NHDPlus 

User Guide

September 1, 2010 
NHDPlus User Guide September 1, 2010 

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NHDPlus User Guide ii September 1, 2010 

This guide is intended for use with the following NHDPlus schema versions. 

NHDPlus Component Schema Version 

Catchment Grid 01 

Catchment Shape 01 

Catchment Flowline Attributes 01 

Elevation Grid 01 

Flow Accumulation & Direction Grids 01 

NHD 01 

Stream Gage Events 01 
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NHDPlus User Guide iv September 1, 2010 

Table of Contents 

Acknowledgments.................................................................................................................... viii

Chapter 1 Introduction to NHDPlus .......................................................................................... 1

Data Package Content and Directory Structure .......................................................................... 3

NHDPlus Schema ....................................................................................................................... 5

Projection Information ................................................................................................................ 7

NHDPlus Versioning System ..................................................................................................... 9

Chapter 2 Feature Class Descriptions ...................................................................................... 13

Chapter 3 Attribute Table Descriptions ................................................................................... 24

Chapter 4 Geographic Coverage of Data Package .................................................................. 39

Chapter 5 Understanding and Using NHDPlus ....................................................................... 41

NHDPlus and Divergences ....................................................................................................... 41

Generating Less Dense Networks from NHDFlowline ............................................................ 44

Understanding NHDPlus Slope ................................................................................................ 44

Finding the Upstream Inflows to an NHDPlus Dataset ............................................................ 45

Finding all the Tributaries to a Stretch of River ....................................................................... 45

Building an NHDPlus Attribute Accumulator .......................................................................... 46

Flowlines with "known flow" vs. Flowlines with “unknown flow” ......................................... 47

Main flowline network vs. isolated networks ........................................................................... 48

Disagreements Between the Flow Accumulation Grid and NHD isolated Networks .............. 50

Why does the Identify tool in ArcMap say that the value and ComID from the cat grid are 

different from the Grid_code and ComID shown in the Catchment shapefile? ....................... 51

Why would drainage areas computed using upstream navigation differ from the cumulative 

drainage areas pre-computed in the NHDPlus? ........................................................................ 52

What is the situation with names assigned to artificial paths inside lake/pond waterbodies? .. 52

Difficulties using NHDPlus Attribute .dbfs in Microsoft Access ............................................. 52

Using the NHDPlus Value Added Attributes (VAAs) for Non-Navigation Tasks .................. 53

Appendix A – Process Descriptions for NHDPlus ................................................................... 65

Appendix B – Data Dictionary ............................................................................................... 101

Appendix C.1 – NLCD Land Cover Classification System Key ............................................ 109

Appendix C.2 – NOAA C-CAP Land Cover Classification System Key .............................. 112

References ............................................................................................................................... 113

Footnotes ................................................................................................................................. 115
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List of Figures 

Figure 1-1 – NHDPlus Schema....................................................................................................... 5

Figure 4-1 – NHDPlus Hydrologic Regions and Production Unit Map ....................................... 39

Figure 5-1 – NHDPlus Complex Hydrography ............................................................................ 41

Figure 5-2 – Main and Minor Paths in NHDPlus ......................................................................... 42

Figure 5-3 – “Local” Divergences ................................................................................................ 42

Figure 5-4 – More Complex Divergent Junction Example ........................................................... 43

Figure 5-5 – Cumulative attributes routed down the main path ................................................... 44

Figure 5-6 – NHD Flowlines With Known and Unknown Flow Direction .................................. 48

Figure 5-7 – Non-contributing Isolated Networks Teal lines are the terminal segments of these 

isolated networks. The straight lines are USGS 7.5-minute quadrangle boundaries .................... 48

Figure 5-8 – Map error The cross-hairs are the edges of USGS quad maps. ............................... 50

Figure 5-9 – Uncommon problem between the NHDPlus network and the flow accumulation grid

....................................................................................................................................................... 51

Figure 5-10 – ThinnerCod = 0 ...................................................................................................... 54

Figure 5-11 – ThinnerCod = 1 ...................................................................................................... 55

Figure 5-12 – ThinnerCod = 1 or 2 ............................................................................................... 56

Figure 5-13 – Streams Greater than or Equal to 100 Kilometers in Length ................................. 57

Figure 5-14 – The Mainstem of the Potomac River By Selecting LevelPathi=9169600001 ....... 58

Figure 5-15 – The Potomac River Basin By Selecting TerminalPA = 9169600001 .................... 59

Figure 5-16 – Profile Plot of the Mainstem Potomac River “MinElevSmo” values .................... 60

Figure 5-17 – Stream Orders in a Part of the Midatlantic Region ................................................ 61

Figure 5-18 – Stream Orders in a Part of the Midatlantic Region with Order 1 Streams Removed

....................................................................................................................................................... 62

Figure 5-19 – StreamLevel Values at a flowline Junction ............................................................ 63

Figure A-1 – (a) Differences in drainage between the NHD and flow paths of a NED-derived 

stream, (b) Resultant NHD catchment delineations using unmodified NED DEM data, and (c) 

Resultant NHD catchment delineations using AGREE-modified NED data. .............................. 73

Figure A-2 – Schematic of AGREE process................................................................................. 74

Figure A-3 – 3-D Perspective view of modified DEM with walling of existing Watershed 

boundaries and burning of NHD streams ...................................................................................... 75

Figure A-4 – Illustration showing multiple polygon features defining a catchment area for a 

flowline ......................................................................................................................................... 77

Figure A-5 – Illustration comparing the horizontal displacement between the NHD streams of an 

isolated network (in blue) to the synthetic streams of the “filled” HydroDEM ........................... 79

Figure A-6 – Assigning Minimum and Maximum Stream Channel Elevations to NHD Flowlines

....................................................................................................................................................... 81

Figure A-7 – Example of an international catchment on the Canadian border ............................ 82

Figure A-8 – Stream Gages in Region 21 ..................................................................................... 82

Figure A-9 – Average Unit Runoff on Puerto Rico Mainland...................................................... 82

Figure A-10 – Digitized Mean Annual Runoff Values On Puerto Rico Mainland ...................... 82

Figure A-11 – Results of using TopoGrid to Develop an Interpolated Raster Grid of Mean 

Annual Runoff .............................................................................................................................. 92

Figure A-12 – Downstream Elevation Smoothing ........................................................................ 99

Figure A-13 – Upstream Elevation Smoothing ............................................................................ 99
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Figure A-14 – Hybrid Elevation Smoothing ............................................................................... 100
NHDPlus User Guide viii September 1, 2010 

Acknowledgments 

NHDPlus is the result of considerable efforts by many organizations and individuals over time. 

The initial goal of estimating flow volume and velocity for the National Hydrography Dataset 

(NHD) led us to integrating the NHD with the National Elevation Dataset and the Watershed 

Boundary Dataset to determine stream segment catchments and their associated drainage areas. 

This integration made possible many additional geospatial data products found in NHDPlus. We 

expect that the resulting suite of geospatial products will become a valued data source for the 

water resources community. A special thank you goes to the primary contributors to the 

NHDPlus development effort who are listed below. 

Tommy Dewald, Project Manager, EPA Office of Water 

The NHDPlus Team 

Tim Bondelid – Independent Consultant (under contract to EPA) 

Craig Johnston – U.S. Geological Survey (USGS) 

Cindy McKay – Horizon Systems Corporation (under contract to EPA) 

Rich Moore – U.S. Geological Survey (USGS) 

Alan Rea – U.S. Geological Survey (USGS) 

Other Participants in the Initial NHD Catchment Development Evaluation 

Jon Goodall – University of Texas at Austin (UT) 

Sue Greenlee – U.S. Geological Survey (USGS) 

David Maidment – University of Texas at Austin (UT)

Greg Schwarz – U.S. Geological Survey (USGS) 

Pete Steeves – U.S. Geological Survey (USGS) 

Kris Verdin – Hughes STX (under contract to USGS) 

Bruce Worstell – Hughes STX (under contract to USGS) 
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NHDPlus User Guide 1 September 1, 2010 

Chapter 1 Introduction to NHDPlus 

NHDPlus is an integrated suite of application-ready geospatial data products, incorporating many 

of the best features of the National Hydrography Dataset (NHD), the National Elevation Dataset 

(NED), and the National Watershed Boundary Dataset (WBD). NHDPlus includes a stream 

network based on the medium resolution NHD (1:100,000 scale), improved networking, feature 

naming, and “value-added attributes” (VAA). NHDPlus also includes elevation-derived 

catchments produced using a drainage enforcement technique first broadly applied in New 

England, and thus dubbed “The New-England Method.” This technique involves enforcing the 

1:100,000-scale NHD drainage network by modifying the NED elevations to fit with the network 

via trenching and using the WBD, where certified WBD is available, to enforce hydrologic 

divides. The resulting modified digital elevation model (DEM) was used to produce hydrologic 

derivatives that closely agree with the NHD and WBD. An interdisciplinary team from the U.S. 

Geological Survey (USGS) and the U.S. Environmental Protection Agency (EPA) found this 

method to produce the best-quality agreement among the ingredient datasets among the various 

methods tested. 

The VAAs include greatly enhanced capabilities for upstream and downstream navigation, 

analysis, and modeling. Examples include rapidly retrieving all flowlines and catchments 

upstream of a given flowline, using structured queries rather than slower traditional flowline-byflowline navigation; subsetting a stream level path sorted in hydrologic order for stream profile 

mapping, analysis, and plotting; and calculating cumulative catchment attributes using 

streamlined VAA hydrologic sequencing routing attributes. VAA-based routing techniques were 

used to produce the NHDPlus cumulative drainage areas and land cover, temperature, and 

precipitation distributions. These cumulative attributes are used to estimate mean annual flow 

and velocity. 

NHDPlus contains a static copy of the 1:100,000 scale NHD that has been extensively improved. 

While these updates will eventually make their way back to the central USGS NHD repository, 

this will not happen prior to distribution of NHDPlus because the update process for the central 

NHD database at USGS was under development at the time these improvements were being 

made. Consequently, NHDPlus will contain some temporary database keys. As a result, 

NHDPlus users may not make additional updates to the NHD portions of NHDPlus with the 

intent of sending these updates back to the central NHD database. Once the NHDPlus updates 

have been posted to the central NHD database, a fresh copy of the improved data can be pulled 

from the NHD Web site (http://nhdgeo.usgs.gov) and that copy will be usable for data 

maintenance. 

The geospatial datasets included in NHDPlus already have been used in an application to 

develop estimates of mean annual streamflow and velocity for each NHD Flowline in the 

conterminous United States. The results of these analyses are included with the NHDPlus data. 

EPA and USGS have already linked numerous water quality databases to the underlying NHD by 

assigning NHD stream (Reach) addresses to these entities, which include gaging stations, water 

quality monitoring sites, and impaired waters, enabling them to be queried and analyzed in 
NHDPlus User Guide 2 September 1, 2010 

up/downstream order. The USGS gaging stations and associated data that were used to validate 

the NHDPlus flow volume and velocity estimates are included with the NHDPlus data. Figure 

1-1 illustrates the NHDPlus Schema. 

Additional information, tools, exercises, training opportunities, news, and the latest NHDPlus 

data can be found at http://www.epa.gov/waters. 
NHDPlus User Guide 3 September 1, 2010 

Data Package Content and Directory Structure 

ProductionUnits (shapefile) 

\NHDPlusRR, where RR is the Hydrologic Region number 

 \drainage 

Cat (grid) 

 catchment (shapefile) 

\info (info tables for cat grid) 

\hydrography 

 nhdflowline (shapefile) 

 nhdwaterbody (shapefile) 

 nhdpoint (shapefile) 

 nhdline (shapefile) 

 nhdarea (shapefile) 

\hydrologicunits 

 Basin (empty placeholder1

 shapefile) 

 Region (empty placeholder shapefile) 

 Subbasin (shapefile) 

 Subregion (empty placeholder shapefile) 

 Subwatershed (empty placeholder shapefile) 

 Watershed (empty placeholder shapefile) 

 \elev_unit_a (elevation grids for production unit a) 

 elev_cm (grid) 

 \info (info tables for grids in unit_a) 

(elevation grids for additional production units) 

 \fac_fdr_unit_a (fac and fdr grids for production unit a) 

 fac (grid) 

 fdr (grid) 

 \info (info tables for grids in unit_a) 

(fac and fdr grids for additional production units)

catchmentattributesNLCD (dBase file) 

 catchmentattributesTempPrecip (dBase file) 

flowlineattributesFlow (dBase file) 

flowlineattributesNLCD (dBase file) 

flowlineattributesTempPrecip (dBase file) 

headwaternodearea (dBase file) 

NHDFcode (dBase file) 

NHDFeatureToMetadata (dBase file) 

NHDFlow (dBase file) 

NHDFlowlineVAA (dBase file) 
NHDPlus User Guide 4 September 1, 2010 

NHDHydroLineEvent (empty placeholder dBase file) 

NHDHydroPointEvent (empty placeholder dBase file) 

NHDMetadata (dBase file) 

NHDProcessingParameters (empty placeholder dBase file) 

NHDReachCode_Comid (empty placeholder dBase file) 

NHDReachCrossReference (dBase file) 

NHDSourceCitation (dBase file) 

NHDStatus (empty placeholder dBase File) 

NHDVerticalRelationship (dBase file) 

openme.txt (text) 

StreamGageEvent (shapefile) 

Figure 1-1 contains a schema diagram of the NHDPlus. The feature classes and tables contained 

in the grey area are the standard NHD content. The feature classes and tables outside of the grey 

area are the components added during the building of NHDPlus. 
NHDPlus User Guide 5 

NHDPlus Schema Figure 1-1 – NHDPlus Schema 
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NHDPlus User Guide 7 September 1, 2010 

Projection Information 

All geospatial datasets are stored in one of three projections/coordinate systems. 

All vector data in shapefile format use the following projection/coordinate system: 

Projection GEOGRAPHIC 

Datum NAD83 

Zunits NO 

Units DD 

Spheroid GRS1980 

Xshift 0.0000000000 

Yshift 0.0000000000 

All grid datasets (cat, fac, fdr, elev_cm) for the conterminous U.S. are stored in an Albers EqualArea projection: 

Projection ALBERS 

Datum NAD83 

Zunits NO2

 

Units METERS 

Spheroid GRS1980 

Xshift 0.0000000000 

Yshift 0.0000000000 

Parameters 

29 30 0.000 /* 1st standard parallel 

45 30 0.000 /* 2nd standard parallel 

-96 0 0.000 /* central meridian 

23 0 0.000 /* latitude of projection’s origin 

0.00000 /* false easting (meters) 

0.00000 /* false northing (meters) 

Grid datasets (cat, fac, fdr, elev_cm) for Hawaii (hydrologic region 20) are stored in the 

Universal Transverse Mercator (UTM) projection: 

Projection UTM 

Zone 4 

Datum NAD83 

Zunits NO2

Units Meters 

Spheroid GRS1980 

Xshift 0.0000000000 

Yshift 0.0000000000 
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Grid datasets (cat, fac, fdr, elev_cm) for Puerto Rico and the US Virgin Islands (hydrologic 

region 21) are stored in the Lambert projection: 

Projection LAMBERT 

Datum NAD83 

Zunits NO2

Units Meters 

Spheroid GRS1980 

Xshift 0.0000000000 

Yshift 0.0000000000 
NHDPlus User Guide 9 September 1, 2010 

NHDPlus Versioning System 

NHDPlus has a dual versioning system; both the data model schema and the data content are 

versioned. NHDPlus download .ZIP files each contain the version information in the filename in 

the form of "Vss_cc", where “ss” is the schema version and “cc” is the data content version. 

Each component can be versioned and distributed without the need to re-release all components. 

For example, at any given time, both NHDPlus10LV02_03_CatShape.zip and 

NHDPlus10LV01_02_NHD.zip might be available for download. In this example, the 

Catchment shape file has schema version 02 and data content version 03 while the NHD 

component has schema version 01 and data content version 02. 

The NHDPlus download site will contain the most recent version for each component. When a 

change in NHDPlus affects more than one component, the new version of all affected 

components will be made available at the same time. Therefore, users can be assured that all 

components on the download site, regardless of their indicated versions, are compatible with 

each other. 

In order to be able to determine which version has been uncompressed onto your computer, the 

.ZIP files contain a .TXT file with the same name as the .ZIP file. For example, 

NHDPlus08V01_02_NHD.zip will contain a file called NHDPlus08V01_02_NHD.txt. The file 

you are reading is one such file. 

When NHDPlus .ZIP files are uncompressed, the version text files are stored in the upper level 

directory of the NHDPlus data. The existence of these .TXT files on your computer means that 

you, at one time, installed the indicated versions of the indicated NHDPlus components. For 

example, the presence of the file named NHDPlus08V01_02_NHD.txt means that you have 

installed Version V01_02 of the NHD component for hydrologic region 08. 

If you retain these .TXT files and uncompress updates into the same location, these files will not 

be overwritten and will serve as a history of what NHDPlus components and versions you have 

installed. 

When you download a current version of an NHDPlus component and wish to replace a 

previously installed version, you must first delete the existing version of the component from 

your computer. This is best done with ArcCatalog, but may also be accomplished using 

Windows Explorer. Once you have deleted the component, use the instructions in the NHDPlus 

User Guide for unpacking the new version of the component. 

Instructions for deleting with ArcCatalog: 

Component Delete

CatGrid \NHDPlusrr\Drainage\cat 

CatShape \NHDPlusrr\Drainage\catchment

Cat_Flowline_Attr \NHDPlusrr\catchmentattributesnlcd 

 \NHDPlusrr\catchmentattributestempprecip 
NHDPlus User Guide 10 September 1, 2010 

 \NHDPlusrr\flowlineattributesflow 

 \NHDPlusrr\flowlineattributesnlcd 

 \NHDPlusrr\flowlineattributestempprecip 

 \NHDPlusrr\headwaternodearea 

Elev_Unit_x \NHDPlusrr\elev_unit_x 

FAC_FDR_Unit_x \NHDPlusrr\fac_fdr_unit_x 

NHD \NHDPlusrr\Hydrography 

\NHDPlusrr\HydrologicUnits 

 \NHDPlusrr\NHDFcode 

 \NHDPlusrr\NHDFeatureToMetadata 

 \NHDPlusrr\NHDFlow 

 \NHDPlusrr\NHDFlowlineVAA 

 \NHDPlusrr\NHDHydroLineEvent

 \NHDPlusrr\NHDHydroPointEvent 

 \NHDPlusrr\NHDMetadata 

 \NHDPlusrr\NHDProcessingParameters 

 \NHDPlusrr\NHDReachCode_Comid 

 \NHDPlusrr\NHDReachCrossReference 

 \NHDPlusrr\NHDStatus 

 \NHDPlusrr\NHDVerticalRelationship 

 \NHDPlusrr\TNavwork 

 \NHDPlusrr\TNavigation_Events_table 

 \NHDPlusrr\TNavigation_Events 

ProductionUnits \NHDPlus\ProductionUnits 

Instructions for deleting with Windows Explorer: 

Component Delete

CatGrid \NHDPlusrr\Drainage\cat 

 \NHDPlusrr\Drainage\info 

 \NHDPlusrr\Drainage\cat.* 

CatShape \NHDPlusrr\Drainage\catchment.* 

Cat_Flowline_Attr \NHDPlusrr\catchmentattributesnlcd.* 

 \NHDPlusrr\catchmentattributestempprecip.* 

 \NHDPlusrr\flowlineattributesflow.* 

 \NHDPlusrr\flowlineattributesnlcd.* 

 \NHDPlusrr\flowlineattributestempprecip.* 

 \NHDPlusrr\headwaternodearea.* 

Elev_Unit_x \NHDPlusrr\elev_unit_x 

FAC_FDR_Unit_x \NHDPlusrr\fac_fdr_unit_x 

NHD \NHDPlusrr\Hydrography 

 \NHDPlusrr\HydrologicUnits 

 \NHDPlusrr\NHDFcode.* 

 \NHDPlusrr\NHDFeatureToMetadata.* 

 \NHDPlusrr\NHDFlow.* 

 \NHDPlusrr\NHDFlowlineVAA.* 
NHDPlus User Guide 11 September 1, 2010 

 \NHDPlusrr\NHDHydroLineEvent.* 

 \NHDPlusrr\NHDHydroPointEvent.* 

 \NHDPlusrr\NHDMetadata.* 

 \NHDPlusrr\NHDProcessingParameters.* 

 \NHDPlusrr\NHDReachCode_Comid.* 

 \NHDPlusrr\NHDReachCrossReference.* 

 \NHDPlusrr\NHDStatus.* 

 \NHDPlusrr\NHDVerticalRelationship.* 

 \NHDPlusrr\TNav*.* 

ProductionUnits \NHDPlus\ProductionUnits 

NHDPlus documentation is versioned by the schema version only (see first page of guide). 

When you download a component containing a new schema version, you should also download 

new documentation. 
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NHDPlus User Guide 13 September 1, 2010 

Chapter 2 Feature Class Descriptions 

cat (catchment grid)

Description: An Environmental Systems Research Institute (ESRI) integer grid dataset that 

associates each cell with a catchment. 

Field Name Description 

Value The value stored in grid cells 

A unique identification number for each catchment 

(compressed numbering system) 

Also known as Grid_code in related tables 

Count Number of cells with a particular value in the Value field 

The count equals the number of 30x30 meter grid cells in each 

catchment 

ComID Common identifier of an NHD Flowline 

Prod_unit Production unit identifier 

Catchment (shapefile)

Description: Contains a catchment polygon for each NHD Flowline that received a catchment. 

Note: Some polygons may be multipart polygons. 

Field Name Description 

ComID Common Identifier of an NHD Flowline 

Grid_code The value stored in grid cells 

A unique identification number for each catchment 

(compressed numbering system) 

Grid_count Number of cells with a particular value in the value field 

The count equals the number of 30x30 meter grid cells in each 

catchment 

Catchment area can be computed from this field 

Prod_unit Production unit identifier 

AreaSqKm Feature area in square kilometers 
NHDPlus User Guide 14 September 1, 2010 

elev cm (elevation grid)

Description: An ESRI integer grid dataset that gives the elevation in centimeters (from the 

North American Vertical Datum of 1988). The elevation grid does not contain an associated 

value attribute table (VAT). The grid was derived from the 30-meter resolution NED and was 

projected into the national Albers projection. 

fac (flow accumulation grid)

Description: An ESRI integer grid dataset that counts the number of cells draining to each cell 

in the grid. The flow accumulation grid does not contain an associated VAT. 

fdr (flow direction grid)

Description: The values in this grid are codes indicating the direction water would flow from 

each grid cell. 

Field Name Description 

Value The value stored in grid cells. A grid cell can be assigned one of 

eight possible values: 

 1 – Flow is to the East 

 2 – Flow is to the Southeast 

 4 – Flow is to the South 

 8 – Flow is to the Southwest 

 16 – Flow is to the West 

 32 – Flow is to the Northwest 

 64 – Flow is to the North 

128 – Flow is to the Northeast 

Count Number of cells with a particular value in the Value field 
NHDPlus User Guide 15 September 1, 2010 

NHDFlowline (shapefile)3

Description: NHD linear features of types: stream/river, canal/ditch, pipeline, artificial path, 

coastline, and connector. 

Note: The edits made to these features during the building of NHDPlus will be loaded into the 

National NHD database at USGS sometime after NHDPlus is released. New flowlines, split 

flowlines, and merged flowlines have temporary ComIDs of the format 9nnnnnnnn. Permanent 

ComIDs will be assigned when the edits are processed by USGS. 

Field Name Description 

ComID Common identifier of the NHD feature 

FDate Feature Currency Date 

Resolution Always “Medium” (i.e., 1:100K scale) 

GNIS_ID Geographic Names Information System ID for the value in 

GNIS_Name 

GNIS_Name Feature Name from the Geographic Names Information System 

LengthKM Feature length in kilometers 

ReachCode Reach Code assigned to feature 

Flowdir Flow direction is “WithDigitized” or “Uninitialized” 

WBAreaComI ComID of an NHD polygonal water feature through which an 

NHD “Artificial Path” flowline flows 

FType NHD Feature Type 

FCode Numeric codes for various feature attributes in the NHDFCode 

lookup table 

Shape_Leng Feature length in decimal degrees 

Enabled Always “True” 
NHDPlus User Guide 16 September 1, 2010 

NHDWaterbody (shapefile) 3

Description: NHD polygonal features of types: Playa, Ice Mass, LakePond, Reservoir, 

SwampMarsh, and Estuary. 

Note: Some waterbody features in the National NHD database at USGS have been merged 

across quadline boundaries. Therefore, some waterbody features distributed with NHDPlus are 

slightly different from those in the National NHD database. However, after combining 

waterbody features by Reach Code in either the National NHD database or in NHDPlus, the 

waterbody Reaches derived should be the same. 

Field Name Description 

ComID Common identifier of the NHD feature 

FDate Feature Currency Date 

Resolution Always “Medium” (i.e., 1:100K scale) 

GNIS_ID Geographic Names Information System ID for the value in 

GNIS_Name 

GNIS_Name Feature Name from the Geographic Names Information System 

AreaSqKm Feature area in square kilometers 

Elevation Feature elevation in feet 

ReachCode Reach Code assigned to feature 

FType NHD Feature Type 

FCode Numeric code for various feature attributes; definitions for codes 

found in the NHDFCode lookup table 

Shape_Leng Feature length in decimal degrees 

Shape_Area Feature area in square decimal degrees 
NHDPlus User Guide 17 September 1, 2010 

NHDPoint (shapefile) 3

Description: NHD point features of types: Gate, Lock Chamber, Rapids, Reservoir, Rock, 

SinkRise, SpringSeep, Water IntakeOutflow, Waterfall, and Well. The National NHD database 

contains a small sample of gaging station features in NHDPoint. These have been deleted from 

NHDPlus and replaced with a separate shapefile of all active stream gages (see 

StreamGageEvent shapefile below). 

Field Name Description 

ComID Common identifier of the NHD feature 

FDate Feature Currency Date 

Resolution Always “Medium” (i.e., 1:100K scale) 

GNIS_ID Geographic Names Information System ID for the value in 

GNIS_Name 

GNIS_Name Feature Name from the Geographic Names Information System 

ReachCode Reach Code assigned to feature 

FType NHD Feature Type 

FCode Numeric code for various feature attributes; definitions for codes 

found in the NHDFCode lookup table 

NHDLine (shapefile) 3

Description: NHD linear features of types: Bridge, DamWeir, Flume, Gate, Lock Chamber, 

Nonearthen Shore, Rapids, Reef, SinkRise, Tunnel, Wall, Waterfall, Sounding Datum Line, and 

Special Use Zone Limit. 

Field Name Description 

ComID Common identifier of the NHD feature 

FDate Feature Currency Date 

Resolution Always “Medium” (i.e., 1:100K scale) 

GNIS_ID Geographic Names Information System ID for the value in 

GNIS_Name 

GNIS_Name Feature Name from the Geographic Names Information System 

LengthKM Feature length in kilometers 

FType NHD Feature Type 

FCode Numeric codes for various feature attributes; definitions for 

codes found in the NHDFCode lookup table 

Shape_Leng Feature length in decimal degrees 
NHDPlus User Guide 18 September 1, 2010 

NHDArea (shapefile) 3

Description: NHD polygonal features of types: Area to be Submerged, BayInlet, Bridge, 

CanalDitch, DamWeir, Flume, Foreshore, Hazard Zone, Lock Chamber, Inundation Area, 

Rapids, SeaOcean, Special Use Zone, Spillway, StreamRiver, Submerged Stream, Wash, Water 

IntakeOutflow, and Area of Complex Channels. 

Note: Some of these features in the National NHD database at USGS have been merged across 

quadline boundaries and split at Subbasin boundaries. Therefore, some area features distributed 

with NHDPlus are slightly different from those in the National NHD database. 

Field Name Description 

ComID Common identifier of the NHD feature 

FDate Feature Currency Date 

Resolution Always “Medium” (i.e., 1:100K scale) 

GNIS_ID Geographic Names Information System ID for the value in 

GNIS_Name 

GNIS_Name Feature Name from the Geographic Names Information System 

AreaSqKm Feature area in square kilometers 

Elevation Feature elevation in feet 

FType NHD Feature Type 

FCode Numeric codes for various feature attributes; definitions for 

codes found in the NHDFCode lookup table 

Shape_Leng Feature length in decimal degrees 

Shape_Area Feature area in square decimal degrees 
NHDPlus User Guide 19 September 1, 2010 

StreamGageEvent (shapefile)

Description: The StreamGageEvent shape file contains the physical locations of the USGS 

stream gages as well as their location on NHDFlowline features through events linked to reach 

codes and measures. More information can be found at: 

http://water.usgs.gov/GIS/metadata/usgswrd/XML/streamgages.xml and 

http://www.usbr.gov/pmts/hydraulics_lab/twahl/bfi/index.html. 

Field Name Description 

ComID Not populated 

EventDate Date event was created 

Reachcode Reachcode on which Stream Gage is located

ReachSMDat Reach Version Date – Not populated 

Reachresol Reach Resolution, always “Medium” (i.e., 1:100K scale) 

FeatureCom Reserved for future use 

FeatureCla Reserved for future use 

Source_ori Originator of Event 

Source_Dat Description of point entity 

Source_fea Gage Identifier/USGS Site Number 

Featuredet URL where detailed gage data can be found (NWISWEB) 

Measure Measure along reach where Stream Gage is located in percent 

from downstream end 

Offset Always zero 

EventType “StreamGage” 

Agency_cd Gov. Agency responsible for the Stream Gage 

Station_nm Station name 

State_cd 2 digit state FIPS code of the WSC maintaining the gage. Puerto 

Rico is listed as a state. 

State 2 character state postal abbreviation of the WSC maintaining the 

gage. Puerto Rico is listed as a state. 

Sitestatus Active (A) or Inactive (I) where active Stream Gage has 

streamflow data in water year(s) 2003 and/or 2004 

DA_SQ_Mile Reported drainage area in square miles. Stations with drainage 

area -999999 means there is no reported drainage area in the 

National Water Information System. 

Lon_site Longitude of the Stream Gage (site) location - gage house in 

decimal degrees, NAD83 

Lat_site Latitude of the Stream Gage (site) location - gage house in 

decimal degrees, NAD83 

Lon_NHD Longitude of the NHD location in decimal degrees, NAD83 

Lat_NHD Latitude of the NHD location in decimal degrees, NAD83 

NHD2Gage_d Distance between Stream Gage and NHD Reach 

Reviewed Flag to indicate location review status - Y or N 

BFIyrs Number of years used in the base-flow index computation 

BFI_Ave Average annual base-flow index value (fraction) 
NHDPlus User Guide 20 September 1, 2010 

Field Name Description 

BFI_Stdev Standard deviation of annual base-flow index (fraction) 

GotBFI Flag indicating BFI data (1) or no BFI data (2) 

Day1 First date of flow data (yyyymmdd) 

DayN Last date of flow data (yyyymmdd) 

NDays Number of days of flow data 

NDaysGT0 Number of days of non-zero flow 

MIN_ Minimum daily flow for the period of record (cubic feet per 

second) 

P1 1st percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P5 5th percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P10 10th percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P20 20th percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P25 25th percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P30 30th percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P40 40th percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P50 50th percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P60 60th percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P70 70th percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P75 75th percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P80 80th percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P90 90th percentile of daily flow for the period of record. Negative 
NHDPlus User Guide 21 September 1, 2010 

Field Name Description 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P95 95th percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

P99 99th percentile of daily flow for the period of record. Negative 

values indicate reverse flow; tidal or backwater. (cubic feet per 

second) 

Max_ Maximum daily flow for the period of record. (cubic feet per 

second) 

Ave Average daily flow for the period of record. (cubic feet per 

second) 

Stdev Standard deviation of daily flow for the period of record. (cubic 

feet per second) 

GOTQ Flag indicating flow data (1) or no flow data (0) 

HUC Hydrologic Cataloging Unit (8-digit HUC) of the Stream Gage 

HUC_Reg Hydrologic Region (2-digit HUC) of the Stream Gage 

Subregion Hydrologic sub-region (4-digit HUC) of the Stream Gage 

Accounting Hydrologic accounting unit (6-digit HUC) of the Stream Gage 

Subbasin (shapefile) 3

Description: Boundaries of 8-digit Hydrologic Units (HUC8) used to assign NHD 1:100,000-

scale Reach Codes. These HUC8 boundaries are a derivative of the 1:250,000-scale boundaries 

published by USGS in 1970. These boundaries are not compatible with the more recent 

Watershed Boundary Dataset. 

Field Name Description 

ObjectID Internal identifier 

Source Source of boundary: 

0 – Watershed Boundary Dataset 

1 – NHD 

2 – Other 

HUC_8 8-digit Hydrologic Unit Code, also known as Subbasin code 

(formerly known as Cataloging Unit code) 

HU_8_Name Text name of Subbasin 

Shape_Leng Feature length in decimal degrees 

Shape_Area Feature area in square decimal degrees 

Region (shapefile) 3

Description: This table is always empty in NHDPlus and is included for completeness of the 

NHD data model. 
NHDPlus User Guide 22 September 1, 2010 

SubRegion (shapefile) 3

Description: This table is always empty in NHDPlus and is included for completeness of the 

NHD data model. 

Basin (shapefile) 3

Description: This table is always empty in NHDPlus and is included for completeness of the 

NHD data model. 

ProductionUnit (shapefile)

Description: The sub-divisions used to process the elevation data into flow direction and 

accumulation grids. The production units are distributed as a national shapefile. 

Field Name Description 

Prod_Unit Production unit identifier 

Area Area of the production unit 

Perimeter Perimeter of the production unit 
NHDPlus User Guide 23 September 1, 2010 

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NHDPlus User Guide 24 September 1, 2010 

Chapter 3 Attribute Table Descriptions 

Some fields in the attribute tables contain special coded values as follows: 

The value “-9998” signifies that the applicable value for the field is missing or 

undetermined. 

The value “-9999” signifies that there is no applicable value and one will never be 

assigned. 

CatchmentAttributesNLCD for All Hydrologic Regions Except 20 (Hawaii) (dBase file)

Description: National Land Cover Dataset 1992 (NLCD) attributes derived for each flowline 

catchment. 

Note: The NLCD was available only for the conterminous United States. Percentages of the 

NLCD categories pertain only to the portion of a catchment within the United States but are 

computed as a percentage of the total area. Thus, any non-zero percentages in fields PCT_CN or 

PCT_MX must be added to the percentages in the NLCD categories to account for the entire 

catchment area. 

Field Name Description 

ComID Common identifier of an NHD Flowline 

Grid_code Value field from Catchment Grid 

NLCD_11 % of catchment area classified as Open Water in NLCD 

NLCD_12 % of catchment area classified as Perennial Ice/Snow in NLCD 

NLCD_21 % of catchment area classified as Low Intensity Residential in 

NLCD 

NLCD_22 % of catchment area classified as High Intensity Residential in 

NLCD 

NLCD_23 % of catchment area classified as Commercial/Industrial/ 

Transportation in NLCD 

NLCD_31 % of catchment area classified as Bare Rock/Sand/Clay in 

NLCD 

NLCD_32 % of catchment area classified as Quarries/Strip Mines/Gravel 

Pits in NLCD 

NLCD_33 % of catchment area classified as Transitional in NLCD 

NLCD_41 % of catchment area classified as Deciduous Forest in NLCD 

NLCD_42 % of catchment area classified as Evergreen Forest in NLCD 

NLCD_43 % of catchment area classified as Mixed Forest in NLCD 

NLCD_51 % of catchment area classified as Shrubland in NLCD 

NLCD_61 % of catchment area classified as Orchards/Vineyards/Other in 

NLCD 

NLCD_71 % of catchment area classified as Grasslands/Herbaceous in 
NHDPlus User Guide 25 September 1, 2010 

Field Name Description 

NLCD 

NLCD_81 % of catchment area classified as Pasture/Hay in NLCD 

NLCD_82 % of catchment area classified as Row Crops in NLCD 

NLCD_83 % of catchment area classified as Small Grains in NLCD 

NLCD_84 % of catchment area classified as Fallow in NLCD 

NLCD_85 % of catchment area classified as Urban/Recreational Grasses in 

NLCD 

NLCD_91 % of catchment area classified as Woody Wetlands in NLCD 

NLCD_92 % of catchment area classified as Emergent Herbaceous 

Wetlands in NLCD 

PCT_CN % of catchment area in Canada and not classified in NLCD 

PCT_MX % of catchment area in Mexico and not classified in NLCD 

SUM_PCT Sum of the % catchment areas 

CatchmentAttributesNLCD for Hydrologic Region 20 (Hawaii) (dBase file) 

Description: The NOAA Coastal Change Analysis Program (C-CAP) attributes derived for 

each catchment. 

Field Name Description 

ComID Common identifier of an NHD Flowline 

Grid_code Value field from Catchment Grid 

HILC_1 % of catchment area classified as Unclassified in National 

Oceanic and Atmospheric Administration (NOAA) C-CAP

HILC_2 % of catchment area classified as High Intensity Developed in 

NOAA C-CAP 

HILC 3 % of catchment area classified as Low Intensity Developed in 

NOAA C-CAP 

HILC 4 % of catchment area classified as Cultivated Land in NOAA CCAP 

HILC 5 % of catchment area classified as Grassland in NOAA C-CAP 

HILC 6 % of catchment area classified as Deciduous Forest in NOAA CCAP 

HILC_7 % of catchment area classified as Evergreen Forest in NOAA CCAP 

HILC_8 % of catchment area classified as Mixed Forest in NOAA CCAP 

HILC_9 % of catchment area classified as Scrub/Shrub in NOAA C-CAP 

HILC 10 % of catchment area classified as Palustrine Forested Wetland in 

NOAA C-CAP 

HILC_11 % of catchment area classified as Palustrine Scrub/Shrub 

Wetland in NOAA C-CAP 
NHDPlus User Guide 26 September 1, 2010 

Field Name Description 

HILC_12 % of catchment area classified as Palustrine Emergent Wetland 

in NOAA C-CAP 

HILC 13 % of catchment area classified as Estuarine Forested Wetland in 

NOAA C-CAP 

HILC_14 % of catchment area classified as Estuarine Scrub/Shrub 

Wetland in NOAA C-CAP 

HILC_15 % of catchment area classified as Estuarine Emergent Wetland 

in NOAA C-CAP 

HILC 16 % of catchment area classified as Unconsolidated Shore in 

NOAA C-CAP 

HILC 17 % of catchment area classified as Bare Land in NOAA C-CAP 

HILC_18 % of catchment area classified as Water in NOAA C-CAP 

HILC_19 % of catchment area classified as Palustrine Aquatic Bed in 

NOAA C-CAP 

HILC_20 % of catchment area classified as Estuarine Aquatic Bed in 

NOAA C-CAP 

HILC 21 % of catchment area classified as Tundra in NOAA C-CAP 

HILC_22 % of catchment area classified as Snow/Ice in NOAA C-CAP 

PCT_CN % of catchment area in Canada and not classified in NOAA CCAP 

PCT_MX % of catchment area in Mexico and not classified in NOAA CCAP 

SUM_PCT Sum of the % catchment areas 

CatchmentAttributesTempPrecip (dBase file)

Description: NHDPlus attributes derived for each flowline catchment. 

Note: Precipitation and temperature values are the average values over the catchment from the 

PRISM 1961-90, 2.5-minute (approximately 4 km) resolution data by Daly and Taylor (1998). If 

a catchment extends into Canada or Mexico, the value will be the average over only the U.S. 

portion of the catchment. TEMP values are not provided for Hydrologic Region 20 (Hawaii) 

because TEMP is not needed for the regression-based flow estimates in that region (refer to Step 

6 in Appendix A). 

Note: In Hydrologic Region 21 (Puerto Rico and the Virgin Islands) Temp values are not 

provided and Precip values are provided for Puerto Rico only. 

Field Name Description 

ComID Common identifier of an NHD Flowline 

Grid_code Value field from Catchment Grid 

Precip Mean annual precipitation in mm 

Temp Mean annual temperature in degrees centigrade * 10 
NHDPlus User Guide 27 September 1, 2010 

FlowlineAttributesFlow for All Hydrologic Regions Except 21 (dBase file)

Description: NHDPlus attributes derived for NHD Flowlines. 

Field Name Description 

ComID Common identifier of an NHD Flowline 

Grid_code Value field from Catchment Grid 

CumDrainag Cumulative drainage area in square kilometers(sq km) at bottom 

of flowline 

MAFlowU Mean Annual Flow in cubic feet per second (cfs) at bottom of 

flowline as computed by Unit Runoff Method 

MAFlowV Mean Annual Flow (cfs) at bottom of flowline as computed by 

Vogel Method. In Hydrologic Region 20 (Hawaii), this value is 

the median annual flow (cfs) as computed using the method of 

Fontaine, et. al. (1992). 

MAVelU Mean Annual Velocity (fps) at bottom of flowline as computed 

by Jobson Method (1996) using the flow in MAFlowU. 

MAVelV Mean Annual Velocity (fps) at bottom of flowline as computed 

by Jobson Method (1996) using the flow in MAFlowV. 

IncrFlowU Incremental Flow (cfs) for Flowline as computed by the Unit 

Runoff Method 

MaxElevRaw Maximum elevation (unsmoothed) in meters, populated only for 

headwater Flowlines, -9998 for all non-headwater Flowlines 

MinElevRaw Minimum elevation (unsmoothed) in meters

MaxElevSmo Maximum elevation (smoothed) in meters 

MinElevSmo Minimum elevation (smoothed) in meters 

Slope Slope of flowline (m/m) 
NHDPlus User Guide 28 September 1, 2010 

FlowlineAttributesFlow For Region 21(dBase file)

Description: NHDPlus attributes derived for NHD Flowlines. 

Field Name Description 

ComID Common identifier of an NHD Flowline 

Grid_code Value field from Catchment Grid 

CumDrainag Cumulative drainage area in square kilometers(sq km) at bottom 

of flowline 

MAFlowU Mean Annual Flow in cubic feet per second (cfs) at bottom of 

flowline as computed by Unit Runoff Method 

MAVelU Mean Annual Velocity (fps) at bottom of flowline as computed 

by Jobson Method (1996) using the flow in MAFlowU. 

IncrFlowU Incremental Flow (cfs) for Flowline as computed by the Unit 

Runoff Method 

MaxElevRaw Maximum elevation (unsmoothed) in meters

MinElevRaw Minimum elevation (unsmoothed) in meters, populated only for 

headwater Flowlines, -9998 for all non-headwater Flowlines 

MaxElevSmo Maximum elevation (smoothed) in meters 

MinElevSmo Minimum elevation (smoothed) in meters 

Slope Slope of flowline (m/m) 

FlowlineAttributesNLCD for All Hydrologic Regions Except 20 (Hawaii) (dBase file)

Description: NHDPlus cumulative attributes derived for NHD Flowlines. 

Note: The NLCD 1992 was available only for the conterminous United States. Percentages of 

the NLCD categories pertain only to the portion of a drainage area within the United States but 

are computed as a percentage of the total drainage area. Thus, any non-zero percentages in fields 

PCT_CN or PCT_MX must be added to the percentages in the NLCD categories to account for 

the entire drainage area. The cumulative values represent values at the bottom of the flowline. 

Field Name Description 

ComID Common identifier of an NHD Flowline 

Grid_Code Value field from Catchment Grid 

CumNLCD_11 % of cumulative drainage area classified as Open Water in 

NLCD 

CumNLCD_12 % of cumulative drainage area classified as Perennial Ice/Snow 

in NLCD 

CumNLCD_21 % of cumulative drainage area classified as Low Intensity 

Residential in NLCD 

CumNLCD_22 % of cumulative drainage area classified as High Intensity 

Residential in NLCD 
NHDPlus User Guide 29 September 1, 2010 

Field Name Description 

CumNLCD_23 % of cumulative drainage area classified as Commercial/ 

Industrial/Transportation in NLCD 

CumNLCD_31 % of cumulative drainage area classified as Bare Rock/Sand/ 

Clay in NLCD 

CumNLCD_32 % of cumulative drainage area classified as Quarries/Strip 

Mines/Gravel Pits in NLCD 

CumNLCD_33 % of cumulative drainage area classified as Transitional in 

NLCD 

CumNLCD_41 % of cumulative drainage area classified as Deciduous Forest in 

NLCDD 

CumNLCD_42 % of cumulative drainage area classified as Evergreen Forest in 

NLCD 

CumNLCD_43 % of cumulative drainage area classified as Mixed Forest in 

NLCD 

CumNLCD_51 % of cumulative drainage area classified as Shrubland in NLCD 

CumNLCD_61 % of cumulative drainage area classified as Orchards/Vineyards/ 

Other in NLCD 

CumNLCD_71 % of cumulative drainage area classified as Grasslands/ 

Herbaceous in NLCD 

CumNLCD_81 % of cumulative drainage area classified as Pasture/Hay in 

NLCD 

CumNLCD_82 % of cumulative drainage area classified as Row Crops in 

NLCD 

CumNLCD_83 % of cumulative drainage area classified as Small Grains in 

NLCD 

CumNLCD_84 % of cumulative drainage area classified as Fallow in NLCD 

CumNLCD_85 % of cumulative drainage area classified as Urban/Recreational 

Grasses in NLCD 

CumNLCD_91 % of cumulative drainage area classified as Woody Wetlands in 

NLCD 

CumNLCD_92 % of cumulative drainage area classified as Emergent 

Herbaceous Wetlands in NLCD 

Cumpct_CN % of cumulative drainage area in Canada and not classified in 

NLCD 

Cumpct_MX % of cumulative drainage area in Mexico and not classified in 

NLCD 

CUMSUM_PCT Sum of the % cumulative drainage areas 
NHDPlus User Guide 30 September 1, 2010 

FlowlineAttributesNLCD for Hydrologic Region 20 (Hawaii) (dBase file) 

Field Name Description 

ComID Common identifier of an NHD Flowline 

Grid_code Value field from Catchment Grid 

CUMHILC_1 % of cumulative drainage area classified as Unclassified in 

NOAA C-CAP 

CUMHILC_2 % of cumulative drainage area classified as High Intensity 

Developed in NOAA C-CAP 

CUMHILC_3 % of cumulative drainage area classified as Low Intensity 

Developed in NOAA C-CAP 

CUMHILC 4 % of cumulative drainage area classified as Cultivated Land in 

NOAA C-CAP 

CUMHILC 5 % of cumulative drainage area classified as Grassland in NOAA 

C-CAP 

CUMHILC_6 % of cumulative drainage area classified as Deciduous Forest in 

NOAA C-CAP 

CUMHILC 7 % of cumulative drainage area classified as Evergreen Forest in 

NOAA C-CAP 

CUMHILC 8 % of cumulative drainage area classified as Mixed Forest in 

NOAA C-CAP 

CUMHILC 9 % of cumulative drainage area classified as Scrub/Shrub in 

NOAA C-CAP 

CUMHILC 10 % of cumulative drainage area classified as Palustrine Forested 

Wetland in NOAA C-CAP 

CUMHILC_11 % of cumulative drainage area classified as Palustrine 

Scrub/Shrub Wetland in NOAA C-CAP 

CUMHILC 12 % of cumulative drainage area classified as Palustrine Emergent 

Wetland in NOAA C-CAP 

CUMHILC 13 % of cumulative drainage area classified as Estuarine Forested 

Wetland in NOAA C-CAP 

CUMHILC 14 % of cumulative drainage area classified as Estuarine 

Scrub/Shrub Wetland in NOAA C-CAP 

CUMHILC 15 % of cumulative drainage area classified as Estuarine Emergent 

Wetland in NOAA C-CAP 

CUMHILC 16 % of cumulative drainage area classified as Unconsolidated 

Shore in NOAA C-CAP 

CUMHILC 17 % of cumulative drainage area classified as Bare Land in NOAA 

C-CAP 

CUMHILC 18 % of cumulative drainage area classified as Water in NOAA CCAP 

CUMHILC 19 % of cumulative drainage area classified as Palustrine Aquatic 

Bed in NOAA C-CAP 

CUMHILC 20 % of cumulative drainage area classified as Estuarine Aquatic 

Bed in NOAA C-CAP 

CUMHILC_21 % of cumulative drainage area classified as Tundra in NOAA C-
NHDPlus User Guide 31 September 1, 2010 

Field Name Description 

CAP 

CUMHILC_22 % of cumulative drainage area classified as Snow/Ice in NOAA 

C-CAP 

CUMPCT_CN % of cumulative drainage area in Canada and not classified in 

NOAA C-CAP 

CUMPCT_MX % of cumulative drainage area in Mexico and not classified in 

NOAA C-CAP 

CUMSUM_PCT Sum of the % cumulative drainage areas 

FlowlineAttributesTempPrecip (dBase file)

Description: NHDPlus cumulative attributes derived for NHD Flowlines. 

Note: AreaWtMAT values are not provided for Hydrologic Region 20 (Hawaii) because 

Temperature is not needed for the regression-based flow estimates in this region; refer to Step 6 

in Appendix A. 

Note: In Hydrologic Region 21 (Puerto Rico and the Virgin Islands) AreaWtMAT values are 

not provided and AreaWtMAP values are provided for Puerto Rico only. 

Field Name Description 

ComID Common identifier of an NHD Flowline 

Grid_Code Value field from Catchment Grid 

AreaWtMAP Area Weighted Mean Annual Precipitation at bottom of flowline 

in mm 

AreaWtMAT Area Weighted Mean Annual Temperature at bottom of flowline 

in degree C * 10 

HeadWaterNodeArea (dBase file)

Description: For each headwater node in the surface water network, the HeadWaterNodeArea 

table contains the size of the land area that drains to the node at the upstream end of the flowline. 

Field Name Description 

ComID Common identifier of an NHD Flowline 

Grid_Code Value field from Catchment Grid 

HwNodesqkm Catchment area in square kilometers that drains to the headwater 

node of the flowline indicated by ComID 
NHDPlus User Guide 32 September 1, 2010 

NHDFCode (dBase file) 3

Description: The FCode table describes attribute codes used in the FCode fields of feature 

tables. 

Field Name Description 

FCode A numeric code that represents the feature type plus its encoded 

attribute values 

Descriptio Text description of feature type and the encoded attributes 

CanalDitch Canal Ditch Type (aqueduct, unspecified) 

Constructi Construction material (earthen, nonearthen, unspecified) 

Hydrograph Intermittent or perennial 

Inundation Inundation Area Type (debris basin, dewatering area, duck pond, 

general case, percolation basin, retarding basin) 

Operationa Operational Status (abandoned, operational, under construction) 

PipelineTy Pipeline type (aqueduct, general case, penstock, siphon) 

Positional Positional accuracy (approximate, definite, indefinite, not 

applicable) 

Relationsh Relationship to surface (abovewater, at or near, elevated, 

underground, underwater, unspecified) 

ReservoirT Reservoir type (aquaculture, decorative pool, disposal-tailings 

pond, disposal-unspecified, evaporator, swimming pool, 

treatment-cooling pond, treatment-filtration pond, treatmentsettling pond, treatment-sewage treatment pond, unspecified 

water storage) 

Stage Elevation stage (Normal Pool, Flood Elevation, Average Water 

Elevation, Date of Photography, High Water Elevation, Spillway 

Elevation) 

SpecialUse Special use category (dump site, spoil area) 

NHDFeaturetometadata (dBase file) 3

Description: Links metadata to features. 

Field Name Description 

ComID Common identifier for an NHD feature 

DUUID Metadata identifier 
NHDPlus User Guide 33 September 1, 2010 

NHDFlow (dBase file) 3

Description: A geometry-independent flow table that is QA/QC’ed for internal consistency and 

external agreement with flowline geometry. The flow table contains entries for: (1) every pair of 

flowlines that exchange water, (2) the beginning of each network, and (3) each network terminus 

where water flows into the ground. At the shoreline, network flowline features have a “nonflowing” connection to coastline features. Coastline features also have “non-flowing” 

connections to each other. 

Field Name Description 

FromComID Common identifier for an NHD Flowline 

ToComID Common identifier for an NHD Flowline 

DeltaLevel Numerical difference between stream level for FromComID and 

stream level for ToComID 

Direction 714 – coastal connection (FromComID flowline may be a 

coastline and ToComID flowline is always a coastline) 

709 – flowing connection 

712 – network start (ToComID flowline is a headwater) 

713 – network end (FromComID flowline is a network end) 

ToComIDMea Not valued 
NHDPlus User Guide 34 September 1, 2010 

NHDFlowlineVAA (dBase file) 3

Description: Value Added Attributes (VAAs) for each flowline that appears in the NHDPlus 

Flow table. The NHDFlowlineVAA table is an official part of the NHD schema, however, with 

the exception of stream level, the VAAs not populated in the NHD data. It’s the NHDPlus 

building process that populates the VAAs. For additional descriptive information about the 

VAAs, see Appendix A, “Step 1”. “Understanding and Using NHDPlus” contains many 

examples of how to accomplish tasks using the VAAs. 

Field Name Description

ComID Common identifier of NHD Flowline 

StreamLeve Stream level 

StreamOrde Strahler stream order. Always 0. 

FromNode From node number (top of flowline) 

ToNode To node number (bottom of flowline) 

Hydroseq Hydrologic sequence number 

LevelPathi Hydrologic sequence number of most downstream flowline in level path 

PathLength Distance to terminal flowline downstream along the mainpath (kilometers) 

TerminalPa Hydrologic sequence number of terminal flowline 

ArbolateSu An estimate of miles of stream upstream of a flowline. Always 0. (square 

kilometers 

Divergence 0 – not part of a divergence 

1 – main path of a divergence 

2 – minor path of a divergence 

StartFlag 0 – not a headwater flowline 

1 – a headwater flowline 

TerminalFl 0 – not a terminal flowline 

1 – a terminal flowline 

DnLevel Streamlevel of mainstem downstream flowline 

ThinnerCod Ordinal value used to display various network densities 

UpLevelPat Upstream mainstem level path identifier

UpHydroSeq Upstream mainstem hydrologic sequence number 

UpMinHydro Upstream minimum hydrologic sequence number 

DnLevelPat Downstream mainstem level path identifier 

DnMinHydro Downstream minor path hydrologic sequence number 

DnDrainCou Number of flowlines immediately downstream 

NHDHydroLineEvent (dBase file) 3

Description: This table is always empty in NHDPlus and is included for completeness of the 

NHD data model. 
NHDPlus User Guide 35 September 1, 2010 

NHDHydroPointEvent (dBase file) 3

Description: This table is always empty in NHDPlus and is included for completeness of the 

NHD data model. 

NHDMetadata (dBase file) 3

Description: Holds NHD metadata records that can be linked to individual features through the 

NHDFeaturetoMetadata table. 

Field Name Description 

DUUID Metadata identifier 

ProcessDes Process Description 

ProssDat Process Date 

AttributeA Attribute Accuracy Report 

LogicalCon Logical Consistency Report 

Completene Completeness Report 

HorizPosit Horizontal Positional Accuracy Report 

VertPositi Vertical Positional Accuracy Report 

MetadataSt Metadata Standard Name 

Metadata_1 Metadata Standard Version 

MetadataDa Metadata Date 

DataSetCre Dataset Credit 

ContactOrg Contact Organization 

AddressTyp Address Type 

Address Address 

City City 

StateorPro State or Province 

PostalCode Postal Code 

ContactVoi Contact Voice Telephone 

ContactIns Contact Instructions 

NHDProcessingParameters (dBase file) 3

Description: This table is always empty in NHDPlus and is included for completeness of the 

NHD data model. 

NHDReachcode_ComID (dBase file) 3

Description: This table is always empty in NHDPlus and is included for completeness of the 

NHD data model. 
NHDPlus User Guide 36 September 1, 2010 

NHDReachCrossReference (dBase file) 3

Description: This table tracks the creation, change, and deletion of Reach Codes. 

Field Name Description 

OldReachCo Old Reach Code 

OldReachDa Old Reach date 

NewReachCo New Reach Code 

NewReachDa New Reach date 

OldUpMI Not used 

NewUPMI Not used 

ChangeCode Change code 

“A”dd, “D”elete, “11” = 1-1, “P1” or “1M” = Partial-1, “1P” or 

“M1” = 1-Partial, 

PP = Partial-Partial 

Process Process code 

ReachFileV Reach file version 

OldHUCode Substr(OldReachCode,1,8) 

NewHUCode Substr(NewReachCode,1,8) 

NHDSourceCitation (dBase file) 3

Description: This table contains NHD metadata source citation records that can be linked to 

individual features through the NHDFeaturetoMetadata table. 

Field Name Description 

Title Title of data source used as input for creating or updating NHD 

SourceCita Source Citation Abbreviation 

Originator Originator 

Publicatio Publication Date 

BeginningD Beginning Date 

EndingDate Ending Date 

SourceCont Source Contribution 

SourceScal Source Scale Denominator 

TypeofSour Type of Source Media 

CalendarDa Calendar Date 

SourceCurr Source Currentness Reference 

DUUID Digital Update Unit Identifier 
NHDPlus User Guide 37 September 1, 2010 

NHDStatus (dBase file) 3

Description: This table is always empty in NHDPlus and is included for completeness of the 

NHD data model. 

NHDVerticalRelationship (dBase file) 3

Description: This table describes locations where NHD Flowline features cross but do not 

intersect. 

Field Name Description 

ComID Common identifier for the vertical relationship 

AboveComID Common identifier for an NHD Flowline 

BelowComID Common identifier for an NHD Flowline 

Openme.txt

Description: This text file provides a file handle for file browse dialogues in user applications. 

It also contains a small amount of general information about the NHD data. 
NHDPlus User Guide 38 September 1, 2010 

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NHDPlus User Guide 39 September 1, 2010 

Chapter 4 Geographic Coverage of Data Package 

All NHDPlus data (except grids) are distributed by hydrologic region, with two exceptions: 

Region 10 is split into upper and lower and sub-region 0318 is distributed both inside Region 03 

and as a standalone area. For NHDPlus grids, the hydrologic regions are divided into production 

units and all grids are distributed by these units. Figure 4-1 shows the production units for 

NHDPlus components. 

Figure 4-1 – NHDPlus Hydrologic Regions and Production Unit Map 

The two-digit Hydrologic Region designations are based on the Hydrologic Unit Coding system 

in which the United States is divided and sub-divided into successively smaller hydrologic units 

which are classified into four levels: regions, sub-regions, accounting units, and cataloging units. 

Additional information about the coding system is described at 

http://water.usgs.gov/GIS/huc.html and 

http://www.ncgc.nrcs.usda.gov/products/datasets/watershed/.
NHDPlus User Guide 40 September 1, 2010 

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NHDPlus User Guide 41 September 1, 2010 

Chapter 5 Understanding and Using NHDPlus 

NHDPlus and Divergences 

The NHDPlus network includes complex network components, especially divergent and 

complex flow paths. These types of network components are illustrated in Figure 5-1. 

Convergent junctions are the simplest types of junctions and pose no problems in downstream 

routing and accumulating attributes, such as drainage area. Divergent and other types of complex 

junctions, however, pose particular issues in computing cumulative values. These issues and how 

the NHDPlus FlowlineAttribute tables compute cumulative values are described below. 

NHDPlus: Complex Hydrography

Convergent

Junction

Divergent

Junction

Complex

Junction

Figure 5-1 – NHDPlus Complex Hydrography 

The DIVERGENCE field in the NHDFlowlineVAA Table defines “main” and “minor” paths at 

divergences. A single path is designated as the main path and is given a DIVERGENCE field 

value of “1”. All other paths in the divergence are designated as minor paths and are given a 

DIVERGENCE field value of “2”, as illustrated in Figure 5-2. 
NHDPlus User Guide 42 September 1, 2010 

Main Path

Divergence = 1

Minor Path

Divergence = 2

Figure 5-2 – Main and Minor Paths in NHDPlus 

In many cases, the divergences are “local”, for instance, as shown in Figure 5-3, the red 

flowlines represent the divergences. The blue lines represent flowlines not affected by these 

divergences because the divergent streams rejoin at a downstream point. 

Figure 5-3 – “Local” Divergences 
NHDPlus User Guide 43 September 1, 2010 

There are many situations in NHDPlus which are much more complex; for instance multiple 

divergences and divergences where the divergent flowlines never re-join the network 

downstream. A somewhat more complicated case is shown in Figure 5-4 -. In routing and 

accumulating downstream, cumulative values will be affected by divergences on the red 

flowlines while the blue flowlines are not affected by the divergences. As can be seen, the 

divergences can affect multiple flowlines. There are many divergent areas in NHDPlus which are 

much more complex; such as braided streams and in coastal areas. 

Figure 5-4 -– More Complex Divergent Junction Example 

How Cumulative Values in the FlowlineAttributeFlow, FlowlineAttributesTempPrecip, and 

FlowlineAttributesNLCD Tables are valued with Divergences

Various options were considered, such as splitting the drainage areas, flows, etc. evenly between 

the main and minor paths or setting a default percentage split, such as 75% down the main path 

and 25% down the minor path. It is essential that the proportional split add up to 100%, or else 

there would eventually be double-counting of attributes when divergent paths re-entered the 

network downstream. 

The decision made for NHDPlus is to route and accumulate all values down the main path 

(DIVERGENCE=1), and treat the minor path as essentially a “start/headwater” flowline. This is 
NHDPlus User Guide 44 September 1, 2010 

illustrated in Figure 5-5. The rationale behind this decision is that, given no other contextual 

information, there is no basis for selecting any particular proportional split. The result of this 

decision is that, on minor divergent flowlines and the flowlines downstream of the minor 

divergence that have not re-joined the main path, the values (drainage area, flow, and cumulative 

Temp, Precip, and NLCD) will not include the cumulative drainage values upstream of the 

divergence. 

Main Path

Divergence = 1

Minor Path

Divergence = 2

Cumulative Attributes

Routed down the main path

Figure 5-5 – Cumulative attributes routed down the main path 

Generating Less Dense Networks from NHDFlowline 

A connected network that forms the mainpaths of the 8-digit Hydrologic Unit Codes (i.e., 

Cataloging Units or Subbasins) may be generated by selecting NHDPlus flowlines that have 

NHDFlowlineVAA.Thinner = 1. Progressively denser networks may be generated by selecting 

NHDPlus flowlines that have NHDFlowlineVAA.Thinner <= 2 then 3, 4, 5, and 6. 

Understanding NHDPlus Slope 

NHDPlus slope is unit-less. It can be viewed as cm/cm or m/m or km/km. The units are the 

same in both the numerator and denominator and therefore cancel out. Cm/cm appears 

elsewhere in this documentation to show that it is unit-less. 

Minimum and maximum smoothed elevations for flowlines, in the FlowlineAttributesFlow table, 

are expressed in meters and flowline length, in the NHDFlowline table, is in kilometers. 

Therefore when slope is calculated with these fields the result is slope in meters per kilometer 

(m/km): 
NHDPlus User Guide 45 September 1, 2010 

maxelevsmo(m) - minelevsmo(m) 

 ____________________ = slope in m/km 

 lengthkm(km) 

To get the unit-less slope given in NHDPlus the units must be converted as follows: 

slope in m/km * 1 km/1000m = slope (unit-less) given in NHDPlus. NHDPlus slopes are 

constrained to be greater than or equal to 0.00005.

Finding the Upstream Inflows to an NHDPlus Dataset 

All NHDPlus regional datasets are hydrologically complete drainage areas except the datasets 

that make up the Colorado River (NHDPlus14 and NHDPlus15) and the Mississippi River 

(NHDPlus05, NHDPlus06, NHDPlus07, NHDPlus08, NHDPlus10L, NHDPlus10R, 

NHDPlus11, and NHDPlus0318). When navigating the stream network in either of these areas, 

it is necessary to determine if the navigation should be continued in an upstream or downstream 

NHDPlus dataset. 

It is possible to determine upstream inflows to any NHDPlus dataset by selecting 

NHDflow.tocomids where the NHDflow.fromcomid is not in NHDFlowline. If those tocomids 

are in a particular upstream navigation result, the navigation may be continued in the upstream 

NHDPlus dataset by starting at the fromcomids. 

It is possible to determine downstream outflows from any NHDPlus dataset by selecting 

NHDflow.fromcomids where the NHDflow.tocomid is not in NHDFlowline. If those 

fromcomids are in a particular downstream navigation result, the navigation may be continued in 

the downstream NHDPlus dataset by starting at the tocomids. 

Finding all the Tributaries to a Stretch of River 

First, find the stretch of interest along the main river using one of these methods: 

Method 1: Navigate upstream mainstem on the major river from the desired starting 

flowline for the desired distance. 

Method 2: Query all flowlines with the major river’s levelpathid where (pathlength - 

StartingPathlength) <= desired distance. If the desired stretch of river does not start at 

the mouth of the river, remove from the query any NHDFlowlineVAA.Hydroseq < the 

downstream end of the desired stretch NHDFlowlineVAA.Hydroseq. 

Then, find the tributaries to the stretch: 

Join the NHDFlow.tocomid to the list of comids from Method1 or Method2. 

All the NHDflow.fromcomid's in the joined records are the downstream flowlines of the 

tributaries to the desired stretch of main river. 
NHDPlus User Guide 46 September 1, 2010 

Building an NHDPlus Attribute Accumulator 

There are two requirements for attribute accumulation: site specific or throughout the entire 

network. Site specific accumulation can be done easily with upstream navigation followed by 

aggregation, based on the navigation results, of any attributes that have been assigned to 

flowlines or their associated catchments. An entire network accumulation is one where the 

desired attributes are accumulated for each flowline and saved in an attribute table for future use. 

Entire network accumulations need a program or script to accomplish the accumulation task. 

This section addresses the specifications for such a program. 

For example, assume that a new attribute has been defined and that incremental values for the 

attribute have been assigned to each flowline/catchment in the stream network. The objective of 

accumulation is to aggregate the incremental values such that, at any particular 

flowline/catchment in the network, the total value of the attribute upstream of the 

flowline/catchment is computed. Aggregation uses different mathematical operators depending 

on the attribute being aggregated. For example, drainage area is additive, while the percent of 

area in forest is computed using an area-weighted average. 

There are two essential techniques for accumulating attributes throughout the network: 

downstream routing and upstream navigation. 

The downstream routing method was employed to do the NHDPlus cumulative attributes. This 

method starts at the top of the network and moves downstream aggregating together the 

incremental values and storing the result at each flowline/catchment. The advantage of this 

method is that it is fast, taking only minutes to run. The disadvantage of this method is that it 

must make decisions at flow splits (divergences) about which way to route the accumulated 

value. The value may not be routed down both paths of a divergence because, if those diverging 

paths come back together (which is frequently the case), the accumulation will begin to doublecount the attribute. In the NHDPlus accumulation, the decision was made to route the entire 

accumulated value down the major path of each divergence. (Refer to the “NHDPlus and 

Divergences” section for additional information.) It is easy to see that the downstream method is 

very sensitive to errors in divergence classifications. When the wrong path is designated as the 

major path, the accumulation goes down the wrong path. In addition, flowlines that are 

downstream of divergences that have not yet returned to the major network path (i.e., unresolved 

divergences) will not receive the full accumulated value from upstream. This may be 

appropriate for some attributes but not for others.

The upstream approach is similar to the site specific method where the accumulation for each 

flowline aggregates all the incremental values from upstream. The advantages of this method are 

that it is not sensitive to errors in divergence classifications and always gives the full 

accumulated value regardless of the presence of upstream unresolved divergences. The 

disadvantage of this method is that it takes some time to run – hours, not minutes. 

Since the simplest approach to coding an accumulation script is the downstream routing method, 

specifications for that method are provided here. As an example, begin with a file that contains 

flowline/catchment comid and the incremental value for a single attribute that has been assigned 
NHDPlus User Guide 47 September 1, 2010 

to each flowline or catchment. For this specification, assume that the file is called 

IncrementalAttributeFile and that it has the fields comid and AttrValue. 

1. Add to IncrementalAttributeFile a field for the cumulative value for the attribute. Let’s 

call this CumAttrValue. 

2. Join IncrementalAttributeFile with NHDFlowlineVAA using comid. For performance, 

we’ll delete from the joined file every record that has hydroseq = 0. These lines are not 

in the NHDPlus stream network and also do not get catchments, therefore they are not 

needed in an accumulation. 

3. Sort the joined file by Hydroseq descending. 

4. Accumulation procedure: 

4.1. Get next record from the sorted file. If end of file, quit. 

4.2. If Startflag = 1 (i.e., this is a headwater and there is nothing upstream) or 

divergence = 2 (i.e., nothing is routed down the minor paths of the divergence), 

then set CumAttrValue = AttrValue and go to step 4.1. 

4.3. Find all the inflows to this current flowline: inflows are records in the joined file 

where the tonode = fromnode of the current flowline. 

4.4. Set CumAttrValue = AttrValue + the CumAttrValue for each inflow. 

4.5. Go to step 4.1. 

This procedure routes the accumulation down the mainpath at each divergence. Alternatively, the 

accumulation may be apportioned to the different paths in the divergence as long as 100% 

(neither less nor more) of the accumulation is routed. 

Flowlines with "known flow" vs. Flowlines with “unknown flow”

There are over 2.9 million flowline features in NHDPlus. Of those, 2.6 million have a known 

flow direction. This information is contained in an attribute called Flowdir in the NHDFlowline 

feature class attribute table. Flowdir can have the values “With Digitized” (known flow 

direction) or “Uninitialized” (unknown flow direction). The flowlines having unknown flow 

direction are primarily of three types: isolated stream segments, canal/ditches, and some channels 

inside braided networks. The flowlines with known flow direction are the subset of the 

NHDFlowline feature class which makeup the NHDPlus surface water network. The “plus” part 

of NHDPlus is built just for the flowlines with known flow direction. In other words, the 

catchment shapefile, CatchmentAttributesNLCD, CatchmentAttributesTempPrecip, 

FlowlineAttributesFlow, FlowlineAttributesNLCD, and FlowlineAttributesTempPrecip contain 

records for flowlines with known flow direction. When using NHDPlus, it is useful to symbolize 

the NHDFlowline feature class using the Flowdir attribute. This will help eliminate confusion 

about what is considered in the NHDPlus surface water network and what is not. In Figure 5-6, 

the dark blue lines are those NHDFlowlines with known flow direction and, consequently, are 

included in the “plus” part of NHDPlus. The broad cyan lines are NHDFlowlines with unknown 

flow direction and, consequently, are not part of the “plus” part of NHDPlus. 
NHDPlus User Guide 48 September 1, 2010 

Figure 5-6 – NHD Flowlines With Known and Unknown Flow Direction 

Main flowline network vs. isolated networks

The majority of the NHDPlus surface water network features drain to the Atlantic Ocean, Pacific 

Ocean, Gulf of Mexico, or to one of the Great Lakes. These features are the ones that compose 

the NHDPlus “main” flowline network. In addition, NHDPlus contains many isolated networks 

throughout the U.S. An isolated network is one that appears to terminate into the ground. Many 

isolated networks truly flow into the ground. These are often called “non-contributing” networks 

and, while they can occur in any part of the country, they are found primarily found in 

hydrologic region 16 (The Great Basin) and in south western parts of hydrologic region 17 

(Pacific Northwest). Some isolated networks are mapping errors. These networks should be 

connected to the main NHDPlus network. Figure 5-7 and Figure 5-8 illustrate isolated networks 

that are non-contributing and mapping errors, respectively. 
NHDPlus User Guide 49 September 1, 2010 

Figure 5-7 – Non-contributing Isolated Networks 

Teal lines are the terminal segments of these isolated networks. The straight lines are USGS 7.5-minute 

quadrangle boundaries. 
NHDPlus User Guide 50 September 1, 2010 

Figure 5-8 – Map error 

The cross-hairs are the edges of USGS quad maps. 

Isolated networks may be located in any NHDPlus drainage area. To find isolated networks, join 

the NHDflowlineVAA attribute table to the NHDFlowline feature class using the Comid field in 

each. Then select all flowlines with NHDFlowlineVAA.Terminalfl = 1. The flowlines selected 

will be those with known flow direction that are considered by NHDPlus as terminal flowlines. 

Disagreements Between the Flow Accumulation Grid and NHD 

isolated Networks 

Figure 5-9 illustrates an uncommon problem between the NHDPlus network and the flow 

accumulation grid (FAC). The dark blue lines are the drainage channels defined by the FAC. 

The green lines are the mapped streams in the NHDFlowline feature class. According to the 

NHD, the teal stream is a terminal flowline of an isolated network. In the NHDFlowline feature 

class, all the features in this isolated network are flowing toward the teal stream. As shown by 

the solid blue area of the FAC, this terminal network should have flowed east toward the main 

network. The flowlines to the southwest of the solid blue area are pointed in the correct 

direction, while the flowlines north of the solid blue area are pointing north and should be 

pointed south. A flowline is missing from the NHDPlus near the center of the solid blue area. It 

should carry flow from the isolated network and connect to the network to the east, 

approximately following the path taken by the FAC. There is a dam in the area of the missing 
NHDPlus User Guide 51 September 1, 2010 

flowline. Because the flowline was missing, the burning process did not cut through the dam. 

The filling process filled up the flat area (reservoir) upstream of the dam, resulting in the pattern 

of flow accumulation that does not follow the flowlines closely, however it did eventually 

overtop the dam and flow down the stream channel. The smoothed elevations in the 

FlowAttributesFlow table may also exhibit some strange behavior in areas where the NHD 

network disagrees with the FAC. 

Figure 5-9 – Uncommon problem between the NHDPlus network and the flow accumulation grid 

Why does the Identify tool in ArcMap say that the value and ComID 

from the cat grid are different from the Grid_code and ComID shown 

in the Catchment shapefile? 

In ArcMap version 9.1, the identify tool appears to round grid cell values to six significant digits. 

Thus a grid cell having the value “2769195” through “2769204” all are reported as having the 

value “2769200”, and the other grid attributes shown are those that go with cell value 

“2769200”. If you select the record in the cat grid attribute table, the grid cells having that value 

are highlighted on the map. You can use this method to verify that the grid values are in 

agreement with the Grid_code values in the Catchment shapefile. This issue has been reported 

to ESRI and has been fixed in ARCGIS version 9.2.. 
NHDPlus User Guide 52 September 1, 2010 

Why would drainage areas computed using upstream navigation 

differ from the cumulative drainage areas pre-computed in the 

NHDPlus? 

The cumulative drainage areas pre-computed in NHDPlus are calculated using a downstream 

routing technique and at divergences all the drainage area is routed down the major path (see 

section “How to Use NHDPlus” – “NHDPlus and Divergences”). Infrequently, NHDPlus chose 

the wrong path as the major path and, of those cases, sometimes that path does not return to the 

main network. In these cases, drainage areas computed using navigation results will be correct 

and will be greater than the pre-computed NHDPlus drainage which are incorrect. This same 

issue affects all NHDPlus cumulative attributes such as the NLCD land categories, temperature, 

and precipitation. 

What is the situation with names assigned to artificial paths inside 

lake/pond waterbodies? 

When NHD was originally designed, flowlines inside waterbodies were combined into a single 

reach, often referred to as a branched reach. When a name was assigned to the reach inside the 

waterbody, all of the flowlines in the branched reach received that name, thus creating a 

branched name. When NHD was converted to ArcGIS geodatabase in January 2004, a critical 

review of the NHD data model was performed and the decision was made to deconstruct the 

branched reaches into individual reaches; one for each flowline. This affected many thousands 

of reaches across the U.S. Due to resource constraints, the branched names were not corrected at 

that time. Therefore, as a named river path is followed, the named path will be linear outside of 

lake/pond features and branched when it passes through lake/pond features. 

Difficulties using NHDPlus Attribute .dbfs in Microsoft Access 

When trying to open an NHDPlus attribute table in native dBase format (dbf), you may get the 

following error message: 

“The Microsoft Jet database engine could not find the object ‘NHDtable_name.dbf’. Make sure 

the object exists and that you name its name and path name correctly.” 

This error message occurs after trying to open the NHDPlus dbf file directly from the Open 

dialogue box from the MS Access File pull-down menu. The reason for this error is that 

Microsoft Access 2003 and earlier versions only recognizes dbfs with the DOS 8.3 naming 

convention, consisting of base file names of 8 characters or less followed by the .dbf file type 

extension. Many NHDPlus dbf files have much longer names and will not import into Access. 

To correct the problem, first copy the file and rename it to a name consisting of 8 characters or 

less, such as “myfile.dbf”. It is recommended that you do not rename the original copy of the 
NHDPlus User Guide 53 September 1, 2010 

file because tools built for NHDPlus may need the file and will look for the file using its original 

file name. 

Using the NHDPlus Value Added Attributes (VAAs) for Non-Navigation 

Tasks 

The attributes in the NHDFlowLineVAA table provide several powerful capabilities for users. 

Several of the exercises/tutorials available for the NHDPlus show the power of the VAAs for 

navigation. The VAAs also provide many other non-navigation capabilities that can be of great 

value to users of NHDPlus. The objective of this section is to demonstrate several of these nonnavigation capabilities and, in the process, these examples can help users better understand and 

use the VAA data content. All of the figures in the following examples use Hydrologic Region 2, 

the Mid-Atlantic. 

Details on the computation of the VAAs can be found in Appendix A, Step 2: Computation of 

Value Added Attributes (VAA). 

Example 1: ThinnerCod 

The ThinnerCod is an ordinal value that helps to display various network densities. The 

ThinnerCod values range from 0 to 6. ThinnerCod=0 will show all non-networked flowlines, 

including coastlines and isolated flowlines not included in the network. Figure 5-10 shows an 

example of ThinnerCod=0 highlighted in red. 
NHDPlus User Guide 54 September 1, 2010 

Figure 5-10 – ThinnerCod = 0 

A ThinnerCod value of 1 contains the major rivers at a density appropriate for map displays at a 

small scale. The ThinnerCod = 1 is also very important because it has been built as the backbone 

network that connects all of the HUC-8’s. This can be very useful when you want to extract a 

complete hydrologically networked set of HUC-8’s as a subset of NHDPlus. Figure 5-11 shows 

ThinnerCod = 1 highlighted in red. 
NHDPlus User Guide 55 September 1, 2010 

Figure 5-11 – ThinnerCod = 1 
NHDPlus User Guide 56 September 1, 2010 

Increasing ThinnerCod values provide increasing density of the stream network. For instance, 

Figure 5-12 shows ThinnerCod values of 1 and 2. Note the increased density in relation to the 

previous figure. Selection of ThinnerCod values from 1 to 6 will incrementally increase the 

density until the entire set of networked flowlines is displayed. 

Figure 5-12 – ThinnerCod = 1 or 2 
NHDPlus User Guide 57 September 1, 2010 

Example 2: Using LevelPathi to Build Your Own “ThinnerCod” based on Stream Length 

The mainstem of each stream is assigned a unique identifier named “LevelPathi”. LevelPathi is 

equal to the Hydroseq value of the most downstream flowline on that river. This feature of 

LevelPathi can be used in conjunction with the flowline Lengthkm attribute found in the 

NHDFlowline table. The following SQL statement will build a table of the total lengths for each 

mainstem of every networked stream/river: 

SELECT NHDFlowlineVAA.LEVELPATHI, Sum(NHDFlowline!LENGTHKM) AS strmlength 

INTO strmleng 

FROM NHDFlowline INNER JOIN NHDFlowlineVAA ON Flowline.COMID = 

NHDFlowlineVAA.COMID GROUP BY NHDFlowlineVAA.LEVELPATHI 

HAVING (((NHDFlowlineVAA.LEVELPATHI)>0)); 

The above SQL statement creates a variable named strmlength as the sum of the lengths of all 

flowlines by LevelPathi and puts the LevelPathi and strmlength variables into a table named 

“strmleng”. Figure 5-13 highlights all of the mainstem rivers greater than or equal to 100 Km in 

length. Note that any length threshold criteria can be used as desired. 

Figure 5-13 – Streams Greater than or Equal to 100 Kilometers in Length 
NHDPlus User Guide 58 September 1, 2010 

Example 3: Selecting an Individual River or an Individual Terminal River Basin 

One use of the LevelPathi was shown in Example 2. That example used the information that 

every stream has Levelpathi as a unique identifier. In the following examples, uses for 

LevelPathi and TerminalPa are shown. We will use the Potomac River as our example river. The 

most downstream Hydroseq for the Potomac River is 9169600001. This means that by the VAA 

conventions, the LevelPathi for the Potomac mainstem is assigned this value and every 

networked flowline in the Potomac Basin is assigned this value as the TerminalPA. Figure 5-14 

shows the selection of LevelPathi = 9169600001, which selects the mainstem of the Potomac 

River. Figure 5-15 shows the selection of TerminalPA = 9169600001 which selects the entire 

Potomac River Basin. 

Figure 5-14 – The Mainstem of the Potomac River By Selecting LevelPathi=9169600001 
NHDPlus User Guide 59 September 1, 2010 

Figure 5-15 – The Potomac River Basin By Selecting TerminalPA = 9169600001 
NHDPlus User Guide 60 September 1, 2010 

Example 4: Profile Plots 

Plots of data along a river where the x-axis is the river mile (or river kilometer) are widely used 

for showing data and modeling results. The VAAs contain the basic information to readily 

develop profile plots. Previous VAA examples showed how the LevelPathi can be used to 

identify every flowline on a river. Another VAA, PathLength, is the length from the bottom of 

the flowline to the end of the network. For instance, every flowline in the Missouri Drainage 

Basin has a PathLength value that tells how far away it is from the mouth of the Mississippi 

River. 

The basic profile plotting procedure is to select the LevelPathi for the river of interest and assign 

your data values to the comids of the flowlines of interest. Include the PathLength in the dataset, 

and then plot your data using PathLength as the x-axis and your data as the y-axis. Of course, 

multiple types of data can be shown on one graph, such as data versus model results. 

This example uses the mainstem of the Potomac River PathLength variable as the x-axis and the 

“MinElevSmo” elevation values from the FlowLineAttributesFlow table for the y-axis values. 

This particular plot is interesting because the elevation change near PathLength 180 is dramatic; 

this is where the Potomac River changes from free-flowing to estuarine. This plot goes from 

downstream to upstream but it is a simple matter to reverse the x-axis as desired. 

Elevation Along the Potomac River Mainstem

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700

Pathlength (kilometers)

Flowline Elevation (meters)

Figure 5-16 – Profile Plot of the Mainstem Potomac River “MinElevSmo” values 
NHDPlus User Guide 61 September 1, 2010 

Example 5: Stream Order 

The NHDPlus stream order is based on the Strahler Method. Stream order is a classic method 

for ranking streams according to size. Stream order computed for the NHDPlus flowlines is 

distributed as an NHDPlus data extension in a table called SOSC.dbf

Mapping or classifying flowlines on the basis of stream order can help to rank flowlines by size 

within the network, selecting out streams of only certain orders, or aggregating data by stream 

order. A recent example of this last capability, classifying data by stream order can be found in 

(Alexander, et. al., 2007) 

Some examples of mapping by stream order are shown below. Figure 5-17 shows different 

colors for each stream order for an area in the Midatlantic Region. This figure illustrates how 

stream order helps rank streams by relative size. Figure 5-18 shows the same area but with 

stream order 1 removed. This is one method to “thin” the network based on hydrologic criteria. 

There are other excellent ways to rank or thin the NHDPlus network, especially by using mean 

annual flow as a criteria; this method is not illustrated here. 

Figure 5-17 – Stream Orders in a Part of the Midatlantic Region 
NHDPlus User Guide 62 September 1, 2010 

Figure 5-18 – Stream Orders in a Part of the Midatlantic Region with Order 1 Streams Removed 
NHDPlus User Guide 63 September 1, 2010 

Example 6: Stream Level 

The use of Stream Levels, the variable StreamLeve, is often misunderstood or misused by users 

of the VAAs. Quite often, users think of StreamLeve “as the opposite of Stream Order”. But, 

this is not true in any sense. Streamleve = 1 will apply to the Mississippi mainstem but also to 

every small or large stream that terminates on the coastline. Therefore, StreamLeve has nothing 

to do with stream size. 

The only valid use of StreamLeve for users is to identify, at a particular junction, what is the 

mainstem and what is the tributary stream. The lower valued stream levels are the mainstem and 

the higher valued stream levels are the tributaries. Figure 5-19 illustrates this. The flowlines are 

labeled with the StreamLeve values. The flowlines going in the north-south direction are Level 2, 

and the flowline coming in from the West is Level 3. Therefore, the North-South flowlines are 

the mainstem and the flowline coming in from the West is the tributary. 

There are additional aids in the VAAs, for instance using PathLength to determine flow 

direction. If you want to know which way the North-South stream is flowing, check the 

Pathlength values of both of these flowlines. In this case, the Pathlength of the South flowline is 

400.1 and the Pathlength of the northern flowline is 397.5. Therefore, the northern flowline is 

closer to the terminus, so the flow is going from south to north. The Hydroseq can also be used 

to determine the flow direction at this junction. The smaller Hydroseq value will be the 

downstream flowline. 

Figure 5-19 – StreamLevel Values at a flowline Junction 
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NHDPlus User Guide 65 September 1, 2010 

Appendix A – Process Descriptions for NHDPlus 

NHDPlus is built in a series of seven steps: 

Step 1: Improvements to NHD 1:100K Linear Network and Feature Attributes 

Step 2: Computation of Value Added Attributes 

Step 3: Development of Catchments, Max/Min Elevations, Flow Accumulation, and Flow 

Direction Grids 

Step 4: Development of International Catchment Areas 

Step 5: Development of Catchment Attributes 

Step 6: Development of Flow Volume and Velocity Estimates 

Step 7: Elevation Post-Processing, Smoothing, and Slope Calculations 

Following these seven steps, the data is packaged and QA/QC’ed. 

Each of these steps is described in detail in the following sections. 
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NHDPlus User Guide 67 September 1, 2010 

Step 1: Improvements to NHD4 1:100K Linear Network and Feature 

Attributes 

During 2004 and 2005, the 1:100,000-scale NHD surface water network was QA/QC’ed and 

corrected where necessary. An automatic process was used to identify: 

 Reaches with invalid combination of flowline feature types 

 Reachable flowline feature that is not part of a linear Reach 

 Circular Reaches 

 Flowlines that touch internally or more than once 

 Non-linear Reaches 

 Non-linear flowlines 

 Coordinate order that is not consistent with flow or opposing flow, according to flow table 

 Flowlines that flow and do not touch, according to flow table 

 Flow table entries that are never navigated 

 Non-Terminal flowline with no outgoing flow table entry 

 Invalid flow table entries 

 Non-Start flowline with no incoming flow table entry 

 Potential loop in flow table 

 Possible outflowing inter-cu connection that needs to be validated 

 Possible incoming inter-cu connection that needs to be validated 

 Duplicate flow table entry 

 Incomplete divergence in flow table 

QA/QC and editing was performed at the Subbasin level. Both the flowline geometry and the 

flow table were edited to correct the network. When a Subbasin was error free, it was navigated 

from its pour point(s) to find any flowlines that were not connected to the main network. These 

isolated flowlines were connected where it was possible to determine the proper connection 

points without reference to external information such as digital raster graphics (DRG) or digitalortho-photo quads (DOQ)5

. 

When all Subbasins in a Hydrologic Region were deemed error free, the Subbasins were 

appended into a regional dataset, and a regional navigation was performed. Large sets of isolated 

flowlines were examined with DRGs as a backdrop. If the proper connection points could be 

determined, the connections were made in both the NHD geometry and the flow table. It was not 

possible to connect all isolated flowlines. 

In addition to the network connectivity QA/QC, the flowline feature names were also 

QA/QC’ed. Data from the Geographic Names Information System (GNIS) were compared to the 

names on the NHD Flowlines. Name corrections and additions were made as needed. 

Because much of the NHD editing was performed without external reference material, it is 

possible that flow direction may not be 100 percent correct; however, during Step 7, the NHD 

network drainage areas are compared to National Water Information System (NWIS) flow gage 

drainage areas as a final QA/QC procedure. 
NHDPlus User Guide 68 September 1, 2010 

Step 2: Computation of Value Added Attributes (VAA)

The VAAs are designed to enhance NHD for display, navigation, and analysis. The attributes 

are computed from existing NHD content rather than additional data collection. The attributes 

require a fully completed stream network from headwaters to mouth and are computed for large 

sections of the NHD as follows: Region 01; Region 02; Region 03 (except HUC4 0318); Regions 

05, 06, 07, 08, 10, 11, and HUC4 0318; Region 12; Region 13; Regions 14 and 15; Region 16; 

Region 17; Region18; and Region 20. 

The attributes require three full passes of the data. The first pass is from upstream to 

downstream, followed by a pass from downstream to upstream, with a final pass from upstream 

to downstream. 

There are 20 attributes, as follows: 

From Node (FromNode) 

A nationally unique ID for the “from” node (i.e. the upstream endpoint) of the flowline. These 

IDs are independent of the node IDs in an .NAT table in a coverage format workspace. The From 

Node and To Node numbers provide a node-to-node traversal method used by some modeling 

software. 

To Node (ToNode) 

A nationally unique ID for the “to” node (i.e. the downstream endpoint) of the flowline. These 

IDs are independent of node IDs in an .NAT table in a coverage format workspace. The From 

Node and To Node numbers provide a node-to-node traversal method used by some modeling 

software. 

Hydrologic Sequence Number (Hydroseq) 

A nationally unique sequence number assigned to each flowline; this number places the 

flowlines into hydrologic sequence. If flowlines are processed by hydrologic sequence number 

in descending order (i.e., starting at headwaters and proceeding downstream to the network 

termini), when a flowline is processed, all the flowlines upstream have already been processed. 

If flowlines are processed by hydrologic sequence number in ascending order (i.e., starting at the 

network termini and proceeding upstream to the headwaters), when any flowline is processed, all 

the downstream flowlines have been processed. Hydrologic Sequence Number supports several 

new navigation methods including traversal through SQL queries. 

For a given flowline, it is true that all flowlines upstream have higher hydrologic sequence 

numbers and all flowlines downstream have lower hydrologic sequence numbers. However, for 

a given flowline, it is not true that all flowlines with higher hydrologic sequence numbers are 

upstream nor are all flowlines with lower hydrologic sequence numbers downstream. 

Start Flag (StartFlag) 

Indicates which flowlines are headwaters (i.e., network starts) according to the flowline flow 

table. This flag is set to “1” if the flowline is a headwater flowline; otherwise, it is set to “0.” 
NHDPlus User Guide 69 September 1, 2010 

Terminal Flag (TerminalFl) 

Indicates which flowlines are network ends according to the flowline flow table. This flag is set 

to “1"” if the flowline is a terminal flowline; otherwise, it is set to “0.” A terminal flowline stops

at an ocean, the Great Lakes, Canada, Mexico, or it flows into the ground. 

Terminal Path Identifier (TerminalPa) 

A unique identifier for all the flowlines which flow to the same network terminus based on the 

flowline flow table. The Hydrologic Sequence Number of the terminal flowline is used as the 

Terminal Path Identifier. Terminal Path Identifier can be thought of as a “drainage area ID”. 

See also “Terminal Flag”. 

Level Path Identifier (LevelPathI) 

A unique identifier for a stream which is assigned to all the flowlines from the stream’s mouth to 

the stream’s headwater. The Hydrologic Sequence Number of the flowline at the mouth of the 

stream is used for the value of the Level Path Identifier. This attribute is based on the flowline 

flow table and stream level. Level Path Identifier can be thought of as a “stream ID” and can be 

used to support applications such as river mile indexes. 

Arbolate Sum (Arbolatsu) 

Based on the flowline flow table, this is the sum of the lengths of all flowlines above the 

downstream end of a flowline. This field is empty in the distributed NHDPlus data. 

Path Length (PathLength) 

Distance from a flowline’s downstream end to its terminal flowline’s downstream end according 

to the flowline flow table. Path length is in kilometers. 

Thinner Code (ThinnerCod) 

An ordinal value designed to allow selection of progressively denser networks. The least dense 

network is obtained by selecting thinner values of 1 which is the network of major streams and 

rivers that connect the 8-digit Hydrologic Units (i.e. subbasins or cataloging units). Each 

successive value of Thinner adds more streams to the network. At any Thinner level, the 

network is fully connected. Thinner values are designed to be used for improving the 

performance of Web pages and other applications where the user zooms back and forth between 

large areas and small areas. There is no hydrologic basis, other than connectivity, for the thinner 

values and they should NOT be used for stream classification or analysis. 

Divergence Flag (Divergence) 

If the flow splits into more than one branch (i.e. a flow divergence), and the flowline is one 

branch of the flow split, the divergence flag is set as follows: “1” if the flowline is the main 

branch and “2” if the flowline is not a main branch. If the flowline is not a branch of a flow split, 

the divergence flag = 0. 

Stream Level (StreamLeve) 

Stream levels are assigned beginning at network termini and working upstream. If the network 

terminus is at the ocean, the stream level begins with 1. If the network terminus is at the Great 

Lakes, the stream level begins with 2. If the network ends at the Canadian or Mexican border, the 
NHDPlus User Guide 70 September 1, 2010 

stream level begins with 3. If the network terminus flows into the ground, the stream level begins 

with 4. The stream level value is continued upstream, following the main path, until the 

headwater of the mainpath is reached. Tributaries to the mainpath are assigned the next integral 

stream level beginning at their mouth and continuing to their headwaters. This process is 

repeated for each additional level of tributaries until all streams have been assigned a stream 

level. For example, the Mississippi River is level 1; tributaries to the Mississippi, like the Ohio 

River, are level 2; and tributaries to the Ohio River, like the Tennessee River, are level 3. Stream 

level supports upstream mainstream navigation and is NOT intended to be used for stream 

classification or analysis. 

Downstream Level (DNLevel) 

Downstream flowline level is the stream level of the downstream mainstem flowline. This 

attribute supports downstream mainstem navigation. 

 

Stream Order (StreamOrde) 

This attribute has been replaced by the Stream Order/Stream Calculator data distributed as an 

NHDPlus data extension. The table is called SOSC.dbf. The field 

NHDFlowlineVAA.StreamOrde has been set to 0 to encourage the use of the better values found 

in SOSC.dbf. 

Upstream Level Path Identifier (UpLevelPat) 

This is the level path identifier of the mainstem flowline which is immediately upstream. This 

attribute supports navigation traversals through SQL queries. 

Upstream Hydrologic Sequence Number (UpHydroSeq) 

Hydrologic Sequence Number of the immediately upstream mainstem flowline. This attribute 

supports navigation traversals through SQL queries.

Upstream Minimum Hydrologic Sequence Number (UpMinHydro) 

Minimum Hydrologic Sequence Number of all immediately upstream flowlines. This attribute 

supports navigation traversals through SQL queries.

Downstream Level Path ID (DnLevelPat) 

This is the level path identifier of the downstream mainpath flowline. This attribute supports 

navigation traversals through SQL queries. 

Downstream Flowline Count (DnDrainCou) 

This is the number of flowlines immediately downstream. This attribute supports navigation 

traversals through SQL queries. 
NHDPlus User Guide 71 September 1, 2010 

Downstream Minor Hydrologic Sequence Number (DNMinHydro) 

At a divergence, the Hydrologic Sequence Number of the immediately downstream minor path 

flowline. If multiple minor paths exist, this is the maximum hydrologic sequence number of all 

minor paths. 
NHDPlus User Guide 72 September 1, 2010 

Step 3: Development of Catchments, Max/Min Raw Elevations, Flow 

Accumulation and Flow Direction Grids, Max/Min Raw 

Stream Channel Elevations, and Headwater Node Areas

Catchments 

Catchments were generated for each NHD Flowline that appears in the NHDFlow table. To 

create catchments, the flowlines were rasterized to serve as the source grid for the ARC/INFO 

GRID module command, WATERSHED (ESRI, 1999). Catchments were developed upslope 

from these stream-network grid cells. A flow direction grid derived from a Digital Elevation 

Model (DEM) was also required as input for the WATERSHED command. The flow direction 

grid was produced using a hydrologically-conditioned DEM called HydroDEM. The source 

DEM was obtained from the 30-meter resolution NED and was projected into the national Albers 

projection for each production unit. These projected DEMs (elevation grids), are provided in the 

NHDPlus product suite. 

Modifications were applied to the DEMs to produce the HydroDEM. These modifications were 

considered necessary because often the drainage path (flowpath) defined by the NED surface 

does not exactly match the 1:100,000-scale NHD. In many cases, the NHD streams and NEDderived streams are parallel or offset from each other. Figure A-1a illustrates a common example 

of the differences in the horizontal positions of NHD streams and NED-derived streams. If this 

offset distance is greater than one grid-cell width, then some cells may not be identified as being 

upslope from the NHD stream segment and therefore would be erroneously excluded from the 

delineated catchment (Figure A-1b). 

To mitigate this mismatch of stream locations, the NHD vector drainage was integrated into the 

raster NED data, often referred to as “stream burning” (Saunders, 2000). This process uses 

computer algorithms in an Arc Macro Language (AML) program called AGREE, developed by 

Hellweger (1997). Figure A-1c illustrates how the AGREE program corrects for DEM flow path 

displacement errors when delineating catchments. 
NHDPlus User Guide 73 September 1, 2010 

Figure A-1 – (a) Differences in drainage between the NHD and flow paths of a NED-derived stream, (b) 

Resultant NHD catchment delineations using unmodified NED DEM data, and (c) Resultant NHD catchment 

delineations using AGREE-modified NED data. 

AGREE “burns” a “canyon” into the NED-based DEM by subtracting a specified vertical 

distance from the elevation beneath the NHD vector streamlines. The vertical exaggeration of the 

canyon is controlled by specifying a “Sharp Drop/Raise Distance.” For the HydroDEM, a 

negative “sharp” drop distance (10,000 meters) was applied to retain the new NHD stream flow 

path after subsequent depression filling processes needed for catchment delineation. 

AGREE also “smoothes” the elevation adjacent to NHD stream cell locations in the DEM within 

a buffer distance specified by the AGREE program user. Typically, the buffer distance is related 

to a common horizontal displacement error between NHD and NED-derived streams; this error is 

seldom exceeded. For HydroDEM production, the buffer distance was set to 160 meters on each 

side of the NHD streamline. The smoothing process changes the DEM grid-cell elevations within 

the buffer area to create a downward sloping gradient towards the modeled canyon beneath the 

NHD streams. The steepness of the slope within the buffer is controlled by the AGREE “Smooth 

Drop/Raise Distance” option. For the HydroDEM, a smooth drop distance of 500 meters was 

specified, with acceptable results. Figure A-2 illustrates how AGREE changes the original DEM 

using all the specified parameters of AGREE. 
NHDPlus User Guide 74 September 1, 2010 

Figure A-2 – Schematic of AGREE process 

The use of AGREE’s 160 meter smooth/drop buffer distance of the NHD streams may cause 

potential problems at headwater flowlines because they begin at or near drainage divides in the 

DEM. The 160 meter buffer distance at these headwater streams may extend across the DEM 

drainage divides and into the adjacent basin area, thereby including areas outside the true 

catchment area. 

To minimize the problem of extending headwater streams into adjacent watersheds, an AML 

program was created that selects only headwater streams from the NHD stream network and 

trims the NHD headwater vector streamlines back 90 meters from the starting point. The streamtrimming program is fully automated and is run prior to the AGREE program. 

The hydrologic-conditioning of the NED data also includes a process developed for the New 

England SPARROW water-quality models (Moore et al., 2004). This “New England Method” 

uses AGREE for drainage enforcement and establishes Watershed divides, if available, from the 

Watershed Boundary Dataset (WBD). The process of conditioning DEM data to WBD 

Watersheds is called “walling” and uses an AML, written by Moore and Johnston (2004), to 

vertically exaggerate DEM elevations corresponding to the location of WBD ridgelines. The 

vertical distance used to exaggerate the cells is a specified constant added to the elevation grid 

cells above the WBD. Breaks in the walls were created at locations where the stream network 

crosses the WBD to insure proper passage of water from one WBD SubWatershed unit to 

another. A graphic 3-D representation of a hydrologically-conditioned DEM with WBD walling 

and the NHD “burning” is shown in Figure A-3. 
NHDPlus User Guide 75 September 1, 2010 

Watershed Boundary Dataset (WBD)

added to DEM surface in "walling"

technique

NHD stream cells

subtracted from

DEM surface in "burning"

technique

Figure A-3 – 3-D Perspective view of modified DEM with walling of existing Watershed boundaries and 

burning of NHD streams 

The New England Method for producing catchments was compared with other methods in an 

EPA-sponsored, NHD-NED Synchronization pilot study in cooperation with the USGS. The 

results of the study showed that the New England Method provides the most accurate catchment 

delineations, using nationally available data and automated methods. 

The New England Method was further refined by the USGS (Rea and Skinner, written commun., 

2004) by imposing a “bathymetric gradient” within two-dimensional NHDWaterbody features 

(i.e., stream/river, lake/pond). The bathymetric gradient ensures that the catchments generated 

for artificial path flowlines within waterbodies are based on a gradient directed towards the 

artificial path flowlines. The gradient is applied prior to running AGREE. The bathymetric 

gradient process applies GRID algorithms, similar to those used in AGREE, to create a broad 

sloping gradient with shorelines upslope from the artificial path flowline(s). 

The last step in the HydroDEM creates a “filled” DEM surface grid with the ARC/INFO GRID 

command “FILL,” which removes depressions. This insures all elevation cells in the basin have a 

defined drainage direction. The required flow direction grid for the WATERSHED command is 

produced from the filled HydroDEM. 
NHDPlus User Guide 76 September 1, 2010 

Due to the resolution of the NED data, catchments were not generated for many flowlines 

approximately 42 meters or less in length (42 meters is the diagonal distance across a 30 meter 

grid cell). 

In rare circumstances, flowlines longer than 42 meters may not have been assigned a catchment, 

depending on the spatial configuration of a flowline with other flowlines. In these cases, 

flowlines may run parallel with each other within a given cell and may continue for several cells 

over the entire length of one of the flowlines. In other rare cases, the trimming back of the NHD 

headwater stream segments did not allow for enough of the remaining flowline to be assigned a 

catchment and cells were assigned instead to a neighboring flowline. Trimback errors are 

especially rare since the trim streams program is designed to limit these types of errors. For 

Region 17, with approximately 237,000 flowlines greater than 42 meters, three catchments were 

not generated as a result of spatially configured flowlines running parallel to each other, and two 

catchments were not generated as a result of the trimming back of headwater flowlines. 

The catchments data are available in the native GRID format and as vector polygon feature-class 

shapefiles. It is important to note that catchment features in a shapefile may be composed of one 

or more vector polygon features. Multiple polygon features occur as a result of the source 30 

meter grid-cell resolution and the grid-to-vector conversion process. In these situations, one or 

more cells with directional flow traveling diagonally into an adjacent cell along a catchment 

boundary may create a separate polygon in the vector data model when these data are converted 

from a GRID (see Figure A-4). 
NHDPlus User Guide 77 September 1, 2010 

Figure A-4 – Illustration showing multiple polygon features defining a catchment area for a flowline 

In creating the catchment shapefiles, the catchment data in GRID format were converted to a 

vector polygon ARC/INFO Coverage. This polygon coverage of catchments was then combined 

using the ARC/INFO Regions data model to ensure multiple polygons with the same ComID 

were represented as one multi-part area feature. The Region feature class coverage was then used 

to create the catchment shapefile, which retains the combined polygon features as one multi-part 

polygon. If the catchments are converted from shapefile to Coverage format, it will be necessary 

to rebuild the Region class features to ensure that each catchment feature, for each ComID, is 

represented by a single unique area feature. 

Flow Direction and Accumulation GRIDs 

The flow direction grid was created by using the ESRI ARC/INFO command 

FLOWDIRECTION. A flow direction grid contains integers representing the direction from each 

cell to its steepest downslope neighbor. The elevation grid used to compute flow direction was 

created with the “FILL” command. 

The flow accumulation grid was created by using the ESRI ARC/INFO command 

FLOWACCUMULATION. A flow accumulation grid contains integer values equal to the 

number of cells uphill from that cell. The flow direction grid was used as input in 

FLOWACCUMULATION to determine the total number of cells that flow into each downslope 

cell. 
NHDPlus User Guide 78 September 1, 2010 

In this process, flow is ultimately directed to “sinks” created by placing “no-data cells” at certain 

locations, such as at the outlet to each processing unit. For Hydrologic Regions that drain 

directly into the ocean, the entire coastline is used as a sink. For networks that drain to Canada or 

Mexico, a sink is also applied at the network’s terminus along the international border. Isolated 

drainage networks are generally eliminated by “filling” to create flow direction and accumulation 

grids. Sinks are only placed at the network ends of isolated networks if they are within 8-digit 

Hydrologic Units identified as closed basins (with the exception of Hydrologic Region 16, where 

sinks were applied region-wide). 

A procedure for placing sinks in closed basins was applied to avoid: 1) placement in high 

precipitation areas (mean annual precipitation greater than 14 inches), 2) 1:100,000-scale map 

boundaries where network end may be erroneous due to source quadrangle mapping 

inconsistencies, and 3) placement closer than 90 meters to the main network to which the 

isolated network either should be connected or there is apt to be highly permeable alluvium. 

Figure A-5 shows how isolated networks are treated. Catchments are delineated for the isolated 

networks in the same manner as any other NHD Flowline. The flowlines are rasterized and 

converted to “NODATA” or “sinks” in the elevation grid. The FILL process, followed by 

FLOWDIRECTION, directs flow to these NODATA cells. The rasterized NHD Flowlines are 

then used as the seeds for catchment delineation using the WATERSHED function. This process 

produces the best representation of catchments for isolated networks. 

The DEM is then processed with FILL a second time - this time to produce the final 

flowdirection grid. In this process, sinks are established only at the outlet of the processing unit, 

unless there are Subbasins (8-digit HUCs) identified as closed basins. Therefore, the isolated 

networks fill up and spill over, producing a drainage network similar to that which would be 

produced using a DEM without the stream burning process. 

The reason for generally letting the accumulated cell counts continue beyond the isolated 

networks is identification of likely flowlines to which the isolated network should (perhaps) be 

connected. Using this information, a user could choose to fix isolated networks that should be 

connected to the main network or determine watersheds that include the isolated network areas. 

In Figure A-5, the synthetic hydrography (i.e., the hydrography derived from the DEM 

FLOWACCUMULATION function) is plotted in red. The NHD Flowlines are plotted in blue 

over the red. In most cases, the agreement is very good and the blue closely overplots the red. 

However, the isolated network in the top center of the figure shows a side effect of the AGREE 

process. For this isolated network, the synthetic streams are horizontally displaced with the NHD 

and even cross over from one stream to another. Since the trench caused by the isolated network 

had to be filled back up until it could spill over, the surface became flat within the AGREE 

buffer area. There seems to have been very little overall slope in this area; therefore, nearly the 

entire isolated network was affected. Within the flat area, the flow direction and flow 

accumulation are not well controlled and suffer— to a limited extent— from the same problems 

occurring in DEMs processed without the benefit of stream burning. These effects are not 

common or widespread but may occur wherever there are isolated networks. 
NHDPlus User Guide 79 September 1, 2010 

Figure A-5 – Illustration comparing the horizontal displacement between the NHD streams of an isolated

network (in blue) to the synthetic streams of the “filled” HydroDEM 

The processes outlined above were applied to each “production unit” (an area equal to or less 

than 73,000 square miles). The restricted size is due to GRID processing limits. The Production 

Unit map (Figure 4-1) shows the order of processing of the production units. Flow direction and 

flow accumulation grids are not merged for each Hydrologic Region because the accumulation 

values only represent upstream cells within a defined area; they do not include cells in upstream 

production units. Catchment grids, on the other hand, are combined for final distribution. The 

catchment areas are not affected by excluding upstream accumulations from other processing 
NHDPlus User Guide 80 September 1, 2010 

units. The user should bear in mind, however, that the flow accumulation values (cell counts) 

include cells accumulated from within a 10 kilometer buffer. 

Assigning Minimum and Maximum Raw Stream Channel Elevations 

(unsmoothed) to NHD Flowlines and Headwater Node Areas 

NED was used as the source elevation dataset because the elevations in the “burned” NHD 

stream paths in the HydroDEM are greatly modified. The maximum flowline elevation 

represents the elevation at the upstream end of the flowline and the minimum elevation is at the 

downstream end. Due to the varying degrees of accuracy of the NED, these “raw” elevations can 

produce negative slopes and, therefore, the elevations were later smoothed as described in Step 

7. 

A difficulty in estimating minimum and maximum stream elevations is often caused by poor 

agreement between the location of the stream depicted on the NHD and the flowpath generated 

by the elevation data alone. The locations of the NHD Flowlines typically are much more 

accurate. However, the minimum elevation value in the entire catchment is generally a 

reasonable estimate of the elevation of the stream as it leaves the catchment area. Using this 

value avoids the problems of horizontal displacement in the two stream networks (see NEDderived stream in red and NHD stream in blue in Figure A-6). The maximum elevation for each 

flowline is the minimum elevation in the immediately upstream catchments (Figure A-6). 

A different process was needed for the maximum elevation on headwater flowlines. Temporary 

catchments were generated for the upstream node of each headwater flowline. The minimum 

elevation of that temporary headwater catchment is taken as the maximum elevation of the 

headwater flowline. Headwater node areas (in square kilometers) are included in the NHDPlus 

HeadWaterNodeArea table. 
NHDPlus User Guide 81 September 1, 2010 

Figure A-6 – Assigning Minimum and Maximum Stream Channel Elevations to NHD Flowlines 
NHDPlus User Guide 82 September 1, 2010 

Step 4 - Development of International Catchment Areas 

Hydrologic Regions with upstream areas in Canada or Mexico present special problems for 

computing streamflow or other hydrologic factors because many of the datasets are available 

only for the conterminous United States but not for Canada or Mexico. 

Catchment areas for streams receiving flow from Canada or Mexico were identified using 

generalized hydrography and watershed datasets. The extended catchment area for an NHD 

Flowline encompassed the entire non-U.S. upstream area for that stream; thus, these catchments 

are sometimes very large compared to most NHD Flowline catchments. Figure A-7 shows an 

example along the Canadian border. The light blue lines show the generalized hydrography used 

for Canada, and darker blue lines show the NHD hydrography. The boundary of the DEMderived catchment is shown in white, where the light blue line enters the United States. This 

catchment has been extended to include the entire area, shown in gold. Other catchments are 

shown in green. All catchments receiving major streams from Canada were expanded in a similar 

manner. 

Figure A-7 – Example of an international catchment on the Canadian border 
NHDPlus User Guide 83 September 1, 2010 

Different datasets were used to develop the catchment areas for different regions. Details on the 

data sources used may be found in the Release Notes for each region having international 

catchments. 

Because of the previously described data issues, catchment areas and catchment characteristics, 

as well as cumulative drainage areas and characteristics near an international border, are less 

accurate than in other areas. This inaccuracy is greatest in catchments touching the border. The 

greater the percentage of a catchment is in non-U.S. areas, the greater the data inaccuracy. The 

effect diminishes farther downstream as the ratio of non-U.S. to U.S. catchment areas becomes 

smaller. 
NHDPlus User Guide 84 September 1, 2010 

Step 5: Development of Catchment Attributes 

Catchment attributes were computed using ArcInfo Grid, version 9.0 (ESRI, 2004). Mean 

Annual Precipitation and Mean Annual Temperature data for 1961-1990 were obtained from 

PRISM (Daly and Taylor, 1998). The PRISM datasets were projected from geographic 

coordinates to Albers Equal Area projection, and the 2.5-arc-minute grid-cell resolution was 

transformed to approximately 4 km. The ArcInfo Grid function “ZONALSTATS” was used to 

compute the mean annual precipitation and temperature values for each catchment. 

Catchments covering area in Canada or Mexico had missing data in the mean annual temperature 

and mean annual precipitation grids underlying the non-U.S. portions of the catchments. The 

values computed for these catchments reflect the mean precipitation or temperature only for the 

catchment portion in the U.S. 

The National Land Cover Dataset (NLCD 1992) data were assembled for the Hydrologic Region 

being processed. The ArcInfo Grid function COMBINE was used to create a grid with a unique 

value for each unique combination of catchment number and NLCD category. The cell counts 

were converted to area percentage of each catchment. A custom program, named 

GROUP2ROW.AML, reformatted the resulting value attribute table to a table containing one 

record per catchment, with columns of area percentages for each NLCD category in that 

catchment. Empty columns were added for any NLCD categories not present. 

The NLCD grid was extended to cover the non-U.S. areas, specifying a code of 98 for Canada 

and 99 for Mexico. Subsequent processes operated on these catchments in the same way as with 

any other catchments. Attribute summaries for catchments and flowlines may include 

percentages of catchment areas and cumulative drainage areas in Canada and Mexico. Total 

drainage areas are generated by combining the percentages of area in Canada or Mexico with the 

percentages of all NLCD categories. 

The PCT_CN and PCT_MX fields in the CatchmentAttributesNLCD.dbf file and the 

Cumpct_CN and Cumpct_MX fields in the FlowlineAttributesNLCD.dbf file contain the 

percentages of catchment and total drainage areas in Canada and Mexico, respectively. Wherever 

these fields contain values other than zero, the user needs to take into account the potential 

effects of the non-U.S. areas on the particular application. 
NHDPlus User Guide 85 September 1, 2010 

Step 6: Development of Flow Volume and Velocity Estimates 

The Flow Volume and Velocity estimates are contained in the FlowlineAttributes table, and 

records are matched to the NHDPlusFlow table. The values in the FlowlineAttributes table are 

integrated from the NHDFlowlineVAA, the CatchmentAttributes tables, and the flowline 

max/min elevations. The NHDFlowlineVAA provides the data needed to route and accumulate 

information from the CatchmentAttributes. The process for calculating the smoothed elevation 

and slope values is described in Step 8. 

The FlowlineAttributes table is cumulative for all flowlines and associated catchments upstream 

of, and including, any flowlines selected or of interest. This accumulation is performed using the 

hydrologic routing information contained in the VAAs. 

The cumulative drainage area at the downstream end of a flowline is calculated as: 

 CumArea = ∑ i = 1 to n (Ai) 

where 

n = number of catchments upstream of the flowline (including that flowline), and 

Ai = the catchment area of the flowline. 

Divergences 

A flow divergence occurs when two or more drains converge at a junction, and the flow 

downstream splits into two flowlines. One of the downstream flowlines is designated as the 

“major” flow path, and the other flowline is designated as the “minor” flow path. At this stage of 

NHDPlus development, there is no information on the percentage of flow for either the major or 

minor paths. Therefore, all drainage areas, flows, etc. are routed and accumulated along the 

major flow path. The minor path is in effect treated as a “start” flowline, with the cumulative 

values initialized to the values for that minor path flowline. Most flow divergences re-converge 

with the major flow path and, at the re-convergence point, the total cumulative values will 

represent the sums from the major path and the minor path. 

Climate Data 

Mean annual air temperature (MAT) and mean annual precipitation (MAP) data are required for 

Vogel-based estimates of mean annual flow (Vogel et. al., 1999). These values are accumulated 

and averaged for each drain: 
NHDPlus User Guide 86 September 1, 2010 

AreaWtMAP – Area Weighted Precipitation at bottom of flowline in mm 

 

 ∑ i=1 to n (Pi * Ai) 

= 

 _______________________ 

 ∑ i = 1 to n (Ai) 

where 

Pi

 and Ai are the precipitation and catchment area for each flowline upstream. 

AreaWtMAT – Area Weighted Temperature at bottom of flowline in degree C * 10 

 ∑ i=1 to n (Ti * Ai) 

= 

 _______________________ 

 ∑ i = 1 to n (Ai) 

where 

Ti and Ai are the temperature and catchment area for each flowline upstream. 

Land Cover Cumulative Characteristics 

The cumulative NLCD % areas are computed by aggregating all of the individual NLCD 

catchment drainage areas: 

CUMNLCD_xx = % of cumulative drainage area classified as NLCD Class xx at the 

bottom of the flowline: 

 

 ∑ i=1 to n (NLCD_xxi * Ai) 

= 

 _______________________ 

 ∑ i = 1 to n (Ai) 

where 

NLCD_xxi

 = Percent of the catchment area in land cover class xx for flowline I 

(for instance, “xx”= “11” is land cover class 11=Open Water), and 

Ai = the catchment area for the ith flowline. 

Mean Annual Flow Estimates 

Two methods are used for estimating mean annual flow for each flowline. Values for the 

attribute “MAFlowU” are based on the Unit Runoff Method (UROM), which was developed for 

the National Water Pollution Control Assessment Model (NWPCAM) (Research Triangle 

Institute, 2001). Values in “MAFlowV” are based on methods from Vogel et al., 1999. 

NHDPlus utilizes two flow estimation procedures, both developed by using the HydroClimatic 

Data Network (HCDN) of gages. These gages are usually not affected by human activities, such 

as major reservoirs, intakes, and irrigation withdrawals; thus, the mean annual flow estimates are 
NHDPlus User Guide 87 September 1, 2010 

most representative of “natural” flow conditions. These estimation methods used the HCDN 

gages because each method is developed for use at large scales; such as Hydrologic Regions. It 

was beyond the scope and capabilities of both methods to determine the human-induced effects 

at this scale. However, the QA comparisons of NHDPlus flow estimates are compared to the full 

set of gages to provide users with information on the overall performance of each method. 

UROM Flow Estimates 

The UROM flow estimates use flowline catchment area estimates and unit runoff (cfs/km2

) data 

from associated watersheds (i.e., 8-digit Subbasin). The USGS stream gages in HCDN were 

selected for developing the unit runoff values because those gages represent relatively natural 

hydrologic conditions and are not influenced by controlled releases from reservoirs. Further, only 

gages with a drainage area smaller than the drainage area of the 8-digit Subbasin where the gage 

is located were selected, so that the discharge data represents runoff for only that Subbasin. For 

instance, a gage on the Mississippi River at St. Louis is not representative of the unit runoff from 

that Subbasin. At the national level, a total of 1,338 HCDN gages were identified for this dataset. 

Based on the drainage area comparisons, the dataset of 1,338 HCDN gages and the dataset of 

associated stream discharge data for these gages were used to derive mean annual and mean 

summer unit runoffs (ft3

/sec/km2) for each 8-digit Subbasin. The nearest HCDN gages were 

identified using a 200 mile maximum search radius from the centroid of an 8-digit Subbasin. In 

most Subbasins, five gages were selected, but some Subbasins had fewer than five within the 200 

mile search radius. Mean annual and mean summer unit runoffs for each 8-digit Subbasin were 

calculated using a weighted-average technique based on the square of the distance of the selected 

HCDN gages from the centroid of the Subbasin. The computations are defined as follows: 

QCU_MA = Σ(QHCDN_MA × 1/D2

CU_HCDN)/Σ(1/D2CU_HCDN) 

where 

 QCU_MA = estimated mean annual unit discharge for the 8-digit Subbasin of 

interest, 

 QHCDN_MA = mean annual unit discharge for the selected HCDN gage, and 

 D2

CU_HCDN = square of distance from the selected HCDN gage to the centroid of 

 the 8-digit Subbasin of interest. 

IncrFlowU is the incremental flow at the bottom of the flowline, computed as: 

 IncrFlowU = A * CU_MA 

where 

A = Drainage Area of the catchment (km2

), and 

 CU_MA = Unit Runoff for the 8-digit Subbasin (cfs/ km2). 

The UROM-based mean annual flow for each flowline (MAFlowU) is computed as: 

∑ i=1 to n (IncrFlowUi). 
NHDPlus User Guide 88 September 1, 2010 

UROM “Tuning” Using Intermittent Flow Adjustment Factors 

The development of the UROM was done as part of the development of the National Water 

Pollution Control Assessment Model (NWPCAM) (Research Triangle Institute, 2001). For 

Hydrologic Regions west of the Mississippi River, initial NWPCAM estimates of routed 

discharge generally were observed to be greater than the HCDN gage values. Consequently, for 

the Western Hydrologic Regions, a method was developed to better match (quasi-calibrate) 

discharge estimates to observed data. The discharge estimates were lowered by incorporating 

only a percentage of the stream segment-specific runoff for intermittent segments. The method 

calculates discharge estimates assuming various contributions (e.g., 100, 50, 25, 10, and 1 

percent) of the unit runoff for intermittent flowlines. This method proved successful in 

improving the match between gage flows and UROM-based flow estimates. The method is 

employed in the Western Hydrologic Regions in NHDPlus. The best fit is selected based on 

graphical analyses that compare the UROM flow estimates to the gaging data. As NHDPlus is 

produced, this tuning process will be completed in each Hydrologic Region west of the 

Mississippi (Regions 9, 10, 11, 12, 13, 14, 15, 16, 17, and 18). In Hydrologic Region 17, an 

intermittent unit runoff contribution of 10 percent appears to work best and is included as the 

UROM estimates in the distribution datasets. 

UROM Estimates in Areas with International Drainage

For a given flowline, the UROM bases each incremental flow contribution on unit runoff 

estimates in the HUC8. There are no unit runoff estimates for areas outside of the U.S.; therefore, 

international drainage areas do not have equivalent values developed. A multi-step process is 

employed to compensate for the lack of equivalent values. To begin, the flow volume module is 

run, assuming a unit runoff in the international area equals the unit runoff for the HUC8 where 

that drainage area comes into the U.S. Gages on flowlines that enter the U.S. are then identified, 

and their mean annual flow is compared to the UROM mean annual flow estimate. Finally, unit 

runoff values are calculated, making the UROM flow equal the gage flow. In Hydrologic Region 

17, where the Canadian contribution was relatively small (on the order of the area of one HUC8 

or less), the default HUC8 unit runoff produced mean annual flow estimates close to the 

observed gage flow. In the Columbia River, the unit runoff coefficient for the flowline receiving 

the Canadian drainage needed to be adjusted to match the gage flow. This adjustment re-sets the 

UROM flow estimate to be equal to the gage at the border. The process is repeated at each 

international drainage location. The final run of the flow estimation procedure uses these 

adjusted values for boundary flowlines. 

“Vogel” Mean Annual Flow Estimates 

The MAFlowV estimates are based on the work of Vogel et al., 1999. This method uses a log-log 

regression approach based on drainage area, precipitation, and temperature data from HCDN 

gages. With this method, the mean annual flow for a drain is computed as: 
NHDPlus User Guide 89 September 1, 2010 

 Convert AreaWtMAP from Deg. C * 10 to Deg. F * 10:

 V_AreaWtMAP = (AreaWtMAT / 10 * 9 / 5 + 32) * 10 

MAFlowV = ea

 * CumAREAb * AreaWtMAPc * V_AreaWtMATd * BCF * 35.31467

where 

a, b, c, and d are Hydrologic Region-specific regression coefficients, and 

BCF = Bias Correction Factor by Hydrologic Region. 

35.31467 = conversion factor from cubic meters per second to cubic feet per 

second 

The BCF is needed because the regression is log-log space. In addition, the Vogel flow estimates 

are valid only within the ranges of the original data used for computing the regressions. The 

regression coefficients, BCFs, and valid drainage area ranges for the Vogel Flow estimates are 

shown in Table 16. For cumulative drainage areas that fall outside of these ranges, the Vogel 

flow and velocities are set to missing values in the distributed data. 

Hydrologic 

region 

 a b c d BCF AreaMin (Sq. 

Km.) 

AreaMax 

(Sq. Km.) 

R01 -9.4301 1.01238 1.21308 -0.5118 1.004042 5.179976221 14672.28265

R02 -2.707 0.97938 1.6251 -2.051 1.007174 2.58998811 29940.26256

R03 -10.102 0.98445 2.2599 -1.607 1.014347 12.94994055 44547.7955

R04 -5.678 0.96519 2.2889 -2.3191 1.012719 72.51966709 5982.872535

R05 -4.891 0.99319 2.32521 -2.5093 1.007174 2.58998811 74164.30954

R06 -8.82 0.96418 1.3581 -0.7476 1.009752 12.94994055 6622.599598

R07 -11.861 1.00209 4.5596 -3.8984 1.009752 93.23957197 308208.5851

R08 0 0.98399 3.157 -4.1898 1.011187 132.0893936 7283.046566

R09 0 0.81629 6.4222 -7.6551 1.062826 51.79976221 16757.22307

R10 -10.927 0.89405 3.2 -2.4524 1.156028 10.35995244 53491.02444

R11 -18.627 0.96494 3.8152 -1.9665 1.044031 62.15971465 46236.46775

R12 0 0.84712 3.8336 -4.7145 1.146124 85.46960764 101032.8462

R13 0 0.77247 1.9636 -2.8284 1.122542 28.48986921 25200.58431

R14 -9.856 0.98744 2.469 -1.8771 1.08462 90.64958386 116160.9667

R15 0 0.8663 2.5065 -3.427 1.286895 23.30989299 68634.68492

R16 0 0.83708 2.1672 -3.0535 1.118034 18.12991677 12975.84043

R17 -10.18 1.00269 1.86412 -1.1579 1.059481 20.71990488 35094.3389

R18 -8.438 0.97398 1.99863 -1.5319 1.109234 15.53992866 8062.632987

Table 1: Vogel Flow Values by Hydrologic Region 

The “Vogel” based flow and, therefore, velocity estimates depend upon estimates for mean 

annual precipitation and temperature, as well as drainage area. In cases where there is drainage 

entering from Canada or Mexico, the temperature and precipitation values for the U.S. portion of 

that international catchment are assigned to the entire catchment. For small catchments, this 

probably does not result in large errors, but some international catchments are very large, with 

only a very small area in the U.S. Therefore, the Vogel-based flow estimates may be erroneous 

where there is a relatively large international drainage contribution. In this NHDPlus release, if 
NHDPlus User Guide 90 September 1, 2010 

the percentage of cumulative international drainage area for a flowline is greater than or equal to 

25 percent, the Vogel-based flow and velocity estimates are assigned missing values of -9998. 

 Median Annual Flow Estimates For Hydrologic Region 20 (Hawaii) 

The regression-based flow estimates in Hawaii are based on the work of Fontaine, et. al. (1992). 

In subbasins 20060000, 20050000, and 20010000 (Oahu, Molokai, and Hawaii, respectively) the 

median annual flow is computed as: 

Q50 = 4.25 * (DA)1.04

 

In subbasins 20070000 and 20020000 (Kauai and Maui, respectively) the median annual flow is 

computed as: 

Q50 = 4.49 * (DA)0.808 * (CE)-0.641 * (P)0.985

Where: 

 Q50 = Median annual flow (cfs), 

 DA = Drainage area (square miles), 

 CE = mean altitude of the main stream channel (feet), and 

 P = mean annual precipitation (inches) 

Mean Annual Flow Estimates For Hydrologic Region 21 (Puerto Rico) 

Hydrologoc Region 21, Puerto Rice and the Virgin Islands, has 3 primary issues: 

1. A regression model, similar to the “Vogel” method could not be located. Therefore, there 

will not be a set of regression-based mean annual flow and velocity in the final Region 

Flowlineattributesflow.dbf file. 

2. No data for Mean annual Temperature (MAT), mean annual precipitation (MAP), or land 

cover (NLCD) were developed for Region 21, so the catchment-level MAP, MAP, and 

NLCD and the cumulative MAP, MAT and NLCD tables are not available for Region 21. 

Note that the MAP and MAT values are not needed to support a regression-based 

estimation method equivalent to the “Vogel” method.

3. There is no equivalent to the HCDN gages that represent “natural” flow that is used as the 

basis for UROM flows in the continental U.S. The logical alternative to this method is 

presented below. The Puerto mainland is divided into four HUC-8’s (21010002, 

21010003, 21010004, 21010005 ) and the islands are assigned their own HUC-8 

numbers. 

A map of the stream gages is shown in Fig. A-8. 
NHDPlus User Guide 91 September 1, 2010 

Figure A-8. Stream Gages in Region 21 

Developing a Unit Runoff Methodology for the Puerto Rico Mainland 

To develop HCDN-equivalent runoff, figure A-9 below is used as the UROM source, which 

contains the citation for the figure. 

Figure A-9. Average Unit Runoff on Puerto Rico Mainland 
NHDPlus User Guide 92 September 1, 2010 

A digital format of the runoff isopleths was not available, so the map was extracted, registered to 

the Puerto mainland and then the isopleth lines were digitized. Figure A-10 shows the original 

runoff map with the digitized lines. Note the very high variability in runoff in areas in the eastern 

portion of HUC 21020005. This shows why a single unit runoff value by HUC would not 

produce good results. 

Figure A-10. Digitized Mean Annual Runoff Values On Puerto Rico Mainland 

The next step is to develop a rasterized version of the digitized lines to interpolate between the 

runoff isopleths. The ArcGIS TOPO-TO-GRID function was used for this. The basic results of 

this process are shown in Fig. A-11. This map uses the same runoff category ranges as the 

original runoff isopleths, but it is important to note that the individual rasterized values vary 

based on the interpolation technique in the ArcGIS processing. 

Figure A-11. Results of using TopoGrid to Develop an Interpolated Raster Grid of Mean Annual Runoff 

The rasterized data was then overlayed onto the catchments, which assigned a UROM 

value (cfs/sq km) to each catchment. 
NHDPlus User Guide 93 September 1, 2010 

The mean annual runoff values for the islands were done based on the gages available in each of 

the HUC-8’s. Due to a lack of gages in 21010006, no UROM flows and velocities were 

developed. UROM flow and velocity estimates were developed for 21020001 and 21020002. 

Velocity Estimates 

Velocities are estimated for mean annual flow conditions using the work of Jobson (1996). This 

method uses regression analyses on hydraulic variables for over 980 time-of-travel studies, 

which represent about 90 different rivers in the U.S. These rivers represent a range of sizes, 

slopes, and channel geometries. Four principal Flowline variables are used in the Jobson 

methods: drainage area, Flowline slope, mean annual discharge, and discharge at the time of the 

measurement. Based on his analyses, regression equations were developed to relate velocity 

(meters/second) to drainage area, a dimensionless drainage area, Flowline slope, discharge, and a 

dimensionless relative discharge. 

Because all Flowlines have slopes greater than or equal to 0.00005, the “slope” regression 

method is used. The section “Understanding NHDPlus Slope“ in the “Understanding and Using 

NHDPlus” section of this User Guide provides more information on NHDPlus Slope. Also, see 

Steps 3 and 7 for additional information on how slope calculations are done. 

Caveats and Considerations in Using the NHDPlus Velocity Estimates

Care should be exercised in using these velocity estimates: 

1. These velocities represent estimates for flowing streams and rivers and are not applicable 

to lakes or estuaries. The velocity estimates are computed and reported for all networked 

Flowlines, but users should exercise care when using them in lakes or estuaries. 

2. Artificial path Flowlines that are in lakes (natural and impounded) can be determined as 

follows: Select all Flowlines in the NHDFlowline table with an FCODE = 55800 

(Artificial path). Join these Flowlines to the NHDWaterBody Table using WBAreaComI 

in NHDFlowline to Comid in the NHDWaterBody table. All artificial path Flowlines 

with NHDWaterBody FCODE values in the 390xx series are lakes. 

3. Users need to be aware that there are impounded waterbodies not identified in the 

medium-resolution NHD that is the basis for NHDPlus, so there is no way to ensure that 

all Flowlines in impoundments can be identified. 

4. Estuarine Flowlines have not been identified in NHDPlus so performing estuarinespecific velocities is the user’s responsibility. 

The equations for velocity estimates are described below: 

The dimensionless relative discharge (Q’a) (Jobson, 1996) is expressed as 

Q’a = Q/Qa

where 

Q = Flowline discharge at the time of measurement (cubic meters/second), and 

Qa = mean annual discharge. 
NHDPlus User Guide 94 September 1, 2010 

The dimensionless drainage area (D’a) (Jobson, 1996) is expressed as 

D’a = (Da

1.25 * g0.5)/Qa

where 

 Da = drainage area (square meters), 

g = acceleration of gravity (9.8 meters/second/second), and 

Qa = mean annual discharge (cubic meters/second). 

The “Slope” method Flowline velocity (VelA_p) (Jobson, 1996) is 

 VelA_p = 0.094 + (0.0143 * (D’a 

0.919) * (Q’a-0.469) * (slope0.159) * (Q/Da)). 

For purposes of NHDPlus, Q is assumed equal to Qa, so that the dimensionless relative discharge 

(Q’a) has a value of 1. Flowline slopes are described in Step 8. 

Jobson has also specified a “noslope” velocity equation. However, the noslope equation is not 

used in NHDPlus. 

Because velocities are in part based on flow, velocity estimates are computed for both the 

UROM (MAVelU) and the Vogel (MAVelV) Methods. 

Quality Assurance (QA) For NHDPlus Cumulative Drainage Area and Flow 

Overview of Procedures Used

The basic procedure is to compare NHDPlus Drainage Areas and Flows to values reported in the 

National Water Information System (NWIS) for USGS Gaging Stations. The gaging station 

drainage areas and mean annual period-of-record flows from the NWIS database are considered 

as “truth” for the flowline to which the gaging station is assigned. The gaging station values are 

plotted on the x-axis and the corresponding NHDPlus values are plotted on the y-axis. With both 

axes at the same scale, a 45 degree line of values indicates agreement between NHDPlus and 

NWIS. Values not on the line represent the amount that NHDPlus cumulative drainage areas or 

flows are valid “outliers”, a systematic issue, or NHDPlus cumulative values are inaccurate. 

The gaging station location data was provided by Dave Stewart, USGS. The gage locations were 

snapped to the nearest 1:100,000-scale NHD flowline and then reviewed to ensure the snapped 

location is representative of the position on the stream network being measured by the gage. 

Summary flow statistics from the gage records were taken from Wolock, (2003). 

Each Hydrologic Region release contains a QA spreadsheet with a “QA_notes” worksheet noting 

specific issues found during the QA of that Hydrologic Region. The spreadsheet is contained in 

“NHDPlusrrVss_dd_QA/QC_SINKS.zip”. 
NHDPlus User Guide 95 September 1, 2010 

Systematic Issues

There are three types of systematic issues found in the QA results. The first two types of 

systematic issues usually appear as a sequence of gaging stations that are approximately parallel 

to the 45 degree line, either above or below. These gaging stations will be along a given river so 

that the “problem” at the most upstream gaging station is carried downstream to subsequent 

gaging stations along that river. This situation usually occurs for one of the first two reasons 

listed below. The third systematic issue can show up at very small drainage areas, where 

NHDPlus appears to over-estimate the drainage area. 

1. NHDPlus has unconnected isolated areas upstream of the gage. The parallel Line will in 

this case be below the 45 degree line which indicates that NHDPlus is under-estimating 

the drainage area in relation to USGS gaging station data. This situation can be 

considered to be caused by a difference between what the USGS considers total drainage 

area for a gage and what NHDPlus considers total contributing area. 

2. NHDPlus connects a large drainage area that is not considered to be part of the gaging 

station drainage area. The most obvious occurrence of this is in the Klamath River Basin 

in Hydrologic Region 18; where there is a diversion canal that joins the Lost River to the 

Klamath mainstem. The gaging stations do not consider the Lost River to be part of the 

Klamath drainage area, so there is a series of Klamath River gages above the 45 degree 

line, indicating that NHDPlus is over-estimating the drainage area in relation to the gage 

data. 

3. The NHDPlus cumulative drainage areas include the entire catchment area for the given 

flowline. A gage may be located at any point along a flowline. Therefore, the gage may 

be measuring an area that is less than the full catchment area. In these cases, the 

NHDPlus drainage area will be greater than the gage area. This is not an error, per se, in 

the NHDPlus drainage area, but it can show up as an overestimation by NHDPlus for 

these small drainage areas. This issue becomes undetectable and of little consequence 

with more downstream flowlines having larger drainage areas. Additional processing is 

possible using the NHDPlus flowdirection grids to split the catchments at the gages in 

order to eliminate this bias, but this processing was beyond the scope of the QA process. 

Outliers

Significant outliers occur primarily in situations where the gaging station is on the minor path of 

a divergence, the gage is in the wrong location, or the gage is on a tributary in a lake or reservoir.

For more information, see the section in the User Guide on Divergences. For examples of these 

outliers, see the NHDPlus presentations from the February 2006 NHDPlus Workshop titled: 

“Tue_1455_CumulativeCatchmentAttributes_Bondelid” and 

“Tue_1455_FlowVolumeVelocityEstimates_Bondelid”. 

These can be found on the NHDPlus website and FTPsite. 
NHDPlus User Guide 96 September 1, 2010 

Structure of Excel QA file

The QA table is designed to develop graphs and subsequent diagnostic analyses for outliers and 

other deviations from the 45 degree line as described above. 

The data table is in a worksheet named “FVVQARnn”, where nn refers to the particular 

Hydrologic Region. There follows a series of QA graphs, one set for cumulative drainage area 

and one for mean annual flows. The drainage area graphs start with the prefix “DA QA”. The 

flow graphs start with the prefix “Flow QA”. There is always more than one QA graph for DA 

and Flow. The basic graph shows the full range of data. The other graphs “zoom” to the lower 

left corner of the data by changing the x and y maximum scale values. These graphs are 

constructed because the full range of data used in the QA is quite large and the majority of x-y 

points tend to be clustered at the lower end of the graphs. There can be several graphs, each one 

“zooming” into the lower sets of data values. 

The Excel data table worksheet contains the following data elements: 

SITE_NO: The site number of the USGS gaging station

STATION_NM: the name of the USGS gaging station 

COM_ID: the comid of the NHDPlus flowline that the gage falls upon 

GAGEAREA: The NWIS reported drainage area of the gage in square kilometers. 

Stations need to have a drainage area value to be considered in these analyses. 

CUMDRAINAG: The NHDPlus cumulative drainage area in square kilometers 

NDAYS: The number of days the gaging station has been active. Stations need at least 10 

years of data to be considered in these analyses. 

gageavgQ: The mean annual flow over the period of record reported for that gage in cfs. 

MAFLOWU: The UROM Mean annual flow in cfs. 

MAFLOWV: The “Vogel” based mean annual flow in cfs. Note that there will be 

numerous times this field is unvalued (-9999 or -9998). See Step 6 in Appendix A 

of the NHDPlus User Guide for more information on why this field can be 

unvalued. 

BESTEVENTX: The longitude in decimal degrees that best places the gage on an 

NHDPlus flowline. 

BESTEVENTY: The latitude in decimal degrees that best places the gage on an 

NHDPlus flowline. 

The table is sorted by descending GAGEAREA. All of the graphical QA is built using these data 

elements. 
NHDPlus User Guide 97 September 1, 2010 

Step 7: Elevation Post-Processing, Smoothing, and Slope Calculations 

The raw flowline elevations developed in Step 3 provide upstream elevations at all headwater 

flowlines and downstream elevations for all flowlines. These raw elevation values may result in 

negative slopes where elevations decrease as the flowlines are traversed from downstream to 

upstream. To develop non-negative slope estimates for all flowlines and consistent elevations at 

nodes, several post-processing steps are performed. The post-processing and elevation smoothing 

take full advantage of advanced NHDPlus network traversal capabilities. The elevations go 

through the following processes: 

First, the minimum elevations for flowlines that join at a downstream node are independently 

developed and may not be equal. The elevations at each node are made equal by taking the 

minimum elevation of the two (or more) flowlines that are immediately upstream of the node. 

Figure A-6 in Step 3 illustrates this process. 

Second, the node elevations are also assigned as the maximum elevation for each flowline that is 

immediately downstream of the node. 

The results of these two processes are consistent node elevations for flowlines that have 

catchments. When all of the flowlines immediately upstream of a node are too short to generate 

catchments, the node will have a “missing” elevation. 

Third, raw elevations are smoothing so that most flowlines will have non-negative slopes. With 

raw elevations, flowlines can have minimum elevation greater than the maximum elevation 

which results in a negative flowline slope; essentially, the water flows “uphill.” This problem is 

not uncommon when using digital elevation models for estimating flowline slopes. The solution 

used in NHDPlus is to smooth the elevations along a flow path so that the negative slopes are 

removed. This process involves interpolating between elevations upstream and downstream of 

flowlines that have negative slopes. The result of the smoothing is that all of the flowlines will 

have a positive (“downhill”) slope. NHDPlus slopes are constrained to be greater than or equal to 

0.00005. Another important reason to perform the smoothing is to ensure that all networked 

flowlines have elevations and slopes. For nodes with missing elevations, as described above, ; 

the smoothing process fills in these elevations and slopes based on the elevation values of the 

flowlines upstream and downstream. 

The results of the elevation processing are stored in the FlowlineAttributes table. 

One of the many powerful features of NHDPlus is the ability to extract all of the flowlines for a 

stream path and sort them in an upstream or downstream order. This capability permits 

smoothing to be done on a stream level path basis (e.g., the Ohio River mainstem). The elevation 

smoothing is done sequentially, going from the mainstem to tributaries. 
NHDPlus User Guide 98 September 1, 2010 

Smoothing Techniques 

Three basic approaches to elevation smoothing have been evaluated. The first approach, referred 

to as “downstream smoothing,” interpolates progressively downstream. This approach generates 

a smoothed elevation set that forms the lower envelope of the elevation profile. An example of 

this approach is shown in Figure A-8. The second approach, “upstream smoothing,” interpolates 

in the upstream direction and forms the upper envelope of the elevation profile. An example is 

shown in Figure A-9. A third approach, a hybrid downstream-upstream approach, was also 

evaluated. The hybrid approach mainly uses the downstream elevation smoothing technique and 

then uses the upstream smoothing technique until a slope greater than zero is produced (Figure 

A-10). 

Smoothed Elevations and Slopes for NHDPlus 

Of the three smoothing techniques evaluated as part of the development of NHDPlus, the 

upstream smoothing technique was selected. The downstream smoothing proved unsatisfactory 

because of ramifications of the method used for assigning downstream elevations of flowlines. 

The downstream elevations are determined using the lowest elevation in the catchment. While 

this method works in most cases, sometimes the minimum elevation is in a “sink,” such as a rock 

quarry or mine, that is at a much lower elevation than the true downstream elevation of the 

flowline. The downstream and hybrid smoothing techniques will then set all flowline elevations 

downstream of an artificially low elevation equal to the “sink” value, until a flowline elevation is 

encountered that is lower than the “sink” value. The effect of this process results in many 

flowlines having artificially low elevations and zero slopes. The upstream smoothing technique 

avoids this problem. 

In NHDPlus, the FlowlineAttributes table contains smoothed elevations by LevelPathid, using 

the upstream smoothing approach, with slopes constrained to be greater than or equal to 0.00005. 

A relatively small number of flowline connections exist where the minimum elevation of the 

inflowing flowlines and the maximum elevation of the out flowing flows are not all equal. These 

elevation inconsistencies occur only where some level paths meet. As a result of elevation 

smoothing, every flowline in the network receives a slope greater than, or equal to, 0.00005. 
NHDPlus User Guide 99 September 1, 2010 

Downstream Elevation Smoothing

0

10000

20000

30000

1000 1100 1200 1300 1400 1500

pa t hl e ngt h ( k m)

Original

Smoot hed

Figure A-12 – Downstream Elevation Smoothing 

Upstream Elevation Smoothing

0

10000

20000

30000

1000 1100 1200 1300 1400 1500

P a t h Le ngt h ( Km)

Original

Smoot hed

Figure A-13 – Upstream Elevation Smoothing 
NHDPlus User Guide 100 September 1, 2010 

Hybrid Smoothing

8000

9000

10000

0 50 100 150 200

pa t hl e ngt h ( k m)

Original

Smoothed

Figure A-14 – Hybrid Elevation Smoothing 
NHDPlus User Guide 101 September 1, 2010 

Appendix B – Data Dictionary 

Accounting – Hydrologic accounting unit (6-digit HUC) of a stream gage 

AboveComID – Common identifier of feature that is above another (see BelowComID) 

Address – Metadata Address 

AddressTyp – Metadata Address Type 

Agency_Cd – Gov. Agency responsible for a stream gage 

ArbolateSu – An estimate of miles of stream upstream of a flowline. Not populated. 

AreaSqKm – Feature area in square kilometers 

AreaWtMAP – Area Weighted Mean Annual Precipitation at bottom of flowline in mm 

AreaWtMAT – Area Weighted Mean Annual Temperature at bottom of flowline in degree C * 

10 

AttributeA – Metadata Attribute Accuracy 

Ave – Average daily flow for the period of record for a stream gage 

BCF – Vogel flow estimate bias correction factor 

BeginningD – Metadata Beginning Date 

BelowComID – Common identifier of feature that is below another (see AboveComID) 

BFIYrs – Number of years used in the base-flow index computation for a stream gage 

BFI_Ave – Average annual base-flow index value for a stream gage 

BFI_StDev – Standard deviation of annual base-flow index for a stream gage 

CalendarDa – Metadata Calendar Date 

CanalDitch – Canal Ditch Type 

Cat_Area – Area of catchment in square kilometers 

City – Metadata City Name 

ComID – Common identifier of an NHD feature or relationship 

Completene – Metadata Completeness 

Constructi – Construction status 

ContactIns – Metadata Contact Instructions 

ContactOrg – Metadata Contact Organization 

ContactVoi – Metadata Contact Voice Telephone 

Count – Number of cells with a particular value in the Value field of a grid 

CumDrainag – Cumulative drainage area in square kilometers 

CUMHILC_1 – % of cumulative drainage area classified as Unclassified in NOAA C-CAP 

CUMHILC_2 – % of cumulative drainage area classified as High Intensity Developed in NOAA 

C-CAP 

CUMHILC_3 – % of cumulative drainage area classified as Low Intensity Developed in NOAA 

C-CAP 

CUMHILC_4 – % of cumulative drainage area classified as Cultivated Land in NOAA C-CAP 

CUMHILC_5 – % of cumulative drainage area classified as Grassland in NOAA C-CAP 

CUMHILC_6 – % of cumulative drainage area classified as Deciduous Forest in NOAA C-CAP 

CUMHILC_7 – % of cumulative drainage area classified as Evergreen Forest in NOAA C-CAP 

CUMHILC_8 – % of cumulative drainage area classified as Mixed Forest in NOAA C-CAP 

CUMHILC_9 – % of cumulative drainage area classified as Scrub/Shrub in NOAA C-CAP 

CUMHILC_10 – % of cumulative drainage area classified as Palustrine Forested Wetland in 

NOAA C-CAP 

CUMHILC_11 – % of cumulative drainage area classified as Palustrine Scrub/Shrub Wetland in 

NOAA C-CAP 
NHDPlus User Guide 102 September 1, 2010 

CUMHILC_12 – % of cumulative drainage area classified as Palustrine Emergent Wetland in 

NOAA C-CAP 

CUMHILC_13 – % of cumulative drainage area classified as Estuarine Forested Wetland in 

NOAA C-CAP 

CUMHILC_14 – % of cumulative drainage area classified as Estuarine Scrub/Shrub Wetland in 

NOAA C-CAP 

CUMHILC_15 – % of cumulative drainage area classified as Estuarine Emergent Wetland in 

NOAA C-CAP 

CUMHILC_16 – % of cumulative drainage area classified as Unconsolidated Shore in NOAA CCAP 

CUMHILC_17 – % of cumulative drainage area classified as Bare Land in NOAA C-CAP 

CUMHILC_18 – % of cumulative drainage area classified as Water in NOAA C-CAP 

CUMHILC_19 – % of cumulative drainage area classified as Palustrine Aquatic Bed in NOAA 

C-CAP 

CUMHILC_20 – % of cumulative drainage area classified as Estuarine Aquatic Bed in NOAA 

C-CAP 

CUMHILC_21– % of cumulative drainage area classified as Tundra in NOAA C-CAP 

CUMHILC_22 – % of cumulative drainage area classified as Snow/Ice in NOAA C-CAP 

CumNLCD_11 – % of cumulative drainage area classified as Open Water in NLCD 

CumNLCD_12 – % of cumulative drainage area classified as Perennial Ice/Snow in NLCD 

CumNLCD_21 – % of cumulative drainage area classified as Low Intensity Residential in 

NLCD 

CumNLCD_22 – % of cumulative drainage area classified as High Intensity Residential in 

NLCD 

CumNLCD_23 – % of cumulative drainage area classified as 

Commercial/Industrial/Transportation in NLCD 

CumNLCD_31 – % of cumulative drainage area classified as Bare Rock/Sand/Clay in NLCD 

CumNLCD_32 – % of cumulative drainage area classified as Quarries/Strip Mines/Gravel Pits in 

NLCD 

CumNLCD_33 – % of cumulative drainage area classified as Transitional in NLCD 

CumNLCD_41 – % of cumulative drainage area classified as Deciduous Forest in NLCD 

CumNLCD_42 – % of cumulative drainage area classified as Evergreen Forest in NLCD 

CumNLCD_43 – % of cumulative drainage area classified as Mixed Forest in NLCD 

CumNLCD_51 – % of cumulative drainage area classified as Shrubland in NLCD 

CumNLCD_61 – % of cumulative drainage area classified as Orchards/Vineyards/Other in 

NLCD 

CumNLCD_71 – % of cumulative drainage area classified as Grasslands/Herbaceous in NLCD 

CumNLCD_81 – % of cumulative drainage area classified as Pasture/Hay in NLCD 

CumNLCD_82 – % of cumulative drainage area classified as Row Crops in NLCD 

CumNLCD_83 – % of cumulative drainage area classified as Small Grains in NLCD 

CumNLCD_84 – % of cumulative drainage area classified as Fallow in NLCD 

CumNLCD_85 – % of cumulative drainage area classified as Urban/Recreational Grasses in 

NLCD 

CumNLCD_91 – % of cumulative drainage area classified as Woody Wetlands in NLCD 

CumNLCD_92 – % of cumulative drainage area classified as Emergent Herbaceous Wetlands in 

NLCD 
NHDPlus User Guide 103 September 1, 2010 

Cumpct_CN – % of cumulative drainage area in Canada and not classified in NLCD 

Cumpct_MX – % of cumulative drainage area in Mexico and not classified in NLCD 

Cumsum_pct – Sum of the % cumulative drainage areas

DA_Sq_Mile – Reported drainage area in square miles of a stream gage. Stations with drainage 

area of -999999 means there is no reported drainage area in National Water Information 

System. 

DataSetCre – Metadata Dataset Credit 

Day1 – First date of flow data (yyyymmdd) for a stream gage 

DayN – Last date of flow data (yyyymmdd) for a stream gage 

DeltaLevel – Numerical difference between stream level for FromComID and stream level for 

ToComID in the NHDFlow table 

Descriptio – Text description of feature type and the encoded attributes 

Direction – 714 for coastal connection, 709 for flowing connection, 712 for network starts, 713 

for network ends 

Divergence – 0 if flowline is not part of a divergence, 1 if flowline is the main path of a 

divergence, 2 if flowline is a minor path of a divergence 

DnDrainCou – Number of flowlines immediately downstream 

DnLevel – Stream level of mainstem downstream flowline 

DnLevelPat – Downstream mainstem level path identifier 

DnMinHydro – Downstream minor path hydrologic sequence number 

DUUID – Metadata identifier 

Elevation – Feature elevation in feet 

Enabled – Always “True” 

EndingDate – Metadata Ending Date 

EventDate – Date an event was created 

EventType – Type of entity in an event 

FCode – Numeric code that contains the feature type and its attributes as found in the 

NHDFCode lookup table 

FDate – Feature Currency Date 

FeatureCom – Reserved for future use 

FeatureCla – Reserved for future use 

FeatureDet – URL where detailed event entity data can be found 

Flowdir – Flow direction is “WithDigitized” or “Uninitialized” 

FromComID – The common identifier for a flowline in a flow relationship from which water 

flows (see ToComID) 

FromNode – A unique number assigned to the implied node at the upstream end of an NHD 

Flowline 

FType – NHD feature type 

GNIS_ID – Geographic Names Information System ID for the value in GNIS_Name 

GNIS_Name – Feature Name as found in the Geographic Names Information System 

GOTBFI – Flag indicating BFI data (1) or no BFI data (2) for a stream gage 

GOTQ – Flag indicating flow data (1) or no flow data (0) for a stream gage 

Grid_code – Value stored in grid cells; a unique identification number for each catchment 

(compressed numbering system) 

Grid_count – Number of cells with a particular value in the value field; equals the number of 

30x30 meter grid cells in each catchment; catchment area can be computed from this field 
NHDPlus User Guide 104 September 1, 2010 

HILC_1 – % of catchment area classified as Unclassified in NOAA C-CAP 

HILC_2 – % of catchment area classified as High Intensity Developed in NOAA C-CAP 

HILC_3 – % of catchment area classified as Low Intensity Developed in NOAA C-CAP 

HILC_4 – % of catchment area classified as Cultivated Land in NOAA C-CAP 

HILC_5 – % of catchment area classified as Grassland in NOAA C-CAP 

HILC_6 – % of catchment area classified as Deciduous Forest in NOAA C-CAP 

HILC_7 – % of catchment area classified as Evergreen Forest in NOAA C-CAP 

HILC_8 – % of catchment area classified as Mixed Forest in NOAA C-CAP 

HILC_9 – % of catchment area classified as Scrub/Shrub in NOAA C-CAP 

HILC_10 – % of catchment area classified as Palustrine Forested Wetland in NOAA C-CAP 

HILC_11 – % of catchment area classified as Palustrine Scrub/Shrub Wetland in NOAA C-CAP 

HILC_12 – % of catchment area classified as Palustrine Emergent Wetland in NOAA C-CAP 

HILC_13 – % of catchment area classified as Estuarine Forested Wetland in NOAA C-CAP 

HILC_14 – % of catchment area classified as Estuarine Scrub/Shrub Wetland in NOAA C-CAP 

HILC_15 – % of catchment area classified as Estuarine Emergent Wetland in NOAA C-CAP 

HILC_16 – % of catchment area classified as Unconsolidated Shore in NOAA C-CAP 

HILC_17 – % of catchment area classified as Bare Land in NOAA C-CAP 

HILC_18 – % of catchment area classified as Water in NOAA C-CAP 

HILC_19 – % of catchment area classified as Palustrine Aquatic Bed in NOAA C-CAP 

HILC_20 – % of catchment area classified as Estuarine Aquatic Bed in NOAA C-CAP 

HILC_21– % of catchment area classified as Tundra in NOAA C-CAP 

HILC_22 – % of catchment area classified as Snow/Ice in NOAA C-CAP 

HorizPosit – Metadata Horizontal Positional Accuracy 

HU_8_Name –Text name of Subbasin 

HUC – Hydrologic Cataloging Unit (8-digit HUC) of the gage 

HUC_8 – 8-digit Hydrologic Unit Code, also known as Subbasin code (formerly known as 

catalog unit code) 

HUC_REG – Hydrologic Region (2-digit HUC) of the gage 

HwNodesqkm –Catchment area in square kilometers that drains to the headwater node of the 

flowline indicated by ComID 

Hydrograph – hydrographic category, Intermittent or perennial 

Hydroseq – Hydrologic sequence number 

IncrFlowU – Incremental Flow (cfs) for Flowline as computed by the Unit Runoff Method 

Inundation – Inundation Area Type 

Lat_NHD – Latitude of the NHD location in decimal degrees, NAD83 

Lat_Site – Latitude of the streamgage (site) location - gage house in decimal degrees, NAD83 

LengthKM – Feature Length in kilometers 

LevelPathi – Hydrologic sequence number of most downstream flowline in level path 

LogicalCon – Metadata Logical Consistency 

Lon_NHD – Longitude of the NHD location in decimal degrees, NAD83 

Lon_Site – Longitude of the streamgage (site) location - gage house in decimal degrees, NAD83 

MAFlowU – Mean Annual Flow (cfs) at bottom of flowline as computed by Unit Runoff Method 

MAFlowV – Mean Annual Flow (cfs) at bottom of flowline as computed by Vogel Method 

MAVelU – Mean Annual Velocity (fps) at bottom of flowline as computed by Unit Runoff 

Method 

MAVelV – Mean Annual Velocity (fps) at bottom of flowline as computed by Vogel Method 
NHDPlus User Guide 105 September 1, 2010 

MaxElevRaw – Maximum elevation (unsmoothed) in meters 

MaxElevSmo – Maximum elevation (smoothed) in meters

Measure – Measure along reach where a point event is located, in percent from downstream end 

Metadata_1 – Metadata Standard Version 

Max_ – Maximum daily flow for the period of record for a stream gage 

MetadataDa – Metadata Date 

MetadataSt – Metadata Standard Name 

Min_ – Minimum daily flow for the period of record for a stream gage 

MinElevRaw – Minimum elevation (unsmoothed) in meters 

MinElevSmo – Minimum elevation (smoothed) in meters

NewHUCode – Substr(NewReachCo,1,8) 

NewReachCo –New Reach Code in a Reach cross reference entry 

NewReachDa –New Reach date in a Reach cross reference entry 

NewUPMI – not used 

NDays – Number of days of flow data for a stream gage 

NDaysGT0 – Number of days of non-zero flow for a stream gage 

NHD2Gage_D – Distance between a Stream Gage and the NHD Reach to which it is linked 

NLCD_11 – % of catchment area classified as Open Water in National Land Cover Dataset 1992 

(NLCD) 

NLCD_12 – % of catchment area classified as Perennial Ice/Snow in NLCD 

NLCD_21 – % of catchment area classified as Low Intensity Residential in NLCD 

NLCD_22 – % of catchment area classified as High Intensity Residential in NLCD 

NLCD_23 – % of catchment area classified as Commercial/Industrial/Transportation in NLCD 

NLCD_31 – % of catchment area classified as Bare Rock/Sand/Clay in NLCD 

NLCD_32 – % of catchment area classified as Quarries/Strip Mines/Gravel Pits in NLCD 

NLCD_33 – % of catchment area classified as Transitional in NLCD 

NLCD_41 – % of catchment area classified as Deciduous Forest in NLCD 

NLCD_42 – % of catchment area classified as Evergreen Forest in NLCD 

NLCD_43 – % of catchment area classified as Mixed Forest in NLCD 

NLCD_51 – % of catchment area classified as Shrubland in NLCD 

NLCD_61 – % of catchment area classified as Orchards/Vineyards/Other in NLCD 

NLCD_71 – % of catchment area classified as Grasslands/Herbaceous in NLCD 

NLCD_81 – % of catchment area classified as Pasture/Hay in NLCD 

NLCD_82 – % of catchment area classified as Row Crops in NLCD 

NLCD_83 – % of catchment area classified as Small Grains in NLCD 

NLCD_84 – % of catchment area classified as Fallow in NLCD 

NLCD_85 – % of catchment area classified as Urban/Recreational Grasses in NLCD 

NLCD_91 – % of catchment area classified as Woody Wetlands in NLCD 

NLCD_92 – % of catchment area classified as Emergent Herbaceous Wetlands in NLCD 

Offset – Display offset for an event 

OID – Internal ESRI Table row ID 

OldHUCode – Substr(OldReachCo,1,8) 

OldReachCo – Old Reach Code in a reach cross reference entry 

OldReachDa – Old Reach Date in a Reach cross reference entry 

OldUpMI –Not used 

Operationa – Operational status 
NHDPlus User Guide 106 September 1, 2010 

Originator – Metadata Originator 

P1 – 1st percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P5 – 5th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P10 – 10th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P20 – 20th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P25 – 25th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P30 – 30th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P40 – 40th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P50 –50th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P60 – 60th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P70 – 70th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P75 – 75th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P80 – 80th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P90 – 90th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P95 – 95th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

P99 – 99th percentile of daily flow for the period of record of a stream gage. Negative values 

indicate reverse flow; tidal or backwater 

PathLength – Distance to terminal flowline 

Pct_CN – % of catchment area in Canada and not classified in NLCD 

Pct_MX – % of catchment area in Mexico and not classified in NLCD 

PipelineTy – Pipeline type 

Positional – Metadata Positional accuracy 

PostalCode – Metadata Postal Code 

Precip – Mean annual precipitation in mm 

Process –In a Reach cross reference entry, the name of the process that created the Reach Code 

change 

ProcessDes – Metadata Process Description 

Prod_unit – Production unit identifier 

ProssDat – Metadata Process Date 

Publicatio – Metadata Publication Date 

ReachCode – Reach Code assigned to feature or reach on which an event is located 

ReachFileV – Reach file version in a Reach cross reference entry 
NHDPlus User Guide 107 September 1, 2010 

ReachsmDat – Reach Version Date 

ReachResol – Reach Resolution 

Relationsh – Relationship to surface 

ReservoirT – Reservoir type 

Resolution – Always “Medium” 

Reviewed – Flag to indicate review status - Y or N – of an event location. 

Shape_Area – ESRI feature area in square decimal degrees 

Shape_Leng – ESRI feature length in decimal degrees

SiteStatus – Active (A) or Inactive (I) where active StreamGageEvents have streamflow data in 

water year(s) 2003 and/or 2004 

Slope – Slope of flowline (cm/cm) 

Source – Source of boundary;, 0 = Watershed Boundary Dataset, 1 = NHD, 2 = Other 

SourceCita – Metadata Source Citation Abbreviation 

SourceCont – Metadata Source Contribution 

SourceCurr – Metadata Source Currentness Reference 

SourceScal – Metadata Source Scale Denominator 

Source_Ori – Originator of an event 

Source_Dat – Description of event entity 

Source_Fea – Unique Identifier of event entity, link to external data about entity 

SpecialUse – Special use category 

Stage – Elevation stage 

StartFlag – 0 if a flowline is not a headwater flowline, 1 if a flowline is a headwater flowline 

State – 2 char. state postal abbreviation of the USGS Water Science Center maintaining the gage. 

Puerto Rico is listed as a state. 

State_Cd – 2-digit state FIPS code of the WSC maintaining the gage. Puerto Rico is listed as a 

state. 

Station_NM – Station name 

StateorPro – Metadata State or Province 

StDev – Standard deviation of daily flow for the period of record 

StreamLeve –Stream level (dimensionless) 

StreamOrde – Strahler stream order. Not populated. See NHDPlus data extension table 

SOSC.dbf. 

SubRegion – Hydrologic sub-region (4-digit HUC) 

Sum_pct – Sum of the % catchment areas 

Temp –Mean annual temperature in degrees centigrade * 10 

TerminalFl – 0 if a flowline is not a network terminus, 1 if a flowline is a network terminus 

TerminalPa – Hydrologic sequence number of terminal flowline 

ThinnerCod – Ordinal value used to display various network densities 

Title – Metadata title of source data used as input for creating or updating NHD 

ToComID – Common identifier for a flowline which is receiving flow in a flow relationship (see 

FromComID) 

ToComIDMea – Not valued 

ToNode – A unique number assigned to the implied node at the downstream end of a flowline 

TypeofSour – Metadata type of Source Media 

UpHydroSeq – Upstream mainstem hydrologic sequence number 

UpLevelPat – Upstream mainstem level path identifier 
NHDPlus User Guide 108 September 1, 2010 

UpMinHydro – Upstream minimum hydrologic sequence number 

Value – The value stored in grid cells; also known as Grid_code in related tables 

VertPositi – Metadata Vertical Positional Accuracy 

WBAreaComI – ComID of an NHD polygonal water feature through which an NHD “Artificial 

Path” flowline flows 
NHDPlus User Guide 109 September 1, 2010 

Appendix C.1 – NLCD Land Cover Classification System Key 

Used for Continental US Only 

(Rev. July 20, 1999) 

Water 

All areas of open water or permanent ice/snow cover. 

11. Open Water – All areas of open water; typically at least 25 percent of pixel or cell is 

water. 

12. Perennial Ice/Snow – All areas characterized by year-long cover of ice and/or snow. 

Developed

Areas characterized by at least 30 percent of constructed materials (e.g., asphalt, concrete, 

buildings, etc). 

21. Low Intensity Residential – Areas with a mixture of constructed materials and 

vegetation. Constructed materials account for 30-80 percent of the cover; the 

remaining percentage is vegetation. These areas most commonly include singlefamily housing units. Population densities are lower than in the high intensity 

residential class. 

22. High Intensity Residential – Highly developed areas where large numbers of people 

reside, such as apartment complexes and row houses. Vegetation occupies less than 

20 percent of the area, and constructed materials cover 80 to100 percent. 

 

23. Commercial/Industrial/Transportation – Includes infrastructure (e.g., roads, 

railroads, etc.) and all highly developed areas not classified as High Intensity 

Residential. 

Barren 

Areas characterized by bare rock, gravel, sand, silt, clay, or other earthen material, with little or 

no “green” vegetation present, regardless of any inherent ability to support life. Vegetation, if 

present, is sparse and scrubby compared to other vegetated categories, and lichen may be 

extensive. 

31. Bare Rock/Sand/Clay – Perennially barren areas of bedrock, desert pavement, 

scarps, talus, slides, volcanic material, glacial debris, beaches, and other 

accumulations of earthen material. 

32. Quarries/Strip Mines/Gravel Pits – Areas of extractive mining activities with 

significant surface expression. 
NHDPlus User Guide 110 September 1, 2010 

33. Transitional – Areas of sparse vegetative cover (less than 25 percent of area) that are 

dynamically changing from one land cover to another, often because of human 

activities. Examples include forest clearcuts, transition between forest and 

agricultural land, temporary removal of vegetation, and changes due to natural 

causes (e.g., fire, flood, etc.). 

Forested Upland – Areas characterized by tree cover (natural or semi-natural woody vegetation, 

generally greater than 6 meters tall). The tree canopy accounts for 25-100 

percent of the land cover. 

41. Deciduous Forest – Areas dominated by trees where 75 percent or more of the tree 

species shed foliage simultaneously in response to seasonal change. 

 

42. Evergreen Forest – Areas dominated by trees where 75 percent or more of the tree 

species maintain their leaves all year. Canopy is never without green foliage. 

43. Mixed Forest – Areas dominated by trees where neither deciduous nor evergreen 

species represent more than 75 percent of the land cover. 

Shrubland – Areas characterized by natural or semi-natural woody vegetation that is generally 

less than 6 meters tall. Individual shrubs or clumps may be isolated or interlocking. Shrubland 

includes evergreen and deciduous species of true shrubs, young trees, and small or stunted trees 

or shrubs. 

51. Shrubland – Areas dominated by shrubs, with shrub canopy covering 25-100 percent 

of the land. Shrub cover is generally greater than 25 percent when tree cover is 

less than 25 percent. Shrubs may cover less than 25 percent where no other 

vegetation type has a greater percentage to establish a distinct classification. 

Non-Natural Woody – Areas dominated by non-natural woody vegetation occupying 25-100 

percent of the area. Classifying non-natural woody land cover depends upon the availability of 

ancillary data to differentiate non-natural from natural woody vegetation. 

61. Orchards/Vineyards/Other – Orchards, vineyards, and other areas planted or 

maintained for the production of fruits, nuts, berries, or ornamentals. 

Herbaceous Upland – Upland areas characterized by natural or semi-natural herbaceous 

vegetation that accounts for 75-100 percent of the cover. 

 

71. Grasslands/Herbaceous – Areas dominated by upland grasses and forbs. In rare 

cases, herbaceous cover is less than 25 percent but exceeds the combined cover of 

the woody species present. These areas are not subject to intensive management, 

although they are often grazed. 
NHDPlus User Guide 111 September 1, 2010 

Planted/Cultivated – Areas characterized by herbaceous vegetation that has been planted or is 

intensively managed for the production of food, feed, or fiber or is maintained in developed 

settings for specific purposes. Herbaceous vegetation accounts for 75-100 percent of the cover. 

81. Pasture/Hay – Areas of grasses, legumes, or grass-legume mixtures planted for 

livestock grazing or the production of seed or hay crops. 

82. Row Crops – Areas used for the production of crops such as corn, soybeans, 

vegetables, tobacco, and cotton. 

83. Small Grains – Areas used for the production of graminoid crops such as wheat, 

barley, oats, and rice. 

84. Fallow – Areas used for the production of crops that are temporarily barren or with 

sparse vegetative cover due to land management that alternates between cropping 

and tillage. 

85. Urban/Recreational Grasses – Vegetation (primarily grasses) planted in developed 

settings for recreation, erosion control, or aesthetic purposes. Examples include 

parks, lawns, golf courses, airport grasses, and industrial site grasses. 

Wetlands – Areas where water covers or saturates the soil or substrate periodically, as defined 

by Cowardin et al. 

91. Woody Wetlands – Areas where forest or shrubland vegetation accounts for 25-100 

percent of the cover, and the soil or substrate is periodically saturated with, or 

covered with, water. 

92. Emergent Herbaceous Wetlands – Areas where perennial herbaceous vegetation 

accounts for 75-100 percent of the cover, and the soil or substrate is periodically 

saturated with, or covered with, water. 
NHDPlus User Guide 112 September 1, 2010 

Appendix C.2 – NOAA C-CAP Land Cover Classification System Key 

Used for Hawaii Only 

 0 Background 

 1 Unclassified 

 2 High Intensity Developed 

 3 Low Intensity Developed 

 4 Cultivated Land 

 5 Grassland 

 6 Deciduous Forest 

 7 Evergreen Forest 

 8 Mixed Forest 

 9 Scrub/Shrub 

 10 Palustrine Forested Wetland 

 11 Palustrine Scrub/Shrub Wetland 

 12 Palustrine Emergent Wetland 

 13 Estuarine Forested Wetland 

 14 Estuarine Scrub/Shrub Wetland 

 15 Estuarine Emergent Wetland 

 16 Unconsolidated Shore 

 17 Bare Land 

 18 Water 

 19 Palustrine Aquatic Bed 

 20 Estuarine Aquatic Bed 

 21 Tundra 

 22 Snow/Ice 
NHDPlus User Guide 113 September 1, 2010 

References 

Alexander, Richard B., Elizabeth W. Boyer, Richard A. Smith, Gregory E. Schwarz, and Richard 

B. Moore, 2007. The Role of Headwater Streams in Downstream Water Quality. Journal of 

the American Water Resources Association (JAWRA) 43(1):41-59. DOI: 10.1111/j.1752-

1688.2007.00005x 

Daly, C. and Taylor, G., United States Average Monthly or Annual Mean Temperature, 1961-90

(Corvallis, OR: Spatial Climate Analysis Service at Oregon State University, 1998). 

Daly, C. and Taylor, G., United States Average Monthly or Annual Precipitation, 1961-90

(Corvallis, OR: Spatial Climate Analysis Service at Oregon State University, 1998). 

Environmental Systems Research Institute, Inc. (ESRI), “ARC/INFO Command Reference,” 

ARC/INFO Help, Version 9.0 (Redlands, CA.: ESRI, 2004). 

Environmental Systems Research Institute, Inc. (ESRI), Using ARC GRID with ARC/INFO, 

Version 2 (Redlands, CA: ESRI, 1999). 

Fontaine, R.A., Wong, M.F., Matsuoka, I., Estimation of Median Streamflows At Perennial 

Stream Sites In Hawaii, U.S. Geological Survey Water-Resources Investigations Report 92-4099 

(1992), U.S. Geological Survey. 

Hellweger, F., Maidment, D., and the Center for Research in Water Resources, AGREE-DEM 

Surface Reconditioning System (Austin: University of Texas, 1998). 

http://www.crwr.utexas.edu/gis/gishyd98/quality/agree/agree.htm

Jobson, H. E., Prediction of Traveltime and Longitudinal Dispersion in Rivers and Streams, U.S. 

Geological Survey Water Resources Investigations Report 96-4013 (1996), U.S. Geological 

Survey. 

Johnston, C.M., Dewald, T.G., Bondelid, T.R., Worstell, B.B., McKay, L.D., Rea, Alan, Moore, 

R.B., and Goodall, J.L., 2009, Evaluation of catchment delineation methods for the mediumresolution National Hydrography Dataset: U.S. Geological Survey Scientific Investigations 

Report 2009–5233, 88 p. (Also available at http://pubs.usgs.gov/sir/2009/5233/.) 

Moore, R.B., Johnston, C.M., Robinson, K.W., and Deacon, J.R., Estimation of Total Nitrogen 

and Phosphorus in New England Streams Using Spatially Referenced Regression Models, 

U.S. Geological Survey Scientific Investigations Report 2004-5012, pp. 1-42 (2004), U.S. 

Geological Survey. 

http://pubs.water.usgs.gov/sir2004-5012. 

National Elevation Dataset (NED) Web page 

http://ned.usgs.gov/
NHDPlus User Guide 114 September 1, 2010 

National Hydrography Dataset (NHD) Data Distribution Web page 

http://nhdgeo.usgs.gov

National Hydrography Dataset (NHD) Information Web page 

http://nhd.usgs.gov 

National Land Cover Dataset (NLCD) Web page 

http://landcover.usgs.gov/natllandcover.asp

National Oceanic and Atmospheric Administration (NOAA) Coastal Change Analysis Program 

(C-CAP) Web page http://www.csc.noaa.gov/crs/lca/ccap.html

National Watershed Boundary Dataset (WBD) Web page 

http://www.ncgc.nrcs.usda.gov/products/datasets/Watershed/

Research Triangle Institute, The National Water Pollution Control Assessment Model 

(NWPCAM) Version 2 Draft Report, prepared for the U.S. Environmental Protection Agency 

(Research Triangle Park, NC: Research Triangle Institute, 2001). 

Saunders, W., “Preparation of DEMs for Use in Environmental Modeling Analysis,” Hydrologic 

and Hydraulic Modeling Support, Maidment, D. and Djokic, D. [eds.], pp. 29-51 (Redlands, 

CA: Environmental Systems Research Institute, Inc., 2000). 

Stewart, D.W., Rea, A., and Wolock, D.M., USGS Streamgages Linked to the Medium 

Resolution NHD, U.S. Geological Survey Data Series 195 (2006), U.S. Geological Survey. 

Vogel, R.M., Wilson, I.W., and Daly, C., “Regional Regression Models of Annual Streamflow 

for the United States,” Journal of Irrigation and Drainage Engineering Vol. 125, No. 3, pp. 

148-157, 1999). 

Wolock, D., 2003, Flow characteristics at U.S. Geological Survey streamgages in the 

conterminous United States, U.S. Geological Survey Open-File Report 03-146, downloaded 

from http://water.usgs.gov/lookup/getspatial?qsitesdd . 
NHDPlus User Guide 115 September 1, 2010 

Footnotes 

 

1

 All referenced placeholder shapefiles and dBase files are included to complete the official NHD data model and 

are empty in NHDPlus. 

2

 The elev_cm grids have “Zunits 100” instead of “Zunits NO.” 

3Additional information about the NHD content and format can be found at the NHD Web site: http://nhd.usgs.gov. 

The NHD Schema is described at http://nhd.usgs.gov/NHD.pdf. 

4

 Additional information about the NHD content and format are available on the NHD Web site at 

http://nhd.usgs.gov. 

5

 In Hydrologic Regions 01, 02, and 03, USGS WRD field offices were able to specify NHD network updates that 

were based on local knowledge and/or the use of DRGs. 

6

 Table 1 contains published and unpublished material from Vogel (2005). The information in columns BCF, 

AreaMin, and AreaMax is unpublished and was supplied by Vogel through e-mail and telephone communication to 

Timothy R. Bondelid, Consulting Engineer.