
343 DamWeir Barrier constructed to control the flow or raise the level of water.
367 Gaging Station Structure used to measure the characteristics of a hydrographic feature.
369 Gate Structure that may be swung, drawn, or lowered, to block an entrance or passageway.
398 Lock Chamber Enclosure on a waterway used to raise/lower vessels as they pass from one level to another.
431 Rapids Area of swift current in a stream or river, characterized by standing waves or by boulders and rocks.
436 Reservoir Constructed basin formed to contain water or other liquids.
441 Rock Concreted mass of stony material.
450 SinkRise Place at which a stream disappears underground or reappears at the surface in a karst area.
458 SpringSeep Place where water issues from the ground naturally.
485 Water IntakeOutflow Structure through which water enters or exits a conduit.
487 Waterfall Vertical or near vertical descent of water over a step or ledge in the bed of a river.
488 Well Pit or hole, dug or bored into the earth for the extraction of water or other fluids, or gases.

NHDPointEventFC : Point Events Are Tied To A Specific Location On A Stream Network By A Reachcode And A Measure. While Several Types Of Point Events Are Accepted Back Into The National Database, Additional Point Event Types May Be Used On An Individual Basis.

Name Definition Type Allow Nulls Length Domain Default Value Comments
EventDate Date an event was created or modified. Date True 8      
EventOffset Distance from the network to be used to display event. Double True       Negative offsets display the event to the left of the network and positive offsets display the event to the right of the line. Offsets are useful for displaying overlapping events.
EventType Type of feature reference as an event. Long Integer False   Point Event Type    
FeatureClassRef NHD feature class that holds FeatureComID. Long Integer True        
FeatureDetailURL URL where detailed event entity data can be found. Text True 255      
Feature_Permanent_Identifier Permanent_Identifier of NHD feature that the event is referenced to. Text False 40      
Measure Measure along the reach, in percent from downstream end, where a point event is located. Double False        
OBJECTID Internal feature or event number. OBJECTID False        
Permanent_Identifier A 40-character globally unique ID (GUID) value that uniquely identifies the occurrence of each feature or event in The National Map. Text False 40      
ReachCode

Unique identifier. The first eight digits are the WBD_HUC8. The next six digits are randomly assigned, sequential numbers that are unique within a HUC8.

 Text True 14     For event feature classes, this value is the ReachCode on which the event is located.
ReachResolution Source resolution. Long Integer False       Currently NHD is available as separate resolutions. Domain of values:Local > 1:12,000High 1:24,000/12,000Medium: 1:100,000
ReachSMDate Reach spatial modification date. Date True 8    

The ReachCodeMaintenance table is updated by the NHD Update Tool. When a geometric edit is performed on a feature that contains a ReachCode (NHDFlowline or NHDWaterbody), the NHDReachCodeMaintenance table is updated to the current date to reflect the last spatial modification (SM) date

of the associated ReachCode. Any previous records for that Resolution (Medium or High, depending on the target feature class resolution) are overwritten. The Permanent_Identifier field is unique to this table and is not related to NHDFlowline or Waterbody features. The GNIS_ID and GNIS_Name

are updated, as these are unique per ReachCode. MValue updates are not considered spatial modifications and thus do not trigger ReachSMDate updates. For events (NHDPointEvent, NHDLineEvent, NHDAreaEvent), when an event is created by the Hydrography Event Management (HEM) Tool, the

tool pulls the current ReachSMDate from the ReachCodeMaintenance table for the ReachCode the event is associated with. So, if underlying hydrography features are updated, and events are not, the ReachSMDate in the event table will be out of date in relation to the current hydrography. Users can

either synchronize their events using the HEM Tool or they may not, depending on their needs. For example, a user may not want to synchronize their events to the current hydrography if a study was performed on a certain version of the NHD.
Shape Feature geometry. Geometry True        
Source_DataDesc Brief narrative of the source dataset. Text True 100      
Source_FeatureID Identifier of the feature or event in the source dataset. Text True 100      
Source_Originator Name of the organization or individual that developed the source dataset. Text True 130    

 

NHDLineEventFC : Linear Events Are Used To Attach Information About A Flowline Segment To The NHD. Linear Events Are Built Into The NHD Model But Are Not Accepted Back Into The National Database. They Are Meant To Be Used On An Individual Basis. They Also Need A From And To Location And A Reachcode.

Name Definition Type Allow Nulls Length Domain Default Value Comments
EventDate Date an event was created or modified. Date True 8      
EventOffset Distance from the network to be used to display event. Double True       Negative offsets display the event to the left of the network and positive offsets display the event to the right of the line. Offsets are useful for displaying overlapping events.
EventType Type of feature reference as an event. Long Integer False   Line Event Type    
FeatureClassRef NHD feature class that holds FeatureComID. Long Integer True        
FeatureDetailURL URL where detailed event entity data can be found. Text True 255      
Feature_Permanent_Identifier Permanent_Identifier of NHD feature that the event is referenced to. Text False 40      
FMeasure Measure along the reach, in percent from downstream end, where a linear event begins (from). Double False        
OBJECTID Internal feature or event number. OBJECTID False        
Permanent_Identifier A 40-character globally unique ID (GUID) value that uniquely identifies the occurrence of each feature or event in The National Map. Text False 40      
ReachCode Unique identifier. The first eight digits are the WBD_HUC8. The next six digits are randomly assigned, sequential numbers that are unique within a HUC8. Text True 14     For event feature classes, this value is the ReachCode on which the event is located.
ReachResolution Source resolution. Long Integer False       Currently NHD is available as separate resolutions. Domain of values:Local > 1:12,000High 1:24,000/12,000Medium: 1:100,000
ReachSMDate Reach spatial modification date. Date True 8    

The ReachCodeMaintenance table is updated by the NHD Update Tool. When a geometric edit is performed on a feature that contains a ReachCode (NHDFlowline or NHDWaterbody), the NHDReachCodeMaintenance table is updated to the current date to reflect the last spatial modification (SM)

date of the associated ReachCode. Any previous records for that Resolution (Medium or High, depending on the target feature class resolution) are overwritten. The Permanent_Identifier field is unique to this table and is not related to NHDFlowline or Waterbody features. The

GNIS_ID and GNIS_Name are updated, as these are unique per ReachCode. MValue updates are not considered spatial modifications and thus do not trigger ReachSMDate updates. For events (NHDPointEvent, NHDLineEvent, NHDAreaEvent), when an event is created by the Hydrography

Event Management (HEM) Tool, the tool pulls the current ReachSMDate from the ReachCodeMaintenance table for the ReachCode the event is associated with. So, if underlying hydrography features are updated, and events are not, the ReachSMDate in the event table will be out of date in relation to the current hydrography. Users can either synchronize their events using the HEM Tool or they may not, depending on their needs. For example, a user may not want to synchronize their events to the current hydrography if a study was performed on a certain version of the NHD.
Shape Feature geometry. Geometry True        
Shape_Length Length of the feature, which may differ from the field measured length due to differences in calculation. Units are map units. Double True       All features should have a positive integer value.
Source_DataDesc Brief narrative of the source dataset. Text True 100      
Source_FeatureID Identifier of the feature or event in the source dataset. Text True 100      
Source_Originator Name of the organization or individual that developed the source dataset. Text True 130      
TMeasure Measure along the reach, in percent from downstream end, where a linear event ends (to). Double False      

 

NHDAreaEventFC : Area Event Must Be Tied To A NHDWaterbody. They Cannot Be Linked To A Linear Feature Or Point Feature. Area Events Are Built Into The NHD Model But Are Not Accepted Back Into The National Database. They Are Meant To Be Used On An Individual Basis.

Name Definition Type Allow Nulls Length Domain Default Value Comments
EventDate Date an event was created or modified. Date True 8      
EventType Type of feature reference as an event. Long Integer False   Area Event Type Domain    
FeatureClassRef NHD feature class that holds FeatureComID. Long Integer True        
FeatureDetailURL URL where detailed event entity data can be found. Text True 255      
Feature_Permanent_Identifier Permanent_Identifier of NHD feature that the event is referenced to. Text False 40      
OBJECTID Internal feature or event number. OBJECTID False        
Permanent_Identifier A 40-character globally unique ID (GUID) value that uniquely identifies the occurrence of each feature or event in The National Map. Text False 40      
ReachCode Unique identifier. The first eight digits are the WBD_HUC8. The next six digits are randomly assigned, sequential numbers that are unique within a HUC8. Text True 14     For event feature classes, this value is the ReachCode on which the event is located.
ReachResolution Source resolution. Long Integer False       Currently NHD is available as separate resolutions. Domain of values:Local > 1:12,000High 1:24,000/12,000Medium: 1:100,000
ReachSMDate Reach spatial modification date. Date True 8    

The ReachCodeMaintenance table is updated by the NHD Update Tool. When a geometric edit is performed on a feature that contains

a ReachCode (NHDFlowline or NHDWaterbody), the NHDReachCodeMaintenance table is updated to the current date to reflect the

last spatial modification (SM) date of the associated ReachCode. Any previous records for that Resolution (Medium or High,

depending on the target feature class resolution) are overwritten. The Permanent_Identifier field is unique to this table and

is not related to NHDFlowline or Waterbody features. The GNIS_ID and GNIS_Name are updated, as these are unique per

ReachCode. MValue updates are not considered spatial modifications and thus do not trigger ReachSMDate updates. For events

(NHDPointEvent, NHDLineEvent, NHDAreaEvent), when an event is created by the Hydrography Event Management (HEM) Tool,

the tool pulls the current ReachSMDate from the ReachCodeMaintenance table for the ReachCode the event is associated with. So,

if underlying hydrography features are updated, and events are not, the ReachSMDate in the event table will be out of date in

relation to the current hydrography. Users can either synchronize their events using the HEM Tool or they may not, depending on

their needs. For example, a user may not want to synchronize their events to the current hydrography if a study was performed on

a certain version of the NHD.
Shape Feature geometry. Geometry True        
Shape_Area Area of feature in map units squared. Double True        
Shape_Length Length of the feature, which may differ from the field measured length due to differences in calculation. Units are map units. Double True       All features should have a positive integer value.
Source_DataDesc Brief narrative of the source dataset. Text True 100      
Source_FeatureID Identifier of the feature or event in the source dataset. Text True 100      
Source_Originator Name of the organization or individual that developed the source dataset. Text True 130