July 2011

December 2011

February 2011

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2014–5128

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

Flood-Inundation Maps for the North Branch Elkhart River at 

Cosperville, Indiana
Cover: 

Background: An example of a flood-inundation map along the North Branch Elkhart River and West Lakes Chain area. 

Photos: Images of North Branch Elkhart River at Cosperville, Indiana. Photos were taken looking downstream from 900 North Road 

bridge (by Edward G. Dobrowolski, USGS, at various times in 2011).
Flood-Inundation Maps for the North 

Branch Elkhart River at Cosperville, Indiana

By Moon H. Kim and Esther M. Johnson

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

Scientific Investigations Report 2014–5128

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: 2014

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

Suggested citation:

Kim, M.H., and Johnson, E.M., 2014, Flood-inundation maps for the North Branch Elkhart River at Cosperville, Indiana: 

U.S. Geological Survey Scientific Investigations Report 2014–5128, 9 p., http://dx.doi.org/10.3133/sir20145128.

ISSN 2328-0328

http://dx.doi.org/10.3133/sir20145128
iii

Contents

Acknowledgments........................................................................................................................................iv

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

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

Purpose and Scope ..............................................................................................................................3

Study Area Description........................................................................................................................3

Previous Studies ..................................................................................................................................3

Creation of Flood-Inundation-Map Library................................................................................................3

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

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

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

Hydraulic Structures ...................................................................................................................4

Energy-Loss Factors....................................................................................................................5

Hydraulic Model...........................................................................................................................5

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

Development of Flood-Inundation Maps ..........................................................................................6

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

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

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

Summary..........................................................................................................................................................8

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

Figures

1. Map showing location of study reach for the North Branch Elkhart River and location 

of USGS streamgage 04100222...................................................................................................2

2. Map showing example of a flood-inundation map for the North Branch Elkhart River 

at Cosperville, Indiana, corresponding to a stage of 8.00 feet and an elevation of 

887.68 feet (NAVD 88) at USGS streamgage 04100222............................................................7

Tables

1. USGS streamgage information for study basin, North Branch Elkhart River at 

Cosperville, Indiana......................................................................................................................4

2. Comparison of water-surface elevations at USGS streamgage 04100222, North 

Branch Elkhart River at Cosperville, Indiana, with water-surface elevations 

output from the hydraulic model ................................................................................................5

3. Comparison of hydraulic-model output and preliminary high-water-mark elevations 

from the flood of March 1982 for the North Branch Elkhart River at 

Cosperville, Indiana......................................................................................................................5

4. Stages and corresponding discharge estimates for selected locations within the 

study reach for simulated water-surface profiles, North Branch Elkhart River 

at Cosperville, Indiana .................................................................................................................6
iv

Conversion Factors

Inch/Pound 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)

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).

Acknowledgments

The authors wish to thank the many local, State, and Federal agencies that have cooperated in 

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

the Indiana Department of Natural Resources. Special thanks are given to Noble County, Indiana, for their cooperation in this study and to the National Weather Service for their continued 

support of the USGS flood-inundation mapping program. 
Flood-Inundation Maps for the North Branch Elkhart River 

at Cosperville, Indiana

By Moon H. Kim1 and Esther M. Johnson2

Abstract

Digital flood-inundation maps for a reach of the North 

Branch Elkhart River at Cosperville, Indiana (Ind.), were 

created by the U.S. Geological Survey (USGS) in cooperation with the U.S. Army Corps of Engineers, Detroit District. 

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 selected 

water levels (stages) at USGS streamgage 04100222, North 

Branch Elkhart River at Cosperville, Ind. Current conditions 

for estimating near-real-time areas of inundation using USGS 

streamgage information may be obtained on the Internet at 

http://waterdata.usgs.gov/in/nwis/uv?site_no=04100222. 

In addition, information has 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 AHPS forecasts 

flood hydrographs at many places that are often colocated with 

USGS streamgages, including the North Branch Elkhart River 

at Cosperville, Ind. NWS AHPS-forecast peak-stage information may be used in conjunction with the maps developed in 

this study to show predicted areas of flood inundation. 

For this study, flood profiles were computed for the North 

Branch Elkhart River reach by means of a one-dimensional 

step-backwater model. The hydraulic model was calibrated 

by using the most current stage-discharge relations at USGS 

streamgage 04100222, North Branch Elkhart River at Cosperville, Ind., and preliminary high-water marks from the flood of 

March 1982. The calibrated hydraulic model was then used to 

determine four water-surface profiles for flood stages at 1-foot 

intervals referenced to the streamgage datum and ranging from 

bankfull to the highest stage of the current stage-discharge 

rating curve. 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]) in order to delineate the area flooded at 

each water level.

1

 U.S. Geological Survey.

2

 U.S. Army Corps of Engineers, Detroit District.

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

04100222, North Branch Elkhart River at Cosperville, Ind., 

and forecast stream stages from the NWS AHPS, provides 

emergency management personnel and residents with information that is critical for flood response activities such as evacuations and road closures, as well as for post-flood recovery 

efforts.

Introduction 

The town of Cosperville, Indiana (Ind.), where a USGS 

streamgage is located, is a relatively small community. This 

community and residents along West Lakes Chain (upstream 

from Cosperville, Ind.; fig. 1), which is a series of lakes 

connected by North Branch Elkhart River, have experienced 

severe flooding numerous times, most recently in 2008 and 

2009. Flood plains along the river are less developed and composed mostly of agricultural areas.

Prior to this study, officials from Cosperville, Ind., and 

Noble County and residents of West Lakes Chain relied 

on several information sources to make decisions on how 

to best alert the public and mitigate flood damages. One 

source of information is the Federal Emergency Management Agency (FEMA) Flood Insurance Study (FIS) for Noble 

County (FEMA, 1979). A second source is USGS streamgage 

04100222, North Branch Elkhart River at Cosperville, Ind., 

(http://waterdata.usgs.gov/in/nwis/current/?type=flow) from 

which current and historical water levels (stage) can be 

obtained. A third source is the NWS’s forecast of peak stage 

through the Advanced Hydrologic Prediction Service (AHPS) 

Web site (http://water.weather.gov/ahps/).

Although the USGS stream stage and the NWS AHPS 

flood forecast information are particularly useful for residents 

in the immediate vicinity of a streamgage, it is generally 

of limited use to residents farther upstream or downstream 

because the water-surface elevation is not constant along 

the entire stream channel. Knowledge of a water level at a 

streamgage is difficult to translate into depth and areal extent 

of flooding at points distant from the streamgage. One way 
0 

0 0.5 

85°30' 85°27' 85°24'

41°30'

41°28'30"

04100222

Cosperville

900 NORTH ROAD

Elkhart River

Waldron Lake

Branch

North

300 WEST ROAD

125 WEST ROAD

800 NORTH ROAD

1050 NORTH ROAD

Steinbarger Lake Tamarack Lake

Jones 

 Lake

WEST

LAKES

River

Branch

North

Branch

Elkhart

Middle

Projection: Indiana State Plane Eastern Zone

Horizontal coordinate information is referenced to the North American Datum of 1983Orthophotography from Indiana Spatial Data Portal, 2011, available at http://gis.iu.edu/datasetInfo/statewide/in_2011.php

Limit of study area

EXPLANATION

USGS streamgage and 

number

Flow arrow—Indicates 

direction of water flow

04100222

Figure 1. Location of study reach for the North Branch Elkhart River and location of USGS streamgage 04100222.
Creation of Flood-Inundation-Map Library 3

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. For this 

study, the USGS, in cooperation with the U.S. Army Corps 

of Engineers (USACE), Detroit District, conducted a project 

to produce a library of flood-inundation maps for the North 

Branch Elkhart River at Cosperville, Ind., and for the area of 

West Lakes Chain community.

Purpose and Scope

The purpose of this report is to describe the development 

of a series of estimated flood-inundation maps for the North 

Branch Elkhart River at Cosperville, Ind. The maps and other 

flood information are available on the USGS Flood Inundation Mapping Science Web site and the NWS AHPS Web site. 

Internet users can select estimated inundation maps that correspond to flood stages at USGS streamgage 04100222 and the 

NWS AHPS forecast peak stage.

The scope of the study for hydraulic modeling was limited to the North Branch Elkhart River reach extending about 

4.8 miles (mi) upstream of USGS streamgage 04100222 at the 

900 North Road Bridge and about 1.0 mi downstream of the 

streamgage (fig. 1). Additional GIS techniques were used to 

extend the flood-inundation mapping area to include the West 

Lakes Chain community. The maps cover a range in stage 

from 5 to 8 feet (ft), gage datum. The 5-ft stage is approximately bankfull and is defined by the NWS 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 significant hydrologic activity. The 8-ft stage is approximately the highest recorded water 

level at the streamgage. 

Study Area Description

The drainage area of the North Branch Elkhart River 

is about 133 square miles (mi2) at the upstream end of the 

modeled reach, which is near the outlet of the Waldron Lake; 

142 mi2 at USGS streamgage 04100222, North Branch Elkhart 

River at Cosperville, Ind.; and about 144 mi2 at the downstream extent of the study reach (USGS, 2013a). The headwaters originate in Noble County, and the stream flows generally 

in a westerly direction. There are no significant tributaries 

to the North Branch Elkhart River as it flows through the 

modeled reach. The study reach for the modeling is approximately 5.8 mi long and has an average top-of-bank channel 

width of about 200 ft and an average channel slope of about 

1.1 feet per mile. The flood-inundation mapping area also 

includes the West Lakes Chain area, which comprises Waldron, Steinbarger, Tamarak, and Jones Lakes (Indiana Silver 

Jackets, 2010). Most of the land contiguous to the study reach 

is either agricultural or natural area with a few residences. In 

the identified North Branch Elkhart River/West Lakes Chain 

area of concern, 303 structures currently are within the area 

of the 1-percent annual exceedance probability (100-year) 

flood plain. Of those 303 structures (primarily residential), 

121 (36 percent) are within areas also included in 50-percent 

annual exceedance probability (2-year) flood plain. Many of 

these structures were built prior to the adoption of local flood 

plain ordinances (Indiana Silver Jackets, 2010). Within the 

modeled reach, four major road crossings lie within the main 

channel or the adjacent flood plain. 

Previous Studies 

The current effective FIS for Noble County was published in 1979. A preliminary FIS document and an interim 

Digital Flood Insurance Rate Map (DFIRM) were obtained 

from the Indiana Department of Natural Resources Web site 

(http://www.in.gov/dnr/water/6665.htm). A Special Flood Hazards Area map from the interim DFIRM was used for comparison to the maps created in this study. An estimate of the peak 

discharge for the 1.0- and 0.2-percent annual exceedance probability flood (1,060 ft3

/s and 1,270 ft3/s, respectively) near the 

Cosperville streamgage (300 West Road) on the North Branch 

Elkhart River was obtained from the FIS (FEMA, 1979).

Creation of Flood-Inundation-Map 

Library

The USGS has standardized the procedures for creating 

flood-inundation maps for flood-prone communities (U.S. 

Geological Survey, 2013b) so that the process followed and 

products produced are similar regardless of which USGS 

office is responsible for the work. Tasks specific to construction of the maps were (1) compilation of flow data from 

streamgage 04100222, (2) collection of topographic data and 

geometric data (for structures/bridges) throughout the study 

reach, (3) estimation of energy-loss factors (roughness coefficients) in the stream channel and flood plain, (4) computation of water-surface profiles by use of the U.S. Army Corps 

of Engineers’ HEC–RAS computer program (USACE, 2010), 

(5) production of estimated flood-inundation maps at various 

stream stages by use of the U.S. Army Corps of Engineers’ 

HEC–GeoRAS computer program (USACE, 2009) and a 

GIS computer program called ArcGIS (ESRI, 2013), and (6) 

development of a Web interface that links to USGS real-time 

streamgage information and NWS AHPS forecast peak stage 

to facilitate the display of user-selected flood-inundation maps 
4 Flood-Inundation Maps for the North Branch Elkhart River at Cosperville, Indiana

on the Internet. Most of the tasks listed above were conducted 

and managed by the USACE including the development of 

the hydraulic model. The USGS provided support and guidance in collection of the hydraulic data, in development of 

flood-inundation GIS layers, and in development of the Web 

interface mentioned above. Both the USACE and the USGS 

provided quality-control reviews of hydraulic model and its 

related datasets and resulting flood-inundation maps. Methods 

used are generally cited from previously published reports. If 

techniques varied significantly from previously documented 

methods in response to local hydrologic conditions or availability of data, they are described in detail in this report. Four 

maps were produced for water levels referenced to the stage 

at USGS streamgage 04100222, North Branch Elkhart River 

at Cosperville, Ind., and range from approximately bankfull to 

the highest stage on the current stage-discharge rating curve. 

Computation of Water-Surface Profiles

The water-surface profiles used to produce the four floodinundation maps in this study were simulated by using HEC–

RAS, version 4.0 (USACE, 2010). HEC–RAS is a one-dimensional step-backwater model 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 completed with the steady-state flow computation 

option.

Hydrologic Data

The study area hydrologic network consists of one 

streamgage (table. 1), which has been in operation since 1971. 

Water level (stage) is measured continuously at this site, and 

continuous records of streamflow are computed. All water-surface elevations are referenced to the North American Vertical 

Datum of 1988 (NAVD 88). The streamgage is equipped with 

a satellite radio transmitter that allows data to be transmitted 

routinely on the Internet within an hour of collection. Preliminary high-water marks were documented after the flood 

that occurred in March 1982 (Indiana Department of Natural 

Resources, Division of Water, written commun., 2012) and 

also were used for model calibration.

Steady-flow data consisted of flow regime, boundary 

conditions (normal depth), and peak-discharge information. 

The steady-flow data for the model were obtained from field 

measurements of streamflow at USGS streamgage 04100222, 

North Branch Elkhart River at Cosperville, Ind. All computations were based on discharge values with known stages from 

actual streamflow measurements or stage-discharge relations. 

Topographic and Bathymetric Data

Thirty-one channel cross sections were developed 

from American Survey and Engineering surveys that were 

conducted in December 2011; these cross sections provide 

detailed channel-elevation data below the water surface and 

were collected by using hydroacoustic instrumentation to measure depth and Differential Global Positioning System (DGPS) 

instrumentation to determine horizontal position. A total of 32 

synthetic cross sections were generated by use of the DEM. 

In-channel data for all synthetic cross sections were estimated 

by combining LiDAR overbank data and bathymetric channel 

profiles.

LiDAR data were used to obtain digital elevation data 

for the portions of the cross sections that were above the 

water surface at the time of the surveys. The LiDAR data for 

the North Branch Elkhart River at Cosperville, Ind. (Noble 

County LiDAR) were collected for the Indiana Statewide 

Imagery and LiDAR Program (http://gis.iu.edu/datasetInfo/

statewide/in_2011.php) and processed by Wolpert, Inc. in 

2012. The 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. A detailed description of 

the methods used to acquire and process the topographic and 

bathymetric data can be found in Bales and others (2007). 

Hydraulic Structures

Various manmade drainage structures (bridges, culverts, 

roadway embankments, levees, and dams) in and along the 

North Branch Elkhart River affect or have the potential to 

affect water-surface elevations during floods along the stream. 

To properly account for these features in the model, structural 

Table 1. USGS streamgage information for study basin, North Branch Elkhart River at Cosperville, Indiana. 

[mi2, square miles; NAD 83, North American Datum of 1983; NAVD 88, North American Vertical Datum of 1988; ft, feet]

Streamgage name Streamgage 

number

Drainage 

area (mi2

)

Latitude 

(NAD 83)

Longitude 

(NAD 83)

Streamgage 

datum 

(ft, NAVD 88)

Period 

of record

Maximum flood 

elevation 

(ft, NAVD 88 

and date)

North Branch Elkhart River 

at Cosperville, Indiana

04100222 142 41°28′54′′ 85°28′32′′ 879.68 October 1971 

to present

887.80; 

March 23,1982.
Creation of Flood-Inundation-Map Library 5

dimensions for four bridges and an inline structure (Waldron 

Lake outlet control structure) were measured and surveyed in 

the field concurrently with the stream-channel surveys (Indiana Silver Jackets, 2010).

Energy-Loss Factors

Hydraulic analyses require the estimation of energy 

losses that result from frictional resistance exerted by a channel on flow. Field observations, aerial photos, and the 1979 

FIS report were used to select initial channel and flood-plain 

friction coefficients. These friction coefficients, commonly 

called Manning’s roughness coefficients or Manning’s n

values, account for energy (friction) loss in the model (Arcement and Schneider, 1989). 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 Manning’s n values were set 

as 0.048 for the main channel and ranged from 0.05 to 0.1 for 

the overbank areas modeled in this analysis. 

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 section that matched target water-surface elevations. 

These target elevations coincided with even 1-ft increments of 

stage, referenced to the local gage datum. Subcritical (tranquil) 

flow regime was assumed for the simulations. Normal depth 

was used as the reach’s downstream boundary condition.

The hydraulic model was calibrated to the most current 

stage-discharge relation (USGS rating no. 15.1) at USGS 

streamgage 04100222, North Branch Elkhart River at Cosperville, Ind., and preliminary high-water marks from the flood 

of March 1982 (Indiana Department of Natural Resources, 

Division of Water, written commun., 2012). The estimated 

peak discharge for the 1982 flood was 919 ft3

/s at an estimated 

stage of about 8.12 ft at the streamgage. Model calibration was 

accomplished by adjusting Manning’s n values and, in some 

cases, changing the channel cross section or slope until the 

results of the hydraulic computations closely agreed with the 

known flood discharge and stage values. Differences between 

measured and simulated water levels for measured or rated 

flows at USGS streamgage 04100222 were less than or equal 

to about 0.11 ft (table 2). Differences between measured and 

simulated water levels for models calibrated to preliminary 

high-water marks in the study reach from the flood of 1982 

were less than or equal to about 0.83 ft (table 3). An additional 

comparison was made to flood profiles from the FIS (FEMA, 

1979) for the North Branch Elkhart River to check the modelderived water-surface elevations. The results demonstrate that 

the model is capable of simulating reasonable water levels 

over a wide range of flows in the basin. Details on techniques 

used in model development and calibration can be found in 

Bales and others (2007).

Development of Water-Surface Profiles

The calibrated hydraulic model was used to generate 

water-surface profiles for a total of four stages at 1-ft intervals between 5 ft and 8 ft as referenced to USGS streamgage 

04100222, North Branch Elkhart River at Cosperville, Ind. 

These stages correspond to elevations of 884.68 ft and 

887.68 ft, NAVD 88, respectively. Discharges corresponding to the various stages were obtained from the most current 

stage-discharge relation (rating no. 15.1) at the North Branch 

Elkhart River streamgage. 

Discharges for all profiles were selected with the assumption that there are no significant tributary inflows within the 

5.8-mi modeled reach. The discharges were estimated to be 

uniform and steady throughout the modeled reach. However, 

Table 2. Comparison of water-surface elevations at USGS 

streamgage 04100222, North Branch Elkhart River at Cosperville, 

Indiana, with water-surface elevations output from the hydraulic 

model.

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

Stage 

(ft)

Measured watersurface elevation 

(ft, NAVD 88)

Modeled watersurface elevation 

(ft, NAVD 88)

Elevation 

difference 

(ft)

5.00 884.68 884.78 0.10

6.00 885.68 885.75 0.07

7.00 886.68 886.71 0.03

8.00 887.68 887.57 -0.11

Table 3. Comparison of hydraulic-model output and preliminary 

high-water-mark elevations from the flood of March 1982 for the 

North Branch Elkhart River at Cosperville, Indiana.

[HWM, high-water mark; ft, feet; NAVD 88, North American Vertical Datum 

of 1988]

Location 

description

Preliminary 

observed HWM 

(ft, NAVD 88)

Modeled watersurface elevation 

(ft, NAVD 88)

Elevation 

difference 

(ft)

300 West Road 886.60 886.05 -0.55

900 North 

Road (USGS 

streamgage)

887.82 887.40 -0.42

Waldron Lake 

Outlet

889.82 888.99 -0.83

125 West Road 889.85 889.18 -0.67
6 Flood-Inundation Maps for the North Branch Elkhart River at Cosperville, Indiana

because the difference in drainage area between the location 

at the streamgage and at the upstream extent of the modeled reach was greater than 5 percent, two change of flow 

locations in the hydraulic model were included: one at the 

Cosperville streamgage (900 North Road bridge) and one at 

the upstream extent of the modeled area near 125 West Road 

Bridge. Discharge at the upstream extent of the model was 

estimated by, first, calculating cubic feet per second per square 

mile (CFSM) that corresponded to the measured discharges 

at USGS streamgage 04100222, then multiplying this CFSM 

value by drainage area at the upstream extent of the model 

(table 4). The CFSM is defined as the average number of cubic 

feet of water per second flowing from each square mile of area 

drained by a stream, assuming that the runoff is distributed 

uniformly in time and area.

Development of Flood-Inundation Maps

Flood-inundation maps were created for a reach of the 

North Branch Elkhart River at Cosperville, Ind. The maps 

were created in a GIS by combining the water-surface profiles and DEM data (an example is shown on fig. 2). The 

DEM data for Cosperville, Ind. (Noble County LiDAR) were 

collected for the Indiana Statewide Imagery and LiDAR 

Program (http://gis.iu.edu/datasetInfo/statewide/in_2011.

php). Estimated flood-inundation boundaries for each simulated profile were developed with HEC–GeoRAS software 

(USACE, 2009). HEC–GeoRAS is a set of procedures, tools, 

and utilities for processing geospatial data in ArcGIS using a 

graphical user interface (ESRI, 2013). 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 boundary between modeled 

cross sections relative to the contour data for the land surface 

(Whitehead and Ostheimer, 2009). The resulting inundation 

maps have a vertical accuracy of about plus or minus 1.0 ft.

Additional GIS techniques were used to extend the floodinundation mapping area to include the West Lakes Chain 

area. Because the upstream extent of the modeled area ends at 

the confluence of the North Branch Elkhart River and Waldron 

Lake, flood-extent polygons and depth grids for all profile 

stages were extended to include the West Lakes Chain area by, 

first, determining the modeled water-surface elevation at the 

upstream extent of model for each profile stage, then applying 

GIS techniques to subtract DEM elevations. This technique 

of extending flood-inundation polygons and depth grids was 

possible because the water-surface elevation at each modeled 

(steady-state) profile stage was assumed to remain constant 

throughout the West Lakes Chain area.

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 were found, 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 depth-grid 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.”

Table 4. Stages and corresponding discharge estimates for selected locations within the study reach for 

simulated water-surface profiles, North Branch Elkhart River at Cosperville, Indiana.

[mi2, square miles; ft3/s, cubic feet per second]

Location Drainage area 

(mi2

)

Stage, in feet above streamgage datum 

5.00 6.00 7.00 8.00

Discharge (ft3

/s)

At the outlet of Waldron Lake 133 237 389 630 937

USGS streamgage 04100222 142 251 413 668 994
85°30' 85°27' 85°24'

41°30'

41°28'30"

04100222

Cosperville

900 NORTH ROAD

Elkhart River

Waldron Lake Branch

North

300 WEST ROAD

125 WEST ROAD

800 NORTH ROAD

1050 NORTH ROAD

Steinbarger Lake Tamarack Lake

Jones Lake

WEST

LAKES

El

River

Branch

North

Branch

Elkhart

Middle

C

EXPLANATION

USGS streamgage and number

Limit of study area

Flow arrow—Indicates direction

of water flow

04100222

Flood-inundation area

Figure 2. 

Projection: Indiana State Plane Eastern Zone

Horizontal coordinate information is referenced to the North American Datum of 1983Orthophotography from Indiana Spatial Data Portal, 2011, available at http://gis.iu.edu/datasetInfo/statewide/in_2011.php

0 

0 0.5 

Figure 2. Example of a flood-inundation map for the North Branch Elkhart River at Cosperville, Indiana, corresponding to a stage of 8.00 feet elevation of 887.68 feet (NAVD 88) at USGS streamgage 04100222.
8 Flood-Inundation Maps for the North Branch Elkhart River at Cosperville, Indiana

Flood-Inundation Map Delivery

The flood-inundation maps from this study depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at the USGS streamgage 

04100222, North Branch Elkhart River at Cosperville, Ind. 

The current study documentation is available online at the 

USGS Publications Warehouse (http://dx.doi.org/10.3133/

sir20145128). Also, a Flood Inundation Mapping Science 

Web site has been established to provide a portal for USGS 

flood-inundation study information to the public at http://

water.usgs.gov/osw/flood_inundation/. That Web portal has 

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

html) to a mapping application that presents map libraries and 

provides detailed information on flood extents and depths for 

selected sites. The mapping application enables the production of customized flood-inundation maps from the map 

library for North Branch Elkhart River at Cosperville, Ind. 

At the map library site, each stream reach displayed contains further links to NWISWeb graphs of the current stage 

and streamflow at USGS streamgage 04100222 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 forecast peak stage. 

The NWS does not continuously forecast stage at this site but 

does so only as needed during times of high-stage flows. 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. 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 mean 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 (Bales and Wagner, 2009). The 

flood boundaries shown were estimated on the basis of water 

stages and streamflows at selected USGS streamgages. Watersurface 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(s). The hydraulic model reflects the 

land-cover characteristics and any bridge, dam, levee, or other 

hydraulic structures existing as of November 2013. 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 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 digital elevation 

model used to simulate the land surface. 

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

conjunction with NWS river forecasts, the user should be 

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

models to estimate the quantity and timing of water flowing 

through selected stream reaches in the United States. These 

forecast models (1) estimate the amount of runoff generated 

by precipitation and snowmelt, (2) simulate the movement 

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

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

a given location (AHPS forecast point) throughout the forecast 

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

For more information on AHPS forecasts, please see: http://

water.weather.gov/ahps/pcpn_and_river_forecasting.pdf. 

Summary

Estimated flood-inundation maps were developed in 

cooperation with U.S. Army Corps of Engineers, Detroit District for the North Branch Elkhart River at Cosperville, Ind., 

from about 4.8 mi upstream of USGS streamgage 04100222 at 

the 900 North Road bridge to about 1.0 mi downstream of the 

streamgage. Additional GIS techniques were used to extend 

the flood-inundation mapping area to include the West Lakes 

Chain community. 

The maps were developed by using the U.S. Army Corps 

of Engineers’ HEC–RAS and HEC–GeoRAS programs and 

ESRI’s ArcGIS program to compute water-surface profiles 

and to delineate estimated flood-inundation areas for selected 
References Cited 9

stream stages. The simulated water-surface profiles were then 

combined with a geographic information system (GIS) digital 

elevation model derived from Light Detection and Ranging 

(LiDAR) 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 

maps show estimated (shaded) flood-inundation areas of the 

study area for stream stages between 5 ft and 8 ft at the North 

Branch Elkhart River at Cosperville streamgage. The flood 

maps are available through a mapping application that can be 

accessed on the USGS Flood Inundation Mapping Science 

Web site (http://water.usgs.gov/osw/flood_inundation).

Interactive use of the maps on this mapping application 

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

point by using the mouse cursor to click within the shaded 

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

data from the USGS streamgage 04100222 and NWS AHPS 

flood-stage forecasts, 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., Jr., and Schneider, V.R., 1989, Guide for 

selecting Manning’s roughness coefficients for natural channels and flood plains: U.S. Geological Survey Water-Supply 

Paper 2339, 38 p.

Bales, J.D., and Wagner, C.R., 2009, Sources of uncertainty in 

flood inundation maps: Journal of Flood Risk Management, 

2, p. 139–147. 

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.

ESRI, 2013, ArcGIS, accessed November 4, 2013, at 

http://www.esri.com/software/arcgis/.

Federal Emergency Management Agency (FEMA), 1979, 

Flood insurance study for Noble County, Indiana: Washington D.C., Flood Insurance Study Number 180183V000, 

149 p.

Federal Geographic Data Committee, 1998, Geospatial positioning accuracy standards, part 3—National standard for 

spatial data accuracy: 25 p., available at http://www.fgdc.

gov/standards/projects/FGDC-standards-projects/accuracy/

part3/chapter3.

Indiana Silver Jackets, 2010, North Branch Elkhart River West 

Lakes Task Team Report: available at http://www.nfrmp.us/

state/docs/Indiana/IndianaReport/IndianaReport.cfm.

U.S. Army Corps of Engineers (USACE), Hydrologic 

Engineering Center, 2009, HEC–GeoRAS, GIS tools for 

support of HEC–RAS using ArcGIS, user’s manual [variously paged]: Available at http://www.hec.usace.army.mil/

software/hec-ras/hec-georas_downloads.html.

U.S. Army Corps of Engineers (USACE), Hydrologic Engineering Center, 2010, HEC–RAS river analysis system—

Hydraulic reference manual, version 4.1 [variously paged]: 

Available at http://www.hec.usace.army.mil/software/hecras/documentation/HEC-RAS_4.1_Reference_Manual.pdf.

U.S. Geological Survey (USGS), 2013a, StreamStats for 

Indiana streams: Available at http://streamstats.usgs.gov/

indiana.html. 

U.S. Geological Survey (USGS), 2013b, USGS Flood Inundation Mapping Science: U.S. Geological Survey, accessed 

November 10, 2013, at http://water.usgs.gov/osw/flood_

inundation.

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., 11 pl.


Kim and Johnson—Flood-Inundation Maps for the North Branch Elkhart River at Cosperville, Indiana—Scientific Investigations Report 2014–5128

 ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20145128