U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2017–1128 

Prepared in cooperation with the Iowa Department of Transportation and the Iowa Highway 

Research Board (Project HR–140) 

Flood of August 24–25, 2016, Upper Iowa River and 

Turkey River, Northeastern Iowa 

Upper Iowa River Basin

Turkey River Basin

IOWA

Iowa

Flood of August 24–25, 2016, Upper Iowa 

River and Turkey River, Northeastern Iowa 

By S. Mike Linhart and Padraic S. O’Shea 

Prepared in cooperation with the Iowa Department of Transportation and the 

Iowa Highway Research Board (Project HR–140) 

Open-File Report 2017–1128

U.S. Department of the Interior

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

RYAN K. ZINKE, Secretary

U.S. Geological Survey

William H. Werkheiser, Deputy Director 

exercising the authority of the Director

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

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

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

Suggested citation:

Linhart, S.M., and O’Shea, P.S., 2018, Flood of August 24–25, 2016, Upper Iowa River and Turkey River, northeastern 

Iowa: U.S. Geological Survey Open-File Report 2017–1128, 20 p. with appendix, 

https://doi.org/10.3133/ofr20171128.

ISBN 978-1-4113-4201-9

ISSN 0196-1497 (print)

ISSN 2331-1258 (online)
iii

Acknowledgments 

The authors express their gratitude to Harry J. Hillaker, State Climatologist, Iowa Department 

of Agriculture and Land Stewardship, for providing an isohyetal map of rainfall for the 24-hour 

period ending 12:00 p.m. on August 24, 2016. 

The authors also recognize U.S. Geological Survey employees Dave Eash, Roger Haschemeyer, 

Alex Laffoon, Jason McVay, Sophie Pierce, and Chris Rasmussen for collecting field data for the 

determination of water-surface and bench-mark elevations listed in this report. 
iv
v

Contents

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

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

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

Purpose and Scope .............................................................................................................................1

Study Basins ..................................................................................................................................................2

Upper Iowa River .................................................................................................................................2

Turkey River ..........................................................................................................................................2

Description of the Storms and Flood .........................................................................................................2

Storm Timeline ......................................................................................................................................2

Flood Description .................................................................................................................................5

Flood Discharge ...................................................................................................................................5

Annual Exceedance Probabilities .....................................................................................................5

Flood Profile ..........................................................................................................................................7

Summary .......................................................................................................................................................15

References Cited .........................................................................................................................................15

Appendix 1. List of Bench Marks and Reference Points .....................................................................17

References ..........................................................................................................................................19

Figures

1. Map showing the upper Iowa River Basin and lines of equal rainfall for 24 hours

ending at 12 p.m., August 24, 2016, northeastern Iowa ......................................................... 3

2. Map showing the Turkey River Basin and lines of equal rainfall for 24 hours ending

at 12 p.m., August 24, 2016, northeastern Iowa ...................................................................... 4

3. Hydrographs showing discharge and annual exceedance probabilities for A, the

Upper Iowa River near Dorchester, Iowa; B, the Turkey River at Spillville, Iowa; 

and C, the Turkey River near Eldorado, Iowa; August 23–27, 2016 ...................................... 6

4. Graph showing profile of the August 24–25, 2016, flood in the Upper Iowa River, river

miles 3–19, northeastern Iowa .................................................................................................. 9

5. Graph showing profile of the August 24–25, 2016, flood in the Turkey River, river

miles 59–118, northeastern Iowa ............................................................................................ 10

6. Graph showing profile of the August 24–25, 2016, flood in the Turkey River, river

miles 59–70, northeastern Iowa .............................................................................................. 11

7. Graph showing profile of the August 24–25, 2016, flood in the Turkey River, river

miles 70–90, northeastern Iowa .............................................................................................. 12

8. Graph showing profile of the August 24–25, 2016, flood in the Turkey River, river

miles 90–110, northeastern Iowa ............................................................................................ 13

9. Graph showing profile of the August 24–25, 2016, flood in the Turkey River, river

miles 110–118, northeastern Iowa .......................................................................................... 14
vi

Tables

1. Maximum stages and discharges and corresponding annual exceedance-probability

ranges for selected peak flows at streamgages in the Upper Iowa River and 

Turkey River Basins, northeastern Iowa .................................................................................. 7

2. Annual exceedance-probability and equivalent flood-recurrence interval for

selected probabilities .................................................................................................................. 7

3. Locations and elevations of high-water marks used in the Upper Iowa River

flood profile, flood of August 24–25, 2016, northeastern Iowa ............................................. 8

4. Locations and elevations of high-water marks used in the Turkey River flood

profile, flood of August 24–25, 2016, northeastern Iowa ....................................................... 8

1–1. Bench marks and reference points used in the Upper Iowa River and Turkey River 

flood profiles, flood of August 24–25, 2016, northeastern Iowa ......................................... 17
vii

Conversion Factors 

U.S. customary units to International System of Units 

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square meter (m2)

Flow rate

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

Datum

Elevation or vertical coordinate information is referenced to the National Geodetic Vertical 

Datum of 1929 (NGVD 29). Elevation refers to distance above or below NGVD 29. NGVD 29 can 

be converted to the North American Vertical Datum of 1988 by using the National Geodetic 

Survey conversion utility available at http://www.ngs.noaa.gov/TOOLS/Vertcon/vertcon.html.

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

Supplemental Information

Water year is the 12-month period from October 1 through September 30. The water year is 

designated by the calendar year in which the water year ends and that includes 9 of the 12 

months. Thus, the water year beginning on October 1, 2015, and ending September 30, 2016, is 

called the “2016 water year.”
viii
Flood of August 24–25, 2016, Upper Iowa River and Turkey 

River, Northeastern Iowa 

By S. Mike Linhart and Padraic S. O’Shea

Abstract 

Major flooding occurred August 24–25, 2016, in the Upper 

Iowa River Basin and Turkey River Basin in northeastern 

Iowa following severe thunderstorm activity over the region. 

About 8 inches of rain were recorded for the 24-hour period 

ending at 4 p.m., August 24, at Decorah, Iowa, and about 6 

inches of rain were recorded for the 24-hour period ending at 

7 a.m., August 24, at Cresco, Iowa, about 14 miles northwest 

of Spillville, Iowa. A maximum peak-of-record discharge 

of 38,000 cubic feet per second in the Upper Iowa River at 

streamgage 05388250 Upper Iowa River near Dorchester, 

Iowa, occurred on August 24, 2016, with an annual exceedance-probability range of 0.2–1 percent. High-water marks 

were measured at six locations along the Upper Iowa River 

between State Highway 26 near the mouth at the Mississippi 

River and State Highway 76 about 3.5 miles south of Dorchester, Iowa, a distance of 15 river miles. Along the profiled reach 

of the Turkey River, a maximum peak-of-record discharge of 

15,300 cubic feet per second at streamgage 05411600 Turkey River at Spillville, Iowa, occurred on August 24, 2016, 

with an annual exceedance-probability range of 1–2 percent. 

A maximum peak discharge of 35,700 cubic feet per second 

occurred on August 25, 2016, along the profiled reach of the 

Turkey River at streamgage 05411850 Turkey River near 

Eldorado, Iowa, with an annual exceedance-probability range 

of 0.2–1 percent. High-water marks were measured at 11 locations along the Turkey River between County Road B64 in 

Elgin and 220th Street, located about 4.5 miles northwest of 

Spillville, Iowa, a distance of 58 river miles. The high-water 

marks were used to develop flood profiles for the Upper Iowa 

River and Turkey River.

Introduction 

Severe thunderstorms following a wetter than usual summer in northeastern Iowa contributed to record flooding in the 

Upper Iowa River and Turkey River in northeastern Iowa on 

August 24–25, 2016. Heavy rainfall totals during a 24-hour 

period were a result of repeated rounds of thunderstorms 

during the evening of August 23rd into the morning hours of 

August 24th (National Centers for Environmental Information, 

National Oceanic and Atmospheric Administration [NOAA], 

2016). As a result, fields were flooded, and highways were 

closed throughout the basins. Maximum peak discharges of 

record were measured at one streamgage located along the 

profiled reach of the Upper Iowa River and at one of the two 

streamgages located along the profiled reach of the Turkey 

River. 

Purpose and Scope 

This report is part of an ongoing program of documenting large flood events and the effects of selected highways 

and bridges on flood levels of rivers and streams in Iowa. The 

program is funded in cooperation with the Iowa Department of 

Transportation (Iowa DOT) and the Iowa Highway Research 

Board (Research Board project HR–140). A list of other Iowa 

flood profile reports can be found in Eash (2014) or can be 

obtained by accessing https://ia.water.usgs.gov/flood/reports.

html.

This report provides information about the thunderstorms 

and the resulting flooding on August 24–25, 2016, in the Upper 

Iowa River Basin and the Turkey River Basin. The estimated 

annual exceedance-probability (AEP) ranges of the flood 

discharges at one continuous-record streamgage in the Upper 

Iowa River Basin and two continuous-record streamgages 

in the Turkey River Basin in the profiled reaches are also 

described. High-water marks (HWM) at selected sites along 

the Upper Iowa River are presented in a flood profile from 

State Highway 26 near the mouth of the Upper Iowa River at 

the Mississippi River to State Highway 76 south of Dorchester, Iowa, a distance of 15 river miles (mi). The HWMs at 

selected sites along the Turkey River are presented in a flood 

profile from County Road B64 in Elgin, Iowa, to 220th Street 

northwest of Spillville, Iowa, a distance of 58 river mi.
2 Flood of August 24–25, 2016, Upper Iowa River and Turkey River, Northeastern Iowa

Study Basins

Upper Iowa River

The Upper Iowa River is a tributary of the Mississippi 

River in northeastern Iowa (fig. 1). The headwaters are in 

Mower County, Minnesota, and a small part of Mitchell 

County, Iowa. The river flows east primarily through Howard, 

Winneshiek, and Allamakee Counties in Iowa. Short segments of the river lie in Fillmore County, Minnesota, as the 

river channel meanders across the Iowa/Minnesota border. 

Northern parts of the basin also lie in Houston County, Minnesota, near the eastern end of the basin. The river mouth is at 

the Mississippi River in northeastern Allamakee County. The 

drainage area at the mouth is 999 square miles (mi2) (Fischer 

and Eash, 2010). 

The Upper Iowa River Basin lies in two of Iowa’s 

landform regions, the Iowan Surface and the Paleozoic Plateau 

(Prior, 1991; not shown in fig. 1). The headwaters of the river 

are on the Iowan Surface; the river crosses onto the Paleozoic 

Plateau near Lime Springs. The topography of the Iowan 

Surface “appears slightly inclined to gently rolling with long 

slopes, low relief, and open views to the horizon” (Prior, 

1991). In contrast, the topography of the Paleozoic Plateau 

“include[s] abundant rock outcroppings, a near absence of 

glacial deposits, many deep, narrow valleys containing cool, 

fast-flowing streams, and more woodlands” (Prior, 1991). In 

the eastern one-half of Allamakee County, the Upper Iowa 

River flood plain becomes wide and flat before the river 

empties into the Mississippi River. More extensive 

descriptions of the landform regions and physiography of the 

Upper Iowa River Basin are available from the Iowa Natural 

Resources Council (1958) and Prior (1991).

Land use in the Upper Iowa River Basin is primarily 

agricultural in the Iowan Surface landform region and 

agricultural and forest in the Paleozoic Plateau landform 

region (Prior, 1991). The Upper Iowa River flows through 

Decorah, the only urban community in the basin, in 

Winneshiek County (fig. 1). Parts of the city are protected by 

levees. The Upper Iowa River is a popular recreation venue 

for much of its length.

Turkey River

The Turkey River is a tributary of the Mississippi River 

in northeastern Iowa. The Turkey River Basin originates in 

Howard County and flows about 148 mi through the cities of 

Spillville, Clermont, Elgin, and Elkader to its mouth at the 

Mississippi River in southeastern Clayton County (fig. 2). The 

river flows southeast primarily through Howard, Winneshiek, 

Fayette, and Clayton Counties in Iowa. The drainage area at 

the mouth is 1,684 mi2 (Larimer, 1957).

Most of the Turkey River Basin lies in two of Iowa’s 

landform regions, the Iowan Surface and the Paleozoic Plateau 

(Prior, 1991; not shown in fig. 2). The northwestern or upper 

part of the basin drains the low-relief plain of the Iowan Surface landform region (Prior, 1991). Although streams draining 

the Iowan Surface are well established, stream gradients are 

low. In Winneshiek and Fayette Counties, the Turkey River 

Basin crosses from the Iowan Surface landform region to the 

Paleozoic Plateau landform region. In Clayton County, the 

southeastern or lower part of the basin drains the Paleozoic 

Plateau. The bedrock-dominated, erosional topography of the 

Paleozoic Plateau is characterized by plateau-like uplands, 

integrated drainage networks with steep gradients, and deeply 

entrenched valleys (Iowa Natural Resources Council, 1958; 

Horick, 1989; Prior, 1991). More extensive descriptions of the 

landform regions and physiography of the Turkey River Basin 

are available from the Iowa Natural Resources Council (1958) 

and Prior (1991).

Land use in the Turkey River Basin is primarily agricultural in the Iowan Surface landform region and agricultural, 

timber, and some livestock operations in the Paleozoic Plateau 

landform region (Prior, 1991).

Description of the Storms and Flood 

Storm Timeline 

Intense rainfall fell over northeastern Iowa on August 

23–24, 2016. Within the Upper Iowa River Basin, the rainfall amount at Decorah was 8.06 inches (in.) for the 24-hour 

period ending at 4 p.m., August 24; at Cresco, near the boundary of the Upper Iowa River and Turkey River Basins, rainfall 

was 6.04 in. for the 24-hour period ending at 7 a.m., August 

24 (Hillaker, 2016b). One location about 5 mi southeast of 

Decorah recorded 8.46 in. for the 24-hour period ending at 7 

a.m., August 24 (Harry J. Hillaker, State Climatologist, Iowa

Department of Agriculture, written commun., 2016). The

storms followed a wet period for northeastern Iowa during the

first 3 weeks of August. Total rainfall at Decorah for the month

of August was 13.84 in. and is the second highest total for the

131 years of record at Decorah. The highest was 15.11 in. in

2007 (Hillaker, 2016b). A 24-hour isohyetal map compiled by

the Iowa State Climatologist for the period ending at 12 p.m.,

August 24, 2016, is shown for the Upper Iowa River Basin in

figure 1 (Harry J. Hillaker, written commun., 2016).

Within the Turkey River Basin, the rainfall amount at 

Cresco was 6.04 in. for the 24-hour period ending at 7 a.m., 

August 24 (Hillaker, 2016b); at Protivin it was 6.89 in. for 

the 24-hour period ending at 7 a.m., August 24; and for Fort 

Atkinson it was 6.05 in. for the 24-hour period ending at 7 

a.m., August 24, 2016 (Harry J. Hillaker, written commun.,

2016). A 24-hour isohyetal map compiled by the Iowa State

Climatologist for the period ending at 12 p.m., August 24,

2016, is shown for the Turkey River Basin in figure 2 (Harry J.

Hillaker, written commun., 2016).
Description of the Storms and Flood 3Figure 1. Upper Iowa River Basin and lines of equal rainfall for 24 hours ending at 12 p.m., August 24, 2016, northeastern Iowa.

Upper Iowa

River

Creek

Mississippi

River

Dry Run

Creek

76

76

Iowa River Drive

(County Road A26)

26

Morgan Bridge Road

Hartley Drive(County Road X6A)

Lycurgus Road

52

52

139

63

English Bench

Road

Le Roy

Chester

Taopi

Lime

Springs

Florenceville

Kendallville

Bluffton

Dorchester

New Albin

Decorah

Freeport

0 5 10 15 MILES0 5 10 15 KILOMETERS

Base from U.S. Geological Survey digital data, 2006, 1:24,000Universal Transverse Mercator projection, Zone 15

92°30'

92°20'

43°30'

92°40'

92°10'

92°00'

91°50'

05387440

91°40'

91°30'

91°20'

05388250

05388310

43°10'

05387490

05387500 05388000

43°20'

River Iowa

Upper

Waterloo

Upper Iowa River Basin

4 5 6 3 8 8 6 7 7 3 5

Upper IowaRiver Basin MINNESOTA

IOWA

 FILLMORE

 HOUSTON

WINNESHIEK

ALLAMAKEE

HOWARD

Spring Valley Preston

Caledonia

Brownsville

Lansing

Waukon

Cresco

Spillville

MITCHELL

Osage

St Ansgar

Austin

MOWER

Upper

Iowa

River 4 32 5 4 5 2 4 3 6 7 8Upper Iowa River Basin

3

EXPLANATION

Municipal area within basinDrainage basin boundaryRiver reach profiled in this reportLine of equal rainfall—In inches, for 24 hours ending 

at 12:00 p.m., August 24, 2016, (Harry J. Hillaker, State Climatologist, Iowa Department of Agriculture and Land Stewardship, written commun., 2016)

Streamgage and station numberCrest-stage gage and station numberHigh-water marks used in profile (table 3)

0538744005387490
4 Flood of August 24–25, 2016, Upper Iowa River and Turkey River, Northeastern Iowa

Figure 2. Turkey River Basin and lines of equal rainfall for 24 hours ending at 12 p.m., August 24, 2016, northeastern Iowa.

Turkey

Turkey

Little

Turkey

Little Turkey

River

River

River

River

River

Crane

Otter

Volga

Creek

Creek

Creek

Silver

Creek

Roberts

Elk

Creek

52

128

63

325

18

52

9

24

56

3

13

93

193

150

187

18

1 2

0.5

6 5 3 4 1 6 5 7 8

SaratogaSaratoga

Lourdes

Cresco

Protivin

Spillville

Fort Atkinson

Festina

Eldorado

Waucoma

Fayette

Luana

Saint Olaf

Postville

Osterdock

Arlington

Volga

Strawberry

Point

Mederville Elkport

Garber

MillvilleMillville

Littleport

Clermont

Elgin

Elkader

Base from U.S. Geological Survey digital data, 2006, 1:24,000Universal Transverse Mercator projection, Zone 15

42°45'

91°15'

43°15'

92°15'

220th

Street

County

Road

W14

123rd

Street

County

Road

B40

County

Road B64

Turkey

River Basin

0 10 5

0 10 15

15 20 MILES

20 KILOMETERS 5

3

EXPLANATION

Municipal area within basinDrainage basin boundaryRiver reach profiled in this reportLine of equal rainfall—In inches, variable intervals, for 24 

hours ending at 12:00 p.m., August 24, 2016, (Harry J. Hillaker, State Climatologist, Iowa Department of Agriculture and Land Stewardship, written commun., 2016)

Streamgage and station numberCrest-stage gage and station numberHigh-water marks used in profile (table 4)

0541160005412030

05412500

05411600

05411850

05411900

05412020

05412030

05412400

IOWA

Turkey River Basin

Mississippi River

Allamakee

Lansing

Lynxville

McGregor

Guttenburg

Dubuque Delaware

Oelwein

Fayette 1 4 2 3 5 6 7 8 1 4

Turkey River

Winneshiek

Clayton

Fredericksburg

New Hampton

ChickasawChickasaw

Howard

0.5

Turkey

River Basin
Description of the Storms and Flood 5

Flood Description 

The intense rainfall caused widespread flooding throughout 

five counties in northeastern Iowa, August 24–25, 2016. 

Estimated countywide damage to roads and bridges was about 

$480,000 in Howard County (Nick Rissman, Howard County 

Engineer, written commun., 2017), $1.2 million in Winneshiek 

County (Lee Bjerke, Winneshiek County Engineer, written 

commun., 2017), and $40,000 in Clayton County (Rafe 

Koopman, Clayton County Engineer, written commun., 2017). 

In Allamakee County, estimates of damage to secondary 

county roads and bridges were more than $570,000 (Jeremy 

Bjerke, Allamakee County Engineer, written commun., 2017). 

In Fayette County, preliminary estimates of damage to roads 

were $60,000 (Love, 2016). On the evening of August 23 in 

Winneshiek County, there was a lot of street flooding in towns 

across the county, and numerous roads were closed (National 

Weather Service [NWS] and NOAA, 2016a). On the morning 

of August 24, 3 mi east of Protivin, County Road B16 was 

impassable because of rising water. Also on the morning of 

August 24, sand bagging efforts were called off in Spillville 

because of the quickly rising Turkey River, and there were 

reports of water rescues underway near Waukon in Allamakee 

County and east of Decorah in Winneshiek County (NWS 

and NOAA, 2016a). By the end of the day on August 25, the 

Governor of Iowa had issued a disaster proclamation for 8 

counties in northeastern Iowa, and early estimates of damages 

from the flooding to public infrastructure for Winneshiek 

County were $2.4 million and another $1 million for Decorah 

(National Centers for Environmental Information, NOAA, 

2016). On September 19, the Governor of Iowa requested a 

major disaster declaration; on September 29, the President 

of the United States declared that a major disaster exists in 

the State of Iowa. For the Public Assistance request from 

the Governor of Iowa, primarily for damage to roads and 

bridges (that included three additional counties in northeastern 

Iowa), the cost estimate was more than $4.5 million (Federal 

Emergency Management Agency, 2016).

Flood Discharge 

Along the profiled reach of the Upper Iowa River (fig. 1), 

a maximum peak-of-record discharge of 38,000 cubic feet per 

second (ft3/s) at the continuous-record streamgage 05388250 

Upper Iowa River near Dorchester, Iowa, occurred on August 

24, 2016 (U.S. Geological Survey [USGS], 2016a). Along 

the profiled reach of the Turkey River (fig. 2), a maximum 

peak-of-record discharge of 15,300 ft3/s at the continuousrecord streamgage 05411600 Turkey River at Spillville, 

Iowa, occurred on August 24, 2016 (USGS, 2016b). The 

discharge hydrographs for August 23–27, 2016, are shown 

for these two streamgages (figs. 3A and 3B), as well as the 

streamgage 05411850 Turkey River near Eldorado, Iowa, 

(fig. 3C), which also is located along the profiled reach of 

the Turkey River (fig. 2). The peak discharge of 35,700 ft3/s 

for streamgage 05411850 Turkey River near Eldorado, Iowa, 

on August 25, 2016, was the second highest peak discharge 

of record (USGS, 2016c). The maximum peak discharge of 

record for streamgage 05411850 Turkey River near Eldorado 

was 50,100 ft3

/s on June 9, 2008 (USGS, 2008). The peak 

discharges at the streamgages were determined from rating 

curves that were verified by discharge measurements made 

near the time of occurrence of the respective peaks. 

Annual Exceedance Probabilities 

The 2016 flood-peak discharges for the three streamgages 

are listed in table 1. Selected prior-year peak discharges are 

included in the table for comparison purposes. Also included 

in table 1 are AEP ranges for the maximum peak discharges 

at the Upper Iowa River streamgage and the two Turkey 

River streamgages. The AEP is an estimate of the likelihood 

of a flood of specific magnitude occurring in any 1 year, and 

AEP range expresses the uncertainty of estimating precise 

exceedance probabilities. The reporting ranges are greater 

than 10 percent, 4–10 percent, 2–4 percent, 1–2 percent, 

0.2–1 percent, and less than 0.2 percent (Eash, 2001). The 

range is determined by the estimated AEP discharges that 

bracket the observed flood-peak discharge. If the observed 

peak discharge is the same value as an estimated AEP discharge, the lower AEP range is used.

The estimated 4-, 2-, 1-, and 0.2-percent AEP discharges 

at streamgages 05388250 Upper Iowa River near Dorchester, 

05411600 Turkey River at Spillville, and 05411850 Turkey 

River near Eldorado are shown in figure 3 as horizontal lines; 

the AEP ranges are the areas between the lines. The probability discharges at the three streamgages were calculated using 

the Weighting of Independent Estimates (WIE) program (Cohn 

and others, 2012) following guidelines in appendix 8 of Bulletin 17B (Interagency Advisory Committee on Water Data, 

1982).

Exceedance probabilities formerly were reported as flood 

probabilities, or flood-recurrence intervals, expressed in years. 

For example, a 1-percent exceedance-probability discharge is 

the same as the 100-year recurrence-interval flood discharge. 

Because of confusion caused over the years by two or more 

“100-year floods” occurring in a period of much less than 

100 years, the scientific and engineering community has begun 

expressing the annual likelihood of occurrence of flood discharges as a probability (Holmes and Dinicola, 2010). Percent 

probability is the inverse of the recurrence interval multiplied 

by 100. Selected AEPs and equivalent flood-recurrence intervals are listed in table 2. 

For informational purposes, discharges corresponding 

to National Weather Service (NWS) designated flood stages 

(fig. 3) are also shown on the hydrographs. The flood stages 

represent “Minor flooding—minimal or no property damage, 

but possibly some public threat” (NWS and NOAA, 2017). 

The discharges corresponding to the NWS flood stages were 

determined from the respective USGS stage-discharge rating 

curves in use at the time of the flood. At streamgage 05388250 

Upper Iowa River near Dorchester, Iowa, the NWS flood 
6 Flood of August 24–25, 2016, Upper Iowa River and Turkey River, Northeastern Iowa

Figure 3. Hydrographs showing discharge and annual exceedance probabilities for A, the Upper Iowa River near Dorchester, Iowa; B, 

the Turkey River at Spillville, Iowa; and C, the Turkey River near Eldorado, Iowa; August 23–27, 2016. Discharge, in cubic feet per second

0

10,000

20,000

30,000

40,000

50,000

0

10,000

20,000

30,000

40,000

50,000

10,000

20,000

30,000

40,000

50,000

0

August 2016

23 24 25 26 27

Discharges at indicated annual

exceedance probabilities

0.2 percent

1 percent

2 percent

4 percent

Discharge for National Weather Service (NWS) flood stage of 14 feet

Flood peak August 24, discharge

38,000 cubic feet per second

Discharges at indicated annual

exceedance probabilities

0.2 percent

1 percent

2 percent

4 percent

Discharge for NWS flood stage of 9 feet

Flood peak August 24, discharge

15,300 cubic feet per second

Discharge for NWS flood stage of 13 feet

Discharges at indicated annual

exceedance probabilities

0.2 percent

1 percent

2 percent

4 percent

Flood peak August 25, discharge

35,700 cubic feet per second

Unit values for August 25 were not

used in the computation of a daily value

05388250 Upper Iowa River near Dorchester, Iowa

05411600 Turkey River at Spillville, Iowa

05411850 Turkey River near Eldorado, Iowa

A

B

C
Description of the Storms and Flood 7

stage is 14 ft (NWS and NOAA, 2016b), and the discharge is 

8,280 ft3/s (USGS, 2017a). At streamgage 05411600 Turkey 

River at Spillville, Iowa, the NWS flood stage is 9 ft (NWS 

and NOAA, 2016c), and the discharge is 2,290 ft3/s (USGS, 

2017b). At streamgage 05411850 Turkey River near Eldorado, 

Iowa, the NWS flood stage is 13 ft (NWS and NOAA, 2016d), 

and the discharge is 7,820 ft3/s (USGS, 2017c).

Flood Profile 

The USGS located and measured the elevations of HWMs 

at six locations along the Upper Iowa River to develop a flood 

profile (fig. 1 and table 3). The profile is about 15 river miles 

from State Highway 26 near the mouth of the Upper Iowa 

River at the Mississippi River to State Highway 76 south 

of Dorchester, Iowa. The HWM locations include all State 

numbered highway bridges and several county and local road 

bridges.

The USGS also located and measured the elevations of 

HWMs at 11 locations along the Turkey River to develop a 

flood profile (fig. 2 and table 4). The profile is about 58 river 

miles from County Road B64 in Elgin, Iowa, to 220th Street 

located about 4.5 miles northwest of Spillville, Iowa. The 

HWM locations include all Federal and State numbered highway bridges and several county and local road bridges.

The HWMs were located and flagged within 3 days of the 

flood and surveyed to a bench mark at each location within 

30 days. The HWMs were flagged on the upstream and downstream sides of the bridges. The upstream marks were located 

about one bridge length from the bridge to avoid drawdown 

effects from channel contraction, and the downstream marks 

were located immediately downstream from the bridge. Bridge 

deck, bridge low-chord, and low-flow reference-point elevations also were measured with respect to the bench marks. The 

low-flow reference points were established so that watersurface elevations could be measured during a period when the 

streamflow was not directly affected by rainfall from which a 

low-flow profile was constructed. All elevations were subsequently referenced to the National Geodetic Vertical Datum 

of 1929 (NGVD 1929) by surveying level lines to the bench 

marks from other established bench marks or by using Global 

Positioning System (GPS) technology. The bench marks and 

reference points used in this study and a brief discussion 

regarding the elevation-measurement methods are presented in 

an appendix to this report.

The locations of the HWMs were measured in river miles 

from the mouths of the Upper Iowa River and the Turkey 

River at the Mississippi River. The distances to many locations were determined in a previous study (Eash, 2003). In 

Table 1. Maximum stages and discharges and corresponding annual exceedance-probability ranges for selected 

peak flows at streamgages in the Upper Iowa River and Turkey River Basins, northeastern Iowa. 

[AEP, annual exceedance probability; mi2, square mile; ft, foot; ft3/s, cubic foot per second; <, less than] 

Streamgage number and name Peak-flow record 

(water years)

Drainage area 

(mi2

) Date of peak Peak stage 

(ft)

Peak discharge 

(ft3

/s)

AEP range1

(percent)

Upper Iowa River Basin

05388250 Upper Iowa River 

near Dorchester, Iowa

1941, 1976–95, 

1997–2016

770 5/31/1941 21.80 2 30,400 1–2

6/9/2008 22.46 31,200 0.2–1

8/24/2016 24.30 38,000 0.2–1

Turkey River Basin

05411600 Turkey River at 

Spillville, Iowa

1947, 1956–73, 

1978–91, 2010–16

177 6/–/1947 3 18.40 2,4 10,000 4–10

7/12/1972 16.73 8,600 4–10

8/24/2016 20.25 15,300 1–2

05411850 Turkey River near 

Eldorado, Iowa 2001–16

641 6/9/2008 21.46 50,100 <0.2

6/20/2014 18.92 28,800 2–4

8/25/2016 3 21.34 35,700 0.2–1

1

Annual exceedance-probability (AEP) ranges reflect the uncertainty of estimating flood-frequency discharges. The exceedance probability is calculated 

using established techniques but then reported in one of the following ranges: greater than 10 percent, 4–10 percent, 2–4 percent, 1–2 percent, 0.2–1 percent, 

and less than 0.2 percent. Unless noted otherwise, AEP ranges are based on a weighted average of two independent frequency estimates. The Weighting of 

Independent Estimates (WIE) program was used to estimate the AEP following guidelines in appendix 8 of Bulletin 17B (Interagency Advisory Committee on 

Water Data, 1982; Cohn and others, 2012). The WIE program uses the variance and estimate of the Bulletin 17B streamgage-probablity analysis and the variance and estimate of the regional-regression AEP calculation (Eash, 2001) to compute a weighted probability estimate and variance at a streamgage. 

2

Discharge is a historic peak. Historic peaks are events that occur outside periods of systematic data collection. 

3

Gage height determined from floodmark. 

4

Discharge is an estimate. 

Table 2. Annual exceedance-probability and equivalent floodrecurrence interval for selected probabilities. 

Annual exceedance-probability 

(percent)

Flood-recurrence interval 

(years)

20 5

10 10

4 25

2 50

1 100

0.5 200

0.2 500
8 Flood of August 24–25, 2016, Upper Iowa River and Turkey River, Northeastern Iowa

cases where the HWMs were measured at previously unknown 

distances, the distances were determined for the locations 

using a geographic information system (GIS) using the USGS 

National Hydrography Dataset (NHD) data (USGS, 2017d). 

The HWM locations and elevations for the Upper Iowa River 

are listed in table 3. The HWM locations and elevations for 

the Turkey River are listed in table 4. The HWMs in these 

tables and in the profiles (figs. 4–9) are an average of multiple 

upstream or downstream HWMs measured at each location.

The HWMs along the Upper Iowa River are plotted in a 

flood profile in figure 4. The locations are annotated along the 

bottom. The line connecting the HWMs in figure 4 approximates the high-water surface between the marks. This line 

does not account for any features between the surveyed HWM 

locations that may have affected high-water elevations during 

the flood, such as channel morphology and bridges where 

HWMs were not measured. For comparison purposes, the profile from the June 8–9, 2008, flood also is shown. The lower 

line in the figures represents approximate low-flow conditions 

and connects the water-surface elevations that were measured 

November 17, 2008 (Fischer and Eash, 2010). The low-flow 

line also approximates the water surface between measurement locations. 

The HWMs along the Turkey River are plotted in a flood 

profile in figure 5. The profile is expanded in figures 6–9, 

where the locations are annotated. The line connecting the 

HWMs in the figures approximates the high-water surface 

between the marks. For comparison purposes, the profiles of 

the floods of June 15, 1991 (Eash and Koppensteiner, 1996), 

and the floods of March 19, 1979 (Iowa Natural Resources 

Council, 1980), are shown in figures 5–7. The profile of 

the July 12, 1972, flood (Eash and Koppensteiner, 1996) is 

also shown in figure 5 and figures 7–9. The lower lines in 

the figures represent approximate low-flow conditions and 

connect the water-surface elevations that were measured 

December 1, 2016 (figs. 5–9), September 21, 1992 (figs. 5–7) 

(Eash and Koppensteiner, 1996), and July 1–2, 1981 (figs. 5 

and 7–9) (Eash and Koppensteiner, 1996). The low-flow line 

also approximates the water surface between measurement 

locations.

Only bridges where HWMs were measured are shown in 

the figures. They are symbolized by an I-beam symbol where 

the bottom flange represents the lowest elevation of the low 

chord and the top flange represents the elevation of the bridge 

deck above the lowest low chord. The vertical lines along the 

bottom of the figures also show locations of roads and bridges 

where HWMs were measured. Selected notable landmarks and 

other sites where HWMs were measured in previous studies 

are also shown for reference. 

Table 3. Locations and elevations of high-water marks used in the Upper Iowa River flood profile, flood of August 24–25, 2016, 

northeastern Iowa. 

[HWM, high-water mark; NGVD 29, National Geodetic Vertical Datum of 1929; ND, not determined; USGS, U.S. Geological Survey]

Distance from mouth

(river miles) Location Downstream HWM

(feet above NGVD 29)

Upstream HWM

(feet above NGVD 29)

3.25 State Highway 26, south of New Albin 636.07 637.31

5.44 Ray's Landing at Morgan Bridge Road 642.17 643.57

10.94 Lycurgus Road (County Road X20), adjacent to intersection with Iowa River Drive 

(County Road A26) 660.40 661.19

12.01 Hartley Drive (County Road X6A) 664.17 ND

15.24 English Bench Road at intersection with Iowa River Drive (County Road A26) 672.83 ND

18.28 USGS streamgage 05388250, State Highway 76, south of Dorchester 684.30 685.10

Table 4. Locations and elevations of high-water marks used in the Turkey River flood profile, flood of August 24–25, 2016, 

northeastern Iowa. 

[HWM, high-water mark; NGVD 29, National Geodetic Vertical Datum of 1929; USGS, U.S. Geological Survey]

Distance from mouth

(river miles) Location Downstream HWM

(feet above NGVD 29) 

Upstream HWM

(feet above NGVD 29) 

59.65 County Road B64, Elgin 806.43 807.27

64.38 U.S. Highway 18, Clermont 832.77 834.20

71.90 County Road B40, northwest of Clermont 866.18 867.85

78.22 County Road B40, southeast of Eldorado 893.57 894.18

83.59 USGS streamgage 05411850, County Road B40, east of Eldorado 911.34 912.57

87.06 State Highway 150, Eldorado 928.36 931.02

95.19 123rd Street, west of Festina 977.70 978.43

101.14 State Highway 24, Fort Atkinson 1,011.26 1,013.63

110.30 State Highway 325, Spillville 1,051.92 1,053.57

110.82 USGS streamgage 05411600, County Road W14, Spillville 1,057.03 1,057.20

117.95 220th Street, northwest of Spillville 1,082.75 1,083.82
Description of the Storms and Flood 9Figure 4. Profile of the August 24–25, 2016, flood in the Upper Iowa River, river miles 3–19, northeastern Iowa. 

700690680670660650640630620

Elevation in feet above National Geodetic Vertical Datum of 1929 (NGVD 29)

Distance upstream from mouth of Upper Iowa River, in river miles

20 15 10 5 0

Maximum discharge at streamgage 05388250 Upper 

Iowa River near Dorchester, Iowa, 38,000 cubic feet 

per second, August 24, 2016 Flood profile (August 24–25, 2016) Flood profile (June 8–9, 2008) 

(Fisher and Eash, 2010)

Low-flow profile (November 17, 2008) (Fisher 

and Eash, 2010)

Bridge-deck elevationLow-bridge-chord elevation

Iowa, Chicago and Eastern Railroad Bridge

State Highway 26 (100 04–15 SE)

Morgan Bridge Road (100 04–28 NW)

Hartley Drive (100 04–31 NW)

Hartley Drive

(County Road X6A) (100 05–34 SE)

Lugurgus Road (100 05–35 SE)

Green Leaf Road

(99 05–05 NW) (Not shown in fig. 1)

English Bench Road (99 05–05 NW)

Mouth of Irish Hollow Creek

(Not shown in fig. 1)

Mouth of Clear Creek

(Not shown in fig. 1)

Mouth of Silver Creek (Not shown in fig. 1)

Mouth of Mineral Creek (Not shown in fig. 1)

U.S. Geological Survey stream gage 05388250

State Highway 76 (99 06–01 NW)

EXPLANATION
10 Flood of August 24–25, 2016, Upper Iowa River and Turkey River, Northeastern Iowa

Figure 5. Profile of the August 24–25, 2016, flood in the Turkey River, river miles 59–118, northeastern Iowa.

Figure 9

980960940920900880860840820800780

1,1001,0801,0601,0401,0201,000

Distance upstream from mouth of Turkey River, in river miles

50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130

Flood profile, August 24–25, 2016Low-flow profile, December 1, 2016Flood profile, June 15, 1991 

(Eash and Koppensteiner, 1996)

Low-flow profile, September 21, 1992 

(Eash and Koppensteiner, 1996)

Flood profile, March 19, 1979 

(Iowa Natural Resources Council, 1980)

Low-flow profile, July 1–2, 1981 

(Eash and Koppensteiner, 1996)

Flood profile, July 12, 1972 

(Eash and Koppensteiner, 1996)

Bridge-deck elevationLow-bridge-chord elevation

Locations indicated by these vertical lines are described in figures 6–9

Figure 6 Figure 7 Figure 8

Elevation in feet above National Geodetic Vertical Datum of 1929 (NGVD 29) EXPLANATION
Description of the Storms and Flood 11 Figure 6. Profile of the August 24–25, 2016, flood in the Turkey River, river miles 59–70, northeastern Iowa.

County Road B64 (94 07–13 NW)

County Road B40 (95 07–29 SW)

County Road B40 (95 07–30 SE)

County Road W51

(94 07–10 NE) (Not shown in fig. 2)

Mouth of Dry Run Creek

(Not shown in fig. 2)

U.S. Highway 18 (99 06–01 NW)

890880870860850840830820810800790780770760

Flood profile, August 24–25, 2016Low-flow profile, December 1, 2016Flood profile, June 15, 1991 

(Eash and Koppensteiner, 1996)

Low-flow profile, September 21, 1992

(Eash and Koppensteiner, 1996)

Flood profile, March 19, 1979 (Iowa Natural Resources 

Council, 1980)

Bridge-deck elevationLow-bridge-chord elevation

Elgin Clermont

Low-water elevation estimated

50 55 60 65 70

Distance upstream from mouth of Turkey River, in river miles

Clermont Dam (95 07–34 SW)

Elevation in feet above National Geodetic Vertical Datum of 1929 (NGVD 29) EXPLANATION
12 Flood of August 24–25, 2016, Upper Iowa River and Turkey River, Northeastern Iowa

Figure 7. Profile of the August 24–25, 2016, flood in the Turkey River, river miles 70–90, northeastern Iowa.

Distance upstream from mouth of Turkey River, in river miles

70 75 80 85 90

Flood profile, August 24–25, 2016Low-flow profile, December 1, 2016Flood profile, June 15, 1991 (Eash and Koppensteiner, 1996)Low-flow profile, September 21, 1992 (Eash and Koppensteiner, 1996)Flood profile, March 19, 1979 (Iowa Natural Resources Council, 1980)Low-flow profile, July 1–2, 1981 (Eash and Koppensteiner, 1996)Flood profile, July 12, 1972 (Eash and Koppensteiner, 1996)Bridge-deck elevationLow-bridge-chord elevation

960950940930920910900890880870860850840830820

Maximum discharge at streamgage 05411850 Turkey River near Eldorado, Iowa, 35,700 cubic feet per second, August 25, 2016

Eldorado

EXPLANATION

State Street (abandoned) (95 08–07 SW)

(Not shown in fig. 2)

State Highway 150(95 08–18 NW)

County Road B40 (95 08–25 NE)

County Road B40 (95 08–15 SE)

County Road W42 (95 08–16 NE)

(Not shown in fig. 2)

Ironwood Road (95 08–22 SE)

(Not shown in fig. 2)

Mouth of Nutting Creek

(Not shown in fig. 2)

Mouth of Dry Branch Creek

(Not shown in fig. 2)

Mouth of Little Turkey River

U.S. Geological Survey streamgage 05411850

County Road B40 (95 08–08 SE)

Elevation in feet above National Geodetic Vertical Datum of 1929 (NGVD 29)
Description of the Storms and Flood 13Figure 8. Profile of the August 24–25, 2016, flood in the Turkey River, river miles 90–110, northeastern Iowa.

Flood profile, August 24–25, 2016Low-flow profile, December 1, 2016Low-flow profile, July 1–2, 1981 

(Eash and Koppensteiner, 1996)

Flood profile, July 12, 1972 

(Eash and Koppensteiner, 1996)

Bridge-deck elevationLow-bridge-chord elevation

90 95 100 105 110

Distance upstream from mouth of Turkey River, in river miles

Orange Road (95 09–02 SE) (Not shown in fig. 2)

Mouth of Bass Creek (Not shown in fig. 2)

Pheasant Road (95 09–03 SE) (Not shown in fig. 2)

Fayette-Winneshiek County Line

Little Church Road (96 09–34 SW) (Not shown in fig. 2)

Mouth of Brockcamp Creek (Not shown in fig. 2)

Little Church Road (96 09–27 SE) (Not shown in fig. 2)

123rd Street (96 09–21 SE)

County Road B32 (96 09–16 NW) (Not shown in fig. 2)

Mouth of Goddard Creek (Not shown in fig. 2)

State Highway 24 (96 09–08 SE)

SOO Line Railroad

150th Street (96 09–08 NE) (Not shown in fig. 2)

160th Street (96 09–06 NW) (Not shown in fig. 2)

Fort Atkinson

990980970960950940930920

1,0601,0501,0401,0301,0201,0101,000

Elevation in feet above National Geodetic Vertical Datum of 1929 (NGVD 29) EXPLANATION
14 Flood of August 24–25, 2016, Upper Iowa River and Turkey River, Northeastern Iowa

State Highway 325 (97 09–19 SE)

Mouth of Burr Oak Creek (Not shown in fig. 2)

Mouth of Bohemian Creek (Not shown in fig. 2)

Mouth of Wonder Creek (Not shown in fig. 2)

Flood profile, August 24–25, 2016Low-flow profile, December 1, 2016Low-flow profile, July 1–2, 1981 

(Eash and Koppensteiner, 1996)

Flood profile, July 12, 1972 

(Eash and Koppensteiner, 1996)

Bridge-deck elevationLow-bridge-chord elevation

110 115 120 125 130

Distance upstream from mouth of Turkey River, in river miles

210th Street (97 10–11 NE) (Not shown in fig. 2)

220th Street (97 10–03 NE)

1,1401,1301,1201,1101,1001,0901,0801,0701,0601,0501,0401,030

Maximum discharge at streamgage 05411600 Turkey River at Spillville, Iowa, 15,300 cubic feet per second, August 24, 2016.

Spillville

U.S. Geological Survey streamgage 05411600

County Road W14 (97 09–19 NE)

Elevation in feet above National Geodetic Vertical Datum of 1929 (NGVD 29) EXPLANATION

Figure 9. Profile of the August 24–25, 2016, flood in the Turkey River, river miles 110–118, northeastern Iowa.
References Cited 15

Summary 

The Upper Iowa River in northeastern Iowa flooded 

throughout the lower part of the basin on August 24–25, 2016, 

following severe thunderstorm activity over northeastern 

Iowa. Within the Upper Iowa River Basin, the rainfall amount 

at Decorah, Iowa, was about 8 inches (in.) for the 24-hour 

period ending at 4 p.m. on August 24; at Cresco, Iowa, near 

the boundary of the Upper Iowa River and Turkey River 

Basins, rainfall was about 6 in. for the 24-hour period ending 

at 7 a.m. on August 24. One location about 5 miles southeast 

of Decorah recorded more than 8 in. overnight on August 23. 

Along the profiled reach, a maximum peak-of-record discharge of 38,000 cubic feet per second (ft3

/s) at streamgage 

05388250 Upper Iowa River near Dorchester, Iowa, occurred 

on August 24, 2016. The annual exceedance probability (AEP) 

range of the peak discharge is 0.2–1 percent. High-water 

marks measured at six locations along the lower reach of the 

Upper Iowa River were presented in a flood profile between 

State Highway 26 near the mouth at the Mississippi River and 

State Highway 76 south of Dorchester, Iowa. The length of the 

profile is 15 river miles. 

The Turkey River in northeastern Iowa flooded throughout 

much of the basin on August 24–25, 2016, following severe 

thunderstorm activity over northeastern Iowa. Within the Turkey River Basin, the rainfall amount at Cresco was about 6 in., 

at Protivin rainfall was almost 7 in., and just over 6 in. of rain 

fell at Fort Atkinson for the 24-hour period ending at 7 a.m. on 

August 24, 2016. Along the profiled reach, a maximum peakof-record discharge of 15,300 ft3

/s at streamgage 05411600 

Turkey River at Spillville, Iowa, occurred on August 24, 2016. 

The AEP range of the peak discharge is 1–2 percent. The peak 

discharge of 35,700 ft3/s at streamgage 05411850 Turkey 

River near Eldorado on August 25, 2016, was the second highest peak discharge of record with an AEP range of the peak 

discharge of 0.2–1 percent. High-water marks measured at 11 

locations along the Turkey River were presented in a flood 

profile between County Road B64 in Elgin and 220th Street 

northwest of Spillville, Iowa, a distance of 58 river miles. 

References Cited 

Cohn, T.A., Berenbrock, Charles, Kiang, J.E., and Mason, 

R.R., Jr., 2012, Calculating weighted estimates of peak

streamflow statistics: U.S. Geological Survey Fact Sheet

2012–3038, 4 p. [Also available at https://pubs.usgs.gov/

fs/2012/3038/pdf/fs2012-3038.pdf.]

Eash, D.A., and Koppensteiner, B.A., 1996, Floods of July 

12, 1972, March 19, 1979, and June 15, 1991, in the Turkey River Basin, northeast Iowa: U.S. Geological Survey 

Open-File Report 96–560, 55 p. with app. [Also available at

https://pubs.usgs.gov/of/1996/0560/report.pdf.]

Eash, D.A., 2001, Techniques for estimating flood-frequency 

discharges for streams in Iowa: U.S. Geological Survey 

Water-Resources Investigations Report 00–4233, 88 p. 

[Also available at https://pubs.er.usgs.gov/publication/

wri004233.]

Eash, D.A., 2003, Main-channel slopes of selected streams 

in Iowa for estimation of flood-frequency discharges: U.S. 

Geological Survey Water-Resources Investigations Report 

03–4120, 215 p. [Also available at https://pubs.er.usgs.gov/

publication/wri034120.]

Eash, D.A., 2014, Summary of U.S. Geological Survey reports 

documenting flood profiles of streams in Iowa, 1963–2012: 

U.S. Geological Survey Scientific Investigations Report 

2014–5085, 32 p. [Also available at https://pubs.usgs.gov/

sir/2014/5085/.]

Federal Emergency Management Agency, 2016, Iowa severe 

storms, straight-line winds, and flooding (DR–4281), 

accessed June 20, 2017, at https://www.fema.gov/disaster/4281.

Fischer, E.E., and Eash, D.A., 2010, Flood of June 8–9, 2008, 

Upper Iowa River, Northeast Iowa: U.S. Geological Survey 

Open-File Report 2010–1087, 17 p. with app. [Also available at https://pubs.usgs.gov/of/2010/1087/pdf/OF2010-

1087.pdf.]

Hillaker, H.J., 2016a, Iowa Annual Weather Summary – 2016: 

Des Moines, Iowa, Iowa Department of Agriculture and 

Land Stewardship, accessed May 19, 2017, at http://www.

iowaagriculture.gov/climatology/weatherSummaries/2016/

fas2016.pdf.

Hillaker, H.J., 2016b, Iowa climate review August 2016: 

Des Moines, Iowa, Department of Agriculture and Land 

Stewardship, v. 30, no. 8, 21 p., accessed May 19, 2017, at 

http://www.iowaagriculture.gov/climatology/ClimateReview/2016/IowaClimateReview201608.pdf.
16 Flood of August 24–25, 2016, Upper Iowa River and Turkey River, Northeastern Iowa

Holmes, R.R., Jr., and Dinicola, K., 2010, 100-year flood—It’s 

all about chance: U.S. Geological Survey General Information Product 106, 4 p., accessed September 25, 2017, 

at http://pubs.usgs.gov/gip/106/pdf/100-year-flood-handout-042610.pdf.

Horick, P.J., 1989, Water resources of northeast Iowa with a 

section on Surface-water resources by P.J. Soenksen: Iowa 

Department of Natural Resources Water Atlas No. 8, 133 p. 

[Also available at https://s-iihr34.iihr.uiowa.edu/publications/uploads/WA-08.pdf.]

Interagency Advisory Committee on Water Data, 1982, Guidelines for determining flood flow frequency: Hydrology 

Subcommittee Bulletin 17B, 28 p. and app.

Iowa Natural Resources Council, 1958, An inventory of water 

resources and water problems, northeastern Iowa River 

Basins: Des Moines, Iowa, Bulletin No. 7, 74 p.

Iowa Natural Resources Council, 1980, Turkey/Volga River 

flood of March 19, 1979: Des Moines, Iowa, 25 p.

Larimer, O.J., 1957, Drainage areas of Iowa streams: Iowa 

Highway Research Board Bulletin No. 7 (reprinted 

1974), 439 p. [Also available at http://www.iowadot.gov/

research/reports/Year/2003andolder/fullreports/HR-29%20

FINAL%20Drainage%20Areas%20of%20Iowa%20

Streams.pdf.]

Love, Orlan, 2016, September 1, Last week’s Iowa flood damage estimated at $5 million and growing. Damage to homes 

from last week’s sudden flooding still being tabulated: 

Cedar Rapids-Iowa City Gazette, accessed September 14, 

2017, at http://www.thegazette.com/subject/news/government/last-weeks-iowa-flood-damage-estimated-at-5-millionand-growing-20160901.

National Centers for Environmental Information, National 

Oceanic and Atmospheric Administration (NOAA), 

2016, Storm Events Database, accessed June 19, 2017, 

at https://www.ncdc.noaa.gov/stormevents/choosedates.

jsp?statefips=19%2CIOWA.

National Weather Service (NWS) and National Oceanic and 

Atmospheric Administration (NOAA), 2016a, Flooding of 

August 23–25, 2016, accessed June 19, 2017, at http://www.

weather.gov/arx/aug2416.

National Weather Service (NWS) and National Oceanic and 

Atmospheric Administration (NOAA), 2016b, Advanced 

Hydrologic Prediction Service, accessed February 24, 

2017, at http://water.weather.gov/ahps2/hydrograph.

php?wfo=arx&gage=dchi4&hydro_type=2.

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Atmospheric Administration (NOAA), 2016c, Advanced 

Hydrologic Prediction Service, accessed February 24, 

2017, at http://water.weather.gov/ahps2/hydrograph.

php?wfo=arx&gage=spli4&hydro_type=2.

National Weather Service (NWS) and National Oceanic and 

Atmospheric Administration (NOAA), 2016d, Advanced 

Hydrologic Prediction Service, accessed February 24, 

2017, at http://water.weather.gov/ahps2/hydrograph.

php?wfo=arx&gage=edri4&hydro_type=2.

National Weather Service (NWS) and National Oceanic and 

Atmospheric Administration (NOAA), 2017, Hydrologic 

Information on the Web, A Manual for Users, accessed 

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resources/Hydrologic_Web_Products_Manual.pdf.

Prior, J.C., 1991, Landforms of Iowa: Iowa City, University of 

Iowa Press, 154 p.

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for the Nation: National Water Information System 

(NWISWeb), accessed January 30, 2017, at https://nwis.

waterdata.usgs.gov/usa/nwis/peak/?site_no=05411850.

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for site 05388250: National Water Information System 

(NWISWeb), accessed January 30, 2017, at https://waterdata.usgs.gov/ia/nwis/wys_rpt/?site_no=05388250.

U.S. Geological Survey (USGS), 2016b, Water-year summary 

for site 05411600: National Water Information System 

(NWISWeb), accessed January 30, 2017, at https://waterdata.usgs.gov/ia/nwis/wys_rpt/?site_no=05411600.

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for site 05411850: National Water Information System 

(NWISWeb), accessed January 30, 2017, at https://waterdata.usgs.gov/ia/nwis/wys_rpt/?site_no=05411850.

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National Water Information System (NWISWeb), accessed 

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get_ratings?file_type=exsa&site_no=05388250.

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National Water Information System (NWISWeb), accessed 

September 12, 2017, at https://waterdata.usgs.gov/nwisweb/

get_ratings?file_type=exsa&site_no=05411600.

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National Water Information System (NWISWeb), accessed 

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gov/NHD_High_Resolution.html.
Appendix 1. List of Bench Marks and Reference Points 17

Appendix 1. List of Bench Marks and Reference Points 

The U.S. Geological Survey (USGS) used the bench marks 

and reference points listed in table 1–1 to facilitate measuring 

the elevations of high-water marks, low-flow water surfaces, 

bridge decks, and bridge low chords. Temporary bench marks 

were established at sites where bench marks were not available. In general, bench marks are points that were specifically 

designed to mark an elevation, such as USGS elevation disks 

and Iowa Department of Transportation bench marks (roundtop rods embedded in concrete at one or more corners of a 

bridge). Temporary bench marks are marks such as chiseled 

squares, chiseled arrows, or file marks. Reference points 

were established above water on the downstream side of each 

bridge to facilitate measuring low-flow water-surface elevations. Users are cautioned that the bench marks and reference 

points used for this flood profile might have been altered or 

destroyed since being used in 2016.

The bench marks and reference points are listed in 

upstream order. Each bench mark is identified by an index 

number composed of the Public Land Survey System township, range, section number, and quarter section for each 

bench-mark location. For example, T100N R4W 15 SE means 

“township 100 north, range 4 west, section 15, southeast 

quarter section.” Where two or more bench marks/reference 

points are in the same location, the points are distinguished 

by a sequence number in parentheses. “Right” and “left” in 

the descriptions refer to the side of the river determined as an 

observer looks downstream.

A combination of Global Positioning System (GPS) technology and differential leveling was used to measure benchmark/reference-point elevations at each site except where 

noted otherwise in table 1–1. The GPS data were collected by 

the USGS using Real Time Kinematic (RTK) surveys. The 

RTK surveys of GPS data were processed using the IaRTN 

SmartNet, a Global Navigation Satellite System (GNSS) reference station network service provided by Iowa Department 

of Transportation and Leica Geosystems (Iowa Department 

of Transportation, IaRTN SmartNet, 2016). The quality of 

the RTK GPS data are based on an average of multiple sets 

of GPS data collected using satellite configurations spaced 

at least 30 minutes apart and on comparisons of elevations 

between RTK GPS surveys of GPS bench marks and published elevations. 

Table 1–1. Bench marks and reference points used in the Upper Iowa River and Turkey River flood profiles, flood of August 24–25, 2016, 

northeastern Iowa. 

[Bench marks and reference points are listed in upstream order. Where two or more bench marks/reference points are in the same location, the points are distinguished by a sequence 

number in parentheses. NGVD 29, National Geodetic Vertical Datum of 1929; TBM, temporary bench mark; GPS, Geographical Positioning System; RP, reference point; BM, bench 

mark; DOT, Department of Transportation]

Public Land Survey System 

(township, range, section, 

quarter section, sequence 

number at same location)

Mark 

classification Location Mark

Elevation 

(feet above 

NGVD 1929)

Elevation determination method

Upper Iowa River Basin

T100N R4W 15 SE (1) TBM About 2 miles south of New Albin, on State Highway 26 bridge over the 

main channel (south side of valley), on left upstream wingwall.

Chiseled 

square

647.03 GPS

T100N R4W 15 SE (2) RP

About 2 miles south of New Albin, on State Highway 26 bridge over 

the main channel (south side of valley), on downstream side of bridge 

between 23rd and 24th vertical supports from left end of bridge. 

Chiseled 

arrow 647.20 GPS

T100N R4W 28 NW (1) TBM

About 3 miles southwest of New Albin, on Morgan Bridge Road east 

of intersection with Iowa River Drive (County Road A26), on right 

downstream concrete rail.

Chiseled 

square

654.14 GPS

T100N R4W 28 NW (2) RP

About 3 miles southwest of New Albin, on Morgan Bridge Road east of 

intersection with Iowa River Drive (County Road A26), on downstream 

concrete rail near center of bridge.

Three file 

marks 654.88 GPS

T100N R5W 35 SE (1) BM

About 6 miles southwest of New Albin, on Lycurgus Road bridge 

adjacent to the intersection of Iowa River Drive (County Road A26) 

and Lycurgus Road, on left downstream wingwall.

Round-top 

rod embedded 

in concrete

676.44 GPS 

T100N R5W 35 SE (2) RP

About 6 miles southwest of New Albin, on Lycurgus Road bridge 

adjacent to the intersection of Iowa River Drive (County Road A26) 

and Lycurgus Road, on downstream barrier wall near third barrier-wall 

seam from left end of bridge, about 4 ft right of seam. 

Chiseled 

arrow 673.21 GPS 

T99N R6W 1 NW BM

About 3.5 miles south of Dorchester, site of streamgage 05388250 Upper 

Iowa River near Dorchester, Iowa, on State Highway 76 bridge, on right 

upstream concrete guard rail.

Iowa DOT 

bench mark 693.01

Streamgage 

elevation 

data

Turkey River Basin

T94N R7W 13 NW (1) TBM About 0.1 miles east of Elgin on County Road B64, on left downstream 

wingpost.

Chiseled 

square

816.02 GPS

T94N R7W 13 NW (2) RP About 0.1 miles east of Elgin on County Road B64, 5th drainhole from 

left side of bridge on downstream curb.

Chiseled 

arrow 814.08 GPS 
18 Flood of August 24–25, 2016, Upper Iowa River and Turkey River, Northeastern Iowa

Table 1–1. Bench marks and reference points used in the Upper Iowa River and Turkey River flood profiles, flood of August 24–25, 2016, 

northeastern Iowa.—Continued 

[Bench marks and reference points are listed in upstream order. Where two or more bench marks/reference points are in the same location, the points are distinguished by a sequence 

number in parentheses. NGVD 29, National Geodetic Vertical Datum of 1929; TBM, temporary bench mark; GPS, Geographical Positioning System; RP, reference point; BM, bench 

mark; DOT, Department of Transportation]

Public Land Survey System 

(township, range, section, 

quarter section, sequence 

number at same location)

Mark 

classification Location Mark

Elevation 

(feet above 

NGVD 1929)

Elevation determination method

Turkey River Basin—Continued

T95N R7W 34 SW (1) TBM On the southwestern side of Clermont, on U.S. Highway 18 bridge, on 

top of right downstream guardrail.

Chiseled 

cross 849.49 GPS 

T95N R7W 34 SW (2) RP On the southwestern side of Clermont, on U.S. Highway 18 bridge, on 

top of downstream guardrail, one foot to the right of wire weight.

Chiseled 

arrow 849.70 GPS 

T95N R8W 25 NE (1) TBM About 3.9 miles northwest of Clermont on County Road B40 bridge 

over Turkey River, on left upstream corner of wingpost.

Chiseled 

square

878.68

Historic 

surveyed level 

line from 1st or 

2nd order BM

T95N R8W 25 NE (2) RP

About 3.9 miles northwest of Clermont on County Road B40 bridge 

over Turkey River, 8 feet right of third drainhole from left downstream 

side of bridge.

Chiseled 

arrow 880.96 Surveyed level 

line from TBM

T95N R8W 15 SE (1) TBM

Approximately 3.5 miles southeast of Eldorado on County Road B40 

bridge over Turkey River, on top of concrete guardrail on left downstream end of bridge.

Chiseled 

square

902.81

Historic 

surveyed level 

line from 1st or 

2nd order BM

T95N R8W 15 SE (2) RP

About 3.5 miles southeast of Eldorado on County Road B40 bridge over 

Turkey River, left of 10th concrete section from right downstream 

wingwall.

Chiseled 

square

907.31 Surveyed level 

line from TBM

T95N R8W 8 SE (1) TBM

About 1.4 miles east of Eldorado, site of streamgage 05411850 Turkey 

River near Eldorado, on County Road B40 bridge over Turkey River, 

on top of right downstream wingwall.

Chiseled 

cross 922.99

Streamgage 

elevation 

data

T95N R8W 18 NW (1) TBM At Eldorado, on State Highway 150 bridge over Turkey River, on left 

downstream abutment and 10 feet right of wingwall curb.

Chiseled 

square

938.16

Historic 

surveyed level 

line from 1st or 

2nd order BM

T95N R8W 18 NW (2) RP At Eldorado, on State Highway 150 bridge over Turkey River, on 19th 

metal plate of old guardrail from right downstream end of bridge.

Three file 

marks 940.93 Surveyed level line from TBM

T96N R9W 21 SE (1) TBM

About 2.6 miles southeast of Fort Atkinson, on 123rd Street bridge 

over Turkey River, on left downstream I-beam of truss bridge on left 

most rivet.

Chiseled 

cross 979.28 GPS

T96N R9W 21 SE (2) RP

About 2.6 miles southeast of Fort Atkinson, on 123rd Street bridge over 

Turkey River, on downstream side of bridge 15 feet right of the center 

bridge pier and of "V" formed by truss bridge.

Two file 

marks 983.63 GPS

T96N R9W 8 SE (1) BM At Fort Atkinson, on State Highway 24 bridge over Turkey River, on top 

of right downstream concrete guardrail.

Iowa DOT 

bench mark 1,017.78 GPS 

T96N R9W 8 SE (2) RP

At Fort Atkinson, on State Highway 24 bridge over Turkey River, above 

first drain hole from right downstream side of bridge on 

concrete guardrail.

Chiseled 

square/arrow 1,017.82 GPS 

T97N R9W 19 SE (1) BM At Spillville, on State Highway 325 bridge over Turkey River, on left 

upstream wingwall.

Winneshiek 

County tablet 1,056.93 GPS 

T97N R9W 19 SE (2) RP At Spillville, on State Highway 325 bridge over Turkey River, in the 

middle of the upstream concrete guardrail.

Chiseled 

square 1,056.46 GPS 

T97N R9W 19 NE (1) TBM

At Spillville, site of streamgage 05411600 Turkey River at Spillville, 

on County Road W14 bridge over Turkey River, on top of right downstream wingwall.

Chiseled 

square 1,057.56

Streamgage 

elevation 

data

T97N R10W 03 NE (1) TBM

About 4.5 miles northwest of Spillville, on 220th Street bridge over 

Turkey River, on right downstream corner of bridge deck on downstream landward rivet.

Chiseled 

cross 1,084.64

Historic 

surveyed level 

line from 1st or 

2nd order BM

T97N R10W 03 NE (2) RP

About 4.5 miles northwest of Spillville, on 220th Street bridge over 

Turkey River, about 50 feet from left downstream side of bridge on top 

of fourth vertical guardrail post.

Three file 

marks 1,088.41 Surveyed level 

line from TBM
References 19

References 

Iowa Department of Transportation, IaRTN SmartNet, 2016, 

accessed July 6, 2017, available online at https://iowadot.

gov/rtn and http://smartnet.iartn.com/.
For additional information contact:

Director, Central Midwest Water Science Center

U.S. Geological Survey

400 S. Clinton Street

Iowa City, IA 52240 

Publishing support provided by the 

Madison and Sacramento Publishing Service Centers

Linhart and O’Shea—Flood of August 24–25, 2016, Upper Iowa River and Turkey River, northeastern Iowa—Open-File Report 2017–1128 

ISSN 0196-1497 (print)

ISSN 2331-1258 (online)

http://doi.org/10.3133/ofr20171128 Printed on recycled paper