Water Resources Update

USGS Illinois Water Science Center Newsletter

Fall/Winter 2007 

U.S. Department of Interior

U.S. Geological Survey

Illinois Water Science Center

1201 W University Ave Ste 100

Urbana IL 61801-2347

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

Compiled by D.M. Ayers and J.B. Sharpe

Message from the Director

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

Table of Contents

Message from the Director.......................................................................................................................................................1

NEXRAD Radar Precipitation Data: Studies and Use at the USGS Illinois Water Science Center .......................................2

Employee Spotlight ..................................................................................................................................................................4

Statewide Geospatial Coordinating Activities .........................................................................................................................5

Preliminary Assessment of the Water Resources of Kendall County......................................................................................6

Salt Creek Hydrologic Information to be Analyzed, Disseminated in an Integrated Browsable Format ................................8

August 2007 Flooding in Northeastern Illinois..................................................................................................................... 10

Illinois Streamflow Conditions for October 2006 through September 2007 .........................................................................12

For hydrologic problems, many facets of technology are often brought to bear to study and solve these problems. Twenty-five years ago, many of us knew little about computerized geographic information systems (GIS) or

what it could do for us. Today, GIS and associated digital geospatial information is a crucial part of the science of

hydrology. The efforts of the U.S. Geological Survey (USGS) to coordinate with State and local agencies in the

geospatial arena are being spearheaded by USGS liaisons located primarily in the USGS Water Science Centers.

Shelley Silch is the USGS liaison for Illinois, sitting here in the USGS Illinois Water Science Center. You can read

about her activities in this newsletter issue. Two other technological areas being utilized by the hydrologic community are NEXRAD radar and the World Wide Web. NEXRAD provides rainfall at a spatial density not practical

with physical rain gages. This increased rainfall information has enhanced our rainfall-runoff modeling capabilities

as is shown in the USGS Illinois Water Science Center work in northern Illinois and discussed in this issue. The

World Wide Web allows us to organize and share data between agencies and scientists, maximizing collaboration

and time spent on science, while minimizing the time spent searching for data. The article by Audrey Ishii outlining the work we are conducting with the University of Illinois for the Salt Creek watershed is a perfect example of

this collaboration.


NEXRAD Radar Precipitation Data:

Studies and Use at the USGS Illinois Water Science Center

by

Thomas Over, Hydrologist

Background

	 In 1990, the National Weather Service (NWS)

began deploying the Next Generation Radar (NEXRAD)

WSR-88D weather radars around the United States and at

selected military bases around the world; deployment was

completed in 1997 (figure 1). In Illinois, NEXRAD radars

are located at Romeoville and Lincoln, and radar data

from several radars in surrounding states are also relevant

for Illinois. NEXRAD radars provide information on

many atmospheric parameters, including the storm motion

and vertical structure, and hail and tornado indication; but

the parameter of primary interest for hydrology and water

resources is the precipitation rate.

NEXRAD radars are scanning radars, which means

they scan radially, using different elevation angles to

provide information on vertical atmospheric structure and

to avoid man-made or topographic obstacles (figure 2).

There are several scanning patterns from which the operators can choose; the most important distinction is between

“clear-air” and “precipitation” modes. Usually the lowest

valid elevation angle is the best one to use for estimating

precipitation at ground level. Therefore, raw NEXRAD

data follows a radial coordinate system defined by azimuth, elevation angle, and range (distance from the radar).

Initial processing of the raw radar data is performed

automatically at the radar installation and includes the following steps: (1) combination of different elevation angles

into the “best” single scan; (2) removal of non-precipitation returns; (3) converting reflectivity (Z) to rain rate (R)

by use of a Z-R relation, Z = aRb; (4) correcting for hail

returns; (5) correcting for range bias; and (6) conversion

from radial coordinates to the Hydrologic Rainfall Analysis Project (HRAP) grid, whose pixels are approximately

4 by 4 km in size. Execution of these steps, among others,

creates the Digital Precipitation Array (DPA). This array

is passed on to the river forecasting centers (RFC’s) of the

NWS, where DPA fields from different radars are combined together and the precipitation rates are adjusted by

NWS hydrometeorologists by comparison with rain gages

that report in real-time. The result is called the Multisensor Precipitation Estimate (MPE). Various NEXRAD

radar precipitation estimates are available from archives

maintained by the NWS and the National Climatic Data

Center and are accessible via the World Wide Web.

Use of NEXRAD Data at the USGS Illinois Water 

Science Center

MPE fields created at the North Central RFC

(NCRFC) in Chanhassen, Minnesota, are sent to the

USGS Illinois Water Science Center (IWSC), processed,

and made available to the Salt Creek near-real-time

streamflow simulation project. The project is run cooperatively with the DuPage County Stormwater Management Division in order to supplement the available rain

gage data, which may be subject to various kinds of errors

or may be missing (figure 3). See the article, Salt Creek

Figure 1. NEXRAD radar sites in the continental United States (figure from 

http://www.ncdc.noaa.gov/nexradinv/)

Figure 2. NEXRAD Volume Coverage Pattern (VCP) 11, used for severe 

and non-severe precipitation (from Federal Meteorological Handbook, No. 

11, Part C, 2006). 


Hydrologic Information to be Analyzed, Disseminated in

an Integrated Browsable Format, on page 8 of this newsletter. The MPE data is available 2 to 12 hours after the

precipitation actually fell. Before the MPE data is available, the automatically processed DPA data is available

to be used as an initial estimate of the radar precipitation

value.

The IWSC also provides MPE data over the whole

NCRFC domain, along with IWSC rain gage totals, to the

public in a precipitation mapping interface at http://munster.

er.usgs.gov/rainfall/ and has

been used by IWSC hydrologists to spatially distribute the

precipitation for modeling the

July 1996 flood in Blackberry

Creek (see report at http://pubs.

usgs.gov/sir/2005/5270).

Comparison of MPE and Rain 

Gage Data in DuPage County

In order to assess the

accuracy of NEXRAD data, in

particular the MPE product, for

Salt Creek streamflow simulation, a study was carried out at

the IWSC, in cooperation with

the DuPage County Stormwater

Management Division, to compare the precipitation measured

by the DuPage County tipping-bucket rain gage network

and the NEXRAD MPE data

provided by the NCRFC. The

comparison was done at the

daily time scale during abovefreezing conditions between the

amount of rain recorded at each

rain gage and the MPE total in

the cell in which each gage lies.

The main lesson learned from

this study is that the correspondence between the gage and

NEXRAD rainfall values has

fluctuated over time, but has

been quite close, when averaged over all the gages, during

the period from 2001 through

2005 (figure 4). A similar study is ongoing to compare the

DPA and MPE values.

The Future of NEXRAD at IL WSC

We expect continued use of NEXRAD radar precipitation data in the Salt Creek forecasting project and in

rainfall-runoff studies, such as an ongoing study of Kishwaukee River headwaters in Kane County. A test of the

possible value of NEXRAD-based “nowcasting” for the

Figure 3. Salt Creek watershed in DuPage and Cook Counties, with rain gages and NEXRAD grid.


Salt Creek project. This project, which is planned for the

coming year, uses the observed motion of precipitation

systems over the past few hours to predict their motion

over the next few hours. NEXRAD radar precipitation

data will also figure prominently in a new partnership with

the University of Illinois at Urbana-Champaign, Department of Civil and Environmental Engineering, and the

National Center for Supercomputing Applications. Salt

Creek will be used as a test-bed for the development of a

“digital watershed”.

Figure 4. Double-mass curve analysis of NEXRAD versus gage 

precipitation in DuPage County.

NEXRAD Radar Precipitation Data: Studies and Use at the 

USGS Illinois Water Science Center—Continued. EMPLOYEE SPOTLIGHT

Jon Hortness

(Hydrologist)

Jon Hortness is a Hydrologist/

Engineer in the USGS Illinois Water

Science Center’s DeKalb Office. As

part of the Hydrologic Data Col- lection and Analysis Section, Jon’s

current duties include oversight of

streamflow, sediment, ground-water, and rainfall data

collection efforts at over 80 locations in northern Illi- nois, as well as assisting with data collection and analy- sis efforts for specific hydrologic investigations in the

area.

Jon holds BS and MS degrees in Civil Engineering

from the South Dakota School of Mines and Technol- ogy in Rapid City. He also is a registered Professional

Engineer in Illinois, Idaho, and Wisconsin. Jon began

his career with the USGS in 1996 in the South Dakota

Water Science Center while pursuing his MS degree.

Following that, he spent 8 years with the Idaho Water

Science Center in the Scientific Investigations Section

as project chief for various surface water projects. This

work included flood modeling, surface-water/groundwater interactions, analyses of low-flow and droughts,

regionalization of streamflow estimates, and analysis of

in-stream aquatic habitats. Jon also served as the West- ern Region specialist for Hydroacoustics and Cable- ways, and provided and assisted with training in these

areas.

Jon, his wife Nicole (also a Civil Engineer who

previously worked for DuPage County) and children,

Brooke (11), Bradley (6), and Kyle (1), moved to Illi- nois in the summer of 2006 to be closer to family. Jon

worked a short time for an engineering consulting firm

on various water resources type projects. A majority of

the work was being performed for the Illinois Depart- ment of Transportation and Metropolitan Water Recla- mation District of Greater Chicago. In March 2007, Jon

accepted the position in the DeKalb Office.

Although Jon’s previous experience dealt mainly

with specific project work, he understands the impor- tance of quality water resources data. He said, “When- ever I was working on a project, I would collect the

necessary data myself or make sure that the people who

were collecting the data knew exactly what it was going

to be used for. The final result of any analysis is only as

good as the data that went into it.” Jon feels that quality

data that is collected consistently across the Nation and

is readily accessible to the public is key to the USGS

mission. “In my short career, I’ve seen a huge increase

in the public’s awareness and use of our data. I think it’s

important that we continue to try to improve our data

collection techniques with new methods and technology

so we can be as accurate and efficient as possible.”


The National Spatial Data Infrastructure (NSDI)1

Cooperative Agreements Program (CAP) is an annual

program to assist the geospatial data community through

funding and other resources in implementing the components of the NSDI. This program is open to Federal,

State, local and tribal governments, academia, commercial, and non-profit organizations. This program provides

small seed grants to initiate sustainable on-going NSDI

implementations. The program emphasizes partnerships,

collaboration and the leveraging of geospatial resources in

achieving its goals. The State of Illinois is a recipient of a

2007 CAP grant for $50,000 in the Fifty States Initiative2

category.

The Fifty States Initiative is a partnership between

the National States Geographic Information Council

(NSGIC)3 and the Federal Geographic Data Committee

(FGDC)4. This initiative is designed to bring all public and

private stakeholders together as Statewide GIS coordination bodies that help to form effective partnerships and

lasting relationships. Illinois has been an active member

of NSGIC for a number of years. In addition to the initiative, NSGIC has published nine criteria that members

believe are essential for effective Statewide coordination

of geospatial information technologies. These nine criteria include: (1) A full-time, paid coordinator position is

designated and has the authority to implement the State’s

business and strategic plans; (2) a clearly defined authority

exists for Statewide coordination of geospatial information

technologies and data production; (3) the Statewide coordination office has a formal relationship with the State’s

Chief Information Officer (or similar office); (4) a champion (politician or executive decision maker) is aware and

involved in the process of coordination; (5) responsibilities for developing the NSDI and a State Clearinghouse

are assigned; (6) the ability exists to work and coordinate

with local governments, academia, and the private sector;

(7) sustainable funding sources exist to meet projected

needs; (8) coordinators have the authority to enter into

contracts and become capable of receiving and expending

funds; and (9) the Federal Government works through the

Statewide coordinating authority.

As a recipient of the 2007 CAP grant, Illinois is

interested in revitalizing the activities of the Illinois Geographic Information Council (ILGIC), revise the existing

State strategic plan, and develop a business plan to support

geospatial activities in Illinois. The strategic planning process will build on the existing administrative foundation of

ILGIC. Two of the primary goals of this process will be to

provide strategic direction to ILGIC and to strengthen its

effectiveness as the principal geospatial oversight group

in Illinois. The Strategic and Business Plans for Illinois

will identify the needs for enhanced geospatial coordination and integration among all levels of government, the

private sector, and stakeholders. By using the NSGIC

FiftyStates Initiative as a model, the core project team

will focus on the development of practical strategies to

hasten a successful outcome. The revised 5-year strategic

and business plans will serve as roadmaps that will guide

future efforts concerning the fiscal, administrative, and

technical requirements of an integrated geospatial technology infrastructure for Illinois.

The first Statewide stakeholder meeting was held in

Champaign, Illinois on July 25, 2007. There were over

140 attendees at this first gathering. Two primary goals of

this meeting were: (1) explain the current status of coordination and collaboration throughout the State, and (2)

garner input from stakeholders for the purpose of crafting

the strategic and business plans. An additional goal of this

meeting was to recruit nominations for a smaller group

to begin work on the strategic and business plans. Nominations were accepted and a core group of stakeholders

was selected to work on the second step of the process.

This second step encompasses the work needed to outline and draft the strategic and business plans. This core

stakeholder group had their first meeting in Springfield on

August 28, 2007. Future meetings are planned for October

and November 2007. The final phase of this project will

be to publicize the plans and to incorporate comments and

suggestions. For aditional information and to keep up-todate with the activities of this project, please visit: http://

www.ilgisa.org/GIS_Initiative_2007/index.html.

Statewide Geospatial Coordinating Activities

by

Shelley L. Silch, Physical Scientist

1

	 The NSDI is a means to assemble geographic data Nationwide to serve a variety of users.

2

	 Initiative that identifies the criteria, characteristics, and activities that will identify effective coordination councils.

3

	 NSGIC is an organization committed to efficient and effective government through the prudent adoption of geospatial information

technologies.

4

	 FGDC is an interagency committee that promotes the coordinated development, use, sharing, and dissemination of geospatical data on

a National basis.


Preliminary Assessment of the Water Resources of Kendall County

by

Robert T. Kay, Hydrologist

Kendall County is located on the fringe of the Chicago Metropolitan area in northeastern Illinois (figure 1).

The population of Kendall County has increased steadily

since about 1950, reaching an estimated 66,565 people in

2003. This population growth is expected to continue and

by 2030, the population of Kendall County is projected

to be about 170,000—nearly 10 times the population in

1950.

As a result of population growth, water use in Kendall

County also has increased from about 1.2 million gallons

per day in 1957 to more than 5 million gallons per day in

2000. Water use in Kendall County will increase substantially in the future as the population continues to increase.

To help meet future demands for clean drinking water, the

USGS and the County made a preliminary assessment of

the water resources in Kendall County. This assessment is

presented in USGS Scientific Investigations Report 2005-

5122, available at http://il.water.usgs.gov/pubs/sir2005-

5122.pdf.

The Fox River is the primary surface-water body in

Kendall County and is used for both wastewater disposal

and as a drinking-water supply upstream of the county.

Water from the Fox River requires treatment for use as

drinking water, but the river is a potentially viable additional source of water for the county.

Water supply needs in Kendall County are met exclusively from ground water derived from glacial drift aquifers and bedrock aquifers open to Silurian, Ordovician,

and Cambrian age formations (figure 2).

The full extent of glacial drift aquifers capable of

yielding sufficient water for municipal supply is not

know, but they are likely present in northern Kendall

County along the Fox River, and in the Newark Valley

and its tributaries (figure 3). Known glacial drift aquifers

capable of yielding sufficient water for residential supply

are present in most of the county, with the exception of

the southeastern portion. Volatile organic compounds and

trace metals and pesticides have been detected at concentrations below levels of concern in glacial drift aquifers

near waste-disposal sites. Agricultural-related chemical

constituents have been detected infrequently in glacial

drift aquifers near agricultural areas. However, widespread

problems with water quality are not apparent in these

aquifers. These aquifers are a viable source for additional

water supply, but require further study to determine their

full extent and potential prior to full development.

The shallow bedrock aquifer is composed of the

sandstone units of the Ancell Group, the Prairie du Chien

Group, and Galena-Platteville dolomite, the Maquoketa

Group, and the Silurian dolomite where these units are the

bedrock surface under the glacial drift. The availability of

water from the shallow bedrock aquifer depends primarily on the geologic formation used. The Silurian dolomite,

Figure 1. Location of Kendall County and the Chicago Metropolitan area 

(pink shading) in northeastern Illinois.


Figure 3. Well yields of glacial drift in Kendall County (modified from Schicht and others, 1976).

Galena-Platteville dolomite, and

Ancell Group can yield sufficient

water for residential and municipal

supply in at least some parts of the

county.

The Cambrian-Ordovician

aquifer system comprises the

most widespread, productive aquifer in northen Illinois and its use

for municipal-water supply has

increased within the county in the

past several years. Water levels in

the Cambrian-Ordovician aquifer

system have declined by as much

as 600 feet in Kendall County

since the late 1800s and the aquifer

frequently contains concentrations

of radium above established health

guidelines, necessitating treatment

of this water.

References

Schicht, R.J., Adams, J.R., and Stall,

J.B., 1976, Water resources availability, quality, and cost in northeastern

Illinois: Illinois State Water Survey

Report of Investigation 83, 90 p.

Figure 2. Generalized hydrogeologic column showing stratigraphy and hydrogeologic units in 

Kendall County. 


regarding reservoir management and other flood-control

measures.

The USGS, together with DPCSMD, operates 36 rainfall gages throughout and near DuPage County. Stream

elevations are monitored at more than 15 locations, and

streamflows at 11 sites are monitored, computed, and

published by the USGS. NWS NEXRAD estimates of

precipitation data for 4-kilometer by 4-kilometer areas

are formatted for streamflow simulation models and made

available through the Internet (see the related article in

this issue). Meteorological data collected by Argonne

National Laboratory are reviewed annually, missing periods estimated, and made available in an hourly format for

use in long-term simulations.

For the Salt Creek watershed, a near real-time streamflow simulation system has been developed that incorporates real-time sensor data, including stage, computed

streamflow, precipitation (including the Quantitative

Precipitation Forecast [QPF] produced by the National

Weather Service) data and NEXRAD precipitation estimates, temperature, wind, dew point, and solar radiation

into a continuous hydrologic model (HSPF). The resulting

runoff is then routed through the dynamic wave model

Full-Equations (FEQ), to determine water elevations at

key locations along the lower Salt Creek. Selected hydrologic and meteorologic data collection stations in the Salt

Creek area are shown in the figure below.

The Digital Watershed project will graphically present the NEXRAD data and provide comparison with the

precipitation-gage and streamgage data in real time. The

forecast elevations determined through the computer

models operated by the DPCSMD will be improved by the

access to the analyzed and displayed data. The computer

model results will be also incorporated into the interface

for operational decision support.

Also funded through the AESIS initiative, several

other research projects focus on aspects of water-use

decisions, optimization of data-collection networks, water

detention basin effects on West Nile virus outbreaks,

human impacts on watershed management, and stormwater management optimization.

Located in the Greater Chicago Metropolitan Region

(GCMR), the Salt Creek Watershed drains from Lake

County, through Cook and DuPage Counties to the Des

Plaines River. In August 1987, the GCMR experienced

heavy flooding resulting in 4 deaths and damages in

excess of $62.4 million (Curtis, 1990), the most severe of

which was in the communities along the Des Plaines River

and Salt Creek (Balding et al., 1992). Subsequently, with

expanded authority from the State, DuPage County (DPC)

strengthened its development of a stormwater management program including the construction and management

of two operational flood control facilities with hydrologic

data collection by the U.S. Geological Survey - Illinois

Water Science Center (USGS-IWSC) as one of its cornerstones.

Over the next two years (August 2007-May 2009)

the DuPage County Stormwater Management Division

(DPCSMD) and the USGS-IWSC will be working with

researchers funded by the University of Illinois at UrbanaChampaign (UIUC) through the Adaptive Environmental

Sensing and Information Systems (AESIS) initiative. One

of the five projects the AESIS initiative will be funding

is—An Urban Digital Watershed—Real-time Hydrological Data Dissemination and Analysis using an Integrated

Stormwater Management Information System in and near

the Salt Creek watershed.

This cooperative work is to enhance the Salt Creek

Real-Time Streamflow Simulation System, developed by

the DPCSMD and the USGS. This project will incorporate real-time streamflow, NEXRAD precipitation estimates, and precipitation gage information collected by

DPCSMD, the Metropolitan Water Reclamation District

of Greater Chicago (MWRDGC), the National Weather

Service (NWS), the USGS, and other agencies.

The real-time data presentation will be accessible as

a map interface overlaying aerial photograph images with

hydrologic data that will improve public access and understanding of streamflow-related conditions such as flooding

and potential flooding in the Salt Creek watershed. The

real-time data analysis, especially the data summaries and

the improved detection of anomalous data, and data gaps

will assist DPCSMD engineers and other emergency and

flood control agencies in operational decision-making

Salt Creek Hydrologic Information to be Analyzed, Dissemination in an 

Integrated Browsable Format

by

Audrey L. Ishii, Chief, Surface-Water Investigations Section


According to Barbara Minsker, University of Illinois

professor of Civil and Environmental Engineering and

director of AESIS, “...the Salt Creek watershed provides

an excellent test bed for prototyping the Digital Watershed

in supporting both research and decision making, given

the large investments made in data collection networks

and modeling infrastructure by the SMD and other agencies.”

AESIS is funded by the University of Illinois Urbana

Champaign Vice Chancellor for Research, National Center

for Supercomputing Applications, and Dept. of Civil and

Environmental Engineering. According to James F. Zay,

Chairman of the DuPage County Stormwater Management

Planning Committee, “This research study recognizes the

people of DuPage County who have made a tremendous

investment in proactive stormwater management and flood

damage prevention.”

References

Balding, G.O., Ishii, A.L., 1992, Floods of September 26–

October 4, 1986, and August 14–17, 1987, in Illinois: U. S.

Geological Survey Water-Resources Investigations Report

92-4149, p. 25.

Curtis, G.W., 1990, Storm and floods of August 13 to 15, 1987,

in Cook and Du Page Counties, Illinois, in National Water

Summary 1987—hydrologic events and water supply and

use: U.S. Geological Survey Water-Supply Paper 2350, p. 50.

Figure 1. Locations of precipitation gages and streamflow-gaging stations in vicinity of the Salt Creek Watershed, DuPage and Cook Counties.
10

On August 7, 2007, intense local precipitation of

5–7 inches caused severe urban flooding in downtown

Rockford. The rainfall seemed to be centered on the high

ground separating the Rock River and Kishwaukee River,

threatening the Alpine Dam and flooding streets and viaducts along ravines leading through both the east and west

sides of the city. Although Rockford was not affected as

significantly by subsequent flooding, for the city August

was the wettest month in recorded history. Although the

localized rainfall had little effect on over-all streamflow at

the time, saturated soil conditions created by this earlier

event contributed to the high discharge levels later experienced on the Rock and Kishwaukee Rivers.

On August 19, the remnants of Tropical Storm Erin

began to feed moisture into a stationary front over southeastern Minnesota and southern Wisconsin. The result

was catastrophic flooding in Winona, Minnesota. The

stationary front persisted over southern Wisconsin for the

following week, producing extended periods of heavy

rainfall.

The first effects in northern Illinois were localized

flooding similar to the Rockford event, with the Kishwaukee River rising again from local rainfall. Smaller streams

in the Chicago area were affected by the scattered nature

of the precipitation, with initial peaks

occurring in separate small basins such

as the Fox River tributaries in the western

suburbs, the Skokie River in the north,

and the Little Calumet River tributaries in

the south. 

The long-term effects of the August

19 precipitation began with inflow from

the headwaters of larger streams originating in southern Wisconsin. Initial

flooding began on the Des Plaines River,

followed by the Fox River, and the Rock

River.

The final storm event occurred on

Aug. 23, when heavy rainfall and high

winds tore through the Chicago Area. 

The rainfall was again highly localized. 

The South Branch Kishwaukee River near

DeKalb, Tyler Creek near Elgin, and Deer

Creek near Chicago Heights, all basins hit

by the earlier precipitation on August 19, suffered 100-

year floods. Larger basins such as the DuPage River were

pushed up to the 50-year flood level, while the Salt Creek

basin suffered flooding comparable to the 1987 levels. 

Local rainfall combined with main-stem inflow to push

the Fox River at Algonquin to a 40-year level.

Because the rainfall occurred over an extended period

of time, with several highly localized events over a large

area, the greatest effect was to increase the flow of the

larger basins, often at points far removed from the site of

the storm events. The most pervasive flooding was therefore seen along the downstream reaches of the Rock, Fox,

and Des Plaines Rivers. Although flood recurrence levels

for these larger streams were only in the 5–10 year recurrence range, they remained above flood stage for several

weeks.

In all, over 50 streamgaging sites from the Quad-Cities to Chicago were significantly affected by the persistent

flooding, and crews made over 70 discharge measurements, in many cases on rises and recessions over multiple

events. More information about measurements made and

the flood activities log can be found at

http://il.water.usgs.gov/flooddata/view.cgi?date=20070820

August 2007 Flooding in Northeastern Illinois

by

Marvin Harris 

Flooded neighborhood east of the Kishwaukee River in De Kalb, Illinois.
11

Downstream side of the U.S. Route 6 bridge on Aux Sable Creek, 

Grundy County.

Graphs developed at http://nwis.waterdata.usgs.gov/il/nwis/
12

Daily mean discharge from October 1, 2006 through September 30, 2007 compared with percentile distribution of mean daily discharged 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 normalflow 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.

Illinois Streamflow Conditions for October 2006 through September 2007