U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2020–5060

Prepared in cooperation with Missouri Department of Transportation, St. Charles County, and the 

Cities of O’Fallon and St. Peters, Missouri

Flood-Inundation Maps for Dardenne Creek in St. Charles 

County, Missouri, 2019
Cover. Inundated areas along Dardenne Creek in St. Louis County, Missouri. Photograph from the 

U.S. Geological Survey Flood Inundation Mapper.
Flood-Inundation Maps for Dardenne Creek 

in St. Charles County, Missouri, 2019

By David C. Heimann, Jonathon D. Voss, and Paul H. Rydlund, Jr.

Prepared in cooperation with Missouri Department of Transportation, St. Charles 

County, and the Cities of O’Fallon and St. Peters, Missouri

Scientific Investigations Report 2020–5060

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

Suggested citation:

Heimann, D.C., Voss, J.D., and Rydlund, P.H., Jr., 2020, Flood-inundation maps for Dardenne Creek in St. Charles 

County, Missouri, 2019: U.S. Geological Survey Scientific Investigations Report 2020–5060, 14 p., https://doi.org/ 

10.3133/ sir20205060.

Associated data for this publication:

Heimann, D.C., Voss, J.D., and Rydlund, P.H., Jr., 2020, Geospatial datasets for the flood-inundation study of 

Dardenne Creek, St. Charles County, Missouri, 2019: U.S. Geological Survey data release, https://doi.org/10.5066/

P9QPY9MI.

ISSN 2328-0328 (online)
iii

Acknowledgments

The authors wish to thank the Missouri Department of Transportation, St. Charles County, 

and the Cities of O’Fallon and St. Peters, Missouri, for support in the development of floodinundation maps and the operation and maintenance of the streamgages used for this study. 

The authors acknowledge Wood Environment and Infrastructure Solutions, Inc., for providing the original hydraulic model used in this study. Special thanks are given to the National 

Weather Service for their continued support of the U.S. Geological Survey Flood Inundation 

Mapping Program.

v

Contents

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

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

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

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

Study Area Description ........................................................................................................................4

Previous Studies ...................................................................................................................................4

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

Computation of Water-Surface Profiles ............................................................................................5

Hydrologic Data............................................................................................................................5

Topographic and Bathymetric Data ..........................................................................................5

Hydraulic Structures ...................................................................................................................7

Energy-Loss Factors ....................................................................................................................7

Hydraulic Model ...........................................................................................................................7

Development of Water-Surface Profiles ..................................................................................8

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

Flood-Inundation Map Delivery .................................................................................................9

Disclaimer for Flood-Inundation Maps ..................................................................................11

Uncertainties and Limitations Regarding Use of Flood-Inundation Maps .......................11

Summary........................................................................................................................................................12

References Cited..........................................................................................................................................12

Figures

1. Map showing location of study reach for Dardenne Creek at St. Peters, 

Missouri, and vicinity ...................................................................................................................3

2. Flood-inundation map for Dardenne Creek in St. Charles County, Missouri, 

corresponding to a stage of 32.0 feet at the U.S. Geological Survey streamgage 

05514860 .......................................................................................................................................10

3. Graph showing relation between the water-surface elevation at the Mississippi 

River at Grafton, Illinois, and the calculated water-surface slope between the 

Grafton and Mississippi River at Alton, Illinois, streamgages ............................................11

Tables

1. U.S. Geological Survey streamgages for Dardenne Creek at St. Peters, 

Missouri, and vicinity ...................................................................................................................2

2. Peak streamflows for selected annual exceedance probabilities for Dardenne 

Creek in St. Charles County, Missouri .......................................................................................4

3. Vertical datums of U.S. Geological Survey streamgages used in this study ......................5

4. Estimated streamflows for corresponding stages and water-surface elevations 

at selected locations, used in the hydraulic model of Dardenne Creek at Old 

Town St. Peters, Missouri ............................................................................................................6

5. Calibration of model to target water-surface elevations at U.S. Geological 

Survey streamgage 05514840 on Dardenne Creek at O’Fallon, Missouri ............................8
vi

6. Calibration of model to target water-surface elevations at U.S. Geological 

Survey streamgage 05514860 on Dardenne Creek at St. Peters, Missouri .........................8

7. Calibration of model to water-surface elevations at selected high-water mark 

locations from the December 27, 2015, flood along Dardenne Creek ..................................9

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)

acre 4,047 square meter (m2)

Flow rate

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

Datum

Vertical coordinate information is referenced to (1) stage, the height above an arbitrary datum 

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

Datum of 1988 (NAVD 88) unless otherwise stated.

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

Abbreviations

AEP annual exceedance probability

AHPS Advanced Hydrologic Prediction Service

DEM digital elevation model

FEMA Federal Emergency Management Agency

FIS flood insurance study

GIS geographic information system

HEC–GeoRAS Hydrologic Engineering Center’s Geospatial River Analysis System

HEC–RAS Hydrologic Engineering Center’s River Analysis System

lidar light detection and ranging

n Manning's roughness coefficient

NGVD 29 National Geodetic Vertical Datum of 1929

NWIS National Water Information System

NWS National Weather Service

USACE U.S. Army Corps of Engineers

USGS U.S. Geological Survey

Flood-Inundation Maps for Dardenne Creek in St. Charles 

County, Missouri, 2019

By David C. Heimann, Jonathon D. Voss, and Paul H. Rydlund, Jr.

Abstract

Digital flood-inundation maps for a 9.9-mile reach of 

Dardenne Creek, St. Charles County, Missouri, were created by the U.S. Geological Survey (USGS), in cooperation 

with the Missouri Department of Transportation, St. Charles 

County, and the Cities of O’Fallon and St. Peters, Mo. The 

flood-inundation maps, which can be accessed through 

the USGS Flood Inundation Mapping Program website 

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

science/flood-inundation-mapping-fim-program, depict 

estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at the USGS 

streamgages 05514860 Dardenne Creek at Old Town 

St. Peters, Mo., and 05587450 Mississippi River at Grafton, 

Illinois. Near-real-time stages at these streamgages may 

be obtained 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/ahps2/hydrograph.php?wfo=

lsx&gage=drcm7 and https://water.weather.gov/ahps2/

hydrograph.php?wfo=lsx&gage=grfi2, which also forecasts 

flood hydrographs at these sites (sites DRCM7 and GRFI2).

Flood profiles were computed for the Dardenne Creek 

stream reach by means of a one-dimensional model for 

simulating water-surface profiles with steady-state flow 

computations. The model was calibrated by using the current 

stage-streamflow relation at the USGS streamgages 05514840 

Dardenne Creek at O’Fallon, Mo., and 05514860 Dardenne 

Creek at Old Town St. Peters, Mo., and the documented highwater marks from the flood of December 2015.

The hydraulic model was then used to compute 17 watersurface profiles for flood stages at 1-foot (ft) intervals referenced to the streamgage datum and ranging from 16 ft, or 

near bankfull, to 32 ft at the reference streamgage 05514860. 

Stages in the lower Dardenne Creek can be affected by backwater from the Mississippi River; therefore, several sets of 

water-surface profiles were developed representing the extent 

of varying levels of backwater as referenced to the USGS 

streamgage 05587450 on the Mississippi River at Grafton, 

Ill. The upper stage for each map library exceeds the stage 

corresponding to the estimated 0.2-percent annual exceedance probability flood (500-year recurrence interval flood) at 

the streamgage location. 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 0.26-ft vertical accuracy and 0.71-ft horizontal resolution) to delineate the area flooded at each water level.

The availability of these maps, along with realtime information regarding current stage from the USGS 

streamgage and forecasted high-flow stages from the National 

Weather Service, will provide emergency management 

personnel and residents with information that is critical for 

flood mitigation, preparedness and planning, flood-response 

activities such as evacuations and road closures, and postflood 

recovery efforts.

Introduction

During September 2008, December 2015–January 2016, 

and May 2017, the major flood stage, as defined by the 

National Weather Service (NWS), was exceeded along 

Dardenne Creek in St. Charles County, Missouri. Flooding 

along lower Dardenne Creek and downstream Mississippi 

River contributed to St. Charles County being included in a 

Federal Major Disaster Declaration in January 2016 (Federal 

Emergency Management Agency [FEMA], 2020). The 

residents of O’Fallon, St. Peters, and unincorporated areas of 

St. Charles County lacked the resources needed to fully determine the status and consequences of water levels (stages) and 

streamflows along Dardenne Creek to mitigate and prepare for 

flood conditions that threaten lives and property and maximize 

response and recovery efforts.

Before this study, emergency responders in O’Fallon 

and St. Peters relied on several information sources (all of 

which are available on the internet) to make decisions on 

how to best alert the public and mitigate flood damages along 

Dardenne Creek. One source is the FEMA flood insurance 

study (FIS) for St. Charles County, dated June 2018 (FEMA, 

2018). A second source of information is the U.S. Geological 

Survey (USGS) streamgages 05514840, Dardenne Creek at 

O’Fallon, Mo., and 05514860, Dardenne Creek at Old Town 

St. Peters, Mo., from which current (USGS, 2020a, b) and 

historical (since 1999) water levels and streamflows, including annual peak flows, can be obtained. A third source of 
2 Flood-Inundation Maps for Dardenne Creek in St. Charles County, Missouri, 2019

flood-related information is the NWS Advanced Hydrologic 

Prediction Service (AHPS), which displays the USGS stage 

data from the O’Fallon and St. Peters streamgages and 

also issues forecasts of stage for the St. Peters streamgage 

(NWS, 2019a).

Although the current stage at a USGS streamgage is 

particularly useful for residents near a streamgage, it is of limited use to residents farther upstream or downstream because 

the water-surface elevation is not constant along the entire 

stream reach. Knowledge of a water level at a streamgage is 

difficult to translate into depth and areal extent of flooding at 

points distant from the streamgage. One way to address these 

informational gaps is to produce a library of flood-inundation 

maps that are referenced to the stages recorded at the USGS 

streamgage. By referring to the appropriate map, emergency 

responders can discern the severity of flooding (depth of 

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

be flooded, and make plans for notification or evacuation 

of residents in harm’s way for some distance upstream and 

downstream from the streamgage. In addition, the capability 

to visualize the potential extent of flooding has been shown to 

motivate residents to take precautions and heed warnings that 

they previously might have disregarded. In 2019, the USGS, in 

cooperation with the Missouri Department of Transportation, 

St. Charles County, and the Cities of O’Fallon and St. Peters, 

Mo., conducted a project to produce a library of floodinundation maps for a reach of Dardenne Creek extending 

through O’Fallon, St. Peters, and unincorporated St. Charles 

County, Mo.

Purpose and Scope

This report describes the development of a series 

of estimated flood-inundation maps for Dardenne Creek, 

St. Charles County, Mo., and identifies where on the internet 

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

be downloaded. The study extent includes a 9.9-mile (mi) 

reach from 0.12 mi upstream from the USGS streamgage in 

O’Fallon, Mo., to about 0.82 mi downstream from the USGS 

streamgage in St. Peters, Mo. (fig. 1). The maps were produced for flood levels using hydrologic data from four USGS 

streamgages (05514840, 05514860, 05587450, and 05587498; 

fig. 1; table 1) including two gages in the Dardenne Creek 

study reach (05514840 and 05514860) and two streamgages 

on the Mississippi River (05587450 and 05597498). Flood 

levels were referenced to the stage recorded at streamgage 

05514860, Dardenne Creek at Old Town St. Peters, Mo., near 

the downstream extent of the study reach; and maps indicating the potential extent of Mississippi River backwater in 

the study reach were referenced to streamgage 05587450, 

Mississippi River at Grafton, Illinois.

The flood-inundation maps of Dardenne Creek cover 

stages ranging from 16.0 to 32.0 feet (ft), referenced to the 

Old Town St. Peters streamgage local datum. The 16-ft stage 

is approximately bankfull and is defined by the NWS (2019b)

as the “action stage” or that stage which, when reached 

by a rising stream, requires the NWS or a partner to take 

some type of mitigation action in preparation for possible 

Table 1. U.S. Geological Survey streamgages for Dardenne Creek at St. Peters, Missouri, and vicinity.

[Station location is shown in figure 1. Latitude and longitude are given in degrees (°), minutes (′), and seconds (′′). mi2, square mile; NAD 83, North American 

Datum of 1983; ft, foot; NAVD 88, North American Vertical Datum of 1988; ft3/s, cubic foot per second; --, no data]

Station name Station 

number

Drainage 

area 

(mi2)

Latitude 

(NAD 83)

Longitude 

(NAD 83)

Period of 

peak-flow 

record 

(water 

year1)

Maximum recorded 

stage (ft), 

corresponding gage 

datum elevation (ft, 

NAVD 88), and date

Maximum 

streamflow 

(ft3/s) 

and date

Dardenne Creek at 

O’Fallon, Missouri

05514840 61 38°44′25.3′′ 90°41′42.2′′ 2000–20 19.85 (481.83)

December 27, 

2015

8,620

December 27, 

2015

Dardenne Creek at Old 

Town St. Peters, 

Missouri

05514860 102 38°48′10.95′′ 90°37′42.54′′ 2000–20 24.03 (449.42)

December 27, 

2015

10,600

December 27, 

2015

Mississippi River at 

Grafton, Illinois

05587450 171,300 38°58′04.7′′ 90°25′44.4′′ 1933–2020 38.17(441.96)

August 1, 1993

2598,000

August 1, 

1993

Mississippi River Pool 

at Lock and Dam 26 

at Alton, Illinois

05587498 -- 38°53′11.2′′ 90°10′57.17′′ 1987–2020 39.12 (439.20)

August 1, 1993

--

1A water year is the 12-month period from October 1 through September 30 of the following year and is designated by the calendar year in which it ends.

2Maximum streamflow affected to unknown degree by regulation or diversion.
Introduction 3

90°48' 90°44' 90°40' 90°36' 90°32' 90°28'

39°00'

38°56'

38°52'

38°48'

38°44'

38°40'

0 2 4 6 8 MILES

0 2 4 6 8 KILOMETERS

MISSOURI

St. Charles County

Map extent

05514840

05514860

Flow

05587450

05587498

15 miles

Highway K

Norfolk Southern RR

#

#

#

Dardenne Creek

Missouri River

Mississippi River

Schote Creek

Crooked Creek

Dardenne

Flow

Map image is the intellectual property of Esri and is used herein under license. 

Copyright © 2020 Esri and its licensors. All rights reserved

World Geodetic System 1984 Web Mercator (Auxillary Sphere) projection

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

City of O’Fallon

City of St. Peters

Old Town levee

Study reach extent

Flow-change location

U.S. Geological Survey

streamgage and identifier

EXPLANATION

05514860#

 Creek

 Figure 1. Location of study reach for Dardenne Creek at St. Peters, Missouri, and vicinity.
4 Flood-Inundation Maps for Dardenne Creek in St. Charles County, Missouri, 2019

significant hydrologic activity. The 32-ft stage exceeds the 

stage that corresponds to the estimated 0.2-percent annual 

exceedance probability (AEP) flood (500-year recurrence 

interval flood). The maps depicting the extent of backwater 

from the Mississippi River in the Dardenne Creek study 

reach cover a range from 18 to 40 ft referenced to USGS 

streamgage 05587450, Mississippi River at Grafton, Ill. 

The 18-ft stage is approximately the NWS flood stage at the 

Grafton streamgage, and the 40-ft stage exceeds the estimated 

0.2-percent AEP flood at the Mississippi River at Grafton as 

determined by the U.S. Army Corps of Engineers (USACE; 

USACE, 2004).

Study Area Description

Dardenne Creek is in east-central Missouri in St. Charles 

County, and the study reach includes, but is not limited to, the 

cities of O’Fallon and St. Peters (fig. 1). The drainage area 

upstream from the USGS streamgage 05514840 in O’Fallon 

is 61 square miles (mi2), and the drainage area upstream 

from USGS streamgage 05514860 at Old Town St. Peters is 

102 mi2. Minor tributaries that join Dardenne Creek within 

the study reach, and between the two streamgages, include 

Schote Creek (drainage area=5.0 mi2) and Crooked Creek 

(drainage area=7.2 mi2; fig. 1). The Dardenne Creek Basin 

falls within the Interior River Valley and Hills ecoregion 

characterized by smooth to moderately dissected, forested 

river side-slopes and bluffs. The region, which lies along the 

Mississippi and Missouri Rivers, is a transition zone between 

the loess- and till-covered plains to the north and the interior 

Ozark Highlands to the south (U.S. Environmental Protection 

Agency, 2020). The primary land cover of the study basin 

upstream from the St. Peters streamgage is developed lands 

(41 percent) followed by forest (32 percent) and agriculture 

(24 percent) based on 2016 National Land Cover Data (Yang 

and others, 2018). The population of the cities of O’Fallon and 

St. Peters increased 11 and 7.5 percent, respectively, between 

2010 and 2018 (U.S. Census Bureau, 2020). The study reach 

is 9.9 mi with a mean top-of-bank width of 110 ft and mean 

slope of 3.8 feet per mile based on cross-section data obtained 

from a hydraulic model of Dardenne Creek (Alecia Williams, 

Wood Environment and infrastructure Solutions, Inc., written 

commun., 2019) developed for the 2018 FIS for St. Charles 

County, Mo. (FEMA, 2018). Flood impacts near the Dardenne 

Creek at St. Peters streamgage over the range of stages from 

the NWS-defined “flood stage” to the “major flood” conditions 

are documented at NWS (2020).

A total of 12 bridges are represented in the Dardenne 

Creek hydraulic model reach and have the potential to affect 

water-surface elevations during flooding along the stream. 

These 12 bridges are 2 major four-lane highway bridges, 

7 two-lane highways and county road bridges, 1 railroad 

bridge, and 2 pedestrian trail bridges. The downstream section 

of the study reach includes a segment of the St. Peters Old 

Town Levee System constructed after flooding in 1993 (fig. 1). 

This section of the levee spans about 4.8 mi, protects about 

668 acres, and is included in the National Levee Database 

(USACE, 2020; https://levees.sec.usace.army.mil/#/).

Previous Studies

The latest FIS for Dardenne Creek in St. Charles County 

(FEMA, 2018) was completed by Wood Environment and 

Infrastructure Solutions, Inc. in 2018. A hydraulic model 

developed in 2010 (Alecia Williams, Wood Environment and 

Infrastructure Solutions, Inc., written commun., 2019) was 

used in the current FIS. The FIS uses estimates of the peak 

streamflows with 10-, 2-, 1-, and 0.2-percent AEPs (table 2) 

and their associated water-surface elevations for Dardenne 

Creek. These peak streamflow estimates originally were 

developed by the USACE in a previously published watershed 

study of Dardenne Creek (USACE, 2007).

Table 2. Peak streamflows for selected annual exceedance probabilities for Dardenne Creek in St. Charles County, Missouri.

[Data from Federal Emergency Management Agency (2018) and U.S. Army Corps of Engineers (2007). mi2, square mile; ft3/s, cubic foot per second; RR, 

railroad]

Location on Dardenne Creek 

(fig. 1)

Drainage 

area 

(mi2)

Estimated streamflows (ft3/s) for indicated 

annual exceedance probability (percent)

10 2 1 0.2

At State Highway K 61.2 9,960 16,830 19,910 30,550

At Norfolk Southern RR 102.8 10,370 17,170 19,400 29,460

At mouth 154.2 10,310 14,230 17,440 25,960
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, 

2020c) so that the process followed and products produced 

are similar regardless of which USGS office is responsible 

for the work. Tasks specific to the development of the floodinundation maps for this study included (1) acquiring the 

hydraulic model that is used in the current FIS for Dardenne 

Creek in O’Fallon and St. Peters, Mo. (Alicia Williams, 

Wood Environment and Infrastructure Solutions, Inc., written 

commun., 2019), (2) surveying bridge cross-sections at all 

bridges within the study reach, (3) calibrating energy-loss 

factors (roughness coefficients) in the stream channel and 

floodplain and determining steady-state flow data, (4) computing water-surface profiles using the USACE Hydrologic 

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

computer program (USACE, HEC, 2019), (5) producing estimated flood-inundation maps for selected stream stages using 

HEC–RAS and a GIS, and (6) preparing the maps as shapefile 

polygons that depict the areal extent of flood inundation at 

various stages, and as depth grids that provide the depth of 

floodwaters for display on a USGS flood-inundation mapping 

application.

Computation of Water-Surface Profiles

The hydraulic model used in this study was developed 

in 2010 by Wood Environment and Infrastructure Solutions, 

Inc. for an update of the FIS for O’Fallon and St. Peters, 

Mo. (Alecia Williams, Wood Environment and Infrastructure 

Solutions, Inc., written commun., 2019). This model, developed using HEC–RAS version 5.0.7 (USACE, HEC, 2019), 

was calibrated by the USGS and used to produce the floodinundation maps in this study. HEC–RAS is a one-dimensional 

model for simulation of water-surface profiles with steadystate (gradually varied) or unsteady-state flow computation options.

Hydrologic Data

This study uses hydrologic data from four USGS 

streamgages (05514840, 05514860, 05587450, and 05587498; 

fig. 1; table 1); two of these streamgages (05514840 and 

05514860) are located in the Dardenne Creek study reach 

at which stage is measured every 15 minutes. Stage is measured at the Mississippi River streamgages (05587450 and 

05597498) every 30 minutes. The stages are transmitted 

hourly by a satellite radio at each streamgage and are made 

available on the internet through the USGS National Water 

Information System (NWIS) database (USGS, 2020d). Stage 

data from these streamgages are referenced to a local datum 

but can be converted to water-surface elevations referenced 

to the North American Vertical Datum of 1988 (NAVD 88) 

or National Geodetic Vertical Datum of 1929 by adding the 

corresponding vertical datum (table 3). Continuous records of 

streamflow for the Dardenne Creek streamgages are computed from a stage-streamflow relation (Turnipseed and Sauer, 

2010). The streamflow records are available through the USGS 

NWIS database.

The estimated streamflows for specific stages used in 

the model simulations (table 4) were obtained from a stagestreamflow rating (rating 10.0) at the Dardenne Creek at Old 

Town St. Peters streamgage that was generated from discrete 

streamflow measurements. Several minor tributaries join 

Dardenne Creek within the 9.9-mile study reach between the 

O’Fallon and St. Peters streamgages, and a flow-change location was included at reach mile 5.9 in the model at a location 

downstream from several tributaries (fig. 1; table 4). The mean 

ratio (0.89) of peak streamflows from concurrent peaks at the 

O’Fallon and St. Peters streamgages over the range of recorded 

conditions and overall period of record was used to determine 

the corresponding upstream model boundary flows (table 4).

Topographic and Bathymetric Data

All topographic data used in this study are referenced 

vertically to NAVD 88, unless otherwise stated, and horizontally to the North American Datum of 1983. Cross-section 

Table 3. Vertical datums of U.S. Geological Survey streamgages used in this study.

[NAVD 88, North American Vertical Datum of 1988; NGVD 29, National Geodetic Vertical Datum of 1929]

Station name Station number Vertical datum, in feet above 

NAVD 88 (or NGVD 29)

Dardenne Creek at O’Fallon, Missouri 05514840 461.98

Dardenne Creek at Old Town St. Peters, Missouri 05514860 425.39

Mississippi River at Grafton, Illinois 05587450 (403.79)

Mississippi River at Lock and Dam 26 at Alton, Illinois 05587498 (400.00)

1Streamgage vertical datum established or checked using a Level II survey with accuracy within 0.26 foot as defined in Rydlund and Densmore (2012).
6 Flood-Inundation Maps for Dardenne Creek in St. Charles County, Missouri, 2019

elevation data from the 2010 model obtained from Wood 

Environment and Infrastructure, Inc (Alecia Williams, Wood 

Environment and Infrastructure Solutions, Inc., written 

commun., 2019) were updated to a digital elevation model 

(DEM) that was derived from light detection and ranging 

(lidar) data collected in February 2017 by Merrick-Surdex 

Joint Venture, Greenwood Village, Missouri, through a 

contract with the Metropolitan St. Louis Sewer District and 

available through the USGS National Map Viewer (USGS, 

2019). Postprocessing of these data was completed by Surdex 

Corporation on August 17, 2017. The bare-earth lidar data 

were processed using USGS Base Lidar Specifications version 

1.3 (Heidemann, 2018) that met or exceeded the National Map 

Accuracy standards for vertical and horizontal accuracy guidelines for 2-ft contours (American Society for Photogrammetry 

and Remote Sensing, 1990, 2004). The lidar data have a horizontal accuracy of 1.97 ft (60 centimeters) root mean square 

error and vertical accuracy of 0.607 ft (18.5 centimeters) root 

mean square error. The final DEM, which has a 3.28-ft gridcell size, has a vertical accuracy of plus or minus 1 ft.

By using the USACE Hydrologic Engineering Center’s 

Geospatial River Analysis System (HEC–GeoRAS; Ackerman, 

2009), a set of procedures, tools, and utilities for processing 

geospatial data in ArcGIS, elevation data were extracted from 

the DEM for the model cross sections (fig. 1) and subsequently input to the HEC–RAS model. Because lidar data 

cannot provide ground elevations below a stream’s water 

surface, channel cross sections in the HEC–RAS model were 

surveyed by Wood Environment and Infrastructure Solutions 

during 2010 (Alicia Williams, Wood Environment and 

Infrastructure Solutions, written commun., 2019) and verified 

at bridge openings by USGS field crews in September 2019 

to account for any fluvial changes since the original surveys. 

The Old Town levee surface also was surveyed by a USGS 

field crew in September 2019 for verification of model data. 

Cross-sectional depths were measured by taping down from a 

known bridge elevation at all surveyed locations. A differential 

global positioning system with real-time kinematic technology 

was used to derive vertical reference elevations at tape down 

locations and to collect levee topographic elevation points. A 

Table 4. Estimated streamflows for corresponding stages and water-surface elevations at selected locations, used in the hydraulic 

model of Dardenne Creek at Old Town St. Peters, Missouri.

[ft, foot; NAVD 88, North American Vertical Datum of 1988; ft3/s, cubic foot per second]

Stage of water-surface profile 

(ft)1

Water-surface elevation

(ft, NAVD 88)

Estimated streamflow at indicated location (ft3/s)

At upstream end of study reach 

(reach mile 9.9)2 At reach mile 5.9 in study reach2

16 441.39 2,380 2,680

17 442.39 2,890 3,250

18 443.39 3,520 3,950

19 444.39 4,270 4,800

20 445.39 5,070 5,700

21 446.39 6,010 6,750

22 447.39 7,030 7,900

23 448.39 8,230 9,250

324 449.39 9,430 10,600

25 450.39 10,600 11,900

26 451.39 11,800 13,300

27 452.39 13,000 14,600

28 453.39 13,400 15,100

29 454.39 16,400 18,400

30 455.39 17,100 19,200

31 456.39 22,100 24,800

32 457.39 26,700 30,000

1Water-surface profiles are 1-ft increments of stage, referenced to the local gage datum of the U.S. Geological Survey streamgage 05514860, Dardenne Creek 

at Old Town St. Peters, Missouri.

2The downstream extent of Hydrologic Engineering Center’s River Analysis System model (fig.1) is reach mile 0.0.

3Highest streamflow measurement corresponds to stage of 24.05 ft.
Creation of Flood-Inundation-Map Library 7

Level IV survey (Rydlund and Densmore, 2012) procedure 

was used in acquiring reference elevations with a resulting 

vertical accuracy of reference points within 0.32 ft. The bathymetric data were incorporated into the HEC–RAS model, and 

the “RAS Mapper” feature in HEC–RAS was used to generate 

a DEM of channel bathymetry and to merge the bathymetry 

DEM with the terrain DEM. Additional information from asbuilt bridge plans (Dale Henderson, Missouri Department of 

Transportation, written commun., 2019) were used to revise 

cross sections at bridges that were constructed after the original model was developed (2010).

Hydraulic Structures

A total of 12 bridges are represented in the Dardenne 

Creek hydraulic model and have the potential to affect watersurface elevations during flooding along the stream. These 

12 bridges are 2 major four-lane highway bridges, 7 twolane highways and county road bridges, 1 railroad bridge, 

and 2 pedestrian trail bridges. Initial bridge-geometry data 

were obtained from a HEC–RAS model developed by Wood 

Environment and Infrastructure Solutions (Alicia Williams, 

Wood Environment and Infrastructure Solutions, written 

commun., 2019), and updated and verified through field 

surveys and from as-built bridge plans by personnel from the 

USGS Central Midwest Water Science Center. The Old Town 

levee along the downstream east bank of the study reach was 

included in the HEC–RAS model of the study reach as a levee 

(fig. 1). As such, the landward side of the levee remained dry 

until the estimated Dardenne Creek water surface exceeded 

the levee height. Although the levee is overtopped at Dardenne 

Creek at St. Peters at stages of approximately 28 ft and greater, 

the water depths in the leveed area cannot be estimated with 

certainty using a steady-state simulation, and, therefore, the 

leveed area is shown as an area of uncertainty throughout the 

range of simulated stages.

Energy-Loss Factors

Hydraulic analyses require the estimation of energy 

losses that result from frictional resistance exerted by a 

channel on flow. These energy losses are quantified by the 

Manning’s roughness coefficient (“n” value). Initial (precalibration) n values were selected on the basis of field observations, high-resolution aerial photographs collected through 

the U.S. Department of Agriculture’s National Agriculture 

Imagery Program and available through the Missouri Spatial 

Data Information Service (2019), and tabulated estimates of n

values (Chow, 1959).

As part of the calibration process, the initial n values were varied by flow and adjusted until the differences 

between simulated and observed water-surface elevations 

at the streamgage and elsewhere along the study reach were 

minimized. The final n values ranged from 0.04 to 0.048 for 

the main channel and from 0.03 to 0.12 for the overbank areas 

simulated in this analysis. The lowest channel coefficients 

were placed in straight, upstream sections of the model reach, 

and the highest were placed in sinuous, low-gradient, finematerial substrate reaches with vegetated banks in the downstream sections of the model reach. The lowest roughness 

coefficients on the floodplain were placed in open water bodies 

(lakes) and the highest in densely forested areas.

Hydraulic Model

The HEC–RAS analysis for this study was performed 

using the steady-state flow computation option. A onedimensional model with steady-state flow option was used as 

the flow direction was primarily in the streamwise direction 

without substantial floodplain storage. The areas behind the 

levees at the downstream end of the model reach in which 

storage could be substantial are indicated as “areas of uncertainty” in the flood-inundation map products. Steady-state 

flow data consisted of flow regimes, boundary conditions, 

and peak flows that produced water-surface elevations at 

the streamgage cross sections that matched target watersurface elevations. These target elevations coincided with 

1-ft increments of stage, referenced to the local gage datum. 

Subcritical (tranquil) flow regime was assumed for the simulations. Normal depth, based on an estimated mean watersurface slope of 0.0008, was used as the reach’s downstream 

boundary condition. The normal depth condition accurately 

represented the range of peak streamflow conditions that 

were documented during the 20-years of gage operations 

at the Dardenne Creek at St. Peters streamgage. The flood 

profiles generated using the normal depth boundary condition, however, do not represent any substantial influences 

from backwater from the Mississippi River. The peak 

flows used in the model were discussed in the “Hydrologic 

Data” section.

The HEC–RAS model was calibrated to a developed 

stage-streamflow relation (rating 5.0) at streamgage 05514840 

on Dardenne Creek at O’Fallon, Mo., a developed stagestreamflow relation (rating 10.0) at streamgage 05514860 on 

Dardenne Creek at Old Town St. Peters, Mo., and to documented high-water marks from the flood of December 27, 

2015. Model calibration was accomplished by adjusting 

Manning’s n values and ineffective flow characteristics until 

the results of the hydraulic computations closely agreed 

with the observed water-surface elevations for given flows. 

Differences between target and simulated water-surface 

elevations for simulated flows at the USGS streamgage 

05514840 were equal to or less than 0.66 ft (table 5) and were 

equal to or less than 0.55 ft at USGS streamgage 05514860 

(table 6). Differences between surveyed and simulated elevations of 10 high-water marks in the study reach for the flood 

of December 27, 2015, were less than or equal to 0.72 ft 

(table 7). The results demonstrate that the model is capable of 

simulating accurate water levels throughout the reach over a 

large range of stages and flows.
8 Flood-Inundation Maps for Dardenne Creek in St. Charles County, Missouri, 2019

Development of Water-Surface Profiles

The calibrated hydraulic model was used to generate 

water-surface profiles for a total of 17 stages at 1-ft intervals 

between 16 and 32 ft as referenced to the local datum of the 

Dardenne Creek at Old Town St. Peters, Mo., streamgage. 

These stages correspond to elevations of 441.39 and 457.39 ft 

NAVD 88, respectively. Streamflows corresponding to the 

various stages were obtained from the current (2020) stagestreamflow relation (rating 10.0) for the Dardenne Creek 

at Old Town St. Peters, Mo., streamgage. Streamflows 

through the study reach were adjusted for tributary inflows 

by including a flow change location (fig. 1; table 4) in the 

model to represent the cumulative addition of primary tributary inflows.

Development of Flood-Inundation Maps

Flood-inundation maps were created for the Dardenne 

Creek study reach and referenced to the USGS streamgage 

05514860 on Dardenne Creek at Old Town St. Peters, 

Mo., a designated NWS flood-forecast point (site DRCM7; 

NWS, 2019a). The DEM data were derived from the same 

Table 5. Calibration of model to target water-surface elevations at U.S. Geological Survey streamgage 05514840 on Dardenne Creek at 

O’Fallon, Missouri.

[ft, foot; NAVD 88, North American Vertical Datum of 1988]

Stage of water-surface profile

(ft)

Target water-surface elevation 

(ft, NAVD 88)

Modeled water-surface elevation 

(ft, NAVD 88)

Difference in elevation

(ft)

12.02 474.00 474.26 −0.26

13.02 475.00 475.41 −0.41

14.02 476.00 476.52 −0.52

15.02 477.00 477.64 −0.64

16.02 478.00 478.66 −0.66

17.02 479.00 479.54 −0.54

18.02 480.00 480.32 −0.32

19.02 481.00 481.05 −0.05

20.02 482.00 481.74 0.26

21.02 483.00 482.33 0.66

Table 6. Calibration of model to target water-surface elevations at U.S. Geological Survey streamgage 05514860 on Dardenne Creek at 

St. Peters, Missouri.

[ft, foot; NAVD 88, North American Vertical Datum of 1988]

Stage of water-surface profile

(ft)

Target water-surface elevation 

(ft, NAVD 88)

Modeled water-surface elevation 

(ft, NAVD 88)

Difference in elevation

(ft)

14.61 440.00 439.92 −0.08

15.61 441.00 440.79 −0.21

16.61 442.00 441.66 −0.34

17.61 443.00 442.56 −0.43

18.61 444.00 443.46 −0.53

19.61 445.00 444.54 −0.46

20.61 446.00 445.59 −0.41

21.61 447.00 446.66 −0.34

22.61 448.00 447.77 −0.23

23.61 449.00 448.85 −0.15

24.61 450.00 450.05 0.05

25.61 451.00 451.55 0.55

26.61 452.00 452.14 0.14
Creation of Flood-Inundation-Map Library 9

lidar data described previously in the “Topographic and 

Bathymetric Data” section and therefore have an estimated vertical accuracy of 2 ft (that is, plus or minus 1 ft). 

Estimated flood-inundation boundaries for each simulated 

profile were developed with HEC–GeoRAS software 

(Ackerman, 2009), which allows the preparation of geometric data for import into HEC–RAS and processes simulation 

results exported from HEC–RAS (USACE, HEC, 2010). 

Shapefile polygons and depth grids of the inundated areas 

for each profile were modified, as required, in the ArcMap 

application of ArcGIS (Esri, 2020) to ensure a hydraulically 

reasonable transition of the flood boundaries between modeled cross sections.

Any inundated areas that were detached from the main 

channel were examined to identify subsurface connections 

with the main river, such as through culverts under roadways. 

Where such connections existed, the mapped inundated areas 

were retained in their respective flood maps; otherwise, the 

erroneously delineated parts of the flood extent were deleted. 

The flood-inundation areas are overlaid on high-resolution, 

georeferenced, aerial photographs of the study area. Bridge 

surfaces are shown as not inundated until the lowest flood 

stage that either exceeds the bridge deck or completely inundates both approaches to the bridge. In these latter circumstances, the bridge surface is depicted as being inundated. 

Estimates of water depth can be obtained from the depth-grid 

data (Heimann and others, 2020) that are included with the 

presentation of the flood maps on an interactive USGS mapping application described in the following section, “FloodInundation Map Delivery.” The flood map corresponding to 

the highest simulated water-surface profile, a stage of 32.0 ft, 

is presented in figure 2.

Inundation maps of the estimated extent of backwater 

from the Mississippi River on the Dardenne Creek study reach 

were generated using GIS software. A linear-regression model 

was developed (fig. 3) between the water-surface elevation 

at the USGS streamgage 05587450 on the Mississippi River 

at Grafton, Ill., and the corresponding water-surface slope 

between the Mississippi River at Grafton and the USGS 

streamgage 05587498 on the Mississippi River at Lock and 

Dam 26 at Alton, Ill., based on observed peak data and estimated flood-frequency stage values from the USACE (2004). 

The estimated water-surface slopes at 1-ft stage increments 

at the Grafton streamgage, for stages ranging from 50- to 

0.2-percent AEP flow conditions, were used to extrapolate 

water-surface elevations to the mouth of Dardenne Creek. A 

planar digital surface was assigned a value corresponding to 

the Mississippi River water-surface elevation at the mouth of 

Dardenne Creek, and the surface was overlain on the basin terrain model to generate inundation polygons and depth grids in 

the Dardenne Creek study reach. This methodology is similar to that used in the development of backwater profiles for 

tributaries as outlined in the FEMA guidelines for the development of flood profiles in FIS reports (FEMA, 2016). In total, 

23 maps depicting Mississippi River backwater conditions 

were developed for Grafton stages of 18 to 40 ft corresponding 

to water-surface elevations at the mouth of Dardenne Creek of 

425.38 to 445.98 ft.

Flood-Inundation Map Delivery

The current study documentation is available online at 

the USGS Publications Warehouse https://doi.org/10.3133/

sir20205060). Also, a Flood Inundation Mapping Program 

Table 7. Calibration of model to water-surface elevations at selected high-water mark locations from the December 27, 2015, flood 

along Dardenne Creek.

[ID, identifier; ft, foot; NAVD 88, North American Vertical Datum of 1988; D, downstream; USGS, U.S. Geological Survey; U, upstream]

Cross-section ID (ft)1

and location

Surveyed watersurface elevation 

(ft, NAVD 88)

Modeled watersurface elevation 

(ft, NAVD 88)

Difference in 

elevation

 (ft)

92,027.5 Highway K 482.00 481.88 −0.12

91,933.7 D (at USGS streamgage 05514840) 481.83 481.63 −0.20

86,727 D Highway 364 476.60 476.41 −0.19

7,9092.7 U Highway N 472.40 471.68 −0.72

78,824 Highway N 472.21 471.57 −0.64

74,125.5 Mid Rivers Mall Road 468.54 467.96 −0.58

51,287 U Interstate 70 455.20 455.18 −0.02

48,743.1 Downstream from Interstate 70 452.60 453.00 0.41

45,558.2 Downstream from Interstate 70 450.60 450.81 0.21

44,594.5 D (at USGS streamgage 05514860) 449.42 449.33 −0.09

1Cross-section identification numbers are referenced to the longitudinal baseline used in the hydraulic model. The downstream model boundary cross-section 

ID corresponds to a value of 40,257 ft and is 40,257 ft from the confluence with the Mississippi River. The upstream boundary of 92,590.8 is 92,590.8 ft 

upstream from the Dardenne Creek-Mississippi River confluence.
10 Flood-Inundation Maps for Dardenne Creek in St. Charles County, Missouri, 2019

90°42' 90°40' 90°38'

38°48'

38°46'

38°44'

#

#

MISSOURI

0 0.5 1 2 MILES

0 0.5 1 2 KILOMETERS

EXPLANATION

Inundation extent at stage of 32.0 feet 

at U.S. Geological Survey (USGS) 

streamgage 05514860

Old Town Levee within study reach

Study reach extent

# 05514860

05514860

05514840

USGS streamgage and identifier

Map image is the intellectual property of Esri and is used herein under license. 

Copyright © 2020 Esri and its licensors. All rights reserved

World Geodetic System 1984 Web Mercator (Auxillary Sphere) projection

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

 Figure 2. Flood-inundation map for Dardenne Creek in St. Charles County, Missouri, corresponding to a stage of 32.0 feet at 

 the U.S. Geological Survey streamgage 05514860.
Creation of Flood-Inundation-Map Library 11

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

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

center_objects=0#qt-science_center_objects; USGS, 2020c) 

has been established to make USGS flood-inundation study 

information available to the public. The website links to a 

mapping application that presents map libraries and provides 

detailed information on flood extents and depths for modeled sites. The mapping application enables the production of 

customized flood-inundation maps from the map libraries for 

Dardenne Creek (Heimann and others, 2020). A link on the 

mapping application website connects to the USGS NWIS 

(USGS, 2020d), which presents the current stage and streamflow at the USGS streamgages 05514860 on Dardenne Creek 

at St. Peters, Mo., and 05587450 on the Mississippi River at 

Grafton, Ill., to which the inundation maps are referenced. A 

second link connects to the NWS AHPS site (NWS, 2019a) 

so that the user can obtain applicable information on forecasted peak stages at the two reference locations. Additionally, 

a link is provided on the mapping application to the USGS 

WaterAlert application (USGS, 2020e), which notifies the user 

when a specified stage threshold is reached. The estimated 

flood-inundation maps are displayed in sufficient detail so 

that preparations for flooding and decisions for emergency 

response can be performed efficiently. Depending on the flood 

magnitude, roadways are shown as shaded (inundated and 

likely impassable) or not shaded (dry and passable) to facilitate emergency planning and use. Bridges are shaded—that 

is, shown as inundated—when the flood stage exceeds the 

elevation of the bridge deck. A shaded building should not be 

interpreted to mean that the structure is completely submerged 

but, rather, that bare earth surfaces near the building are inundated. In these instances, the water depth (as indicated in the 

mapping application by holding the cursor over an inundated 

area) near the building would be an estimate of the water level 

inside the structure, unless flood-proofing measures had been 

implemented.

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 on the basis of water stages and streamflows at 

selected USGS streamgages. Water-surface elevations along 

the stream reaches were estimated by steady-state hydraulic 

modeling, assuming unobstructed flow, and used streamflows and hydrologic conditions anticipated at the USGS 

streamgage(s). The hydraulic model reflects the land-cover 

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

structures existing as of September 2019. Unique meteorological factors (timing and distribution of precipitation) may cause 

actual streamflows along the modeled reach to vary from those 

assumed during a flood, which may lead to deviations in the 

water-surface elevations and inundation boundaries shown. 

0

0.05

0.01

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

415 420 425 430 435 440 445

Calculated water-surface slope of the Mississippi River 

betwen Grafton and Alton, Illinois, in feet per mile (y)

Water-surface elevation at Mississippi River at Grafton, Illinois, 

in feet above National Geodetic Vertical Datum of 1929 (x)

y = −0.0071 x + 3.3938

Coefficient of determination (R 2

) = 0.58 

Line of best fit

 Figure 3. Relation between the water-surface elevation at the Mississippi River at Grafton, Illinois, and the 

 calculated water-surface slope between the Grafton and Mississippi River at Alton, Illinois, streamgages.
12 Flood-Inundation Maps for Dardenne Creek in St. Charles County, Missouri, 2019

Additional areas may be flooded due to unanticipated conditions such as changes in the streambed elevation or roughness, 

backwater into major tributaries along a main-stem river, or 

backwater from localized debris or ice jams. The accuracy of 

the floodwater extent portrayed on these maps will vary with 

the accuracy of the DEM used to simulate the land surface. An 

additional source of uncertainty in the prediction of watersurface elevations at the Dardenne Creek confluence with the 

Mississippi River, and corresponding backwater extents, is the 

potential variability resulting from changing slope conditions 

of the Mississippi River.

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 to 5 days out in 

many locations). For more information on AHPS forecasts, 

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

forecasting.pdf.

Eight model scenarios exceed the highest streamflow 

measurement made at the Dardenne Creek at St. Peters 

streamgage corresponding to a stage of approximately 24 ft, 

therefore, there is additional uncertainty for flood-inundation 

maps at stages greater than 24 ft. Incremental changes in 

inundation area and water depths are not displayed on the 

USGS Flood Inundation Program web site for the Old Town 

levee area within the Dardenne Creek study reach (fig. 2). The 

leveed area is displayed on the web mapper as a designated 

area of uncertainty.

Summary

A series of digital flood-inundation maps were developed by the U.S. Geological Survey (USGS) in cooperation 

with the Missouri Department of Transportation, St. Charles 

County, and the Cities of O’Fallon and St. Peters, Missouri, 

for Dardenne Creek, in St. Charles County, Missouri. The 

maps cover a reach about 9.9 miles long corresponding to the 

approximate limits of Dardenne Creek within the O’Fallon 

and St. Peters city limits. The maps were developed by using 

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

Center’s River Analysis System (HEC–RAS) and Hydrologic 

Engineering Center’s Geospatial River Analysis System 

(HEC–GeoRAS) programs 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 stage-streamflow 

relation at the USGS streamgage 05514840 Dardenne Creek 

at O’Fallon, USGS streamgage 05514860 Dardenne Creek 

at St. Peters, and to observed high-water marks from the 

December 2015 flood. The model was used to compute 

17 water-surface profiles for flood stages at 1-foot (ft) intervals referenced to the local streamgage datum and ranging 

from 16.0 ft, or near bankfull, to 32.0 ft, which exceeds the 

stage corresponding to the estimated 0.2-percent annual 

exceedance probability flood (500-year recurrence interval). 

In total, 23 maps also were developed showing inundation 

area within the study reach displaying the extent of backwater 

from the Mississippi River in the study reach that were referenced to the USGS streamgage 05587450 Mississippi River 

at Grafton, Illinois.

The simulated water-surface profiles were then combined 

with a geographic information system digital elevation model 

derived from light detection and ranging data to delineate 

estimated flood-inundation 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 Program 

website (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 are used in conjunction with the realtime stage data from the U.S. Geological Survey reference 

streamgages (05514860 on Dardenne Creek at St. Peters, Mo., 

and 05587450 on the Mississippi River at Grafton, Ill.) and 

forecasted flood stage data from the National Weather Service 

Advanced Hydrologic Prediction Service. The joint products 

can help guide the general public in taking individual safety 

precautions and provides emergency management personnel 

with a tool to mitigate and prepare for flood-related emergencies, efficiently manage emergency flood operations, and 

effectively conduct postflood recovery efforts.

References Cited

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of HEC–RAS using ArcGIS—User’s manual (ver. 4.2): 

U.S. Army Corps of Engineers, CPD–83, [variously paged], 

accessed May 6, 2019, at https://www.hec.usace.army.mil/

software/hec-georas/downloads.aspx.

American Society for Photogrammetry and Remote 

Sensing, 1990, ASPRS accuracy standards for largescale maps: American Society for Photogrammetry 

and Remote Sensing, accessed December 11, 2019, at 

http://www.asprs.org/a/society/committees/standards/1990_

jul_1068-1070.pdf.
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American Society for Photogrammetry and Remote Sensing, 

2004, ASPRS guidelines—Vertical accuracy reporting 

for lidar data: American Society for Photogrammetry 

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profiles: Federal Emergency Management Agency, 

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Engineers, 64 p.

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analysis system—Hydraulic reference manual (ver. 

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For more information about this publication, contact:

Director, USGS Central Midwest Water Science Center 

1400 Independence Road

Rolla, MO 65401

573–308–3667

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

Publishing support provided by the

Rolla Publishing Service Center
Heimann and others—Flood-Inundation Maps for Dardenne Creek in St. Charles County, Missouri, 2019—SIR 2020–5060

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20205060