Prepared in cooperation with the Village of Ottawa, Ohio, and 

the U.S. Department of Agriculture, Natural Resources Conservation Service

Development of a Flood-Warning Network and 

Flood-Inundation Mapping for the Blanchard River 

in Ottawa, Ohio

Scientific Investigations Report 2011–5189

U.S. Department of the Interior

U.S. Geological Survey
Cover: Floodwaters from the Blanchard River at the Elm Street bridge over the Blanchard River in Ottawa, Ohio (looking north). 

(Photo taken February 2008 by Mary Terry. Courtesy of Findlay Engineer’s Office, reproduced with permission.)
Development of a Flood-Warning Network 

and Flood-Inundation Mapping for the 

Blanchard River in Ottawa, Ohio

By Matthew T. Whitehead

Prepared in cooperation with the Village of Ottawa, Ohio, and 

the U.S. Department of Agriculture, Natural Resources Conservation Service

Scientific Investigations Report 2011–5189

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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Suggested citation:

Whitehead, M.T., 2011, Development of a flood-warning network and flood-inundation mapping for the 

Blanchard River in Ottawa, Ohio: U.S. Geological Survey Scientific Investigations Report 2011–1189, 8 p., 12 plates.
iii

Contents

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

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

Description of the Study Area ............................................................................................................2

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

Installation and Upgrade of Streamgages ................................................................................................3

Hydrology and Hydraulics ............................................................................................................................4

Previous Study.......................................................................................................................................4

Model Calibration..................................................................................................................................4

Model Validation ...................................................................................................................................5

Determination of Water-Surface Profiles.........................................................................................7

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

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

Acknowledgments ........................................................................................................................................8

References Cited............................................................................................................................................8

Plates

(Separate documents)

1. Flood-inundation areas along the Blanchard River near the Village of Ottawa, Ohio, 

for a stage of 20.0 feet at U.S. Geological Survey streamgage 04189260

2. Flood-inundation areas along the Blanchard River near the Village of Ottawa, Ohio, 

for a stage of 21.0 feet at U.S. Geological Survey streamgage 04189260

3. Flood-inundation areas along the Blanchard River near the Village of Ottawa, Ohio, 

for a stage of 22.0 feet at U.S. Geological Survey streamgage 04189260

4. Flood-inundation areas along the Blanchard River near the Village of Ottawa, Ohio, 

for a stage of 23.0 feet at U.S. Geological Survey streamgage 04189260

5. Flood-inundation areas along the Blanchard River near the Village of Ottawa, Ohio, 

for a stage of 24.0 feet at U.S. Geological Survey streamgage 04189260

6. Flood-inundation areas along the Blanchard River near the Village of Ottawa, Ohio, 

for a stage of 25.0 feet at U.S. Geological Survey streamgage 04189260

7. Flood-inundation areas along the Blanchard River near the Village of Ottawa, Ohio, 

for a stage of 26.0 feet at U.S. Geological Survey streamgage 04189260

8. Flood-inundation areas along the Blanchard River near the Village of Ottawa, Ohio, 

for a stage of 27.0 feet at U.S. Geological Survey streamgage 04189260

9. Flood-inundation areas along the Blanchard River near the Village of Ottawa, Ohio, 

for a stage of 28.0 feet at U.S. Geological Survey streamgage 04189260

10. Flood-inundation areas along the Blanchard River near the Village of Ottawa, Ohio, 

for a stage of 29.0 feet at U.S. Geological Survey streamgage 04189260

11. Flood-inundation areas along the Blanchard River near the Village of Ottawa, Ohio, 

for a stage of 30.0 feet at U.S. Geological Survey streamgage 04189260

12. Flood-inundation areas along the Blanchard River near the Village of Ottawa, Ohio, 

for a stage of 31.4 feet at U.S. Geological Survey streamgage 04189260
iv

Figures

1. Map showing the Blanchard River watershed and the corporate boundary 

for Ottawa, Ohio ............................................................................................................................2

2. Map showing the locations of existing and new USGS streamgages 

(as of September 2009) in and near Ottawa, Ohio...................................................................3

3. Profile plot of HEC-RAS modeled Blanchard River in Ottawa and 

surveyed high-water marks from August 2007 ........................................................................5

Tables

1. Drainage areas of streamgages near Ottawa, Ohio...............................................................4

2. Stage and streamflow values measured by USGS field crews in 

March 2011 on the Blanchard River at Ottawa, Ohio .............................................................4

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

elevations from the August 23, 2007, flood on the Blanchard River.....................................6

4. Stages and elevations (NAVD88), with corresponding streamflow 

estimates at the Blanchard River at Ottawa streamgage......................................................7

5. Streamflow estimates for selected recurrence intervals at the 

Blanchard River at Ottawa streamgage taken from the StreamStats 

Web site at http://water.usgs.gov/osw/streamstats/ohio.html .............................................7

Conversion Factors

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)

Slope

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

Flow rate

cubic foot per second (ft3

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

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).
Development of a Flood-Warning Network and FloodInundation Mapping for the Blanchard River in Ottawa, 

Ohio

By Matthew T. Whitehead 

Abstract 

Digital flood-inundation maps of the Blanchard River 

in Ottawa, Ohio, were created by the U.S. Geological Survey 

(USGS) in cooperation with the U.S. Department of Agriculture, Natural Resources Conservation Service and the Village 

of Ottawa, Ohio. The maps, which correspond to water levels 

(stages) at the USGS streamgage at Ottawa (USGS streamgage 

site number 04189260), were provided to the National 

Weather Service (NWS) for incorporation into a Web-based 

flood-warning Network that can be used in conjunction with 

NWS flood-forecast data to show areas of predicted flood 

inundation associated with forecasted flood-peak stages.

Flood profiles were computed by means of a step-backwater model calibrated to recent field measurements of streamflow. The step-backwater model was then used to determine 

water-surface-elevation profiles for 12 flood stages with corresponding streamflows ranging from less than the 2-year and up 

to nearly the 500-year recurrence-interval flood. The computed 

flood profiles were used in combination with digital elevation 

data to delineate flood-inundation areas. Maps of the Village 

of Ottawa showing flood-inundation areas overlain on digital 

orthophotographs are presented for the selected floods. 

As part of this flood-warning network, the USGS 

upgraded one streamgage and added two new streamgages, 

one on the Blanchard River and one on Riley Creek, which is 

tributary to the Blanchard River. The streamgage sites were 

equipped with both satellite and telephone telemetry. The telephone telemetry provides dual functionality, allowing village 

officials and the public to monitor current stage conditions and 

enabling the streamgage to call village officials with automated warnings regarding flood stage and/or predetermined 

rates of stage increase. Data from the streamgages serve as a 

flood warning that emergency management personnel can use 

in conjunction with the flood-inundation maps by to determine 

a course of action when flooding is imminent.

Introduction 

The Village of Ottawa (hereafter referred to as Ottawa) 

is a small urban community with an estimated population of 

4,400 (U.S. Bureau of Census, 2009), making it the largest 

municipality in Putnam County, Ohio. The Ohio Department of Natural Resources (ODNR) estimates that more than 

330 flood-insurance policies are in effect in Ottawa, with 

approximately $25 million worth of property insured against 

flood damages (Steve Ferryman, ODNR, oral commun., 2008). 

Before August 2007, the insured losses paid for Ottawa totaled 

about $6.8 million (Steve Ferryman, ODNR, oral commun., 

2008). Damage costs for the flood that occurred in August 

2007 are reported to be $9.5 million (Denise Balbaugh, 

Village of Ottawa, 2009, written communication).

The unprecedented losses from the August 2007 flood 

prompted a study by the U.S. Geological Survey (USGS), in 

cooperation with Ottawa. Before this study, Ottawa officials 

relied on several information sources from which 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) (1986) 

for Ottawa. A second source of information is the USGS 

streamgage on the Blanchard River at Ottawa (04189260), 

from which water-level (stage) data can be accessed via telephone or the Web. The third source is the National Weather 

Service (NWS) forecasts of peak stage.

The NWS has statutory responsibility for hydrologic 

forecasts throughout the Nation. Peak-stage forecasts are 

based partly on data from precipitation gages and streamgages. 

In Ohio, the forecasts originate with the NWS River Forecast 

Center in Wilmington, Ohio, and warnings are issued to the 

public by regional NWS offices in Wilmington or Cleveland. 

Although stage information could be obtained from the USGS 

streamgage in Ottawa (04189260) before this study, upgrades 

and additions to the flood warning network were expected to 

enhance the flood-forecasting capabilities of the NWS for the 

Blanchard River in Ottawa (Brian Astifan, National Weather 

Service, oral communication, April 2007). 
2 Development of a Flood-Warning Network and Flood-Inundation Mapping for the Blanchard River in Ottawa, Ohio

Description of the Study Area

Ottawa is in northwest Ohio, in east-central Putnam 

County (fig. 1). The headwaters of the Blanchard River 

originate in Hardin County, where the river flows generally 

north before turning west in central Hancock County. The 

Blanchard River flows through the middle of Ottawa before 

discharging to the Auglaize River, which eventually drains 

into Lake Erie. One major tributary to the Blanchard River 

near Ottawa is Riley Creek, which flows generally north and 

west into the Blanchard River just upstream from the Ottawa 

corporate limit. The basin terrain is relatively flat, and most 

of the basin is rural. The Blanchard River study reach has an 

average stream-channel slope of approximately 1.3 ft/mi and a 

total length of approximately 7.4 mi. The study reach extends 

from Township Road I–9 upstream to Road 8, which are the 

approximate corporate boundaries of Ottawa.

Purpose and Scope

The purpose of this report is to describe methods and 

results of hydrologic and hydraulic analyses of the Blanchard 

River within the corporate limits of Ottawa, Ohio. A series of 

flood-inundation maps was developed for selected stages of 

the Blanchard River at Ottawa streamgage (04189260). 

Tasks specific to this study and discussed in this report 

were to (1) upgrade one existing streamgage and install two 

new streamgages, (2) install equipment enabling Ottawa 

officials to receive automated warnings about flood stage and/

or predetermined rates of stage increase from the streamgages, 

and (3) estimate the areas of Ottawa that will be flooded at 

selected stages at the streamgage by developing flood-inundation maps.

0 5

0 5 10

10 MILES

15 KILOMETERS

EXPLANATION

Village of Ottawa corporate

limits

Blanchard River drainage area

County boundary

Selected streams

Base from U.S. Geological Survey, variously scaled, 2007

State Plane Coordinate System (feet), Ohio North

Horizontal coordinate information is referenced to the North American Datum

 of 1983 (NAD83)

1,500,000 1,600,000 1,700,000

1,500,000 1,600,000 1,700,000

500,000

400,000

500,000

400,000

OHIO

Blanchard River 

watershed

Auglaize

River

Riley

Creek

Blanchard

River

PUTNAM

ALLEN

HARDIN

HANCOCK

WYANDOT

Ottawa

Figure 1. Blanchard River watershed and the corporate boundary for Ottawa, Ohio.
Installation and Upgrade of Streamgages 3

Installation and Upgrade of Streamgages 

The USGS upgraded one streamgage and installed two 

new streamgages for this study (fig. 2). The existing USGS 

streamgage, Blanchard River at Ottawa (04189260), was put 

into operation in 1995. Prior to this study, only stage information was published for that gage. In 2009, USGS field 

crews began to make streamflow measurements at the Ottawa 

streamgage in an effort to establish a stage-discharge relation commonly referred to as a rating curve. From March 

2009 to April 2011, 15 streamflow measurements were made 

at the Ottawa streamgage at stages ranging from 4.75 ft to 

28.35 ft and were used to develop a stage-discharge relation at 

this location.

The USGS installed two new streamgages, Blanchard 

River at Gilboa (04189131) and Riley Creek below Pandora (04189174), in September 2009. Both streamgages are 

equipped with Geostationary Operational Environmental 

Satellite (GOES) transmitters and voice modems. Data are 

transmitted via GOES hourly to facilitate near-real-time monitoring of equipment performance and stage. The voice modem 

provides dual functionality, allowing village officials to call 

the gage to monitor current stage conditions and enabling the 

gage to call village officials with automated warnings regarding flood stage and/or predetermined rates of stage increase. 

Streamflow and stage data from these new streamgages, as 

well as other USGS streamgages in Ohio, can be found at 

http://waterdata.usgs.gov/oh/nwis/current/?type=flow.

0 1

0 1 2

2 MILES

3 KILOMETERS

EXPLANATION

New USGS streamgage 

and identifier

Existing USGS streamgage 

and identifier

Streams

U+

04189174

U+

04189260

Base from U.S. Geological Survey, variously scaled, 2007

Orthophotography from Ohio Department of Administrative Services, Office of

 Information Technology, Ohio Geographically Referenced Information

 Program, Ohio Statewide Imagery Program, 2006

State Plane Coordinate System (Feet), Ohio North

Horizontal coordinate information is referenced to the North American Datum

 of 1983 (NAD83)

1,540,000 1,550,000 1,560,000 1,570,000 1,580,000

1,540,000 1,550,000 1,560,000 1,570,000 1,580,000

510,000

500,000

490,000

480,000

470,000

510,000

500,000

490,000

480,000

470,000

Figure 2. Locations of existing and new USGS streamgages (as of September 2009) in and near Ottawa, Ohio. 
4 Development of a Flood-Warning Network and Flood-Inundation Mapping for the Blanchard River in Ottawa, Ohio

Locations of the newly installed streamgages were 

selected with input from officials at NWS and Ottawa with the 

goal of enhancing the ability of NWS to predict peak stage at 

the Blanchard River at Ottawa streamgage. Specifically, gage 

locations were selected to improve the coverage of streamflow 

data and provide information on changing upstream waterlevel conditions. The drainage areas for streamgages installed 

and upgraded for this study range from 70.3 to 628 mi2

(table 1).

Table 1. Drainage areas of streamgages near Ottawa, Ohio. 

[mi2, square miles]

Streamgage

name

USGS site 

number

Drainage 

area

(mi2)

Blanchard River at Ottawa 04189260 628

Blanchard River at Gilboa 04189131 503

Riley Creek below Pandora 04189174 70.3

Hydrology and Hydraulics

The hydraulic analyses were done with the U.S. Army 

Corps of Engineer’s Hydrologic Engineering Center River 

Analysis System (HEC-RAS), version 4.0 (U.S. Army Corps 

of Engineers, 2008). HEC-RAS is a one-dimensional stepbackwater model for computing water-surface profiles with 

steady-state (gradually varied) or unsteady-state flow computation options. HEC-RAS is accepted by FEMA for use in 

the National Flood Insurance Program (NFIP). All hydraulic 

analyses for this report were done with the steady-state flow 

computation option.

Previous Study

Prior to this study, the Ottawa area had been a part of a 

larger modeling effort of the Blanchard River Basin extending 

from the mouth of the Blanchard River up to its headwaters 

(87 mi on Blanchard River), including some of its tributaries. The U.S. Army Corps of Engineers (USACE), Buffalo 

District, constructed that model to address flood-protection 

projects that are not relevant to this study. The USGS obtained 

the HEC-RAS model from USACE and modified the model 

for this study. Some modifications included (1) shortening the model to include only the area of interest in Ottawa, 

(2) adjusting selected cross-section overbank orientations, and 

(3) adding cross sections to shorten reach lengths between 

specific cross sections. 

Model Calibration

On March 2, 2011, flooding at the Blanchard River at 

Ottawa attained a peak stage of 28.45 ft (726.88 ft NAVD). 

Between March 1 and 4, 2011, USGS field crews made four 

streamflow measurements at stages ranging from 21.90 to 

28.35 ft and streamflows ranging from 4,070 to 13,600 ft3/s, 

respectively (table 2). The two measurements of 13,200 and 

13,600 ft3/s have inversely proportionate stage values, but the 

measured streamflows are within 3 percent of each other. In an 

effort to be conservative, it was decided to calibrate the model 

to the streamflow measurement of 13,600 ft3/s at a stage of 

28.32 ft. 

Table 2. Stage and streamflow values measured by USGS field 

crews in March 2011 on the Blanchard River at Ottawa, Ohio. 

[ft3/s, cubic feet per second; ft, feet]

Date and time Stage

(ft)

Streamflow

(ft3/s)

2011–03–01 17:48 27.86 12,900

2011–03–02 12:20 28.35 13,200

2011–03–02 13:16 28.32 13,600

2011–03–04 11:15 21.90 4,070

To calibrate the model, Manning’s roughness coefficients were uniformly raised from the original estimates in the 

HEC-RAS model provided by the USACE. Final Manning’s 

roughness coefficients for the channel range from 0.053 to 

0.055 and the overbanks from 0.050 to 0.236. These numbers 

may appear high at first glance, but the high degree of sinuosity of the stream and the vegetation on the banks warrant the 

high numbers. The final HEC-RAS model, with a streamflow 

of 13,600 ft3/s, produced a stage of 28.29 ft, which is 0.03 ft 

different from the observed stage of the calibration target, 

28.32 ft.
Hydrology and Hydraulics 5

Model Validation

On August 23, 2007, a near-record peak stage of 

31.40 ft (730.13 ft NAVD88) occurred at the Blanchard River 

at Ottawa streamgage. High-water marks were flagged and 

surveyed along the Blanchard River throughout the Ottawa 

area to help document the flooding (Straub and others, 2009). 

The 28 high-water marks surveyed showed fairly good local 

agreement, with the exception of 4 marks that appear to be 

outliers, as indicated by the trend suggested by the bulk of the 

other high-water marks (fig. 3). 

The HEC-RAS model that was previously calibrated to 

the March 2, 2011 measurement was then used to estimate 

the streamflow associated with the August 23, 2007 stage of 

31.40 ft (729.83 ft NAVD88). A profile using 20,600 ft3/s produced a stage of 31.40 ft at the Ottawa streamgage. Figure 3 

shows the modeled water-surface profile (using 20,600 ft3/s) 

and the high-water marks surveyed from the 2007 flood 

in Ottawa. 

A tabular comparison of water-surface elevations from 

the HEC-RAS model and elevations of high-water marks 

surveyed following the 2007 flood is given in table 3. Most of 

the high-water marks were not co-located with model cross 

sections. Therefore, to compare the modeled results to the 

high-water-mark profile, the water-surface elevations at the 

locations of the high-water marks were determined by linear 

interpolation from water-surface elevations at the nearest 

upstream and downstream cross sections defined in the HECRAS model.

The modeled and surveyed water-surface elevations are 

in close agreement with the exception of mark numbers 7, 9, 

14 and 15 that are highlighted in table 3. As previously mentioned, these four high-water marks are outliers with respect 

to the other marks and are therefore suspect. Including all 

28 high-water marks, the Root Mean Square (RMS) error of 

the differences in elevation is 0.72 ft. If the four suspect marks 

are removed from the RMS error calculation, the RMS error 

decreases to 0.24 ft.

726

727

728

729

730

731

732

 

20.0 21.0 22.0 23.0 24.0 25.0 26.0 27.0 28.0 29.0

STATIONING, IN MILES ABOVE MOUTH

ELEVATION, IN FEET (NAVD88)

EXPLANATION

 HEC-RAS water-surface profile

 2007 High-water marks

Figure 3. Profile plot of HEC-RAS modeled Blanchard River in Ottawa and surveyed high-water marks from 

August 2007.
6 Development of a Flood-Warning Network and Flood-Inundation Mapping for the Blanchard River in Ottawa, Ohio

Table 3. Comparison of hydraulic-model output and selected high-water-mark elevations from the 

August 23, 2007, flood on the Blanchard River. 

High-water-mark 

number

River

station

(mi)

High-watermark elevation

(NAVD88, feet)

Model water-surface elevation

(NAVD88, feet)

Elevation 

difference 

(feet)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

20.77

21.30

21.72

21.94

22.94

23.31

23.38

23.44

23.49

23.59

23.80

23.96

24.00

24.05

24.19

24.19

24.19

24.73

25.21

25.48

25.74

26.35

26.81

27.30

27.69

27.75

28.04

28.05

728.03

728.59

728.25

728.51

728.70

728.77

727.06

728.88

726.93

728.9

729.2

729.21

729.19

728.32

727.71

730.28

729.77

730.28

730.68

730.26

730.29

731.01

730.45

730.72

730.4

731.45

731.47

731.36

727.94

728.15

728.30

728.33

728.49

728.69

728.74

728.78

728.91

729.01

729.09

729.21

729.26

729.40

729.99

729.98

729.97

730.31

730.35

730.37

730.52

730.71

730.79

730.87

731.05

731.10

731.43

731.43

0.09

0.44

−0.05

0.18

0.21

0.08

−1.68

0.10

−1.98

−0.11

0.11

0.00

-0.07

−1.08

−2.28

0.30

−0.20

−0.03

0.33

−0.11

−0.23

0.30

−0.34

−0.15

−0.65

0.35

0.04

−0.07
Development of Flood-Inundation Maps 7

Determination of Water-Surface Profiles

Water-surface profiles were determined for a total of 

12 stages (20.0, 21.0, 22.0, 23.0, 24.0, 25.0, 26.0, 27.0, 28.0, 

29.0, 30.0, and 31.4 ft) at the Blanchard River at Ottawa 

streamgage. After the HEC-RAS model was calibrated to the 

March 2011 measurements, streamflows corresponding to 

desired stage values were determined by means of an iterative 

process in which streamflows were changed until target stage 

values were obtained. A summary of resulting streamflows for 

the 12 modeled stages is given in table 4. The lowest stage of 

20.0 is defined as the Action Stage by NWS, and the highest stage of 31.4 was the peak stage for the 2007 flood. The 

12 estimates of peak discharge range from approximately 

below the 2-year to nearly the 500-year recurrence interval 

flood, which are shown in table 5.

Development of Flood-Inundation Maps

The USGS used topographic data developed in 2007 by 

means of LiDAR (Ohio Geographically Referenced Information Program, 2007) as the base mapping for the floodplain 

delineations. The digital 2-ft contours were generated by the 

USACE and used in the creation of the HEC-RAS model, as 

well as the modifications made to the model by the USGS.

Flood-inundation boundaries were initially determined 

with HEC-GeoRAS software (U.S. Army Corps of Engineers, 

2002). HEC-GeoRAS is a software framework for processing 

geospatial data in ArcGIS using a graphical user interface. The 

interface facilitates extraction of geometric data for import 

into HEC-RAS and processes simulation results exported from 

HEC-RAS (U.S. Army Corps of Engineers, 2002). USGS personnel modified the HEC-GeoRAS results to ensure a logical 

transition of the flood-inundation boundary between modeled 

cross sections relative to the contour data for the land surface. 

The flood-inundation boundaries were then overlain onto digital georeferenced aerial photography from the Ohio Statewide 

Imagery Program (Ohio Geographically Referenced Information Program, 2007) that was flown in 2007. The resulting 

estimated flood-inundation boundaries for the 12 stages can be 

found at the Web site http://pubs.usgs.gov/sir/2011/5189/.

Table 4. Stages and elevations (NAVD88), with corresponding streamflow estimates at the Blanchard River at Ottawa streamgage. 

[ft3/s, cubic feet per second; ft, feet]

Stage

(ft) 20.0 21.0 22.0 23.0 24.0 25.0 26.0 27.0 28.0 29.0 30.0 31.4

Elevation

(ft, NAVD88) 718.4 719.4 720.4 721.4 722.4 723.4 724.4 725.4 726.4 727.4 728.4 729.8

Streamflow

(ft3

/s) 3,310 4,070 5,040 6,130 7,350 8,620 9,950 11,400 13,000 15,200 17,300 20,600

Table 5. Streamflow estimates for selected recurrence intervals at the Blanchard River 

at Ottawa streamgage taken from the StreamStats Web site at http://water.usgs.gov/osw/

streamstats/ohio.html.

Recurrence interval 2-year 10-year 50-year 100-year 500-year

Streamflow (ft3

/s) 7,510 12,400 16,200 17,800 21,100
8 Development of a Flood-Warning Network and Flood-Inundation Mapping for the Blanchard River in Ottawa, Ohio

Summary

A flood-warning network was developed for the Ottawa, 

Ohio, area by upgrading and adding streamgages to the existing network, installing equipment that enables emergencyresponse personnel and the public to quickly and easily access 

the predicted flood-inundation information, and delineating 

flood-inundation boundaries corresponding to selected flood 

stages. 

The existing streamgage network was enhanced by 

beginning determination of streamflow at the Blanchard River 

at Ottawa streamgage and establishing two new streamgages 

upstream in the basin, one on the Blanchard River and one 

on Riley Creek. The streamflow and stage data from these 

streamgages will be used by the National Weather Service to 

improve the peak-stage predictions for the Blanchard River 

at Ottawa streamgage. In addition, Ottawa officials can now 

receive automated warnings about the current stage from the 

Blanchard River at Ottawa streamgage via a dedicated phone 

line with callout capabilities.

Water-surface profiles were determined by means of a 

step-backwater model, and corresponding flood-inundation 

boundaries were delineated within Ottawa for 12 stages at 

the Blanchard River at Ottawa, streamgage (04189260). The 

flood-inundation boundaries were overlain on digital georeferenced aerial photography. The stages for the 12 profiles correspond to streamflows with recurrence intervals ranging from 

approximately the 2-year flood to nearly the 500-year flood.

Near real-time streamgage information, flood-forecast 

predictions, and flood-inundation mapping corresponding 

to the flood forecasts can be accessed on various Web sites 

hosted by the USGS and the NWS. The increased availability 

of streamflow data, the enhanced flood-prediction capability, and public access to the data will improve the ability of 

officials in Ottawa to assess flood conditions, take appropriate 

steps to protect life and property, and reduce flood damages.

Acknowledgments 

The author thanks the many local, state, and Federal 

agencies that support the operation and maintenance of the 

stream gages throughout the country. Individual thanks go to 

Jeffrey Loehrke, Community Development Director, Village 

of Ottawa, and Jason Phillips, Wastewater Director, Village of 

Ottawa, for their help with initial coordination of this study.

References Cited

Federal Emergency Management Agency, 1986, Flood Insurance Study, Village of Ottawa, Ohio, Putnam County: Community Number 390472, January 3, 1986 [variously paged].

Ohio Geographically Referenced Information Program, 

2007, Ohio Statewide Imagery Program, Putnam County: 

Accessed March 13, 2008, at http://ogrip.oit.ohio.gov/.

Straub, D.E., Ebner, A.D., and Astifan, B.M., 2009, Floods 

of August 21–24, 2007, in northwestern and north-central 

Ohio: U.S. Geological Survey Open-File Report 2009–

1094, 76 p.

U.S. Army Corps of Engineers, Hydrologic Engineering 

Center, 2002, HEC-GeoRAS: Accessed November 27, 

2007, at http://www.hec.usace.army.mil/software/hec-ras/

hec-georas.html.

U.S. Army Corps of Engineers, Hydrologic Engineering 

Center, 2008, HEC-RAS River Analysis System, hydraulic 

reference manual, Version 4 [variously paged].

U.S. Bureau of the Census, 2009, State population datasets—

Population, population change and estimated components 

of population change: April 1, 2000, to July 1, 2009 (NST_

EST2006_ALLDATA), accessed July 18, 2011, at http://

www.census.gov/popest/cities/SUB-EST2009-states.html.

opment of a Flood-Warning Network and Flood-Inundation Mapping for the Blanchard River in Ottawa, Ohio—Scientific Investigations Report 2011–5189