National Water Quality Program

UFINCH—A Method for Simulating Unit and Daily Flows 

in Networks of Channels Described by NHDPlus Using 

Continuous Flow Data at USGS Streamgage

Scientific Investigations Report 2016–5074

U.S. Department of the Interior

U.S. Geological Survey
Cover figure. Main graphical user interface (MainGUI) for UFINCH.
UFINCH—A Method for Simulating Unit 

and Daily Flows in Networks of Channels 

Described by NHDPlus Using Continuous 

Flow Data at USGS Streamgages

By David J. Holtschlag

National Water Quality Program

Scientific Investigations Report 2016–5074

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

RYAN K. ZINKE, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2018

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as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Holtschlag, D.J., 2016, UFINCH—A method for simulating unit and daily flows in networks of channels described by 

NHDPlus using continuous flow data at U.S. Geological Survey streamgages: U.S. Geological Survey Scientific Investigations Report 2016–5074, 17 p., https://doi.org/10.3133/sir20165074.

ISSN 2328-0328 (online)
iii

Contents

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

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

Purpose and Scope .......................................................................................................................................2

Methodology...................................................................................................................................................2

Model Assumptions and Limitations .................................................................................................3

Software Installation............................................................................................................................4

Data Structure.......................................................................................................................................4

UFINCH Processing and Results.................................................................................................................6

Discussion.....................................................................................................................................................15

Summary........................................................................................................................................................16

Acknowledgments.......................................................................................................................................16

References Cited..........................................................................................................................................17

Figures

1. Map of two-digit NHDPlus Hydrologic Regions showing two-digit 

NHDPlus regions for the conterminous United States...........................................................5

2. Main graphical user interface (MainGUI) for UFINCH...........................................................6

3. RegionMapGUI for Hydrologic Region 07 Upper Mississippi showing 

names of hydrologic subregions, with subregion St. Croix selected...................................7

4. SubRegionMapGUI for Region 07 Upper Mississippi, Subregion 03 St. Croix, 

showing flowlines and streamgages.........................................................................................7

5. Hydrologic subregion 0703 with selected streamgage (05333500) St. Croix River 

near Danbury, Wisconsin, and upstream flow network identified.......................................8

6. Inventory of data at the selected streamgage (05333500) St. Croix River 

near Danbury, Wisconsin............................................................................................................9

7. Daily and interpolated 15-minute flows at streamgage (05333500) St. Croix River 

near Danbury, Wisconsin..........................................................................................................10

8. Hydrograph and plot of the empirical cumulative distribution function 

comparing measured and simulated flows at streamgage (0533500) 

St. Croix River near Danbury, Wisconsin................................................................................11

9. Hydrograph and plot of the empirical cumulative distribution function 

comparing measured with UFINCH simulated and statically adjusted flows at 

streamgage (05332500) Namekagon River near Trego, Wisconsin, based 

on measured flows at streamgage (0533500) St. Croix River near 

Danbury, Wisconsin ...................................................................................................................12

10. Example input dialog box for model documentation ............................................................13

11. Example unit flow output file following static adjustment...................................................14

12. Hydrograph and plot of the empirical cumulative distribution function 

comparing measured with UFINCH simulated and statically adjusted flows at 

streamgage (05331833) Namekagon River at Leonards, Wisconsin, based 

on measured flows at streamgage (0533500) St. Croix River near 

Danbury, Wisconsin ...................................................................................................................15
iv

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

cubic mile (mi3) 4.168 cubic kilometer (km3) 

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F – 32) / 1.8.

Abbreviations

AFINCH Analysis of Flows in Networks of Channels

ARMA autoregressive-moving average

ECDF Empirical Cumulative Distribution Function

HUC hydrologic unit code

LCLU land-cover land-use

MCR Matlab Compiler Runtime

MOVE Maintenance Of Variance Extension

NAWQA National Water-Quality Assessment Project

NHD National Hydrography Dataset

NHDPlus National Hydrography Dataset with value-added attributes

OLS ordinary least square

PRISM Parameter-elevation Regressions on Independent Slopes Model

R2 coefficient of determination

REG regression

RMSE root mean square error

RPN regression plus noise

UFINCH Unit Flows in Networks of CHannels

USGS U.S. Geological Survey
UFINCH—A Method for Simulating Unit and Daily Flows 

in Networks of Channels Described by NHDPlus Using 

Continuous Flow Data at USGS Streamgages

By David J. Holtschlag

Abstract

The Unit Flows In Networks of Channels (UFINCH) 

computer application can be used to simulate daily and unit 

flows in networks of streams based on geospatial data in the 

National Hydrography Dataset NHDPlus (with value added 

attributes), and U.S. Geological Survey daily streamflow data 

from a downstream (or base) streamgage. Among streamflow 

augmentation methods, UFINCH has the unique capability to 

estimate time series of flows from a single base (downstream) 

streamgage to many upstream reaches, while conserving flows 

within the basin. UFINCH also provides a simple statistical 

model to adjust simulated flows to better match continuous 

flows from data at an upstream streamgage. Parameters of 

the statistical model are estimated using overlapping periods 

of record at the two streamgages, but the adjustment can be 

applied to all years of record available at the base streamgage. 

This report describes the main features of UFINCH and 

presents results from a sample application. Interactive graphical user interfaces and automated geographical information 

processing facilitate flow-data retrievals and provide an intuitive environment for efficient and effective generation of flow 

information in a network. UFINCH is coded in the Matlab 

programming language and can be run in the Matlab programming environment, with supporting statistical, optimization, 

and mapping toolboxes, or from compiled code on a Microsoft 

Windows computer. 

Introduction

The U.S. Geological Survey (USGS) provides publically 

accessible streamflow information at numerous streamgages 

in the Nation. Each streamgaged site occurs within a drainage network of interconnected stream segments that receive 

surface runoff, interflow, and groundwater flow from upstream 

catchments. This system of catchments and stream segments 

transport water throughout the basin to the outlet. Without 

developing a continuous hydrologic process model, there is 

currently (2016) no simple method for estimating flows in a 

stream network at a unit or daily time step that conserves flow 

in a basin, is consistent with measured flows at the outlet, 

and provides incremental increases in flow between stream 

segments that is proportional to drainage area increments. 

Unit Flows In Networks of Channels (UFINCH) provides this 

capability to support hydrologic and ecologic studies requiring 

coherent, continuous flow information in a detailed stream 

network. 

In the medium resolution version (2) of the National 

Hydrography Dataset with value-added attributes (NHDPlus) 

system (McKay and others, 2015), drainage networks in the 

Nation have been discretized into approximately 4 million 

georeferenced catchments and stream segments; thus, each 

catchment has an average drainage area of about 1 square 

mile (mi2). Data in NHDPlus can be used to describe the connectivity between catchment areas and stream segments and 

among stream segments, specifies flow directions for stream 

segments, and estimates lengths and velocities in stream 

segments. Collectively, NHDPlus data provide a geospatial 

framework for simulating flows in all stream segments of a 

basin. This framework can be used to help compare or extend 

streamflow records at an individual upstream streamgage 

based on measured flows at a downstream streamgage. 

Hirsch (1982) compared four streamflow record extension techniques by use of Monte Carlo simulations. The 

four methods were ordinary least-squares regression (REG), 

regression plus noise (RPN), and two methods for Maintenance Of Variance Extension (MOVE) techniques (MOVE.1 

and MOVE.2), where MOVE.1 is equivalent to a method 

widely used in psychology and geomorphology that is sometimes referred to as the line of organic correlation (Hirsch, 

1982). Hirsch (1982) showed that MOVE.1 estimates were 

less biased and more accurate than REG and RPN, and that 

MOVE.2 estimates had marginally lower bias and higher accuracy than the MOVE.1 technique. MOVE.2 uses the same four 

parameters estimated in MOVE.1, but their estimation is based 

on more information (Hirsch, 1982). Where outliers may be 

present in the series, Khalil and Adamowski (2014) indicate 

that a robust version of the line of organic correlation may be 

preferable. In this report, MOVE refers generally to the family 

of Maintenance of Variance Estimators. 
2 UFINCH: Simulation of Unit Flows in Networks of Channels Described by NHDPlus

Streamflow record extension methods discussed by 

Hirsch (1982) have been used (Nielsen, 1999; Emerson, 2005) 

to estimate daily flows at a streamgage having a shorter period 

of record on the basis of daily values from a streamgage with a 

longer period of record. Unlike UFINCH, a MOVE estimator 

cannot be used to estimate flows for ungaged stream segments 

or provide consistent estimates of flow increments associated with increments in drainage area along a stream or flow 

network.

In contrast to MOVE as a one-to-one streamgage estimator, UFINCH is a one-to-many estimator, including ungaged 

sites, which is based on a drainage area ratio approach and on 

travel times described by NHDPlus attributes. The UFINCH 

approach provides flow information for all NHDPlus stream 

segments in a basin and conserves flow within a drainage 

network. In addition, simulated flows monotonically increase 

in proportion to increasing downstream drainage area. Where 

streamflow records are available for upstream segments, a 

simple statistical corrector can be applied to improve the fit 

between measured and simulated flows. This corrector can be 

applied to simulated flows outside the interval of measured 

flows at the target site. The extended series (measured plus 

UFINCH simulated and [or] corrected flows) at an upstream 

target site can be used in subsequent UFINCH applications 

to propagate flows further upstream in the network. Although 

UFINCH can be used to estimate flows in an upstream 

network of stream segments based on flows at a single base 

streamgage, upstream flow information can minimally be used 

to confirm basic assumptions underlying the UFINCH model 

and understand the uncertainty of simulated flows. 

Purpose and Scope

The purpose of UFINCH is to help extend unit and 

daily flow information in stream networks defined within the 

NHDPlus geospatial framework (McKay and others, 2015) 

by use of continuous flow information at USGS streamgages. 

Historically, the USGS has operated about 18,500 streamgages 

nationwide (Whal and others, 1995). Preliminary testing 

indicates that UFINCH may be most applicable for simulating unregulated, non-estuarial, flows in basins as large as 

3,000 mi2 in area. Simulated flows can be compared with 

and adjusted to better match measured flows at upstream 

streamgages within UFINCH. Adjusted flows have shown 

close comparisons to measured flows in subbasins that are as 

much as two orders of magnitude smaller than the basin being 

simulated. This report documents the capabilities and features 

of the UFINCH model for simulating unit and daily flows in 

networks of channels described by NHDPlus based on continuous flows at USGS streamgages.

Methodology

Streamflow monitored at streamgaged sites represents 

accumulated catchment runoff, including overland flow, 

interflow, or groundwater outflow, which has flowed downstream through a network of channels. As a first approximation, water yields from upstream catchments are assumed 

to be uniformly distributed across the streamgaged basin in 

a UFINCH analysis. Basin water yields, in feet per day, are 

computed as (runoff) streamgaged flow divided by drainage 

area. Basin water yields are distributed backward in time and 

applied to individual upstream catchments so that differences 

in travel times from catchments to the outlet are accounted for 

in the analysis. Travel times are proportional to average stream 

segment velocities and cumulative stream segment lengths (as 

defined in NHDPlus) from individual catchments to the outlet. 

To initiate a UFINCH analysis, a streamgage with continuous flow data is selected as the downstream terminus for 

a stream network of interest. This downstream streamgage at 

the basin outlet is referred to as the base streamgage, and is 

used to identify the upstream catchments and interconnected 

flowlines. Additional streamgages may be upstream in the 

network, and data from those streamgages provide a basis for 

comparing and adjusting simulated flows. Any streamgages 

upstream from the base streamgage may be referred to as target streamgages. Variations in flows at the base streamgage are 

expected to reflect variations in average water yields throughout the upstream basin. Particular exceptions to plausible 

selections of base streamgages are streamgages located on 

estuaries, those affected by significant water regulation, or on 

large drainage basins. 

A UFINCH analysis proceeds by retrieving daily streamflow values for the base streamgage. For USGS streamgages, 

an automated process has been developed for retrieving a data 

inventory from the water data website (waterdata.usgs.gov/

nwis/inventory/) and daily flows data from the water services 

website (waterservices.usgs.gov). The daily flow series are 

automatically interpolated to 15-minute (unit) value series and 

divided by drainage area at the base streamgage to form a timeseries of basin-wide-average water yields at unit (15-minute) 

time steps. Interpolated daily flows are used as the default for 

UFINCH simulations because unit flow variations often reflect 

effects of local factors that are not representative of fluctuations 

in water yields throughout the contributing basin. 

Historically daily flows, rather than unit flows, have 

been considered as the primary flow record; thus, unit flows 

have not been the focus of quality control to the extent that 

daily flows have been. In addition, unit flows are commonly 

unavailable for periods of missing (stage) record, or for periods when flows are ice affected. Flows are interpolated using 

“shape-preserving piecewise cubic interpolation” (http://www.

mathworks.com/help/matlab/ref/interp1.html, accessed July 

29, 2015) referred to as “pchip” interpolation in Matlab (The 

MathWorks, Inc., 2015a). This type of interpolation maintains 
Methodology 3

the appearance of differentiability in daily intervals while 

constraining interpolated values to the range of bounding 

daily values. Alternatively, the user may provide a data file of 

measured unit flows for UFINCH simulations or develop unit 

flow estimates that are consistent with stochastic variations in 

unit flow data. 

Unit intervals were chosen for UFINCH simulation time 

steps because the minimum travel time in most stream segments, based on NHDPlus flowline lengths and average flow 

velocities, is about 15 minutes. UFINCH computes the travel 

times from the base streamgage to all upstream catchments 

and applies the unit water yields to these catchments with 

appropriate lead times so that flow through the network arrives 

synchronously at the base streamgage. 

Spatial variations in water yields commonly occur in 

natural basins because of persistent differences in the spatial 

distribution of rainfall patterns, land-cover land-use characteristics, or other factors. Thus, simulation of catchment flows 

based on average basin water yields may produce simulated 

flows that systematically differ from measured flows at some 

target streamgages. UFINCH has two methods for adjusting 

simulated flows to better match measured flows at upstream 

streamgages. The static method approximates the discrepancy 

between (log10 transformed) measured and simulated flows 

as a regression equation with possible linear and quadratic 

terms of log10 simulated flows. Parameters for these regression 

equations can be estimated by use of ordinary least squares 

or robust techniques (The MathWorks, 2015b). When the 

parameters of the regression equation are statistically significant, predicted values from this regression can be added to 

simulated flows to improve the match with measured flows. 

The regression method is parsimonious, which may facilitate 

regionalization, and can readily be applied to simulated values 

during unmeasured periods at the target streamgages to synthetically extend streamflow records. 

Alternatively, the Empirical Cumulative Distribution 

Function (ECDF) method provides a more flexible, but less 

parsimonious, approach than static regression for improving the match between measured and simulated flow characteristics. The ECDF method computes sample cumulative 

probabilities and corresponding quantiles for measured and 

simulated flows. These sample cumulative probabilities have 

the same length as the number of 15-minute time steps in 

the simulation. To reduce the size of this set, measured and 

simulated quantiles are interpolated at 0.001 intervals of probability from 0 to 1 using the sample estimates. A set of 1,000 

flow ratios is computed by dividing the interpolated measured 

quantiles by the interpolated simulated quantiles. 

To reduce the irregularities in consecutive ECDF ratios, a 

double exponential smoothing filter (Kalekar, 2004) is applied 

to smooth the sequence. A smoothing parameter, which is 

applied to level components and trend components of the filter 

and is user specified through a linked edit-text field and slider 

control on the AssessAdjustGUI graphical user interface in 

UFINCH. The paired interpolated quantiles of simulated flows 

and smoothed ratios can be exported to an ASCII file and 

applied to future simulated flows to provide a flow adjustment during non-overlapping periods of record. Matching the 

measured and simulated ECDFs may not improve the match 

between measured and simulated flows, as two white noise 

sequences can have the same ECDF but remain uncorrelated. 

UFINCH can simulate zero flows measured at the base 

streamgage by applying zero water yields to upstream catchments. In geographic areas where loss of water with downstream distance in a stream reach is common, UFINCH flows 

would generally underestimate upstream flows. Simulation 

of flows in stream networks with losing reaches, however, is 

inconsistent with the assumption implicit in UFINCH simulations that flows at the base streamgage are proportional to, or 

through adjustments for water use can be made proportional 

to, water yields throughout the basin. In UFINCH, both the 

static and ECDF methods for error correction involve simulated flows in the denominator of the corrector; thus, application of these correctors requires positive (no-zero) simulated 

streamflow values. 

UFINCH is designed for application anywhere within 

the United States based on medium-resolution NHDPlus 

geospatial data and daily streamflow data available from 

the USGS. The extensive geospatial dataset supporting the 

application includes both catchment and streamflow topology, 

and information on the USGS streamgage network available 

from the NHDPlus website (http://www.horizon-systems.

com/nhdplus/). Streamflow data can be accessed on demand 

in UFINCH, provided an internet connection is available. 

Software installation, features, and operation of the UFINCH 

program and the supporting data are described in the following 

paragraphs. 

Model Assumptions and Limitations

UFINCH is applicable to basins where continuous daily 

streamflow data are available for an extended period at the 

basin outlet. A streamgage at the basin outlet is referred to 

as the base streamgage in this report. Temporal variations in 

flow at the streamgage are assumed to be generally consistent 

with temporal variations in water yields throughout the basin. 

Specifically, basins where daily flows at the base streamgage 

are commonly affected by artificial controls, substantial (in 

stream) water uses, diversions or flow augmentations, losing 

stream reaches, or estuary conditions are not consistent with 

assumptions underlying the UFINCH model, unless the effect 

of these variations can be abstracted from the flow record at 

the base streamgage before application of UFINCH. Basins 

larger than 3,000 mi2 have not been extensively evaluated but 

may act similarly to large impoundments that would substantially degrade the relation between outlet flows and catchment 

water yields. The period of record extension for the upstream 

flow network is limited to the period of record, either measured or extended by other means, at the outlet. 
4 UFINCH: Simulation of Unit Flows in Networks of Channels Described by NHDPlus

Software Installation

UFINCH is written in the Matlab programming language (The MathWorks, 2015a) and uses functions from the 

Statistics and Machine Learning Toolbox (The MathWorks, 

2015a), the Optimization Toolbox (The MathWorks, 2015c), 

the Mapping Toolbox (The MathWorks, 2015d), as well as the 

base Matlab functions. Computers equipped with this suite of 

software can run UFINCH from the source code. Alternatively, 

UFINCH can be run on 64-bit Windows-based computers 

without the Matlab programming environment by use of an 

executable version compiled under Matlab R2015a or later. 

For distribution within the U.S. Department of the Interior, the file UFinch_Installer_web.exe, which will be shared 

through the USGS Google Drive, is designed to facilitate this 

process, but requires administrative privileges for software 

installation. Once initiated, the installer should automatically 

download the 2015a version of the Matlab Compiler Runtime (MCR) program from the MathWorks Web site, unless it 

already is installed. The MCR translates Matlab code to binary 

instructions that Windows can execute. Once the MCR file is 

installed, the executable UFINCH program, UFinch.exe, and 

updates compiled for Matlab 2015a (also shared through the 

Google Drive), can be run from the Windows command line 

or desktop icon. Hopple and Holtschlag (2018) provide code, 

data, executables, and other guidance for using UFINCH on 

Microsoft Windows computers. 

Data Structure

In addition to the UFINCH software, geographic information and flow data are needed to support the application. 

Given the extensive geographic information system (GIS) data 

involved in UFINCH applications, the GIS data has been partitioned by hydrologic regions, as defined in NHDPlus. These 

regional units generally correspond to 21 USGS Hydrologic 

Regions (fig. 1; U.S. Geological Survey, 2008), although some 

of the regions have been subdivided in NHDPlus to form 

23 regions (Horizon Systems Corporation, 2014). Within the 

contiguous United States, region 03 South Atlantic-Gulf has 

been partitioned into 03 North (03N), 03 South (03S), and 

03 West (03W) divisions, and Region 10 Missouri has been 

partitioned into 10 Upper (10U) and 10 Lower (10L) divisions. 

Also, region 13 Rio Grande, as defined by NHDPlus, has been 

extended into Mexico. Outside the contiguous United States, 

region 20 covers Hawaii, and region 21 describes Puerto Rico 

and the U.S. Virgin Islands. Preparation of NHDPlus data 

for Alaska (region 19) is in progress. UFINCH GIS data are 

partitioned into folders consistent with this NHDPlus GIS data 

structure.

UFINCH uses a relative folder structure for locating and 

storing files. The UFINCH program is expected to be run from 

the folder ..\UFinch\UWork, where ..\ can be any folder on a 

computer system. An additional folder, ..\UFinch\HR00\GIS, 

is needed to provide supporting GIS data. This data has two 

basic types: GIS data specific to individual hydrologic units 

and a national streamgaging dataset. Any or all of the twodigit hydrologic region [xx] datasets can be loaded in subfolders under ..\UFinch\HR00\GIS\. These subfolders are named 

(HR01, HR02, HR03N, HR03S, HR03W,...,HR21) corresponding to the NHDPlus convention, and can be downloaded 

from the designated Google Drive. In addition, the streamgage 

shapefile set also should be downloaded and stored in the GIS 

folder ..\UFinch\HR00\GIS\Streamgage\. 

In the first analysis of any two-digit hydrologic region 

[xx], UFINCH will create a new subfolder named ..\UFinch\

HR[xx]\GIS\. Region-specific GIS data will be copied to this 

subfolder from the ..\UFinch\HR00\GIS\HR[xx]\ folder. In 

addition, a FlowData subfolder will be created along with 

subfolders for storing unit and daily simulated and measured 

flows. Subsequent analysis will use the region-specific folder 

to access GIS and flow data. The region-specific data include 

(1) binary and supporting files of the boundary of the hydrologic region (two-digit) along with subregional (four-digit) 

boundaries in the shapefile set HUC02wHUC04.*, where the 

‘*’ refers to a set of common filename extensions commonly 

associated with shapefiles (shp, sbn, sbx, shx, prj, dbf); (2) 

binary and supporting files in flowline shapefile set NHDFlowline.*; (3) text files NHDFlowlineVAA.txt and PlusFlow.

txt containing value added attributes describing flowline 

connectivity, flowline lengths, and corresponding catchment 

drainage areas; and (4) text file EROM_MA0001.txt of average flow velocity for individual flowlines identified uniquely 

by ComID. Nationwide GIS data for the USGS streamgage 

locations and attributes are stored in the binary and supporting shapefile set StreamGageEvent.*. These GIS shapefile 

sets for all U.S. streamgages are stored in folder ..\HR00\GIS\

Streamgage\. 
Methodology 5

Figure 1. Map of two-digit NHDPlus Hydrologic Regions showing two-digit NHDPlus regions for the conterminous United States.

50 N

90°

Base from U.S. Geological Survey Watershed Boundary Database,

graticule from ESRI

0 250 500 1,000 MILES 

Pacific 

Northwest

(17)

Great Basin

(16)

California

(18)

Lower 

Colorado

(15) Rio

Grande

(13)

Upper

Colorado

(14)

Missouri

(10)

Arkansas-White-Red

(11)

Texas-Gulf

(12)

Upper

Mississippi

(07)

Lower

Mississippi

(08)

Souris-RedRainy

(09)

New

England

(01)

Mid

Atlantic

(02)

Ohio

(05)

Tennessee (06)

South Atlantic-Gulf

(03)

Great Lakes

(04)

80° 70°

50°

40°

130° 120° 110° 100°

50°

40°

120° 110° 100° 90° 80°

30° 30°
6 UFINCH: Simulation of Unit Flows in Networks of Channels Described by NHDPlus

UFINCH Processing and Results

If the UFINCH software is properly installed and the 

folder HR[xx], for the region of interest, and the Streamgage 

folder and expected contents are in place at ..\UFinch\HR00\

GIS\, the user can initiate a UFINCH analysis. After launching UFINCH, the main GUI is displayed (fig. 2). The main 

GUI provides access to much of the functionality of UFINCH, 

including selection of the two-digit hydrologic region for 

study, selection of the four-digit hydrologic study area, selection of base and target streamgages, and specification of the 

simulation period. There is a button on the main GUI labeled 

“Display Map of Hydrologic Regions in Contiguous US” that 

displays a (nonclickable) map of NHDPlus hydrologic regions 

for reference (fig. 3). 

Once a two-digit [xx] named region is selected from a 

drop-down list in the upper left-hand corner of the MainGUI, 

UFINCH will determine if the corresponding folder ..\UFinch\

HR[xx] exists. If the folder does not exist, UFINCH will 

prompt for permission to create the folder structure and copy 

regional GIS data from ..\UFinch\HR00\GIS\ HR[xx] to populate ..\UFinch\HR[xx]. Otherwise, data in the existing regional 

folder will be used. 

Following selection of the two-digit region, the RegionMapGUI will be displayed showing the names of all hydrologic subregions (fig. 3). The user then selects a four-digit 

subregion within this region by left clicking on the RegionMapGUI, which causes the corresponding subregion map 

component to be highlighted in blue. A right click ends the 

selection process. The RegionMapGUI then closes, and a new 

SubRegionMapGUI is displayed (fig. 4) showing the outline 

of the selected subregion. The user then can click the buttons 

labeled “Display Flowlines” and “Display Streamgages” to 

show NHDPlus flowlines and streamgages within the selected 

subregion on the SubRegionMapGUI. To facilitate flowline 

and streamgage file selection, UFINCH will launch an open 

file dialog box and prompt for the expected file name of the 

corresponding coverage in the expected directory location. For 

standard applications, the user can merely accept the default 

file location by clicking the “Open” button on the dialog box. 

Otherwise, the user can navigate the open file dialog box to 

the location of the custom user-created shapefile. 

Figure 2. Main graphical user interface (MainGUI) for UFINCH.
UFINCH Processing and Results 7

Figure 3. RegionMapGUI for Hydrologic Region 07 Upper Mississippi showing names of hydrologic 

subregions, with subregion St. Croix selected. 

Figure 4. SubRegionMapGUI for Region 07 Upper Mississippi, Subregion 03 St. Croix, showing 

flowlines and streamgages. (Streamgages active in water year 2010 are highlighted in dark blue).
8 UFINCH: Simulation of Unit Flows in Networks of Channels Described by NHDPlus

Flowline shapefiles provide detailed geometry for tens of 

thousands of flowlines in a region. These files tend to be large, 

greater than 50 megabytes, and require about a minute to read 

and display, depending on the performance characteristics 

of the computer. A message dialog box is displayed indicating this expected time requirement and is closed when the 

process is complete. Before selecting a base streamgage, the 

user may use the “Specify Water Year” edit text box to enter 

a year. Those triangular streamgage symbols displayed on the 

SubRegionMapGUI are greyed out if the streamgage was not 

active in the specified year (fig. 4). This feature may be helpful 

in visually identifying streamgages that were active during a 

particular time periods. 

The SubRegionMapGUI can be used to identify 

streamgages and record characteristics by left clicking on the 

triangular symbols representing streamgages. Both blue highlighted and greyed-out symbols are clickable. Attributes of 

clicked streamgage symbols are displayed on the MainGUI in 

the “Identify Streamgage Attributes” panel. Attributes include 

streamgage number and name, first and last date of data collection, latitude, longitude, drainage area, and the ComID, 

which uniquely identifies the flowline (stream segment) 

on which the streamgage is located. Once the desired base 

streamgage is identified, the base streamgage can be selected 

for analysis by use of the “Select Base Streamgage” button in 

the “Select Streamgage as Network Base” panel. Selection of 

the base streamgage highlights the streamgage and flowline 

network upstream of the streamgage on the SubRegionMapGUI (fig. 5). Fields on the MainGUI in the “Select Streamgage 

as Network Base” panel also are populated, including those 

identifying the streamgage and the number of flowlines in the 

network. The drop down list in the mainGUI “Select Target 

Streamgage” panel also is populated with streamgage numbers for all streamgages at or upstream from the selected base 

streamgage. The static text field labeled “Number” displays 

the number of streamgages at or upstream from the base 

streamgage in the network. 

The user may then select the “Read 15-min Flows” button on the MainGUI to retrieve or access unit flow data. Once 

this button is selected, UFINCH will prompt for the expected 

name of the flow data file in the expected directory. For example, if base streamgage 05333500 is selected in the St. Croix 

subregion of the Upper Mississippi region (HR07), UFINCH 

will prompt for a data file 05333500*.uFloMea in the folder ..\

UFinch\HR07\FlowData\ Measured\Unit. 

If no data file has been previously retrieved or created for 

this streamgage, the user can select the “Cancel” button in the 

get file dialog box. This action launches a question dialog box 

with buttons labeled “Retrieve Data,” “Reselect Gage,” and 

“Cancel.” Selecting the “Retrieve Data” button will initiate an 

Figure 5. Hydrologic subregion 0703 with selected streamgage (05333500) St. Croix River near Danbury, Wisconsin, 

and upstream flow network identified.
UFINCH Processing and Results 9

input dialog box for the station number (that is populated with 

the base streamgage number) and two boxes for the start and 

end date of data retrieval. This date range can be based on an 

inventory of available data that is initiated from UFINCH and 

automatically displayed in a browser window returned from 

an NWIS query (fig. 6). Also, the beginning and ending dates 

for data retrieval should extend a few days before and after the 

period for simulation to allow for travel time from the upper 

catchments of the target basin to the outlet.

The specified streamgage and date range are used in a 

water services data (http://waterservices.usgs.gov/) retrieval to 

obtain daily flows. The daily flows are interpolated to 15-minute increments for simulation and are overlain on one or more 

hydrographs of measured flows in a new figure window. Multiple hydrographs, and corresponding data files, are sometimes 

returned to span all the continuous periods of record at the 

streamgage. Multiple periods of continuous record within the 

streamgaged period are not evident from information displayed 

in the data inventory. Separate data files are created for each 

period of continuous record and are labeled to identify the beginning and ending dates of the period. For example, data retrieval 

for 05331833 from October 1, 1997, to September 30, 2014, 

created two data files named 05331833_1997Oct01_2001Sep30.

uFloMea and 05331833_2005May02_2014Sep30.uFloMea that 

were stored in folder ..\UFinch\HR07\FlowData\Measured\Unit\. 

Once a unit flow file is generated, the user can select the data 

file for the period of interest using the “Open” button on the file 

dialog box. This selection causes UFINCH to read in the unit 

flow data. A hydrograph of this data is displayed in a new figure 

window (fig. 7), and attributes of the flow data are shown in the 

panel labeled “Retrieve Flow Data Inventory and Daily Flows” 

panel in the upper right corner of the MainGUI. 

Travel times through the network are computed as the 

product of flowline length and average flow velocity defined in 

NHDPlus. Flow velocities in NHDPlus reflect particle velocities in streams. The user can proportionately adjust NHDPlus 

flow velocities to better reflect the speed of a wave in an open 

channel (wave celerity), which potentially improves the match 

between measured and simulated hydrographs. In particular, 

the user may specify a multiplier to adjust mean flow velocities 

in each flowline by use of controls in the panel named “Compute Travel Times in Streamgage Network.” The default of 1 

can be changed by adjusting the linked slider/edit-text box to a 

preferred value. Based on limited testing, a value of 2.5 often 

produces a closer match between simulated and measured flows 

at the base streamgage than a value of 1.0. The default value 

of 1 may produce simulated hydrographs that are dampened 

with respect to measured (interpolated) values. The adjusted 

velocities in UFINCH are not intended to reflect information on 

particle velocities in streams. 

Figure 6. Inventory of data at the selected streamgage (05333500) St. Croix River near Danbury, Wisconsin.
10 UFINCH: Simulation of Unit Flows in Networks of Channels Described by NHDPlus

Figure 7. Daily and interpolated 15-minute flows at streamgage (05333500) St. Croix River near Danbury, Wis.

Once the multiplier is specified, travel times in the 

network can be computed by selecting the “Compute Travel 

Times” button. A summary of minimum and maximum travel 

times in the network in 15-minute time increments, and days 

are tabulated in the “Travel Time Statistics” table to the 

right of this button. Travel times determine the apparent lead 

time needed for water to travel from a catchment to the base 

streamgage. Basin water yields are computed for each time 

step on the basis of interpolated flows at the base streamgage. 

Basin yields are applied to upstream catchments with time 

leads designed so that corresponding flows appear to arrive 

synchronously at the base streamgage. 

The simulation period can be specified in the “Compute 

Unit Flows in Streamgage Network” panel. Start- and end-time 

values are prespecified in the editable text boxes based on the 

period of record in the flow file. The number of computational 

time steps for the simulation is displayed in a static text box to 

the right of the simulation period. Computational requirements 

are proportional to the product of the number of time steps and 

the number of flowlines, which is displayed in the panel labeled 

“Number of Flowlines in the Gage Network.” For example, the 

simulation of the highlighted network in figure 5, which has 

781 flowlines, 140,161 time steps from October 1, 2010, to September 30, 2014, or about 10 million flowline-time steps, was 

completed in 6.5 minutes on a conventional workstation using a 

single processor. A wait bar is displayed during the simulation to 

indicate the temporal progress of the computations. 

Finally, the user may select a target streamgage to compare measured and simulated flows. The streamgage numbers 

in the drop down list shown in the “Select Target Streamgage” 

panel include all streamgages at or upstream from the base 

streamgage. Selecting a target streamgage from this list highlights the corresponding streamgage on the SubRegionMapGUI. To confirm the connectivity of the catchments and the 

flow network for the base streamgage, the user may wish to 

initially specify the target streamgage as the base streamgage. 

Connectivity would be confirmed if the average simulated 

flow is consistent with the average measured flow. Alternatively, if simulated flows are consistently less than measured 

flows, drainage from some catchment areas may not be represented at the base streamgage. One possible reason for this 

difficulty is that UFINCH may not have correctly interpreted 

the network topology. 

Selecting the “Assess Fit and Adjust Flow” button in the 

“Base and Target Gages” panel on the MainGUI will initiate 

an input file dialog box defaulting to a file name associated 

with the target streamgage number, commonly an eight-digit 

value [yyyyyyyy], with an extension for unit flows measured 
UFINCH Processing and Results 11

Figure 8. Hydrograph and plot of the empirical cumulative distribution function comparing measured and simulated 

flows at streamgage (0533500) St. Croix River near Danbury, Wis.

at the target streamgage in folder ..\UFinch\HR[xx]\FlowData\

Measured\Unit\. For example, if target streamgage 05333500 

St. Croix River near Danbury, Wisconsin, were selected for the 

target site, the default file name would be 05333500*.uFloMea. 

The asterisk embedded in the file name would enable display of 

files with unit flows at the selected site with continuous flows 

during multiple time periods. Again, if no data files had been 

previously retrieved for the target site, the user could press 

“Cancel” in the input file dialog box. Cancelling would again 

initiate a question dialog box to facilitate retrieving daily flows 

and interpolating them to unit values. A data inventory would be 

retrieved to help the user specify the period of record. 

Results for the example scenario involving streamgage 

05333500 are displayed on the AssessAdjustGUI (fig. 8). 

Measured and simulated flows are plotted on hydrographs and 

ECDFs in this figure. In this scenario, careful inspection is 

required to confirm that both measured and simulated flows 

are displayed because of their close correspondence. These 

results appear to confirm the connectivity of the flow network and that flow is conserved in UFINCH. Controls in the 

“Hydrographs and ECDF Series” panel can be used to clear 

or select sets of flow series for display. Slider controls in the 

“Scale Hydrograph with Time Domain Limits” can be used to 

zoom in on the time axis of the hydrograph. In this case, there 

is little potential for improving the match between simulated 

and measured flows by applying adjustments. Selecting the 

“Clear and Exit” button in the lower right hand corner of the 

AssessAdjustGUI will close the figure and return the user to 

the MainGUI.

Once the connectivity and directionality of the flow 

network is confirmed, the user may wish to compare simulated 

and measured flows at one or more upstream streamgages. 

This process will be illustrated with streamgage (05332500) 

Namekagon River near Trego, Wis., and streamgage 

(05331833) Namekagon River at Leonards, Wisconsin. 

Selecting streamgage number 05332500 in the “Select Target 

Streamgage” panel displays characteristics of the streamgage 

and flow record in the “Streamgage Attributes” panel on the 

MainGUI. The period of record at 05332500 extends from 

1928 to 2014, thus providing a temporal overlap with the simulated period. The drainage area at the streamgage is 488 mi2

, or 

about 31 percent of the area at the base streamgage. Selecting 

the “Assess Fit and Adjust Flow” button will again provide 

the opportunity to use an existing unit flow data file or retrieve 

daily flows. In this scenario, a data file was created from data 

retrieved for the period October 1, 1990, to September 30, 2014 

(05332500_1990Oct_2014Sep30.uFloMea). Selecting this file 

initiates the AssessAdjustGUI shown in figure 8. 
12 UFINCH: Simulation of Unit Flows in Networks of Channels Described by NHDPlus

Figure 9. Hydrograph and plot of the empirical cumulative distribution function comparing measured with UFINCH simulated and 

statically adjusted flows at streamgage (05332500) Namekagon River near Trego, Wisconsin, based on measured flows at 

streamgage (0533500) St. Croix River near Danbury, Wis.

In this comparison, measured and simulated flows at 

streamgage 05332500 are quite distinct. The hydrograph 

indicates that measured flows tend to be more variable than 

simulated flows. The ECDF indicates that at lower flows, simulated values commonly underestimate measured flows, but 

that at higher flows simulated values overestimate measured 

flows. Based on this comparison, a static regression model was 

developed to adjust simulated flows to better match measured 

flows. In particular, a constant and linear term was selected 

from the “Static Adjustment” panel to estimate this adjustment 

(fig. 9). A quadratic term also can be added to improve estimation in some cases. The form of the error correction is

log log log , 10 Q Q ε ( )t m 10 ea( )t s 10 Q im( )t = ( ) − ( )

where is the modelled error component, and Qε ( )t

log log log , 10 0 1 10 2 10

2

Q Q t sim t Q t sim t ε β β β δ ( ) ( ) = + ⋅ ( ) + ⋅ ( ) +

( )

ˆ ˆ ˆ

where , and are estimated parameters for constant, 

linear, and quadratic models, respectively.

β β ˆ

0 1 + ˆ β2

ˆ

, log log Qstt t

Q Q sim t t

( )

( )+

= ( ) ( ) 10 10 10 ε ˆ ˆ

where is the statistically corrected flow estimate. Qstt t( ) ˆ
UFINCH Processing and Results 13

Estimates of the magnitudes and uncertainties of this 

model are displayed in the table to the right of the selected 

parameters. Because of the high autocorrelation expected for 

unit flows in residual series, the conventional t-Statistics and 

p-Values shown for the corresponding parameters in the model 

have only marginal utility. The R2 (coefficient of determination) value displayed in the panel indicates that the estimated 

linear function of log10 simulated flows explains about 38 percent of the variability in the residuals between log10 measured 

and log10 simulated flows. Adjusting the simulated flows by 

the regression model appears to improve the match in hydrographs and reduce the bias in the ECDFs. 

Given the observed improvement in fit, the user may 

wish to document the model and save the adjusted flow 

information. To document the model, the user can apply 

controls in the “Write Selected Unit Flows to File” panel. In 

this case, the “Statically Adjusted Flows” radio button might 

be selected. The “Document Model” button launches an input 

dialog box with editable fields prepopulated with base and 

target streamgage information (fig. 10). Selecting the “Write 

Selected Flows” button launches an input file dialog box 

with a default file name in an expected folder location. In 

this example, the default folder is ..\UFinch\HR07\FlowData\

Simulated\Unit\ and the default file is 05332500_05333500

_2010Oct01_2014 Sep27.uFloStt to indicate that this is unit 

flows (uFlo) that have been statically (Stt) adjusted for target 

streamgage 05332500 conditioned on flow at base streamgage 

05333500 from October 1, 2010, to September 27, 2014. 

The contents of the output flow file are shown in figure 11. 

The file begins with header information that is delimited by an 

opening /* and closing */, which provides documentation for 

the analysis but is ignored by UFINCH when the file is read 

in for possible future simulations. The “Clear and Exit” button 

on the lower right hand corner of the AssessAdjustGUI returns 

control to the MainGUI.

The second upstream target streamgage selected for 

analysis was streamgage (05331833) Namekagon River at 

Leonards, Wis. The streamgage measures flow from a basin of 

126 mi2

, or about 8 percent of the flow at the base streamgage 

(fig. 12). The hydrograph shows that simulated and measured 

flows are generally consistent. The ECDF, however, shows 

that simulated flows are generally biased below measured 

flows, with this tendency decreasing with higher measured 

flows. A quadratic term in the regression was not significant 

in reducing this local bias. In general, the hydrograph shows 

that the adjustment generally improved the match between 

statically adjusted simulated flows and measured flows. The 

robust parameter estimation technique, rather than ordinary 

least squares, was selected for this analysis by use of controls 

in the radio button panel labeled “Estimation Technique.” In 

particular, the robust parameters may provide an adjustment 

that improves the match between measured and statically 

adjusted flows at higher flow magnitudes. Robust techniques 

are less sensitive to outliers than ordinary least square techniques. Model document and adjusted simulated unit flow may 

output as discussed previously before selecting the “Clear and Figure 10. Example input dialog box for model documentation.
14 UFINCH: Simulation of Unit Flows in Networks of Channels Described by NHDPlus

Figure 11. Example unit flow output file following static adjustment.

Exit” button on the AssessAdjustGUI to return to the MainGUI. Parts of the adjusted simulated unit flow series can be 

replaced with available measured flows at the target site to 

form a hybrid series that spans the time interval at both the 

base and target streamgages. This hybrid series can be used as 

a base flow series in subsequent UFINCH analysis to propagate measured or adjusted flows further upstream. 

The MainGUI provides several minor features that may 

be of interest. The button labeled “Generate Equations” lists 

the time-indexed equations that UFINCH uses to route flow 

from the upper catchments downstream through the flow 

network to the outlet at the base streamgage. The output is 

listed to the computer console. This listing may have utility in 

identifying UFINCH coding limitations for unusual network 

configurations or NHDPlus network anomalies when flow is 

apparently not conserved. 

The “Aggregate” button in the “Unit to Daily Values for All 

ComIDs” panel aggregates unit values to daily flows for all flowlines in the network. These simulated daily flows can be saved to 

an ASCII output file by use of the labeled “Save” button for further 

analysis. The aggregation may require several moments to complete the computation for large networks and extended simulation 

periods. Unit flows for all flowlines also can be saved in Matlab 

binary format by selecting the “Save All Unit Flows as MLBinary,” 

although the large size of this binary tends limit its perceived utility. 

The “Exit” button on the MainGUI will end the application 

and exit to the operating system. Before exiting, the Microsoft 

notepad application will be launched to display the contents 

of an automatically generated, time-stamped log file entitled 

“uFinchSummary[yyyymmmdd_HHMM].txt. This file will 

contain model documentation for any models documented during 

the session. Finally, UFINCH will display a question dialog box 

requesting to close any open figures. 
Discussion 15

Figure 12. Hydrograph and plot of the empirical cumulative distribution function comparing measured with UFINCH simulated and 

statically adjusted flows at streamgage (05331833) Namekagon River at Leonards, Wisconsin, based on measured flows at streamgage 

(0533500) St. Croix River near Danbury, Wis.

Discussion

This report documents the capabilities and features of the 

UFINCH model for simulating unit and daily flows in networks 

of channels described by NHDPlus based on continuous flows 

at USGS streamgages. UFINCH provides a basis for comparing 

simulated flows with measured flows at upstream streamgages, 

and designing a filter to improve the match between overlapping periods of record at the base and target streamgages. This 

filter can be applied to simulated flows during periods when the 

target streamgage was not operating to synthetically extend the 

period of record at the target streamgage. By integrating periods of measured and simulated flows at the target streamgage, 

UFINCH can be reinitialized to use the integrated flows as the 

base streamgage and progressively extend streamflow information further upstream in the basin. 

Because flow is conserved in a basin, a filter designed 

to improve the match between simulated flows at a base 

streamgage and measured flows at a target streamgage may 

have transfer value to the remaining parts of the basin. If 

a filter systematically increases simulated flows at a target 

streamgage during low flow periods, then simulated low 

flows elsewhere in the network may need to be systematically 

reduced to conserve flows within the entire basin during these 

periods. In basins with multiple upstream target streamgages, 

a corresponding set of filters may be able to further improve 

flow simulations in intervening areas. A set of such filters 

may provide a basis for assessing how spatial variations in 

precipitation patterns or land-use, land-cover characteristics 

within a basin effect flow characteristics. 
16 UFINCH: Simulation of Unit Flows in Networks of Channels Described by NHDPlus

Future UFINCH enhancements could provide access 

to simulated unit flows at all flowlines in the network. Currently (2016), individual flowlines on the SubRegionMapGUI 

are clickable if flowlines are the active layer, rather than the 

streamgage layer. The “Active Layer” radio button panel 

on the MainGUI is used to select the active layer, which 

defaults to the streamgage layer. Characteristics of the selected 

flowlines currently (2016) can be displayed in the “Flowline 

Attributes” panel on the MainGUI. A feature for accessing, 

plotting, and exporting the simulated unit flows may be helpful, although additional feature layers, such as major roads, 

may be needed to facilitate flowline selection. 

Another feature that may have utility in future versions 

of UFINCH would be the ability to use discrete flow measurements at miscellaneous sites to assess and adjust simulated 

flows. In particular, the static regression model for adjusting 

simulated flows is parsimonious, which would allow the 1 to 

4 needed model parameters to be estimated from a relatively 

small number of discrete measurements. Such relatively 

limited data requirements could be helpful in confirming and 

improving model simulations for ecological investigations on 

small streams and other applications. 

Integration of UFINCH with AFINCH (Analysis of 

Flows in Networks of Channels; Holtschlag, 2009) would 

eliminate the assumption of uniform water yields underlying 

UFINCH. In particular, AFINCH uses the same NHDPlus 

network of catchments and flowlines and streamgage network 

as UFINCH to compute monthly flows. The AFINCH application conditions the spatial distribution of monthly water-yields 

on monthly climatic data (PRISM Climate Group, 2013), 

including precipitation and temperature, and selected landuse, land-cover characteristics using a constrained regression 

approach. Within the U.S. Great Lakes area, monthly AFINCH 

water yields are precomputed for all NHDPlus catchments 

from 1951 to 2012 (Luukkonen and others, 2015). Finally, 

adjustment of measured flows at base or target streamgages 

with water use data may facilitate the application of UFINCH 

to regulated streams. 

Summary

The UFINCH (Unit Flows In Networks of Channels) 

computer application can be used to simulate daily and unit 

flows in networks of streams based on geospatial data in the 

National Hydrography Dataset NHDPlus (with value added 

attributes), and U.S. Geological Survey daily streamflow data 

from a downstream (or base) streamgage. Among streamflow 

augmentation methods, UFINCH has the unique capability to 

estimate time series of flows from a single base streamgage 

to many upstream reaches, while conserving flows within the 

basin. UFINCH also provides a simple statistical model to 

adjust simulated flows to better match continuous flows from 

data at an upstream streamgage. Parameters of the statistical 

model are estimated using overlapping periods of record at the 

two streamgages, but the model can be applied to all years of 

record available at the base streamgage. This report describes 

the main features of UFINCH and presents results from a 

sample application. 

To simulate unit (15-minute) flows, measured or interpolated unit flows at an outlet (base) streamgage are converted to 

basin average unit water yields by dividing flows by the area 

drained at the outlet. Unit yields are then shifted backwards in 

time based on their expected travel times from catchments to 

the outlet, using NHDPlus flow velocities and reach lengths 

for intervening channel segments (NHDPlus flowlines). Time 

delayed yields are applied to upstream catchments to produce 

catchment flows, in a process that conserves flows throughout 

the basin. Catchment flows are then translated downstream 

through intervening flowlines. Simulated flows can be compared with measured upstream flows and adjusted by use of 

tools in the UFINCH application to improve the match. Simulations using long-term flow records at the outlet can be used 

to extend unit flows at upstream flowlines, with adjustments 

derived from overlapping periods of record. 

Interactive graphical user interfaces and automated geographical information processing facilitate flow-data retrievals 

provide an intuitive environment for efficient and effective 

generation of flow information in a network. UFINCH is 

coded in the Matlab programming language and can be run in 

the Matlab programming environment, with supporting statistical, optimization, and mapping toolboxes, or from compiled 

code on a Microsoft Windows computer. 

Acknowledgments

The author would like to acknowledge the contributions 

of Paul Capel, team lead of the USGS NAWQA Integrated 

Watershed Studies Group, for supporting refinements that substantially contributed to the usability of the UFINCH program. 

Also, Howard Reeves, Research Hydrologist, USGS Michigan 

Water Science Center, substantially contributed to the development of both AFINCH and UFINCH by providing code to 

select four-digit hydrologic subregions. In addition, the author 

is indebted to colleague reviewers and those who provided 

final editing and formatting for publication. 
References Cited 17

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Holtschlag—UFINCH: Simulation of Unit Flows in Networks of Channels Described by NHDPlus—Scientific Investigations Report 2016–5074

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20165074