1

U.S. Department of Interior

U.S. Geological Survey

 November 2005

Science Center Web Site: http://il.water.usgs.gov/ Compiled by D.M. Ayers

Illinois Water Science Center

1201 W University Ave Ste 100

Urbana IL 61801-2347

Water Resources Update

USGS Illinois Water Science Center Newsletter

On June 26, 2005, Illinois Governor Rod 

Blagojevich activated the State’s Drought 

Response Task Force. This task force is 

made up of various agencies of State government along with Federal Agencies, such 

as the U.S. Geological Survey Illinois 

Water Science Center (USGS). Periodic 

meetings are held to assess various facets of 

the drought’s impact on the State, including 

agriculture, water supply, ecosystem, economic, and public helath and to make any 

appropriate recommendations for action. 

Currently, drought conditions are present 

within the State, particularly west-central 

and northern Illinois. The Illinois State 

Water Survey reports that the northeast, 

northwest, and central climate divisions of 

the State have experienced their 2nd or 3rd

driest March-September periods on record. 

(http://www.sws.uiuc.edu/hilites/drought/

DTFSummary20050929.pdf)

The USGS streamflow-gaging stations 

are an integral part of the drought assessment for the State. One index of drought 

condition is to determine how the current 

streamflow compares with the historical 

record of streamflow at that location for 

that date or range of dates. This index of 

streamflow conditions is expressed in percentiles of streamflow. A percentile is a 

value on a scale of 100 that indicates the 

percent of a distriution that is equal to or 

below the value. For example, on the map 

of daily streamflow conditions to the right, 

a streamflow at the 90th percentile is equal 

to or greater than 90 percent of the flow values recorded on this day of the year during 

all years that measurements have been 

made. In general, a percentile between 25 

and 75 percent is considered normal with 

percentiles less than 25 being below normal and tending toward hydrologic drought 

conditions as the percentile value 

decreases. As of October 2005, many locations in central and northern Illinois are 

experiencing record low flows for this time 

of the year as compared to the historical 

record (more than 90 years in some locations). The Illinois River, in particular, is 

experiencing record low flows due not only 

to the lack of precipitation in tributary 

basins but also due to the decrease in diversion from Lake Michigan. The Illinois 

River at Valley City had a flow of 3,090 

cubic feet per second, which is 810 cubic 

feet per second lower than the previous 

minimum low flow for all the October 16’s 

measured for the period of record (since 

1938).

A map of real-time USGS streamflow 

percentiles for Illinois can be found at 

http://water.usgs.gov/cgi-bin/

waterwatch?map_type=real&state=il.

Other USGS drought-related information 

for Illinois can be found on our home page 

http://il.water.usgs.gov/. Drought information for the State of Illinois Drought 

Response Task Force can be found at 

http://www.sws.uiuc.edu/hilites/drought/.

Robert R. Holmes, Jr., PhD, P.E.

Director, USGS Illinois Water 

Science Center

MESSAGE FROM THE DIRECTOR

TABLE OF CONTENTS

Message from the Director . . . . . . 1

Illinois Streamflow Conditions 

for Nov. 2004 through Oct. 2005 . 2

Determining Resistance Coefficients 

for Illinois Streams . . . . . . . . . . . . 3

Employee Spotlight . . . . . . . . . . . 5

The Future of Streamflow 

Gaging in Illinois . . . . . . . . . . . . . 6

From the Mailbag . . . . . . . . . . . . . 8

Newsletter Format Preference . . . 8

USGS Illinois Water Science 

Center Publications. . . . . . . . . . . . 8
2

ILLINOIS STREAMFLOW CONDITIONS FOR NOVEMBER 2004 THROUGH OCTOBER 2005

Daily mean discharge from November 1, 2004 through October 31, 2005 compared with percentile distribution of mean daily discharges for the 30-year period, 1961-90, for 3 representative streamgaging stations. A 

daily mean discharge is in the deficient-flow if its value is less than or equal to the 25th percentile, in the normal-flow range if its value is between 25th and 75th percentiles, and in the excessive-flow range if its value is 

equal to or greater than the 75th percentile.
3

DETERMINING RESISTANCE COEFFICIENTS FOR ILLINOIS STREAMS

BY

TERESA M. HALFAR, CIVIL ENGINEER

The USGS Illinois Water Science 

Center, in cooperation with the Illinois 

Department of Natural Resources, Office 

of Water Resources (IDNR-OWR), has 

been collecting and analyzing data to 

assess streamflow-resistance coefficients 

for Illinois streams since 2000. A resistance coefficient is a measure of friction, 

in terms of either momentum or energy 

losses, from roughness factors along the 

flow boundary in resisting the flow. 

Flow-resistance coefficients, such as 

Manning’s n (n-value), are used in a wide 

range of hydraulic and hydrologic analyses. The results of these analyses affect 

the design, operation, and management of 

water-resources projects. However, 

despite advancements in hydrodynamic 

theories and data-collection practices, in 

general, the determination of flow-resistance coefficients in a natural environment is still a challenge to engineers. 

Manning’s n is selected for presentation 

in this study because it is the most widely 

used resistance coefficient in the United 

States and because it gives reasonable 

results over a range of flow conditions. 

The primary goal of this study is to 

develop a method to assist users in estimating n-values for sites of interest 

throughout Illinois. The purpose of this 

article is to give a brief description of the 

background and progress to date (July 

2005) of this study.

Site-selection criteria for determining 

n-values in Illinois include bed and bank 

material, channel cross-sectional geometry, longitudinal profile, channel alignment, and the associated characteristics of 

the drainage basin in which the channel is 

located. For a given stream, a representative reach is identified first. Then, one or 

more study reaches within the representative reach are selected according to the 

consistency of surface roughness and 

channel geometry, whether a reach contains abrupt expansion and/or contraction 

sections, and the feasibility of setting 

measurement points so that sufficient 

reach length is secured for measuring distinct water-surface slope. For practical 

reasons, sites near USGS streamflowgaging stations have been given first priority for site selection.

Streamflow measurements, along 

with simultaneous measure of water-surface elevations at two or more fixed 

points in a study reach for slope calculation, were made at each study site. Data 

were collected over a range of stage, but 

did not exceed bankful flow. Photographs 

of streams were taken at the time of the 

measurement to help illustrate channel 

hydraulic properties that affect the magnitude of the n-value for a given stage. In 

addition, ancillary data including site 

information, photographs of low-flow 

conditions, cross-sectional data (at least 

three cross sections), and bed-material 

data were collected to assist in the analysis. Streamflow measurements were 

made using either the conventional current-meter method or acoustic Doppler 

current profiler (ADCP) method.

As of July 2005, a total of 177 n-values have been determined for 37 study 

sites throughout the State. Data and 

results are presented in a format similar 

to Barnes (1967) and are available at 

http:il.water.usgs.gov/proj/

nvalues/index.htm. The format is useful 

for data interpretation and comparison of 

n-values to sites with similar hydrologic 

and geomorphic characteristics. The nvalues presented are reach-wise, based 

on the energy concept, and applicable to 

one-dimensional flow computations. All 

n-values presented were determined from 

field data. The primary data set consists 

of natural and constructed channels in 

Illinois, in both rural and urban settings. 

Users can link to “Site Descriptions” and 

view the list of current study sites, the 

range in n-values per site, and site photos 

of low-flow conditions. Each site name 

links to the individual data tables and 

visual presentations. Users can download 

the report in a PDF format or link to other 

reports on the same topics published by 

other USGS Water Science Centers.

Four types of images are prepared 

for presenting the field data (see page 3). 

Examples of graphics and data table 

available on the Web page are shown 

below. The location of the study site is 

identified on the USGS quadrangle map. 

An aerial photo, which clearly shows the 

study site, is used for illustrating the 

characteristics of the study reach. Representative corss-sectional shapes are presented for reviewing the geometric 

factors. Locations of the cross sections 

are identified on the aerial photograph. 

Bed and bank materials can be visualized during low-flow conditions. Whenever possible, photographs of the 

channel were taken at the time of each 

n-values survey. Ideally, four to five 

measurements under a wide range of 

flow conditions, with accompanying 

photographs are needed for a study site. 

The site photographs are annotated in 

the office with site name, view, data, and 

flow conditions. Later, the computed nvalue is added to the corresponding 

photo. Photographs like these can be 

used to assist in understanding bed and 

bank, flow, and channel conditions. 

Mean values of the hydraulic properties, 

averaged among the cross sections used 

in each study reach, are reported as the 

reach-wise properties and are listed in 

the table along with the computed n-values. In addition to the images and data 

table, nine headers are included in the 

data presentation for describing the 

channel, study reach, and site characteristics.

Planned future work includes identifying and developing study sites on 

small streams in urban areas, both natural and constructed channels, for additional data collection. A search engine 

will be developed to search the database 

for streams in a predetermined range of 

n-values, for example, or to find streams 

based on certain channel characteristics 

specified by the user. Users will be able 

to access a list of various equations, calculate an n-value from known hydraulic 

properties, and then search the database 

for streams with that value.

For additional information concerning this study, please go to the Web site 

listed previously or contact the USGS 

Illinois Water Science Center.

Reference Cited

Barnes, H.H., 1967, Roughness Characteristics of Natural Channels: U.S. 

Geological Survey Water-Supply 

Paper 1849, 213 p.
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Date of 

Observation

Discharge 

(ft3

/s)

Average CrossSection Area 

(ft2

)

Hydraulic 

Radius (ft)

Mean Velocity 

(ft/s) Slope

Coefficient of 

Roughness n

7/9/2004 1440.0 895.2 3.10 1.68 0.000328 0.033

3/26/2004 2230.0 1141.1 3.82 2.02 0.000371 0.032

12/11/2003 2360.0 1168.5 3.90 2.09 0.000348 0.031

5/19/2004 4640.0 1518.0 4.89 3.14 0.000290 0.022

5/21/2004 4790.0 1608.0 5.13 3.07 0.000386 0.026

Fox River at Montgomery, Illinois

Average Hydraulic Parameters and Computed n-Values
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Teresa Halfar began her career 

as a hydrologist at an early age. As a 

child growing up in rural, smalltown Illinois, she spent many happy 

hours with her brothers disrupting 

the flow of Salt Creek by constructing dams in the stream out of river 

rock, tree branches, and clay. From 

those humble beginnings, she eventually found her way to the USGS.

Teresa started working at the 

USGS as a student in 1998, while 

attending the University of Illinois 

in Urbana/Champaign. After completing her B.S. in Civil Engineering in the Environmental Hydrology 

and Hydraulic Systems program, 

Teresa began her career in earnest as 

a hydrologist with the USGS Illinois Water Science Center.

Presently, Teresa is a member of 

the Surface-Water Investigations 

Section of the USGS Illinois Water 

Science Center. Her work activities 

include collecting and processing 

hydrologic data as part of the 

national streamflow-gaging network and assisting in special 

project work related to surface 

water. She is currently part of the 

team collecting and analyzing data 

in order to assess streamflow resistance coefficients for Illinois 

streams described in the previous 

article. She also is involved with 

steady and unsteady one-dimensional hydraulic modeling in northeastern Illinois.

In addition to her work as a 

hydrologist at the Science Center, 

Teresa enjoys the distinction of 

being a soldier in the Illinois Army 

National Guard. She holds the rank 

of staff sergeant and is a member of 

the Headquarters and Headquarters 

Detachment, 634th Forward Support 

Battalion, 66th Infantry Brigade, 35th

Infantry Division. Her unit was activated during the Great Flood of 1993 

to provide emergency support and 

levee security. In September, Teresa’s 

National Guard Unit was activated to 

help with Hurricane Katrina relief 

activities.

Teresa Halfar lives in Champaign 

with her husband Marty and daughter 

Jessica. She and her family enjoy 

hiking, camping, trail running, and, 

of course, disrupting the flow of 

small streams by constructing dams 

out of river rock, tree branches, and 

clay.

EMPLOYEE SPOTLIGHT

TERESA M. HALFAR (CIVIL ENGINEER)
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THE FUTURE OF STREAMFLOW GAGING IN ILLINOIS

BY

GARY P. JOHNSON

CHIEF, HYDROLOGIC DATA COLLECTION AND ANALYSIS SECTION

ship at the USGS for identifying and 

evaluating new technologies and methods that might have potential to completely change the paradigm in the 

streamflow-gaging program. A broad 

spectrum of techniques, including acoustics, image methods, laser, and radar, is 

being considered. USGS Research 

Hydrologist Dr. John Costa (Vancouver, 

Washington) discussed Hydro-21 at the 

Governor’s Conference on the Management of the Illinois River System in Peoria, Illinois in October 2005. Dr. Costa 

talked about an experiment in Washington State where USGS personnel measured surface velocities using a 

pulsed Doppler radar and river depth 

using ground-penetrating radar 

(GPR). Both radars were mounted on 

a helicopter and flown over rivers in 

a series of approximately 1-minute 

passes from 2 to 15 meters above the 

water surface. The magnitude of the 

uncertainty in velocity and depth 

measurements indicates that the 

method error is in the range of 5 percent. The results of this experiement 

indicate that helicopter-mounted 

radar can make rapid, accurate 

streamflow measurements needed in 

The USGS operates more than 7,000 

streamflow-gaging stations on rivers 

throughout the Nation. Because of the 

importance of the streamflow-gaging program, the USGS continues to be at the forefront of a systematic effort in search of new 

technologies tha may enable the direct, continuous, non-contact measurement of openchannel streamflow. These new technologies have the potential to reduce the costs, 

improve the accuracy, and reduce the hazards associated with conventional streamflow-gaging methods (fig.1).

One USGS program, called Hydro-21, 

was initiated to provide vision and leaderFigure 1. USGS Hydrologic Technician Phil Dennis making a conventional discharge measurement using a 4-wheel base, 

sounding weight, and spinning-cup current meter on the Boneyard Creek at Urbana, Illinois (University of Illinois Campus).
7

remote locations and during major floods 

(fig. 1). In addition, GPR experiments were 

conducted with the GPR antenna suspended 

above the water surface from a bridge. 

Traverses were made across stream channels 

to collect radar-profile plots of the stream

bed. Initial tests indicate that GPR is capable 

of producing a reasonably accurate (+/- 20 

percent) stream-channel profile and streamflow far more quickly than conventional 

streamflow-gaging methods (fig. 1), while 

avoiding the problems and hazards associated with placing instruments in the water 

(fig.2). More information on Hydro-21 is 

available at 

http://or.water.usgs.gov/hydro21/index

/shtml.

In the USGS Illinois Water Science Center, we also are currently using and experimenting with various new technologies to 

facilitate more efficient, more accurate, 

and safer streamflow gaging. The Center 

now has 15 acoustic Doppler current profilers (ADCPs). These ADCPs make the 

old, extremely heavy and awkward 

sounding-weight and spinning-cup current meters used in conventional streamflow gaging almost obsolete. With the 

ADCPs, we now are able to collect more 

accurate streamflow data, in a safer manner that with conventional methods 

because appreciably less time is spent on 

bridges and boats. Also, we recently 

installed our first radar stage sensor in 

Illinois. This new radar unit meets USGS 

standards for accuracy and precision and 

recently became commercially available. Thus far, the unit has worked well 

and has the advantage of not being in 

direct contact with the stream. In addition, the radar unit is much easier to 

install than conventional pressuresystem gages. Use of this unit should 

reduce maintenance (repair of and/or 

digging out of destroyed/buried orifice lines) and installation costs 

(fig.3).

USGS remains committed to 

providing high-quality streamflow 

data. As new technologies become 

available, USGS systematically tests 

these new technologies at the USGS 

Hydrologic Instrumentation Facility 

(HIF) in Bay St. Louis, Mississippi, 

to ensure sufficient accuracy and precision. Many new technologies show 

great promise. The USGS, when 

accuracy and precision are not sacrificed, will continue to apply and promote these new technologies that will 

make quality data collection safer 

and more economical.

Figure 3. Newly installed non-contact 

radar gage on Copper Slough near 

Champaign, Illinois. Note that none of 

the stage-sensing equipment comes in 

contact with the stream; thus, making 

installation and maintenance much 

easier.

Figure 2. Helicopter-mounted radar experiment. Note the two microwave antennas 

located just below the cabin on both sides, 

and the GPR antenna located in the rear 

middle of the helicopter.
8

FY 2005

SIR 2004-5103, Estimating Flood-Peak 

Discharge Magnitudes and Frequencies for Rural Streams in Illinois, by D.T. Soong, A.L. Ishii, J.B. 

Sharpe, and C.F. Avery

SIR 2004-5136, A Cross-Site Comparison of Methods Used for Hydrogeologic Characterization of the 

Galena-Platteville Aquifer in Illinois and Wisconsin, with Examples 

from Selected Superfund Sites, by 

R.T. Kay, P.C. Mills, C.P. Dunning, 

D.J. Yeskis, J.R. Ursic, and M. 

Vendl

OFR 2005-1020, Comparison of Potential Evapotranspiration Calculated 

by the LXPET (Lamoreux Potential Evapotranspiration) Program 

and by the WDMUtil (Watershed 

Data Management Utilitiy) Program, by E.A. Murphy

SIR 2005-5060, Evaluation of Measurements Collected with Multi-Parameter Continuous Water-Quality 

Monitors in Selected Illinois 

Streams, 2001-03, by G.E. 

Groschen and R.B. King

SIR 2005-5218, Physical, chemical, and 

biological responses to urbanization 

in the Fox and Des Plaines River 

Basins of northeastern Illinois and 

southeastern Wisconsin, by M.A. 

Harris, B.C. Scudder, F.A. Fitzpatrick, and T.L. Arnold (printing 

stage)

SIR 2005-5122, Surface-Water and 

Ground-Water Resources of Kendall County, Illinois, by R.T. Kay, 

P.C. Mills, J.L. Hogan, and T.L. 

Arnold

SIR 2005-5223, Framework for 

Regional Synthesis of Water-Quality Data for the Glacial Aquifer 

System in the United States, by 

K.L. Warner and T.L. Arnold (printing stage)

USGS ILLINOIS WATER

SCIENCE CENTER

PUBLICATIONS

Listed below are publications that 

were published recently. Federal Fiscal Year (FY) covers October 1 

through September 30. Our policy is 

to provide copies of our publications 

to requestors at no cost as long as the 

publication is in stock in the USGS 

Illinois Water Science Center. To 

obtain copies of the following, or any 

other USGS Illinois Water Science 

Center publication, you may contact 

Donna Ayers at (217) 344-0037, 

extension 3053 or by e-mail at 

dmayers@usgs.gov. 

Reports also can be found at: 

http://il.water.usgs.gov/pubs/ 

search.html.

Newsletter Format Preference

Beginning with this issue, you will have a choice in 

how you receive the newsletter: hard copy as at present, or 

electronically. If you wish to continue receiving a hard 

copy, you need to do nothing. If, however, you prefer an 

electronic copy, please send an e-mail to Donna Ayers at 

dmayers@usgs.gov indicating you wish to receive the 

newsletter electronically. When the next issue is ready, you 

will receive an e-mail with the newsletter attached as a PDF 

along with instructions on how to access the current newsletter and back issues in PDF format from the USGS Illinois 

Water Science Center Web page.

From the Mailbag

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