Prepared in cooperation with the Indiana Department of Transportation

Flood-Inundation Maps for Cedar Creek at 18th Street at 

Auburn, Indiana

Scientific Investigations Report 2017–5156

U.S. Department of the Interior

U.S. Geological Survey
Cover, front. Cedar Creek at 18th Street at Auburn, Indiana, Downstream 

Channel. April 20, 2015.

Cover, inside front. Cedar Creek at 18th Street at Auburn, Indiana, 

Downstream Channel with Acoustic Doppler Current Profiler (ADCP). 

February 24, 2014.

All photos taken by U.S. Geological Survey personnel. 
Flood-Inundation Maps for Cedar Creek at 

18th Street at Auburn, Indiana

By Kathleen K. Fowler

Prepared in cooperation with the Indiana Department of Transportation

Scientific Investigations Report 2017–5156

U.S. Department of the Interior

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

RYAN K. ZINKE, Secretary

U.S. Geological Survey

William H. Werkheiser, Deputy Director

 exercising the authority of the Director

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

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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:

Fowler, K.K., 2018, Flood-inundation maps for Cedar Creek at 18th Street at Auburn, Indiana: U.S. Geological Survey 

Scientific Investigations Report 2017–5156, 10 p., https://doi.org/10.3133/sir20175156.]

ISSN 2328-0328 (online)
iii

Contents

Acknowledgments.........................................................................................................................................1

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

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

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

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

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

Creation of Flood-Inundation Map Library ................................................................................................4

Computation of Water-Surface Profiles............................................................................................4

Hydrologic Data............................................................................................................................4

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

Hydraulic Structures ...................................................................................................................5

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

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

Development of Water-Surface Profiles..................................................................................7

Development of Flood-Inundation Maps ..........................................................................................7

Flood-Inundation Map Delivery.................................................................................................7

Disclaimer for Flood-Inundation Maps ....................................................................................7

Uncertainties and Limitations Regarding Use of Flood-Inundation Maps .........................7

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

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

Figures

1. Map showing locations of the study reach for Cedar Creek at 18th Street at

Auburn, Indiana; U.S. Geological Survey streamgage 04179520; and

National Weather Service forecast site ABBI3.......................................................................3

2. Flood-inundation map for Cedar Creek at 18th Street at Auburn, Indiana,

corresponding to a stage of 13.0 feet at the U.S. Geological Survey streamgage

(station number 04179520)...........................................................................................................8

Tables

1. U.S. Geological Survey streamgage information for Cedar Creek at

18th Street at Auburn, Indiana (station number 04179520)....................................................2

2. Coordinated discharges for selected annual exceedance probabilities

for Cedar Creek at 18th Street at Auburn, Indiana..................................................................4

3. Estimated discharges for corresponding stages and water-surface

elevations at U.S. Geological Survey streamgage Cedar Creek at

18th Street at Auburn, Indiana (station number 04179520)....................................................5

4. Calibration of hydraulic model to target water-surface elevations at

U.S. Geological Survey streamgage Cedar Creek at 18th Street at

Auburn, Indiana (station 04179520)............................................................................................6

5. Calibration of hydraulic model to water-surface elevations at selected

locations along Cedar Creek at Auburn, Indiana, for the flood of March 11, 2009 ............6
iv

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 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) or the National Geodetic Vertical Datum of 1929 (NGVD 29).

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

Acknowledgments

The author wishes to thank the Maumee River Basin Commission for cooperating in the 

funding for the operation and maintenance of the streamgage used for this study. Special thanks 

are given to the Indiana Department of Transportation for their cooperation in this study and to 

the National Weather Service for their continued support to the U.S. Geological Survey 

flood-inundation mapping initiative.
Flood-Inundation Maps for Cedar Creek at 18th Street 

at Auburn, Indiana

By Kathleen K. Fowler 

Abstract

Digital flood-inundation maps for a 1.9-mile reach of 

Cedar Creek at Auburn, Indiana (Ind.), from the First Street 

bridge, downstream to the streamgage at 18th Street, then ending approximately 1,100 feet (ft) downstream of the Baltimore 

and Ohio railroad, were created by the U.S. Geological Survey 

(USGS) in cooperation with the Indiana Department of Transportation. The flood-inundation maps, which can be accessed 

through the USGS Flood Inundation Mapping Science web 

site at https://water.usgs.gov/osw/flood_inundation/, depict 

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

on Cedar Creek at 18th Street at Auburn, Ind. (station number 

04179520). Near-real-time stages at this streamgage may be 

obtained from the USGS National Water Information System 

at https://waterdata.usgs.gov/ or the National Weather Service Advanced Hydrologic Prediction Service at http://water.

weather.gov/ahps/, although forecasts of flood hydrographs are 

not available at this site (ABBI3).

Flood profiles were computed for the stream reach by 

means of a one-dimensional step-backwater model. The 

hydraulic model was calibrated by using the most current 

stage-discharge relation at the Cedar Creek at 18th Street at 

Auburn, Ind. streamgage and the documented high-water 

marks from the flood of March 11, 2009. The calibrated 

hydraulic model was then used to compute seven watersurface profiles for flood stages referenced to the streamgage 

datum and ranging from 7 ft, or near bankfull, to 13 ft, in 

1-foot increments. The simulated water-surface profiles were

then combined with a geographic information system digital

elevation model (derived from light detection and ranging

[lidar] data having a 0.98-ft vertical accuracy and 4.9-ft horizontal resolution) to delineate the area flooded at each water

level.

The availability of these maps, along with internet information regarding current stage from the USGS streamgage at 

Cedar Creek at 18th Street at Auburn, Ind., and stream information 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

The city of Auburn in DeKalb County, Indiana (Ind.), has 

an estimated population of 12,806 (U.S. Census Bureau, 2010). 

Auburn and the surrounding area have experienced flooding 

numerous times, most recently in 2008, 2009, 2012, and 

2013. The majority of flood damages in the Auburn area have 

occurred along both overbanks of Cedar Creek (Federal Emergency Management Agency [FEMA], 2007). According to 

FEMA, most flooding occurs along Cedar Creek in Auburn as 

a result of runoff that is in excess of the existing channel capacity. The low areas of Eckhart Park and the county fairgrounds 

are the first to flood. As the stage increases, residential and 

commercial buildings are inundated, followed by agricultural 

areas (FEMA, 2006). Flood plains along the river are moderately developed and contain a mix of residential, commercial, 

and agricultural areas.

Prior to this study, emergency responders in Auburn 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 insurance study (FIS) for DeKalb County 

(FEMA, 2006). A second source of information is the U.S. 

Geological Survey (USGS) streamgage, Cedar Creek at 18th 

Street at Auburn, Ind. (04179520), from which current (USGS, 

2017c) and historical (USGS, 2017e) water levels (stage) and 

discharges can be obtained. A third source is the National 

Weather Service (NWS) web site for the streamgage, which 

displays stage at the USGS streamgage (NWS, 2017).

Although the current stage at a USGS streamgage is 

particularly useful for residents in the immediate vicinity of 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 
2 Flood-Inundation Maps for Cedar Creek at 18th Street at Auburn, Indiana

upstream and downstream from the streamgage. In addition, 

ease in visualizing the potential extent of flooding has been 

shown to motivate residents to take precautions and heed warnings that they previously might have disregarded. In 2016–17, 

the USGS, in cooperation with the Indiana Department of 

Transportation, conducted a project to produce a library of 

flood-inundation maps for Cedar Creek in Auburn, Ind.

Purpose and Scope

This report describes the development of a series of estimated flood-inundation maps for Cedar Creek at Auburn, Ind., 

and identifies where on the internet the maps can be accessed 

and ancillary data (geographic information system [GIS] flood 

polygons and depth grids) can be downloaded. Internet users 

can select estimated inundation maps that correspond to 

(1) flood stages at streamgage 04179520 and (2) the NWS site 

ABBI3. The scope of the study was limited to a 1.9-mile reach 

of Cedar Creek extending from the First Street bridge, downstream to the streamgage at 18th Street, and then ending 1,100 ft

downstream of the Baltimore and Ohio railroad bridge (fig. 1).

The flood-inundation maps were produced for flood 

levels referenced to the stage recorded at streamgage 04179520 

(table 1); the streamgage is on the west bank of Cedar Creek at 

the 18th Street bridge. The maps cover a range in stage from 

7 to 13 feet (ft) in 1-ft increments. The 7-ft stage is just above 

bankfull stage. A stage of 13 ft is the highest stage of the stagedischarge rating number 1.2 (effective March 11, 2009). During 

a recent flood at Auburn on March 11, 2009, the stage was 

12.3 ft, the highest recorded stage at this site (USGS, 2017d).

Study Area Description

Cedar Creek near the city of Auburn is in northeast Indiana near the center of the Auburn Morainal Complex physiographic section of the Northern Moraine and Lake Region 

(Gray, 2000). The drainage area is 87 square miles (mi2) at 

the upstream end of the study reach, 90.2 mi2

 at streamgage 

04179520, and 90.7 mi2 at the downstream end of the study 

reach (USGS, 2017c, 2017b). The headwaters originate in 

Dekalb County, Ind. at the outflow of Cedar Lake (not shown), 

and the stream flows generally southeastward and then swings 

back to the southwest as it flows through Auburn. Within the 

study reach, Cedar Creek has no significant tributaries.

 Generally, the area is characterized by till ridges of moderate relief (Gray, 2000). The 1.9-mi study reach has an average top-of-bank channel width of about 62 ft and has an average channel slope of 0.0011 (5.7 feet per mile). Much of the 

land contiguous to the study reach north of Ensley Avenue is 

residential and commercial. The land south of Ensley Avenue 

is a combination of residential, commercial, and agricultural.

The population of Auburn has increased in recent years 

from 12,806 in 2010 to 13,052 in 2015 (U.S. Census Bureau, 

2015). According to the U.S. Census Bureau, the city has a 

total area of 7.1 mi2. The main channel and adjacent flood 

plain within the study reach have seven major road crossings with bridges at; First Street, Highway 8, Ninth Street, an 

abandoned railroad, 19th Street, Auburn Drive, and the Baltimore and Ohio railroad. There are two pedestrian walkways 

(park bridges), two utility service bridges, and a bridge to the 

fairgrounds.

Table 1. U.S. Geological Survey streamgage information for Cedar Creek at 18th Street at Auburn, Indiana (station number 04179520).

[Station location is shown in figure 1. mi2, square miles; NAD 83, North American Datum of 1983; NGVD 29, National Geodetic Vertical Datum of 1929: 

NAVD 88, North American Vertical Datum of 1988; ft3/s, cubic feet per second; ̊, degree; ‘, minutes; “, seconds; ft, feet]

Streamgage 

name

Streamgage 

number

Drainage 

area 

(mi2

)

Latitude 

(NAD 83)

Longitude 

(NAD 83)

Period of 

record

Datum of 

streamgage 

(NGVD 29)

Maximum 

recorded stage and 

date

Maximum 

discharge (ft3

/s) 

during period of 

record and date

Cedar Creek at 

18th Street 

at Auburn, 

Indiana

04179520 90.2 41 ̊ 21’ 36” 85 ̊ 02’57” September 

2001 to 

present 

(2017)

844.02 ft 12.30 ft on 

March 11, 2009 

(corresponds to 

an elevation of 

855.84 

(NAVD 88)1

)

2,2902

, 

March 11, 2009

1

Datum of 843.54 (NAVD 88) was used to convert stage to water-surface elevation.

2

Discharge based on U.S Geological Survey rating number 1.2.
Introduction 3

Figure 1. Locations of the study reach for Cedar Creek at 18th Street at Auburn, Indiana; U.S. Geological Survey streamgage 

04179520; and National Weather Service forecast site ABBI3.

85°4' 85°3'30" 85°3' 85°2'30"

41°22'

41°21'30"

41°21'

0 0.25 0.5 MILES

0 0.25 0.5 KILOMETERS

INDIANA

Study area in 

DeKalb County

EXPLANATION

8

U.S. Geological Survey 

streamgage and number

State Road marker

Flow arrow—Indicates direction

of water flow

04179520

Auburn town boundary

ABBI3

National Weather Service 

Advanced Hydrologic 

Predictive Service site

Limit of study area

River reach studied

04179520

ABBI3

OLD BRICK

BALTIMORE and OHIO RAILROAD

Auburn

Creek

Cedar

AUBURN DRIVE

WATER UTILITY SERVICE BRIDGE

UTILITY DRIVE

PARK BRIDGE

FAIRGROUND BRIDGE

HIGHWAY 8

FIRST STREET

8

ROAD

ECKHART 

PARK 

ENSLEY AVENUE

PARK BRIDGE

NINTH STREET

18TH STREET

19TH STREET

Abandoned Railroad

Projection: Universal Transverse Mercator, Zone 16

Horizontal coordinate information is referenced to the North American Datum of 1983

Orthophotography from U.S. Department of Agriculture-FAS Aerial Photography Field Office, 

2012, available from National Agriculture Imagery Program (NAIP).
4 Flood-Inundation Maps for Cedar Creek at 18th Street at Auburn, Indiana

Previous Studies

The most recent FIS that provides information for the 

study area including Cedar Creek at 18th Street at Auburn 

is the FIS for Dekalb County (FEMA, 2006). The FIS for 

Dekalb County covers the geographic area of Dekalb County, 

Ind., including the community of Auburn. The hydrologic 

and hydraulic analysis for the county study was performed 

by Fuller, Mossbarger, Scott, and May Engineers, Inc. for the 

Federal Insurance Administration under Task Order number 

EMC–2003–TO–013 and was completed in May of 2004.

FEMA has produced Digital Flood Insurance Rate Maps 

that include the study area in DeKalb County (FEMA, 2007). 

These maps outline the special flood-hazard areas in Dekalb 

County and the town of Auburn. 

The Indiana Department of Natural Resources, the 

USGS, the Natural Resources Conservation Service, and the 

U.S. Army Corps of Engineers (USACE) have agreed upon 

discharges for annual exceedance probabilities for sites along 

many rivers in Indiana; the values are termed “coordinated dis

charges” and assure consistency among the State and Federal 

agencies that undertake streamflow studies (Indiana Department of Natural Resources, 2014). The coordinated discharges

for Cedar Creek at 18th Street at Auburn were obtained from 

the USGS StreamStats Program for Indiana streams (USGS, 

2017b) and are listed in table 2. These coordinated discharges 

are for the 10 and 1 percent annual exceedance probabilities. 

From 1943 to 1973, the Cedar Creek at Auburn 

streamgage (04179500) was located at Ninth Street, 0.42 mi 

upstream of the current location. Peak stage at this location 

was 10.63 ft with a discharge of 2,100 cubic feet per second.

-

Table 2. Coordinated discharges for selected annual 

exceedance probabilities for Cedar Creek at 18th Street at 

Auburn, Indiana.

[mi2, square miles; ft3/s, cubic feet per second; USGS, U.S. Geological 

Survey]

Location Drainage 

area (mi2

)

Coordinated discharges (ft3

/s)1,2 

for indicated annual exceedance 

probabilities (in percent)

10 1

At USGS 90.2 1,490 2,110

streamgage 

number 

04179520

1

Data from The StreamStats Program (U.S. Geological Survey, 2017b).

2

Data from Indiana Department of Natural Resources coordinated 

discharges for Cedar Creek at 18th Street at Auburn, Indiana.

Creation of Flood-Inundation Map 

Library

The USGS has standardized the procedures for creating 

flood-inundation maps for flood-prone communities so that the 

process followed and products produced are similar regardless of which USGS office is responsible for the work (USGS, 

2017a). Tasks specific to development of the flood maps for 

Auburn, Ind. were (1) collection of topographic and bathymetric data for selected cross sections and geometric data for the 

bridges at First Street, Highway 8, Ninth Street, an abandoned 

railroad, 19th Street, Auburn Drive, the Baltimore and Ohio 

railroad, two pedestrian walkways (park bridges), two utility 

service bridges, and a bridge to the fairgrounds; (2) estimation 

of energy-loss factors (roughness coefficients) in the stream 

channel and flood plain and determination of steady-flow data; 

(3) computation of water-surface profiles using the USACE

Hydrologic Engineering Center’s River Analysis System

(HEC–RAS) computer program (USACE, 2017); (4) production of estimated flood-inundation maps at various stream

stages using the USACE HEC–GeoRAS computer program

(USACE, 2011) and a GIS; and (5) preparation of the maps,

both as shapefile polygons that depict the areal extent of

flood inundation 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 water-surface profiles used to produce the seven 

flood-inundation maps in this study were simulated by using 

HEC–RAS, version 5.0.3 (USACE, 2017). HEC–RAS is a 

step-backwater model for simulation of water-surface profiles 

with steady-state (gradually varied) or unsteady-state flow 

computation options. The HEC–RAS analysis for this study 

was done using the steady-state (gradually varied) flow computation option.

Hydrologic Data

The study reach consists of one streamgage 04179520 

(fig. 1; table 1), which has been in operation since September 

2001 and is colocated with the NWS Advanced Hydrologic 

Prediction Service site ABBI3. The streamgage has a continuous record of measured water level (stage) and computed 

streamflow. Stage is measured every 15 minutes, transmitted hourly by a satellite radio in the streamgage, and made 

available on the internet through the USGS National Water 

Information System (NWIS; USGS, 2017e). Stage data from 

this streamgage 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) by adding 

843.54 ft. The current datum at the Cedar Creek gage is 
Creation of Flood-Inundation Map Library 5

844.02 ft above National Geodetic Vertical Datum of 1929 

(NGVD 29) (table 1). In order to compare elevations with 

the channel surveys, which are in NAVD 88, a -0.48 ft height 

conversion from the VERTCON utility was applied (National 

Geodetic Survey, 2017). Continuous records of streamflow 

are computed from a stage-discharge relation, which has been 

developed for the streamgage, and are available through the 

USGS NWIS web site (USGS, 2017c).

The steady-flow data necessary for the hydraulic model 

consisted of boundary conditions (normal depth) and peak-discharge information. The peak flows used in the model simulations (table 3) were taken from the current stage-discharge 

relation (USGS rating number 1.2, effective May 3, 2017) for 

streamgage 04179520 and corresponded with the target stages.

All computations used discharge values with known stages 

from actual streamflow measurements or the stage-discharge 

relation at the gage. No major tributaries join Cedar Creek 

within the 1.9 mi study reach; therefore, the gage-derived discharges were not adjusted for tributary inflows but were held 

constant throughout the study reach for a given profile.

Topographic and Bathymetric Data

All topographic data used in this study are referenced 

vertically to NAVD 88 and horizontally to the North American Datum of 1983 (NAD 83). Cross-section elevation data 

were obtained from a digital elevation model (DEM) that was 

derived from light detection and ranging (lidar) data that were 

collected as part of a statewide project during 2011–13 by 

Woolpert, Inc. (2011). The lidar data for Dekalb County were 

collected in 2013. The DEM was obtained from the Indiana 

Spatial Data Portal (Indiana University, 2013). The original 

lidar data have horizontal resolution of 4.9 ft and vertical accuracy of 0.98 ft at a 95-percent confidence level based on a root 

mean squared error of 0.49 ft for the “open terrain” land-cover 

category. By these criteria, the lidar data support production 

of 2-ft contours (Dewberry, 2012); the final DEM, which was 

resampled to a grid-cell size of 5 ft by 5 ft to decrease the GIS 

processing time, has a vertical accuracy of plus or minus 1 ft. 

By using HEC–GeoRAS (a set of procedures, tools, and utilities for processing geospatial data in ArcGIS), elevation data 

were extracted from the DEM for 36 cross sections. These 

data subsequently were input to the HEC–RAS model.

Because lidar data cannot provide ground elevations 

below the water surface of a stream, channel cross sections 

were surveyed by USGS field crews during November 2016. 

Cross-sectional depths were measured by using hydroacoustic 

instrumentation at 24 locations. A differential global positioning system with real-time kinematic technology was used 

to derive horizontal locations and the elevation of the water 

surface at each surveyed cross section. Georeferenced cross 

sections were made to coincide with the locations of the 

within-channel field-surveyed cross sections, using the HEC–

GeoRAS program, version 10.2. HEC–GeoRAS is a set of 

procedures, tools and utilities for processing geospatial data in 

ArcGIS and was used to extract elevation data from the DEM 

for 24 cross sections. For these 24 cross sections, within-channel field data were directly merged with the DEM data.

The DEM-generated cross section data were used in 

conjunction with the RAS Mapper tool in HEC–RAS 5.0.3 to 

interpolate below-water ground elevations through the study 

reach (USACE, 2017). The RAS Mapper creates an interpolation surface between each cross section. The interpolated 

surface is then used with the DEM-generated cross section 

data to create a grid of elevation data in between two cross 

sections. In this study, a grid of 5 ft by 5 ft was created for the 

in-channel DEM. The merged DEM of the lidar and in-channel data was used to create the remaining 17 DEM-generated 

cross sections in HEC–GeoRAS, for input to the HEC–RAS 

model. The 41 cross-section lines were drawn to best represent 

flow vectors in the channel and flood plain. Instructions for 

creation of a terrain model of the channel data are presented 

in Chapter 2 of the HEC-RAS 2D Modeling User’s Manual 

(USACE, 2016).

Hydraulic Structures

Twelve structures, consisting of bridges at seven road 

crossings (First Street, Highway 8, Ninth Street, an abandoned 

railroad, 18th Street, Auburn Drive, and the Baltimore and 

Ohio railroad), two pedestrian walkways (park bridges), two 

utility service bridges, and a bridge to the fairgrounds have 

the potential to affect water-surface elevations during floods 

along the river. Bridge-geometry data were obtained from 

field surveys conducted by personnel from the USGS IndianaKentucky Water Science Center using a differential global 

positioning system with real-time kinematic technology.

Table 3. Estimated discharges for corresponding stages and 

water-surface elevations at U.S. Geological Survey streamgage 

Cedar Creek at 18th Street at Auburn, Indiana (station number 

04179520).

[ft, feet; NAVD 88, North American Vertical Datum of 1988; USGS, 

U. S. Geological Survey; ft3/s, cubic feet per second]

Stage of 

water-surface 

profile (ft)

Water-surface 

elevation 

(ft, NAVD 88)

Estimated discharge2 at 

USGS streamgage number 

04179520 (ft3

/s)

7

8

9

10

11

12

13

850.54

851.54

852.54

853.54

854.54

855.54

856.54

869

1,110

1,360

1,630

1,910

2,200

2,490

1

Discharge from U.S. Geological Survey rating number 1.2, effective 

March 11, 2009.
6 Flood-Inundation Maps for Cedar Creek at 18th Street at Auburn, Indiana

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) (Arcement and Schneider, 

1989). Initial (precalibration) n-values were selected based on 

field observations and high-resolution aerial photographs. An 

n-value of 0.031 was selected for the main channel because it 

is natural, fairly clean, and low gradient. An n-value of 0.09

was used for the overbank areas, which are dominated by agricultural fields and forest in the rural sections of the study reach,

and the residential and commercial areas of Auburn both east

and west of the creek.

The initial n-values were adjusted as part of the calibration process, which involved minimizing the differences 

between simulated and observed water-surface elevations at the 

streamgage and elsewhere along the study reach. Roughnesscoefficient adjustment factors were varied by flow and adjusted 

until the simulated water-surface elevations approximated the 

target water-surface elevations. The actual n-values were computed by multiplying the initial n-value by each of the roughness-coefficient adjustment factors. Main channel n-values 

ranged from 0.029 to 0.040, and overbank values ranged from 

0.085 to 0.17.

Hydraulic Model

The HEC–RAS analysis for this study was done by using 

the steady-state flow computation option. Steady-state flow 

data consisted of flow regime, boundary conditions, and peak 

flows that produced water-surface elevations at the streamgage 

cross sections that matched target water-surface elevations 

within 0.36 ft of the current rating for streamgage 04179520. 

These target elevations coincided with even 1-ft increments of 

stage, referenced to the local streamgage. Subcritical (tranquil) 

flow regime was assumed for the simulations. Normal depth, 

based on an estimated average water surface slope of 0.0021 

at the downstream end of the study reach, was used as the 

downstream boundary condition of the reach. The peak flows 

that were used in the model are discussed in the “Hydrologic 

Data” section.

The hydraulic model was calibrated to the most current 

stage-discharge relation at Cedar Creek streamgage and to the 

documented high-water marks from the flood of March 11, 

2009. Model calibration was accomplished by adjusting Manning’s n-values until the results of the hydraulic computations 

closely agreed with the observed water-surface elevations for 

given flows. Absolute differences between target and simulated 

water-surface elevations for the seven simulated flows at the 

USGS streamgage were equal to or less than 0.36 ft (table 4). 

Differences between surveyed high-water marks from the flood 

of March 11, 2009 and simulated water-surface elevations were 

equal to or less than 0.98 ft (table 5). The results demonstrate 

that the model is capable of simulating accurate water levels 

over a wide range of flows in the study reach.

Table 4. Calibration of hydraulic model to target water-surface 

elevations at U.S. Geological Survey streamgage Cedar Creek at 

18th Street at Auburn, Indiana (station 04179520).

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

Stage of 

water-surface 

profile (ft)

Target 

water-surface 

elevation 

(ft, NAVD 88)

Simulated 

water-surface 

elevation 

(ft, NAVD 88)

Elevation 

difference (ft)

7.00 850.54 850.78 0.24

8.00 851.54 851.70 0.16

9.00 852.54 852.44 –0.10

10.00 853.54 853.32 –0.22

11.00 854.54 854.20 –0.34

12.00 855.54 855.30 –0.24

13.00 856.54 856.18 –0.36

Table 5. Calibration of hydraulic model to water-surface 

elevations at selected locations along Cedar Creek at Auburn, 

Indiana, for the flood of March 11, 2009.

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

River 

station 

( ft)1

Surveyed 

high-water 

mark elevation 

(ft, NAVD 88)2

Modeled 

water-surface 

elevation 

(ft, NAVD 88)3

Elevation 

difference 

(ft)

1,570.00 849.81 849.02 –0.79

1,939.60 850.10 849.70 –0.40

2,203.60 850.38 850.16 –0.22

2,626.00 851.67 850.78 –0.89

2,890.00 851.81 851.22 –0.59

3,259.60 851.87 851.56 –0.31

3,523.60 852.14 851.86 –0.28

4,474.00 853.83 852.90 –0.93

4,685.20 854.17 853.19 –0.98

5,107.60 854.13 854.03 –0.10

5,371.60 854.34 854.21 –0.13

6,480.40 855.68 855.15 –0.53

6,586.00 855.71 855.31 –0.40

6,902.80 855.99 856.18 –0.19

7,061.20 855.95 856.25 –0.30

8,645.20 857.35 856.86 –0.49

8,909.20 857.37 856.99 –0.38

9,331.60 857.84 857.47 –0.37

9,701.20 858.28 858.05 –0.23

9,859.60 858.31 858.13 –0.18

10,229.20 858.81 858.31 –0.50

10,387.60 858.39 858.36 –0.03

1

River station references the distance upstream to the high-water mark 

from the most downstream point (starting point) in the hydraulic model.

2

Elevations surveyed by Indiana Department of Natural Resources.

3

Elevation from hydraulic model profile.
Creation of Flood-Inundation Map Library 7

Development of Water-Surface Profiles

The calibrated hydraulic model was used to generate 

water-surface profiles for a total of seven stages at 1-ft intervals between 7 ft and 13 ft as referenced to the Cedar Creek 

streamgage. These stages correspond to elevations between 

850.54 ft and 856.54 ft, NAVD 88.

Development of Flood-Inundation Maps

Flood-inundation maps were created in a GIS for the 

seven water-surface profiles by combining the profiles and 

digital elevation model data. The DEM data were derived 

from the same 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 (USACE, 

2011), which allows the preparation of geometric data for 

import into HEC–RAS and processes simulation results 

exported from HEC–RAS (USACE, 2017). Shapefile polygons 

and depth grids of the inundated areas for each profile were 

modified, as required, in the ArcMap application of ArcGIS 

to ensure a hydraulically reasonable transition of the flood 

boundaries between modeled cross sections. The datasets used 

in this study are available through a data release at https://doi.

org/10.5066/F72806GR (Fowler, 2017).

Any inundated areas that were detached from the main 

channel were examined to identify subsurface connections 

with the main stream, 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 highresolution, georeferenced, aerial photographs of the study 

area. Bridge surfaces are displayed as inundated regardless 

of the actual water-surface elevation in relation to the lowest 

structural chord of the bridge or the bridge deck.

Estimates of water depth can be obtained from the depthgrid data that are included with the presentation of the flood 

maps on an interactive USGS mapping application described 

in the following section, “Flood-Inundation Map Delivery.” 

The flood-inundation map corresponding to the highest 

simulated water-surface profile, a stage of 13.0 ft, is presented 

in figure 2. A stage of 13.0 ft is based on the extended rating, number 1.2, and is 0.7 ft above the highest measured 

discharge.

Flood-Inundation Map Delivery

The current study documentation is available online at the 

USGS Publications Warehouse (https://doi.org/10.3133/sir

20175156). Also, a Flood Inundation Mapping Science web 

site (USGS, 2017b) has been established to make USGS floodinundation study information available to the public; that Flood 

Inundation Mapping Science web site 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 library 

for Cedar Creek at 18th Street at Auburn, Ind. A link on 

this web site connects to the USGS NWIS (USGS, 2017c), 

which presents the current stage and streamflow at USGS 

streamgage 04179520 to which the flood-inundation maps 

are referenced. A second link connects to the NWS Advanced 

Hydrologic Prediction Service site (NWS, 2017) so that the 

user can obtain applicable information on stage. The estimated 

flood-inundation maps are displayed in sufficient detail so 

that preparations for flooding and decisions for emergency 

response can be performed efficiently. According to model 

output, some of the first public areas to experience flooding 

are the county fairgrounds and Eckhart Park at a stage between 

6 and 7 ft. 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—

regardless of the flood magnitude. A shaded building should 

not be interpreted to indicate that the structure is completely 

submerged, rather that bare earth surfaces in the vicinity of 

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 a selected USGS streamgage. Water-surface elevations 

along the stream reaches were estimated by steady-state 

hydraulic modeling, assuming unobstructed flow, and using 

streamflows and hydrologic conditions anticipated at the 

USGS streamgage. The hydraulic model reflects the landcover characteristics and any bridge, embankment, or other 

hydraulic structures existing as of November 2016. 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 
8 Flood-Inundation Maps for Cedar Creek at 18th Street at Auburn, Indiana

sir20175156_fig 02

85°4' 85°3'30" 85°3' 85°2'30"

41°22'

41°21'30"

41°21'

0 0.25 0.5 MILES

0 0.25 0.5 KILOMETERS

EXPLANATION

8

U.S. Geological Survey 

streamgage and number

State Road marker

Flow arrow—Indicates direction

of water flow

04179520

Auburn town boundary

ABBI3

National Weather Service 

Advanced Hydrologic 

Predictive Service site

Limit of study area

River reach studied

Flood-inundation area

INDIANA

Study area in 

DeKalb County 

Projection: Universal Transverse Mercator, Zone 16

Horizontal coordinate information is referenced to the North American Datum of 1983

Orthophotography from U.S. Department of Agriculture-FAS Aerial Photography Field Office, 

2012, available from National Agriculture Imagery Program (NAIP).

04179520

ABBI3

OLD BRICK

AUBURN DRIVE

WATER UTILITY SERVICE BRIDGE

UTILITY DRIVE

PARK BRIDGE

FAIRGROUND BRIDGE

HIGHWAY 8

8

ROAD

ECKHART 

 PARK 

PARK BRIDGE

Auburn

Creek

Cedar

B ALTIMORE and OHIO RAILROAD

ENSLEY AVENUE

FIRST STREET

NINTH STREET

19TH STREET

18TH STREET

Abandoned Railroad

Figure 2. Flood-inundation map for Cedar Creek at 18th Street at Auburn, Indiana, corresponding to a stage of 13.0 feet* 

at the U.S. Geological Survey streamgage (station number 04179520).

*Thirteen feet is based on the extended rating curve and is 0.7 feet higher than the peak gage height.
References Cited 9

boundaries shown. Additional areas may be flooded because 

of unanticipated conditions such as changes in the streambed 

elevation or roughness, backwater into tributaries along a main 

stem river, blockage of water due to earthen embankments, 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.

Summary

A series of seven digital flood-inundation maps were 

developed in cooperation with the Indiana Department of 

Transportation for a 1.9-mile reach of Cedar Creek at Auburn, 

Indiana (Ind.). The stream reach flows from the First Street 

bridge, downstream to the streamgage at 18th Street, then ends 

approximately 1,100 feet (ft) downstream of the Baltimore and 

Ohio railroad bridge. The maps were developed by using the 

U.S. Army Corps of Engineers’ Hydrologic Engineering Center’s River Analysis System (HEC–RAS) and 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 current stage-discharge relation at the Cedar 

Creek streamgage at 18th Street at Auburn (04179520) and 

the documented high-water marks from the flood of March 11, 

2009. The model was used to compute seven water-surface 

profiles for flood stages referenced to the streamgage datum 

and ranging from 7 ft, or just above bankfull, to 13.0 ft. 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 (USGS) Flood Inundation Mapping Science web site 

(https://water.usgs.gov/osw/flood_inundation).

Interactive use of the maps on the USGS mapping application can give users a general indication of depth of water at 

any point by using the cursor to click within the shaded areas. 

The mapping application enables the production of customized flood-inundation maps from the map library for Cedar 

Creek at 18th Street at Auburn, Ind. These maps, in conjunction with the real-time stage data from the USGS streamgage, 

Cedar Creek at 18th Street at Auburn, Ind. (station number 

04179520), and flood stage data from the National Weather 

Service will help to 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 WaterSupply Paper 2339, 38 p.

Dewberry, 2012, National enhanced elevation assessment: 

Fairfax, Va., Dewberry, 84 p., accessed July 2014, at http://

www.dewberry.com/services/geospatial/national-enhancedelevation-assessment.

Esri, 2014, ArcGIS: Esri, accessed July 2014, at http://www.

esri.com/software/arcgis/.

Federal Emergency Management Agency (FEMA), 2006, 

Flood insurance study number 18033CV000A, DeKalb 

County, Indiana, and unincorporated areas: Washington, 

D.C., Federal Emergency Management Agency, 67 p.,

32 pls.

Federal Emergency Management Agency (FEMA), 2007, 

National Flood Hazard Layer, vector files, and associated 

attributes, DeKalb County: accessed June, 2017, at https://

msc.fema.gov/portal/advanceSearch.

Fowler, K.K., 2017, Geospatial datasets for Cedar Creek at 

18th Street at Auburn, Indiana—Flood inundation study: 

U.S. Geological Survey data release, accessed December 

2017 at https://doi.org/10.5066/F72806GR.

Gray, H.H., 2000, Physiographic divisions of Indiana: Bloomington, Indiana Geological Survey Special Report 61, 15 p., 

1 pl.

Indiana Department of Natural Resources, 2014, Coordinated 

discharges of selected streams in Indiana: Indiana Department of Natural Resources, accessed June 2017, at http://

www.in.gov/dnr/water/4898.htm.

Indiana University, 2013, Indiana spatial data portal: Indiana 

University database, accessed March 2017, at http://gis.

iu.edu/.

National Geodetic Survey, 2017, VERTCON—North American Vertical Datum Conversion: National Geodetic Survey 

web page, accessed April, 2017, at http://www.ngs.noaa.

gov/TOOLS/Vertcon/vertcon.html.

National Weather Service (NWS), 2017, Cedar Creek 

at 18th street in Auburn [Indiana] [ABBI3; USGS 

gaging station 04179520]: National Weather Service, 

Advanced Hydrologic Prediction Service, accessed January 2017, at http://water.weather.gov/ahps2/hydrograph.

php?wfo=ind&gage=ABBI3.
10 Flood-Inundation Maps for Cedar Creek at 18th Street at Auburn, Indiana

U.S. Army Corps of Engineers (USACE), 2011, HEC–GeoRAS—GIS tools for support of HEC–RAS using ArcGIS—

User’s manual (ver. 43.93): U.S. Army Corps of Engineers, 

Hydrologic Engineering Center, [variously paged], accessed 

June 2014, at http://www.hec.usace.army.mil/software/hecgeoras/documentation/HEC-GeoRAS_43_Users_Manual.

pdf.

U.S. Army Corps of Engineers (USACE), 2017, HEC–RAS 

river analysis system—Software version 5.0.3, available at 

http://www.hec.usace.army.mil/software/hec-ras/downloads.

aspx.

U.S. Army Corps of Engineers (USACE), 2016, HEC–RAS 

river analysis system—Hydraulic reference manual (ver. 

5.0): U.S. Army Corps of Engineers, Hydrologic Engineering Center, [variously paged], accessed April 10, 2017, at 

http://www.hec.usace.army.mil/software/hec-ras/documentation/HEC-RAS%205.0%20Reference%20Manual.pdf.

U.S. Census Bureau, 2010 Census interactive population 

search—IN-Auburn city: Washington, D.C., U.S. Census Bureau, accessed June 2017, at https://www.census.

gov/2010census/popmap/ipmtext.php?fl=18:1802674.

U.S. Census Bureau, 2015, QuickFacts—Auburn city,

Indiana: Washington, D.C., U.S. Census Bureau, accessed 

June 2017, at https://www.census.gov/quickfacts/fact/table/

auburncityindiana/PST045216.

U.S. Geological Survey (USGS), 2017a, Flood Inundation 

Mapping (FIM) Program: U.S. Geological Survey web 

site, accessed March 2017, at https://water.usgs.gov/osw/

flood_inundation.

U.S. Geological Survey (USGS), 2017b, StreamStats in Indiana: U.S. Geological Survey StreamStats Program, accessed 

April 2017, at https://streamstats.usgs.gov/ss/.

U.S. Geological Survey (USGS), 2017c, USGS 04179520 

Cedar Creek at 18th Street at Auburn, IN—Current/historical observations: U.S. Geological Survey National Water 

Information System, accessed January 2017, at http://nwis.

waterdata.usgs.gov/in/nwis/uv?site_no=04179520.

U.S. Geological Survey (USGS), 2017d, USGS 04179520 

Cedar Creek at 18th Street at Auburn, IN—Peak streamflow 

for Indiana: U.S. Geological Survey National Water Information System, accessed March 2017, at https://nwis.waterdata.usgs.gov/in/nwis/peak?site_no=04179520&agency_

cd=USGS&format=html.

U.S. Geological Survey (USGS), 2017e, USGS 04179520 

Cedar Creek at 18th Street at Auburn, IN—Summary 

of all available data: U.S. Geological Survey National 

Water Information System, accessed March 2017, at 

https://nwis.waterdata.usgs.gov/in/nwis/nwisman/?site_

no=04179520&agency_cd=USGS.

Woolpert, Inc., 2011, Indiana statewide digital orthoimagery 

[metadata]: Indiana University, Woolpert Order No. 71177, 

prepared by Woolpert, Inc., Geospatial Services [Dayton, 

Ohio], accessed December 16, 2015, at http://gis.iu.edu/

files/documents/in2011_ortho.txt.
Cover, front. Cedar Creek at 18th Street at Auburn, Indiana, Downstream Channel. 

April 20, 2015.

Cover, inside front. Cedar Creek at 18th Street at Auburn, Indiana, Downstream Channel 

with Acoustic Doppler Current Profiler (ADCP). February 24, 2014.

Cover back, upper. Cedar Creek at 18th Street at Auburn, Indiana, Upstream Channel. 

September 7, 2016.

Cover back, lower. Cedar Creek at 18th Street at Auburn, Indiana, Upstream Channel. 

December 21, 2015. 

All photos taken by U.S. Geological Survey personnel. 
Fowler—Flood-Inundation Maps for Cedar Creek at 18th Street at Auburn, Indiana—Scientific Investigations Report 2017–5156

)

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20175156