U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2020–5074

Prepared in cooperation with the U.S. Army Corps of Engineers

Flood-Inundation Maps for the Little Calumet River from 

Lansing to South Holland, Illinois, 2020
Cover photo. Photographs showing flooded road and park near the U.S. Geological Survey 

streamgage on the Little Calumet River at South Holland, Illinois, and (inset) flooded park near the 

U.S. Geological Survey streamgage on the Little Calumet River at South Holland, Ill. Photographs 

taken May 13, 2002, by Dave Schrader, U.S. Geological Survey.
Flood-Inundation Maps for the Little 

Calumet River from Lansing to South 

Holland, Illinois, 2020

By Andrew P. Dunn, Timothy D. Straub, and Adam E. Manaster

Prepared in cooperation with the U.S. Army Corps of Engineers

Scientific Investigations Report 2020–5074

U.S. Department of the Interior

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

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

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Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

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

Suggested citation:

Dunn, A.P., Straub, T.D., and Manaster, A.E., 2020, Flood-inundation maps for the Little Calumet River from 

Lansing to South Holland, Illinois, 2020: U.S. Geological Survey Scientific Investigations Report 2020–5074, 10 p., 

https://doi.org/ 10.3133/ sir20205074.

Associated data for this publication:

Dunn, A.P., Straub, T.D., and Manaster, A.E., 2020, Geospatial datasets for the flood-inundation study of Little Calumet 

River from Lansing to South Holland, Illinois, 2020: U.S. Geological Survey data release, https://doi. org/10.5066/

P99L14DN.

U.S. Geological Survey, 2018, USGS water data for the Nation: U.S. Geological Survey National Water Information 

System database, https://doi.org/10.5066/F7P55KJN.

ISSN 2328-0328 (online)
iii

Acknowledgments

The authors wish to thank the U.S. Army Corps of Engineers and the Little Calumet River Basin 

Development Commission for cooperating in the funding for the operation and maintenance of 

the streamgages used for this study. Special thanks to the U.S. Army Corps of Engineers for their 

cooperation in this study, the Metropolitan Water Reclamation District of Greater Chicago for 

furnishing the hydraulic models, and the National Weather Service for their continued support to 

the U.S. Geological Survey flood-inundation mapping initiative.

v

Contents

Acknowledgments........................................................................................................................................iii

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

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

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

Study-Area Description .......................................................................................................................2

Previous Studies ...................................................................................................................................2

Creation of Flood-Inundation-Map Library ................................................................................................5

Computation of Water-Surface Profiles ............................................................................................6

Hydrologic Data............................................................................................................................6

Topographic/Bathymetric Data .................................................................................................6

Hydraulic Structures ...................................................................................................................6

Energy-Loss Factors ....................................................................................................................6

Hydraulic Model ...........................................................................................................................6

Development of Water-Surface Profiles ..................................................................................6

Development of Flood-Inundation Maps ...................................................................................................8

Flood-Inundation Map Delivery ..........................................................................................................8

Disclaimer for Flood-Inundation Maps .............................................................................................8

Uncertainties and Limitations Regarding Use of Flood-Inundation Maps ..................................8

Summary..........................................................................................................................................................9

References Cited............................................................................................................................................9

Figures

1. Map showing the study reach for the Little Calumet River and Thorn Creek, 

Illinois, and locations of U.S. Geological Survey streamgages ............................................3

2. Graphs showing the hydraulic model ratings for the 2.0-, 1.0-, and 0.2-percent 

annual-exceedance probability flood events for cross sections near three 

U.S. Geological Survey streamgages ........................................................................................7

Tables

1. U.S. Geological Survey streamgage and miscellaneous site information for the 

study basin, Little Calumet River and Thorn Creek, Illinois ....................................................4

2. Stages and water-surface elevations for the streamgages on the Little Calumet 

River and Thorn Creek for selected simulated water-surface profiles ...............................5
vi

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2)

Flow rate

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

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Datum

Vertical elevation information is referenced to either (1) stage, the height above an arbitrary 

datum established at a streamgage, or (2) elevation, the height above North American Vertical 

Datum of 1988 (NAVD 88).

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

Abbreviations

AHPS Advanced Hydrologic Prediction Service

DEM digital elevation model

DWP Detailed Watershed Plan

FEMA Federal Emergency Management Agency

HEC–GeoRAS U.S. Army Corps of Engineers Hydrologic Engineering Centers Geospatial 

River Analysis System

HEC–RAS U.S. Army Corps of Engineers Hydrologic Engineering Centers River

Analysis System

MWRDGC Metropolitan Water Reclamation District of Greater Chicago

NWS National Weather Service

USGS U.S. Geological Survey
Flood-Inundation Maps for the Little Calumet River from 

Lansing to South Holland, Illinois, 2020

By Andrew P. Dunn, Timothy D. Straub, and Adam E. Manaster

Abstract

Digital flood-inundation maps for about an 8-mile 

reach of the Little Calumet River, Illinois, were created by 

the U.S. Geological Survey (USGS) in cooperation with the 

U.S. Army Corps of Engineers. The flood-inundation maps, 

which can be accessed through the USGS Flood Inundation 

Mapping Science website at https://www.usgs.gov/missionareas/water-resources/science/flood-inundation-mappingfim-program, depict estimates of the areal extent and depth 

of flooding corresponding to selected water levels (stages) 

at three USGS streamgages: Little Calumet River at South 

Holland, Ill. (USGS station 05536290); Little Calumet 

River at Munster, Indiana (USGS station 05536195); and 

Thorn Creek at Thornton, Ill. (USGS station 05536275). 

Near-real-time stages at these streamgages may be obtained 

on the internet from the USGS National Water Information 

System at https://doi.org/10.5066/F7P55KJN or the National 

Weather Service Advanced Hydrologic Prediction Service at 

https://water.weather.gov/ahps/, which also forecasts flood 

hydrographs at these sites.

Flood profiles were computed for the stream reaches 

using a one-dimensional unsteady flow step-backwater 

hydraulic model. The model performance was evaluated using 

historical streamflow measurements and the most current 

stage-discharge relations at the USGS streamgages at Little 

Calumet River at South Holland, Ill.; Little Calumet River at 

Munster, Ind.; and Thorn Creek at Thornton, Ill. The model 

was used to compute 24 water-surface profiles at 1-foot 

intervals referenced to the streamgage datum and ranging from 

bankfull to about the 0.2-percent annual-exceedance probability flood (500-year recurrence interval flood). The simulated 

water-surface profiles were then combined with a geographic 

information system digital elevation model (derived from light 

detection and ranging data having a 0.6-foot vertical accuracy and a 2-foot horizontal resolution) to delineate the area 

flooded at each water level.

The availability of these maps, along with internet 

information regarding current stage from USGS streamgages 

and forecasted high-flow stages from the National Weather 

Service, will provide emergency management personnel and 

residents with information that is critical for flood-response 

activities such as evacuations and road closures, as well as for 

postflood recovery efforts.

Introduction

South Holland, Lansing, and Calumet City within the 

Chicago metropolitan area in Cook County, Illinois, are 

densely developed cities with mostly flat terrain, and subject to flooding. The area was affected by major flooding in 

2008. The President signed the Major Disaster Declaration, 

FEMA–DR–1800, on October 3, 2008, for seven counties 

within the State of Illinois, including Cook County, after the 

September 2008 flooding (Federal Emergency Management 

Agency [FEMA], 2008a).

Before this study, emergency responders and city officials 

relied on several information sources to make decisions on 

how to best alert the public and mitigate flood damages. One 

source is the FEMA Flood Map Service Center (FEMA, 2020). 

A second source of information is the Detailed Watershed Plan 

(DWP) developed by the Metropolitan Water Reclamation 

District of Greater Chicago (MWRDGC) (Metropolitan Water 

Reclamation District of Greater Chicago [MWRDGC], 2008).

The U.S. Geological Survey (USGS) streamgages on 

the Little Calumet River (stations 05536195 and 05536290) 

and Thorn Creek (station 05536275) in the National Water 

Information System database (USGS, 2018) are another source 

from which current or historical water levels (stage) can be 

obtained. Additionally, the National Weather Service (NWS) 

forecast of peak stage at the USGS streamgages through the 

Advanced Hydrologic Prediction Service (AHPS) site at 

https://water.weather.gov/ahps/ is available. Although USGS 

current stage and NWS forecast stage information is particularly useful for residents near a streamgage, it is of slight 

use to residents farther upstream or downstream because the 

water-surface elevation is not constant along the entire stream 

channel. Knowledge of a water level at a streamgage is not 

easily translated into the depth and areal extent of flooding at 

points distant from the streamgage. One way to address this 

problem is to produce a library of flood-inundation maps that 
2 Flood-Inundation Maps for the Little Calumet River from Lansing to South Holland, Illinois, 2020

are referenced to stages recorded at the USGS streamgages. 

By examining the appropriate maps, emergency responders can estimate the projected severity of flooding (depth of 

water and areal extent), identify roads that are or may soon be 

flooded, and make plans for notification or evacuation.

Purpose and Scope

This report describes the development of a series of 

estimated flood-inundation maps for the Little Calumet River 

from Lansing to South Holland, Ill., and identifies where on 

the internet the maps can be found and ancillary data (geographic information system flood polygons and depth grids) 

can be downloaded. The location and extent of the study reach 

is about 8 miles long from 0.4 mile downstream from the 

Little Calumet River at Munster, Indiana (hereafter referred 

to as “station 05536195”), to about 0.5 mile downstream 

from the Little Calumet River at South Holland, Ill. (hereafter 

referred to as “station 05536290”) (fig. 1).

The maps were produced for flood levels referenced to 

the stage recorded at three USGS streamgages on the Little 

Calumet River from Lansing to South Holland, Ill. (table 1); 

the gages are station 05536195, station 05536290, and 

Thorn Creek at Thornton, Ill. (hereafter referred to as “station 05536275”; fig. 1). The hydraulic model was then used 

to develop flood-inundation maps for this report that include 

24 combinations of water-surface elevations at the three 

streamgages (table 2). The maps range from bankfull to about 

the 0.2-percent annual-exceedance probability flood (500-year 

recurrence interval flood). The flood maps are available 

through a mapping application that can be accessed on the 

U.S. Geological Survey Flood Inundation Mapping Science 

website (https://www.usgs.gov/mission-areas/water-resources/

science/flood-inundation-mapping-fim-program). The data 

release associated with this report can be found on ScienceBase (https://doi.org/10.5066/P99L14DN; Dunn and others, 

2020).

Study-Area Description

The Little Calumet River is in northeastern Illinois, 

and the drainage area ranges from 90 square miles (mi2) at 

station 05536195 to 208 mi2 near the downstream extent of 

the study reach at station 05536290. The headwaters originate in Indiana, and the stream generally flows westward 

before entering Illinois. Thorn Creek, a tributary to the Little 

Calumet River, joins the main stem as it flows through South 

Holland. The basin terrain is mostly flat. The urban study 

includes about an 8-mile (mi) reach of the Little Calumet 

River with an average channel slope of 0.72 foot per mile 

(ft/mi; 0.000136 foot per foot [ft/ft]). The main channel of the 

study reach has various structures (bridges, culverts, roadway 

embankments, and levees) that lie within the channel or the 

adjacent flood plain.

Previous Studies

The current flood-insurance study for Cook County is 

available at the FEMA Flood Map Service Center (FEMA, 

2020). The study provided information about the 1.0- and 

0.2-percent annual-exceedance probability water-surface 

profiles and associated flood-plain maps for the Little Calumet 

River and Thorn Creek within the study area. As part of the 

Little Calumet River DWP development by the MWRDGC 

(MWRDGC, 2008), inundation maps were produced to provide a comparison to the effective FEMA flood-plain mapping. The MWRDGC study used the hydraulic model HEC–

RAS 4.0 (U.S. Army Corps of Engineers [USACE], 2008).

Flooded road and park near the 

U.S. Geological Survey streamgage on the 

Little Calumet River at South Holland, Illinois. 

Photograph taken May 13, 2002, by Dave 

Schrader, U.S. Geological Survey.
Creation of Flood-Inundation-Map Library 3

0 0.5 1 1.5 2 KILOMETERS

Base from Farm Service Agency, National Agricultural Imagery Program for Illinois, 2015 0 0.5 1 1.5 2 MILES

Universal Transverse Mercator projection, zone 15 North

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

Study

location

ILLINOIS

COOK COUNTY

Stream Mapping extent

294 U.S. route marker 394 State route marker

U.S. Geological Survey streamgage and identifier 05536275

EXPLANATION

394

294

294

94

80 94

80 Th o rn

Cr e e k

05536290

05536275

05536195

87°38' 87°36' 87°34' 87°32'

41°36'

41°34'

41°32'

 Figure 1. The study reach for the Little Calumet River and Thorn Creek, Illinois, and locations of U.S. Geological Survey streamgages.
Table 1. U.S. Geological Survey streamgage and miscellaneous site information for the study basin, Little Calumet River and Thorn Creek, Illinois. [Vertical elevation information is referenced to the height above North American Vertical Datum of 1988; USGS, U.S. Geological Survey; NWS, National Weather Service; mi2minute; ", second] USGS station name USGS station number NWS site name1 Drainage area (mi2) Latitude Longitude Period of record Maximum 

surface ele

and 

Little Calumet River at South Holland, Illinois 05536290 SHLI2 208 41°36'25" 87°35'52" Oct. 1947–current year 595.18; 11/Little Calumet River at Munster, Indiana 05536195 LCMI3 90.0 41°34'39" 87°31'20" July 1958–current year 597.63; 09/Thorn Creek at Thornton, Illinois 05536275 THNI2 104 41°34'06" 87°36'28" April 1947–current year 603.17; 06/

1The NWS forecast site names are presented (forecasts are issued as needed during times of high water).
Creation of Flood-Inundation-Map Library 5

Creation of Flood-Inundation-Map 

Library

The USGS has standardized the procedures for creating 

flood-inundation maps for flood-prone communities (USGS, 

2019) so that the process followed and products produced are 

similar regardless of which USGS office is responsible for 

the work. Tasks specific to development of the flood maps 

were (1) retrieval of historical streamflow measurements and 

current rating (as of March 30, 2018) information from three 

streamgages on the Little Calumet River and Thorn Creek 

(table 1), (2) retrieval of the most recent (as of January 20, 

2010) existing hydraulic model for the Little Calumet River 

and Thorn Creek from the MWRDGC, (3) computation of 

water-surface profiles by use of the USACE Hydrologic 

Engineering Center’s River Analysis System (HEC–RAS) 

computer program (USACE, 2008), (4) production of estimated flood-inundation maps at various stream stages by use 

of the U.S. Army Corps of Engineers Hydrologic Engineering 

Centers Geospatial River Analysis System (HEC–GeoRAS) 

computer program (USACE, 2009) and a geographic information system, and (5) implementation into a web interface 

that links to USGS real-time streamgage information and 

(or) the NWS-forecasted peak stage to facilitate the display 

of user-selected flood-inundation maps on the internet. Maps 

were produced for water levels referenced to the stage at 

stations 05536290, 05536195, and 05536275 ranging from 

bankfull to about the 0.2-percent annual-exceedance probability flood (500-year recurrence interval flood).

Table 2. Stages and water-surface elevations for the streamgages on the Little Calumet River (U.S. Geological Survey 

stations 05536290 and 05536195) and Thorn Creek (U.S. Geological Survey station 05536275) for selected simulated water-surface 

profiles.

[Elevations are in feet above the North American Vertical Datum of 1988; ft, foot]

Profile number

U.S. Geological Survey 

station 05536290

U.S. Geological Survey 

station 05536195

U.S. Geological Survey 

station 05536275

Elevation (ft) Stage (ft) Elevation (ft) Stage (ft) Elevation (ft) Stage (ft)

1 585 10.32 589 8.66 592 5.89

2 586 11.32 590 9.66 594 7.89

3 587 12.32 591 10.66 595 8.89

4 587 12.32 592 11.66 593 6.89

5 588 13.32 592 11.66 597 10.89

6 589 14.32 592 11.66 597 10.89

7 589 14.32 593 12.66 599 12.89

8 589 14.32 594 13.66 599 12.89

9 590 15.32 594 13.66 599 12.89

10 590 15.32 595 14.66 599 12.89

11 591 16.32 595 14.66 599 12.89

12 591 16.32 596 15.66 600 13.89

13 592 17.32 595 14.66 597 10.89

14 592 17.32 596 15.66 600 13.89

15 592 17.32 597 16.66 600 13.89

16 593 18.32 596 15.66 598 11.89

17 593 18.32 597 16.66 601 14.89

18 594 19.32 598 17.66 602 15.89

19 595 20.32 597 16.66 602 15.89

20 595 20.32 598 17.66 603 16.89

21 596 21.32 598 17.66 607 20.89

22 597 22.32 599 18.66 607 20.89

23 598 23.32 599 18.66 607 20.89

24 599 24.32 600 19.66 604 17.89
6 Flood-Inundation Maps for the Little Calumet River from Lansing to South Holland, Illinois, 2020

Computation of Water-Surface Profiles

The MWRDGC hydraulic models for the Little Calumet 

River and Thorn Creek developed in HEC–RAS 4.0 (USACE, 

2008) were updated to HEC–RAS 5.0.3 (USACE, 2016) to 

produce the 24 flood-inundation maps for the mapping extent 

in this study (fig. 1). HEC–RAS is a one-dimensional, stepbackwater model for simulation of water-surface profiles with 

gradually varied, steady-, and unsteady-state flow computation 

options. The HEC–RAS analysis for this study was done using 

the unsteady-state flow computation option.

Hydrologic Data

The study reach includes three USGS streamgages (fig. 1; 

table 1). All three of the streamgages already were in operation when this project began in 2016. Water level (stage) 

is measured every 15 minutes and made available on the 

internet through the USGS National Water Information System 

(NWIS, USGS, 2018). Stage data from these streamgages are 

referenced to a local datum but can be converted to watersurface elevations referenced to the North American Vertical 

Datum of 1988 listed in table 1. Continuous records of streamflow were computed at all the sites from a stage-discharge 

relation (Turnipseed and Sauer, 2010).

A normal depth boundary condition was assumed 

downstream (with a friction slope estimated from the average 

streambed slope from the downstream mapping extent to station 05536195). To obtain the water-surface profiles for mapping, the HEC–RAS model was run in unsteady-state mode for 

the 50- (2-year flood), 20- (5-year flood), 10- (10-year flood), 

4- (25-year flood), 2- (50-year flood), 1- (100-year flood), and 

0.2- (500-year flood) percent annual-exceedance probability flood events already available in the model (MWRDGC, 

2008). The model performance was evaluated using historical streamflow measurements and the most current stagedischarge relations (USGS, 2018) at the three streamgages.

Topographic/Bathymetric Data

The USGS did not do any surveying in the field to change 

channel cross sections in the model as documented in the 

DWP (MWRDGC, 2008). Also, in the DWP model, a digital 

elevation model (DEM) with a grid size of 2 feet (ft) and vertical accuracy of 0.6 ft was used to represent the ground surface 

for parts of the cross sections that were above the water 

surface. The DEM was created by Cook County, Ill., from a 

light detection and ranging dataset collected in 2003 (Cook 

County, 2004).

Hydraulic Structures

Various structures (bridges, culverts, roadway embankments, and levees) in and along the stream affect or have the 

potential to affect water-surface elevations during floods. To 

properly account for these features in the model, structural 

dimensions were included in the MWRDGC (2008) model. 

It was verified in 2017 from the Illinois Department of 

Transportation database and oral communication at a stakeholder meeting that bridges within the mapping extent were 

not modified since the MWRDGC (2008) model development.

Energy-Loss Factors

Manning’s roughness coefficients (“n” values) are used 

in hydraulic modeling for energy- (friction) loss calculations 

(Arcement and Schneider, 1989). For the Little Calumet River 

and Thorn Creek, the Manning’s n values used ranged from 

0.043 to 0.076, and most of the values ranged from 0.04 to 

0.05 for the channel modeled in this analysis. The Manning’s n

values ranged from 0.03 to 0.2 for the upper bank and overbank areas modeled in this analysis.

Hydraulic Model

The hydraulic model ratings for the 2.0-, 1.0-, and 

0.2-percent annual-exceedance probability flood events for 

cross sections near the three USGS streamgages are shown 

in figure 2; figure 2A shows hydraulic model ratings for 

station 05536290, figure 2B shows hydraulic model ratings 

for station 05536195, and figure 2C shows hydraulic model 

ratings for station 05536275. USGS measurement data for the 

period of record (table 1) and the current streamgage rating 

are also shown in figure 2. The purpose of the mapping is to 

estimate the projected severity of flooding on a near-real-time 

basis. For this reason, it is important to ensure the model 

results encapsulate the maximum observed water-surface 

elevations. The simulated water-surface elevation results at 

each of the three streamgages are within 0.5 ft of the maximum measured water-surface elevation for a given streamflow. 

The model and measurements at station 05536290 (fig. 2A) 

do not indicate substantial hysteresis from unsteady-state 

flow conditions, but at the other two streamgages, the scatter in the measurements and hysteresis loops in the model 

results indicate unsteady flow conditions. However, at all 

three streamgages, the model results encapsulate the measured 

data for all conditions mapped. The results demonstrate that 

the model is capable of simulating accurate water levels for a 

range of flows in the basin.

Development of Water-Surface Profiles

The hydraulic model was used to develop floodinundation maps for this report that include 24 combinations 

of water-surface elevations at the three streamgages (table 2). 

The maps range from bankfull to about the 0.2-percent 

annual-exceedance probability flood (500-year recurrence 

interval flood). Profiles were developed for a total of 15 elevations at 1-ft intervals between 585 and 599 ft, as referenced 

to station 05536290. Profiles were developed for a total of 
Creation of Flood-Inundation-Map Library 7

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

Discharge, in cubic feet per second

585

590

595

600

605

610

C. Thorn Creek at Thornton, Illinois (USGS station 05536275)

582

584

586

588

590

592

594

596

598

600

602

0 500 1,000 1,500 2,000 2,500 3,000

Elevation , in feet

B. Little Calumet River at Munster, Indiana (USGS station 05536195)

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

575

580

585

590

595

600

A. Little Calumet River at South Holland, Illinois (USGS station 05536290)

USGS rating curve

Model 2.0-percent 

annual-exceedance

rating

Model 1.0-percent

annual-exceedance

rating

Model 0.2-percent

annual-exceedance

rating

USGS measurements

EXPLANATION

Figure 2. The hydraulic model ratings for the 2.0-, 1.0-, and 0.2-percent annual-exceedance probability flood events for cross sections 

near three U.S. Geological Survey (USGS) streamgages. A, Little Calumet River at South Holland, Illinois (USGS station 05536290); 

B, Little Calumet River at Munster, Indiana (USGS station 05536195); and C, Thorn Creek at Thornton, Ill. (USGS station 05536275). 

Measurement data for the period of record (table 1) and the current rating are shown.
8 Flood-Inundation Maps for the Little Calumet River from Lansing to South Holland, Illinois, 2020

12 elevations at 1-ft intervals between 589 and 600 ft, as 

referenced to station 05536195. Profiles were developed for 

a total of 13 elevations at nearly 1-ft intervals between 592 

and 607 ft, as referenced to station 05536275. The unsteady 

model results did not take place everywhere on 1-ft intervals; 

however, for all 24 combinations, the difference between the 

1-ft interval and the simulated result averaged 0.10, 0.18, 

and 0.11 ft at stations 05536290, 05536195, and 05536275, 

respectively.

Development of Flood-Inundation Maps

Flood-inundation maps were created for 24 combinations 

of water-surface elevations at the three USGS streamgages, all 

of which have been designated as intermittent NWS floodforecast points where forecasts are issued as needed during 

times of high water (as of 2018). The maps were created 

using HEC–GeoRAS and a geographic information system 

by combining the water-surface profiles and DEM data (Cook 

County, 2004). DEM data were derived from 2-ft horizontal 

resolution light detection and ranging data with a vertical 

accuracy of 0.6 ft. The DEM was obtained from MWRDGC 

(Jack T.P. Chan, MWRDGC, written commun., 2017). Any 

inundated areas that were detached from the main channel 

were examined to identify artificial connections with the main 

rivers, such as through culverts under roadways. Where such 

connections existed, the mapped inundated areas were retained 

in their respective flood maps; otherwise, the disconnected 

inundation areas were deleted.

Flood-Inundation Map Delivery

A Flood Inundation Mapping Science website has 

been established at https://www.usgs.gov/mission-areas/

water-resources/science/flood-inundation-mapping-fimprogram to provide a portal for USGS flood-inundation 

study information to the public. That web portal has a link 

(https://fim.wim.usgs.gov/fim/) to the interactive online 

flood inundation maps. The data release associated with 

this report can be found on ScienceBase (https://doi.org/

10.5066/P99L14DN; Dunn and others, 2020). At the web 

portal, each stream reach displayed contains additional links 

to USGS National Water Information System web graphs of 

the current stage and streamflow at USGS streamgages at stations 05536290 and 05536195 to which the inundation maps 

are referenced. A link also is provided to the NWS AHPS 

website (https://water.weather.gov/ahps/) so that the user 

can obtain applicable information on the forecasted peak 

stage. The estimated flood-inundation maps are displayed in 

sufficient detail to note the extent of flooding with respect 

to individual structures so that preparations for flooding and 

decisions for emergency response can be performed efficiently. Roadways and bridges were closely reviewed and are 

shown as shaded (inundated and likely impassable) or not 

shaded (dry and passable) to facilitate emergency planning 

and use; however, buildings that are shaded do not reflect 

inundation but denote that bare-earth surfaces near the buildings are inundated. When the water depth (as indicated in 

the web mapping application by holding the cursor over an 

inundated area) adjacent to the building of interest exceeds 

the height of that building, the structure can be considered 

fully submerged.

Disclaimer for Flood-Inundation Maps

The flood-inundation maps should not be used for 

navigation, regulatory, permitting, or other legal purposes. 

The USGS provides these maps “as-is” for a quick reference, 

emergency planning tool but assumes no legal liability or 

responsibility resulting from the use of this information.

Uncertainties and Limitations Regarding Use of 

Flood-Inundation Maps

Although the flood-inundation maps represent the boundaries of inundated areas with a distinct line, some uncertainty 

is associated with these maps. The flood boundaries shown 

were estimated based on water stages and streamflows at 

selected USGS streamgages. Water-surface elevations along 

the stream reaches were estimated by unsteady-state hydraulic modeling, assuming unobstructed flow, and used streamflows and hydrologic conditions anticipated at the USGS 

streamgages. The hydraulic model reflects the land-cover 

characteristics and any bridge, dam, levee, or other hydraulic 

structures existing as of January 2018. Unique meteorological 

factors (timing and distribution of precipitation) may cause 

actual streamflows along the simulated reach to vary from 

those assumed during a flood, which may lead to deviations 

in the water-surface elevations and inundation boundaries 

shown. Additional areas may be flooded due to unanticipated 

conditions such as changes in the streambed elevation or 

roughness, backwater into major tributaries along a mainstem river, or backwater from localized debris or ice jams. 

The accuracy of the floodwater extent portrayed on these 

maps will differ with the accuracy of the DEM used to simulate the land surface.

If this series of flood-inundation maps will be used in 

conjunction with NWS river forecasts, the user should be 

aware of additional uncertainties that may be inherent or factored into NWS forecast procedures. The NWS uses forecast 

models to estimate the quantity and timing of water flowing 

through selected stream reaches in the United States. These 

forecast models (1) estimate the amount of runoff generated 

by precipitation and snowmelt, (2) simulate the movement 

of floodwater as it proceeds downstream, and (3) predict 

the flow and stage (and water-surface elevation) for the 

stream at a given location (AHPS forecast point) throughout the forecast period (every 6 hours and 3–5 days out in 

many locations). For more information on AHPS forecasts, 
References Cited 9

please see https://water.weather.gov/ahps/pcpn_and_river_

forecasting.pdf. Additional uncertainties and limitations pertinent to this study may be described elsewhere in this report.

Summary

A series of 24 digital flood-inundation maps were developed in cooperation with the U.S. Army Corps of Engineers 

for the Little Calumet River between Lansing and South 

Holland, Illinois. The maps cover a reach about 8 miles 

long from 0.4 mile downstream from the U.S. Geological 

Survey (USGS) streamgage Little Calumet River at Munster, 

Indiana (station 05536195), to about 0.5 mile downstream 

from the USGS streamgage Little Calumet River at South 

Holland, Ill. (station 05536290). The maps were developed 

using the U.S. Army Corps of Engineers’ HEC–RAS and 

HEC–GeoRAS and a geographic information system program to compute water-surface profiles and to delineate 

estimated flood-inundation areas and depths of flooding for 

selected stream stages. The HEC-RAS hydraulic model was 

calibrated to the current stage-discharge relation at stations 05536195, 05536290, and 05536275 (USGS streamgage 

Thorn Creek at Thornton, Ind.). The model was used to 

compute 24 water-surface profiles at 1-foot (ft) intervals 

referenced to the streamgage datum and ranging from bankfull to the 0.2-percent annual-exceedance probability flood 

(500-year recurrence interval flood). The simulated watersurface profiles were then combined with a geographic 

information system digital elevation model derived from 

light detection and ranging data to delineate estimated floodinundation areas as shapefile polygons and depth grids for 

each profile. These flood-inundation polygons were overlaid 

on high-resolution, georeferenced aerial photographs of the 

study area. The flood maps are available through a mapping application that can be accessed on the U.S. Geological 

Survey Flood Inundation Mapping Science web site 

(https://www.usgs.gov/mission-areas/water-resources/science/

flood-inundation-mapping-fim-program).

Interactive use of the maps on this mapping application 

can give users a general indication of depth of water at any 

point by using the mouse cursor to click within the shaded 

areas. These maps, in conjunction with the real-time stage 

data from the two U.S. Geological Survey streamgages (stations 05536195 and 05536290), and forecasted flood stage 

data from the National Weather Service Advanced Hydrologic 

Prediction Service will help guide the general public in taking 

individual safety precautions and will provide emergency 

management personnel with a tool to efficiently manage emergency flood operations and postflood recovery efforts.

References Cited

Arcement, G.J., and Schneider, V.R., 1989, Guide for selecting Manning’s roughness coefficients for natural channels 

and flood plains: U.S. Geological Survey Water-Supply 

Paper 2339, 38 p. [Also available at https://doi.org/10.3133/

wsp2339.]

Cook County, 2004, Cook County Photogrammetry Project 

2003, digital terrain model “bare earth” for Cook County, 

Illinois: Triangulated Irregular Network, version 1.0.

Dunn, A.P., Straub, T.D., and Manaster, A.E., 2020, 

Geospatial datasets for the flood-inundation study of 

Little Calumet River from Lansing to South Holland, 

Illinois, 2020: U.S. Geological Survey data release, 

https://doi.org/10.5066/P99L14DN.

Federal Emergency Management Agency [FEMA], 2008, 

Illinois severe storms and flooding: Illinois, FEMA–1800–

DR, accessed January 29, 2018, at https://www.fema.gov/

pdf/news/pda/1800.pdf.

Federal Emergency Management Agency [FEMA], 2020, 

FEMA flood map service center: FEMA web page, accessed 

April 9, 2020, at https://msc.fema.gov/portal/home.

Metropolitan Water Reclamation District of Greater Chicago 

[MWRDGC], 2008, Inundation maps and hydraulic 

profiles: Metropolitan Water Reclamation District of 

Greater Chicago web page, accessed February 1, 2017, at 

https://www.mwrd.org/irj/portal/anonymous?NavigationTarget=

navurl://094fe826dea8925d364f136d40bf5142. 

[Also available at 

https://legacy.mwrd.org/irj/servlet/prt/portal/prtroot/pcd!3aportal_

content!2fMWRD!2fMWRDInternet!2fRoles!2fServices_

Facilities!2fStormWaterManagement!2fInundation_

Maps_and_Hydraulic_Profiles!2fInundation_Maps_and_

Hydraulic_Profiles.]

Turnipseed, D.P., and Sauer, V.B., 2010, Discharge measurements at gaging stations: U.S. Geological Survey 

Techniques and Methods, book 3, chap. A8, 87 p. [Also 

available at https://doi.org/10.3133/tm3A8.]

U.S. Army Corps of Engineers [USACE], 2008, HEC–RAS 

River Analysis System—Hydraulic reference manual, version 4.0: Davis, Calif., USACE, Hydrologic Engineering 

Center [variously paged].
10 Flood-Inundation Maps for the Little Calumet River from Lansing to South Holland, Illinois, 2020

U.S. Army Corps of Engineers [USACE], 2009, HEC–

GeoRAS, GIS Tools for Support of HEC–RAS using 

ArcGIS—User’s manual, version 4.2: Davis, Calif., 

USACE, Hydrologic Engineering Center [variously paged].

U.S. Army Corps of Engineers [USACE], 2016, HEC–RAS 

River Analysis System—Hydraulic reference manual, version 5.0: Davis, Calif., USACE, Hydrologic Engineering 

Center [variously paged].

U.S. Geological Survey [USGS], 2018, USGS water data 

for the Nation: U.S. Geological Survey National Water 

Information System database, accessed March 2018 at 

https://doi.org/10.5066/F7P55KJN.

U.S. Geological Survey, [USGS], 2019, Flood inundation mapping (FIM) program, U.S. Geological 

Survey Water Mission Area, accessed October 2019 at 

https://www.usgs.gov/mission-areas/water-resources/

science/flood-inundation-mapping-fim-program?qt-science_

center_objects=0#qt-science_center_objects.
For more information about this publication, contact:

Director, USGS Central Midwest Water Science Center 

405 North Goodwin

Urbana, IL 61801

217–328–8747

For additional information, visit: https://www.usgs.gov/centers/cmwater

Publishing support provided by the 

Rolla and Madison Publishing Service Centers
Dunn and others—Flood-Inundation Maps for the Little Calumet River from Lansing to South Holland, Illinois, 2020—SIR 2020–5074

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20205074