Scientific Investigations Report 2009–5233

U.S. Department of the Interior

U.S. Geological Survey

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2009–5233

Prepared in cooperation with the U.S. Environmental Protection Agency

Evaluation of Catchment Delineation 

Methods for the Medium-Resolution 

National Hydrography Dataset
Cover. National Hydrography Dataset (NHD) streams and associated catchments overlaid on a 3-dimensional perspective view 

(facing southeast) of Mount Hood, Oregon. Imagery provided by Environmental Systems Research Institute (ESRI) ArcGIS Online 

Standard Map Services.
Evaluation of Catchment Delineation 

Methods for the Medium-Resolution 

National Hydrography Dataset

By Craig M. Johnston1, Thomas G. Dewald2, Timothy R. Bondelid3, 

Bruce B. Worstell4, Lucinda D. McKay5, Alan Rea1, Richard B. Moore1, and 

Jonathan L. Goodall6

Prepared in cooperation with the U.S. Environmental Protection Agency

Scientific Investigations Report 2009–5233

U.S. Department of the Interior

U.S. Geological Survey

1 U.S. Geological Survey.

2 U.S. Environmental Protection Agency.

3 Consultant, Woodville, VA.

4 Hughes Corporation, Sioux Falls, SD.

5 Horizon Systems Corporation, Herndon, VA.

6 University of Texas at Austin.
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2009

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reproduce any copyrighted materials contained within this report.

Suggested citation:

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 medium-resolution National Hydrography Dataset: 

U.S. Geological Survey Scientific Investigations Report 2009–5233, 88 p., available at http://pubs.usgs.gov/

sir/2009/5233.
iii

Foreword

The U.S. Geological Survey (USGS) and the U.S. Environmental Protection Agency (USEPA) 

have long shared the goal of creating a nationally consistent digital database of important 

environmental and natural resource information, termed a national geospatial surface-water 

framework. For water resources, this means the creation of a dataset that links mapped streams 

to the landscape, and that essentially allows a drop of water to be followed, from where it 

falls on the land surface, to the stream, and all the way to the ocean. This requires an accurate 

geospatial data model that includes both the necessary digital data and the processes to 

manipulate and interpret the data.

Towards this goal, the National Hydrography Dataset (NHD) was created by the USEPA and 

USGS to provide the necessary stream network for this geospatial model. The NHD is a 

comprehensive set of digital spatial data representing the surface water of the United States 

and includes common water features such as lakes, ponds, streams, rivers, canals, and oceans. 

The NHD contains a flow-direction network that traces the water downstream or upstream. It 

also uses a reach addressing system that permits the linking of specific information such as 

wastewater discharges or water-quality monitoring sites to specific locations along the 

stream network.

This report represents the next step towards the national goal of linking the mapped stream network to the landscape—the identification of catchments or contributing drainage areas to individual stream segments. The catchments were used in computing streamflow and velocity estimates for NHD streams. The catchment creation effort was coordinated by the USEPA involving 

a team of experts from the USGS, USEPA, the private-consulting community, and academia. This 

report documents the collective efforts to determine the most accurate and appropriate means 

to delineate catchments, which establish the linkage between the NHD stream network and 

the landscape. 

Since the conclusion of the study described in this report, the catchment delineation process 

that provides the most accurate catchments has been completed for the medium resolution 

1:100,000-scale NHD in the conterminous United States. The results are the first national 

dataset that links the mapped stream network to the landscape. The data, called NHDPlus, are 

distributed for all States, except Alaska, through the website http://www.epa.gov/waters. 

The dataset is a milestone for geospatial data infrastructure for the Nation and we at the USGS 

are pleased to be a part of the team that developed it.

Matthew C. Larsen

Associate Director for Water
iv

Acknowledgments

The authors wish to thank staff at contributing U.S. Geological Survey (USGS) Water Science 

Centers who provided streamgage and Watershed Boundary Dataset boundary data for 

verification purposes: William Ellis, Karen Hanson, David Litke, Mark Lowery, Theresa Olsen, 

and Chris Sanocki.

Thanks also goes to those who provided technical review for the project, including those at 

USGS: Susan Greenlee, Curtis Price, Gregory Schwarz, Peter Steeves, and David Wolock, as 

well as Kristine Verdin (Hughes Corporation, Sioux Falls, SD), David Maidment (University of 

Texas at Austin, Austin, TX), and Tracey R. Szajgin (consultant, Reston, VA).
v

Contents

Foreword ........................................................................................................................................................iii

Acknowledgments........................................................................................................................................iv

Terminology.....................................................................................................................................................x

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Background.....................................................................................................................................................2

National Hydrography Dataset...........................................................................................................2

Concept of National Hydrography Dataset Catchments................................................................5

National Elevation Dataset..................................................................................................................5

Elevation Derivatives for National Applications..............................................................................8

Watershed Boundary Dataset............................................................................................................8

Catchment Delineation Methods ................................................................................................................9

Raster Seeding Method.......................................................................................................................9

New England Method with Watershed Boundary Dataset .........................................................10

New England Method without Watershed Boundary Dataset....................................................15

Outlet Matching Method ...................................................................................................................15

Thiessen Polygon Method.................................................................................................................18

Testing the Catchment Delineation Methods..........................................................................................20

Study Subbasins..................................................................................................................................20

Basis for Comparison.........................................................................................................................20

Datasets Obtained for Verification in the Comparison Analysis.................................................20

Streamgage Data.......................................................................................................................22

Boundaries from the Watershed Boundary Dataset ...........................................................23

Evaluation Metrics..............................................................................................................................23

Coefficient of Areal Correspondence.....................................................................................24

Normalizing Coefficient of Areal Correspondence ..............................................................27

Polygon-Area Percent Error ....................................................................................................30

Cumulative Drainage-Area Analysis ......................................................................................30

Convergence Analysis ..............................................................................................................31

Evaluation of Catchment Delineation Methods ......................................................................................32

Summary........................................................................................................................................................35

References Cited..........................................................................................................................................36

Glossary.........................................................................................................................................................37

Appendix. Detailed Discussion for each Study Subbasin .................................................................45
vi

Figures

1. Map showing the medium-resolution National Hydrography Dataset surface-water 

drainage system, central New Hampshire...............................................................................3

2. Map showing the United States with the source map scales of the medium-resolution 

National Hydrography Dataset...................................................................................................4

3. Map showing an example of isolated networks in the medium-resolution National 

Hydrography Dataset (NHD), east-central Tennessee...........................................................6

4. Map showing the National Hydrography Dataset flowlines and their associated 

catchments ....................................................................................................................................7

5. Schematic design showing three vector National Hydrography Dataset flowline 

features (blue lines) overlaid onto their raster representations, along with the 

corresponding catchments generated by the Raster Seeding Method..............................9

6. Schematic design showing multiple polygon features that define the catchment 

boundary for a National Hydrography Dataset (NHD) flowline ..........................................10

7. Map showing the spatial detail of the stream network and 42,000 catchments used 

for the New England SPAtially Referenced Regressions On Watershed attributes 

(SPARROW) model......................................................................................................................11

8. Maps showing (A) horizontal displacement between the National Hydrography 

Dataset flowlines and the Elevation Derivatives for National Applications (EDNA) 

synthetic streams, (B) catchment delineations using the Raster Seeding Method with 

the EDNA flow direction grid, and (C) catchment delineations using the New England 

Method with a new flow-direction grid created using the AGREE computer program 

with the National Elevation Dataset........................................................................................12

9. Schematic design showing the manner in which the AGREE computer program 

modifies the digital elevation model (DEM) of the National Elevation Dataset (NED) 

to align with the National Hydrography Dataset (NHD) flowlines......................................13

10. Schematic design showing a three-dimensional perspective view of a modified 

digital elevation model with walling of the Watershed Boundary Dataset and stream 

burning, using the National Hydrography Dataset................................................................14

11. Schematic design showing the Junction Intersect technique of the Outlet 

Matching Method .......................................................................................................................16

12. Schematic design showing the Drainage Point Proximity technique of the Outlet 

Matching Method .......................................................................................................................16

13. Schematic design showing the Next Downstream Area technique of the Outlet 

Matching Method .......................................................................................................................17

14. Map showing Thiessen Polygon Method catchments for National Hydrography 

Dataset flowlines ........................................................................................................................19

15. Map showing the location of the six study Subbasins in the continental 

United States ...............................................................................................................................21

16. Schematic design showing how Coefficient of Areal Correspondence (CAC) score 

is computed .................................................................................................................................25

17. Map showing boundaries from the Watershed Boundary Dataset (WBD) 

Subwatersheds and the corresponding boundaries from the New England Method 

without WBD (NEM-without-WBD), National Hydrography Dataset (NHD) flowlines 

including those most closely corresponding to the WBD outlets, and Coefficient of 

Areal Correspondence scores, Pine River Subbasin, MN...................................................26

18. Schematic design showing a mismatch between a Watershed Boundary Dataset 

(WBD) Subwatershed boundary and the corresponding New England Method with 

WBD boundary caused by the WBD outlet not coinciding with the downstream end 

of the corresponding NHD flowline .........................................................................................27
vii

Tables

1. Hierarchal structure of the Watershed Boundary Dataset...................................................8

2. Subbasin name, Hydrologic Unit Code, State, and description for six study 

Subbasins in the United States ................................................................................................20

3. Description of National Water Information System streamgages, boundaries, and 

associated drainage-area measurements used for verification datasets........................22

4. Summary of Watershed Boundary Dataset Hydrologic Units used for comparative 

analysis of National Hydrography Dataset catchment boundary delineation 

methods........................................................................................................................................23

5. Mean normalized Coefficient of Areal Correspondence scores for the four methods 

used in the Watershed Boundary Dataset comparison analysis, by study Subbasin ....33

6. Mean normalized polygon-area percent errors for catchment delineation methods 

used in the Watershed Boundary Dataset comparison analysis .......................................33

7. Mean cumulative drainage-area errors, by drainage-area size category, for 

catchment delineation methods for all study Subbasins, except Willapa Bay................34

19. Schematic design showing a Watershed Boundary Dataset Subwatershed and 

corresponding boundaries from the New England Methods and the Raster Seeding 

Method, with Coefficient of Areal Correspondence (CAC) scores before and after 

normalization ...............................................................................................................................28

20. Graph showing the non-normalized and normalized Coefficient of Areal Correspondence (CAC) scores for the New England Method without the Watershed Boundary 

Dataset (NEM-without-WBD) in relation to the corresponding boundaries from the 

Watershed Boundary Dataset labeled by National Hydrography Dataset flowline 

outlet ComID in the Great Egg Harbor Subbasin, NJ............................................................29

21. Graph showing the Watershed Boundary Dataset cumulative drainage-area 

measurements (verification) in relation to the cumulative drainage-area measurements of the methods tested, Great Egg Harbor Subbasin, NJ..........................................31

22. Graph showing percent error of convergence for drainage-area measurements for 

all methods tested in relation to the Watershed Boundary Dataset verification 

cumulative drainage-area measurements, in the Seneca River Subbasin, SC ...............32
viii

Conversion Factors, Datum, and Abbreviations

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

Multiply By To obtain

Length

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

Area

square meter (m2) 10.76 square foot (ft2)

square kilometer (km2) 0.3861 square mile (mi2)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

ABBREVIATIONS AND ACRONYMS USED IN THIS REPORT

AML Arc Macro Language

CAC Coefficient of Areal Correspondence

ComID Common Identifier (a unique identifier for an NHD feature)

DEM digital elevation model

DLG Digital Line Graph

DOQ Digital Orthophoto Quadrangle

DRG Digital Raster Graphic

EDNA Elevation Derivatives for National Applications

ESRI Environmental Systems Research Institute

GIS geographic information system

GNIS Geographic Names Information System

HUC Hydrologic Unit Code

ID identifier

LIDAR Light Detection and Ranging

NED National Elevation Dataset

NEM New England Method
ix

NHD National Hydrography Dataset

NRCS Natural Resources Conservation Service

NWIS National Water Information System (USGS)

RF1 USEPA Reach File Version 1.0

RF3 USEPA Reach File Version 3.0

SPARROW SPAtially Referenced Regressions On Watershed attributes

U.S. United States

USEPA United States Environmental Protection Agency

USGS U.S. Geological Survey

WBD Watershed Boundary Dataset
x

Terminology

The Glossary at the end of this report provides a comprehensive list of key and specialized 

terms used in this report along with their definitions. The following information provides a brief 

overview of certain key terms and their relations. The initial use of a Glossary term is italicized 

in this report. Many of the terms used in this report are common hydrologic terms, but they may 

be used in a different context in this report. 

Surface-water drainage refers to the process by which water flows downhill following the lay 

of the land. A drainage area defines the geographic extent of the land surface that drains to a 

specific location. A drainage-area measurement is the number that defines a drainage area in 

terms of square miles or kilometers. A drainage-area boundary is the polygon that defines the 

perimeter of a drainage area. The incremental drainage area for a specific hydrologic feature, 

such as a stream segment, defines the local area that drains directly into that feature. In 

figure 4, for example, the incremental drainage-area boundaries are shown for each hydrologic 

feature in the pictured drainage system. The incremental drainage area for a hydrologic 

feature found in the National Hydrography Dataset (NHD) is known as a catchment. Lastly, the 

cumulative drainage area for a specific hydrologic feature includes its incremental drainage area 

as well as the drainage area upstream from that feature, that is, all the way to the headwaters 

(farthest upstream). In figure 4, the entire yellow area shown is the cumulative drainage area 

for the hydrologic feature at the downstream end of the pictured drainage system. Figure 4 also 

illustrates that when a particular hydrologic feature is the farthest upstream feature, such as a 

headwater stream segment, the incremental drainage area and the cumulative drainage area 

for that feature are the same. When the term drainage area is used unqualified in this report, it 

means the same as cumulative drainage area.

This report reserves the terms Region, Subregion, Basin, Subbasin, Watershed, and 

Subwatershed for use when discussing the Watershed Boundary Dataset as it relates to the 

project. These terms are the proposed names for the six levels of Hydrologic Units defined 

within the Watershed Boundary Dataset.
Evaluation of Catchment Delineation Methods for the 

Medium-Resolution National Hydrography Dataset

By Craig M. Johnston, Thomas G. Dewald, Timothy R. Bondelid, Bruce B. Worstell, Lucinda D. McKay, 

Alan Rea, Richard B. Moore, and Jonathan L. Goodall

Abstract

Different methods for determining catchments 

(incremental drainage areas) for stream segments of the 

medium-resolution (1:100,000-scale) National Hydrography 

Dataset (NHD) were evaluated by the U.S. Geological 

Survey (USGS), in cooperation with the U.S. Environmental 

Protection Agency (USEPA). The NHD is a comprehensive set 

of digital spatial data that contains information about surfacewater features (such as lakes, ponds, streams, and rivers) 

of the United States. The need for NHD catchments was 

driven primarily by the goal to estimate NHD streamflow and 

velocity to support water-quality modeling. The application 

of catchments for this purpose also demonstrates the 

broader value of NHD catchments for supporting landscape 

characterization and analysis.

Five catchment delineation methods were evaluated. 

Four of the methods use topographic information for the 

delineation of the NHD catchments. These methods include 

the Raster Seeding Method; two variants of a method first 

used in a USGS New England study—one used the Watershed 

Boundary Dataset (WBD) and the other did not—termed 

the “New England Methods”; and the Outlet Matching 

Method. For these topographically based methods, the 

elevation data source was the 30-meter (m) resolution National 

Elevation Dataset (NED), as this was the highest resolution 

available for the conterminous United States and Hawaii. The 

fifth method evaluated, the Thiessen Polygon Method, uses 

distance to the nearest NHD stream segments to determine 

catchment boundaries. 

Catchments were generated using each method for NHD 

stream segments within six hydrologically and geographically 

distinct Subbasins to evaluate the applicability of the method 

across the United States. The five methods were evaluated 

by comparing the resulting catchments with the boundaries 

and the computed area measurements available from several 

verification datasets that were developed independently using 

manual methods. 

The results of the evaluation indicated that the two 

New England Methods provided the most accurate catchment 

boundaries. The New England Method with the WBD 

provided the most accurate results. The time and cost to 

implement and apply these automated methods were also 

considered in ultimately selecting the methods used to 

produce NHD catchments for the conterminous United States 

and Hawaii.

This study was conducted by a joint USGS–USEPA team 

during the 2-year period that ended in September 2004. During the following 2-year period ending in the fall of 2006, the 

New England Methods were used to produce NHD catchments 

as part of a multiagency effort to generate the NHD streamflow and velocity estimates for a suite of integrated geospatial 

products known as “NHDPlus.”

Introduction

The medium-resolution (1:100,000-scale) National 

Hydrography Dataset (NHD) (U.S. Geological Survey, 1999a) 

is a comprehensive set of digital spatial data that contains 

information about surface-water features such as lakes, ponds, 

streams, and rivers. The NHD was produced by and is maintained as a collaborative effort between the U.S. Geological 

Survey (USGS), the U.S. Environmental Protection Agency 

(USEPA), and State cooperators. These organizations have 

linked sites from many different water-related databases, 

including streamgages, water-quality monitoring sites, pointsource discharge sites, and impaired waters, to the underlying 

NHD by assigning an NHD stream address to each site. These 

linkages enable upstream/downstream query and analysis of 

the sites and their associated data.

To enhance this basic NHD capability, the USGS and 

USEPA established the goal of developing estimates of 

streamflow and velocity for each NHD stream segment in the 

United States. The streamflow and velocity estimates support 

pollutant dilution modeling and other water-resource modeling 

applications. Streamflow combined with pollutant concentration measurements collected through water-quality monitoring activities provide a means to estimate the total amount of 

pollutants (pollutant load) in a stream. Stream velocity and 

measured distance provide a means to estimate average travel 

times between contamination sources and other locations in 
2 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

the stream network. To develop these estimates of streamflow 

and velocity for NHD features using regression techniques, 

drainage-area measurements and attributes are needed. From 

a practical standpoint, given the large number of NHD features, this is best accomplished by delineating a catchment for 

each relevant feature. A catchment is the incremental drainage 

area for a single NHD hydrologic feature, such as a stream 

segment. The catchment boundaries enable simple computation of the incremental drainage-area measurement and 

may also be overlaid on other ingredient data for computing 

streamflow and velocity (such as temperature and precipitation) to associate these attributes with the NHD features. 

The resulting NHD catchments are expected to support 

a variety of applications beyond their initial use in estimating 

streamflow and velocity. Catchments are essential in determining the relations between any land-surface information (such 

as soil types, land use, land cover, and crop maps) and streams 

and waterbodies. In addition, catchments can be an aid in 

understanding the relations between atmospheric information 

(such as precipitation, temperature, and air-pollutant deposition), and streams and waterbodies. Thus, by relating these 

land-surface and atmospheric characteristics to streams, users 

have the ability to build comprehensive, integrated models of 

the land, atmosphere, and surface waters.

The goal of estimating streamflow and velocity for 

the NHD led the USGS and USEPA to integrate the NHD 

(1:100,000-scale) with the National Elevation Dataset (30-m) 

(U.S. Geological Survey, 1999b) and the Watershed Boundary 

Dataset (WBD) (where it existed) (U.S. Department of Agriculture, 2004) for purposes of determining NHD catchment 

boundaries. This integration made possible many additional 

geospatial data products found in what is now known as 

NHDPlus (U.S. Environmental Protection Agency, 2006). 

The purpose of this report is to present the results of 

different NHD catchment boundary delineation methods that 

were tested for six study Subbasins from across the United 

States, each having distinct hydrologic characteristics. The 

delineation methods consisted of the New England Method 

with the WBD (NEM-with-WBD), the New England Method 

without WBD (NEM-without-WBD), the Raster Seeding 

Method, the Outlet Matching Method, and the Thiessen 

Polygon Method. 

The catchment boundary delineations produced by the 

different methods were compared with verification datasets 

that included existing drainage-area boundaries in geographic 

information system (GIS) format and computed drainage-area 

measurements. The evaluation of the catchment drainage-area 

measurements and boundaries was conducted using analysis 

metrics, including the Coefficient of Areal Correspondence 

(CAC), polygon-area percent error, cumulative drainage area, 

and drainage-area convergence analysis. Detailed findings 

for each study Subbasin and method are presented in 

the appendix. 

The evaluation described in this report was used to 

determine the most accurate catchment boundary delineation 

method for producing NHD catchments. Though not presented 

in this report, the time and cost to implement and apply these 

automated methods also were considered in ultimately selecting the method used to produce NHD catchments for the 

conterminous United States and Hawaii.

Background

The NHD stream network is discussed in this section 

along with the concept of NHD catchments. Also described in 

this section are the other national geospatial datasets used by 

the methods evaluated. 

National Hydrography Dataset

The linear surface-water network in the NHD is 

represented by linear features (such as streams and canals) 

along with artificial path features that provide flow paths 

through areal features (lakes, ponds, and other waterbodies) in 

the network. An example of the linear and areal features in the 

NHD is shown in figure 1.

In the medium-resolution NHD, the content of the USGS 

1:100,000-scale Digital Line Graph (DLG) hydrography 

data (U.S. Geological Survey, 1996) is integrated with the 

reach-related information from USEPA’s Reach File Version 

3.0 (RF3) (U.S. Environmental Protection Agency, 1994). 

DLG hydrography data are digital representations of the 

surface-water features shown on the USGS 1:100,000-

scale topographic maps. As shown in figure 2, most of the 

1:100,000-scale DLGs for the United States were developed 

from 1:24,000-scale USGS 7.5-minute topographic quadrangle 

maps. At the time the 1:100,000-scale DLGs were produced, 

1:24,000-scale maps did not exist for the entire country 

and, therefore, USGS relied on older USGS 1:62,500-scale 

15-minute quadrangle maps for these areas (fig. 2). The data 

were compiled by 30 × 60-minute quadrangles. The source 

hydrography was photo-reduced, edge-matched, and digitized 

at the 1:100,000 scale. 

The NHD contains unique permanent identifiers, known 

as reach codes, for most linear and areal features. This 

includes coastline features that represent the shorelines of 

the Great Lakes, the Atlantic and Pacific Oceans, and the 

Gulf of Mexico. Reach codes provide the mechanism for 

linking many types of water-resource information to NHD 

hydrologic features in the same manner that street addresses 

are used to associate houses with specific locations on 

streets. The NHD provides a national framework of reach 

addresses for linking water-related entities, such as pointsource pollution discharges, impaired water designations, 

drinking-water intakes, water-quality monitoring sites, wild 

and scenic river designations, and streamgages. The USGS 

and USEPA have linked numerous water-related databases 

to the NHD by assigning NHD stream (reach) addresses in 

this manner (http://www.epa.gov/waters). The NHD provides 

the analytical framework to support hydrologic modeling, 
Background 3

71°50' 71°45' 71°40'

43°35'

43°40'

43°45'

EXPLANATION

NHDWaterbody

National Hydrography Dataset (NHD) layers

NHDArea NHDFlowline

Lake/Pond

Swamp/Marsh

Stream/River

Artificial path

Stream/River

0 1 2 4 MILES

0 1 2 4 KILOMETERS

Base from 1:100,000-scale National Hydrography Dataset, 2003

Figure 1. The medium-resolution National Hydrography Dataset surface-water drainage system, central New Hampshire.
4 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

water-quality studies, characterization of fish and other aquatic 

organism habitat, and many other applications. Some major 

characteristics of the NHD are listed below.

• It is a feature-based dataset that interconnects and 

uniquely defines the stream segments that comprise the 

surface-water drainage system of the United States.

• Permanent identifiers known as “reach codes” are 

assigned to NHD stream network and waterbody 

features.

• Reach codes on linear features, along with a measurement system, form “reach addresses” that establish the 

locations of surface-water entities on the NHD surfacewater drainage network.

• Once the upstream/downstream relations of waterrelated entities and associated information are linked to 

the NHD by their reach addresses, they can be analyzed using various software tools.

• The medium-resolution NHD is based on the content of 

the USGS 1:100,000-scale DLG data, giving it spatial 

resolution similar to that found on the 1:100,000-scale 

USGS topographic maps. 

• The high-resolution NHD for the conterminous United 

States, which is based on a 1:24,000 scale or better 

source, was finished in 2007 after this study had been 

completed.

• NHD datasets are maintained using one consistent 

spatial reference—geographic (latitude/longitude coordinates in decimal degrees) referenced to the North 

American Datum of 1983.

• Names with Geographic Names Information Systems

(GNIS) identification numbers are included for lakes, 

other water bodies, and many stream courses 

(http://nhd.usgs.gov/gnis.html).

8-digit Hydrologic Unit Code Subbasins

 from U.S. Geological Survey National

 Hydrography Dataset (NHD), 2007

7.5-minute quadrangles from U.S. Geological

 Survey Quadrangle Map Index, 2002

States from U.S. Census Bureau 1:100,000-scale 

 TIGER, 2001 

*1:62,500-scale source data were determined

by selecting all quadrangles with a provisional map

published in 1987 or later. This method identifies

quadrangles that were unlikely to have 1:24,000-scale

data at the time of the creation of the 1:100,000-scale 

Digital Line Graph (DLG) product. 

Subbasin boundary

Likely 1:62,500-scale quadrangles* (4,671 total)

Likely 1:24,000-scale quadrangles (60,897 total)

EXPLANATION

0 100 200 300 400 MILES

0 200 400 KILOMETERS

Figure 2. The United States with the source map scales of the medium-resolution National Hydrography Dataset.
Background 5

• The data contain many feature attributes such as flow 

directions, names, and stream levels.

• The NHD is maintained through a national stewardship 

program led by USGS and implemented by Federal 

and State stewards. 

The flowline is the basic unit of the NHD linear surfacewater network. An NHD reach is a uniquely identified linear 

feature that consists of one or more flowlines. Flowline features are segmented at stream confluences and at changes of 

NHD feature types and attributes along the network. Flowline 

features include streams, rivers, intermittent streams, canals, 

ditches, pipelines, coastlines, and artificial paths (through areal 

water bodies). The set of connected flowlines, with known 

flow direction, forms the drainage network. 

Isolated networks are those networks with known flow 

direction that stop at a dead-end or terminus (that is, without 

connecting to a downstream flowline). In the NHD, stream 

features may be present on one source quadrangle, but not 

continued on the adjacent source map because of inconsistently applied production procedures across quadrangles. In 

these situations, a stream mapped as flowing downstream 

toward an adjacent quadrangle may seem to end at the quadrangle boundary. Actually, the stream does continue onward to 

connect to the downstream network, but this is not reflected in 

the NHD. This is an example of an erroneous isolated network 

associated with quadrangle boundaries. Isolated networks are 

not always found at quadrangle boundaries, and they may or 

may not be legitimate. Legitimate isolated networks are those 

streams that percolate into the ground or deliver water to 

playas such as the evaporative salt flats found in the western 

part of the United States. An example of two isolated NHD 

networks in a karst terrain setting is shown in figure 3.

The NHD flow table was of particular importance during 

this study. The flow table is a database table that contains 

the interconnections between the flowlines. Only flowlines 

with known flow directions are included in the flow table. 

Where two flowlines exchange water, a flow relationship 

is established within the flow table. In cases where two 

coastline features touch, a nonflowing relationship is included 

in the flow table. Where a stream flows into the Pacific or 

Atlantic Ocean, the Great Lakes, or the Gulf of Mexico, 

a nonflowing relationship in the flow table connects the 

stream to the coastline. These nonflowing relations enable 

network navigation along the coasts to identify water-related 

information that has been linked to the coastlines.

For all the methods evaluated, the NHD flowlines 

were first projected into the National Albers Equal-Area 

coordinate system and converted to an ArcInfo coverage 

format. Catchments were delineated only for NHD flowlines 

having known flow direction and, for that reason, are included 

in the flow table. All features with unknown flow direction 

were deleted from the ArcInfo coverage prior to catchment 

boundary delineation. 

Concept of National Hydrography Dataset 

Catchments

The goal of this study was to determine the most accurate method for delineating catchment boundaries for NHD 

flowlines. An NHD catchment is the land surface that drains 

directly into an NHD flowline without first flowing into an 

upstream flowline (fig. 4). A catchment boundary is a polygon 

that extends upstream from the terminus (downstream end) of 

the flowline and defines the incremental drainage area for that 

flowline. Combining the catchment boundary for a specific 

flowline with the catchments associated with all upstream 

flowlines defines the cumulative drainage area for that 

flowline (fig. 4). 

National Elevation Dataset

The National Elevation Dataset (NED) (U.S. Geological 

Survey, 1999b) is a raster (grid) product assembled by the 

USGS (http://ned.usgs.gov) that provides nationwide elevation 

data in a seamless form referenced to a common coordinate 

system. The NED contains data corrections made during the 

assembly process to minimize production artifacts, perform 

edge matching, and fill sliver areas of missing data. 

NED is available in multiple resolutions. A one arcsecond resolution NED (approximately 30-m cell size) is 

available for the conterminous United States, Hawaii, Puerto 

Rico, and island territories. The one arc-second resolution 

NED currently provides the most extensive coverage for the 

United States, with the exception of Alaska (Alaska has a 

two-arc-second resolution, or approximately a 60-m cell size). 

A NED of one-third arc-second resolution (approximately 

10-m cell size) is available for Hawaii and about two-thirds 

of the conterminous United States. The highest resolution 

NED of one-ninth arc-second (approximately 3-m cell size) 

is available for selected areas across the United States and is 

derived from large-scale planimetric contours or newer digital 

topographic capture methods, such as Light Detection and 

Ranging (LIDAR).

As higher resolution or higher quality elevation data 

become available, the NED is updated bimonthly to incorporate best-available coverage. The NED data dictionary, release 

notes, and update information can be found on the NED 

Web site at http://ned.usgs.gov/ned/downloads.asp. A visual 

index documenting the individual source elevation datasets is 

found in the Data Source Index for NED on the Web site. The 

digital elevation models (DEMs) used to construct the NED 

have a wide range of source-data characteristics. The NED is 

designed to incorporate the most accurate source data for the 

one-ninth, one-third, and one arc-second grid spacing. For 

instance, if a new one-ninth arc-second NED is produced, the 

coarser resolutions of one-third and one arc-second NED are 

updated by resampling the one-ninth arc-second data. Seamless NED data are distributed through the Seamless Data 

Distribution System (http://seamless.usgs.gov/). 
6 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

EXPLANATION

Isolated network NHD flowlines

Connected network NHD flowlines 

85° 84°52'30"

35°52'30"

35°45'

0 1 2 4 MILES

0 1 2 4 KILOMETERS

Base from 1:100,000-scale, National Hydrography Dataset (NHD), 2003

Figure 3. An example of isolated networks in the medium-resolution National Hydrography Dataset (NHD), eastcentral Tennessee.
Background 7

Intermittent stream

Stream/River

Artificial path

NHD Lake/Pond

EXPLANATION

Catchment for NHD

flowline features

NHD flowline features

NHD waterbody features

National Hydrography Dataset (NHD) data

layers and features

 

Figure 4. The National Hydrography Dataset flowlines and their associated catchments.
8 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

For the purpose of this study, the one arc-second NED 

was selected as the elevation data source for delineating 

NHD catchment boundaries, as it was the highest resolution 

NED available for the conterminous United States and 

Hawaii. National coverage is essential in meeting the goal of 

estimating streamflow and velocity for the flowlines in the 

medium-resolution NHD.

Elevation Derivatives for National Applications

The Elevation Derivatives for National Applications 

(EDNA) is a suite of data layers that are commonly used for 

topographic analyses. These layers include aspect, shaded 

relief, slope, and synthetic streamlines (http://edna.usgs.

gov/). Several of these layers have importance for hydrologic 

applications. The EDNA data are based on the one arc-second 

NED. In EDNA, elevation data have been projected to a coordinate system appropriate for direction and area analysis and 

processed to remove spurious sinks so that flow routing across 

the entire elevation surface can be achieved. 

The EDNA flow direction and flow accumulation grids 

provide a digital representation of land-surface flow. For each 

cell in the grid, the EDNA flow direction grid determines 

the direction of flow in relation to its neighboring cells. The 

flow direction grid makes it possible to delineate drainagearea boundaries from EDNA data. For each cell in the grid, 

the EDNA flow accumulation grid provides the structure to 

determine the number of upstream cells that flows into that 

cell. Using the flow accumulation grid, EDNA “synthetic” 

stream lines were generated to an upstream threshold of 

1.74 square miles (mi2); that is, the synthetic lines extend 

upstream until the total area of the upstream cells reached 

1.74 mi2. EDNA catchment boundaries are then produced 

for each synthetic stream. These synthetic stream lines do 

not always follow the same flow path as the mapped NHD 

flowlines, and in some cases differ considerably. In addition, 

all EDNA synthetic stream lines begin and end at confluences, 

whereas NHD flowlines begin and end at both confluence and 

NHD feature-type changes. 

The development of the EDNA dataset is envisioned as 

a three-stage process. Stage 1, the current stage of the dataset, 

is mostly automated. The main component of this step is a 

blind pass filling of spurious sinks to create the depressionless 

DEM. Stage 2 focuses on identifying potential errors in the 

data with the assistance of local agencies that use EDNA 

stage 1 data and who are familiar with the hydrology in their 

geographic area. In stage 3, the errors identified in stage 2 

will be addressed to create an improved dataset (Kost and 

others, 2003).

Watershed Boundary Dataset

The Watershed Boundary Dataset (WBD) is a national 

seamless framework for the compilation of digital hydrologic 

area features delineated using manual interpretive methods 

from 1:24,000-scale USGS topographic maps (U.S. Department of Agriculture, 2004). These WBD hydrologic area 

features, also known as Hydrologic Units, support a variety 

of water-quality reporting uses. The term Subwatershed refers 

to the subdivisions of a Watershed (table 1) in a hierarchal 

system that subdivides the landscape into successively smaller 

Hydrologic Units (Seaber and others, 1987). Hydrologic 

Units are spatially nested within one another and each unit is 

assigned a unique Hydrologic Unit Code (HUC). HUCs are 

2 to 12 digits in length, based on the hierarchy of geographic 

areas defined within the WBD. The largest Hydrologic Units 

subdivide the United States into 22 major geographic areas, 

called Regions, and are identified by unique 2-digit HUCs. A 

Subwatershed, the smallest Hydrologic Unit, is identified by a 

unique 12-digit HUC and is generally 20 to 60 mi2 in size. The 

hierarchal structure of the Hydrologic Units contained in the 

WBD is given in table 1. These hierarchal relations enable the 

aggregation of smaller Hydrologic Units into larger Hydrologic Units based upon the HUCs. Many individual WBD 

hydrologic units are not complete drainage areas since they do 

not extend all of the way upstream to the headwaters.

The WBD is the culmination of collaborative efforts by 

Federal, State, and local agencies. The WBD delineations 

go through various stages of review before final certification 

and entry into the national WBD database. During the review 

process, delineations are checked for accuracy against 

1:24,000-scale Digital Raster Graphics (DRG) to ensure that 

subdivisions meet defined hydrologic and cartographic criteria. 

DRGs are digital versions of the same USGS topographic 

maps that served as the source for the medium-resolution 

NHD and, as such, align well with NHD features. WBD 

interstate edge-matching issues are resolved during the review 

process. Once all Hydrologic Units in a State are certified, the 

WBD for that State becomes available to the public. The WBD 

is maintained by the Natural Resources Conservation Service 

(NRCS) in partnership with USGS and State cooperators. For 

more information, visit the WBD Web site at (http://www.

ncgc.nrcs.usda.gov/products/datasets/watershed). 

Table 1. Hierarchal structure of the Watershed Boundary 

Dataset.

Hydrologic Unit 

name

Hydrologic Unit Code 

(HUC) length in digits

Approximate number 

nationwide

Region 2 22

Subregion 4 222

Basin 6 352

Subbasin 8 2,149

Watershed 10 22,000

Subwatershed 12 160,000
Catchment Delineation Methods 9

Catchment Delineation Methods

Five NHD catchment delineation methods were tested. 

Four methods used elevation information as the basis for 

catchment delineation: the Raster Seeding Method; two 

variants of an approach first used in a USGS New England 

study (termed the “New England Method”)—one variant 

with WBD and one variant without WBD—and the Outlet 

Matching Method. A fifth method, the Thiessen Polygon 

Method, determines catchment boundaries by evenly splitting 

the distance between nearby NHD flowlines. As previously 

noted, catchments are only generated for NHD flowlines with 

known flow direction (that is, flowlines with flow relations 

defined in the NHD flow table). 

Raster Seeding Method

The Raster Seeding Method uses the NHD and EDNA 

datasets. The method converts the vector NHD flowlines 

into a raster ArcInfo Grid (Environmental Systems Research 

Institute, Inc., 1999) data model to be used as “seeds” 

for elevation-based drainage-area delineation (fig. 5). 

This approach has been used in other studies to delineate 

catchments for cartographic streams (Nolan and others, 2003).

In the Raster Seeding Method, NHD flowline features are 

rasterized to a 30-m × 30-m grid cell resolution and aligned 

to the EDNA flow-direction grid. The NHD flowline common 

identifier (ComID) codes are used as the grid values in the 

raster representation of the flowlines. The rasterized NHD 

flowlines and the EDNA flow direction grid are the required 

inputs to the Environmental Systems Research Institute 

(ESRI) ArcInfo Grid WATERSHED command (Environmental 

Systems Research Institute, Inc., 1999), which is used to 

generate catchments for each unique NHD flowline. The 

WATERSHED command delineates catchments upstream 

from seed cells (in this case, those cells that make up the 

rasterized NHD flowlines) using an algorithm developed by 

Jenson and Dominque (1988). 

To facilitate the spatial analyses used to compare results 

of the different catchment boundary delineation methods, 

the boundaries were converted from raster format to vector 

format (ArcInfo coverage data model). Vector catchment 

boundaries were used for many of the evaluation metrics 

discussed later in this report. The coverage format associates 

all noncontiguous areas for any multipart catchments by 

assigning them the same ComID. They are recognized as 

one vector feature in the ArcInfo region subclass data model. 

These multiple-part polygon features are created during the 

raster-to-vector conversion process, when one or more cells 

with directional flow traveling diagonally into an adjacent cell 

along a catchment boundary result in separate polygons in the 

vector data model (fig. 6). In addition, catchment boundaries 

are not generated by the WATERSHED command for very 

short NHD flowlines (less than about 42 m) because of the 

30-m resolution of the ingredient EDNA dataset.

22743041

EXPLANATION

NHD flowlines 

NHD catchment boundary

NHD flowlines represented

as grid cells; grid cell colors

represent each unique NHD

common identifier (ComID)

NHD ComID

22743007

22743005

22743041

Figure 5. Schematic design showing three vector National 

Hydrography Dataset (NHD) flowline features (blue lines) 

overlaid onto their raster representations, along with the 

corresponding catchments generated by the Raster Seeding 

Method.
10 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

NHD flowline

has five polygons

that define the

catchment 

area (in red) 

(1)

(2)

(3)

(4)

(5)

Figure 6. Schematic design showing multiple polygon features that define the catchment boundary for a National Hydrography 

Dataset (NHD) flowline.

New England Method with Watershed Boundary 

Dataset

The New England Method with Watershed Boundary 

Dataset (NEM-with-WBD) was developed for the New 

England SPAtially Referenced Regressions On Watershed 

attributes (SPARROW) water-quality model (Moore and 

others, 2004). This method was also employed without the 

WBD as described in the section “New England Method 

without Watershed Boundary Dataset.”

The SPARROW model requires a hydrologically 

connected representation of a stream network and associated 

catchments through which stream nutrient loads are 

transported downstream, thus relating upstream sources to 

downstream monitored nutrient data. Previous SPARROW 

models in the United States were based on the USEPA River 

Reach File Version 1.0 (RF1) (Dewald and others, 1985). The 

need for improved resolution in the New England models 

resulted in the selection of the medium-resolution NHD as 

the base hydrography for the model. For comparison, in New 

England, there are 2,462 RF1 catchments (mean size 29.2 m2) 

and 42,000 NHD catchments (mean size 1.7 m2). The spatial 

detail of the NHD in New England is shown in figure 7. 
Catchment Delineation Methods 11

74°

72°

70°

68°

42°

44°

46°

0

0

100 MILES 50

50 100 KILOMETERS

Base from U.S. Geological SurveyDigital Line Graph, 1:2,000,000-scale, 1990–94

National Hydrography Dataset (NHD) catchmentsExtent of basins not modeledNHD flowlineState boundaryCountry boundary

Topographic map

Base from U.S. Geological Survey Center Lovell and North Waterford quadrangles, 1:24,000-scale, 1989

70°52'30"

NHD catchment divide

Subwatershed divide

44°15'

NHD flowline

Saco River Subbasin

EXPLANATION

Kezar Lake Subwatershed

Figure 7. The spatial detail of the stream network and 42,000 catchments used for the New England SPAtially Referenced Regressions On Watershed attributes (SPARROW) model (modified from Moore and others, 2004).
12 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

NHD stream flowline and identifier 

Synthetic stream generated from

EDNA-derived flow directions

3 2

4

3 2

4

3 2

4

A B C

NHD flowline catchments

EXPLANATION

Base from U.S. Geological Survey

Digital Raster Graphic, Stoddard, NH

1:25,000-scale, 1984 0 100 200 METERS

0 400 800 FEET

Figure 8. (A) Horizontal displacement between the National Hydrography Dataset (NHD) flowlines and the Elevation Derivatives 

for National Applications (EDNA) synthetic streams, (B) catchment delineations using the Raster Seeding Method with the EDNA 

flow direction grid, and (C) catchment delineations using the New England Method with a new flow-direction grid created using the 

AGREE computer program with the National Elevation Dataset.

Similar to the Raster Seeding Method, catchments that 

are generated using the NEM-with-WBD were delineated 

using DEM-derived flow directions. The only difference 

between the methods is that the Raster Seeding Method used 

the EDNA flow direction grid and the NEM-with-WBD used 

a new flow direction grid. In the NEM-with-WBD, NED data 

were first modified to enforce drainage to the NHD flowlines, 

and a new flow direction grid was created as the source for 

catchment boundary delineations. 

The NED modifications were considered necessary 

because the flow path defined by the EDNA flow direction grid can at times differ substantially from the mapped 

1:100,000-scale NHD flowlines. This difference, referred to as 

the DEM flow-path displacement, is defined as the horizontal 

positional offset between the mapped NHD streams and the 

inherent drainage pattern of the DEM-based flow direction 

data. A common example of the DEM flow-path displacement 

between NHD flowlines and EDNA-derived streams is shown 

in figure 8A. In many cases, the NHD flowlines and EDNAderived synthetic stream lines run parallel to each other at 

some offset distance. If this offset distance is greater than one 

grid cell width, then part of the catchment generated using the 

Raster Seeding Method is not identified as being uphill from 

the NHD stream flowline. As a result, this part of the catchment is erroneously excluded from the delineated catchment 

boundary (fig. 8B). 

To alleviate displacement problems between NHD 

flowlines and EDNA flow paths (fig. 8A), a new flow direction 

grid was developed by modifying the NED data in a process, 

often referred to as stream burning (Saunders, 2000), which 

integrates the NHD vector flowlines into the raster elevation 

data. A stream burning technique developed by Hellweger 

and Maidment (1997), called DEM surface reconditioning, 

was used with modifications. A series of computer algorithms 

implemented in the computer program called AGREE were 

used. AGREE is based on the Arc Macro Language (AML) 

developed by Hellweger and Maidment (1997). The AGREE 

computer program “burns a canyon” into the DEM by using 

a specified vertical distance, which is subtracted from the 

DEM elevation grid cells that coincide with rasterized NHD 
Catchment Delineation Methods 13

-10,000 meters

“Sharp Drop Distance”

-500 meters

“Smooth Drop Distance”

DEM stream

grid cell

NHD flowline grid cell

AGREE DEM surface

Original DEM surface

Not drawn to scale

AGREE parameters in RED 

160 meters

“Buffer Distance” 160 meters

“Buffer Distance”

Figure 9. Schematic design showing the manner in which the AGREE computer program modifies 

the digital elevation model (DEM) of the National Elevation Dataset (NED) to align with the National 

Hydrography Dataset (NHD) flowlines.

flowlines. The vertical exaggeration of the burned canyon is 

controlled by the AGREE “sharp drop/raise distance” input 

parameter. Figure 8C illustrates how the New England Method 

corrected for the source of error shown in figure 8B, when 

catchments were delineated. In the original New England 

SPARROW model and the study Subbasins, a negative sharp 

drop distance of 10,000 m was applied to ensure that the 

burned NHD stream flow path would remain after the filling 

process was applied in subsequent processing steps. 

AGREE also smooths the elevation cells on both sides 

of the NHD flowline within a specific buffer distance. The 

buffer distance is an input parameter to the AGREE program. 

It is related to the average horizontal displacement distance 

between the NHD flowlines and DEM-derived synthetic 

streams and is intended to remove any artifacts of the 

synthetic streams from the resulting grid. In New England, 

the typical displacement error was found to be 160 m or 

less. In the original New England SPARROW model and the 

study Subbasins, 160 m was specified as the buffer distance 

in AGREE. The 160-m buffer distance is applied to both 

sides of the NHD flowlines. The smoothing process modifies 

the DEM grid cell elevations within the buffer area to create 

a downward sloping gradient toward the burned canyon 

beneath the NHD flowlines. The steepness of the gradient 

slope within the buffer can be controlled by the “smooth 

drop/raise distance” parameter to AGREE. In the original 

New England SPARROW model and the study Subbasins, a 

smooth drop distance of 500 m was specified. The manner in 

which AGREE modifies the original DEM using the specified 

parameters is shown in figure 9. 

The use of the 160-m buffer distance with AGREE poses 

potential problems at headwater NHD flowlines, particularly 

where flowlines exist at drainage divides (ridgelines) defined 

using the NED. The 160-m buffer distance at these headwater streams may extend across the NED ridgeline and into 

an adjacent drainage area. Because elevation cells within 

the entire buffered area are altered by the AGREE program 

to create a sloping gradient toward the NHD streams, parts 

of drainage divides can be erased by this AGREE processing, causing derived flow directions to cross drainage divides 
14 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Figure 10. Schematic design showing a three-dimensional perspective view of a modified digital elevation model with walling of 

the Watershed Boundary Dataset and stream burning, using the National Hydrography Dataset.

Constant value added to digital

elevation model (DEM) along the

Watershed Boundary Dataset (WBD)

Subwatershed boundary (”walling”)

Constant value subtracted

from DEM dataset along National

Hydrography Dataset (NHD) flowlines

(”stream-burning”)

and create errors in catchment delineations. To minimize this 

headwater stream buffer intrusion for the study Subbasins, the 

TRIMSTREAMS AML program was developed to remove 

the most upstream 90 m of all headwater vector flowlines. The 

TRIMSTREAMS program was included in the New England 

Method processing steps before the AGREE processing. 

To generate NHD catchments for the New England 

SPARROW model, the hydrologic conditioning of the NED 

data was taken a step further by creating a series of computer 

algorithms to force the DEM to be consistent with manually 

interpreted drainage-area divides of the WBD. The process 

of conditioning DEM data to WBD drainage areas is called 

walling. The New England Method process of walling was 

implemented using an AML program that increases the 

elevation values of DEM cells that coincide with the location 

of vector divides in the WBD. The vertical distance used to 

increase the drainage divide elevation cells was set arbitrarily 

high at 10,000 m. A three-dimensional representation of a 

hydrologically conditioned DEM showing the effects of 

walling and burning is presented in figure 10. This walling 

technique was used in the five study Subbasins where WBD 

boundaries were available. 

The resulting hydrologically conditioned DEM, with 

stream burning of the NHD and walling of the WBD, was 

filled to remove spurious sinks on the DEM surface and 

used to derive the new flow direction grid. The final step of 

the NEM process is identical to that of the Raster Seeding 

Method where catchments were produced by rasterizing the 

NHD flowlines as input with the new flow direction grid to the 

ArcInfo WATERSHED command. The hydrologically conditioned DEM was discarded after this process, as measures of 

elevation, slope, and aspect would be meaningless for use in 

any analysis. 

As with the Raster Seeding Method, flowlines less than 

42 m in length may not have a catchment delineated by the 

New England Method, owing to the 30-m raster cell size. The 

resulting catchments from the NEM were converted to a vector region ArcInfo coverage data model. 

In the application of the New England Method, the modified walling technique ensured that catchment delineations 

conformed to manually delineated Subwatershed boundaries 

of the WBD. NEM-with-WBD can be used for areas where the 

certified WBD is available. In general, digital drainage-area 

boundaries should not be used in the New England Method
Catchment Delineation Methods 15

walling process if the boundary delineations were made using 

elevation contours of a substantially different scale than the 

DEM data used for the New England Method. For this study, 

WBD boundary delineations (based upon 1:24,000-scale 

maps) were used with comparable one arc-second resolution 

DEM data (approximately 30-m cell size). In addition, the 

New England Method can be used if only part of the landscape 

has WBD boundaries. The use of the WBD also was helpful in 

locating inaccuracies in the NHD spatial and tabular relations. 

For the study Subbasins, no attempts were made to correct 

errors found in either the NHD or the WBD.

New England Method without Watershed 

Boundary Dataset

At the time of this study, many States in the United States 

did not have a certified WBD. Some States possessed digital 

WBD data that were still in the development phase and, as a 

result, were deemed not acceptable for New England Method

walling. Where the WBD is not available, the New England 

Method without Watershed Boundary Dataset (NEM-withoutWBD) can be applied by simply omitting the algorithms 

used in the walling process. For completeness of the methods 

evaluations, the NEM-without-WBD was applied to all study 

Subbasins, including those with available WBD boundaries. 

Outlet Matching Method

The Center for Research in Water Resources at the 

University of Texas at Austin developed the Outlet Matching 

Method to relate a catchment to the point along a river network that most accurately approximates the catchment outlet. 

The algorithm is included in the ArcHydro Tools (Olivera 

and others, 2002) as Store Area Outlets. The Outlet Matching 

tool in ArcHydro Tools links existing catchments to the river 

network when the catchments are developed from a DEM that 

was not conditioned with the river network. For this study, the 

Outlet Matching tool was used to link existing EDNA catchments, derived from a synthetic stream network, with the flowline features that compose the NHD stream network. Using the 

existing DEM-derived EDNA catchments offered the potential 

of producing NHD catchments for less time and cost. 

The Outlet Matching Method supports three different 

techniques for selecting the proper outlet for each EDNA 

catchment. Only one of these techniques may be specified for 

each execution of the Outlet Matching routine, thus requiring 

a GIS analyst to execute the routine several times, applying 

each technique in turn until an outlet has been identified for all 

EDNA catchments. 

In the first technique, Junction Intersect (fig. 11), junction 

points were identified on the NHD network at the intersection 

of the EDNA catchment boundaries and the NHD flowlines. 

It is assumed that the outlet of the catchment will be at or 

near a junction of an NHD flowline and a EDNA catchment 

boundary. When there is more than one junction at the EDNA 

catchment boundary, the appropriate outlet junction will have 

the greatest length of stream network upstream of the junction 

and inside the catchment boundary. 

Figure 11 illustrates that the Junction Intersect technique 

selects the outlet that has the longest upstream network length 

inside the EDNA catchment boundary. Junction Intersect of 

the Outlet Matching technique typically determines outlets for 

more than 75 percent of the EDNA catchments.

In the second technique, Drainage Point Proximity

(fig. 12), it is assumed that the outlet of an EDNA catchment is 

near the bottom of an NHD flowline. This technique is applied 

only to EDNA catchments that did not have an outlet assigned 

using the Junction Intersect technique. In the Drainage Point 

Proximity technique, a set of candidate outlets was defined 

as the downstream ends of the NHD flowlines. The drainage 

point for each EDNA catchment was defined as the lowest 

elevation point in each catchment. On the basis of an analystsupplied tolerance, the Drainage Point Proximity technique 

finds the NHD outlet that is within the tolerance and nearest 

to the catchment drainage point and assigns that NHD outlet 

as the outlet of the catchment. The Drainage Point Proximity 

technique cannot be used with catchments that are not derived 

from elevation data. 

The third technique, Next Downstream Area (fig. 13), 

was used when EDNA catchments were not assigned an outlet 

by either of the previous two techniques. In this technique, it 

is assumed that the topology of the EDNA catchments mimics 

the topology of the NHD stream network. This technique 

locates an adjacent catchment, which is downstream of the 

subject catchment that already has an assigned outlet, and 

then assigns that outlet to the subject catchment as well. The 

EDNA catchment topology is based on unique catchment 

identifiers, known as Pfafstetter codes (Verdin and Verdin, 

1999), and their associated relations, shown as HydroID and 

NexDownID, respectively, in figure 13.

These three techniques were applied in sequence. The 

second technique was used only on those EDNA catchments 

that were not assigned an outlet using the first technique. The 

second technique was applied several times while increasing 

the analyst-specified tolerance and operating only on catchments that had not yet received an outlet. Likewise, the third 

technique was used only for those catchments that did not 

receive an outlet assignment using the first two techniques. 

After running all three techniques, all EDNA catchments were 

assigned an outlet. 

The ultimate goal of this method was to have each 

EDNA catchment linked to a single NHD flowline feature 

rather than to an outlet point. A custom computer program 

was written to perform this final process. For a given EDNA 

catchment, the program relates the assigned outlet for the 

catchment to the flowline underlying the outlet. If an outlet 

was located at the intersection of multiple NHD flowline 

features, the flowline with the largest length within the 

catchment boundary was selected.
16 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

EXPLANATION

NHD flowlines

NHD outlet junction

EDNA catchment drainage point

NHD outlet junction selected

Subject Elevation Derivatives for National Applications 

(EDNA) catchment to be matched to the best corresponding

National Hydrography Dataset (NHD) flowline

Drainage Point

Downstream

Outlet

EXPLANATION

Outlet

NHD flowlines

Junction at intersection of EDNA catchment boundary

and NHD flowlines

Junction not selected (not used)

Outlet junction selected; the flowline at this junction is 

matched to the subject EDNA catchment

Subject EDNA catchment being matched to the best corresponding

National Hydrography Dataset (NHD) flowline

Catchments for synthetic streams from the

Elevation Derivatives for National Applications (EDNA)

Figure 11. Schematic design showing the Junction Intersect technique of the Outlet Matching Method.

Figure 12. Schematic design showing the Drainage Point Proximity technique of the Outlet Matching Method.
Catchment Delineation Methods 17

EXPLANATION

NHD flowline

Outlet point

Outlet selected

Subject Elevation Derivatives for National Applications 

(EDNA) catchment being merged to the next downstream

EDNA catchment

Pfafstetter hydrologic code identifier

Next downstream hydrologic code identifier

EDNA catchment not associated with the NHD 

flowline shown

The EDNA catchment identified as the outlet matched

catchment to the National Hydrography Dataset (NHD) 

flowline shown

NexDownID

(101)

HydroID

(101)

Downstream

Outlet

HydroID

(101)

NexDownID

(101)

Figure 13. Schematic design showing the Next Downstream Area technique of the Outlet Matching Method.
18 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Thiessen Polygon Method

The name “Thiessen” refers to work by Thiessen and 

Alter (1911) that defined areas (polygons) around rain gages 

whose boundaries were computed as half way between the 

nearest rain gages. The Thiessen polygons are constructed 

using a raster or grid-based approach to produce the boundary 

lines halfway between the nearest NHD flowlines. Because 

the Thiessen Method did not require the time-consuming 

processing of topographic information like the other methods, 

it offered the potential of producing NHD catchments for less 

time and cost. 

To define the catchment boundary for each NHD 

flowline with the Thiessen Polygon Method, the vector NHD 

flowlines were first converted to a grid (raster) format having 

30-m grid cells. Then a new grid of 30-m cells, referred to 

as the catchment grid, was created using the ArcInfo Grid 

EUCALLOCATION function (ESRI, 2003). In this step, each 

cell in the new catchment grid is assigned the grid code of the 

nearest NHD flowline grid cell measured using the straightline euclidean distance. The collection of catchment grid cells 

with the grid code of a particular NHD flowline represents 

an approximation of the catchment area for that flowline. 

The catchment grid then is vectorized and assigned attributes 

to create a vector polygon dataset approximating Thiessen 

polygons. The NHD flowline ComID is entered into the 

resulting polygon attribute table using the ArcInfo JOINITEM 

command (ESRI, 2003). 

Thiessen polygon approximations of catchment 

boundaries are called “Thiessen catchments” (fig. 14). 

Because Thiessen catchments are based on purely geometric 

proximity, and terrain elevation information is not taken 

into consideration, the polygons represent a less accurate 

approximation of the true catchment boundaries. Conversely, 

the Thiessen Polygon Method has the advantage of being 

computationally efficient and does not require any dataset 

other than the NHD. 

In addition to the flowlines in a study Subbasin, the NHD 

grid included the flowlines for all surrounding Subbasins. The 

surrounding flowlines were assigned grid codes of zero, and 

their associated areas were subsequently removed from the 

resulting datasets. This technique ensured that the resulting 

catchment boundary for a flowline on the perimeter of a study 

Subbasin was computed in the same manner as a catchment 

boundary for a flowline in the interior of the study Subbasin, 

that is, the boundary is halfway between the nearest NHD 

flowlines, including those in adjacent Subbasins. 
Catchment Delineation Methods 19

106°07' 106°01'30"

39°20'30"

39°15'

EXPLANATION

Thiessen Polygon Method catchment

National Hydrography Dataset (NHD) 

NHD flowlines

0 1 2 4 MILES

0 1 2 4 KILOMETERS

NHD lake/pond

Base from 1:100,000-scale National Hydrography Dataset, 2003

Figure 14. Thiessen Polygon Method catchments for National Hydrography Dataset flowlines.
20 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Testing the Catchment Delineation 

Methods

This section describes the areas where the catchment 

delineation methods were applied, the basis for comparing 

each method, and the evaluation metrics used for 

the comparisons. 

Study Subbasins

To test the catchment boundary delineation methods, 

six study areas within the continental United States were 

chosen (fig. 15). Each study area consists of a single 

headwater Subbasin, identified by its 8-digit HUC as defined 

within the WBD. These study Subbasins, listed in table 2, 

were chosen to represent the typical surface-water network 

morphologies found within the conterminous United States. 

The decision to use only headwater Subbasins was made to 

simplify the comparisons since it limits the upstream extent 

of the study Subbasins. 

Basis for Comparison

Evaluation of the accuracy of the catchment boundaries 

produced by the five delineation methods is based on 

conformance to real-world topographic relief and known 

drainage areas (presumed to be definitive). Catchment 

boundary delineation methods using topographic information 

(the Raster Seeding Method, the New England Method 

variants, and the Outlet Matching Method) are bound to the 

resolution of the nationally available one arc-second (30-m) 

NED. In the conterminous United States, nearly all data in the 

one arc-second NED, at the time of this study, were derived 

from the largest scale topographic data available nationally, 

which is the USGS 1:24,000-scale topographic maps. Also, 

at the time of the study, nearly all one-third arc-second NED 

were derived from the 1:24,000-scale maps. Therefore, until 

the time when the one-ninth arc-second NED is completed 

nationally, the accuracy of the delineation methods can only 

refer to their conformance to the 1:24,000-scale topographic 

map program. 

Datasets Obtained for Verification in the 

Comparison Analysis

A variety of data was used to evaluate the accuracy of the 

catchment boundary delineation methods. These data are listed 

below.

• Published drainage-area measurements for USGS 

streamgages. These published measurements were used 

for comparisons with the drainage-area measurements 

computed during the study for NHD flowlines 

associated with streamgages. 

• Drainage-area boundaries for USGS streamgages and 

draft WBD boundaries. These GIS datasets enable spatial drainage-area comparisons and analysis techniques. 

Table 2. Subbasin name, Hydrologic Unit Code, State, and description for six study Subbasins in the United States.

Subbasin name

Hydrologic 

Unit Code 

(HUC)

State(s) Description

Great Egg Harbor 02040302 New Jersey A headwater Subbasin along the Atlantic Coast in New Jersey, just north of 

Delaware Bay. This area was selected as representative of low-relief areas 

along the east coast.

Seneca River 03060101 North Carolina, 

South Carolina

Headwaters of the Savannah River. This area was selected because of the large 

impoundment, Hartwell Lake, found at the outlet of the Subbasin.

Pine River 07010105 Minnesota The headwater of the Mississippi River in Minnesota. This Subbasin contains 

a complex network of lakes and wetlands.

South Platte Headwaters 10190001 Colorado This Subbasin contains braided streams and divergences that flow into 

the ground.

Pine Valley 16020302 Utah Part of the Great Basin in Utah. This Subbasin is a closed drainage system 

where many isolated stream networks drain into the ground near the center of 

the Subbasin in a salt flat called the Pine Valley Hardpan.

Willapa Bay 17100106 Washington This Subbasin is typical of the rugged terrain along the west coast.
Testing the Catchment Delineation Methods 21 Figure 15. The location of the six study Subbasins in the continental United States.

80°

50°

40°

30°

120° 100°

17100106Willapa Bay,Washington

16020302Pine Valley,Utah

10190001South Platte Headwaters,Colorado

03060101 Seneca River, North and South Carolina

02040302 Great Egg Harbor,New Jersey

07010105 Pine River,Minnesota

0 400 600 MILES 2000 200 600 KILOMETERS 400
22 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

• Digitally scanned images of the USGS 1:24,000-scale 

topographic maps called Digital Raster Graphics 

(DRGs) (U.S. Geological Survey, 2001a). DRGs were 

used to evaluate the delineations only for site-specific 

investigations where results indicated that detailed 

visual review was warranted. 

• Aerial photographs called Digital Orthophoto 

Quadrangles (DOQ) (U.S. Geological Survey, 2001b) 

were used along with the interpretation of DRGs, 

especially for areas of flat relief with limited contour 

detail. DRGs and DOQs were used where warranted 

to evaluate differences between those areas where the 

largest errors occurred. 

Streamgage Data

The national set of currently operating and discontinued 

USGS streamgages provides the most readily available 

information on reported drainage-area measurements for 

evaluation purposes. Streamgage information is stored in the 

USGS’s National Water Information System (NWIS) 

database and can be accessed through the NWIS Web site at 

http://waterdata.usgs.gov/nwis. Streamgage information in 

NWIS includes latitude and longitude coordinates, along with 

the reported drainage-area measurement for each streamgage. 

The streamgage data were also valuable for purposes of 

comparing methods because they provided a wide range of 

streamgage drainage-area sizes (1.1 to 1,084 mi2) across the 

study Subbasins. 

The drainage-area measurements for the streamgages 

typically were manually computed by trained hydrologists 

using paper topographic maps and a mechanical planimeter. 

Drainage area measurements for some of the historical 

streamgages may be based on computations from USGS 

15-minute 1:62,500-scale maps or other topographic maps. 

Topography and other features on the 15-minute map series 

are generalized and can produce different drainage-area 

measurements than those produced using the larger scale 

1:24,000-scale series maps. Drainage-area measurements 

computed manually using the 1:24,000-scale series maps are 

assumed to be the most accurate. No documentation exists 

within NWIS that describes the source map scale used to 

determine the drainage-area measurement for streamgages. 

A point dataset of the streamgages was created using the 

latitude and longitude coordinates from the NWIS database. 

Each streamgage point location was visually displayed along 

with the NHD flowlines and, through manual verification by 

USGS state offices, was linked to the appropriate location 

along the appropriate NHD flowline. Streamgages that were 

successfully linked with NHD flowlines were selected for 

use in the verification process. Drainage-area boundaries for 

these streamgages, in GIS polygon format, were also obtained 

from USGS Water Science Centers. The number of NWIS 

streamgages obtained for each study Subbasin with drainagearea measurements and boundaries that were selected for 

verification is shown in table 3. NWIS streamgage drainagearea measurements were not available for the Pine Valley 

Subbasin, and streamgage drainage-area boundaries were not 

available for the South Platte Headwaters and the Pine 

Valley Subbasins.

Table 3. Description of National Water Information System streamgages, boundaries, and associated drainage-area measurements 

used for verification datasets.

[NWIS, National Water Information System; GIS, geographic information systems; mi2, square miles; n/a, not available]

Subbasin Hydrologic Unit 

Code and name

Number of selected 

NWIS streamgages 

with drainage-area 

measurements

Number of selected 

streamgages with 

GIS drainage-area 

boundaries

Minimum 

drainage area 

(mi2)

Maximum 

drainage area 

(mi2)

Mean 

drainage area

(mi2)

02040302 Great Egg Harbor 2 2 30.77 57.10 43.90

03060101 Seneca River 4 4 46.76 106.00 72.38

07010105 Pine River 1 2 1.03 269.54 177.19

10190001 South Platte Headwaters 15 0 11.80 1,084.00 286.41

16020302 Pine Valley 0 0 n/a n/a n/a

17100106 Willapa Bay 12 12 3.97 219.00 49.07
Testing the Catchment Delineation Methods 23

Table 4. Summary of Watershed Boundary Dataset Hydrologic Units used for comparative analysis of National Hydrography 

Dataset catchment boundary delineation methods.

[WBD, Watershed Boundary Dataset; mi2, square miles; n/a, not available]

Study Subbasin Hydrologic Unit 

Code and name

Category of WBD 

Hydrologic Units

Number of WBD 

Hydrologic Units

Minimum area 

(mi2)

Maximum area 

(mi2)

Mean area 

(mi2)

02040302 Great Egg Harbor 14 digit 46 4.37 51.34 10.80

03060101 Seneca River 12 digit 33 11.63 57.27 31.15

07010105 Pine River 12 digit 28 6.28 53.98 27.85

10190001 South Platte Headwaters 12 digit 55 0.65 81.80 29.17

16020302 Pine Valley 12 digit 9 10.36 50.48 28.73

17100106 Willapa Bay n/a n/a n/a n/a n/a

The minimum, maximum, and mean drainage-area 

measurements are included in table 3 to show the range and 

variation in streamgage drainage areas used in the study. The 

values shown in table 3 were computed using both published 

streamgage drainage-area measurements and drainage-areas 

measurements calculated from streamgage drainage-area 

boundaries where available. 

Boundaries from the Watershed Boundary 

Dataset

A number of USGS Water Science Centers provided draft 

WBD Subwatershed boundaries for use as verification datasets 

for this study. Many of these Subwatershed boundaries have 

been subsequently incorporated into the WBD. At the time 

of the study (2003), only limited coverage of the WBD was 

available, so the study team used draft WBD boundaries for 

the six study Subbasins. These draft WBD boundaries were 

digitized using manual methods from 1:24,000-scale sources 

and were validated by state water managers and staff familiar 

with the hydrology of the areas. The draft WBD boundaries 

were also validated through visual spot checking against contours depicted on DRGs. Where both datasets were available, 

the streamgage drainage-area boundaries were observed to 

be in good spatial agreement with corresponding draft WBD 

boundaries. For the purposes of this report, the draft WBD 

boundaries are simply referred to as WBD. 

Four of the six study Subbasins were delineated to the 

WBD 12-digit Hydrologic Unit Subwatershed level, which 

generally ranges in size from 20 to 60 mi2. The Great Egg 

Harbor Subbasin was delineated to the 14-digit hydrologic unit 

level, which is typically less than 20 mi2. Currently, the WBD 

does not incorporate boundaries for the 14-digit hydrologic 

unit level. The Willapa Bay Subbasin had no WBD boundaries 

available. A summary of the minimum, maximum, and mean 

WBD area measurements for each study Subbasin is presented 

in table 4. 

Evaluation Metrics

Evaluation metrics addressed two distinct characteristics 

of the catchments: physical-boundary accuracy and drainagearea measurement. Shape analysis techniques were used to 

assess the accuracy of the physical boundary delineations, 

and area-size analysis techniques were used to compare the 

drainage-area measurements. The evaluation metrics used 

in this study were the Coefficient of Areal Correspondence 

(CAC), polygon-area percent error, cumulative drainagearea analysis, and convergence analysis. These metrics and 

associated analyses helped identify errors in ingredient data 

and shortcomings in the methods themselves. Collectively, 

they enabled reasonable comparisons of the accuracy of the 

NHD catchment delineations resulting from each method. 

The evaluation metrics were determined for all methods 

for all study Subbasins except for: (1) metrics requiring 

WBD for the Willapa Subbasin, where WBD was absent; and 

(2) the Outlet Matching Method, which was only determined 

for the Great Egg Harbor Subbasin. Outlet Matching Method 

metrics for other Subbasins are not presented because of poor 

performance in the Great Egg Harbor Subbasin.
24 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Coefficient of Areal Correspondence

The CAC is a metric used to quantify the overlap of 

two areas (Taylor, 1977) and is computed by dividing the 

intersection of two areas by the union of the two areas 

(fig. 16). For catchment boundary delineation comparisons, 

the CAC conveys how well a boundary, based on one of the 

five methods, compares with an independent boundary, such 

as one for a WBD Subwatershed or a streamgage drainage 

area. The CAC quantifies the spatial correspondence between 

two boundaries where a CAC value of 100 indicates a perfect 

spatial correspondence. For the catchment delineation method 

comparisons, these CAC values can be thought of as a score, 

where higher scores indicate better performance, and with 100 

being the highest score. 

In figure 16, two squares measuring 30 units per side—

one with a solid black border and one with a dashed red 

border—intersect. The area of the intersection between the 

squares is shown in orange and measures 600 square units 

(20 units wide by 30 units tall). The area of the union between 

the squares includes all colored areas and measures 

1,200 square units (40 units wide by 30 units tall). Dividing 

the intersection area by the union area and multiplying the 

result by 100 produces a CAC score of 50 indicating that half 

of the squares overlap. A CAC score of 100 would indicate 

that the two squares overlap completely since the intersection 

and the union areas would be equal. Both the WBD boundaries 

and the streamgage drainage-area boundaries were used as 

GIS verification datasets for computing CAC scores.

In the comparative analysis with the WBD data, CAC 

scores were computed using each individual WBD boundary 

polygon and the polygon for the same area delineated using 

each of the five catchment boundary delineation methods. 

To perform the comparison, first the NHD flowline that most 

closely corresponds to the outlet of each WBD boundary was 

identified. Using the NHD flow table, the NHD flowlines 

within the WBD boundary were then selected by navigating 

upstream until another WBD outlet flowline was encountered 

or the headwaters were reached. Next, the catchments 

boundaries for those flowlines were combined to create a 

single boundary corresponding to the actual WBD boundary, 

and a CAC score was computed from the two. CAC scores 

were computed in this manner for all study Subbasins having 

WBD boundaries (the Willapa Subbasin did not have WBD 

boundaries and could not be tested in this manner). Figure 17 

shows the WBD boundaries, the corresponding catchmentbased boundaries produced using the NEM-without-WBD, 

and the CAC scores for the Pine River Subbasin. 

CAC scores were also computed for the streamgage 

drainage-area boundaries using the same process just 

described for the WBD boundaries. CAC scores were 

computed in this manner for all study Subbasins having 

streamgage drainage-area boundaries (the South Platte 

Headwaters and the Pine Valley Subbasins did not have 

streamgage drainage-area boundaries and could not be tested 

in this manner). 

Given that the NEM-with-WBD uses the WBD to 

hydrologically condition the elevation when producing NHD 

catchments, one would assume that the CAC scores calculated 

when comparing NEM-with-WBD based WBD boundaries 

with the actual WBD would most often be 100. However, this 

was often not the case. When comparing the NEM-with-WBD 

and WBD boundaries, CAC scores of less than 100 are usually 

attributable to the WBD boundary outlet not matching the 

location of the outlet (downstream end) of the corresponding 

NHD flowline. This is most often the result of differences 

between the 1:100,000-scale NHD flowlines and how the 

WBD boundaries were delineated using 1:24,000-scale 

hydrography on the topographic maps, where either the same 

confluences are in slightly different locations or the WBD 

outlet is located at a 1:24,000-scale stream confluence not 

included in the 1:100,000-scale NHD. An example of a 

WBD/NHD-flowline outlet mismatch that results in a NEMwith-WBD CAC score of 88.6 is shown in figure 18. When 

these WBD/NHD-flowline outlet mismatches occurred, all of 

the methods were affected.

CAC scores for all methods are also affected by NHD 

isolated networks. As shown in figure 17, isolated networks 

are not included when aggregating NHD catchments to 

correspond to the actual WBD boundary and, as a result, will 

lower the CAC scores. 
Testing the Catchment Delineation Methods 25

Figure 16. Schematic design showing how Coefficient of Areal Correspondence (CAC) score 

is computed.

10

30

30

20

20 10

600

1,200

x 100 = 50 (CAC)

EXPLANATION

Area of 900

Area of 900

Intersection area of 600

Union area of 1,200

40

30

30
26 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

94°30'

94°

46°40'

46°50'

NHD flowline

NHD flowline matched to WBD boundary

NEM-without-WBD Coefficient of 

Areal Correspondence (CAC) scores

92.0

EXPLANATION

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

NEM-without-WBD boundaries

NHD non-contributing areas 

(isolated networks)

Base from 1:100,000-scale National Hydrography Dataset, 2003

77.4

88.8

74.1

92.4

88.0

91.9

84.7

92.0

69.4 75.1

74.5

78.5

85.7

73.9

81.8

83.9

81.3

81.3

92.2

90.4

88.9

66.5

87.7

91.0

82.7

93.8

69.2

68.2

WBD Subwatersheds

Pine River Subbasin

Figure 17. Boundaries from the Watershed Boundary Dataset (WBD) Subwatersheds and the corresponding boundaries from 

the New England Method without WBD (NEM-without-WBD), National Hydrography Dataset (NHD) flowlines including those most 

closely corresponding to the WBD outlets, and Coefficient of Areal Correspondence scores, Pine River Subbasin, MN. (The location 

of this Subbasin is shown in figure 15.)
Testing the Catchment Delineation Methods 27

Figure 18. Schematic design showing a mismatch between 

a Watershed Boundary Dataset (WBD) Subwatershed 

boundary and the corresponding New England Method with 

WBD (NEM-with-WBD) boundary caused by the WBD outlet 

not coinciding with the downstream end of the corresponding 

NHD flowline.

Normalizing Coefficient of Areal Correspondence

The WBD/NHD-flowline outlet mismatches and NHD 

isolated networks just described can limit the effectiveness 

of the CAC as a descriptive tool to assess the methods. 

Normalizing the CAC scores by removing these known 

sources of error would bring more focus on the differences 

between the methods, rather than the errors associated with 

these known problems. The NEM-with-WBD was expected to 

be the most accurate method when compared with the WBD, 

since it benefited from hydrologically conditioning the DEM 

with both the NHD network and the WBD. As a result, the 

effect of WBD/NHD-flowline outlet mismatches and NHD 

isolated networks on CAC scores can be removed by using the 

NEM-with-WBD values to normalize the CAC scores of all 

other delineation methods, except the Outlet Matching Method 

(because of the prevalent outlet mismatching that occurred 

between the EDNA catchments and the NHD flowlines). The 

normalization formula shown below and in figure 19 is applied 

to adjust the CAC scores. 

Normalized CAC = (Delineation Method CAC/

NEM-with-WBD CAC) * 100 (1)

The WBD boundary shown in figure 19 has a WBD/

NHD-flowline outlet mismatch. The NEM-with-WBD 

catchment-based boundary follows the WBD boundary, except 

at the mismatched flowline outlet, resulting in a CAC score of 

83.2 for the NEM-with-WBD boundary. CAC scores for each 

catchment delineation method are normalized such that NEMwith-WBD CAC score reflects a 100 percent spatial correspondence. The graph in figure 20 shows how the CAC scores 

for the NEM-with-WBD were adjusted by normalization in 

the Great Egg Harbor Subbasin. Each WBD unit is identified 

on the x-axis by the ComID of the NHD flowline that corresponds to the WBD outlet.

Normalizing CAC scores in this manner highlighted a 

potential issue when analyzing the Raster Seeding Method as 

shown in figure 19. The catchment-based boundaries from the 

Raster Seeding Method and NEM-without-WBD are identical, 

except for the area associated with the NHD-flowline outlet. 

At the NHD-flowline outlet, the two NEMs share the same 

boundary. For the Raster Seeding Method, the boundary delineation associated with the flowline outlet is smaller than the 

areas delineated using the NEM methods because of the affect 

of DEM flow-path displacement. In some cases, such as the 

example shown in figure 19, the normalized CAC score for the 

Raster Seeding Method (103.8) is erroneously higher than the 

NEM-with-WBD score (100). The highest a CAC score can 

be is 100, therefore, any CAC scores for the Raster Seeding 

Method greater than 100 were reviewed to determine what led 

to such a high score. These high scores happen in situations 

where there is both a WBD/NHD-flowline outlet mismatch 

and a Raster Seeding Method error associated with DEM 

flow-path displacement along the outlet flowline. This situation occurs because the Raster Seeding boundary runs parallel 

NHD flowline 

WBD Subwatershed

NEM-with-WBD boundary

EXPLANATION

CAC = 88.6

CAC = 88.6 NEM-with-WBD Coefficient 

of Areal Correspondence (CAC) score
28 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Figure 19. Schematic design showing a Watershed Boundary Dataset Subwatershed and corresponding boundaries from 

the New England Methods and the Raster Seeding Method, with Coefficient of Areal Correspondence (CAC) scores before and 

after normalization. The formula used to normalize the CAC scores is also shown.

Watershed Boundary Dataset (WBD) Subwatershed

Raster Seeding Method boundary 

CAC = 86.4 Normalized CAC = 103.8

New England Method without WBD boundary (NEM-without-WBD)

CAC = 76.6 Normalized CAC = 92.1 

New England Method with WBD boundary (NEM-with-WBD) 

CAC = 83.2 Normalized CAC = 100.0 

EXPLANATION

Normalized CAC = 

Delineation Method

CAC 

NEM-with-WBD

CAC

x 100

Delineation Method, Coefficient of Areal 

Correspondence (CAC), and Normalized CAC

Raster Seeding Method boundary

runs parallel to NHD here

WBD/National

Hydrography

Dataset (NHD) flowline

outlet mismatch
Testing the Catchment Delineation Methods 29

to the outlet NHD flowline for some distance causing this 

Raster Seeding area outside the WBD boundary to be smaller 

(in error) than the NEM methods. Less obvious to find, but 

still prevalent, many Raster Seeding Method normalized CAC 

scores less than 100 can be artificially high where the combination of WBD/NHD-flowline outlet mismatch and DEM 

flow-path displacement occur at the outlet NHD flowline. 

Outlet mismatch errors also occur for the streamgage 

boundaries because a streamgage can be located on any point 

along an NHD flowline. The CAC scores for the streamgage 

drainage-area boundary analysis were normalized in the same 

manner, since both the WBD and most streamgage drainagearea boundaries were manually reviewed against, or manually 

delineated from, 1:24,000-scale sources. As previously noted, 

the streamgage boundaries were also observed to be in good 

spatial agreement with corresponding WBD boundaries. The 

CAC scores for the NEM-with-WBD were used to normalize 

the CAC scores for the other methods (except the Outlet 

Matching Method) in the comparison of the streamgage 

drainage-area boundaries. This CAC normalization was 

performed for all study Subbasins having WBD boundaries 

(the Willapa Bay Subbasin did not). 

In the CAC evaluation, special attention was paid to 

those Subwatersheds that had a CAC (NEM-with-WBD) 

or normalized CAC (NEM-without-WBD and the Raster 

Seeding Method) score less than 80 to determine the cause of 

the specific error. Differences in delineations were examined 

closely using the information from the DRGs and DOQs to 

determine the correct delineation and to consider the effects 

on applications of the delineated boundaries. Low normalized 

CAC scores (less than 80) for the delineations from the 

Thiessen Polygon Method were not evaluated in detail 

because the Thiessen Polygon Method does not incorporate 

topographic information. 

10

20

30

40

50

60

70

80

90

100

NATIONAL HYDROGRAPHY DATASET FLOWLINE COMMON IDENTIFIERS (ComIDs)

COEFFICIENT OF AREAL CORRESPONDENCE (CAC) SCORE

Non-normalized CAC

Normalized CAC

0

943357194340379434039943360394340459434057943407794341719434095943418394341119433653943414394363339434195943406394341919433671943661794337739436361943677194367839436775943636794366299436633943680194363939436799943640394366459436667943686594368579436651943686194364139436687943643394368779436435943643794368919436451

Figure 20. The non-normalized and normalized Coefficient of Areal Correspondence (CAC) scores for the New England Method 

without the Watershed Boundary Dataset (NEM-without-WBD) in relation to the corresponding boundaries from the Watershed 

Boundary Dataset labeled by National Hydrography Dataset flowline outlet ComID in the Great Egg Harbor Subbasin, NJ.
30 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Polygon-Area Percent Error

Polygon-area percent errors were computed between the 

area in the WBD Subwatershed polygons and the area of the 

corresponding catchment-based polygons produced by each 

method that was used in the CAC analysis. Polygon-area 

percent errors, as defined in the following equation, further 

quantify the magnitude of the delineation errors observed in 

the CAC analysis:

Polygon-Area Percent Error = [(|Delineation Method 

Area – WBD Area|)/WBD Area] × 100 (2)

Polygon-area percent errors were computed for all study 

Subbasins having WBD boundaries (the Willapa Bay Subbasin 

did not have WBD boundaries to compute this metric). The 

polygon-area percent errors were also normalized using the 

NEM-with-WBD polygon-area percent errors to remove the 

effects of mismatches between the WBD boundary outlets and 

NHD-flowline outlets. This metric became even more relevant 

when applied to the cumulative drainage areas required for 

streamflow estimates. 

Cumulative Drainage-Area Analysis

The WBD cumulative drainage-area measurements were 

compared with the catchment-based cumulative drainage-area 

measurements from each delineation method. This analysis 

was applied to all study Subbasins having WBD boundaries 

(the Willapa Bay Subbasin did not have WBD boundaries).

To determine the WBD cumulative drainage-area 

measurements, the outlet flowlines identified for each WBD 

Subwatershed in the CAC analysis were used with the NHD 

flow table to determine all flowlines upstream of each WBD 

Subwatershed. Using the Subwatershed outlet flowlines and 

upstream flowlines, the upstream Subwatersheds for each 

Subwatershed can be determined and used to compute the 

WBD cumulative drainage-area measurement. For each of the 

catchment delineation methods, the flowlines for each WBD 

cumulative drainage area were linked to the catchments generated by each method to compute their respective cumulative 

drainage-area measurements. 

For this analysis, X–Y graphs of WBD cumulative 

drainage-area measurements (x-axis) in relation to the cumulative drainage-area measurements for the delineation methods 

(y-axis) were produced. The closer the points are to the one-toone line beginning at the origin, the closer the agreement. For 

example, the graph for the Great Egg Harbor Subbasin cumulative drainage-area measurements in figure 21 shows that 

the results of the two New England Methods and the Raster 

Seeding Method plot close to the one-to-one line, whereas the 

results of the Outlet Matching and Thiessen Polygon Methods 

plot fairly close to the one-to-one line, but tend to underestimate the cumulative drainage-area measurements. 

The cumulative drainage-area analysis was also employed 

using drainage-area measurements from the streamgage 

verification data, which are cumulative by definition in the 

headwater Subbasins. The analysis required the accumulation 

of the catchment areas generated by each method for the NHD 

outlet flowlines on which the streamgages were located. For 

the Pine Valley Subbasin, streamgage data were not available. 

For the South Platte Headwaters Subbasin, streamgage 

drainage-area measurements were available from NWIS, 

but streamgage boundaries were not available. For the other 

study Subbasins, drainage-area data were available from both 

sources, and data from both were used in the analyses. 

Better agreement between the streamgage verification 

drainage-area measurements and the drainage-area 

measurements from the catchment delineation methods 

is obtained when a streamgage is located at or near the 

corresponding NHD-flowline outlet. This agreement is 

true because, at the outlet of the flowline, the boundary 

of the streamgage drainage-area is a close match to the 

corresponding catchment-based boundary for each method. 

Greater differences in drainage areas occur the farther 

upstream a streamgage is located from a corresponding 

NHD-flowline outlet. This situation is similar to the WBD/

NHD-flowline outlet mismatching previously described.

Drainage-area differences attributed to the streamgage 

location in relation to the corresponding NHD-flowline outlet 

occur only within the catchment where the streamgage is 

located. All upstream catchments included in the drainage area 

are unaffected by the location of the streamgage relative to 

the NHD-flowline outlet. For streamgages with large drainage areas, the percentage error contributed by disagreements 

between the streamgage location and the flowline outlet is 

expected to be less than 1 percent, because the outlet catchment area is relatively small compared with the upstream 

accumulated catchment-based drainage area. Conversely, for 

streamgages with small drainage areas, the errors contributed 

by disagreements between the streamgage location and the 

flowline outlet are expected to be larger because the outlet 

catchment area is larger relative to the upstream accumulated 

catchment-based drainage area. 

Since the cumulative drainage-area measurements are the 

direct input into streamflow and velocity estimates, they were 

not normalized for either the cumulative drainage-area analysis or the convergence analysis; thus, all errors in the measurements would be present in these final metrics.
Testing the Catchment Delineation Methods 31

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300 350

WATERSHED BOUNDARY DATASET (WBD) VERIFICATION CUMULATIVE DRAINAGE AREA, IN SQUARE MILES

DELINEATION METHOD CUMULATIVE DRAINAGE AREA, IN SQUARE MILES

New England Method without WBD

New England Method with WBD

Raster Seeding Method

Outlet Matching Method

Thiessen Polygon Method

Figure 21. The Watershed Boundary Dataset cumulative drainage-area measurements (verification) in relation to the 

cumulative drainage-area measurements of the methods tested, Great Egg Harbor Subbasin, NJ.

Convergence Analysis

Convergence analysis was used to better discern 

the results of the cumulative drainage-area analysis by 

determining a drainage-area percent error. Of particular 

interest was whether the errors for each method tended to 

decrease as the point of accumulation moved downstream. 

Determining a percentage error for comparison of each 

cumulative drainage area and graphing the results were used 

in the convergence analysis. Graphs of the data tend to show 

a decrease in drainage-area errors as cumulative drainage-area 

measurements increase. The errors tend to converge closer to 

the 0 percent error line as the drainage areas increase; hence, 

the term “convergence analysis” was developed for this study.

The drainage-area errors are expressed as percent error 

in the following equation that refines the polygon-area percent 

error by using areas that are cumulative drainage-areas.

Percent error = [(|MV – V|)/V] × 100 (3) 

where

V = Cumulative WBD drainage-area 

measurement, and

MV = Cumulative delineation-area method value.

An example of the graph used in the convergence 

analysis for the Seneca River Subbasin is shown in figure 22. 

Graphs of convergence analysis are shown in the appendix for 

each study Subbasin that has WBD boundaries. (The Willapa 

Bay Subbasin did not have WBD boundaries.)

To assist further in the evaluation of the convergence 

analysis, cumulative drainage-area measurement errors for 

each study Subbasin are expressed as a mean error. The 

mean drainage-area measurement errors were computed by 

classifying the WBD cumulative drainage-area measurements 

into the following drainage-area size categories, which for 

convenience are based on the WBD Subbasin, Watershed, and 

Subwatershed size ranges:

1. Less than 20 mi2

2. 20 to 60 mi2

3. Greater than 60 to 390 mi2

4. Greater than 390 mi2

Classifying the results into size categories helped to identify 

the strengths or weaknesses of a particular method for producing drainage-area measurements. 
32 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Evaluation of Catchment Delineation 

Methods

Results from all the analyses for all the study Subbasins 

indicate that the two New England Methods (with and without 

WBD) produced the most accurate catchment boundaries. 

Detailed results for each of the study Subbasins are presented 

in the appendix of this report. The NEM-with-WBD produced 

the most accurate catchment boundaries overall because this 

method incorporates the WBD in the process. For all study 

Subbasins, the mean normalized CAC scores from the WBD 

comparative analysis for each method are listed in table 5. 

Normalized CAC scores for the NEM-with-WBD indicate 

perfect spatial correspondence because this method was the 

basis for normalization. The overall average normalized CAC 

score using the NEM-without-WBD is 92.4 and using the 

Raster Seeding Method is 89.9. The Thiessen Polygon Method 

produced the least accurate spatial correspondence with an 

average normalized CAC score of 74.5. 

The Outlet Matching method was found to have 

numerous limitations in its use as a catchment delineation 

method. The fundamental differences between the NHD 

flowline network and the EDNA synthetic stream network 

used to generate EDNA catchments made it difficult to 

associate the flowlines and catchments using the Outlet 

Matching Method. NHD flowlines begin and end on the basis 

of cartographic collection standards that include minimum 

stream length, confluences, changes in feature types and 

characteristics. EDNA synthetic streams begin and end at 

confluences and are generated using a DEM-derived flow 

accumulation grid and a constant drainage-area threshold of 

1.74 mi2, which result in catchments that often do not align 

favorably with NHD flowlines.

Horizontal displacement between the synthetic streams 

derived from the 30-m EDNA dataset and the NHD flowlines 

can also make the matching of the EDNA catchments to the 

NHD flowlines difficult. In areas of flat-relief, the horizontal 

displacement can be so great that the Outlet Matching Method 

process fails to identify a proper assignment of EDNA 

catchments to the NHD flowlines. In many cases, no match 

of the EDNA catchments to the flowlines could be made. For 

the Great Egg Harbor Subbasin, in 16 percent of the WBD 

comparisons, EDNA catchments could not be outlet-matched 

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 200 400 600 800 1,000 1,200

WATERSHED BOUNDARY DATASET (WBD) CUMULATIVE

DRAINAGE AREA, IN SQUARE MILES

PERCENT ERROR

New England Method without WBD

New England Method with WBD

Raster Seeding Method

Outlet Matching Method

Thiessen Polygon Method

Figure 22. Percent error of convergence for drainage-area measurements for all methods tested in 

relation to the Watershed Boundary Dataset verification cumulative drainage-area measurements, in the 

Seneca River Subbasin, SC. 
Evaluation of Catchment Delineation Methods 33

to the corresponding NHD flowlines assigned to the WBD 

Subwatersheds. Similarly, 11 percent of the EDNA catchments 

in the Pine River Subbasin, 7 percent in the South Platte 

Subbasin, and 3 percent in the Seneca Subbasin could not be 

outlet-matched to NHD flowlines. Appendix figure 1–6 shows 

a major error in the Outlet Matching Method within the 

Great Egg Harbor Subbasin, where an outlet-matched 

boundary for a streamgage erroneously composes of two 

separate polygons. 

These significant difficulties encountered in achieving 

even an approximate coupling of the two datasets through 

database relations make the Outlet Matching Method 

problematic for producing catchments for NHD flowlines. 

Results for the Outlet Matching Method are provided only 

for the Great Egg Harbor Subbasin in the appendix of this 

report because it was representative of the poor performance 

of the Outlet Matching Method. Because of these identified 

problems, Outlet Matching Method analysis results are not 

described further in this report.

The Raster Seeding Method appears to have performed 

slightly more accurately than the NEM-without-WBD for the 

South Platte Headwaters and the Pine Valley Subbasins 

Table 5. Mean normalized Coefficient of Areal Correspondence scores for the four methods used in the Watershed Boundary 

Dataset comparison analysis, by study Subbasin.

[CAC, Coefficient of Areal Correspondence; WBD, Watershed Boundary Dataset; NEM, New England Method]

Catchment delineation 

method

Mean normalized CACs from the WBD comparison analysis for study Subbasins

Great Egg Harbor 

02040302

Seneca River 

Basin 

03060101

Pine River 

Basin 

07010105

South Platte 

Headwaters 

10190001

Pine Valley 

16020302

All study Subbasins 

(except Willapa Bay)

NEM-with-WBD 100.0 100.0 100.0 100.0 100.0 100.0

NEM-without-WBD 87.5 97.4 89.1 94.7 95.9 92.4

Raster Seeding Method 85.8 91.7 81.7 95.6 96.6 89.9

Thiessen Polygon Method 70.9 85.1 66.3 74.7 77.7 74.5

(table 5), but further analysis of the data shows that the error 

for the Raster Seeding Method, resulting from DEM flow-path 

displacement at the outlet flowline and WBD/NHD-flowline 

outlet mismatching, artificially increased the CAC score. This 

is described in detail for the individual study Subbasins in 

the appendix. 

The mean normalized polygon-area percent errors are 

summarized in table 6. Because the NEM-with-WBD was 

used to normalize the results for the other methods, the 

NEM-with-WBD shows 0 percent error for all Subbasins 

tested. The NEM-without-WBD was more accurate than the 

Raster Seeding and Thiessen Polygon Methods for all study 

Subbasins. The differences in normalized CAC scores between 

the NEM-without-WBD and the Raster Seeding Method 

shown in table 5 are further emphasized by the normalized 

polygon-area percent errors shown in table 6. In the South 

Platte Headwaters and Pine Valley Subbasins where the 

Raster Seeding Method appears to have been more accurate 

according to the normalized CAC score results (table 5), the 

normalized polygon-area percent errors for the Raster Seeding 

Method (table 6) are greater than that of NEM-without-WBD 

for the two Subbasins. 

Table 6. Mean normalized polygon-area percent errors for catchment delineation methods used in the Watershed Boundary Dataset 

comparison analysis.

[All values are in percent. WBD, Watershed Boundary Dataset; NEM, New England Method]

Catchment delineation 

method

Mean normalized polygon-area percent errors for the WBD comparison analysis for study Subbasins

Great Egg Harbor 

02040302

Seneca River 

Basin 

03060101

Pine River 

Basin 

07010105

South Platte 

Headwaters 

10190001

Pine Valley 

16020302

All study Subbasins 

(except Willapa Bay)

NEM-with-WBD 0.00 0.00 0.00 0.00 0.00 0.00

NEM-without-WBD 6.89 0.56 5.70 2.74 1.11 3.83

Raster Seeding Method 9.00 5.75 15.44 3.70 2.61 7.42

Thiessen Polygon Method 17.17 5.47 21.95 12.87 10.04 13.93
34 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Table 7. Mean cumulative drainage-area errors, by drainage-area size category, for catchment delineation methods for all study 

Subbasins, except Willapa Bay.

[mi2, square miles; NEM, New England Method; WBD, Watershed Boundary Dataset; All size categories were computed as a weighted average using the 

number of observations as a weights]

Method

Mean cumulative drainage area error, in percent

Drainage-area size category

Less than 20 mi2 20–60 mi2 Greater than 60–390 mi2 Greater than 390 mi2 All drainage areas

NEM-with-WBD 1.88 2.76 0.89 0.64 1.65

NEM-without-WBD 6.01 3.98 1.28 0.56 3.21

Raster Seeding Method 6.39 7.42 2.05 1.48 4.65

Thiessen Polygon Method 16.56 9.31 4.94 1.46 8.85

The Raster Seeding Method rated lower than the two 

New England Methods in the CAC and polygon-area percent 

error analyses because of the errors introduced by DEM flowpath displacement. DEM flow-path displacement errors were 

consistently observed in the Raster Seeding Method, causing 

catchment boundary delineations to erroneously parallel 

the NHD flowlines. As presented in the study Subbasin 

analyses in the appendix, the Raster Seeding Method errors 

were sometimes very large, especially in areas of flat relief 

or for artificial path flowlines within water bodies. The Pine 

River Subbasin has extreme examples of DEM flow-path 

displacement related errors within waterbodies and flat relief.

The Thiessen Polygon Method produced the least 

accurate catchment boundary delineations using the CAC 

analysis. This result was expected because the method does 

not take into account any topographic information. The 

Thiessen Polygon Method polygon-area percent error analysis 

confirmed these findings.

In the comparison of catchment-based delineations from 

the different methods with the streamgage drainage-area 

boundaries, the CAC scores produced are similar to those 

from the WBD comparison. Again, the New England Method 

without WBD was slightly more accurate than the Raster 

Seeding Method, and the Thiessen Polygon Method had the 

least accurate catchment boundaries. 

Values obtained from the cumulative drainage-area 

analysis indicate, for each method, that drainage-area 

estimates increase in relative accuracy as the drainage-area 

size increases. The mean cumulative drainage-area errors for 

each method are listed in table 7. Those results are weighted 

averages, based on the number of observations from five of 

the six study Subbasins (except Willapa Bay, because this 

Subbasin did not have WBD data to compare with). 

Drainage-area percent errors for the NEM-with-WBD 

are attributed to WBD/NHD-flowline outlet mismatching and 

NHD isolated networks. These errors were also present for 

the other methods. The second most accurate method, which 

is based on the mean cumulative drainage-area percent error, 

was the NEM-without-WBD. The NEM-without-WBD was 

more accurate than the Raster Seeding and Thiessen Polygon 

Methods in all drainage-area size categories (table 7). 

The Thiessen Polygon Method provided reasonable 

drainage-area estimates for the larger size drainage areas, 

but was progressively less accurate as the drainage-area size 

decreased. The mean cumulative drainage-area error for the 

Thiessen Polygon Method is 16.56 percent for drainage areas 

less than 20 mi2; for the Raster Seeding Method, 6.39 percent; 

for the NEM-without-WBD, 6.01 percent; and for the NEMwith-WBD, 1.88 percent. 

Performance of the methods did not appear to vary across 

the landscape and hydrologic settings of the study Subbasins. 

For all study Subbasins, the walling of the WBD in the DEM 

conditioning process greatly enhanced the accuracy of the 

delineations. Without the use of walls from the WBD, the 

DEMs were generally less accurate, especially for areas of flat 

relief. In certain cases, a proper comparison with the verification data could not be made because of the limited contour 

detail of the DRGs in flat relief settings. Also, because the 

WBD boundaries were in draft stage, occasional delineations 

of the WBD were observed to provide less accurate boundaries compared with the NEM-without-WBD and the Raster 

Seeding Method. 

The NEM-without-WBD and the Raster Seeding 

Method produced similar results, but the Raster Seeding 

Method showed significant problems in flat-relief settings, 

as observed in the Pine River Subbasin. Consistently across 

study Subbasins, differences between the Raster Seeding 

Method and the NEM-without-WBD were primarily due to the 

horizontal displacement between the DEM flow-path and the 

NHD flowlines associated with the Raster Seeding Method. 

The relative differences in accuracy between the different 

catchment delineation methods decreases (they converge) 

as the drainage-area size increases (table 7). Figure 22 

and appendix figures 1–3, 1–12, 1–20, and 1–26 support 
Summary 35

this observation as well. This convergence implies that the 

accuracy of the catchment delineation methods is most 

important in smaller drainage areas. Collectively, these results 

show that the NEM-with-WBD and NEM-without-WBD are 

the most accurate for smaller drainage areas. This finding is 

important because most of the flowlines in the United States 

have drainage areas less than 20 mi2 (U.S. Environmental 

Protection Agency, 2006). The results of convergence 

analyses imply that the NEM methods will not improve the 

flow estimates for large drainage areas, but these methods 

will improve flow estimates for flowlines with smaller 

drainage areas.

Summary

The need for catchment delineations originated from the 

common goal of the U.S. Environmental Protection Agency 

and U.S. Geological Survey (USGS) to estimate streamflow and velocity for all flowlines (stream segments) of the 

medium-resolution (1:100,000-scale) National Hydrography 

Dataset (NHD) in the conterminous United States and Hawaii. 

Accurate NHD catchment delineations are needed because 

streamflow and velocity estimates are based on drainage areas 

and characteristics of the landscape within the flowline catchment areas. This study was conducted to evaluate the accuracy 

of various methods for determining NHD catchments. 

Five catchment delineation methods were evaluated,

four of which used topographic information. These four were 

(1) the Raster Seeding Method; two variants of a method used 

in a USGS New England study, (2) one using drainage divides 

from the Watershed Boundary Dataset (WBD) and (3) the 

other without, termed the “New England Methods;” and 

(4) the Outlet Matching Method. For each of these topographic delineation methods, the source of elevation data was 

the 30-m resolution National Elevation Dataset (NED), since 

this was the highest resolution available for the conterminous 

United States and Hawaii. (5) The fifth method evaluated, the 

Thiessen Polygon Method, uses distance to the nearest NHD 

flowlines alone to determine a catchment boundary.

The New England Methods and the Raster Seeding 

Method applied the same GIS computer algorithm to determine catchments using the NHD flowlines and a digital 

elevation model (DEM)-derived flow direction grid. The input 

flow direction grid, however, differed between these methods 

in that the New England Methods modified the source DEM 

data, and the Raster Seeding Method did not. 

The New England Methods modified the DEM data to 

ensure that drainage flow paths represented in the flow direction grid matched the drainage network of the NHD. For the 

New England Method that incorporated the WBD, the DEM 

was further modified to ensure that the WBD drainage divides 

also were represented in the DEM. 

The Outlet Matching Method attempted to relate existing 

catchments from the Elevation Derivatives for National 

Applications (EDNA) database to the NHD flowlines. The 

EDNA catchments, which were based on unmodified DEM 

flow paths, represented the areas draining to each EDNA 

synthetic stream. 

The methods were applied to six study areas within 

the conterminous United States. These study areas, called 

“Subbasins,” are designated with 8-digit Hydrologic Unit 

Codes, as defined by the WBD. The six Subbasins chosen 

for this study represent different surface-water morphologies 

found within the United States. The study Subbasins and their 

locations are: Great Egg Harbor, New Jersey; Seneca River, 

North Carolina and South Carolina; Pine River, Minnesota; the 

South Platte Headwaters, Colorado; Pine Valley, Utah; and 

Willapa Bay, Washington. 

The study used verification datasets, including USGS 

streamgages and the WBD, to compare the results of the 

methods. Evaluation metrics included drainage-area measurement and shape analysis techniques, including the Coefficient 

of Areal Correspondence (CAC), polygon-area percent error, 

cumulative drainage-area analysis, and convergence analysis. 

The results of this study show that the New England 

Methods provided the most accurate results overall, especially 

the method that incorporated the WBD drainage divides in 

the DEM. Performance for all methods did not appear to vary 

across the various Subbasins. In general, for topographicbased methods using 30-m NED data, greater accuracy was 

attained in areas of high relief contrasted with flatter areas. 

The accuracy for flatter areas was improved by the integration 

of the WBD into the New England Method.

The Outlet Matching Method was determined to be the 

least effective method because of the fundamental differences 

between the NHD streams and the EDNA synthetic stream 

network. These differences led to the inability to match many 

EDNA catchments to NHD flowlines. Because of this, the 

Outlet Matching Method was deemed unsuitable for determining catchments for the NHD flowlines. 

The Thiessen Polygon Method also was problematic 

because it did not include topographic information in the 

delineation of catchments. The Thiessen Polygon Method did 

not yield accurate drainage area measurements for flowlines 

with relatively small drainage areas. This deficiency is especially important because most of the NHD flowlines have a 

cumulative drainage area of less than 20 square miles.

On the basis of summary statistics of the various evaluation metrics, the Raster Seeding Method results were slightly 

less accurate than the New England Method without WBD. A 

detailed inspection of the larger boundary differences between 

the verification data and the Raster Seeding Method revealed 

problems that were caused by the horizontal displacement 

of the DEM flow paths and the NHD streams. These boundary errors in the Raster Seeding Method caused erroneous 

parallel-to-stream delineations that were sometimes extensive, 

particularly in areas of low relief and within waterbodies. 

Catchments now have been produced nationally using 

this process, integrating the NHD with the NED and WBD. 

These catchments and the related suite of geospatial datasets 

have become known as the “NHDPlus” and currently are 

being used in a wide variety of hydrologic applications.
36 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

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Glossary 37

Glossary

Digital elevation model (DEM) Digital 

raster representations of terrain elevations 

for ground positions at regularly spaced 

horizontal intervals.

Digital Line Graphic (DLG) Digital vector 

representations of cartographic information derived from USGS maps and related 

sources.

Digital Orthophoto Quadrangle (DOQ)

A computer-generated image of an aerial 

photograph in which the image displacement 

caused by terrain relief and camera tilt has 

been removed.

Digital Raster Graphic (DRG) A georeferenced digital image resulting from scanning 

a paper USGS topographic map for use on a 

computer.

Drainage area An area that defines the 

geographic extent of the land surface that 

drains to a specific location. 

Drainage-area boundary The polygon that 

defines the perimeter of a drainage area. 

Drainage-area divide The boundary line 

between two different drainage areas along a 

topographic ridge.

Drainage-area measurement The number 

that defines a drainage area in terms of square 

miles or square kilometers. 

E

Elevation Derivatives for National Applications (EDNA) A set of geospatial layers 

derived from the National Elevation Dataset.

F

Flowline A mapped stream segment or 

a path through a waterbody in the surfacewater network of the National Hydrography 

Dataset. The basic unit of the NHD linear 

surface-water network.

Flow table (also NHD flow table) A database table that contains the interconnections 

between the NHD flowlines.

A

ArcHydro Tools A set of public domain 

utilities developed jointly by the Center for 

Research in Water Resources (http://www.

crwr.utexas.edu) of the University of Texas 

at Austin, and the Environmental Systems 

Research Institute, Inc. These tools support 

terrain processing, watershed delineation and 

attribute management. 

ArcInfo Geographic information systems 

(GIS) software developed by Environmental 

Systems Research Institute.

Arc Macro Language (AML) A computer 

program scripting language used by ArcInfo.

Artificial path A National Hydrography 

Dataset (NHD) flowline feature type that 

represents a flow-path through a waterbody in 

the surface water network of the NHD.

B

Basin The third largest category (level 3) of 

Hydrologic Units defined within the Watershed Boundary Dataset (WBD). See table 1.

C

Catchment The incremental drainage area 

for a linear hydrologic feature found in the 

National Hydrography Dataset (NHD).

Coefficient of Areal Correspondence 

(CAC) A simple measure of the extent 

to which two polygons correspond to one 

another.

Cumulative drainage area The catchment 

area for a specific flowline combined with the 

catchment areas for all upstream flowlines. 

D

DEM flow-path displacement The horizontal positional offset between a mapped stream 

in the NHD and that of a synthetic stream 

derived from a digital elevation model.

DEM surface reconditioning See stream 

burning and walling.
38 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

G

Geographic Names Information Systems 

(GNIS) A database that contains name 

and location information about more than 

two million physical and cultural features 

located throughout the United States and its 

territories.

H

Hydrologic Unit The Hydrologic Unit 

system is a standardized watershed 

classification system developed by USGS 

in the mid 1970s. Hydrologic units are area 

boundaries organized in a nested hierarchy 

by size. They range in size from Region, 

Subregion, Basin, Subbasin, Watershed, 

Subwatershed. See table 1. 

Hydrologic Unit Code (HUC) Codes assigned 

to a series of nested hydrologic divisions of 

the landscape. See table 1.

I

Incremental drainage area For a specific 

hydrologic feature, such as a stream 

segment, it defines the local area that drains 

directly into that feature. Synonymous with 

catchment.

L

Light Detection and Ranging (LIDAR) An 

optical remote sensing technology that measures properties of scattered light to find range 

and (or) other information of a distant target.

N

National Elevation Dataset (NED) A seamless elevation coverage of the conterminous 

United States, Hawaii, Alaska, and the island 

territories.

National Hydrogaphy Dataset (NHD)

A comprehensive set of digital spatial data 

representing the surface water of the United 

States using common features such as lakes, 

ponds, streams, rivers, canals, and oceans.

National Water Information System 

(NWIS) A principal repository of national 

water resources data.

NHD flow table (also Flow table) A database table that contains the interconnections 

between the NHD flowlines.

NHDPlus An integrated suite of applicationready geospatial datasets that incorporate 

many of the best features of the National 

Hydrography Dataset (NHD), the National 

Elevation Dataset (NED), the National Land 

Cover Dataset (NLCD), and the Watershed 

Boundary Dataset (WBD).

NHD Reach (also Reach) A uniquely 

identified linear feature that consists of one or 

more flowlines.

O

Outlet The most downstream location of a 

surface-water feature, such as a flowline or 

catchment.

P

Pfafstetter code A hierarchical watershed 

identifier based upon topology of the land 

surface assigned by a methodology developed 

by Otto Pfafstetter in 1989.

R

Raster A digital computer format for 

representing an image or mapped data 

information. The structure consists of data 

stored in a rectangular grid array of pixels. 

Synonymous with grid.

Reach (also NHD Reach) A uniquely 

identified linear feature that consists of one or 

more flowlines.

Reach code A unique, permanent identifier 

in the National Hydrography Dataset.

Region The largest category (level 1) 

of Hydrologic Units defined within the 

Watershed Boundary Dataset (WBD). 

See table 1.

S

Stream burning Using a mapped stream 

network to trench a DEM to improve how 

accurately the DEM flow paths match the 

streams, to ensure DEM-derived catchment 

boundaries fit the stream network.

Streamflow The volume of water flowing 

past a fixed point in a fixed unit of time.

Stream segment (also see flowline) Part of 

a stream, often extending between tributary 

confluences.
Glossary 39

Subbasin The fourth largest (level 4) 

category of Hydrologic Units defined within 

the Watershed Boundary Dataset (WBD). 

See table 1.

Subregion The second largest category 

(level 2) of Hydrologic Units defined within 

the Watershed Boundary Dataset (WBD). 

See table 1.

Subwatershed The sixth largest category 

(level 6) of Hydrologic Units defined within 

the Watershed Boundary Dataset (WBD). 

See table 1. T

Thiessen polygon A polygon surrounding 

an individual feature whose boundary is 

halfway between that feature and the nearest 

other features. W

Walling Using a representation of the 

known drainage boundaries to build up or 

mathematically warp a DEM to improve how 

accurately catchment boundaries replicate 

known drainage boundaries.

Watershed The fifth largest (level 5) 

category of Hydrologic Units defined within 

the Watershed Boundary Dataset (WBD). 

See table 1.

Watershed Boundary Dataset (WBD)

A base-line hydrologic drainage boundary 

framework, accounting for all land and 

surface areas of the United States. U

USEPA Reach File Version 1.0 (RF1)

A national hydrologic database that uniquely 

identifies and interconnects the stream 

segments or “reaches” that compose the 

Country’s surface water drainage system at a 

1:500,000 scale.

USEPA Reach File Version 3.0 (RF3)

A national hydrologic database that uniquely 

identifies and interconnects the stream 

segments or “reaches” that compose the 

Country’s surface water drainage system at a 

1:100,000 scale.
THIS PAGE INTENTIONALLY LEFT BLANK
41

Appendix. Detailed Discussion for each Study Subbasin

Great Egg Harbor, NJ (02040302)...............................................................................................................45

Comparison of Method Boundaries with WBD Boundaries........................................................45

Comparison of Methods with Streamgage Data ...........................................................................51

Summary of Results for Great Egg Harbor .....................................................................................51

Seneca River, NC and SC (03060101)........................................................................................................54

Comparison of Method Boundaries with WBD Boundaries........................................................54

Comparison of Methods with Streamgage Data ...........................................................................57

Summary of Results for Seneca River.............................................................................................59

Pine River, MN (07010105) ..........................................................................................................................59

Comparison of Method Boundaries with WBD Boundaries........................................................59

Comparison of Methods with Streamgage Data ...........................................................................69

Summary of Results for Pine River ..................................................................................................71

South Platte Headwaters, CO (10190001).................................................................................................71

Comparison of Method Boundaries with WBD Boundaries........................................................71

Comparison of Methods with Streamgage Data ...........................................................................77

Summary of Results for South Platte Headwaters........................................................................80

Pine Valley, Utah (16020302).......................................................................................................................81

Willapa Bay, WA (17100106).......................................................................................................................85

Figures

1–1. Map showing the draft Watershed Boundary Dataset (WBD) boundaries, and 

National Hydrography Dataset (NHD) flowlines, Great Egg Harbor Subbasin, NJ .........46

1–2. Graph showing normalized Coefficient of Areal Correspondence (CAC) scores, by 

National Hydrography Dataset (NHD) flowline common identifier, for all methods 

tested (except the Outlet Matching Method), Great Egg Harbor Subbasin, NJ ..............47

1–3. Graph showing drainage-area percent error in relation to Watershed Boundary 

Dataset cumulative drainage areas, for all methods tested, Great Egg Harbor 

Subbasin, NJ ...............................................................................................................................48

1–4. Map showing (A) Watershed Boundary Dataset (WBD) and the New England Method 

without WBD (NEM-without-WBD) boundaries, (B) area of detail where boundaries 

differ overlaid on a Digital Raster Graphic, and (C) area in detail with boundary 

error overlaid on a Digital Orthophoto Quadrangle, Great Egg Harbor Subbasin, NJ....49

1–5. Map showing location of streamgages and associated drainage areas used as 

verification datasets, Great Egg Harbor Subbasin, NJ ........................................................52

1–6. Map showing (A) the Outlet Matching Method and verification drainage-area 

boundaries for a streamgage (01411000) and (B) the unusual boundary from the Outlet 

Matching Method for a streamgage (01411300), Great Egg Harbor Subbasin, NJ..........53

1–7. Map showing the Watershed Boundary Dataset (WBD) Subwatershed boundaries, 

and National Hydrography Dataset (NHD) flowlines, Seneca River Subbasin, NC 

and SC...........................................................................................................................................55

1–8. Graph showing normalized Coefficient of Areal Correspondence (CAC) scores, by 

National Hydrography Dataset (NHD) flowline common identifier, for all methods 

tested, Seneca River Subbasin, NC and SC...........................................................................56

Appendix 41
1–9. Map showing location of streamgages and associated drainage areas used as 

verification datasets, Seneca River Subbasin, NC and SC..................................................58

1–10. Map showing the draft Watershed Boundary Dataset (WBD) Subwatershed 

boundaries, and National Hydrography Dataset (NHD) flowlines, Pine River 

Subbasin, MN..............................................................................................................................60

1–11. Graph showing normalized Coefficient of Areal Correspondence (CAC) scores, by 

National Hydrography Dataset (NHD) flowline common identifier, for all methods 

tested, Pine River Subbasin, MN .............................................................................................61

1–12. Graph showing drainage-area percent error in relation to Watershed Boundary 

Dataset cumulative drainage areas, for all methods tested, Pine River Subbasin, MN.62

1–13. Map showing (A) Watershed Boundary Dataset (WBD) and New England Method 

without WBD (NEM-without-WBD) boundaries, and (B) and (C) areas of detail 

showing boundary differences at wetlands, Pine River Subbasin, MN............................64

1–14. Map showing (A) Watershed Boundary Dataset (WBD) and New England Method 

without WBD (NEM-without-WBD) boundaries, (B) area of detail where the boundaries differ overlaid on a Digital Raster Graphic, and (C) area in detail with boundary 

error overlaid on a Digital Orthophoto Quadrangle, Pine River Subbasin, MN................65

1–15. Map showing (A) Watershed Boundary Dataset (WBD) and New England Method 

without WBD (NEM-without-WBD) boundaries, (B) area of detail, showing boundary 

differences at Downey Lake, and (C) area of detail, showing boundary differences at 

a wetland, Pine River Subbasin, MN.......................................................................................66

1–16. Map showing Watershed Boundary Dataset (WBD) and the Raster Seeding Method 

boundaries for the two Subwatersheds with the lowest normalized Coefficient of 

Areal Correspondence (CAC) scores, Pine River Subbasin, MN .......................................67

1–17. Map showing location of streamgages and associated drainage areas used as 

verification datasets, Pine River Subbasin, MN....................................................................70

1–18. Map showing the draft Watershed Boundary Dataset (WBD) Subwatershed 

boundaries, and National Hydrography Dataset (NHD) flowlines, South Platte 

Headwaters Subbasin, CO ........................................................................................................72

1–19. Graph showing normalized Coefficient of Areal Correspondence (CAC) scores, by 

National Hydrography Dataset (NHD) flowline common identifier, for all methods 

tested, South Platte Headwaters Subbasin, CO....................................................................73

1–20. Graph showing drainage-area percent error in relation to Watershed Boundary 

Dataset cumulative drainage areas, for all methods tested, South Platte Headwaters 

Subbasin, CO ...............................................................................................................................74

1–21. Map showing (A) the Watershed Boundary Dataset (WBD) and the New England 

Method without WBD (NEM-without-WBD) boundaries for the Antero Reservoir 

Subwatershed and (B) area of detail showing boundary differences overlaid on the 

Digital Orthophoto Quadrangle (DOQ), South Platte Headwaters Subbasin, CO.............76

1–22. Map showing the Watershed Boundary Dataset (WBD) Subwatersheds and Raster 

Seeding Method boundaries with normalized Coefficient of Areal Correspondence 

(CAC) scores and digital elevation model (DEM) flow-path displacement boundary 

errors, South Platte Headwaters Subbasin, CO ....................................................................78

1–23. Map showing location of streamgages used as verification data, South Platte 

Headwaters, CO..........................................................................................................................79

1–24. Map showing the draft Watershed Boundary Dataset (WBD) Subwatershed 

boundaries, and National Hydrography Dataset (NHD) flowlines, Pine Valley, Utah .....82

1–25. Graph showing normalized Coefficient of Areal Correspondence (CAC) scores, by 

National Hydrography Dataset (NHD) flowline common identifier, for all methods 

tested, Pine Valley Subbasin, Utah..........................................................................................83

42 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset
1–26. Graph showing drainage-area percent error in relation to Watershed Boundary 

Dataset cumulative drainage areas, for all methods tested, Pine Valley 

Subbasin, Utah ............................................................................................................................84

1–27. Map showing location of streamgages and associated drainage areas used as 

verification datasets, Willapa Bay, WA ..................................................................................86

1–28. Graph showing the computed Coefficient of Areal Correspondence (CAC) scores 

(not normalized), by streamgage, for the New England Method without Watershed 

Boundary Dataset (NEM-without-WBD), Raster Seeding Method, and Thiessen 

Polygon Method, Willapa Bay Subbasin, WA........................................................................87

1–29. Graph showing drainage-area percent error in relation to streamgage drainage 

areas of the verification data for the New England Method without Watershed 

Boundary Dataset (NEM-without-WBD), Raster Seeding Method and Thiessen 

Polygon Method, Willapa Bay Subbasin, WA........................................................................88

Tables

1–1. Mean normalized Coefficient of Areal Correspondence score by delineation methods 

for Watershed Boundary Dataset boundaries in the Great Egg Harbor Subbasin, NJ ..47

1–2. Mean cumulative drainage-area errors for all delineation methods for various 

drainage-area sizes, Great Egg Harbor Subbasin, NJ .........................................................48

1–3. Mean normalized Coefficient of Areal Correspondence score by delineation methods 

for Watershed Boundary Dataset Subwatersheds in the Seneca River Subbasin, 

NC and SC....................................................................................................................................56

1–4. Mean cumulative drainage-area errors for all delineation methods for various 

drainage-area sizes, Seneca River Subbasin, NC and SC...................................................57

1–5. Mean normalized Coefficient of Areal Correspondence score by delineation methods 

for Watershed Boundary Dataset Subwatersheds in the Pine River Subbasin, MN......61

1–6. Mean cumulative drainage-area errors for all delineation methods for various 

drainage-area sizes, Pine River Subbasin, MN.....................................................................62

1–7. Mean normalized Coefficient of Areal Correspondence score by delineation methods 

for Watershed Boundary Dataset Subwatersheds in the South Platte Headwaters 

Subbasin, CO ...............................................................................................................................73

1–8. Mean cumulative drainage-area errors for all delineation methods for various 

drainage-area sizes, South Platte Headwaters Subbasin, CO............................................74

1–9. Mean drainage-area errors for all delineation methods (except the Outlet Matching 

Method), for the National Water Information System (NWIS) streamgages, grouped 

by various drainage-area sizes, South Platte Headwaters, CO..........................................80

1–10. Mean normalized Coefficient of Areal Correspondence scores by delineation method 

for Watershed Boundary Dataset Subwatersheds in the Pine Valley Subbasin, Utah...83

1–11. Mean cumulative drainage-area errors for all delineation methods for various 

drainage-area sizes, Pine Valley Subbasin, Utah..................................................................84

1–12. Coefficient of Areal Correspondence scores for the New England Method without 

Watershed Boundary Dataset (NEM-without-WBD), Raster Seeding Method, and 

Thiessen Polygon Method, for streamgage drainage-areas, Willapa Bay 

Subbasin, WA..............................................................................................................................87

1–13. Streamgage drainage-areas of verification data, drainage-area percent errors, 

and mean errors for the New England Method without Watershed Boundary Dataset, 

Raster Seeding Method, and Thiessen Polygon Method, Willapa Bay, WA....................88

Appendix 43
ABBREVIATIONS USED IN THIS APPENDIX

CAC Coefficient of Areal Correspondence

ComID Common Identifier, a unique identifier for an NHD feature

DEM digital elevation model

DOQ Digital Orthophoto Quadrangle

DRG Digital Raster Graphic

EDNA Elevation Derivatives for National Applications

GIS geographic information system

HUC Hydrologic Unit Code

NEM New England Method

NHD National Hydrography Dataset

NWIS National Water Information System

USGS United States Geological Survey

WBD Watershed Boundary Dataset

44 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset
Great Egg Harbor, NJ (02040302)

Comparison of Method Boundaries with 

WBD Boundaries

Draft Watershed Boundary Dataset (WBD) boundaries 

delineated to the 14-digit hydrologic unit level, as shown in 

figure 1–1, were obtained for the Great Egg Harbor Subbasin 

in New Jersey. Forty-five WBD boundaries were used in 

the Coefficient of Areal Correspondence (CAC) analysis—

the results of which are shown in figure 1–2 and table 1–1. 

A graph, developed as part of the convergence analysis, 

displaying the distribution of drainage-area percent errors 

is shown in figure 1–3. Convergence analysis of cumulative 

drainage-area percent errors are also summarized by drainagearea size categories, as shown in table 1–2. The Outlet 

Matching Method produced fewer comparisons with the 

WBD because the Outlet Matching Method catchments could 

not always be linked to the National Hydrography Dataset 

(NHD) flowlines. For the Outlet Matching Method, 39 WBD 

boundaries were compared in the analysis.

New England Method with WBD (NEM-with-WBD)

Fourteen of the 45 WBD boundaries have CAC scores 

(before normalization to 100) for the NEM-with-WBD of less 

than 95. For all 14, the lower CAC scores were attributed to 

mismatches between the outlet of the WBD boundaries and 

the NHD flowlines assigned as best representing the WBD 

outlets (WBD/NHD-flowline outlet mismatch). The Great 

Egg Harbor Subbasin had a higher incidence of WBD/NHDflowline outlet mismatches than the other Subbasins owing 

to the greater detail in the divisions of the WBD (14-digit 

Hydrologic Unit Code (HUC) level). WBD data for the Great 

Egg Harbor Subbasin include subdivisions along flowlines 

where no confluences occur in the medium-resolution NHD. 

These subdivisions may represent the location of a 1:24,000-

scale stream confluence or water-quality monitoring site, dam, 

or other feature. 

The mean CAC score (before normalization to 100) for 

the NEM-with-WBD is 91.6, the highest of all the methods. 

The mean cumulative drainage-area error for NEM-with-WBD 

is 1.65 percent (table 1–2) and is attributed to the WBD/NHDflowline outlet mismatch errors. No cumulative drainage areas 

from the NHD flowlines in this Subbasin fit within the 8-digit 

HUC designation.

New England Method without WBD (NEM-without-WBD)

The mean normalized CAC score for the NEM-withoutWBD is 87.5 (table 1–1), the highest score after NEM-withWBD. Twenty-six of the 45 WBD boundaries (58 percent) 

have normalized CAC scores greater than 90. Five WBD 

boundaries (11 percent) have normalized CAC scores less than 

80 (table 1–1). The five lowest individual normalized CAC 

scores are 42.6, 67.2, 73.7, 78.1, and 79.0. 

The lowest normalized CAC score of the NEM-withoutWBD is 42.6. The difference in area between the WBD 

boundary and the corresponding NEM-without-WBD boundary (fig. 1–4A) is 3.25 mi2

, which is the highest normalized 

polygon-area error for this method at 46.4 percent. The WBD 

and the NEM-without-WBD boundaries were overlaid on the 

1:24,000-scale Digital Raster Graphic (DRG) (fig. 1–4B) to 

determine visually which boundary was more accurate. The 

differences in the delineations occur at a wetland and the area 

of difference is attributed, in most part, to the drainage area 

of this wetland. In the WBD dataset, a road grade was used as 

a divide to delineate the WBD boundary through the wetland 

area. On the basis of the DRG, it was difficult to determine 

which boundary was correct (fig. 1–4B). However, on the 

basis of the surface waters depicted on the U.S. Geological 

Survey (USGS) Digital Orthophoto Quadrangle (DOQ), it 

does appear that the WBD data are correct (fig. 1–4C). 

The second lowest normalized CAC score of the 

NEM-without-WBD is 67.2. The area of difference between 

the NEM-without-WBD and the WBD boundary is 3.02 mi2, 

a 25.5 percent normalized polygon-area error. The WBD area 

drains into the tidal portion of the Great Egg Harbor River, 

and large tidal wetlands with complex drainage patterns and 

flood levees are present within the WBD boundary. Both 

delineations appear to be acceptable here on the basis of on 

the complex drainages. 

The NEM-without-WBD boundary with the third lowest 

normalized CAC score at 73.7 has a normalized polygonarea error of 34 percent. There are several areas of difference 

between the WBD and NEM-without-WBD boundaries. On 

the basis of DRG information, it was difficult to determine 

which method produced the more accurate boundary at the 

largest area of difference (approximately 2 mi2). Data from 

the WBD provided a more accurate delineation at another 

area with a difference of 0.5 mi2. Other differences along the 

boundaries involved areas of less substantial sizes. In one 

case, neither the NEM-without-WBD boundary nor the WBD 

boundary is correct. 

Appendix. Detailed Discussion for each Study Subbasin

Appendix 45
46 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

75° 74°40' 74°20'

39°20'

39°40'

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

Atlantic Ocean

New Jersey

Base from 1:100,000-scale National Hydrography Dataset, 2003

Waterbodies on

the network 

Ocean or estuary

Subbasin boundary 

Draft Watershed

Boundary Dataset

(WBD) 

9436775

National Hydrography Dataset (NHD) 

flowlines

Artificial path; Connector

Non-connected flowline

NHD outlet flowline assigned to

draft WBD boundary and 

common identifier (ComID) 

EXPLANATION

Stream/River

9433571

9434039

9434037

9433603

9434045

9434057

9434171

9434183

9434143

9434063 9434191

9433671

9434077

9434195

9433653

9434095

9433773

9434111

9436617

9436783

9436333

9436633

9436645

9436799 9436801

9436629

9436651

9436667

9436687

9436433

9436437 9436435

9436451

9436877

9436891

9436865 9436861

9436857

9436403

9436393

9436361

9436367

9436771

9436775

9436413

Albers Conic Equal-Area Projection

Central Meridian: -96°00'00"

1st Standard Parallel: 29°30'00"

2nd Standard Parallel: 45°30'00"

Latitude of Origin: 23°00'00"

Horizontal Datum: NAD83

Figure 1–1. The draft Watershed Boundary Dataset (WBD) boundaries, and National Hydrography Dataset (NHD) flowlines, 

Great Egg Harbor Subbasin, NJ. (The location of this Subbasin is shown in figure 15.)
Great Egg Harbor, NJ (02040302) 47

Figure 1–2. Normalized Coefficient of Areal Correspondence (CAC) scores, by National Hydrography Dataset (NHD) flowline 

common identifier, for all methods tested (except the Outlet Matching Method), Great Egg Harbor Subbasin, NJ.

Table 1–1. Mean normalized Coefficient of Areal Correspondence score by delineation methods for Watershed 

Boundary Dataset boundaries in the Great Egg Harbor Subbasin, NJ.

[CAC, Coefficient of Areal Correspondence; NEM, New England Method; WBD, Watershed Boundary Dataset]

Method Mean normalized 

CAC

Normalized CACs greater than 90 Normalized CACs less than 80

Number of 

boundaries

Percentage of 

boundaries

Number of 

boundaries

Percentage of 

boundaries

NEM-with-WBD 100 45 100 0 0

NEM-without-WBD 87.5 26 58 5 11

Raster Seeding Method 85.8 20 44 6 13

Thiessen Polygon Method 70.9 1 2 36 80

NORMALIZED CAC SCORE

NATIONAL HYDROGRAPHY DATASET FLOWLINE COMMON IDENTIFIERS (ComIDs)

0

10

20

30

40

50

60

70

80

90

100

9433571943403794340399433603943404594340579434077943417194340959434183

943411194336539434143943633394341959434063943419194336719436617943377394363619436771943678394367759436367943662994366339436801

94363939436799943640394366459436667943686594368579436651943686194364139436687943643394368779436435943643794368919436451

New England Method with WBD

New England Method without WBD

Raster Seeding Method

Thiessen Polygon Method

Outlet Matching Method
48 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

-20

-15

-10

-5

0

5

10

15

20

0 50 100 150 200 250 300 350

WATERSHED BOUNDARY DATASET (WBD) CUMULATIVE DRAINAGE AREA, IN SQUARE MILES

DRAINAGE-AREA PERCENT ERROR

New England Method without WBD

New England Method with WBD

Raster Seeding Method

Outlet Matching Method

Thiessen Polygon Method

Table 1–2. Mean cumulative drainage-area errors for all delineation methods for various drainage-area sizes, Great Egg Harbor 

Subbasin, NJ.

[OM, Outlet Matching; mi2, square miles; NEM, New England Method; WBD, Watershed Boundary Dataset; na, not applicable]

Method 

(61 units total; 54 units OM)

Mean cumulative drainage-area error, in percent

Drainage-area size category

All drainage areas Less than 20 mi2 20–60 mi2 Greater than 60–390 mi2 Greater than 390 mi2

NEM-with-WBD 1.65 2.18 1.96 0.39 na

NEM-without-WBD 4.98 8.06 4.04 0.61 na

Raster Seeding Method 5.25 8.01 4.80 0.88 na

Thiessen Polygon Method 9.86 16.35 4.77 4.03 na

Outlet Matching Method 11.30 18.81 8.50 4.44 na

Figure 1–3. Drainage-area percent error in relation to Watershed Boundary Dataset cumulative drainage areas, for all methods 

tested, Great Egg Harbor Subbasin, NJ.
Great Egg Harbor, NJ (02040302) 49

CAC = 42.6

WBD boundary

NEM-without-WBD

boundary

National Hydrography

Dataset Flowline

EXPLANATION

Area in

Detail

B

C

Delineation at wetland

questionable

Closure of

wetland wrong

A

CAC Coefficient of Areal 

Correspondence (CAC) (normalized)

Figure 1–4. (A) Watershed Boundary Dataset (WBD) and the New England Method without WBD (NEM-without-WBD) 

boundaries, (B) area of detail where boundaries differ overlaid on a Digital Raster Graphic, and (C) area in detail with boundary 

error overlaid on a Digital Orthophoto Quadrangle, Great Egg Harbor Subbasin, NJ. (The location of this WBD boundary is shown 

in figure 1–1.)
50 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

It was difficult to determine which dataset was correct 

for the fourth lowest normalized CAC score, 78.1, for the 

NEM-without-WBD. Cultural features in a heavy urban 

setting depicted on the DRGs made interpreting the underlying 

topographic contours difficult. The digital elevation model 

(DEM) delineation of the NEM-without-WBD appears to 

be correct, but this is not verifiable. The difference in area 

between the dataset boundaries is 0.97 mi2 with a normalized 

polygon-area error of 20.7 percent. 

The fifth lowest CAC score is 79.0. Either the WBD or 

the NEM-without-WBD delineation seems to be possible. 

The WBD includes road grades as drainage-area divides in 

certain areas, which are presumed to be correct. Because the 

NEM-without-WBD delineations rely solely on topographic 

data that do not take into account road grades, differences 

occur between the dataset boundaries. In these road-related 

differences, both boundaries can be considered acceptable 

on the basis of the limited information available. However, 

from the DOQ imagery it does appear that the use of the 

roads as divides in certain areas enhanced the accuracy of the 

boundaries. The difference in area for this WBD boundary is 

0.16 mi2, which represents a normalized polygon-area error of 

2.2 percent. 

In the cumulative drainage-area analysis, the NEMwithout-WBD results closely tracked with the Raster Seeding 

Method results, but were slightly more accurate. The mean 

cumulative drainage-area error is 4.98 percent, compared to 

5.25 percent for the Raster Seeding Method (table 1–2). The 

NEM-without-WBD mean cumulative drainage-area error 

for drainage areas less than 20 mi2 is 8.06 percent, which is 

similar to the Raster Seeding Method error of 8.01 percent. An 

8 percent error for computed drainage areas is somewhat high; 

however, about 2 percent of the error contribution is attributed 

to WBD/NHD-flowline outlet mismatch. 

Raster Seeding Method

The mean normalized CAC score for the Raster Seeding 

Method is 85.8, a close second to the NEM-without-WBD of 

87.5. Twenty of the 45 Raster Seeding Method boundaries 

(44 percent) have normalized CAC scores greater than 90, and 

just 6 (13 percent) have a normalized CAC score less than 80. 

The six normalized CAC scores less than 80 are 29.1, 43.4, 

70.9, 75.7, 77.0, and 79.1. One normalized Raster Seeding 

Method CAC score of greater than 100 (103.8) is explained 

by a combination of DEM flow-path displacement and 

WBD/NHD-flowline outlet mismatch, shown in figure 19 

of this report. 

Parallel stream artifacts from DEM flow-path displacement also contributed to the lowering of normalized CAC 

scores, affecting three of the six lowest Raster Seeding 

Method scores. Overall, the catchment delineations of the 

Raster Seeding Method and the NEM-without-WBD are very 

similar. Of the Raster Seeding Method catchment delineation 

lines, 81 percent are in perfect correspondence to the drainage 

divides of the NEM-without-WBD. Most of the delineation 

differences are due to errors associated with DEM flow-path 

displacement observed with the Raster Seeding Method. 

The lowest normalized CAC score of 29.1 is attributed 

mostly to the DEM flow-path displacement. This compared 

boundary is also where the NEM-without-WBD scored 67.2, 

the second lowest for that method; the area contains tidal 

wetlands with complex drainage patterns. The Raster Seeding 

Method boundary runs parallel to the NHD, leading to a less 

accurate delineation. The area of difference between the 

Raster Seeding Method and WBD boundaries is 6.54 mi2

(a 55.8-percent normalized polygon-area error), and the 

difference between the NEM-without-WBD and the WBD 

boundaries is 3.02 mi2 difference (a 25.5-percent error). 

The second lowest Raster Seeding Method normalized 

CAC score of 43.4 is for the WBD boundary shown in 

figure 1–4, which also had the lowest normalized CAC score 

for the NEM-without-WBD. Delineations from both the Raster 

Seeding Method and NEM-without-WBD are the same at the 

wetland area identified in figure 1–4B. Once again, the WBD 

provided the more accurate delineation. The area of difference 

is 3.61 mi2 between the Raster Seeding Method and the WBD 

boundaries, representing a normalized polygon-area error of 

51.6 percent. 

DEM flow-path displacement led to a less accurate 

delineation and contributed to the third lowest Raster Seeding 

Method normalized CAC score of 70.9. This is the same 

WBD area discussed earlier as the NEM-without-WBD with 

the fifth lowest CAC score (79.0) for that method. As for the 

NEM-without-WBD boundary, the use of roads as divides in 

the WBD contributed to some of the differences between the 

Raster Seeding Method and the WBD boundaries. There is 

a stretch in the Raster Seeding Method boundary where the 

delineation improperly parallels the NHD stream, contributing 

to additional differences from the NEM-without-WBD 

boundary. The area of difference between the Raster 

Seeding Method and corresponding WBD boundary is 

0.63 mi2 (7.3-percent normalized polygon-area error), of 

which about 0.47 mi2 is directly attributable to DEM flowpath displacement.

Both the WBD and the Raster Seeding Method data produced boundary delineations with weaknesses, resulting in the 

fourth lowest normalized CAC score for the Raster Seeding 

Method (75.7). The delineations for this WBD boundary from 

both the Raster Seeding Method and NEM-without-WBD 

are identical in many areas. The effects of DEM flow-path 

displacement contributed to additional errors in the Raster 

Seeding Method boundary. 

A determination could not be made as to which delineation was more accurate for a Raster Seeding boundary with the 

fifth lowest normalized CAC score of 77.0. It was also difficult 

to determine which delineation was the most accurate for the 

boundary with the sixth lowest normalized CAC score (79.1) 

for the Raster Seeding Method. 
Great Egg Harbor, NJ (02040302) 51

Thiessen Polygon Method

The mean normalized CAC score for the Thiessen 

Polygon Method is 70.9. Only one normalized CAC score 

was determined to be greater than 90 (at 90.36). In contrast, 

80 percent of all Thiessen Polygon Method boundaries have 

normalized CAC scores less than 80, compared to just 11 and 

13 percent for the NEM-without-WBD and Raster Seeding 

Method, respectively. The Thiessen Polygon Method has the 

highest mean normalized polygon-area error of 17.17 percent, 

whereas the Raster Seeding Method has a 9 percent mean 

error, and NEM-without-WBD has a 6.89 percent mean error. 

In the cumulative drainage-area analysis, the Thiessen 

Polygon Method has the fourth highest error with a mean 

drainage-area error of 9.86 percent (table 1–2). The mean 

Thiessen Polygon Method cumulative drainage-area error 

for drainage areas less than 20 mi2 is roughly twice that 

of the mean errors for the Raster Seeding Method and the 

NEM-without-WBD. The mean Thiessen Polygon Method 

cumulative drainage-area error (4.77 percent) for drainage 

areas of 20 to 60 mi2 tracks closely with the Raster Seeding 

Method (4.80 percent) and the NEM-without-WBD 

(4.04 percent). For drainage areas greater than 60 to 390 mi2

in size, the Thiessen Polygon Method has a higher mean 

error at 4.03 percent, compared to 0.88 percent for the Raster 

Seeding Method and 0.61 percent for NEM-without-WBD.

Outlet Matching Method

The Outlet Matching Method has the lowest CAC scores 

of all the methods with a mean CAC of 61.4. Thirty-nine 

of the 45 WBD boundaries were used in the CAC analysis 

because six NHD flowlines could not be assigned a corresponding Elevation Derivatives for National Applications 

(EDNA) catchment area. The Outlet Matching Method also 

has the highest polygon-area errors (not normalized) with a 

mean error of 40.17 percent; the Thiessen Polygon Method, 

the Raster Seeding Method, and NEM-without-WBD have 

mean errors of 19.54, 11.71, and 10.46 percent, respectively. 

In the cumulative drainage-area analysis, the Outlet Matching Method has the highest mean error of 11.30 percent. The 

Outlet Matching Method also has the highest mean error in 

each drainage-area size category; the highest is 18.81 percent 

for drainage areas less than 20 mi2 (table 1–2). 

Results for the Outlet Matching Method are provided 

only for the Great Egg Harbor Subbasin in this Appendix 

because it was representative of the poor performance of the 

Outlet Matching Method.

Comparison of Methods with Streamgage Data

Geographic information system (GIS) boundary data 

were obtained for two streamgage drainage areas (fig. 1–5) 

to be used as verification datasets for the Great Egg Harbor 

Subbasin. National Water Information System (NWIS) 

drainage-area measurements also were obtained for the two 

streamgages. The NWIS drainage-area measurement for 

streamgage 01411000 is 57.1 mi2, and the GIS measurement 

is 56.94 mi2. For streamgage 01411300, the NWIS drainage 

area and GIS drainage-area measurements are the same, 

30.77 mi2. The streamgage drainage-area boundaries are the 

same as the WBD boundaries for both streamgages, except at 

the areas near the streamgages. 

Imperfect NEM-with-WBD CAC scores (less than 

100) were obtained for the comparison of the drainage-area 

boundaries for the two streamgages. In both cases, the CAC 

scores can be linked to mismatches between the streamgage 

drainage-area outlet and the NHD-flowline outlet. Streamgage 

01411000 is located at a point that is 62 percent along the 

length of the flowline, resulting in a CAC score of 96.63. The 

location of streamgage 01141130 on its matched NHD flowline is 29 percent along the length of the flowline, resulting in 

a higher CAC score of 98.01. The mean CAC score is 97.32. 

The mean normalized CAC score for the NEM-withoutWBD is 95.88. For both streamgages, the delineations of 

NEM-without-WBD boundaries are acceptable on the basis 

of the limited detail of the contour intervals depicted on the 

DRGs. Differences in the delineations were observed, but no 

major errors could be identified in either dataset. 

The Raster Seeding Method boundaries for the 

streamgages are nearly identical with the NEM-without-WBD 

boundaries in most areas. Boundaries running parallel to 

streams at the matched flowline for both streamgages were 

observed in the Raster Seeding Method. The mean normalized 

CAC score for the Raster Seeding Method of 95.66 is close to 

the NEM-without-WBD score (95.88).

The mean CAC score for the Outlet Matching Method 

is 90.88. An unusual Outlet Matching Method assignment 

for streamgage 01411000 is shown in figure 1–6A. In 

figure 1–6A, two separate drainage areas were assigned as 

contributing areas to the streamgage. The improper assignment 

of the contributing area for streamgage 01411000 reflects the 

errors in the DEM-derived stream network and shows the 

limitations to the Outlet Matching Method. Errors unique 

to the Outlet Matching Method were observed, such as the 

example presented in figure 1–6B, where the delineation error 

occurs at the drainage-area outlet for streamgage 01411300. 

The correct delineation for the streamgage in figure 1–6B 

is depicted in the streamgage drainage-area boundary used 

as verification. 

The Thiessen Polygon Method produced the lowest normalized CAC score (79.89) in the GIS comparison analysis. 

Summary of Results for Great Egg Harbor

The normalized CAC scores show that the NEM-withWBD provided the most accurate results, followed by the 

NEM-without-WBD. The lowest CAC score of the NEMwithout-WBD shows that the WBD boundary is correct and 

the DEM delineation of the NEM-without-WBD is in error. 

Mean cumulative drainage-area errors are as high as 

8.06 percent (table 1–2) for small drainages of less than 

20 mi2 in size and as low as 0.61 percent for drainage areas 

greater than 60 to 390 mi2 in size. 
52 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Atlantic Ocean

EXPLANATION

National Hydrography Dataset (NHD) 

flowlines

Artificial path; Connector

Stream/River

Non-connected flowline

NHD outlet flowline assigned to 

streamgage

Streamgage drainage areas

75° 74°40' 74°20'

39°20'

39°40'

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

01411300

01411000

Streamgage and identifier

01411000

New Jersey

Base from 1:100,000-scale National Hydrography Dataset, 2003

Albers Conic Equal-Area Projection

Central Meridian: -96°00'00"

1st Standard Parallel: 29°30'00"

2nd Standard Parallel: 45°30'00"

Latitude of Origin: 23°00'00"

Horizontal Datum: NAD83

Waterbodies on

the network 

Ocean or estuary

Subbasin and boundary 

Figure 1–5. Location of streamgages and associated drainage areas used as verification datasets, Great Egg Harbor 

Subbasin, NJ. (The location of this Subbasin is shown in figure 15.)
Great Egg Harbor, NJ (02040302) 53

Delineation differences at streamgage 01411300

EXPLANATION

Outlet Matching Method boundary

Streamgage drainage-area boundary

National Hydrography Dataset (NHD) flowline

Streamgage and identifier 01411000

01411300

39°37'30"

39°45'

75°

74°52'30"

01411000

A

B

Figure 1–6. (A) The Outlet Matching Method and verification drainage-area boundaries for a streamgage (01411000) and (B) the 

unusual boundary from the Outlet Matching Method for a streamgage (01411300), Great Egg Harbor Subbasin, NJ. (The location of 

these streamgages are shown in figure 1–5.)
54 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

The mean normalized CAC score of the Raster Seeding 

Method is 85.8, a close second to the NEM-without-WBD 

Method, 87.5 (table 1–1). Eighty-one percent of the boundary lines from the Raster Seeding Method correspond to the 

boundaries from the NEM-without-WBD. Many of the delineation differences of the Raster Seeding Method are due to 

errors associated with parallel-to-stream boundaries observed 

from DEM flow-path displacement. For three of the six Raster 

Seeding Method boundaries with the lowest CAC scores, 

DEM flow-path displacement had negligible effects. Similar 

results were obtained for the Raster Seeding Method and the 

NEM-without-WBD in the cumulative drainage-area analysis. 

The Thiessen Polygon Method boundaries are not topographically derived and, therefore, do not share boundaries 

with the WBD. The Thiessen Polygon Method, according to 

CAC scores, provided inaccurate results in terms of spatial 

correspondence to the WBD data, with a mean normalized 

CAC score of 70.9. The Thiessen Polygon Method also had 

the highest mean normalized polygon-area error. The Thiessen 

Polygon Method produced the fourth highest mean error in the 

cumulative drainage-area analysis, with a mean error as high 

as 16 percent for the smallest drainage-area size category. 

The Outlet Matching Method provided the least accurate 

results of all the methods, with a mean CAC score of 61.4. 

The Outlet Matching Method had the highest cumulative 

drainage-area errors for all drainage-area size categories, with 

mean errors as high as 18.81 percent for drainage areas less 

than 20 mi2 in size (table 1–2). The Outlet Matching Method 

failed to provide a one-to-one correspondence with the NHD 

flowlines used in the analysis. 

In the streamgage comparison, all the methods except the 

Thiessen Polygon Method had normalized CAC scores greater 

than 90. The Thiessen Polygon Method mean normalized CAC 

score is 70.9. The Outlet Matching Method mean CAC score 

was not normalized and has an uncorrected CAC of 90.88. 

The Outlet Matching Method provided erroneous and unusual 

results (fig. 1–6) and, thus, provided the overall least accurate 

results in the comparison. 

Seneca River, NC and SC (03060101)

Comparison of Method Boundaries with 

WBD Boundaries

Previously determined draft WBD Subwatershed boundaries for the Seneca River Subbasin (fig. 1–7), delineated to 

the 12-digit hydrologic unit level, were used in the CAC and 

cumulative drainage-area and convergence analyses. Thirtythree WBD Subwatersheds were used in the CAC analysis, the 

results of which are shown in figure 1–8 and table 1–3. Results 

of the cumulative drainage-area convergence analysis are summarized in table 1–4.

New England Method with WBD (NEM-with-WBD)

WBD/NHD-flowline outlet mismatches and an isolated 

NHD stream network contributed to the CAC scores (before 

normalizing to 100) of the NEM-with-WBD. The Seneca 

River Subbasin’s outlet Subwatershed has the lowest CAC 

score at 76.4 caused by the WBD/NHD-flowline outlet mismatch. The Seneca River flows into a man-made reservoir, 

Lake Hartwell. The WBD boundary subdivides the reservoir 

at the pre-flooded main flow path of the Seneca River at the 

convergence with the Tugaloo River, which together comprise 

the headwaters of the Savannah River. The NHD artificial path 

outlet flowline does not follow the original flow path of the 

Seneca River and drains into Lake Hartwell at another location upstream. WBD/NHD-flowline outlet mismatches also 

occurred at other Subwatersheds. 

An isolated NHD stream network in a headwater 

Subwatershed lowered the CAC score for the NEM-withWBD boundary to 93.0 with a polygon-area error of 

6.77 percent. At the Subbasin flowline outlet, the effect of 

the WBD/NHD-flowline outlet mismatch and the isolated 

stream network was minimal in the cumulative drainage-area 

analysis, with a 0.89 percent error for this 956-mi2 Subbasin.

New England Method without WBD (NEM-without-WBD)

The mean normalized CAC for the NEM-without-WBD 

is 97.4, the highest score after NEM-with-WBD (see 

table 1–3). There were no normalized CAC scores less than 

90 or normalized polygon-area errors greater than 2.01 percent. The mean normalized polygon-area error for the NEMwithout-WBD is 0.56 percent. No major boundary differences 

were observed between the NEM-without-WBD boundaries and the WBD Subwatersheds. Where small differences 

occurred, the WBD provided a more accurate boundary than 

the NEM-without-WBD. 

The cumulative drainage-area convergence analysis 

results summarized in table 1–4 show that the NEM-withoutWBD provided the most accurate results (after NEM-withWBD) for all drainage-area size categories. NEM-withoutWBD was the only method besides NEM-with-WBD that 

produced drainage-area errors of less than 1 percent for 

drainage areas greater than 60 mi2 in size. No cumulative 

drainage-area errors are greater than 6.20 percent. The highest 

cumulative drainage-area error of 6.20 percent is due mostly 

to an isolated stream network. 

Raster Seeding Method

The mean normalized CAC score for the Raster Seeding 

Method is 91.7. Twenty-six of the 33 boundaries compared 

(79 percent) have normalized CAC scores greater than 90, and 

4 boundaries (12 percent) have CAC scores less than 80. The 

four CAC scores less than 80 are 60.6, 60.8, 72.9, and 79.1. 

The Raster Seeding Method has the highest mean 

normalized polygon-area error at 5.75 percent (compared to: 

Thiessen Polygon Method, 5.47 percent; NEM-without-WBD, 
Seneca River, NC and SC (03060101) 55

South 

Carolina

North 

Carolina

Georgia

6270090

6267176

6267172

6267122

6267128

6267074

11749739

11750663

6267022

11749733

11749289

6266982 6266984

11750061

11752695

11749981

11749983

11749665

11749667

11749069

11748981

11748929

11748873

11749617

11749883

11748969

11749001

11749015

11749847

11749815

11749805

11748083 11748087

83° 82°45' 82°30'

34°30'

34°45'

35°

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

Base from 1:100,000-scale National Hydrography Dataset, 2003

Albers Conic Equal-Area Projection

Central Meridian: -96°00'00"

1st Standard Parallel: 29°30'00"

2nd Standard Parallel: 45°30'00"

Latitude of Origin: 23°00'00"

Horizontal Datum: NAD83

Subbasin boundary 

EXPLANATION

Waterbodies on 

the network

National Hydrography Dataset (NHD) 

flowlines

Artificial path; Connector

Stream/River

Non-connected flowline

NHD outlet flowline assigned to 

WBD unit and common

identifier (ComID)

Watershed Boundary 

Dataset (WBD) 

Subwatersheds 

6270090

Figure 1–7. The Watershed Boundary Dataset (WBD) Subwatershed boundaries, and National Hydrography Dataset 

(NHD) flowlines, Seneca River Subbasin, NC and SC. (The location of this Subbasin is shown in figure 15.)
56 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

NATIONAL HYDROGRAPHY DATASET (NHD) FLOWLINE COMMON IDENTIFIERS (ComIDs)

1174808711748083117498471174980511749883117498151174887311749617117489291174896911749015117499811174898111749667117490691174998311749665117492891175006111749001

6266982

6266984

117497331175269511750663

6267022

11749739

626712262671766267128626707462671726270090

NORMALIZED CAC SCORE

New England Method with WBD

New England Method without WBD

Raster Seeding Method

Thiessen Polygon Method

Outlet Matching Method

0

10

20

30

40

50

60

70

80

90

100

Table 1–3. Mean normalized Coefficient of Areal Correspondence score by delineation methods for Watershed 

Boundary Dataset Subwatersheds in the Seneca River Subbasin, NC and SC.

[CAC, Coefficient of Areal Correspondence; NEM, New England Method; WBD, Watershed Boundary Dataset]

Method Mean normalized 

CAC

Normalized CACs greater than 90 Normalized CACs less than 80

Number of 

Subwatersheds

Percentage of 

Subwatersheds

Number of 

Subwatersheds

Percentage of 

Subwatersheds

NEM-with-WBD 100.0 33 100 0 0

NEM-without-WBD 97.4 33 100 0 0

Raster Seeding Method 91.7 26 79 4 12

Thiessen Polygon Method 85.1 7 21 6 18

Figure 1–8. Normalized Coefficient of Areal Correspondence (CAC) scores, by National Hydrography Dataset (NHD) flowline 

common identifier, for all methods tested, Seneca River Subbasin, NC and SC.
Seneca River, NC and SC (03060101) 57

0.56 percent; and NEM-with-WBD, 0 percent). The 

normalized polygon-area errors for the lowest CAC scores 

in the Raster Seeding Method boundaries range from 19.5 

to 39.9 percent. The Raster Seeding Method has the highest 

normalized polygon-area error of 39.9 percent compared to 

29.5 percent for the Thiessen Polygon Method and 

2.01 percent for the NEM-without-WBD.

There was a 69-percent spatial correspondence between 

the drainage-area divides of the Raster Seeding Method catchment delineations and those of the NEM-without-WBD, as 

determined by GIS overlay analysis. Differences in the spatial 

delineations between the Raster Seeding Method and NEMwith-WBD are directly attributed to DEM flow-path displacement errors that occurred in the Raster Seeding Method delineations. In all cases where DEM flow-path displacement errors 

occur, the effects of such errors had negligible effects. DEM 

flow-path displacement was most problematic for flowlines in 

reservoirs; this was observed for the boundaries with the four 

lowest CAC scores for the Raster Seeding Method. 

The highest Raster Seeding Method cumulative drainagearea errors were observed in headwater Subwatersheds. A 

12.4 percent cumulative drainage-area error was observed for 

a 43.6-mi2 Subwatershed. In this Subwatershed, about half of 

the error is linked to an isolated NHD network, whereas the 

other half of the error is attributed to DEM flow-path displacement. DEM flow-path displacement was the most significant 

contributor for a 12.2 percent error in a 13.9-mi2 Subwatershed, and an 11.54 percent error in a 44.4-mi2

 Subwatershed.

The Raster Seeding Method has the third lowest mean 

error in the cumulative drainage-area analysis at 2.35 percent 

(table 1–4). No Raster Seeding Method cumulative drainagearea mean errors greater than 2.80 percent were observed for 

any drainage-area size categories shown in table 1–4. 

Thiessen Polygon Method

The mean normalized CAC score for the Thiessen 

Polygon Method is 85.1. Seven of the 33 Thiessen Polygon 

Method boundaries (21 percent) have normalized CAC scores 

greater than 90. Six Thiessen Polygon Method boundaries 

(18 percent) have normalized CAC scores less than 80. 

In the cumulative drainage-area analysis, the Thiessen Polygon Method has the highest mean drainage-area 

error of just 2.94 percent (table 1–4). The Thiessen Polygon 

Method has the highest mean error of all the methods for 

drainage areas less than 20 mi2 in size, 6.18 percent, and for 

drainage areas 20 to 60 mi2 in size, 3.31 percent. For drainage areas greater than 60 mi2

, the Thiessen Polygon Method 

mean cumulative drainage-area errors are not substantial; the 

method produced slightly lower mean drainage-area errors 

than the Raster Seeding Method. 

Comparison of Methods with Streamgage Data

Four streamgage drainage-area boundaries, shown 

in figure 1–9, were obtained as verification datasets in the 

Seneca River Subbasin. Drainage-area measurements for the 

streamgages range from 47 to 104 mi2. The boundaries from 

the streamgage drainage-area data align with those from the 

WBD Subwatershed boundaries, except at the areas near the 

streamgages. NWIS drainage-area measurements also were 

obtained for these four streamgages. 

CAC scores less than 100 for the NEM-with-WBD are 

directly related to the location of the streamgage along the 

NHD flowline. The farther upstream the streamgage is located 

along the flowline, the lower the CAC score. The lowest CAC 

score (not normalized) of the NEM-with-WBD is 97.75, and 

the mean CAC score of the NEM-with-WBD is 98.39. 

Table 1–4. Mean cumulative drainage-area errors for all delineation methods for various drainage-area sizes, Seneca River 

Subbasin, NC and SC.

[mi2, square miles; NEM, New England Method; WBD, Watershed Boundary Dataset]

Method 

(44 units total)

Mean cumulative drainage-area error, in percent

Drainage-area size category

All drainage areas Less than 20 mi2 20–60 mi2 Greater than 

60–390 mi2

Greater than 

390 mi2

At Subbasin 

outlet 956 mi2

NEM-with-WBD 0.56 0.00 1.01 0.57 0.53 0.89

NEM-without-WBD 1.04 1.39 1.36 0.86 0.54 0.85

Raster Seeding Method 2.35 2.45 2.80 2.60 0.89 1.70

Thiessen Polygon Method 2.94 6.18 3.31 1.89 0.75 1.01
58 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

02185200

02186645

02186699

02186000

South 

Carolina

North 

Carolina

Georgia

83° 82°45' 82°30'

34°30'

34°45'

35°

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

Base from 1:100,000-scale National Hydrography Dataset, 2003

Albers Conic Equal-Area Projection

Central Meridian: -96°00'00"

1st Standard Parallel: 29°30'00"

2nd Standard Parallel: 45°30'00"

Latitude of Origin: 23°00'00"

Horizontal Datum: NAD83

Subbasin and

boundary 

EXPLANATION

Waterbodies on 

the network

Streamgage 

drainage

areas

National Hydrography Dataset (NHD) 

flowlines

Artificial path; Connector

Stream/River

Non-connected flowline

NHD outlet flowline assigned to 

streamgage

Streamgage and identifier 02185200

Figure 1–9. Location of streamgages and associated drainage areas used as verification datasets, Seneca River 

Subbasin, NC and SC. (The location of this Subbasin is shown in figure 15.)
Pine River, MN (07010105) 59

The mean normalized CAC score for the NEM-without-WBD is 98.32. No major errors were observed in the 

NEM-without-WBD boundaries in the comparison with the 

streamgage drainage-area boundaries. The streamgage drainage-area boundaries provided more accurate boundaries than 

the NEM-without-WBD for many areas where differences 

were observed. On the basis of the limited contour information 

of the DRGs, it was difficult to determine which boundary 

was more accurate for some areas where small differences 

were observed. 

The results of the CAC analysis of the Raster Seeding 

Method boundaries were nearly the same as those for the 

NEM-without-WBD boundaries. The mean normalized 

CAC score for the Raster Seeding Method is 98.14, and for 

NEM-without-WBD, 98.32. The streamgage drainage-area 

boundaries from the Raster Seeding Method have a 

92 percent spatial correspondence to the boundaries from the 

NEM-without-WBD. DEM flow-path displacement artifacts 

in the Raster Seeding Method delineations contributed to the 

differences between the Raster Seeding Method and the 

NEM-without-WBD boundaries. 

The Thiessen Polygon Method achieved reasonable CAC 

results for the boundaries of the four streamgage drainage 

areas. The mean Thiessen Polygon Method normalized CAC 

score is 91.23. The highest normalized drainage-area error of 

3.68 percent occurred for streamgage 02186699; it is the highest error obtained for all the methods. 

Summary of Results for Seneca River

The results of the WBD Subwatershed boundary and 

streamgage drainage-area boundary comparisons for the 

NEM-with-WBD were useful in identifying an isolated 

network, WBD/NHD-flowline outlet mismatches, and NHDflowline outlet and streamgage location mismatches. The 

effects of the isolated network in the cumulative drainage-area 

analysis for the NEM-with-WBD were minimal at the outlet 

flowline and within the headwater Subwatershed in which the 

isolated network is located. 

The NEM-without-WBD provided the highest normalized 

CAC scores in the comparisons with WBD Subwatershed and 

streamgage drainage-area boundaries and the most accurate 

areas in the cumulative drainage-area analysis (after the NEMwith-WBD). NEM-without-WBD is the only other method 

besides NEM-with-WBD where no normalized CAC scores 

are less than 90. No major delineation errors were identified in 

the comparison between the NEM-without-WBD boundaries 

and the WBD boundaries. 

DEM flow-path displacement artifacts occurring in 

the Raster Seeding Method contributed to the delineation 

differences between the Raster Seeding Method and the 

NEM-without-WBD boundaries. The Raster Seeding Method 

is the third best method, using CAC analysis with the WBD 

Subwatersheds and streamgage drainage areas. The Raster 

Seeding Method has the highest mean cumulative drainagearea errors for the larger drainage-area size categories; most 

errors are attributed to the DEM flow-path displacement 

artifacts. The Raster Seeding Method also has the highest 

mean normalized Subwatershed polygon-area error and the 

highest polygon-area error of all the methods. DEM flowpath displacement related errors were most problematic 

in waterbodies. No major errors were identified in the 

streamgage drainage-area comparisons; however, DEM flowpath displacement errors were observed. 

The Thiessen Polygon Method was more accurate for 

this Subbasin than for the other study Subbasins. The mean 

normalized CAC score is 85.1 for the WBD comparison and 

91.23 for the streamgage analysis. The Thiessen Polygon 

Method has the highest mean cumulative drainage-area error 

at just 2.94 percent. Thiessen Polygon cumulative drainagearea errors are highest in the two smaller drainage-area size 

categories shown in table 1–4. The highest mean error, 

6.18 percent, was observed for the Thiessen Polygon Method 

for drainage areas less than 20 mi2 in size. In the streamgage 

analysis, the Thiessen Polygon Method has the highest normalized drainage-area error of all the methods at 3.68 percent. 

Pine River, MN (07010105)

Comparison of Method Boundaries with 

WBD Boundaries

Draft WBD Subwatershed boundaries for the Pine 

River Subbasin, MN (fig. 1–10), which were delineated to 

the 12-digit hydrologic unit level, were used in the CAC and 

cumulative drainage-area analyses. Twenty-eight WBD boundaries were used in the CAC analysis; results are shown in 

figure 1–11 and table 1–5. Cumulative drainage-area convergence analysis results are summarized in table 1–6. A graph 

developed as part of the convergence analysis, displaying the 

distribution of drainage-area errors is shown in figure 1–12.

New England Method with WBD (NEM-with-WBD)

WBD/NHD-flowline outlet mismatches and other NHD 

issues contributed to the lowering of the CAC scores (before 

normalizing to 100) of the NEM-with-WBD. NHD issues 

include three isolated stream networks, an improper NHD flow 

direction, and an NHD stream incorrectly crossing a WBD 

divide. WBD/NHD-flowline outlet mismatches, along with the 

other NHD issues, also led to errors in the cumulative drainage-area convergence analysis results shown in table 1–6. 

Three isolated NHD stream networks account for the 

majority of the cumulative drainage-area error computed for 

the outlet flowline of the Subbasin. The three isolated stream 

network drainage areas were not included in the catchment 

drainage-area accumulation for the outlet flowline of the 

Subbasin, thereby introducing an error of 0.61 percent. 

The drainage areas of the three isolated networks are 2.6, 1.8, 

and 0.4 mi2 in size, totaling 4.8 mi2. One isolated network, 
60 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

0 5 10 MILES 2.5

0 5 10 KILOMETERS 2.5

Minnesota

Base from 1:100,000-scale National Hydrography Dataset, 2003

EXPLANATION

4622312

4622312

4622310

4621962

4621480

4621996

4621548

4621966

4621968

4622016

4621530 4621532

4622326

4622062 4622060

4621610

4622056

4622254

4622064

4617824

4617482

4617892

4617782

4621406 4621954

4621448

4621484

4622352

4622350

94°40' 94°20' 94°

46°40'

47°

Albers Conic Equal-Area ProjectionCentral Meridian: -96°00'00"1st Standard Parallel: 29°30'00"2nd Standard Parallel: 45°30'00"Latitude of Origin: 23°00'00"Horizontal Datum: NAD83

Watershed Boundary Dataset (WBD) Subwatersheds 

Waterbodies on the network

Subbasin boundary 

National Hydrography Dataset (NHD) flowlines

NHD outlet flowline assigned to WBDboundary and common identifier (ComID)Artificial path; ConnectorStream/RiverNon-connected flowline

Figure 1–10. The draft Watershed Boundary Dataset (WBD) Subwatershed boundaries, and National Hydrography Dataset (NHD) flowlines, Pine River Subbasin, MN. (The location of this Subbasin is shown in figure 15.)
Pine River, MN (07010105) 61

Figure 1–11. Normalized Coefficient of Areal Correspondence (CAC) scores, by National Hydrography Dataset (NHD) flowline 

common identifier, for all methods tested, Pine River Subbasin, MN.

0

10

20

30

40

50

60

70

80

90

100 4621406

462196246214484621966462196846177824621954462235246178924621480462153046220164621532461748246220564617824462199646215484622326462161046220604622064462225446220624621484462231246223104622350

New England Method with WBD

New England Method without WBD

Raster Seeding Method

Thiessen Polygon Method

NATIONAL HYDROGRAPHY DATASET (NHD) FLOWLINE COMMON IDENTIFIERS (ComIDs)

NORMALIZED CAC SCORE

Table 1–5. Mean normalized Coefficient of Areal Correspondence score by delineation methods for Watershed Boundary 

Dataset Subwatersheds in the Pine River Subbasin, MN.

[CAC, Coefficient of Areal Correspondence; NEM, New England Method; WBD, Watershed Boundary Dataset]

Method Mean normalized 

CAC

Normalized CACs greater than 90 Normalized CACs less than 80

Number of 

Subwatersheds

Percentage of 

Subwatersheds

Number of 

Subwatersheds

Percentage of 

Subwatersheds

NEM-with-WBD 100.0 28 100 0 0

NEM-without-WBD 89.1 14 50 4 14

Raster Seeding Method 81.7 11 39 7 25

Thiessen Polygon Method 66.3 0 0 27 96
62 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Table 1–6. Mean cumulative drainage-area errors for all delineation methods for various drainage-area sizes, Pine River 

Subbasin, MN.

[mi2, square miles; NEM, New England Method; WBD, Watershed Boundary Dataset]

Method 

(40 units total)

Mean drainage-area error, in percent

Drainage-area size category

All drainage areas Less than 20 mi2 20–60 mi2 Greater than 

60–390 mi2

Greater than 

390 mi2

At Subbasin 

outlet 780 mi2

NEM-with-WBD 2.29 2.99 3.86 1.59 0.69 0.61

NEM-without-WBD 4.84 10.10 8.13 2.37 0.52 0.40

Raster Seeding Method 11.32 14.90 24.79 4.13 3.46 3.91

Thiessen Polygon Method 13.69 28.76 19.14 9.07 1.73 2.02

-100

-80

-60

-40

-20

0

20

40

60

0 100 200 300 400 500 600 700 800 900

WATERSHED BOUNDARY DATASET (WBD) CUMULATIVE DRAINAGE AREA, IN SQUARE MILES

DRAINAGE-AREA PERCENT ERROR

New England Method without WBD

New England Method with WBD

Raster Seeding Method

Thiessen Polygon Method

Figure 1–12. Drainage-area percent error in relation to Watershed Boundary Dataset cumulative drainage areas, for all methods 

tested, Pine River Subbasin, MN.
Pine River, MN (07010105) 63

located within a headwater WBD Subwatershed, caused a 

10.6 percent cumulative drainage-area error for that Subwatershed. An improper NHD flow relationship in the flowline 

network caused cumulative drainage-area errors of as much as 

17.38 percent. 

New England Method without WBD (NEM-without-WBD)

The mean normalized CAC score for the NEM-withoutWBD was 89.1, the highest score after NEM-with-WBD 

(table 1–5). Data show that 14 of the 28 NEM-without-WBD 

boundaries (50 percent) have normalized CAC scores greater 

than 90 (fig. 1–11 and table 5), the highest normalized CAC 

scores after the NEM-with-WBD. Just four boundaries, or 

14 percent, have normalized CAC scores less than 80 (the 

lowest after NEM-with-WBD). The four lowest normalized 

CAC scores for the NEM-without-WBD are 67.2, 75.6, 78.7, 

and 79.6. The NEM-without-WBD had the smallest mean 

normalized polygon-area error, after the NEM-with-WBD, 

of 5.7 percent, compared to 15.44 and 21.95 percent for the 

Raster Seeding and Thiessen Polygon Methods. 

Results of the cumulative drainage-area analysis summarized in table 1–6 show that the NEM-without-WBD provided 

the most accurate drainage areas (after NEM-with-WBD) for 

all drainage-area size categories. The NEM-without-WBD 

was the only method besides NEM-with-WBD that produced 

drainage-area errors of less than 1 percent for drainage areas 

greater than 390 mi2. 

The WBD Subwatershed data provided a more accurate 

boundary for the compared boundary of the NEM-withoutWBD, which has the lowest normalized CAC score for its 

method, at 67.2. The NEM-without-WBD boundary and the 

corresponding WBD boundary are shown in figure 1–13. The 

most noticeable areas of difference are shown in figure 1–13A, 

indicated by the colored point symbols inside each area in 

error. The colors designate which delineation method provided 

more accurate results. A 4-mi2 area draining into a wetland 

was the area with the most obvious difference. Information 

from the DRG and DOQ for this area confirms that the WBD 

inclusion of this wetland and its associated drainage area 

is correct (fig. 1–13B). The DEM-based delineation of the 

NEM-without-WBD improperly assigns the wetland-drainage 

area to an adjacent flowline. A smaller wetland-drainage area 

(0.2 mi2) was incorrectly included in the NEM-without-WBD 

boundary (fig. 1–13B). The NEM-without-WBD delineation 

also was wrong for another wetland drainage area identified 

in figure 1–13C. Several additional boundary discrepancies 

affected much smaller areas; however, using the DRG and 

DOQ, it was not possible to determine which method provided 

the most accurate boundaries. This Subwatershed also has the 

highest cumulative drainage-area error of the NEM-withoutWBD at 29.02 percent.

The second lowest normalized CAC score for the NEMwithout-WBD is 75.6. The WBD Subwatershed boundary and 

the NEM-without-WBD boundary are shown in figure 1–14A. 

The contour information depicted on the DRGs was difficult to 

interpret when determining which delineation was correct for 

the largest area of difference, 4.7 mi2. The second largest area 

of difference is the same 4-mi2 area identified in figure 1–13 

of the adjacent Subwatershed. Again, the WBD delineation 

provided the more accurate boundary delineation. The third 

largest area of difference is a 0.7-mi2 wetland area that was 

incorrectly included in the NEM-without-WBD delineation. 

Information from the DRG and DOQ depicted in figure 

1–14B shows that the WBD boundary is correct. The wetland 

drainage area included in the NEM-without-WBD boundary 

clearly drains to the downstream adjacent Subwatershed. 

Several other delineation differences between the WBD and 

NEM-without-WBD affect much smaller areas. In many cases, 

it was not possible on the basis of the limited detail of the 

contours to determine which method is more accurate. In other 

areas of less significance, the WBD Subwatershed provided 

a more accurate boundary, based on the contour information 

of the DRGs. In one case, the areas of difference canceled 

each other out, resulting in a normalized polygon-area error 

of only 0.95 percent; however, the effects of these delineation 

differences are reflected in the cumulative drainage-area 

analysis with an error of 7.88 percent for this 55-mi2

drainage area.

The NEM-without-WBD area with the third lowest 

normalized CAC score of 78.7 (fig. 1–15) has a normalized 

polygon-area error of 17.5 percent. The largest area of 

difference is a 1.94-mi2 drainage area for Downey Lake 

(fig. 1–15B). The NEM-without-WBD boundary does not 

include the lake or its drainage area, whereas the WBD 

boundary does. On the basis of the limited information 

available for the Downey Lake site, a determination of which 

boundary is more accurate could not be made. Information 

from the DRGs indicates that no streams are connected to 

the lake, which would provide an indication of outlet flow 

direction. Two wetlands abut the lake, but no determination 

could be made of the primary drainage for these wetlands. The 

second largest area of difference is a 1.45-mi2 wetland area 

(shown in figure 1–15C), which was omitted from the NEMwithout-WBD boundary. The WBD boundary for this wetland 

is correct on the basis of the DRG and DOQ information. 

The most accurate boundaries for other areas with differences 

could not be established because of limited or complex 

contour detail. For other areas where a determination could be 

made, the WBD provided the most accurate delineation. 

The NEM-without-WBD boundary with the fourth lowest 

score has a normalized CAC score of 79.6. The largest area of 

difference (approximately 6 mi2) between the NEM-withoutWBD and WBD boundaries occurred for the Subwatershed 

that represents the drainage area for Pelican Lake (fig. 1–16). 

Drainage areas for three adjacent lakes to the east are in question. The WBD boundary does not include the lakes, whereas 

the NEM-without-WBD boundary does. The 1:24,000-scale 

DRGs do not show any outlet drainage for these lakes, and 

therefore, no definitive conclusion about which delineation is 

more accurate could be made. It does appear, however, that 

the manual delineation of the WBD uses a road grade as a 
64 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

National Hydrography Dataset (NHD) flowline

NEM-without-WBD boundary

A

B

C

Error in 

NEM-without-WBD

boundary at

this wetland

Error in 

NEM-without-WBD

boundary at this

wetland 

WBD boundary 

delineations 

appear to be correct

Coefficient of Areal Correspondence (CAC) (normalized)

Difference in area between datasets, in square miles (mi2) 

Correct delineation could not be determined

Area of commission in error (WBD)

Area of omission in error (NEM-without-WBD)

0.2 mi2

4.0 mi2

0.5 mi2

4.0 mi2

EXPLANATION

CAC = 67.2

CAC

Watershed Boundary Dataset (WBD) boundary

Figure 1–13. (A) Watershed Boundary Dataset (WBD) and New England Method without WBD (NEM-without-WBD) 

boundaries, and (B) and (C) areas of detail showing boundary differences at wetlands, Pine River Subbasin, MN. (The 

location of this WBD boundary is shown in figure 1–10.)
Pine River, MN (07010105) 65

CAC = 75.6

NEM-without-WBD boundary

Area of omission/commission in error (NEM-without-WBD)

Correct delineation could not be determined

EXPLANATION

4.7 mi2

0.7 mi2

4.0 mi2

0.35 mi2

4.0 mi2 Difference in area between datasets, in square miles (mi2)

Area is shown

in figure 1-13 B.

CAC Coefficient of Areal Correspondence (CAC) (normalized)

A

B

National Hydrography Dataset (NHD) flowline

Watershed Boundary Dataset (WBD) boundary

Figure 1–14. (A) Watershed Boundary Dataset (WBD) and New England Method without WBD (NEM-without-WBD) 

boundaries, (B) area of detail where the boundaries differ overlaid on a Digital Raster Graphic, and (C) area in detail with 

boundary error overlaid on a Digital Orthophoto Quadrangle, Pine River Subbasin, MN. (The location of this WBD boundary is 

shown in figure 1–10.)
66 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Figure 1–15. (A) Watershed Boundary Dataset (WBD) and New England Method without WBD (NEM-without-WBD) boundaries, 

(B) area of detail, showing boundary differences at Downey Lake, and (C) area of detail, showing boundary differences at a wetland, 

Pine River Subbasin, MN. (The location of this WBD boundary is shown in figure 1–10.)

Watershed Boundary Dataset (WBD) boundary

National Hydrography Dataset (NHD) flowline

NEM-without-WBD boundary

Area of omission/commission in error (NEM-without-WBD)

Correct delineation could not be determined

EXPLANATION

This catchment area

assigned to

upstream

WBD unit 

1.45 mi2

1.94 mi2 0.82 mi2

0.17 mi2

0.13 mi2

0.10 mi2

1.94 mi2 Difference in area between datasets, in square miles (mi2)

CAC = 78.7

Drain for 

Downey Lake

is unknown

Road

NEM-without-WBD

error in closure at 

this wetland 

B C

A

CAC Coefficient of Areal Correspondence (CAC) (normalized)
Pine River, MN (07010105) 67

Watershed Boundary Dataset (WBD) boundary

Raster Seeding Method boundary

EXPLANATION

Lake

CAC = 0.5

Pelican Lake

National Hydrography Dataset (NHD) flowline

CAC = 14.6

CDAE = 93.7

CDAE = 99.5

CDAE

CAC Coefficient of Areal 

Correspondence (CAC) (normalized)

Cumulative drainage-area error, 

in percent

Figure 1–16. Watershed Boundary Dataset (WBD) and the Raster Seeding Method boundaries for the two Subwatersheds 

with the lowest normalized Coefficient of Areal Correspondence (CAC) scores, Pine River Subbasin, MN. (The locations of 

these WBD boundaries are shown in figure 1–10.)
68 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

divide to separate these lakes in this area of flat relief. The 

cumulative drainage-area error for this 28-mi2 drainage area is 

22.92 percent, the second highest error for this method in the 

cumulative drainage-area analysis.

Overall, it appears that the WBD data enhanced the delineations when used with the NEM-with-WBD. The Subbasin 

is mostly an area of low relief with many lakes and wetland 

areas where delineations based on USGS 30-m DEM data tend 

to be less accurate.

Raster Seeding Method

The mean normalized CAC score for the Raster Seeding 

Method was 81.7. Two normalized CAC scores greater than 

100 are linked to DEM flow-path displacement at the outlet 

flowline and WBD/NHD-flowline outlet mismatch. Eleven 

of the 28 boundaries compared (39 percent) have normalized 

CAC scores greater than 90, and 7 boundaries (25 percent) 

have a normalized CAC score less than 80. The seven normalized CAC scores less than 80 are 0.5, 14.6, 62.4, 71.14, 74.28, 

77.09, and 79.65. 

In the WBD comparison, the mean normalized polygonarea error for the Raster Seeding Method is 15.44 percent, a 

distant third in percentage following the NEM-without-WBD 

error of 5.70 percent. The Raster Seeding Method has the 

highest error, 99.5 percent, compared with the errors from the 

New England and Thiessen Polygon Methods.

The two boundaries with the lowest Raster Seeding 

Method normalized CAC scores of 0.5 and 14.6 also have 

the highest errors in the cumulative drainage-area analysis. 

Both of these Raster Seeding Method boundaries (shown in 

figure 1–16) had parallel-to-stream boundaries from DEM 

flow-path displacement that led to extreme errors in the Raster 

Seeding Method results. Most of the flowlines within these 

two boundaries are artificial flow paths or streams located 

in relatively flat terrain. The parallel stream effect is greatly 

increased because of the flat surface of the lake or terrain 

in the DEM. The Raster Seeding Method boundaries for 

the NHD flowlines in these flat areas resemble a 30-meter 

buffer surrounding the NHD flowlines, as opposed to correct 

catchment delineations. For the Pelican Lake area, the true 

drainage area is 27.96 mi2, not the 0.14 mi2 area produced by 

the Raster Seeding Method, a cumulative drainage-area error 

of 99.5 percent. Pelican Lake drains to Pelican Brook. The 

Pelican Brook Subwatershed has the second lowest normalized 

Raster Seeding Method CAC score, 14.6, and displays similar 

parallel stream effects for many of its flowlines. The true 

accumulated drainage area for Pelican Brook, which includes 

the Pelican Lake drainage area, is 47.7 mi2, not the 3 mi2 area 

produced by the Raster Seeding Method, a drainage-area error 

of 93.65 percent. 

One WBD Subwatershed downstream from Pelican 

Brook contains the outlet flowline for the entire Pine River 

Subbasin. At the outlet, the accumulation of upstream 

contributing drainage area totals 780 mi2. The Raster Seeding 

Method drainage area for the same outlet flowline is 749 mi2, 

yielding a 31-mi2 difference and a cumulative drainage-area 

error of 3.9 percent.

The Subwatershed boundary with the third lowest normalized CAC score for the Raster Seeding Method, 62.4, also 

has the lowest NEM-without-WBD score, 67.2. The Raster 

Seeding Method area shares the same delineation differences as the NEM-without-WBD area (see figure 1–13) with 

additional errors introduced by DEM flow-path displacement. 

Compared with the NEM-without-WBD, the WBD boundary 

provided the more accurate delineation. This boundary has 

the fifth highest cumulative drainage-area error for the Raster 

Seeding Method at 27.36 percent. 

The primary delineation error observed for the boundary 

with the fourth lowest normalized CAC score (71.14) for 

the Raster Seeding Method could have been avoided in 

the Raster Seeding Method production process. The error 

involves an area of approximately 13.6 mi2 outside the Pine 

River Subbasin that was assigned as an area contributing to a 

headwater flowline in the Pine River Subbasin. If the flowlines 

for the adjacent Subbasin had been used in the Raster Seeding 

Method process as boundary constraints, then the error for 

this area would have been reduced substantially. The NEMwithout-WBD and the Thiessen Polygon Method incorporated 

adjacent flowlines in their catchment delineation process and, 

therefore, did not yield this type of error. Smaller errors 

from DEM flow-path displacement also were observed for 

this boundary. 

The area with the fifth lowest normalized CAC score for 

the Raster Seeding Method, 74.28, is also the area with the 

second lowest normalized CAC score for the NEM-withoutWBD, 75.6. The Raster Seeding Method boundary has the 

same delineation differences as the NEM-without-WBD 

(see figure 1–14) with additional errors introduced by DEM 

flow-path displacement. 

DEM flow-path displacement contributed substantially to 

the sixth lowest normalized CAC score for the Raster Seeding 

Method, 77.09. The NEM-without-WBD score for this same 

boundary is 91.0. The boundary is a headwater Subwatershed 

with a true drainage area of 14.7 mi2. The drainage area of 

the Raster Seeding Method boundary is 12.3 mi2 with a 

15.9 percent cumulative drainage-area error. The drainagearea error for the NEM-without-WBD for this area is just 

0.49 percent and for the Thiessen Polygon Method, 

33.20 percent. DEM flow-path displacement also affected the 

seventh lowest Raster Seeding Method normalized CAC score, 

79.65 (85.69 for NEM-without-WBD). 

Raster Seeding Method catchment boundaries in the 

Pine River Subbasin have a 38 percent correspondence to 

the catchment boundaries of the NEM-without-WBD, the 

lowest correspondence of all the study Subbasins. Differences 

between the catchment boundaries from the NEM-withoutWBD and Raster Seeding Method are mostly the result of 

DEM flow-path displacement errors that occur with the Raster 

Seeding Method. 
Pine River, MN (07010105) 69

DEM flow-path displacement errors in the Raster Seeding Method also caused inaccurate results in the cumulative 

drainage-area convergence analysis (table 1–6). If the parallel 

stream artifact errors of DEM flow-path displacement had 

not occurred in the two boundaries shown in figure 1–16, 

results of the cumulative drainage-area analysis would have 

been improved. By removing the two boundaries with the 

highest cumulative drainage-area errors, the mean error for 

all drainage-area sizes would be 7 percent instead of 

11.32 percent; the mean error for drainage areas 20 to 60 mi2

in size would be 8.84 percent instead of 24.79 percent. The 

Raster Seeding Method had the highest mean error in this 

category. DEM-flow-path displacement errors, though not as 

great a problem as seen in figure 1–16, contributed 32 percent to the mean error shown for the Raster Seeding Method 

in the smallest drainage-area size category of the cumulative 

drainage-area results (table 1–6). 

Thiessen Polygon Method

The mean normalized CAC score for the Thiessen 

Polygon Method is 66.3. No normalized CAC scores are 

greater than 90. Twenty-seven of the 28 Thiessen Polygon 

Method boundaries (96 percent), have normalized CAC scores 

less than 80. The Theissen Polygon Method produced the 

highest mean normalized polygon-area error, 21.95 percent, in 

the WBD Subwatershed comparison, compared to 15.4, 5.7, 

and 0 percent for the Raster Seeding Method, NEM-withoutWBD, and NEM-with-WBD, respectively. 

Thiessen Polygon Method boundaries tested in the 

cumulative drainage-area analysis have a mean drainage-area 

error for all drainage-area sizes of 13.69 percent, the highest 

mean error of all the methods. The Thiessen Polygon Method 

also has the highest mean error of all the methods for drainage 

areas less than 20 mi2 in size, 28.76 percent, and for drainage areas greater than 60 to 390 mi2

 in size, 9.70 percent. A 

complete summary of the results of the cumulative drainagearea analysis for the Thiessen Polygon Method is provided in 

table 1–6. The Thiessen Polygon Method produced reasonably

small errors, about 2 percent or less, for drainage areas greater 

than 390 mi2. 

Comparison of Methods with Streamgage Data

Verification data for two streamgage drainage-areas 

were obtained for the Pine River Subbasin (fig. 1–17). The 

delineations from the WBD data were compared to the GIS 

verification drainage-area boundaries for both streamgages. 

The delineations are the same, except for the areas near the 

streamgage locations. 

The streamgage drainage-area verification measurements 

differed between the NWIS and GIS data. The NWIS drainage-area measurement for the streamgage on Pine River near 

Pine River, MN (05229450), is 261 mi2, and the GIS measurement is 269.54 mi2

, a 3 percent difference. Because the NWIS 

drainage-area measurement probably was based upon older 

delineation methods and source maps, the NWIS drainage area 

is most likely less accurate than the GIS measurement. NWIS 

did not contain a drainage-area measurement for streamgage 

05229430 on Hoblin Creek near Pine River, MN; the GIS 

measurement is 1.03 mi2. 

Imperfect CAC scores (less than 100) were obtained for 

the comparison between the two streamgage drainage-area 

boundaries and the NEM-with-WBD boundaries. For each 

drainage area, the CAC score can be linked to the location 

of the streamgage in relation to the matched NHD-flowline 

outlet. The streamgage on Pine River is located 8 percent 

of the way up the length of the flowline, resulting in a CAC 

score of 98.18. The streamgage on Hoblin Creek is 85 percent 

of the way up the length of the flowline, resulting in a CAC 

score of only 15.65. The CAC scores of the NEM-with-WBD 

were used to normalize CACs from the other methods in order 

to adjust for the streamgage location/NHD-flowline outlet 

mismatch error. 

The mean normalized CAC score for the NEM-withoutWBD is 98.69. For the streamgage on Pine River near Pine 

River, MN, the CAC score is 97.63. No major differences 

were observed between the NEM-without-WBD boundary 

and the streamgage drainage-area boundary. The verification 

boundary provided the more accurate delineation for the 

streamgage on Hoblin Creek. 

The Raster Seeding Method delineation for the Pine 

River streamgage is nearly identical to the NEM-withoutWBD delineation in most areas. A boundary running parallel 

to the flowline that the streamgage is located on was observed 

in the Raster Seeding Method. At 97.51, the normalized 

Raster Seeding Method CAC score for the drainage area for 

the streamgage on Pine River is a close second to NEMwithout-WBD (97.63). 

The normalized Raster Seeding Method CAC score for 

the streamgage on Hoblin Creek is 207.03. This high CAC 

score resulted from an error introduced by DEM flow-path 

displacement and streamgage location mismatch with the 

assigned flowline (see figure 1–17). The verification boundary 

provided the more accurate delineation for the area of discrepancy (same as in the NEM-without-WBD). 

The Thiessen Polygon Method produced the lowest normalized CAC score for the Pine River streamgage (05229450), 

87.91. The Thiessen Polygon Method also has the highest 

cumulative drainage-area error, compared to the other methods, for the streamgage at Pine River, 7.72 percent. The drainage-area error for this streamgage for NEM-without-WBD is 

0.82 percent and the Raster Seeding Method, 0.58 percent. 

The streamgage location/NHD-flowline outlet mismatch made it difficult to quantify the Thiessen Polygon 

Method results for the small drainage area associated with 

the streamgage at Hoblin Creek (05229430). Visual review of 

the Thiessen Polygon Method delineation for this streamgage 

determined that the other methods provided more accurate 

boundary delineations and associated drainage-area statistics.
70 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Figure 1–17. Location of streamgages and associated drainage areas used as verification datasets, Pine River Subbasin, MN. 

(The location of this Subbasin is shown in figure 15.)

94°40' 94°20' 94° 93°40'

46°40'

47°

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

EXPLANATION

Subbasin and

boundary

Waterbodies on 

the network

National Hydrography Dataset (NHD) 

flowlines

Artificial path; Connector

Stream/River

Non-connected flowline

NHD outlet flowline assigned to 

streamgage

Streamgage and identifier

05229450

05229450

05229430

Streamgage

drainage areas

Minnesota

Base from 1:100,000-scale National Hydrography Dataset, 2003

Albers Conic Equal-Area Projection

Central Meridian: -96°00'00"

1st Standard Parallel: 29°30'00"

2nd Standard Parallel: 45°30'00"

Latitude of Origin: 23°00'00"

Horizontal Datum: NAD83
South Platte Headwaters, CO (10190001) 71

Summary of Results for Pine River

The NEM-with-WBD CAC comparative analysis 

revealed errors related to WBD/NHD-flowline outlet mismatches and NHD issues, which had similar effects on all the 

methods. Three isolated NHD stream networks were identified. The effects of the isolated stream networks on the total 

drainage area for the Pine River Subbasin outlet flowline was 

considered minimal with a 0.61 percent cumulative drainagearea error. An isolated network within a headwater WBD 

Subwatershed boundary caused a 10.6 percent drainage-area 

error. An improper NHD flow relationship affected cumulative 

drainage-area analysis results for three Subwatersheds with 

errors as great as 17.38 percent. 

The normalized CAC scores show that the NEMwithout-WBD provided the most accurate results after the 

NEM-with-WBD. The mean normalized CAC score for the 

NEM-without-WBD is 89.1 in the WBD comparison analysis 

and 98.7 in the streamgage analysis. Four boundaries have 

normalized CAC scores less than 80. The lowest normalized 

CAC score for this method indicates that the WBD boundary 

is correct and that the DEM-derived boundary from the 

NEM-without-WBD is in error. Many noticeable differences 

in delineations favored the WBD boundary, yet other 

differences were undeterminable because of the limited or 

complex contour detail depicted on the DRGs. The NEMwithout-WBD also provided the second lowest error in the 

cumulative drainage-area analysis with a mean error of 

4.84 percent for all drainage-area sizes tested. 

For the Raster Seeding Method, the mean normalized 

CAC score in the WBD analysis was 81.7. Only 38 percent of 

the catchment delineations from the Raster Seeding Method 

correspond to the catchments from the NEM-without-WBD. 

Most of the delineation differences for the Raster Seeding 

Method are the result of errors associated with DEM flowpath displacement. For all seven boundaries with the lowest 

normalized Raster Seeding Method CAC scores, parallel 

stream boundary artifacts from DEM flow-path displacement 

had negligible effects. Parallel stream artifacts were especially 

problematic for two WBD Subwatershed boundaries encompassing lakes and flat terrain; in these cases, the delineations 

resembled 30-m buffer zones around the NHD flowlines. The 

normalized Raster Seeding Method CAC scores for the two 

Subwatersheds are 0.15 and 14.3. The cumulative drainagearea errors for these two Subwatersheds are 99 and 93 percent. 

These values skew the results of the Raster Seeding Method 

and make it the least accurate method in the cumulative 

drainage-area analysis for drainage areas of 20 to 60 mi2 and 

greater than 390 mi2. Parallel stream artifacts, though not 

causing as great a problem as those mentioned above, also 

contributed to higher errors for other boundaries in the results 

of the cumulative drainage-area analysis. For the streamgage 

analysis, one streamgage has a normalized CAC score of 97.5, 

whereas the normalized CAC score for the other streamgage is 

207, which is explained by DEM flow-path displacement and 

the streamgage location mismatch with the flowline outlet. 

In the CAC analysis with WBD, the Thiessen Polygon 

Method provided the least accurate results with a mean 

normalized CAC score of 66.3. No normalized CAC scores 

greater than 90 resulted from this method; 96 percent of the 

Thiessen Polygon boundaries resulted in a CAC score of less 

than 80. The Thiessen Polygon Method had the highest mean 

normalized polygon-area error at 21.95 percent with the WBD 

comparisons. The Thiessen Polygon Method also produced the 

highest mean cumulative drainage-area error of 13.69 percent 

and the highest mean drainage-area error of 28.76 percent for 

drainage areas less than 20 mi2. In this method, the largest 

drainage areas (greater than 390 mi2) had fairly small errors, 

2.02 percent or less. 

South Platte Headwaters, CO (10190001)

Comparison of Method Boundaries with 

WBD Boundaries

Draft WBD Subwatershed boundaries in the South Platte 

Headwaters Subbasin (fig. 1–18), delineated to the 12-digit 

hydrologic unit level, were obtained and used in the CAC 

and cumulative drainage-area analyses. Fifty-five WBD 

Subwatershed boundaries were used in the CAC analysis; 

results are shown in figure 1–19 and table 1–7. Results of 

the cumulative drainage-area convergence analyses are 

summarized in table 1–8. A graph developed as part of the 

convergence analysis displaying the drainage-area errors for 

each method is shown in figure 1–20. 

New England Method with WBD (NEM-with-WBD)

WBD/NHD-flowline outlet mismatches, two isolated 

NHD stream networks, and NHD flowlines crossing WBD 

boundaries contributed to the lowering of the CAC scores 

(before normalizing to 100) of the NEM-with-WBD. The 

lowest CAC score of the NEM-with-WBD is 50.3 for a 

catchment-sized boundary in the draft WBD with an area of 

0.65 mi2. (Certified WBD data would not include such a small 

area as found in this draft WBD data.) For this area, the NHD 

stream crosses the WBD boundary at a point where the WBD 

boundary runs parallel and close to the hydrography depicted 

on the 1:24,000-scale DRGs. The 1:100,000-scale NHD 

flowline is shifted slightly from the hydrography on the DRGs 

and actually meanders across the WBD divide, causing the 

delineation to extend beyond the divide. Both New England 

Methods and the Thiessen Polygon Method included areas 

extending beyond the WBD divide. 
72 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Albers Conic Equal-Area Projection

Central Meridian: -96°00'00"

1st Standard Parallel: 29°30'00"

2nd Standard Parallel: 45°30'00"

Latitude of Origin: 23°00'00"

Horizontal Datum: NAD83

106° 105°30'

39°

39°30'

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

EXPLANATION

National Hydrography Dataset (NHD) 

flowlines

Artificial path; Canal/Ditch;

Connector

Stream/River

Non-connected flowline

NHD outlet flowline assigned to 

WBD boundary and common

identifier (ComID)

4622312

Colorado

Base from 1:100,000-scale National Hydrography Dataset, 2003

5239458

5239466

5239500

5240418

5239510

5239520

5239516

5239560

5239562

5240430

5239626 5239682

5239664

5240512

5239674

5239732

5239856 5239864

5239914

5239872

5241086

5241232 5241914

5241892

5241902

5242120

5241238

5241184 5241272

5241192

5240492 5240142

5241116

5242092

5241206

5242018

5241094

5241082

5240034

5240540

5239966

5239964

5239862

5239002

5239048

5239008 5239006

5239828

5239826

5239654

5239656

5239614

5238936

5238912

5238914

Subbasin boundary 

Waterbodies on 

the network

Watershed Boundary 

Dataset (WBD) 

Subwatersheds

Figure 1–18. The draft Watershed Boundary Dataset (WBD) Subwatershed boundaries, and National Hydrography Dataset (NHD) 

flowlines, South Platte Headwaters Subbasin, CO. (The location of this Subbasin is shown in figure 15.)
South Platte Headwaters, CO (10190001) 73

Figure 1–19. Normalized Coefficient of Areal Correspondence (CAC) scores, by National Hydrography Dataset (NHD) flowline 

common identifier, for all methods tested, South Platte Headwaters Subbasin, CO.

0

10

20

30

40

50

60

70

80

90

100

5239466523945852395165239510523891252396145239826523891452396545239520523950052395625239656524041852395605238936524043052405125239964523986252396745239828523962652396825239966523900252396645239856524118452401425239008523973252410825239006524123852398645239914523904852400345240492523987252405405241094524201852410865241206524111652421205241902524189252412725241192524123252420925241914

NATIONAL HYDROGRAPHY DATASET FLOWLINE COMMON IDENTIFIERS (ComIDs)

NORMALIZED CAC SCORE

New England Method with WBD

New England Method without WBD

Raster Seeding Method

Thiessen Polygon Method

off chart (164.6)

Table 1–7. Mean normalized Coefficient of Areal Correspondence score by delineation methods for Watershed Boundary Dataset 

Subwatersheds in the South Platte Headwaters Subbasin, CO.

[CAC, Coefficient of Areal Correspondence; NEM, New England Method; WBD, Watershed Boundary Dataset]

Method Mean normalized 

CAC

Normalized CACs greater than 90 Normalized CACs less than 80

Number of 

Subwatersheds

Percentage of 

Subwatersheds

Number of 

Subwatersheds

Percentage of 

Subwatersheds

NEM-with-WBD 100.0 55 100 0 0

NEM-without-WBD 94.7 49 89 3 5

Raster Seeding Method 95.6 49 89 3 5

Thiessen Polygon Method 74.7 0 0 35 64
74 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

-100

-80

-60

-40

-20

0

20

40

60

0 50 100 150 200 250 300 350 400 450 500

WATERSHED BOUNDARY DATASET (WBD) CUMULATIVE DRAINAGE AREA, IN SQUARE MILES

DRAINAGE-AREA PERCENT ERROR

New England Method without WBD

New England Method with WBD

Raster Seeding Method

Thiessen Polygon Method

Table 1–8. Mean cumulative drainage-area errors for all delineation methods for various drainage-area sizes, South Platte 

Headwaters Subbasin, CO.

[mi2, square miles; NEM, New England Method; WBD, Watershed Boundary Dataset]

Method 

(69 units total)

Mean cumulative drainage-area error, in percent

Drainage-area size category

All drainage areas Less than 20 mi2 20–60 mi2 Greater than

60–390 mi2

Greater than 

390 mi2

At Subbasin 

outlet 1,605 mi2

NEM-with-WBD 1.71 0.16 3.54 1.07 0.69 0.72

NEM-without-WBD 1.97 1.57 3.99 1.43 0.60 0.63

Raster Seeding Method 1.99 1.04 4.02 1.31 0.78 0.72

Thiessen Polygon Method 8.66 15.64 11.05 5.53 1.76 1.32

Figure 1–20. Drainage-area percent error in relation to Watershed Boundary Dataset cumulative drainage areas, for all methods 

tested, South Platte Headwaters Subbasin, CO.
South Platte Headwaters, CO (10190001) 75

There were numerous places where NHD flowlines 

crossed the WBD divides. Based on a review of the DRGs, in 

many cases, the NHD is correct and the draft WBD divides 

are in error. Some of the lowest CAC scores of the NEM-withWBD occurred where these flowlines cross the divides. In one 

case, a connector flowline in the NHD crossed a WBD divide 

and connected with a stream located in the adjacent WBD 

Subwatershed. The affected boundaries have CAC scores of 

76.0 and 61.3 with cumulative drainage-area errors of 22.71 

and 38.39 percent. 

The Subbasin had two isolated NHD stream networks 

with delineated areas totaling 11.39 mi2. The NEM-with-WBD 

CAC scores of the two affected WBD boundaries are 83.6 

and 82.1 with normalized polygon-area errors of 7.06 and 

14.58 percent. The effects of the isolated networks on 

cumulative drainage area were minimal with an error of 

0.72 percent for the outlet of this 1,605-mi2 Subbasin. The 

effects of WBD/NHD-flowline outlet mismatches were 

minimal as most WBD Subwatershed boundary outlets 

matched reasonably well with the confluences in the NHD.

New England Method without WBD (NEM-without-WBD) 

The mean normalized CAC score for the NEM-withoutWBD is 94.7. Forty-nine of the 55 WBD boundaries 

(89 percent) have normalized CAC scores greater than 

90 (table 1–7). Only three normalized CAC scores fall below 

80 (5 percent) with values of 58.0, 72.2, and 79.9. NEMwithout-WBD produced the second smallest mean normalized 

polygon-area error of 2.74 percent; the Raster Seeding Method 

error is 3.7 percent; and the Thiessen Polygon Method error is 

12.9 percent. 

The NEM-without-WBD produced mean cumulative 

drainage-area results similar to those of the NEM-with-WBD 

and Raster Seeding Method. The mean drainage-area error 

for the NEM-without-WBD is 1.97 percent; for the NEMwith-WBD, 1.71 percent; and for the Raster Seeding Method, 

1.99 percent (table 1–8). The mean cumulative drainage-area 

errors for the various drainage-area size categories are similar 

among the two New England Methods and the Raster Seeding Method. The mean cumulative drainage-area errors for 

the NEM-without-WBD were not substantial, especially if the 

errors introduced by isolated networks and other NHD-related 

issues were removed from the analysis. 

The lowest normalized CAC score for the NEM-withoutWBD, 58.0, was calculated for the WBD Subwatershed for 

the Antero Reservoir, which had the highest normalized 

polygon-area error of 49.96 percent. Several delineated areas 

that differ between the Antero Reservoir WBD boundary 

and the corresponding boundary of the NEM-without-WBD 

are shown in figure 1–21. Because of limited information 

on the DRGs or DOQs, the correct delineation for the 

largest area of difference, approximately 9.3 mi2, could not 

be determined. Most of the 9.3-mi2 area is associated with 

an NHD flowline that is not connected to the network, and 

therefore, the associated area has actually been assigned to 

another NHD flowline. Like the NHD, the non-networked 

stream segment, as depicted on the DRG, ends abruptly. At 

the stream termination ending point, the land surface appears 

flat on the DRGs, making it difficult to determine the direction 

of flow past the downstream end of the flowline. The WBD 

delineation for Antero Reservoir does not include the drainage 

area associated with the non-networked flowline, whereas the 

NEM-without-WBD delineation does. 

The next greatest difference in an area for the WBD 

boundary shown in figure 1–21A is 1.8 mi2. Information 

shown on the DOQ for this area indicates that the draft WBD 

divide shown in figure 1–21B is incorrect. For other area 

differences of 1.0 and 0.3 mi2, the WBD data provide a more 

accurate delineation over the NEM-without-WBD. For other 

smaller areas of difference, a determination could not be made 

on the basis of limited contour detail depicted on the DRGs as 

to which method was more accurate. 

The cumulative drainage-area error is 3.3 percent for the 

Subwatershed boundary produced by the NEM-without-WBD, 

which has a WBD cumulative drainage area of 191 mi2

(fig. 1–21A). The 9.3-mi2 area of difference (shown in 

figure 1–21A) was the major contributor of the cumulative 

drainage-area error. An isolated stream network upstream from 

the WBD Subwatershed canceled out some of the error. If the 

2.7-mi2 area associated with the isolated network had been 

included in the cumulative drainage area, the error would have 

been 4.4 percent. 

The 9.3-mi2 delineation area of difference shown in 

figure 1–21A is largely responsible for lowering the CAC 

score for the adjacent boundary. The adjacent boundary has the 

second lowest normalized CAC score of 72.2 and the second 

highest normalized polygon-area error of 20.17 percent. Other 

delineation differences were observed elsewhere for this WBD 

boundary, but none was as significant as the 9.3-mi2 area. 

For many areas, the WBD was correct, whereas the NEMwithout-WBD was more accurate in other areas. The NEMwithout-WBD cumulative drainage-area error for this WBD 

Subwatershed is 1.25 percent. If the effects of an isolated 

stream network were removed, the cumulative drainage-area 

error would be 0.58 percent. 

The third lowest normalized CAC score, 79.9, was determined for a NEM-without-WBD boundary located north of, 

and adjacent to, the WBD boundary shown in figure 1–21A. 

This boundary also has the third highest NEM-without-WBD 

normalized polygon-area error at 18.27 percent. Five distinct 

areas with delineation differences were observed between the 

WBD and NEM-without-WBD boundaries. For the largest 

area of difference, the 1.8-mi2 area shown in figures 1–21A 

and B, the NEM-without-WBD provided the more accurate 

boundary. For this Subwatershed, with an actual drainage area 

of 122 mi2, the NEM-without-WBD cumulative drainage-area 

error is 5.08 percent. An isolated stream network contributed 

2.2 percent of the error. 
76 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Figure 1–21. (A) The Watershed Boundary Dataset (WBD) and the New England Method without WBD (NEM-without-WBD) 

boundaries for the Antero Reservoir Subwatershed and (B) area of detail showing boundary differences overlaid on the Digital 

Orthophoto Quadrangle (DOQ), South Platte Headwaters Subbasin, CO. (The location of this WBD boundary is shown in figure 1–18.)

Antero 

Reservoir

National Hydrography Dataset (NHD) flowline 

CAC = 58.0

9.3 mi2

0.3 mi2

1.0 mi2

0.2 mi2

1.8 mi2

Incorrect 

WBD boundary 

B

A

Watershed Boundary Dataset (WBD) boundary

NEM-without-WBD boundary

Area of omission in error using NEM-without-WBD 

Area of omission in error using WBD 

Correct delineation could not be determined 

Difference in area between datasets, in square miles (mi2)

NHD non-networked flowline 

CAC Coefficient of Areal Correspondence (CAC) (normalized) 

EXPLANATION

1.0 mi2

Lake
South Platte Headwaters, CO (10190001) 77

Raster Seeding Method

The Raster Seeding Method has a mean normalized 

CAC score of 95.6. As observed in the NEM-without-WBD, 

89 percent of the Raster Seeding Method boundaries tested 

had normalized CAC scores greater than 90, with just three 

boundaries less than 80. Two of the boundaries had normalized CAC scores greater than 100, 164.6 and 102.6. The three 

lowest normalized CAC scores for the Raster Seeding Method 

are 36.2, 73.3, and 77.1. The cumulative drainage-area results 

for the Raster Seeding Method compared well with the results 

of the two New England Methods. The Raster Seeding Method 

mean cumulative drainage-area errors for all drainage-area 

size categories were not substantial. Catchment boundaries 

from the Raster Seeding Method have a 75-percent spatial 

correspondence with those from the NEM-without-WBD. 

The 0.65-mi2 catchment-sized WBD boundary, discussed 

previously in the NEM-with-WBD Method section, has a 

normalized Raster Seeding Method CAC score of 164.6. The 

error from DEM flow-path displacement in the Raster Seeding Method, by chance, actually provided the more accurate 

delineation for this WBD boundary. 

The boundary with the lowest normalized CAC score for 

the Raster Seeding Method, 36.2, is the same corresponding 

boundary of the NEM-without-WBD shown in figure 1–21A. 

The 1.8-mi2 area of difference shown in figure 1–21 occurs 

for the Raster Seeding Method boundary as well. Once again, 

for this 1.8-mi2 area, the DEM delineation provided the more 

accurate boundary. The area with the most substantial area 

of difference between the Raster Seeding Method and WBD 

boundaries was a direct result of DEM flow-path displacement. The catchment boundary delineation errors due to DEM 

flow-path displacement are shown in figure 1–22.

The Raster Seeding normalized polygon-area percent 

error for the Antero Reservoir Subwatershed is 43.32 percent. 

For this Subwatershed, the Raster Seeding Method has the 

highest cumulative drainage-area error at 8.48 percent, compared to 1.62 percent for the NEM-with-WBD, 3.03 percent 

for the NEM-without-WBD, and 2.63 percent for the Thiessen 

Polygon Method. If a 4.2-mi2 area associated with an isolated 

NHD flowline had been included in the cumulative drainage 

area for the reservoir, the Raster Seeding Method cumulative 

drainage-area error would have been 6.26 percent. 

A Subwatershed adjacent to the Antero Reservoir Subwatershed (fig. 1–22) has the second lowest normalized Raster 

Seeding Method CAC score of 73.3. This boundary also has 

the second lowest normalized NEM-without-WBD CAC score 

of 72.2. In the Raster Seeding Method boundary, the same 

parallel-to-stream boundary error, caused by DEM flow-path 

displacement, for an artificial path flowline within the Antero 

Reservoir (fig. 1–22) served as a major error. Other delineation errors due to DEM flow-path displacement were observed 

throughout the Subwatershed. Many differences between the 

Raster Seeding Method and WBD boundaries were identical 

to those observed in the NEM-without-WBD boundary. The 

Raster Seeding Method cumulative drainage-area error for the 

boundary is 1.63 percent. If the effects of an isolated stream 

network were removed, the cumulative area in error would 

have been 0.58 percent. 

The boundary with the third lowest normalized CAC 

score (77.1) for the Raster Seeding Method also is adjacent to 

the Antero Reservoir Subwatershed (fig. 1–22). This boundary also has the third lowest normalized CAC score for the 

NEM-without-WBD (79.9). Some of the differences between 

the Raster Seeding Method boundary and the WBD boundary 

were the same as those observed for the NEM-without-WBD 

boundary, including the 1.8-mi2 area identified in figure 1–21. 

Additional Raster Seeding Method errors due to DEM flowpath displacement were observed here. 

Thiessen Polygon Method

The mean normalized CAC for the Thiessen Polygon 

Method is 74.7, the lowest score of all the methods. Thiessen 

Polygon was the only method for which none (0 percent) of 

the boundaries has a normalized CAC score greater than 

90. The Thiessen Polygon Method also has the highest 

percentage of boundaries (64 percent) with normalized CAC 

scores less than 80. For NEM-without-WBD and the Raster 

Seeding Method, just 5 percent of the boundaries have 

scores less than 80. The Thiessen Polygon Method also has 

the highest normalized polygon-area error of 12.87 percent, 

compared with 3.70 percent for the Raster Seeding Method 

and 2.74 percent for NEM-without-WBD. 

The Thiessen Polygon Method has the highest mean 

cumulative drainage-area error at 8.66 percent, and the 

highest mean errors for all the various drainage-area size 

categories shown in table 1–8. Cumulative drainage-area 

errors are especially high for the smaller drainage-area size 

categories. For drainage areas less than 20 mi2 in size, the 

Thiessen Polygon Method mean error is 15.64 percent, greatly 

surpassing the mean errors of the other methods. Errors also 

are high for drainage areas 20 to 60 mi2 in size, with a mean 

error at 11.05 percent.

Comparison of Methods with Streamgage Data

For the streamgage comparative analysis, only published 

drainage-area measurements from the USGS NWIS database 

were used as verification. No streamgage drainage-area boundaries were available at the time of the study. From NWIS, 

15 streamgages were selected for the analysis (fig. 1–23). 

Drainage-area measurements for the streamgages range from 

12 to 1,084 mi2. Mean cumulative drainage-area errors, in 

percent, are summarized in table 1–9. 

NEM-with-WBD, the presumed most accurate delineation method, had drainage-area error contributions from NHDrelated artifacts. NHD artifacts include isolated networks and 

NHD flowlines crossing the streamgage drainage divides. 

Many of the streamgages were located upstream to the outlet 

of the assigned NHD flowline, introducing some errors from 

these artifacts. Cumulative drainage-area errors also could be 
78 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Figure 1–22. The Watershed Boundary Dataset (WBD) Subwatersheds and Raster Seeding Method boundaries with 

normalized Coefficient of Areal Correspondence (CAC) scores and digital elevation model (DEM) flow-path displacement 

boundary errors, South Platte Headwaters Subbasin, CO. (The location of this area is shown in figure 1–18.)

CAC = 36.2

CAC = 73.3

CAC = 88.4

CAC = 97.0

CAC = 77.1

Antero

 Reservoir

National Hydrography 

Dataset (NHD) flowline

Raster Seeding Method boundary 

 

Waterbodies

WBD Subwatersheds

DEM flow-path displacement

boundary error

EXPLANATION

Coefficient of Areal 

Correspondence (CAC) (normalized) CAC
South Platte Headwaters, CO (10190001) 79

Figure 1–23. Location of streamgages used as verification data, South Platte Headwaters, CO. (The location of this Subbasin is 

shown in figure 15.)

106° 105°30'

39°

39°30'

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

Albers Conic Equal-Area Projection

Central Meridian: -96°00'00"

1st Standard Parallel: 29°30'00"

2nd Standard Parallel: 45°30'00"

Latitude of Origin: 23°00'00"

Horizontal Datum: NAD83

Colorado

Base from 1:100,000-scale National Hydrography Dataset, 2003

EXPLANATION

Waterbodies on 

the network

Subbasin and boundary

National Hydrography Dataset (NHD) 

flowlines

Artificial path; Connector

Stream/River

Non-connected flowline

NHD outlet flowline assigned to 

to streamgage

Streamgage and identifier

06699005

06699005

06698500 06697100

06698000

06697450

06696980

06693800

06693980

06694700

06694400

06694100

06695000

06696000

06696200

06699500
80 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

the result of differences in the way the drainage areas were 

computed for NWIS. As discussed in the “Testing the Catchment Delineation Methods” section of the report, the sources 

of the NWIS drainage-area estimates are unknown. The three 

topographic-based delineation methods (New England Methods and Raster Seeding Method) have similar mean NWIS 

drainage-area error results for most of the drainage-area size 

categories shown in table 1–9. 

The Thiessen Polygon Method cumulative drainage areas 

have the highest mean drainage-area error of all the methods, 

6.41 percent. The mean Thiessen Polygon Method drainagearea error for small drainages (less than 20 mi2

) is 18.5 percent; other methods have errors of less than 5 percent. 

Summary of Results for South Platte Headwaters

For the evaluation of the South Platte Headwaters 

Subbasin, 55 draft WBD Subwatersheds were used for 

verification in the CAC analysis. Cumulative drainage-area 

errors also were derived using published drainage-area values 

for 15 streamgages obtained from the NWIS database. 

Several source data factors affected the analysis. Two 

isolated stream networks with a total associated drainage area 

of 11.39 mi2 had minimal effects on the drainage area at many 

downstream Subwatersheds and at the outlet of the Subbasin. 

NHD flowlines crossing divides in the WBD Subwatershed 

data also were observed. In some cases, the NHD flowlines 

meandered across the WBD divides in error, whereas in other 

cases the draft WBD delineations at these intersections were 

in error. 

The New England Methods and the Raster Seeding 

Method provided similar results—having high spatial correspondence with the WBD and acceptable drainage-area errors 

for various drainage-area size categories. For the NEM-without-WBD and Raster Seeding Method, only three boundaries 

for each method (5 percent) have normalized CAC scores 

less than 80, and they are the same units in each of the two 

methods. The catchment delineations from the Raster Seeding Method have a 75 percent spatial correspondence with the 

catchments from the NEM-with-WBD.

The Subwatershed for the Antero Reservoir had the 

lowest NEM-without-WBD and Raster Seeding Method 

CAC scores. A determination could not be made as to which 

method (WBD or NEM-without-WBD) provided the more 

accurate boundary for the largest area (9.3 mi2) of difference 

between the datasets. The Raster Seeding Method boundary is 

definitely in error for this same location, as severe parallel-tostream boundary delineations occurred at artificial path NHD 

flowlines located within the Antero Reservoir. Other parallelto-stream boundary delineation errors from DEM flow-path 

displacement were observed throughout the Subbasin in the 

Raster Seeding Method boundaries. 

The Thiessen Polygon Method, as expected, had the 

lowest spatial correspondence with the WBD Subwatershed 

boundaries as indicated by the CAC analysis. The Thiessen 

Polygon Method is the only method in which no individual 

boundaries have a normalized CAC score greater than 90. 

The Thiessen Polygon Method has the highest number of 

boundaries (64 percent) with normalized CAC scores less 

than 80. The method also produced the highest normalized 

polygon-area error in the WBD comparison analysis. In 

Table 1–9. Mean drainage-area errors for all delineation methods (except the Outlet Matching Method), for the National Water 

Information System (NWIS) streamgages, grouped by various drainage-area sizes, South Platte Headwaters, CO.

[mi2, square miles; NEM, New England Method; WBD, Watershed Boundary Dataset]

Method 

(15 streamgages total)

Mean drainage-area error, in percent

Drainage-area size category

All drainage areas Less than 20 mi2 20–60 mi2 Greater than 60–390 mi2 Greater than 390 mi2

NEM-with-WBD 2.62 4.12 3.93 4.17 0.66

NEM-without-WBD 2.68 4.93 3.94 2.27 0.55

Raster Seeding Method 2.48 4.46 3.45 2.09 0.76

Thiessen Polygon Method 6.41 18.50 2.28 5.25 1.88
Pine Valley, Utah (16020302) 81

the WBD and NWIS streamgage cumulative drainage-area 

analysis, the Thiessen Polygon Method boundaries had the 

highest mean drainage-area errors. The Thiessen Polygon 

Method produced especially high errors for drainage areas 

less than 20 mi2 in size. 

Pine Valley, Utah (16020302)

No streamgage data were available for the Pine Valley 

Subbasin; therefore, the comparative analysis for this Subbasin 

entails the use of the draft WBD only. For this Subbasin, 

available 1:24,000-scale draft WBD Subwatershed boundaries, 

delineated to the 12-digit hydrologic unit level (fig. 1–24), 

were used in the CAC and cumulative drainage-area analyses. 

Nine WBD boundaries were used in the CAC analysis, the 

results of which are shown in figure 1–25 and table 1–10. 

Mean cumulative drainage-area errors derived from the 

WBD data are summarized in table 1–11. The results of the 

convergence analysis, in which drainage-area errors were 

plotted for all methods tested, are shown in figure 1–26. No 

cumulative drainage areas met the largest drainage size criteria 

in the summary results. No outlet for the Subbasin exists; it 

is a closed system with all streams in the Subbasin draining 

toward a salt flat called the Pine Valley Hardpan. 

New England Method with WBD (NEM-with-WBD)

WBD/NHD-flowline outlet mismatches and an isolated 

NHD stream contributed to the lowering of the CAC scores 

(before normalizing to 100) of the NEM-with-WBD. Two 

NHD flowlines were assigned incorrectly to the WBD Subwatershed boundaries, causing some of the mismatch errors. 

The effects of an isolated NHD stream on the results 

of the CAC and drainage-area analyses were minimal. The 

omitted catchment area (0.17 mi2) associated with the isolated 

flowline contributed to a cumulative drainage-area error of just 

0.26 percent. The CAC score of 96.8 for the Subwatershed 

with the isolated stream was also affected by errors from a 

WBD/NHD-flowline outlet mismatch. A WBD/NHD-flowline 

outlet mismatch in another Subwatershed is responsible for a 

CAC score of 76.7, and a cumulative drainage-area error of 

28.98 percent. 

New England Method without WBD (NEM-without-WBD)

The mean normalized CAC score for the NEM-withoutWBD is 95.9, indicating a high spatial correspondence to the 

WBD. All boundaries compared have normalized CAC scores 

greater than 90. The NEM-without-WBD has the second lowest (after NEM-with-WBD) mean normalized polygon-area 

error of 1.1 percent. No normalized polygon-area errors are 

greater than 2 percent. For the Raster Seeding Method, the 

highest normalized area in error is 7.8 percent, and for the 

Thiessen Polygon Method, 32.07 percent. 

The differences in delineations were minor among the 

WBD Subwatersheds and the corresponding boundaries of the 

NEM-without-WBD. On the basis of topographic information 

from the DRGs, the WBD provided the more accurate delineations in the places where there were differences.

In the cumulative drainage-area analysis, the NEMwithout-WBD has a mean error of 3.95 percent. The mean 

cumulative drainage-area error for drainage areas less than 

20 mi2 in size is 16.85; this is attributed mostly to a WBD/

NHD-flowline outlet mismatch at one Subwatershed. 

Raster Seeding Method

The Raster Seeding Method also had a high spatial 

correspondence with the WBD boundaries, with a mean 

normalized CAC score of 96.9. As observed for the two 

New England Methods, all the Raster Seeding Method 

boundaries have normalized CAC scores greater than 90. The 

mean normalized polygon-area error for the Raster Seeding 

Method is 2.61 percent, the third highest mean error after the 

two New England Methods at 0 percent (NEM-with-WBD) 

and 1.1 percent (NEM-without-WBD). 

The mean Raster Seeding Method drainage-area error is 

2.98 percent, the NEM-with-WBD is 3.38 percent, and NEMwithout-WBD is 3.95 percent. For the Raster Seeding Method, 

some of the drainage-area errors were artificially skewed in a 

positive direction as a result of DEM flow-path displacement 

errors at the outlet flowline where WBD/NHD-flowline outlet 

mismatches occurred. Overall, the Raster Seeding Method 

produced good drainage-area delineations tracking closely to 

those of the New England Methods.

Thiessen Polygon Method

The Thiessen Polygon Method produced boundaries that 

had, as expected, the least spatial correspondence to the areas 

of the WBD Subwatershed boundaries with a mean normalized CAC score of 77.7. Unlike the other methods, for which 

100 percent of the boundaries have normalized CAC scores 

greater than 90, the Thiessen Polygon Method has none. 

Forty-four percent of the Thiessen Polygon boundaries have 

normalized CAC scores of less than 80. The Thiessen Polygon 

Method has the highest mean normalized polygon-area error 

of 10.04 percent and the highest normalized polygon-area 

error of 32.07 percent.

The Thiessen Polygon Method also gave the least accurate results in terms of delineated drainage area. In the cumulative drainage-area analysis, the Thiessen Polygon Method 

has the highest mean error at 10.49 percent (about 3 percent of 

that is due to WBD/NHD-flowline outlet mismatches) and the 

highest mean errors for all drainage-area size categories tested. 

Errors are especially high for drainage areas less than 60 mi2

in size (table 1–11).
82 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Playa–Pine Valley Hardpan

EXPLANATION

National Hydrography Dataset (NHD) 

flowlines

Connector

Stream/River

Non-connected flowline

NHD outlet flowline assigned 

to WBD boundary and 

common identifier (ComID)

WBD Subwatersheds

114° 113°40'

38°20'

38°40'

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

Albers Conic Equal-Area Projection

Central Meridian: -96°00'00"

1st Standard Parallel: 29°30'00"

2nd Standard Parallel: 45°30'00"

Latitude of Origin: 23°00'00"

Horizontal Datum: NAD83

Utah

Pine Valley

Hardpan

10402645

10402645

10403233

10402681

10402841

10402843

10402657

10402885

10403255

10402925

Base from 1:100,000-scale National Hydrography Dataset, 2003

Subbasin and boundary

Figure 1–24. The draft Watershed Boundary Dataset (WBD) Subwatershed boundaries, and National Hydrography 

Dataset (NHD) flowlines, Pine Valley, Utah. (The location of this Subbasin is shown in figure 15.)
Pine Valley, Utah (16020302) 83

Figure 1–25. Normalized Coefficient of Areal Correspondence (CAC) scores, by National Hydrography Dataset (NHD) flowline 

common identifier, for all methods tested, Pine Valley Subbasin, Utah.

0

10

20

30

40

50

60

70

80

90

100 10402657

1040264510403233104026811040284110402843104028851040325510402925

NATIONAL HYDROGRAPHY DATASET FLOWLINE COMMON IDENTIFIERS (ComIDs)

NORMALIZED CAC SCORE

New England Method with WBD

New England Method without WBD

Raster Seeding Method

Thiessen Polygon Method

Table 1–10. Mean normalized Coefficient of Areal Correspondence scores by delineation method for Watershed Boundary Dataset 

Subwatersheds in the Pine Valley Subbasin, Utah.

[CAC, Coefficient of Areal Correspondence; NEM, New England Method; WBD, Watershed Boundary Dataset]

Method Mean normalized 

CAC

Normalized CACs greater than 90 Normalized CACs less than 80

Number of 

Subwatersheds

Percentage of 

Subwatersheds

Number of 

Subwatersheds

Percentage of 

Subwatersheds

NEM-with-WBD 100.0 9 100 0 0

NEM-without-WBD 95.9 9 100 0 0

Raster Seeding Method 96.9 9 100 0 0

Thiessen Polygon Method 77.7 0 0 4 44
84 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Figure 1–26. Drainage-area percent error in relation to Watershed Boundary Dataset cumulative drainage areas, for all methods 

tested, Pine Valley Subbasin, Utah.

Table 1–11. Mean cumulative drainage-area errors for all delineation methods for various drainage-area sizes, Pine Valley 

Subbasin, Utah.

[mi2, square miles; NEM, New England Method; WBD, Watershed Boundary Dataset; na, not applicable]

Method 

(10 units total)

Mean cumulative drainage-area error, in percent

Drainage-area size category

All drainage areas Less than 20 mi2 20–60 mi2 Greater than 

60–390 mi2

Greater than 

390 mi2

At Subbasin outlet 

(closed system)

NEM-with-WBD 3.38 14.90 1.46 0.31 na na

NEM-without-WBD 3.95 16.85 1.81 0.49 na na

Raster Seeding Method 2.98 13.28 1.27 0.22 na na

Thiessen Polygon Method 10.49 36.16 8.94 1.46 na na

-20

-10

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

WATERSHED BOUNDARY DATASET (WBD) CUMULATIVE DRAINAGE AREA, IN SQUARE MILES

DRAINAGE-AREA PERCENT ERROR

New England Method without WBD

New England Method with WBD

Raster Seeding Method

Thiessen Polygon Method
Willapa Bay, WA (171001106) 85

Willapa Bay, WA (17100106)

No draft WBD data were available for the Willapa Bay 

Subbasin; therefore, the comparative analysis for this Subbasin 

entails the use of the streamgage drainage-area boundaries 

and NWIS drainage-areas measurements. Twelve streamgage 

drainage-area boundaries were obtained for the evaluation. 

Published drainage-area measurements from the NWIS 

database also were obtained for the 12 streamgages. The 

streamgage drainage areas, shown in figure 1–27, range 

in size from 3.97 to 219 mi2. 

After detailed review of the verification streamgage 

drainage-area boundaries with the DEM-based delineations of 

the New England Methods and the Raster Seeding Method, it 

became apparent that the verification data were not completely 

accurate. The boundaries from the verification dataset, 

confirmed with the DRGs, provided less accurate delineations 

where differences were observed than were obtained for 

the other study areas. The delineation differences were not 

substantial, but where differences were noticeable, the DEM 

based-delineations were more accurate. Also, the verification 

boundaries from the streamgage data did not edgematch 

correctly with each other, further calling their accuracy 

into question. 

The CAC scores could not be normalized for this 

Subbasin because no versions of the WBD were available 

to produce NEM-with-WBD. The CAC scores for the 

streamgages computed for the NEM-without-WBD, Raster 

Seeding Method, and Thiessen Polygon Method, are listed in 

table 1–12 and plotted in figure 1–28. Drainage-area percent 

errors for the methods are listed in table 1–13 and plotted in 

figure 1–29. 

The NEM-without-WBD and Raster Seeding Method 

provided the most accurate boundaries. The mean CAC score 

of 94.41 for NEM-without-WBD is slightly higher than that 

for the Raster Seeding Method, 94.37. Where delineation 

differences were observed, the DEM-based delineations of the 

NEM-without-WBD surpassed the quality of the verification 

data. CAC scores less than 90 and high polygon-area errors 

for the NEM-without-WBD and Raster Seeding Method 

are directly related to NHD flowline and streamgage 

location mismatches. 

The Raster Seeding Method also provided excellent 

delineations, which have a 94-percent spatial correspondence 

with the streamgage drainage boundaries of the NEM-withoutWBD. DEM flow-path displacement errors, inherent with the 

Raster Seeding Method, are the direct cause for the delineation 

differences with the NEM-without-WBD. The areas in error 

from DEM flow-path displacement are not substantial in this 

study Subbasin, as indicated by the results in table 1–13. 

The Thiessen Polygon Method delineations provided the 

least accurate results of the methods, with many CAC scores 

less than 90 (see table 1–12). The Thiessen Polygon Method 

has the highest mean drainage-area in error at 8.82 percent, 

compared to NEM-without-WBD with 4.45 percent and Raster 

Seeding Method with 4.44 percent. Excluding streamgages 

with substantial locational mismatches with the flowline 

outlet, the Thiessen Polygon Method has the highest single 

drainage-area percent error at 22.19 percent for streamgage 

12010700, compared to 0.33 percent and 0.08 percent for the 

NEM-without-WBD and Raster Seeding Method, respectively. 
86 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

124°20' 124° 123°40'

46°20'

46°40'

47°

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

EXPLANATION

Subbasin and 

boundary 

(1:250,000-scale)

National Hydrography Dataset (NHD) 

flowlines

Artificial path; Connector

Stream/River

Non-connected flowline

NHD outlet flowline assigned 

to streamgage

Waterbodies on 

the network

Streamgage 

drainage

areas

Streamgage and identifier

12017000

12017000

12015100

12015500

12013500

12014500

12011500

12012000

12011200

12011000

12010000

12010500 12010700

Washington

Pacific Ocean

Willapa Bay

Albers Conic Equal-Area Projection

Central Meridian: -96°00'00"

1st Standard Parallel: 29°30'00"

2nd Standard Parallel: 45°30'00"

Latitude of Origin: 23°00'00"

Horizontal Datum: NAD83

Base from 1:100,000-scale National Hydrography Dataset, 2003

Ocean or estuary

Figure 1–27. Location of streamgages and associated drainage areas used as verification datasets, Willapa Bay, WA. 

(The location of this Subbasin is shown in figure 15.)
Willapa Bay, WA (171001106) 87

60

65

70

75

80

85

90

95

100

120100001201050012010700120110001201120012011500120120001201350012014500120151001201550012017000

STREAMGAGE IDENTIFIER

COMPUTED CAC SCORES

New England Method without WBD

Raster Seeding Method

Thiessen Polygon Method

Figure 1–28. The computed Coefficient of Areal Correspondence (CAC) scores (not normalized), by streamgage, for the New 

England Method without Watershed Boundary Dataset (NEM-without-WBD), Raster Seeding Method, and Thiessen Polygon 

Method, Willapa Bay Subbasin, WA.

Table 1–12. Coefficient of Areal Correspondence scores for the New England Method without 

Watershed Boundary Dataset (NEM-without-WBD), Raster Seeding Method, and Thiessen Polygon 

Method, for streamgage drainage-areas, Willapa Bay Subbasin, WA. 

[ID, Identifier; NHD, National Hydrography Dataset; NEM, New England Method; WBD, Watershed Boundary Dataset; 

ComID, Common identifier; CAC, Coefficient of Areal Correspondence]

 Station ID NHD flowline 

ComID

NEM-without-WBD 

CAC

Raster Seeding Method 

CAC

Thiessen Polygon Method 

CAC

12010000 23864404 97.98 97.59 91.37

12010500 23864390 86.12 86.21 75.76

12010700 23865092 98.53 98.29 75.45

12011000 23864488 79.87 79.67 76.31

12011200 23864504 98.22 98.22 81.90

12011500 23864670 97.12 97.17 89.36

12012000 23864656 96.98 97.07 81.82

12013500 23864616 97.90 98.10 93.25

12014500 23864588 94.07 93.87 87.46

12015100 23865380 94.51 93.98 75.50

12015500 23864888 93.44 94.10 85.57

12017000 23864810 98.20 98.19 93.78

Mean CAC 94.41 94.37 83.96
88 Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset

Figure 1–29. Drainage-area percent error in relation to streamgage drainage areas of the verification data for the New England 

Method without Watershed Boundary Dataset (NEM-without-WBD), Raster Seeding Method and Thiessen Polygon Method, Willapa 

Bay Subbasin, WA.

-10

-5

0

5

10

15

20

25

4.0 9.5 16.7 17.9 18.1 20.3 27.8 29.7 41.8 54.9 129.9 218.3

STREAMGAGE DRAINAGE AREA, IN SQUARE MILES

DRAINAGE-AREA PERCENT ERROR

New England Method without WBD

Raster Seeding Method

Thiessen Polygon Method

Table 1–13. Streamgage drainage-areas of verification data, drainage-area percent errors, and mean errors for the 

New England Method without Watershed Boundary Dataset, Raster Seeding Method, and Thiessen Polygon Method, 

Willapa Bay, WA. 

[ID, identifier; mi2, square miles; GIS, geographic information systems; NEM, New England Method; WBD, Watershed Boundary Dataset]

Station ID

Streamgaging station 

drainage area 

(mi2) (from GIS data)

Drainage-area percent error

 NEM-without-WBD Raster Seeding Method Thiessen Polygon Method

12015100 3.97 4.17 4.74 20.92

12011200 9.45 0.01 0.14 8.55

12010500 16.73 10.40 10.16 8.91

12010700 17.89 0.33 0.08 22.19

12011000 18.11 23.21 23.57 16.24

12012000 20.28 1.10 0.95 4.94

12014500 27.80 4.14 4.22 4.36

12015500 29.75 5.49 4.77 12.68

12011500 41.76 1.57 1.56 4.86

12010000 54.90 0.57 0.86 0.84

12013500 129.88 1.28 1.08 0.72

12017000 218.29 1.12 1.12 0.59

Mean error 4.45 4.44 8.82
Prepared by the Pembroke Publishing Service Center.

For more information concerning this report, contact:

Director

U.S. Geological Survey

New Hampshire-Vermont Water Science Center

331 Commerce Way, Suite 2

Pembroke, NH 03275

dc_nh@usgs.gov

or visit our Web site at:

http://nh.water.usgs.gov
Johnston and others—Evaluation of Catchment Delineation Methods for the Medium-Resolution National Hydrography Dataset—Scientific Investigations Report 2009–5233