U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3269

Prepared in cooperation with the Indiana Office of Community and Rural Affairs

Flood-Inundation Maps for the Elkhart River 

at Goshen, Indiana

Pamphlet to accompany
Cover. Simulated floods corresponding to a stage of 5.0, 9.0, and 13.0 feet at U.S. Geological Survey streamgage 04100500 on the Elkhart River 

and image of the Elkhart River downstream from the streamgage. Photograph by Edward Dobrowolski, U.S. Geological Survey.
Flood-Inundation Maps for the Elkhart River 

at Goshen, Indiana

By Kellan R. Strauch

Prepared in cooperation with the Indiana Office of Community and Rural Affairs

Pamphlet to accompany

Scientific Investigations Map 3269

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

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

Suggested citation:

Strauch, K.R., 2013, Flood-inundation maps for the Elkhart River at Goshen, Indiana: U.S. Geological Survey Scientific 

Investigations Map 3269, 9 sheets, 7-p. pamphlet, http://dx.doi.org/10.3133/sim3269.

ISSN 2329–132X (online)
iii

Acknowledgments

The author wishes to thank the many local, State, and Federal agencies that have cooperated in 

the funding for the operation and maintenance of the gages used for this study, especially the 

Indiana Department of Transportation. Special thanks are given to the City of Goshen and Elkhart 

County staff for their cooperation in this study by providing data and reviewing flood-inundation 

maps prior to publication, and to the National Weather Service for their continued support of the 

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

Contents

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

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

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

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

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

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

Constructing Water-Surface Profiles.........................................................................................................2

Hydrologic and Steady-Flow Data .....................................................................................................4

Topographic and Bathymetric Data...................................................................................................4

Energy-Loss Factors.............................................................................................................................4

Model Calibration and Performance .................................................................................................5

Development of Water-Surface Profiles...........................................................................................5

Inundation Mapping ......................................................................................................................................6

Elkhart River, Indiana, Flood-Inundation Maps on the Internet ....................................................6

Disclaimer for Flood-Inundation Maps .............................................................................................6

Uncertainties and Limitations Regarding Use of Flood-Inundation Maps ..................................6

Summary..........................................................................................................................................................7

References Cited............................................................................................................................................7

Sheets

[Sheets and additional materials are available online at http://pubs.usgs.gov/sim/3269/]

1–9. Estimated flood-inundation maps for the Elkhart River at Goshen, Indiana, 

referenced to the U.S. Geological Survey streamgage number 04100500 

on the Elkhart River, and corresponding to a stage of:

1. 5.00 ft and an elevation of 774.03 ft (NAVD 88)

2. 6.00 ft and an elevation of 775.03 ft (NAVD 88)

3. 7.00 ft and an elevation of 776.03 ft (NAVD 88)

4. 8.00 ft and an elevation of 777.03 ft (NAVD 88)

5. 9.00 ft and an elevation of 778.03 ft (NAVD 88)

6. 10.00 ft and an elevation of 779.03 ft (NAVD 88)

7. 11.00 ft and an elevation of 780.03 ft (NAVD 88)

8. 12.00 ft and an elevation of 781.03 ft (NAVD 88)

9. 13.00 ft and an elevation of 782.03 ft (NAVD 88)
v

Figures

1. Map showing location of study reach for the Elkhart River, U.S. Geological Survey 

streamgage, and National Weather Service forecast site....................................................3

Tables

1. U.S. Geological Survey streamgage site information for the study area, 

Elkhart River at Goshen, Indiana................................................................................................4

2. Comparison of hydraulic-model output simulated and observed water-surface 

elevations at the Elkhart River at Goshen, Indiana, station number 04100500 ...................5

3. Stages and water-surface elevations with corresponding discharge estimates 

at selected locations along the Elkhart River at Goshen, Indiana, for simulated 

water-surface profiles .................................................................................................................5
vi

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

foot (ft) 30.48 centimeter (cm)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

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

cubic foot per second per square

mile [(ft3/s)/mi2]

0.01093 cubic meter per second per square

kilometer [(m3/s)/km2]

Hydraulic gradient

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

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

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

Datum of 1988 (NAVD 88).

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

Altitude, as used in this report, refers to distance above the vertical datum.
Flood-Inundation Maps for the Elkhart River 

at Goshen, Indiana

By Kellan R. Strauch

Abstract

The U.S. Geological Survey (USGS), in cooperation with 

the Indiana Office of Community and Rural Affairs, created 

digital flood-inundation maps for an 8.3-mile reach of the 

Elkhart River at Goshen, Indiana, extending from downstream 

of the Goshen Dam to downstream from County Road 17. The 

inundation maps, which can be accessed through the USGS 

Flood Inundation Mapping Science Web site at http://water.

usgs.gov/osw/flood_inundation/, depict estimates of the areal 

extent and depth of flooding corresponding to nine selected 

water levels (stages) at the USGS streamgage at Elkhart River 

at Goshen (station number 04100500). Current conditions 

for the USGS streamgages in Indiana may be obtained on the 

Internet at http://waterdata.usgs.gov/. In addition, streamstage data have been provided to the National Weather Service 

(NWS) for incorporation into their Advanced Hydrologic Prediction Service (AHPS) flood-warning system (http://water.

weather.gov/ahps/). The NWS forecasts flood hydrographs at 

many places that are often collocated with USGS streamgages. 

NWS-forecasted peak-stage information may be used in 

conjunction with the maps developed in this study to show 

predicted areas of flood inundation. 

In this study, flood profiles were computed for the stream 

reach by means of a one-dimensional step-backwater model. 

The model was calibrated using the most current stagedischarge relation at the Elkhart River at Goshen streamgage. 

The hydraulic model was then used to compute nine watersurface profiles for flood stages at 1-foot (ft) intervals referenced to the streamgage datum and ranging from approximately bankfull (5 ft) to greater than the highest recorded 

water level (13 ft). The simulated water-surface profiles were 

then combined with a geographic information system (GIS) 

digital-elevation model (DEM), derived from Light Detection and Ranging (LiDAR) data having a 0.37-ft vertical 

accuracy and 3.9-ft horizontal resolution in order to delineate 

the area flooded at each water level. The availability of these 

maps, along with Internet information regarding current stage 

from USGS streamgages and forecasted stream stages from 

the NWS, 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 Goshen in Elkhart County, Indiana (Ind.), 

an urban community with a reported population of 31,719, is 

part of the Elkhart-Goshen Metro Area (pop. 197,561 in 2010; 

U.S. Census Bureau, 2010). Peak streamflows, since 1925, 

and continuous stage measurements, since 1931, have been 

recorded at a U.S. Geological Survey (USGS) streamgage on 

the Elkhart River at Goshen (station number 04100500). The 

peak discharge of record, 6,360 cubic feet per second (ft3/s) 

at a stage of 11.87 feet (ft; gage datum), occurred on February 24, 1985. The most recent flood event with approved flow 

data (stage above 7 ft) occurred April 29, 2011, with a flow of 

3,450 ft3/s and a stage of 7.99 ft. Flood plains within Goshen 

are moderately developed and contain a mix of residential and 

commercial structures.

Prior to this study, Goshen officials 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. One source is the Federal Emergency Management Agency (FEMA) Flood Insurance Study 

(FIS) for Elkhart County, which includes the City of Goshen 

and is dated August 2, 2011 (Federal Emergency Management Agency, 2011). A second source of information is the 

USGS streamgage, Elkhart River at Goshen (station number 

04100500), from which current or historical water levels (stages) can be obtained. A third source is the National 

Weather Service’s (NWS) Advanced Hydrologic Prediction 

Service (AHPS), which also displays current stage data from 

the USGS gage, as well as river forecasts of stage during 

times of high water. Although USGS current stage and NWS 

forecast stage information 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 
2 Flood-Inundation Maps for the Elkhart River at Goshen, Indiana

channel. Also, FEMA and State emergency management 

mitigation teams or property owners typically lack information 

related to how deep the water is at locations other than near 

USGS streamgages or NWS flood-forecast points. In 2011–12, 

the USGS, in cooperation with the Indiana Office of Community and Rural Affairs, conducted a study to produce a 

library of flood-inundation maps for an 8.3-mile (mi) reach 

of the Elkhart River at Goshen. The inundation maps depict 

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

Elkhart River at Goshen (station number 04100500).

Purpose and Scope

The purpose of this report is to describe the development 

of a series of maps showing the estimated flood-inundation 

extent for the Elkhart River at Goshen, Ind. The maps are 

accessed through the USGS Flood Inundation Mapping Science Web site at http://water.usgs.gov/osw/flood_inundation/

and the NWS AHPS Web site at http://water.weather.gov/

ahps/. Internet users can select estimated inundation maps 

that correspond to (1) current stage at the USGS streamgage, 

(2) the NWS-forecasted peak stage, or (3) other stream stages 

of interest.

The scope of the study was limited to the Elkhart River 

from downstream of Goshen Dam to a point 5,450 ft downstream from the County Road 17 bridge (fig. 1). Tasks specific 

to development of the maps were:

1. collection of topographic and bathymetric data for 

selected cross sections and geometric data bridges along 

the study reach, 

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 U.S. 

Army Corps of Engineers (USACE) HEC–RAS computer 

program (U.S. Army Corps of Engineers, 2010), 

4. production of estimated flood-inundation maps at various 

stream stages using the USACE’s HEC–GeoRAS computer program (U.S. Army Corps of Engineers, 2009) and 

a geographic information system (GIS), and

5. preparation of the maps, both as polygon shapefiles that 

depict the areal extent of flood inundation and as depth 

grids that provide the depth of flood waters, as displayed 

on the USGS Flood Inundation Mapper web site (http://

wim.usgs.gov/FIMI/), which can be accessed through the 

USGS Flood Inundation Mapping Science Web site at 

http://water.usgs.gov/osw/flood_inundation/. 

Methods used were generally cited from previously 

published reports. If techniques varied significantly from 

previously documented methods because of local hydrologic 

conditions or available data, they are described in detail in 

this report. Maps were produced for water levels referenced 

to the Elkhart River stage at the Goshen streamgage, which 

ranged from approximately bankfull (5 ft above gage datum) 

to greater than the maximum observed water level (13 ft) at 

the streamgage.

Study Area Description

The study reach of the Elkhart River is in Elkhart County 

in north-central Indiana. The drainage area ranges from 

584 square miles (mi2) at the outlet of Goshen Dam Pond 

to 643 mi2 at the downstream extent of the study reach. The 

drainage area at the Elkhart River at Goshen streamgage is 

594 mi2. The stream’s headwaters originate in Noble County, 

Ind., and the stream flows generally to the northwest before 

entering the city limits. One major tributary to the Elkhart 

River, Rock Run Creek (drainage area 42 mi2), joins the main 

stem as it flows through Goshen. The basin terrain is generally 

flat. The study reach is approximately 8.3 mi long and has an 

average top-of-bank channel width of 186 ft and an average 

channel slope of 2.38 feet per mile (ft/mi) or 0.00045. About 

49 percent of the land contiguous to the study reach is classified as urban or developed, 7 percent as forest, and 4 percent 

as cropland (Homer and others, 2007). The study area is still 

undergoing development, and the population has increased 

8 percent from 29,383 to 31,719 between 2000 and 2010 (U.S. 

Bureau of Census, 2010). The main channel within the study 

reach is bridged by six major roads and a railroad. 

Previous Studies

Although the current countywide FIS became effective 

in 2011 (Federal Emergency Management Agency, 2011), 

the data contained therein that deals with flooding in the City 

of Goshen is from the original FIS completed by Clyde E. 

Williams and Associates in 1977 (Federal Emergency Management Agency, 2011). That study provided information on 

the 10-, 2-, 1- and 0.2-percent annual exceedance probability 

water-surface profiles and associated 1- and 0.2-percent floodplain maps for the Elkhart River and Rock Run Creek. The 

water-surface profiles and the flood frequencies on which they 

were based have not been updated since 1977; however, the 

flood-plain maps in the 2011 FIS do include revised floodinundation delineations that were based on updated, detailed 

land-surface elevation data made possible by the use of Light 

Detection and Ranging (LiDAR).

Constructing Water-Surface Profiles

The water-surface profiles used to produce the nine 

flood-inundation maps in this study were computed using 

HEC–RAS, version 4.1.0 (U.S. Army Corps of Engineers, 

2010). HEC–RAS is a one-dimensional step-backwater model 
Constructing Water-Surface Profiles 3

!.

85°52'30" 85°50'

41°37'30"

41°35'

04100500

Goshen

33

ELKHART ROAD

WEST WILDEN AVENUE

4 WEST LINCOLN AVENUE

COUNTY ROAD 17

119

33

WEST PIKE STREET

15

15

Elkhart

River

Goshen 

Dam Pond Hydraulic 

Canal

INDIANA

Study

area

EXPLANATION

15

03363900

33

Levee

Limit of study area

Flow arrow—Indicates direction

of water flow

U.S. Geological Survey 

streamgage and number

State route marker

U.S. route marker

Projection: Indiana State Plane Eastern Zone

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

Orthophotography from Esri ArcGIS World Imagery, 

2011, available at http://goto.arcgisonline.com/maps/World_Imagery

0 0.5 1 MILE

0 0.5 1 KILOMETER

Figure 1. Location of study reach for the Elkhart River, U.S. Geological Survey streamgage, and National Weather Service 

forecast site.
4 Flood-Inundation Maps for the Elkhart River at Goshen, Indiana

for simulation of water-surface profiles with gradually varied, 

steady-state (or unsteady-state) flow computation options. The 

HEC–RAS analysis for this study was done using the steadystate flow computation option.

Hydrologic and Steady-Flow Data

The study area hydrologic network consists of one 

streamgage (04100500; fig. 1; table 1). Water level (stage) is 

measured continuously at the site, and the continuous record 

of streamflow is computed for the site. All water-surface 

elevations reported herein are referenced to the North American Vertical Datum of 1988 (NAVD 88). The gage is equipped 

with a satellite radio transmitter that allows these data to be 

transmitted routinely for posting on the Internet within an hour 

of collection.

Steady-flow data consisted of flow regime, boundary 

condition set to normal depth, and peak-discharge information. 

Because there are no major tributaries from the upstream limit 

of the study area to the Elkhart River at Goshen streamgage, 

flow data for the upstream end of the study reach were 

obtained from the current stage-to-discharge relation, which 

has been developed from measurements of streamflow at the 

Elkhart River at Goshen streamgage. For the downstream part 

of the study reach, discharge recorded at the streamgage was 

increased proportional to the drainage-area ratio to account 

for the expected increase in flows from Rock Run Creek, a 

tributary that enters the study reach about 403 ft downstream 

from the West Wilden Avenue bridge. These adjusted flow 

values were used in the model from the confluence of Rock 

Run Creek and Elkhart River to the downstream limit of the 

study reach. 

Topographic and Bathymetric Data

 Channel cross sections were surveyed by USGS personnel during April 2012 for locations. These cross sections 

provided detailed channel-elevation data below the water 

surface and were collected using hydroacoustic instrumentation to measure depth and Differential Global Positioning 

System (DGPS) instrumentation to determine horizontal 

position. 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 for 

flood-plain areas were obtained from a LiDAR-derived digital 

elevation model (DEM). The LiDAR data were collected 

during April 2010 by AeroMetric, Inc., Sheboygan, Wisconsin, and postprocessing of these data also was completed by 

AeroMetric, Inc. The original LiDAR data have horizontal 

accuracy of 1.02 ft (31 centimeters), horizontal resolution 

of 3.9 ft (1.2 meters), and vertical accuracy of 0.37 ft at a 

95-percent confidence level for the “open terrain” land-cover 

category (root mean squared error of 0.19 ft [5.8 centimeters]). 

Although a finer horizontal resolution of the DEM was possible given the accuracy of the LiDAR data, the final DEM 

was resampled to a grid-cell size of 10 square feet (ft2) to 

decrease GIS processing time. 

Seven bridges and roadway embankments, and one levee, 

in and along the stream affect or have the potential to affect 

water-surface elevations during floods. To properly account 

for these features in the model, structural dimensions for three 

bridges (West Plymouth Avenue, River Avenue, and West 

Wilden Avenue) were measured and surveyed in the field 

concurrently with the stream-channel surveys. Dimensions 

for West Lincoln Avenue, West Pike Street, and the railroad 

bridges were obtained from input data for a HEC–2 hydraulic 

model, which was developed in 1977 and is still the basis for 

the water-surface profiles and flood maps that are presented 

in the currently effective FIS (Federal Emergency Management Agency, 2011). Structural dimensions for the County 

Road 17 bridge were obtained from design plans provided by 

the Elkhart County Highway Department (Thomas Rushlow, 

Elkhart County Highway Department, written commun., June 

2012 ). A detailed description of the methods used to acquire 

and process the topographic and bathymetric data can be 

found in Bales and others (2007). The Roger’s Park Levee 

runs longitudinally next to the stream between West Lincoln 

Avenue and West Pike Street. The levee protects the Roger’s 

Park area from flood waters for water-surface elevations below 

776.03 ft NAVD 88, but at water-surface elevations above 

776.03 feet the levee is overtopped and the area behind it is 

inundated with flood waters.

Energy-Loss Factors

Field observations and high-resolution aerial photographs were used to select initial (precalibration) Manning’s 

roughness coefficients (“n” values) for energy (friction) -loss 

Table 1. U.S. Geological Survey streamgage site information for the study area, Elkhart River at Goshen, Indiana.

[mi2, square miles; ft, feet; NAVD, North American Vertical Datum of 1988; °, degree; ′, minutes; ′′, seconds]

Station name Station 

number

Drainage area 

(mi2) Latitude Longitude Period of record Maximum recorded flood elevation at gage and date

Elkhart River at 

Goshen, Indiana 04100500 594 41°35′36′′ 85°50′55′′ Oct. 1931 to current year 11.94Mar. 14, 1982
Constructing Water-Surface Profiles 5

calculations. The final Manning’s n values used ranged from 

0.040 to 0.052 for the main channel and 0.088 to 0.165 for the 

overbank areas modeled in this analysis. 

Model Calibration and Performance

The hydraulic model was calibrated to the most current 

stage-discharge relation at the USGS streamgage 04100500, 

Elkhart River at Goshen, Ind. Model calibration was accomplished by adjusting Manning’s n values until the results of 

the hydraulic computations closely agreed with the measured 

flood discharge and stage values. Differences between measured and simulated water levels for measured or rated flows 

at USGS gaging station 04100500 were equal to or less than 

0.02 ft (table 2). Details on techniques used in model development and calibration can be found in Bales and others (2007).

Development of Water-Surface Profiles

Water-surface profiles were developed for a total of 

nine discharges corresponding to flood stages at 1-ft intervals 

between 5 and 13 ft above the gage datum (that is, water-level 

elevations ranging from 774.03 to 782.03 ft, NAVD 88), as 

referenced to the USGS streamgage 04100500, Elkhart River 

at Goshen, Ind. Discharges corresponding to the various index 

stages were obtained from the most current stage-discharge 

relation (no. 20.0) for the streamgage and were applied to the 

upstream half of the modeled reach, that is, from Goshen Dam 

to the confluence of Rock Run Creek with Elkhart River. For 

the downstream part of the study reach, discharge recorded 

at the streamgage was increased proportional to the drainagearea ratio to account for the expected increase in flows from 

Rock Run Creek. The assumption inherent in this calculation is that runoff in the Elkhart River Basin is distributed 

uniformly in time and space, and that the unit-area runoff, 

in cubic feet per second per square mile ((ft3/s)/mi2), in the 

Rock Run Creek Basin is equal to that in the Elkhart River 

Basin upstream from the streamgage at Goshen. Discharges 

for the nine profiles based on the stage-discharge relation at 

the Goshen gage and the adjusted discharges that were applied 

for the reach downstream from Rock Run Creek, are listed 

in table 3. Drainage area for Rock Run Creek was calculated 

using a USGS web-based GIS application, called StreamStats, 

which was accessed at http://water.usgs.gov/osw/streamstats/

indiana.html. 

Table 2. Comparison of hydraulic-model output simulated and 

observed water-surface elevations at the Elkhart River at Goshen, 

Indiana, streamgage (station number 04100500).

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

Stage

(ft)1

Measured watersurface elevation 

(ft, NAVD 88)1

Modeled watersurface elevation 

(ft, NAVD 88)

Elevation 

difference 

(ft)

5.0 774.03 774.01 0.02

6.0 775.03 775.03 0.00

7.0 776.03 776.04 -0.01

8.0 777.03 777.04 -0.01

9.0 778.03 778.02 0.01

10.0 779.03 779.04 -0.01

11.0 780.03 780.04 -0.01

12.0 781.03 781.04 -0.01

13.0 782.03 782.03 0.00

1

Values derived from rating curve no. 20 at U.S. Geological Survey gaging 

station 04100500.

Table 3. Stages and water-surface elevations with corresponding discharge estimates at selected locations along the Elkhart River at 

Goshen, Indiana, for simulated water-surface profiles.

[mi2, square miles; ft, feet; ft3/s, cubic feet per second; stage, in feet above gage datum; values in parentheses are water-surface elevations, in feet above the 

North American Vertical Datum of 1988]

Location

Drainage 

area

(mi2)

Stage (ft)

5 6 7 8 9 10 11 12 13

(774.03) (775.03) (776.03) (777.03) (778.03) (779.03) (780.03) (781.03) (782.03)

Discharge (ft3/s)

U.S. Geological Survey 

streamgage 04100500 594 1,460 2,080 2,750 3,450 4,130 4,810 5,500 6,220 7,000

Downstream from confluence 

with Rock Run Creek 630 1,549 2,206 2,917 3,659 4,380 5,102 5,834 6,597 7,425

Map sheet number 1 2 3 4 5 6 7 8 9
6 Flood-Inundation Maps for the Elkhart River at Goshen, Indiana

Inundation Mapping

Flood-inundation maps were created for the nine watersurface profiles simulated for the Elkhart River. The maps 

were created in a GIS by combining the water-surface profiles 

and DEM data. The DEM was derived from LiDAR data with 

3.9-ft horizontal resolution and a vertical accuracy of 0.37 ft. 

Although a finer resolution of the DEM was possible given 

the accuracy of the LiDAR data, the final DEM had a grid-cell 

size of 10 ft2 to decrease the GIS processing time. Estimated 

flood-inundation boundaries along each simulated profile were 

developed using HEC–GeoRAS software (U.S. Army Corps 

of Engineers, 2009). HEC–GeoRAS is a set of procedures, 

tools, and utilities that facilitates processing geospatial data 

in ArcGIS by providing a graphical user interface (Whitehead 

and Ostheimer, 2009). The interface allows the preparation 

of geometric data for import into HEC–RAS and processes 

simulation results exported from HEC–RAS (U.S. Army 

Corps of Engineers, 2010). USGS personnel then modified the 

HEC–GeoRAS results to ensure a hydraulically reasonable 

transition of the boundaries between modeled cross sections 

relative to the contour data for the land surface (Whitehead 

and Ostheimer, 2009). The resultant maps were compiled to 

show estimated flood-inundated areas overlaid onto highresolution, georeferenced aerial orthophotographs of the study 

area for each of the water-surface profiles that were simulated 

by the hydraulic model.

Elkhart River, Indiana, Flood-Inundation Maps 

on the Internet

The flood-inundation maps and study documentation are 

available online at the USGS Publications Warehouse (http://

pubs.usgs.gov/sim/3269/). Also, a Flood Inundation Mapping 

Science Web site has been established at http://water.usgs.gov/

osw/flood_inundation/ to provide a portal for USGS floodinundation study information to the public. That Web portal 

has a link (http://wim.usgs.gov/FIMI/FloodInundationMapper.

html) to interactive online map libraries that can be downloaded in several commonly used electronic file formats for 

GIS dataset viewers. At the map library site, each stream reach 

displayed contains further links to NWISWeb graphs of the 

current stage and streamflow at USGS streamgage 04100500, 

to which the inundation maps are referenced. A link also is 

provided to the NWS AHPS site (http://water.weather.gov/

ahps/) so that the user can obtain applicable information on 

forecasted peak stage. The estimated flood-inundation maps 

are displayed in sufficient detail to note the extent of flooding with respect to individual structures so that preparations 

for flooding and decisions for emergency response can be 

performed efficiently. Roadways and bridges were closely 

reviewed and are shown as shaded (inundated and likely 

impassable) or not shaded (dry and passable) to facilitate 

emergency planning and use. However, buildings that are 

shaded do not reflect inundation but denote that bare earth 

surfaces in the vicinity of the buildings are inundated. When 

the simulated water depth (as indicated in the Web Mapping 

Application by holding the cursor over an inundated area) in 

the vicinity of a building of interest exceeds that building’s 

height, the structure can be considered fully submerged.

Disclaimer for Flood-Inundation Maps

Inundated areas shown should not be used for navigation, 

regulatory, permitting, or other legal purposes. The USGS 

provides these maps “as is” for a quick reference, emergency 

planning tool but assumes no legal liability or responsibility 

resulting from the use of this information.

Uncertainties and Limitations Regarding Use of 

Flood-Inundation Maps

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

is associated with these maps. The flood boundaries shown 

were estimated based on water stages and streamflows at 

USGS streamgage 04100500, Elkhart River at Goshen, Ind. 

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 land-cover characteristics and any bridge, 

dam, levee, or other hydraulic structures existing as of September 2011. 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. Additional areas may be 

flooded because of 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. Additional uncertainties and limitations pertinent to this study may be described 

elsewhere in this report.

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 
References Cited 7

a given location (AHPS forecast point) throughout the forecast 

period (every 6 hours and 3 to 5 days out in many locations). 

In the case of Elkhart River at Goshen, forecasts are issued as 

needed during times of high water, but are not routinely available at the time of this report (2013). For more information 

on AHPS forecasts, please see: http://water.weather.gov/ahps/

pcpn_and_river_forecasting.pdf. 

Summary

The U.S. Geological Survey (USGS), in cooperation with 

the Indiana Office of Community and Rural Affairs, produced 

digital flood-inundation maps for an 8.3-mile reach of the 

Elkhart River at Goshen, Indiana, extending from downstream 

of the Goshen Dam to 5,450 feet (ft) downstream from the 

County Road 17 bridge. The inundation maps, which can be 

accessed at the USGS Flood Inundation Mapping Science 

Web site at http://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 

04100500, Elkhart River at Goshen, Ind. The nine flood stages 

selected range from approximately bankfull (5 ft above gage 

datum) to greater than the maximum observed water level 

(13 ft) at the streamgage. Current conditions for the USGS 

streamgages in Indiana may be obtained on the Internet at 

http://waterdata.usgs.gov/nwis/. In addition, stream stage data 

have been provided to the National Weather Service (NWS) 

for incorporation into their Advanced Hydrologic Prediction 

Service (AHPS) flood warning system (http://water.weather.

gov/ahps/). The NWS forecasts flood hydrographs at many 

places that are often collocated with USGS streamgages. 

NWS-forecasted peak-stage information may be used in 

conjunction with the maps developed in this study to show 

predicted areas of flood inundation. 

In this study, nine flood profiles were computed for the 

stream reach by means of a one-dimensional step-backwater 

model. The model was calibrated using the most current stagedischarge relation at the Elkhart River at Goshen streamgage. 

The hydraulic model generated water-surface profiles for flood 

stages at 1-ft intervals referenced to the streamgage datum 

and ranging from approximately bankfull (5 ft, gage datum) 

to greater than the highest recorded water level. 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 0.37-ft 

vertical and 3.9-ft horizontal resolution) in order to delineate 

the area flooded at each water level. The availability of these 

maps, along with Internet information regarding current stage 

from USGS streamgages and forecasted stream stages from 

the NWS, 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.

References Cited

Bales, J.D., Wagner, C.R., Tighe, K.C., and Terziotti, Silvia, 

2007, LiDAR-derived flood-inundation maps for realtime flood-mapping applications, Tar River Basin, North 

Carolina: U.S. Geological Survey Scientific Investigations 

Report 2007–5032, 42 p.

Federal Emergency Management Agency, 2011, Flood insurance study, Elkhart County, Indiana, and incorporated areas: 

Washington D.C., Federal Emergency Management Agency, 

40 p., 17 pl.

Homer, C., Dewitz, J., Fry, J., Coan, M., Hossain, N., Larson, 

C., Herold, N., McKerrow, A., VanDriel, J.N., and Wickham, J., 2007, Completion of the 2001 National Land Cover 

Database for the Conterminous United States, Photogrammetric Engineering and Remote Sensing, v. 73, no. 4, 

p. 337–341.

U.S. Army Corps of Engineers, 2009, HEC–GeoRAS, GIS 

tools for support of HEC–RAS using ArcGIS—User’s 

manual, version 4.2: Davis, California, U.S. Army Corps 

of Engineers, Hydrologic Engineering Center, [variously 

paged].

U.S. Army Corps of Engineers, 2010, HEC–RAS River Analysis System hydraulic reference manual, version 4.1: Davis, 

California, U.S. Army Corps of Engineers, Hydrologic 

Engineering Center, [variously paged].

U.S. Census Bureau, 2010, American FactFinder: accessed 

September 27, 2012, at http://factfinder2.census.gov.

Whitehead, M.T., and Ostheimer, C.J., 2009, Development 

of a flood-warning system and flood-inundation mapping 

for the Blanchard River in Findlay, Ohio: U.S. Geological 

Survey Scientific Investigations Report 2008–5234, 9 p.

Publishing support provided by: Columbus and West Trenton 

Publishing Service Centers

For more information concerning this publication, contact:

Director, Indiana Water Science Center

U.S. Geological Survey

5957 Lakeside Blvd.

Indianapolis, IN 46278

(317) 290–3333

Or visit the Indiana Water Science Center Web site at:

http://in.water.usgs.gov/
Strauch—Flood-Inundation Maps for the Elkhart River at Goshen, Indiana—Scientific Investigations Map 3269

ISSN 2329–132X (online)

http://dx.doi.org/10.3133/sim3269