IOWA

South Skunk

River Basin

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2012–1202

Prepared in cooperation with the Iowa Department of Transportation and 

Iowa Highway Research Board (Project HR-140)

Flood of August 11–16, 2010, in the South Skunk River Basin, 

Central and Southeast Iowa

Flood of August 11–16, 2010, in the South 

Skunk River Basin, Central and Southeast 

Iowa

By Kimberlee K. Barnes and David A. Eash

Prepared in cooperation with the Iowa Department of Transportation and Iowa 

Highway Research Board (Project HR-140)

Open-File Report 2012–1202

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: 2012

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

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:

Barnes, K.K., and Eash, D.A., 2012, Flood of August 11–16, 2010, in the South Skunk River Basin, central and southeast Iowa: U.S. Geological Survey Open-File Report 2012–1202, 27 p. with appendix.

ISBN 978-1-4113-3516-5
iii

Acknowledgments

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

Agriculture and Land Stewardship, for providing an isohyetal map of rainfall for the 72-hour 

period ending 5:00 a.m. on August 11, 2010; Bonnie Shepard, National Flood Insurance Program 

Bureau and Statistical Agent, Federal Emergency Management Agency, for providing private 

property damage claims for eight counties in Iowa; and Dennis Harper, State Hazard Mitigation 

Officer, Iowa Homeland Security and Emergency Management Division, for providing public 

assistance project costs for eight counties in Iowa. 

The authors also recognize U.S. Geological Survey employees Mike Linhart and Jim Caldwell for 

collecting field data for the determination of water-surface and bench-mark elevations listed in 

this report.
iv

Contents

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

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

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

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

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

Annual Flood Probability...............................................................................................................................5

Flood History...................................................................................................................................................5

Flood of August 11–16, 2010 .........................................................................................................................5

Storm Description.................................................................................................................................8

Flood Description................................................................................................................................10

Chronology of Flood Effects ..............................................................................................................11

Flood Profile..................................................................................................................................................13

Summary........................................................................................................................................................14

References Cited..........................................................................................................................................14

Appendix. List of Bench Marks and Reference Points..........................................................................24

Figures

1. Map showing South Skunk River Basin and lines of equal rainfall for 72 hours

ending at 5 a.m. on August 11, 2010...........................................................................................2

2. Map showing South Skunk River Basin and landform regions of Iowa..............................4

3. Graphs showing hourly rainfall for August 8–11, 2010, at four rain gages in the

South Skunk River Basin and vicinity........................................................................................9

4. Graphs showing discharge hydrographs for four streamgages on the South Skunk

River, August 8–18, 2010 ............................................................................................................12

5. Graph showing profile of the August 11–16, 2010, flood for the South Skunk River,

river miles 4 to 133 ......................................................................................................................18

6. Graph showing profile of the August 11–16, 2010, flood for the South Skunk River,

river miles 4 to 30 ........................................................................................................................19

7. Graph showing profile of the August 11–16, 2010, flood for the South Skunk River,

river miles 30 to 60 ......................................................................................................................20

8. Graph showing profile of the August 11–16, 2010, flood for the South Skunk River,

river miles 60 to 90 ......................................................................................................................21

9. Graph showing profile of the August 11–16, 2010, flood for the South Skunk River,

river miles 90 to 120 ....................................................................................................................22

10. Graph showing profile of the August 11–16, 2010, flood for the South Skunk River,

river miles 120 to 133 ..................................................................................................................23
v

Tables

1. National Flood Insurance Program Bureau and Statistical Agent Iowa claims

closed with payment for selected counties for disaster number 1930, 

August 11–16, 2010, as of February 28, 2011.............................................................................3

2. Iowa Public Assistance Program project costs for selected counties for disaster

number 1930, June–August 2010, as of April 29, 2011 ............................................................3

3. Maximum stages and discharges for 2010 and selected largest-flood years, and 

the corresponding annual flood-probability ranges, at streamgages in the 

South Skunk River Basin, Iowa ..................................................................................................6

4. Annual flood probability and equivalent flood recurrence interval for selected

probabilities ...................................................................................................................................7

5. Twenty-four-hour rainfall amounts and greatest 48- and 72-hour rainfall totals at

selected rain gages in central, south-central, and southeast Iowa during 

August 8–11, 2010 .......................................................................................................................10

6. Magnitude and annual probability of theoretical rainfall amounts for selected 

storm periods in the Central, South-Central, and Southeast Iowa Climatological 

Divisions .......................................................................................................................................11

7. Locations and elevations of high-water marks used in the South Skunk River flood

profile of August 11–16, 2010 ....................................................................................................14

1–1. Bench marks and reference points used in the August 11–16, 2010, South Skunk

River flood profile........................................................................................................................25

Conversion Factors and Datums

Inch/Pound to SI

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 kilometer (km2) 

Flow rate

cubic foot per second (ft3

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

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 (U.S. Department of Commerce, National Oceanic and Atmospheric 

Administration, and National Climatic Data Center, 2004).

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

Map projections are Universal Transverse Mercator, Zone 15.

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 ending September 30, 2010, is called the “2010 water year.”

Flood of August 11–16, 2010, in the South Skunk River 

Basin, Central and Southeast Iowa

By Kimberlee K. Barnes and David A. Eash

Abstract

Severe thunderstorm activity during August 8–11, 2010 

in central and southeast Iowa resulted in major flooding 

from August 11–16, 2010, in the South Skunk River Basin. 

Rain gages at Ames and Story City recorded 96-hour rainfall 

amounts of 9.61 and 8.70 inches, respectively. The majority of 

the rainfall occurred during a 52-hour period, beginning late 

at night on August 8. Within the South Skunk River Basin, 

peak discharges of 14,800 cubic feet per second (annual floodprobability estimate of 0.2 to 1 percent) at the 05470000 South 

Skunk River near Ames, Iowa streamgage; of 36,200 cubic 

feet per second (annual flood-probability estimate of less than 

0.2 percent) at the 05471000 South Skunk River below Squaw 

Creek near Ames, Iowa streamgage (both on August 11, 2010); 

and of 24,000 cubic feet per second (annual flood-probability 

estimate of 0.2 to 1 percent) at 05471050 South Skunk River 

at Colfax, Iowa streamgage on August 14 are the largest floods 

on record for these sites. Peak discharges at 05470500 Squaw 

Creek at Ames, Iowa streamgage of 22,400 cubic feet per 

second (annual flood-probability estimate of less than 0.2 percent) on August 11; and at 05471500 South Skunk River near 

Oskaloosa, Iowa streamgage, of 25,200 cubic feet per second (annual flood- probability estimate of 1 to 2 percent) on 

August 16 are the second highest floods on record. This report 

provides a description of the watershed, the thunderstorms, 

the flooding, and a profile of high-water marks measured at 

20 locations along the South Skunk River between County 

Road V67/280th Avenue, northeast of Ollie in Keokuk County 

and West Riverside Road in Ames, a distance of 128 river 

miles.

Introduction

This report is part of an on-going program of publishing 

water-surface profiles for major floods on streams in Iowa. 

The program is managed by the U.S. Geological Survey 

(USGS) in cooperation with the Iowa Department of Transportation (Iowa DOT) and the Iowa Highway Research Board 

(Project HR-140). 

Following record statewide precipitation in June and 

July 2010, three consecutive nights of strong thunderstorms 

August 8–11, 2010, caused record flooding on the South 

Skunk River. New maximum peak discharges were recorded 

on August 11, 2010, at streamgages 05470000 South Skunk 

River near Ames (fig. 1, site 4) and 05471000 South Skunk 

River below Squaw Creek near Ames (fig. 1, site 6). The 

August 8–11 storms also caused a new maximum peak discharge on August 14, 2010, at streamgage 05471050 South 

Skunk River at Colfax (fig. 1, site 8). 

Because of flooding in the South Skunk River Basin, 

the counties of Boone, Hamilton, Jasper, Keokuk, Mahaska, 

Marion, Polk, and Story were added to a State disaster proclamation during August 13–23, 2010, which authorized implementation of the State Individual Assistance Grant Program 

to assist eligible residents of those counties (Iowa Homeland 

Security and Emergency Management, 2010). A Federal disaster declaration (number 1930) was issued on July 29, 2010, to 

help the citizens of Iowa recover from losses caused by severe 

storms, flooding, and tornados for the incident period June 1 

to August 31, 2010 (Federal Emergency Management Agency, 

2010). The Federal disaster declaration requested individual 

assistance for 38 counties and public assistance for 59 counties 

in Iowa. Private property damage claims reported for residential and nonresidential buildings in eight selected counties 

in central and southeast Iowa are shown in table 1 (Bonnie 

Shepard, Federal Emergency Management Agency, National 

Flood Insurance Program Bureau and Statistical Agent, written 

commun., May 2011). Approved public assistance costs (assistance to local governments for the repair of disaster-damaged 

public facilities) for the same eight counties in Iowa are shown 

in table 2 (Dennis Harper, Iowa Homeland Security and Emergency Management Division, State Hazard Mitigation Officer, 

written commun., April 2011).

Purpose and Scope

Flood-peak and water-surface-elevation profile information is needed for the economical, safe location, and design of 

bridges and other structures on or over streams and the adjacent flood plains. Defining the limits of flood inundation and 

establishing encroachment limits on flood plains are related 
Figure 1. South Skunk River Basin and lines of equal rainfall for 72 hours ending at 5 a.m. on August 11, 2010.

Ames

Newton

Pella

Nevada

Story City

Oskaloosa

Bondurant

Colfax

JewellJunction

Elkhart

Hedrick

Ollie

Cambridge

Valeria

Rose Hill

Hayesville

Ellsworth

35

210

20 928

383

17

30

69

30

6565

330

223

6

117

14

80

102

163

63

78

149 21

9

8

7

6

5

4

3

2 1

10

Squaw

River

Dick Creek

Long

42°

41°30’

92°30’

93°30’

4

8

6

8

6

4

Branch

Keigley

Creek

In dian Cree

River

k

South

Skunk

Squaw Creek

South

Skunk

8 Base from U.S. Geological Survey digital data, 2006, 1:24,000

Universal Transverse Mercator projectionZone 15 0 15105 20 KILOMETERS

0 5 10 15 20 MILES

Webster City

Marshalltown

Pella

Oskaloosa

Ankeny Colfax

Newton

Boone

Ames

WEBSTER

COUNTY

HARDIN COUNTY

BOONE

COUNTY

STORY

COUNTY

MARSHALL

COUNTY

POLK COUNTY

POWESHIEKCOUNTY

MARION

COUNTY

MAHASKA

COUNTY

KEOKUK

COUNTY

WAPELLO

COUNTY

JEFFERSON

COUNTY

HAMILTON COUNTY

South Skunk River Basin

JASPER COUNTY

6

6

6

6

6

2

2

4

4

4

8

8

8

8

4

2

2

6

4

8

6

IO

EXPLANATION

93

4

Municipal area within basinRiver reach profiled in this reportDrainage basin boundaryLine of equal rainfall—In inches, for 72 hours 

at 5:00 a.m., August 11, 2010 (Harry HillakeClimatologist, Iowa Department of AgriculLand Stewardship, written commun., 2011

Streamgage and map number (table 3)Crest-stage gage and map number (table 3)Ungaged bridge site used in profile (table 7)Rain gage and letter designation (figure 3)

A

D

C

B

B
Introduction 3

Table 1. National Flood Insurance Program Bureau and 

Statistical Agent Iowa claims closed with payment for selected 

counties for disaster number 1930, August 11–16, 2010, as of 

February 28, 2011.

[Bonnie Shepard, Federal Emergency Management Agency, National Flood 

Insurance Program Bureau and Statistical Agent, written commun., May 2011; 

NC, no claims]

County Number of claims Damage payment 

(dollars)

Boone 1 57,436

Hamilton NC NC

Jasper 14 534,374

Keokuk NC NC

Mahaska 3 18,153

Marion 1 1,515

Polk 53 1,392,352

Story 43 5,983,435

Total 115 7,987,265

Table 2. Iowa Public Assistance Program project costs for selected counties for disaster number 1930, June–August 2010, as of 

April 29, 2011.

[Dennis Harper, Iowa Homeland Security and Emergency Management Division, State Hazard Mitigation Officer, written commun., April 29, 2011; 

NC, no claims]

County Number of 

applicants

Debris 

removal

Emergency 

protective 

measures

Roads and 

bridges

Water 

control 

facilities

Buildings 

and 

equipment 

Utilities Parks and 

other Total

Cost (dollars)1

Boone 10 129,406 48,990 1,220,254 4,884 38,082 315,413 507,944 2,264,971

Hamilton 11 30,084 75,061 417,744 515,617 1,560 49,911 41,173 1,131,149

Jasper 12 100,187 155,223 625,251 NC 651,085 124,020 229,503 1,885,269

Keokuk 1 NC 2,965 555,649 NC NC NC NC 558,613

Mahaska 8 11,327 63,591 602,823 NC 56,693 59,664 13,808 807,906

Marion 10 39,304 28,622 997,217 NC 3,180 103,906 79,603 1,251,832

Polk 18 550,663 791,290 1,265,777 491,912 92,376 2,303,377 809,325 6,304,720

Story 18 337,536 354,227 573,481 76,068 96,684 913,394 526,433 2,877,824

Total 88 1,198,506 1,519,968 6,258,196 1,088,481 939,660 3,869,683 2,207,789 17,082,284

1

Cost rounded to whole dollars.

issues dependent on this information. Data for major floods are 

needed to compute annual flood-probability discharges and to 

calibrate water-surface-elevation profile models for sites along 

streams. A list of other USGS flood-profile reports for Iowa 

can be obtained by accessing http://ia.water.usgs.gov/projects/

profiles/.

This report provides rainfall information for August 8–11, 

2010; flooding information during August 11–16, 2010, in 

the South Skunk River Basin; and estimated annual floodprobability ranges at seven continuous-record streamgages and 

two crest-stage gages (CSG) in the basin. High-water marks 

(HWMs) at selected sites along the South Skunk River are presented in a flood profile from County Road V67/280th Avenue 

northeast of Ollie (not shown in fig. 1) in Keokuk County to 

USGS streamgage 05470000 on West Riverside Road (not 

shown in fig. 1) in Ames, a distance of 128 river miles. 

Study Area

The South Skunk River originates near the center of 

the State in Hamilton County and flows southeasterly about 

185 miles through the cities of Ellsworth, Story City, Ames, 

Cambridge, and Colfax, to its confluence with the North 

Skunk River in Keokuk County (fig. 1). The confluence of 

the North Skunk and South Skunk Rivers forms the Skunk 

River, which is a tributary of the Mississippi River. The 

drainage area of the South Skunk River at the confluence is 

1,842 square miles (mi2) and lies in parts of 12 counties. Land 

use in the basin is predominately agricultural. The channel of 

the South Skunk River has been straightened from near Ames 

downstream through Mahaska County. Through this reach, 

the flood plain of the South Skunk River is as much as 2 miles 

(mi) wide (Heinitz and Wiitala, 1978). The drainage basin, the 

river reach profiled, the location of USGS streamgages within 

this river basin, and the location of bridge sites used in the 

August 11–16, 2010, flood profile are shown in figure 1. 
4 Flood of August 11–16, 2010, in the South Skunk River Basin, Central and Southeast Iowa

The South Skunk River Basin lies within two of Iowa’s 

landform regions (fig. 2), the Des Moines Lobe and the Southern Iowa Drift Plain. The Des Moines Lobe landform region is 

characteristic of a young, postglacial landscape that is unique 

with respect to the rest of the State (Prior, 1991). The Des 

Moines Lobe generally comprises low relief terrain, accentuated by natural lakes, potholes, and marshes, where surfacewater drainage typically is poorly defined and sluggish. Soils 

of the Des Moines Lobe generally consist of friable, calcareous loam glacial till with thick deposits of compact, uniform 

pebbly loam (Oschwald and others, 1965; Prior, 1991). The 

Southern Iowa Drift Plain is characteristic of an older, postglacial landscape that has eroded to form a steeply to gently 

rolling topography and a well-established drainage system 

(Prior, 1991). The transition boundary between these two 

landform regions is in northwestern Jasper and southwestern 

Marshall Counties (figs. 1 and 2). Extensive descriptions of 

the landform regions are available from Prior (1991) and Prior 

and others (2009). 

Figure 2. South Skunk River Basin and landform regions of Iowa.

96° 95° 94° 93° 92° 91° 90°

43°

42°

41°

Base from U.S. Geological Survey digital data,

2006, 1:24,000

Universal Transverse Mercator projection,

Zone 15

0 25 50 MILES Landform region data from Prior and others, 2009

0 25 50 KILOMETERS

EXPLANATION

Des Moines Lobe

East-Central Iowa Drift Plain

Iowa-Cedar Lowland

Iowan Surface

Loess Hills

Mississippi River Alluvial Plain

Missouri River Alluvial Plain

Northwest Iowa Plains

Paleozoic Plateau

Southern Iowa Drift Plain

Landform region

" "

" " "

" "

"

"

"

"

" "

" " " "

" "

" "

" " " "

" "

"

"

"

"

" "

"

"

" "

"

"

" "

" "

"

"

"

"

"

"

"

" "

" " " " " "

"

" "

" "

" "

" "

"

"

" "

" "

" "

"

"

"

"

"

" "

" "

" "

" "

""

"

"

""

"" "

" "

" " "

"

""

" "

" "

" "

" "

" "

" "

" " "

" "

" "

" "

"

"

" "

""

" "

"

"" " "" "

" "

"

"

"

" "

" " " " "

" "

"

" "

""

" " " "

"

" "

" "

" "

South Skunk River Basin

Main branch 

 South Skunk River
Flood of August 11–16, 2010 5

Annual Flood Probability

Annual flood probability, also referred to as annual 

exceedance probability, is an estimate of the likelihood of a 

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

annual flood-probability range expresses the uncertainty of 

estimating precise annual flood probabilities. The reporting 

ranges are as follows: greater than 10 percent, 4 to 10 percent, 2 to 4 percent, 1 to 2 percent, 0.2 to 1 percent, and less 

than 0.2 percent. The range is determined from the estimated 

annual flood-probability discharges that bracket the observed 

flood-peak discharge. If the observed flood-peak discharge 

is the same value as an estimated annual flood-probability 

discharge, the lower annual flood-probability range is used. 

In the “Flood Description” section, flood discharges and their 

respective annual flood-probability ranges are discussed and 

are listed in table 3. Unless noted otherwise, annual floodprobability estimates listed in table 3 were computed using the 

Weighted Independent Estimates (WIE) program (Cohn and 

others, 2012), following guidelines in appendix 8 of Bulletin 

17B (Interagency Advisory Committee on Water Data, 1982). 

The WIE program uses the variance and estimate of the Bulletin 17B annual streamgage-probability analysis, and the variance and estimate of the regional-regression annual probability 

calculation (Eash, 2001) to compute a weighted estimate and 

variance at a streamgage. 

Annual flood probabilities change as streamflow records 

get longer. Bulletin 17B annual probability analyses are 

computed for streamgages using annual peak-discharge 

data. As additional annual peak discharges are measured at 

streamgages, Bulletin 17B annual flood-probability estimates 

are updated and become more statistically reliable. A minimum of 10 years of record is recommended to compute Bulletin 17B annual streamgage-probability estimates (Interagency 

Advisory Committee on Water Data, 1982). 

Annual flood probabilities formerly were reported as 

flood recurrence intervals expressed in years. For example, 

a 1-percent annual flood-probability discharge is the same 

as the 100-year recurrence-interval flood discharge (Holmes 

and Dinicola, 2010); however, because of widespread confusion caused in recent 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. Percent probability is the reciprocal of the recurrence 

interval multiplied by 100. Selected annual flood probabilities 

and equivalent flood recurrence intervals are listed in table 4. 

Although the annual probability is an estimate of the likelihood of a flood discharge of a specific magnitude occurring in 

any year, more than one flood discharge with a specific magnitude and annual probability could occur in the same year. For 

example, streamgage 05470000 South Skunk River near Ames 

(fig. 1, site 4) had a theoretical 1-percent annual flood-probability discharge of 9,090 cubic feet per second (ft3

/s) computed 

following the 1993 flood (Eash, 1997). During 1993, however, 

a flood-peak discharge of 11,100 ft3

/s occurred on July 9, 

and another flood-peak discharge of 11,200 ft3

/s occurred on 

August 16 (table 3). Thus, two floods that theoretically each 

had less than a 1-percent chance of occurring during any year 

occurred at this site in the same year. Revised annual flood 

probabilities of 1 to 2 percent are now estimated for these two 

1993 floods based on a longer period of record (table 3). This 

change in the annual flood-probability estimates for the 1993 

floods demonstrates the uncertainty in the estimates and how 

the estimates may change as the annual peak-discharge record 

becomes longer.

Flood History

Continuous records of streamflow have been collected 

in the South Skunk River Basin since as early as May 1919 at 

streamgage 05470500, Squaw Creek at Ames (fig. 1, site 5). 

Minimal information is available about floods before this time. 

Additional information about flooding in the South Skunk 

River Basin is available in U.S. Army Corps of Engineers’ 

(USACE) flood plain information reports (1966, 1975), Lara 

and Heinitz (1976), Heinitz and Wiitala (1978), and Einhellig 

and Eash (1996). At the time, the flood of June 1975 was considered to have caused the greatest urban flood damage in the 

history of the South Skunk River Basin (Heinitz and Wiitala, 

1978). The flood of May 1944 is the largest known flood in 

the South Skunk River Basin. A peak discharge of 37,000 ft3

/s 

(annual flood-probability estimate of less than 0.2 percent) 

was recorded at streamgage 05471500 South Skunk River near 

Oskaloosa (fig. 1, site 10; table 3).

Peak stages and discharges, and the corresponding annual 

flood-probability ranges for the largest known floods, including the August 2010 flood, are listed in table 3 for streamgages 

in the South Skunk River Basin. The streamgages listed in 

table 3 also are listed in the USGS National Water Information 

System (NWIS) database, and users may obtain surface-water 

data for Iowa streamgages, including information on types of 

data available and years of data collection (U.S. Geological 

Survey, 2011a). 

Flood of August 11–16, 2010

The flood of August 11–16, 2010, is one of the greatest 

floods on record in the South Skunk River Basin. The 2010 

flood is the largest flood on record for three streamgages. 

Streamgage 05470000 South Skunk River near Ames (fig. 1, 

site 4) had a peak discharge of 14,800 (ft3

/s), with an annualflood probability estimate of 0.2 to 1 percent. Streamgage 

05471000 South Skunk River below Squaw Creek near 

Ames (fig. 1, site 6) had a peak discharge of 36,200 ft3

/s 

(annual flood-probability estimate of less than 0.2 percent). 

Streamgage 05471050 South Skunk River at Colfax (fig. 1, 

site 8) had a peak discharge of 24,000 ft3

/s (annual floodprobability estimate of 0.2 to 1 percent). 
6 Flood of August 11–16, 2010, in the South Skunk River Basin, Central and Southeast Iowa

Table 3. Maximum stages and discharges for 2010 and selected largest-flood years, and the corresponding annual flood-probability 

ranges, at streamgages in the South Skunk River Basin, Iowa.

[mi2, square miles; ft, feet; ft3/s, cubic feet per second; (ft3/s)/mi2, cubic feet per second per square mile; --, not determined; >, greater than; <, less than]

Map 

number 

(fig. 1)

Streamgage number 

and name

Peak-flow record 

(water years)

Drainage 

area 

(mi2

)

Date of 

peak

Peak stage 

(ft)

Peak 

discharge 

(ft3/s)

Annual flood 

probability 

range1

(percent)

Unit runoff 

[(ft3/s)/mi2]

1 05469860 Mud Lake 

drainage ditch 71 at 

Jewell, Iowa

1966–2009 65.4 6/27/1975 90.04 2

2,300 4–10 35.2

7/9/1993 91.32 3,700 0.2–1 56.6

6/8/2008 91.87 3,120 1–2 47.7

2 05469970 Long Dick 

Creek near Ellsworth, 

Iowa

3

1991–2001, 

2003–10

6.08 8/17/1993 94.73 3-- 3-- 3--

6/8/2008 94.33 3

-- 3-- 3--

3/11/2010 94.05 3

-- 3-- 3--

3 05469990 Keigley 

Branch near Story City, 

Iowa

1966–2010 31.0 6/27/1975 91.38 2,250 4–10 72.6

7/9/1993 91.89 3,200 2–4 103.2

6/17/1996 92.26 2

3,440 2–4 111.0

8/10/2010 91.31 2,170 4–10 70.0

4 05470000 South Skunk 

River near Ames, Iowa

1921, 1930, 

1933–2010

315 5/20/1944 4

13.90 8,060 4–10 25.6

6/28/1975 4

9.98 5,230 >10 16.6

6/17/1990 4

11.84 6,600 >10 21.0

7/9/1993 4

14.15 11,100 1–2 35.2

8/16/1993 4

14.23 11,200 1–2 35.6

6/17/1996 4

15.89 214,000 0.2–1 44.4

6/9/2008 16.93 11,000 2–4 34.9

8/11/2010 19.04 14,800 0.2–1 47.0

5 05470500 Squaw Creek 

at Ames, Iowa

1918, 1920–27, 

1965–2010

204 6/27/1975 14.00 11,300 2–4 55.4

6/17/1990 15.97 12,500 1–2 61.3

7/9/1993 18.54 24,300 <0.2 119.1

6/17/1996 15.29 12,700 1–2 62.3

5/30/2008 15.85 12,600 1–2 61.8

8/11/2010 18.13 22,400 <0.2 109.8

6 05471000 South Skunk 

River below Squaw 

Creek near Ames, Iowa

1944, 1953–79, 

1990, 1992–2010

556 5/19/1944 5,613 10,000 >10 18.0

6/27/1975 6

25.57 14,700 4–10 26.4

6/17/1990 6

25.40 213,000 4–10 23.4

7/9/1993 25.53 26,500 0.2–1 47.7

6/17/1996 25.13 24,400 0.2–1 43.9

5/30/2008 24.70 19,800 1–2 35.6

8/11/2010 26.72 36,200 <0.2 65.1

7 05471040 Squaw Creek 

near Colfax, Iowa

1996–2005 18.40 6/18/1998 13.94 7,020 0.2–1 381.5

5/31/2000 12.85 4,740 2–4 257.6

8 05471050 South Skunk 

River at Colfax, Iowa

1986–2010 803 7/12/1993 21.53 14,200 4–10 17.7

6/14/2008 20.25 10,900 >10 13.6

8/14/2010 23.85 24,000 0.2–1 29.9
Flood of August 11–16, 2010 7

Table 3. Maximum stages and discharges for 2010 and selected largest-flood years, and the corresponding annual flood-probability 

ranges, at streamgages in the South Skunk River Basin, Iowa.—Continued

[mi2, square miles; ft, feet; ft3/s, cubic feet per second; (ft3/s)/mi2, cubic feet per second per square mile; --, not determined; >, greater than; <, less than]

Map 

number 

(fig. 1)

Streamgage number 

and name

Peak-flow record 

(water years)

Drainage 

area 

(mi2

)

Date of 

peak

Peak stage 

(ft)

Peak 

discharge 

(ft3/s)

Annual flood 

probability 

range1

(percent)

Unit runoff 

[(ft3/s)/mi2]

9 05471200 Indian Creek 

near Mingo, Iowa

1944, 1958–75, 

1986–2010

276 5/20/1944 21.40 -- -- --

6/4/1991 19.16 23,500 <0.2 85.1

7/9/1993 18.64 18,600 0.2–1 67.4

5/23/2004 17.27 11,700 4–10 42.4

8/12/2010 17.71 11,000 4–10 39.9

10 05471500 South Skunk 

River near Oskaloosa, 

Iowa

1944, 1946–2010 1,635 5/--/1944 25.80 37,000 <0.2 22.6

6/15/1947 21.26 20,000 4–10 12.2

7/15/1993 24.78 20,700 2–4 12.7

6/12/2008 24.61 17,300 4–10 10.6

8/16/2010 26.40 25,200 1–2 15.4

1

Annual flood-probability ranges reflect the uncertainty of estimating annual flood-probability discharges. The annual flood probability is calculated using 

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

and less than 0.2 percent. Unless noted otherwise, annual flood-probability ranges are based on a weighted average of two independent probability estimates. 

The WIE (weighted independent estimates) program was used to estimate annual flood probabilities 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 annual 

streamgage-probability analysis and the variance and estimate of the regional-regression annual probability calculation (Eash, 2001) to compute a weighted 

probability estimate and variance at a streamgage. 

2

Dishcarge is an estimate (U.S. Geological Survey, 2005).

3

Annual-peak discharges are not determined because stage-discharge relation is not determined.

4

Prior to Oct. 1, 2003, streamgage at different site and at datum 5.00 ft higher.

5

Prior to Oct. 1, 1973, at datum 10.00 ft higher.

6

Prior to Oct. 1991, at site 500 ft upstream.

Table 4. Annual flood probability and equivalent flood 

recurrence interval for selected probabilities.

Annual flood probability 

(percent)

Recurrence interval 

(years)

20 5

10 10

4 25

2 50

1 100

0.5 200

0.2 500

At streamgages 05470500 Squaw Creek at Ames 

(fig. 1, site 5) and 05471500 South Skunk River near Oskaloosa (fig. 1, site 10), the 2010 flood is the second largest 

flood on record. Streamgage 05470500 Squaw Creek at 

Ames had a peak discharge of 22,400 ft3

/s (annual floodprobability estimate of less than 0.2 percent). Streamgage 

05471500 South Skunk River near Oskaloosa had a peak 

discharge of 25,200 ft3/s (annual flood-probability estimates of 1 to 2 percent). Periods of peak-flow record for 

streamgages in the South Skunk River Basin are presented 

in table 3.
8 Flood of August 11–16, 2010, in the South Skunk River Basin, Central and Southeast Iowa

Storm Description

The flood of August 11–16, 2010, was the result of three 

consecutive nights of local, heavy rain in central Iowa from 

August 8–11. The storms were part of an exceptionally wet 

period for Iowa from June through September 2010 that followed a wetter than normal first 6 months of the year. A new 

statewide rainfall record of 10.39 inches (in.) was set for the 

month of June; the old record of 10.33 in. occurred in 1947. 

Overall, 2010, with an average statewide rainfall of 45.10 in., 

was the second wettest year in Iowa in 138 years of record 

(Hillaker, 2010a). Although rainfall during July and August 

2010 was not as great as in June, it was locally more intense 

for a short period of time, which resulted in greater flooding; 

the greatest rain event in August occurred from August 8–11, 

when the Ankeny rain gage (fig. 1) officially recorded 9.86 in. 

and the Ames rain gage recorded 9.61 in. during these 

3 nights. A new record maximum total rainfall of 13.71 in. 

was set for the month of August at Ankeny. The old record 

was 12.87 in., set in 1993 among 60 years of records (Hillaker, 

2010b). 

The following rainfall and flood information is from the 

U.S. Department of Commerce, National Oceanic and Atmospheric Administration, and National Climatic Data Center 

(2010a) search terms Iowa, 8/8/2010 to 8/16/2010, and flood 

were entered to obtain a list of 113 flood events; the following 

quotes were obtained from event numbers (16) Youngstown, 

(23) Ames, and (92) Ames:

“The very wet weather pattern of June and July 

continued into the first two weeks of August. Central 

Iowa was hardest hit by rainfall with three consecutive nights of torrential rains on the 8th, 9th and 

10th. A swath of 2 to 5 inch rainfall extended from 

west central, through central, into parts of southeast 

Iowa. Ankeny recorded 9.86 inches of rain over 

these three nights while Ames had 9.61 inches. 

Record flood impacted much of Story, Polk, Jasper 

and Mahaska counties. The flooding was major 

along the Skunk and parts of the lower Des Moines 

River basin. Following the flash flooding of the 10th 

and 11th, major river flooding continued. Significant crop losses occurred because of the high water 

flooding fields for several days. Major damage was 

done along the Skunk Basin from Ames, through 

Colfax. Numerous roads were covered with flowing 

water of 1 to 2 feet in depth. Water from the South 

Skunk River completely covered portions of US 

Highway 30 near Ames and Interstate 35 just south 

of Ames. Highway 117 just south of Interstate 80 

was closed and barricaded due to water over the 

road from the South Skunk near Colfax. The flash 

flooding claimed one life in central Iowa. Three 

vehicles were swept into the water of Mud Creek 

near Altoona in Polk County. There were 11 people 

involved. Major damage was done to several buildings on the Iowa State Campus. Hilton Coliseum 

reported 4 to 6 feet of water inside flooding the stadium and basketball floor. Cy Stephens Auditorium 

also report[ed] water in the mechanical building up 

to the 1st floor. The water system was knocked out 

in Ames, and threatened in Colfax.” 

Hourly rainfall amounts for August 8–11, 2010, for 

rain gages at Ames, Des Moines, Maxwell, and Story City 

(site A, B, C, D, respectively, figure 1) are shown in figure 3 

(U.S. Department of Commerce, National Oceanic and 

Atmospheric Administration, and National Climatic Data 

Center, 2010b). The graphs provide a general indication of 

the timing and intensity of the rainfall in the South Skunk 

River Basin. The greatest 1-hour rainfall intensity of 2.4 in. at 

Ames 8 WSW, ended at midnight on August 8, 2010 (fig. 3A). 

Data from the four rain gages (fig. 3) indicate that much of 

the rainfall occurred from 10 p.m. on August 8 to 1 a.m. on 

August 11, and also indicate that Story City recorded the 

greatest 24-hour and 48-hour rainfall of 6.3 in. and 7.7 in., 

respectively. 

An isohyetal map of the areal distribution of rainfall for 

the 72-hour period beginning at 5 a.m. on August 8, 2010, 

and ending at 5 a.m. on August 11, 2010, is shown in figure 1; 

data were provided by Harry Hillaker, State Climatologist, 

Iowa Department of Agriculture and Land Stewardship (written commun., November 2011). The isohyetal map shows a 

band of 8 in. of rainfall in the headwaters and along the South 

Skunk River Basin from Story City, south through Ames and 

Ankeny, then southeast through Oskaloosa. Each 24-hour rainfall amount from August 8 to August 11, 2010, for 12 selected 

rain gages in central, south-central, and southeast Iowa is 

listed in table 5 (Hillaker, 2010c). The 72-hour rainfall total 

listed in table 5 from August 8–11 is the time period for which 

the rainfall could be considered as directly contributing to the 

flooding of August 11–16.

The “Rainfall Frequency Atlas of the Midwest” (Huff and 

Angel, 1992) provides a table of the mean distribution of theoretical rainfall amounts for climatological divisions in Iowa 

for selected rain periods and annual probabilities (recurrence 

intervals). The magnitude and annual probability of theoretical 

rainfall amounts for selected rain periods (durations), from the 

table in Huff and Angel (1992), for 3 of the 9 climatological 

divisions in Iowa pertaining to this report are listed in table 6. 

Nine of the 12 rain gages listed in table 5 are in the Central 

Iowa Climatological Division, 2 are located in the South-central Climatological Division, and 1 is located in the Southeast 

Climatological Division (Hillaker, 2010c). A map showing 

the location of climatological divisions in Iowa is in Huff and 

Angel (1992). The greatest 48-hour rainfalls listed in table 5 

equaled or exceeded 6 in. at six rain gages, five of which are 

located in the Central Climatological Division (Ames 8 WSW, 

Ankeny, Des Moines Camp Dodge, Maxwell, and Story City), 

with one rain gage located in the Southeast Climatological 

Division (Oskaloosa). The annual rainfall probability for 

greatest 48-hour rainfalls is estimated to be 4 to 10 percent for 

the Oskaloosa rain gage, 2 to 4 percent for the Ames 8 WSW 

and Maxwell rain gages, 1 to 2 percent for the Ankeny and 
Flood of August 11–16, 2010 9

Figure 3. Hourly rainfall for August 8–11, 2010, at four rain gages in the South Skunk River Basin and vicinity (Central Daylight Time; 

U.S. Dept. of Commerce, National Oceanic and Atmospheric Administration, and National Climatic Data Center, 2010b).

0

0.5

1.0

1.5

2.0

2.5

3.0

0

0.5

1.0

1.5

2.0

2.5

3.0

0

0.5

1.0

1.5

2.0

2.5

3.0

0

0.5

1.0

1.5

2.0

2.5

3.0

A Ames 8 WSW

Hourly rainfall shown for hour 

ending.

Greatest 24–hour rainfall shown 

is 6.0 inches.

Greatest 48–hour rainfall 

shown is 5.3 inches.

Total 96–hour rainfall 

shown is 9.61 inches. 

B Des Moines Airport

Rainfall, in inches

8 9 10 11

August 2010

Hourly rainfall shown for hour ending.

Greatest 24–hour rainfall shown is 3.37 inches.

Greatest 48–hour rainfall shown 

is 3.84 inches.

Total 96–hour rainfall shown 

is 6.5 inches. 

C Maxwell

Hourly rainfall shown for hour ending.

Greatest 24–hour rainfall shown is 4.7 inches.

Greatest 48–hour rainfall shown is 6.4 inches.

Total 96–hour rainfall shown is 6.5 inches. 

D Story City

Hourly rainfall shown for hour ending.

Greatest 24–hour rainfall shown is 6.3 inches.

Greatest 48–hour rainfall shown is 7.7 inches.

Total 96–hour rainfall shown is 8.7 inches. 
10 Flood of August 11–16, 2010, in the South Skunk River Basin, Central and Southeast Iowa

Table 5. Twenty-four-hour rainfall amounts and greatest 48- and 72-hour rainfall totals at selected rain gages in central, south-central, 

and southeast Iowa during August 8–11, 2010.

Rain gage

24-hour rainfall, in inches Greatest 48-hour 

rainfall total, 

in inches

Greatest 72-hour 

rainfall total, 

in inches

Observation 

time

August 8, 

2010

August 9, 

2010

August 10, 

2010

August 11, 

2010

Ames 5 SE1 6 a.m. 0.00 5.03 0.27 4.31 5.30 9.61

Ames 8 WSW2 midnight 4.10 1.90 3.10 0.10 6.00 9.10

Ankeny1 7 a.m. 0.00 2.90 3.30 3.66 6.96 9.86

Boone1 8 a.m. 0.00 3.85 0.42 1.63 4.27 5.90

Des Moines Airport2 midnight 2.42 1.42 1.90 0.76 3.84 5.74

Des Moines Camp Dodge1 midnight 2.03 2.68 3.97 3

0.38 6.65 8.68

Knoxville1 6 a.m. 0.00 2.10 1.36 2.01 3.46 5.47

Maxwell2 midnight 1.70 3.00 3.40 0.70 6.40 8.10

Newton1 7 a.m. 0.00 2.87 1.59 2.61 4.46 7.07

Oskaloosa1 7 a.m. 3

0.02 1.89 4.00 2.30 6.30 8.19

Pella 1S1 7 a.m. 0.00 3.14 2.42 2.50 5.56 8.06

Story City2 midnight 0.90 1.40 6.30 0.10 7.70 8.60

1

Iowa Climate Review (Hillaker, 2010c).

2

Hourly Precipitation Data, Iowa, August 2010 (U.S. Department of Commerce, National Oceanic and Atmospheric Administration, and National Climatic 

Data Center, 2010b).

3

Estimate (Hillaker, 2010c).

Des Moines Camp Dodge rain gages, and less than 1 percent 

for the Story City rain gage (table 6).

Annual flood probabilities for various locations in the 

South Skunk River Basin are listed in table 3 and annual 

probabilities for rainfall for various locations in the South 

Skunk River Basin are listed in table 6. Similar to the concept 

of annual flood probability, annual rainfall probability is an 

estimate of the likelihood of a rainfall of a specific magnitude 

and duration occurring in any year; more than one rainfall with 

a specific magnitude and annual probability could occur in the 

same year.

Flood Description

Major flooding occurred August 11–16, 2010, in the 

South Skunk River Basin as a result of the intense rain 

that fell during August 8–11. The 2010 peak discharges for 

8 streamgages in the South Skunk River Basin are listed in 

table 3. Also listed in the table are selected historical peak 

discharges for the largest-flood years.

Hydrographs of instantaneous discharges recorded at the 

four continuous-record streamgages on the South Skunk River 

are presented in figure 4. The period shown is August 8 to 

August 18, 2010. The streamgages record instantaneous values 

at 15-minute time intervals. Also shown on the hydrographs 

are lines denoting discharge estimates for selected annual 

flood probabilities. The annual flood-probability range listed 

in table 3 for the sites is the range between the annual floodprobability discharges that bracket the flood-peak discharge. 

For example, the 2010 peak discharge at streamgage 05470000 

South Skunk River near Ames (fig. 1, site 4) falls between the 

1-percent and 0.2-percent annual flood-probability estimates 

(table 3 and fig. 4). 

Flooding began on August 9 at streamgages 05471000 

South Skunk River below Squaw Creek near Ames (fig. 1, 

site 6) and 05471050 South Skunk River at Colfax (fig. 1, 

site 8). Flooding began on August 10 and August 14 at 

streamgages 05470000 South Skunk River near Ames (fig. 1, 

site 4) and 05471500 South Skunk River near Oskaloosa 

(fig. 1, site 10), respectively. The peak discharges at two of 

these streamgages occurred on August 11 (fig. 4). The flood 

peaked at streamgage 05470000 South Skunk River near Ames 

at 11:45 a.m. with a discharge of 14,800 ft3

/s, and at 10:00 

a.m. for streamgage 05471000 South Skunk River below 

Squaw Creek near Ames with a discharge of 36,200 ft3

/s 

(fig. 4). The peak discharge of streamgage 05471050 South 

Skunk River at Colfax of 24,000 ft3

/s occurred on August 14 

at 1:30 a.m. and the peak discharge of streamgage 05471500 

South Skunk River near Oskaloosa of 25,200 ft3

/s occurred on 

August 16 at 1:30 a.m. (fig. 4). The 2010 flood is the largest known flood at the following streamgages: 05470000 

South Skunk River near Ames, 05471000 South Skunk River 

below Squaw Creek near Ames, and 05471050 South Skunk 

River at Colfax. The annual flood-probability range of the 

2010 flood at the streamgages 05470000 South Skunk River 

near Ames and 05471050 South Skunk River at Colfax is 

estimated to be 0.2 to 1 percent (table 3). At streamgage 

05471000 South Skunk River below Squaw Creek, the annual 
Flood of August 11–16, 2010 11

Table 6. Magnitude and annual probability of theoretical rainfall 

amounts for selected storm periods in the Central, South-Central, 

and Southeast Iowa Climatological Divisions.

[Rainfall amounts from Huff and Angel (1992)]

Duration Rainfall (inches) for indicated probabilities

(hours) 10 (percent) 4 (percent) 2 (percent) 1 (percent)

Central

24 4.27 5.15 5.87 6.61

48 4.67 5.75 6.52 7.33

72 5.16 6.22 7.06 8.12

120 5.72 6.92 7.98 9.18

240 7.22 8.61 9.66 10.88

South-Central

24 4.65 5.78 6.73 7.74

48 5.06 6.28 7.35 8.60

72 5.64 6.90 7.96 9.24

120 6.26 7.64 8.78 9.99

240 7.57 8.99 10.09 11.04

Southeast

24 4.67 5.67 6.58 7.59

48 5.20 6.35 7.32 8.40

72 5.74 6.95 7.88 8.98

120 6.32 7.60 8.69 9.95

240 7.35 8.45 9.33 10.42

flood-probability range is estimated to be less than 0.2 percent 

(table 3). The 2010 flood is the second largest known flood 

at the streamgage 05471500 South Skunk River near Oskaloosa, with the annual flood-probability range of 1 to 2 percent 

(table 3). Peak discharges at the four streamgages shown in 

figure 4 were determined from stage-discharge rating curves 

that were verified by discharge measurements made near the 

time of occurrence of the respective peaks. In addition to the 

four streamgages shown in figure 4, the 2010 flood also is 

the second largest known flood at the streamgage 05470500 

Squaw Creek at Ames (fig. 1, site 5), where the annual probability of the peak discharge of 22,400 ft3

/s on August 11 is 

estimated to be less than 0.2 percent (table 3). 

For informational purposes, also shown on the four 

hydrographs, are the discharges corresponding to the National 

Weather Service (NWS) designated flood stage effective in 

2010 during the flood (fig. 4). The flood stages represent “an 

established gage height for a given location at which a rise in 

water-surface level begins to impact lives, property, or commerce” (U.S. Department of Commerce, National Oceanic 

and Atmospheric Administration, and National Climatic Data 

Center, 2010c). In February 2012 and effective March 14, 

2012, NWS in Des Moines changed the designated flood stage 

at three of the four river forecast locations shown in figure 

4 (U.S. Department of Commerce, National Oceanic and 

Atmospheric Administration, and National Weather Service, 2012a). The flood stage was not changed at steamgage 

05471500 South Skunk River near Oskaloosa. The discharges 

corresponding to the NWS flood stages in effect prior to February 2012 were determined from the respective USGS stagedischarge rating curves in use at the time of the flood. 

At streamgage 05470000 South Skunk River near Ames, 

the NWS flood stage was 14.0 feet (ft) (discharge 7,030 ft3/s). 

This is the stage at which water affects East 13th Street 

between Meadow Lane and the bridge over the South Skunk 

River (U.S. Department of Commerce, National Oceanic and 

Atmospheric Administration, and National Weather Service, 

2012b). The streamgage South Skunk River near Ames was 

above flood stage during August 10–12, and the peak stage 

of 19.04 ft (table 3) exceeded the flood stage by 5.04 ft. The 

NWS flood stage was changed to 12.5 ft in March 2012.

At streamgage 05471000 South Skunk River below 

Squaw Creek near Ames, the NWS flood stage was 20.0 ft 

(discharge 6,200 ft3

/s). This is the stage at which water affects 

agricultural land from Ames to Cambridge (U.S. Department 

of Commerce, National Oceanic and Atmospheric Administration, and National Weather Service, 2012b). The streamgage 

South Skunk River below Squaw Creek near Ames was above 

flood stage during August 9–13, and the peak stage of 26.72 ft 

(table 3) exceeded the flood stage by 6.72 ft. The NWS flood 

stage was changed to 21.5 ft in March 2012.

At streamgage 05471050 South Skunk River at Colfax, 

the NWS flood stage was 17 ft (discharge 6,710 ft3

/s). At a 

stage of 15.5 ft, storm sewers in the city of Colfax are closed 

and water affects nearby agricultural land; at a stage of 19 ft, 

the earthen levee is overtopped near the Iowa 117 bridge and 

the first two downtown blocks of Colfax adjacent to the river 

are inundated (U.S. Department of Commerce, National Oceanic and Atmospheric Administration, and National Weather 

Service, 2012b). The streamgage South Skunk River at Colfax 

was above flood stage during August 9–17, and the peak stage 

of 23.85 ft (table 3) exceeded the flood stage by 6.85 ft. The 

NWS flood stage was changed to 18 ft in March 2012.

At streamgage 05471500 South Skunk River near Oskaloosa, the NWS flood stage is 24.5 ft (discharge 19,500 ft3

/s), 

the stage at which State Highway Iowa 92 east of Oskalooosa 

is threatened (U.S. Department of Commerce, National Oceanic and Atmospheric Administration, and National Weather 

Service, 2012b). The streamgage South Skunk River near 

Oskaloosa was above flood stage during August 13–16, and 

the peak stage of 26.40 ft (table 3) exceeded the flood stage by 

1.90 ft.

Chronology of Flood Effects

The following flood description information was obtained 

from newspaper articles posted online by the Associated 

Press (Welte, 2010), the Epoch Times (Wu, 2010) and the Des 

Moines Register (Beeman and Petroski, 2010; Belz, 2010), 

and from online sources obtained from the U.S. Department 
12 Flood of August 11–16, 2010, in the South Skunk River Basin, Central and Southeast Iowa

Figure 4. Discharge hydrographs for four streamgages on the South Skunk River, August 8–18, 2010.

0

10,000

20,000

30,000

40,000

0

10,000

20,000

30,000

40,000

0

10,000

20,000

30,000

40,000

8 9 10 11 12 13 14 15 16 17 18

0

10,000

20,000

30,000

40,000

Discharge, in cubic feet per second

August 2010

A 05470000 South Skunk River near Ames, Iowa

B 05471000 South Skunk River below Squaw Creek near Ames, Iowa

C 05471050 South Skunk River at Colfax, Iowa

D 05471500 South Skunk River near Oskaloosa, Iowa

Flood peak August 11, discharge 

14,800 cubic feet per second

Discharge at

indicated annual 

flood probabilities

0.2 percent

1 percent

2 percent

0.2 percent

1 percent

2 percent

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

Flood peak August 11, discharge 

36,200 cubic feet per second

Discharge for NWS flood stage of 20 feet

Flood peak August 14, discharge 

24,000 cubic feet per second

Discharge for NWS flood stage of 17 feet

Flood peak August 16, discharge 25,200 cubic feet per second

Discharge for NWS flood stage of 24.5 feet

0.2 percent

1 percent

2 percent

0.2 percent

1 percent

2 percent
Flood Profile 13

of Commerce, National Oceanic and Atmospheric Administration, and National Climatic Data Center (2010a).

“Strong thunderstorms and heavy rains fell in central 

Iowa for three consecutive nights from August 8 to 10, causing 

extreme flooding. Polk County reported flash flooding in the 

4300 block of Fairview near Dean Avenue and flood waters 

washed away railroad tracks and caused a derailment. The 

Iowa Department of Transportation closed Interstate 35 just 

south of Ames (mile post 97), and both lanes of U.S. Highway 

30 in the area also were closed. Increasing rain on the evening of August 10 caused the evacuation of several hundred 

people from their homes in Ames and also claimed the life 

of a 16-year old female early in the morning on August 11, 

when three cars were swept away by raging floodwaters on a 

rural road between Altoona and Mitchellville (not located on 

a figure). The water treatment plant in Ames was inundated 

and was shut down on August 11 after a series of eight main 

breaks dropped pressure. Major damage also was done to 

several buildings on the Iowa State Campus, with damage estimates around 40–50 million dollars. Hilton Coliseum reported 

4 to 6 ft of water inside and Cy Stephens Auditorium reported 

water in the mechanical building up to the first floor. Downriver from Ames, the town of Colfax was nearly cut off by the 

rising South Skunk River and again, several hundred people 

were evacuated from their homes.” 

Flood Profile

To develop profiles of the 2010 flood for the South 

Skunk River, the USGS measured HWMs at 20 locations. 

The HWMs used in the profile were measured at all Federal 

and State Highway bridges, at USGS streamgages, and at 

selected county and local bridges. The HWMs at bridges 

were located immediately downstream from the bridge and 

one bridge-length upstream from the bridge. The distances 

between most of the profile points are less than about 10 mi 

(fig. 1). The distance between U.S. Highway 63 and County 

Road T33 on the South Skunk River is about 11.3 mi. River 

miles were determined using a geographic information system 

(GIS) (ESRI, 2012) to measure the distance along the South 

Skunk River reach from its confluence with the North Skunk 

River (not located on a figure) and using USGS 1:24,000-scale 

topographic-map data (U.S. Geological Survey, 2011b). 

The HWMs were surveyed to bench marks (see appendix) at bridges within 1 week of the flood peak, and were later 

referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29) by differential leveling or differential positioning using a global positioning system (GPS). In addition, 

bridge deck, low-bridge chord, and reference-point elevations 

were measured with respect to the bench marks. The elevations for the bridge deck and low-bridge chord generally 

were measured on the lowest end of the bridge. The reference points were established so that low-flow water-surface 

elevations could be measured by using a weight suspended 

on a measuring tape. Low-flow water-surface elevations were 

obtained August 17-18, 2011, to indicate a typical range in 

stage along the river and to define the low-water slope. 

The HWMs profiled in figures 5–10 and listed in table 7 

are an average of HWMs measured at each location. The 

profile lines connecting the HWMs in the figures approximate 

the flood elevation between marks. The lines do not account 

for any intermediate features that could affect flood elevation, such as channel morphology or bridges and dams where 

HWMs were not measured. Primary highways referenced 

in the report are shown in figure 1; secondary roads are not 

shown in the figure.

The August 11–16, 2010, flood along the South Skunk 

River is profiled from County Road V67/280th Avenue, northeast of Ollie in Keokuk County upstream to West Riverside 

Road in Ames. The 128-mi river reach is shown in figure 1, 

and the 20 stream sites where HWMs were measured are listed 

in table 7. 

HWMs profiled for the July 1993 flood were obtained 

from U.S. Army Corps of Engineers (1994) for the reach 

downstream of Interstate 35 (river mile 123.34) with the 

exception of the HWMs for USGS streamgages 05471050 

and 05471500, which were obtained from “Floods of June 17, 

1990, and July 9, 1993, along Squaw Creek and the South 

Skunk River in Ames, Iowa, and vicinity” (Einhellig and 

Eash, 1996). HWMs for the June 1990 flood from USGS 

streamgage 05471000, U.S. Highway 30 upstream to USGS 

streamgage 05470000, West Riverside Road in Ames also 

were obtained from Einhellig and Eash (1996). For the June 

1975 flood, HWMs from County Road T22/240th Place 

upstream to USGS streamgage 05470000, West Riverside 

Road in Ames were obtained from “Floods in the Skunk River 

Basin, Iowa” (Heinitz and Wiitala, 1978). HWMs for the May 

1944 flood were obtained from U.S. Army Corps of Engineers 

(1994) from the Keokuk-Mahaska county line upstream to 

USGS streamgage 05470000, West Riverside Road, Ames. 

All HWMs listed in table 7 are shown as part of the profile 

lines in figures 5–10 for the South Skunk River. Also shown 

are low-flow profiles measured in August 2011, March 1976 

(Heinitz and Wiitala, 1978; from County Road V67/280th 

Avenue upstream to Interstate 80), July 1975 (Heinitz and Wiitala, 1978; from USGS streamgage 05471050, State Highway 

117 upstream to E. 13th Street, Ames), and July 1995 (Einhellig and Eash, 1996; from Interstate 35 upstream to USGS 

streamgage 05470000, West Riverside Road, Ames).

At the streamgage 05471500 South Skunk River near 

Oskaloosa (fig. 1, site 10), the 2010 flood peak was higher 

than the 1944 flood peak by about 0.6–1.4 ft (depending on 

whether the 1944 HWM was obtained on the upstream or 

downstream side of the bridge; table 7); however, the peak discharge was less than the 1944 flood discharge. This difference 

between stage and discharge for the 1944 and 2010 floods is 

most likely because of continuing flood-plain and channel 

aggradation at the Oskaloosa location (Eash, 1996).
14 Flood of August 11–16, 2010, in the South Skunk River Basin, Central and Southeast Iowa

Summary

As a result of intense periods of rainfall August 8–11, 

2010, major flooding occurred in the South Skunk River Basin 

during August 11–16. On August 11, 96-hour rainfall amounts 

recorded at Ames and Story City were 9.61 and 8.70 inches, 

respectively. The majority of the rainfall occurred during a 

48-hour period. Within the South Skunk River Basin, peak 

discharges of 14,800 cubic feet per second (ft3

/s) (annual 

flood-probability estimate of 0.2 to 1 percent) at the 05470000 

South Skunk River near Ames; of 36,200 ft3

/s (annual floodprobability estimate of less than 0.2 percent) at the 05471000 

South Skunk River below Squaw Creek near Ames streamgage 

(both on August 11, 2010); and of 24,000 ft3

/s (annual floodprobability estimate of 0.2 to 1 percent) at the 05471050 South 

Skunk River at Colfax streamgage on August 14, 2010, are 

the largest floods on record for these sites. Peak discharges 

of 22,400 ft3

/s (annual flood-probability estimate of less than 

0.2 percent) at the 05470500 Squaw Creek at Ames, and of 

25,200 ft3/s (annual flood-probability estimate of 1 to 2 percent) at the 05471500 South Skunk River near Oskaloosa, 

streamgages are the second highest floods on record at these 

sites. 

References Cited

Beeman, Perry, and Petroski, William, 2010, After flood, 

Ames faces water crisis: The Des Moines Register, accessed 

November 7, 2011, at http://www.desmoinesregister.com/

article/20100813/NEWS/8130358/Ames-faces-water-crisis.

Belz, Adam, 2010, River drops in Colfax, but cleanup has 

to wait: The Des Moines Register, accessed November 7, 2011, at http://www.desmoinesregister.com/

article/20100813/NEWS/8130356/1001/NEWS/River-dropsin-Colfax-but-cleanup-has-to-wait.

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 

2012–2038, 4 p. (Also available at http://pubs.usgs.gov/

fs/2012/3038/.)

Eash, D.A., 1996, Flood-plain and channel aggradation of 

selected bridge sites in the Iowa and Skunk River Basins, 

Iowa: U.S. Geological Survey Water-Resources Investigations Report 95–4290, 44 p.

Table 7. Locations and elevations of high-water marks used in the South Skunk River flood profile of August 11–16, 2010.

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

Distance from mouth

(river miles) Location Downstream HWM(feet above NGVD 29)

Upstream HWM 

(feet above NGVD 29)

4.24 County Road V67/280th Avenue, northeast of Ollie 647.34 648.68

7.19 County Road V5G, north of Ollie 651.99 652.40

17.15 State Highway 149, northeast of Martinsburg 664.91 666.23

22.16 180th Avenue, southwest of Hayesville 671.76 672.51

30.53 State Highway 21, south of Delta 683.17 684.25

39.61 County Road V13/Ventura Avenue, south of Rose Hill 695.58 696.46

42.35 State Highway 92, east of Oskaloosa 698.38 698.76

51.14 USGS streamgage 05471500, U.S. Highway 63, north of Oskaloosa 711.90 712.70

62.48 County Road T33, south of Peoria between Pella and New Sharon 727.93 729.78

70.92 County Road T14, north of Pella 742.83 742.91

75.15 County Road F70/Spencer Street, southwest of Galesburg 749.05 749.41

84.69 State Highway 14, south of Newton 768.61 768.95

95.06 USGS streamgage 05471050, State Highway 117, Colfax 793.85 794.07

97.52 Interstate 80, west of Colfax 796.21 797.14

104.20 U.S. Highway 65, northeast of Bondurant 814.40 ND

109.31 County Roads S14/F22/NE Yoder Drive, east of Elkhart 827.40 827.94

115.82 State Highway 210, southeast of Cambridge 848.08 849.18

123.34 Interstate 35, southeast of Ames 871.83 872.27

126.94 USGS streamgage 05471000, U.S. Highway 30, Ames 883.82 885.07

132.39 USGS streamgage 05470000, West Riverside Road, Ames 907.65 ND
References Cited 15

Eash, D.A., 1997, Effects of the 1993 flood on the determination of flood magnitude and frequency in Iowa: U.S. 

Geological Survey Circular 1120–K, 23 p. (Also available 

at http://pubs.er.usgs.gov/usgspubs/cir/cir1120K.)

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 http://pubs.er.usgs.gov/usgspubs/wri/

wri004233.)

Einhellig, R.F., and Eash, D.A., 1996, Floods of June 17, 

1990, and July 9, 1993, along Squaw Creek and the South 

Skunk River in Ames, Iowa, and vicinity: U.S. Geological 

Survey Open-File Report 96–249, 34 p.

ESRI, 2012, ArcGIS Desktop: Release 10, Redlands, CA: 

Environmental Systems Research Institute.

Federal Emergency Management Agency, 2010, Federal Register Notice, accessed July 6, 2011, at http://www.fema.gov/

news/event.fema?id=13099; http://www.fema.gov/pdf/news/

pda/1930.pdf.

Heinitz, A.J., and Wiitala, S.W., 1978, Floods in the Skunk 

River Basin, Iowa: U.S. Geological Survey Open-File 

Report 79–272, 80 p.

Hillaker, H.J., 2010a, Iowa Annual Weather Summary – 2010, 

accessed January 10, 2012, at http://www.iowaagriculture.

gov/climatology/weatherSummaries/2010/fas2010.pdf.

Hillaker, H.J., 2010b, Iowa Monthly Weather Summary – 

August 2010, accessed January 10, 2012, at http://www.

iowaagriculture.gov/climatology/weatherSummaries/2010/

fms201008.pdf. 

Hillaker, H.J., 2010c, Iowa climate review: Des Moines, Iowa, 

Iowa Department of Agriculture and Land Stewardship, 

v. 24, no. 8, 21 p. 

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

all about chance: U.S. Geological Survey General Information Product 106, 1 p.

Huff, F.A., and Angel, J.R., 1992, Rainfall frequency atlas of 

the Midwest: Champaign, Ill., Illinois State Water Survey, 

Bulletin 71, 141 p. (Also available at http://www.isws.

illinois.edu/pubdoc/B/ISWSB-71.pdf.)

Interagency Advisory Committee on Water Data, 1982, 

Guidelines for determining flood flow frequency: Reston, 

Va., Hydrology Subcommittee Bulletin 17B, 28 p. and 

appendixes. (Also available at http://water.usgs.gov/osw/

bulletin17b/bulletin_17B.html.)

Iowa Homeland Security and Management, 2010, Press 

Releases, accessed February 28, 2011 at http://www.

iowahomelandsecurity.org/documents/releases/2010/

RELEASE_081310.pdf; http://www.iowahomelandsecurity.

org/documents/releases/2010/RELEASE_081510.pdf; http://

www.iowahomelandsecurity.org/documents/releases/2010/

RELEASE_081610.pdf; http://www.iowahomelandsecurity.

org/documents/releases/2010/RELEASE_082310-2.pdf. 

Lara, O.G., and Heinitz, A.J., 1976, Flood of June 27, 1975 

in City of Ames, Iowa: U.S. Geological Survey Open-File 

Report 76–728, 56 p.

Leica Geosystems, 2010, IaRTN SmartNET Connection List, 

Leica Spiderweb, St. Gallen, Switzerland, accessed October 25, 2012, at http://spiderweb.iartn.com/spiderweb/

frmIndex.aspx.

Oschwald, W.R., Riecken, F.F., Dideriksen, R.I., Scholtes, 

W.H., and Schaller, F.W., 1965, Principal soils of Iowa: 

Ames, Iowa, Iowa State University, Department of Agronomy, Special Report no. 42, 77 p.

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

Iowa Press, 154 p.

Prior, J.C., Kohrt, C.J., and Quade, D.J., 2009, The landform 

regions of Iowa: Iowa Geological Survey, Iowa Department 

of Natural Resources, Iowa City, Iowa, accessed July 2011, 

at ftp://ftp.igsb.uiowa.edu/gis_library/ia_state/geologic/

landform/landform_regions.zip.

U.S. Army Corps of Engineers, 1966, Flood plain information 

report on Skunk River and Squaw Creek, Story County, 

Iowa: Rock Island, Ill., U.S. Army Engineer District.

U.S. Army Corps of Engineers, 1975, Flood plain information 

report on Skunk River above Ames, Iowa: Rock Island, Ill., 

U.S. Army Engineer District.

U.S. Army Corps of Engineers, 1994, The great flood of 1993 

post-flood report: U.S. Army Engineers, North Central 

Division, appendix B, plates 89–96, accessed June 15, 

2012, at http://www.mvr.usace.army.mil/PublicAffairsOffice/

HistoricArchives/Floodof1993/Appendix%20B/Plates.pdf, 

plates 91–96.

U.S. Department of Commerce, National Oceanic and Atmospheric Administration, and National Climatic Data Center, 

2004, National Geodetic Survey at http://www.ngs.noaa.

gov/TOOLS/Vertcon/vertcon.html.

U.S. Department of Commerce, National Oceanic and 

Atmospheric Administration, and National Climatic Data 

Center, 2010a, National Climatic Data Center Storm Events, 

accessed January 10, 2012, at http://www.ncdc.noaa.gov/

stormevents/.
16 Flood of August 11–16, 2010, in the South Skunk River Basin, Central and Southeast Iowa

U.S. Department of Commerce, National Oceanic and Atmospheric Administration, and National Climatic Data Center, 

2010b, Hourly precipitation data, Iowa, August 2010: Asheville, N.C., Monthly Summaries, v. 60, no. 8, 19 p.

U.S. Department of Commerce, National Oceanic and Atmospheric Administration, and National Climatic Data Center, 

2010c, National Weather Service Manual 10-950, accessed 

April 4, 2012 at http://www.weather.gov/directives/sym/

pd01009050curr.pdf.

U.S. Department of Commerce, National Oceanic and Atmospheric Administration, and National Weather Service, 

2012a, accessed March 28, 2012, at http://www.crh.noaa.

gov/images/dmx/hydro/PNSDMX_20120206_Various_

SvcChanges_FS_FloodCats_FINAL.pdf

U.S. Department of Commerce, National Oceanic and Atmospheric Administration, and National Weather Service, 

2012b, accessed April 5, 2012, at http://water.weather.

gov/ahps2/hydrograph.php?wfo=dmx&gage=amei4, 

http://water.weather.gov/ahps2/hydrograph.

php?wfo=dmx&gage=aesi4, http://water.weather.

gov/ahps2/hydrograph.php?wfo=dmx&gage=cfxi4, 

and http://water.weather.gov/ahps2/hydrograph.

php?wfo=dmx&gage=ooai4.

U.S. Geological Survey, 2005, accessed March 29, 2011, at 

http://pubs.usgs.gov/wdr/2005/wdr-il-05/misc/peakcods.

htm.

U.S. Geological Survey, 2011a, National Water Information 

System (NWISWeb): U.S. Geological Survey database, 

accessed April 20, 2011, at http://waterdata.usgs.gov/nwis/

sw. 

U.S. Geological Survey, 2011b, The National Map, accessed 

January 5, 2011, at http://nationalmap.gov/ustopo/index.

html.

Welte, Melanie S., 2010, Iowa teen dies in raging floods as 

hundreds flee: Associated Press, accessed November 7, 

2011, at http://www.aolnews.com/2010/08/11/flooding-kills1-in-iowa-hundreds-evacuated/.

Wu, Cheryl, 2010, Iowa flooding in Ames breaks records: The 

Epoch Times, accessed November 7, 2011, at http://www.

theepochtimes.com/n2/united-states/iowa-flooding-in-amesbreaks-records-40794.html.
Figures 5–10
Figure 5. Profile of the August 11–16, 2010, flood for the South Skunk River, river miles 4 to 133.

Distance upstream from confluence with North Skunk River, in river miles

620640660680700720740760780800820840860880900920

Flood profile, August 2010

EXPLANATION

Low-flow profile, August 17–18, 2011Flood profile, July 1993 (U.S. Army Corps of Engineers, 1994)Low-flow profile, July 31, 1995Flood profile, June 1990Flood profile, June 1975Low-flow profile, July 17, 1975Low-flow profile, March 30–31, 1976Flood profile, May 1944 (U.S. Army Corps of Engineers, 1994)Bridge-deck elevationLow-bridge-chord elevation

Locations indicated by vertical lines are described in figures 6 through 10

Elevation, in feet above NGVD 29

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 
Figure 6. Profile of the August 11–16, 2010, flood for the South Skunk River, river miles 4 to 30.

Flood p

EXP

Low-floFlood p

Cor

Low-floBridge-Low-br

Distance upstream from confluence with North Skunk River, in river miles

0 5 10 15 20 2

590600610620630640650660670680690700

Elevation, in feet above NGVD 29

County Road V67/280th Avenue, 

7410-6 SW

County Road V5G, 7411-03 SE

State Highway 149, 7412-02 SW

180th Avenue, 7412-05 SE

162nd Avenue, 7412-06 SW 

(abandoned bridge)
Figure 7. Profile of the August 11–16, 2010, flood for the South Skunk River, river miles 30 to 60.

Flood profile, August 2010

EXPLANATION

Low-flow profile, August 18, 201Flood profile, July 1993 (U.S. ArmLow-flow profile, March 30–31, Flood profile, May 1944 (U.S. ArmBridge-deck elevationLow-bridge-chord elevation

Elevation, in feet above NGVD 29

Distance upstream from confluence with North Skunk River, in river miles

30 35 40 45 50 5

630640650660670680690700710720730740

05471500 South Skunk River near Oskaloosa streamgage located at U.S. Highway 63 (river mile 51.14)

May 1944 Flood peak June 12, 2008March 31, 1976July 15, 1993June 12, 2008August 16, 2010August 18, 2011

37,000

1,000

20,70017,30025,200

305

Discharge, in cubic feet 

per second

State Highway 21, 7513-34 NE

Keokuk-Mahaska County line

County Road V13/Ventura Avenue, 

7514-15 SW

State Highway 92, 7514-07 SE

Queens Avenue, 7515-11 NE

County Road T65, 7615-33 SW

USGS streamgage 05471500, 

U.S. Highway 63, 7616-25 SW
Figure 8. Profile of the August 11–16, 2010, flood for the South Skunk River, river miles 60 to 90.

Elevation, in feet above NGVD 29 Flood profile, August 2010 EXPLANATION

Low-flow profile, August 18, 2011Flood profile, July 1993 (U.S. ArmFlood profile, June 1975Low-flow profile, March 31, 1976Flood profile, May 1944 (U.S. ArmBridge-deck elevationLow-bridge-chord elevation

Reasnor

Distance upstream from confluence with North Skunk River, in river miles

60 65 70 75 80 8

680690700710720730740750760770780790

County Road T33, 7717-28 SE

Mahaska-Marion County line

County Road T22/240th Place, 

7718-23 NE

County Road T14, 7718-03 SE

Marion-Jasper County Line

S. 126th Ave E., 7818-32 SW

County Road F70/Spencer Street, 

7818-30 NE

County Road S74/Red Bridge Street, 

7819-23 SW

County Road F62, 7819-10 NW

State Highway 14, 7919-29 NW
Figure 9. Profile of the August 11–16, 2010, flood for the South Skunk River, river miles 90 to 120.

Elevation, in feet above NGVD 29 EXP

Bridge-dLow-brid

Distance upstream from confluence with North Skunk River, in river miles

Forest Street S., 7921-04 NE

Jasper-Polk County line

U.S. Highway 65, 8022-15 NE

NE 118th Avenue, 8122-32 SE

760770780790800810820830840850860870

Flood proLow-flow Flood pro

Corps 

Flood proLow-flow Low-flow Flood pro

Corps 

Flood peak June 14, 2008

Colfax C

05471050 South Skunk River at Colfax streamgage located at U.S. Highway 117 (river mile 95.06)

July 12, 1993June 14, 2008August 14, 2010August 18, 2011

14,20010,90024,000

108

Discharge, in cubic feet 

per second

90 95 100 105 110 11

County Road F48, 7920-04 NE

Mouth of Indian Creek

USGS streamgage 05471050, State 

Highway 117, 7921-01 SW

Interstate 80, 7921-04 NE

County Road S27/NE 112th Street, 

8022-24 SW

County Roads S14/F22/NE Yoder 

Drive, 8122-30 SW

NE 150th Avenue, 8123-14 NW

NE 158th Avenue, 8123-10 NE

Polk-Story County line
Figure 10. Profile of the August 11–16, 2010, flood for the South Skunk River, river miles 120 to 133.

Elevation, in feet above NGVD 29 Flood p

EXP

Low-floFlood p

Cor

Low-floFlood pFlood pLow-flo

Distance upstream from confluence with North Skunk River, in river miles

120 125 130 

USGS streamgage 05471000, 

U.S. Highway 30, 8324-13 NW

SE 16th St, 8324-12 NW

830840850860870880890900910920930940

Flood peak June 17, 1996

Ames

05471000 South Skunk River below Squaw Creek near Ames streamgage located at U.S. Highway 30 (river mile 126.94), prior to 1992, streamgage located upstream at SE 16th St (river mile 127.12)

May 19, 1944June 27, 1975July 17, 1975June 17, 1990 estimateJuly 9, 1993July 31, 1995June 17, 1996August 11, 2010August 17, 2011

10,00014,700

260

13,00026,500

92

24,40036,200

26

Discharge, in cubic feet per second

05470000 South Skunk River near Ames streamgage located at RiversideDrive (river mile 132.39), prior to 2004, streamgage located upstream at river mile 132.70

May 20, 1944June 28, 1975June 17, 1975July 9, 1993July 31, 1995June 17, 1996 estimateAugust 11, 2010August 17, 2011

8,0605,2306,600

11,100

43

14,00014,800

29

Discharge, in cubic feet per second

Flood p

Cor

Bridge-Low-br

County Road R70/580th Avenue, 

8223-08 NE

280th Street, 8223-05 NW

Interstate 35, 8323-30 SE

265th Street, 8323-30 NW

Mouth of Squaw Creek

Lincoln Way, 8324-12 NW

E. 13th Street, 8424-36 SW

USGS streamgage 05470000, 

Riverside Drive, 8424-23 SW
24 Flood of August 11–16, 2010, in the South Skunk River Basin, Central and Southeast Iowa

Appendix. List of Bench Marks and Reference Points

To facilitate measuring and referencing the high-water 

marks (HWMs) used in the flood profiles to a common datum, 

bench marks (BMs), temporary bench marks (TBMs), and 

reference points (RPs) were found or established by the U.S. 

Geological Survey (USGS) at selected bridges along the 

profiled river reach. All BM, TBM, and RP elevations listed 

in table 1–1 are referenced to the National Geodetic Vertical 

Datum of 1929. The list of 20 sites where the USGS measured 

HWMs for the August 2010 flood is shown in table 7. Of these 

20 sites, BMs or TBMs are listed for all of the sites and RPs 

are listed for 15 of the sites in table 1–1. For 10 of the 20 sites 

listed in this table, elevations for BMs were established by 

another agency and this agency is listed in table 1–1. At USGS 

streamgages, BMs or TBMs are identified as reference marks 

(RMs) that are listed in appendix table 1–1 with a RM number. 

BM, TBM, and RP elevations established by the USGS were 

determined from a combination of global positioning system 

(GPS) technology and differential leveling. For 10 of the 

20 sites listed in this table, elevations were established by 

the USGS using GPS and are noted in the BM, TBM, and RP 

descriptions. GPS data were collected by the USGS using Real 

Time Kinematic (RTK) surveys. 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 (Leica Geosystems, 2010). The quality of the 

RTK GPS data is 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 BMs and published elevations. 

In general, BMs are points that were specifically designed 

to mark an elevation, such as USGS elevation disks and Iowa 

DOT BMs (round-top rods embedded in concrete at one or 

more corners of a bridge). Marks, such as squares and crosses 

that were chiseled or filed on concrete or metal, were used as 

TBMs or RPs. RPs were established to permit water-surface 

elevations to be determined by use of a tape and weight. The 

terms “right” and “left” in the descriptions are determined as 

viewed while facing in the downstream direction. 

The BMs, TBMs, and RPs are designated by an index 

number or legal description derived from their respective 

locations using Public Land Survey System coordinates (township, range, section). Within the section, the quarter section in 

which the BM, TBM, or RP is located is designated by northeast (NE), southeast (SE), northwest (NW), and southwest 

(SW). For example, T74N R10W 06 SW refers to a location 

in Township 74 North, Range 10 West, southwest quarter of 

section 06. A number in parentheses following the quartersection designation indicates the number of the BM, TBM, or 

RP in that particular quarter section. The index number serves 

to describe the legal description of the mark without further 

reference in the body of the description. The physical location 

of the BM or TBM on a bridge dictates the appropriate legal 

description. The RPs, and any additional BMs or TBMs, are 

listed with the related BMs or TBMs and are identified by the 

same legal description though, at times, they are in a different section, range, or township as determined by upstream or 

downstream location. 

The BMs, TBMs, and RPs are listed in table 1–1 in 

upstream order for the South Skunk River. The user of this 

information is cautioned that BMs, TBMs, and RPs listed 

herein might have been disturbed, destroyed, or moved since 

elevations were established. It is the responsibility of the user 

to determine the condition and the suitability of the BM, TBM, 

or RP.
Table 1–1. Bench marks and reference points used in the August 11–16, 2010, South Skunk River flood profile.[Bench marks and reference points are listed in upstream order. NGVD 29, National Geodetic Vertical Datum of 1929, BM, bench mark; TBM, temporary bench mark; RP, refertioning System; T, township; R, range; N, north; W, west; S, south; E, east; RM, reference mark; a number in parentheses following the quarter-section designation indicates the TBM, or RP in that particular quarter section; an RM designation with a number in parentheses following a Mark description indicates the RM is located at a U.S. Geological Su

Public Land Survey 

System (township, range, 

section, quarter section)

Mark 

classification Location Mark

Elevation 

in feet 

(NGVD 192

T74N R10W 06 SW (1) TBM About 3.25 miles northeast of Ollie, at County Road V67/280th Avenue 

bridge over the South Skunk River, on left upstream concrete wingwall.

Chiseled square 655.29 

T74N R10W 06 SW (2) RP About 3.25 miles northeast of Ollie, at County Road V67/280th Avenue 

bridge over the South Skunk River, just right of 5th drain hole from right downstream side of bridge, on end of guardrail post.

Filed arrow 655.28 

T74N R11W 03 SE (1) TBM About 2.75 miles north of Ollie, at County Road V5G bridge over the 

South Skunk River, on left downstream concrete guard rail.

Chiseled square 660.56 

T74N R11W 03 SE (2) RP About 2.75 miles north of Ollie, at County Road V5G bridge over the 

South Skunk River, in middle of 4th concrete section from left downstream end of bridge.

Chiseled square 660.61 

T74N R12W 02 SW (1) BM About 4.25 miles northeast of Martinsburg, at U.S. Highway 149 bridge 

over the South Skunk River, on left upstream concrete guardrail.

Iowa Department 

of Transportation bench mark

674.97 

T74N R12W 02 SW (2) RP About 4.25 miles northeast of Martinsburg, at U.S. Highway 149 bridge 

over the South Skunk River, at 6th drain hole from left downstream end of bridge.

Chiseled square 676.27 

T74N R12W 05 SE (1) TBM About 1.75 miles southwest of Hayesville, at 180th Street bridge over 

the South Skunk River, on left downstream wingwall.

Chiseled square 678.49 

T74N R12W 05 SE (2) RP About 1.75 miles southwest of Hayesville, at 180th Street bridge over 

the South Skunk River, on 35th guardrail post from right downstream end of bridge.

Filed arrow 680.22 

T75N R13W 34 NE (1) BM About 3.75 miles south of Delta, on U.S. Highway 21 bridge over the 

South Skunk River, on left upstream concrete guardrail.

Iowa Department 

of Transportation bench mark

694.34 

T75N R13W 34 NE (2) RP About 3.75 miles south of Delta, on U.S. Highway 21 bridge over the 

South Skunk River, at 5th drain hole from left downstream side of bridge.

Chiseled square 694.67 

T75N R14W 15 SW (1) TBM About 1.4 miles south of Rose Hill, on County Road V13/Ventura 

Avenue bridge over the South Skunk River, on left upstream concrete guardrail.

Chiseled square 703.19 

T75N R14W 15 SW (2) RP About 1.4 miles south of Rose Hill, on County Road V13/Ventura 

Avenue bridge over the South Skunk River, at 5th drain hole from left downstream end of bridge.

Chiseled square 706.10 
Public Land Survey System (township, range, section, quarter section) Mark classification Location Mark Elevation in feet (NGVD 192

T75N R14W 07 SE (1) BM About 5.75 miles east of Oskaloosa, on U.S. Highway 92 bridge over the South Skunk River, on right downstream concrete guardrail. Iowa Department of Transportation bench mark 707.60 

T75N R14W 07 SE (2) RP About 5.75 miles east of Oskaloosa, on U.S. Highway 92 bridge over the South Skunk River, at 3d drain hole from left downstream side of bridge. Chiseled square 708.64 

T76N R16W 25 SW (1) TBM About 3.4 miles north of Oskaloosa, site of streamgage 05471500 South Skunk River near Oskaloosa, on U.S. Highway 63 bridge over the South Skunk River, on right upstream wingwall. Chiseled cross 719.97 

T77N R17W 28 SE (1) BM Between Pella and New Sharon, on County Road T33 bridge over the South Skunk River, on left downstream wingwall. Iowa Department of Transportation bench mark 738.38 

T77N R18W 03 SE (1) BM About 4.8 miles north of Pella, on County Road T14 bridge over the South Skunk River, on left upstream concrete guardrail. Marion County bench mark 748.47 

T77N R18W 03 SE (2) RP About 4.8 miles north of Pella, on County Road T14 bridge over the South Skunk River, at end of 5th concrete section of guardrail from left downstream end of bridge. Chiseled square 750.62 

T78N R18W 30 NE (1) TBM About 2.3 miles southwest of Galesburg, on County Road F70/Spencer Street bridge over the South Skunk River, on right upstream wheel- guard. Chiseled square 759.87 

T78N R18W 30 NE (2) RP About 2.3 miles southwest of Galesburg, on County Road F70/Spen- cer Street bridge over the South Skunk River, at 3d drain from right downstream end of bridge, on metal guardrail. 3 filed marks 760.78 

T79N R19W 29 NW (1) TBM About 4.2 miles south of Newton, on U.S. Highway 14 bridge over the South Skunk River, on left downstream wheelguard. Chiseled square 778.33 

T79N R19W 29 NW (2) RP About 4.2 miles south of Newton, on U.S. Highway 14 bridge over the 

South Skunk River, just right of 3d drain from left downstream end of bridge.

2 chiseled lines 778.56 

T79N R21W 01 SW (1) BM At north edge of Colfax, site of streamgage 05471050 South Skunk 

River at Colfax, on State Highway 117 bridge over the South Skunk River, on left upstream abutment.

Iowa Department 

of Transportation bench mark (RM3)

796.86 

T79N R21W 04 NE (1) TBM About 2 miles west of Colfax, on Interstate 80 bridge over the South 

Skunk River (downstream bridge), on right downstream abutment.

Chiseled cross 809.62 

Table 1–1. Bench marks and reference points used in the August 11–16, 2010, South Skunk River flood profile.—Continued[Bench marks and reference points are listed in upstream order. NGVD 29, National Geodetic Vertical Datum of 1929, BM, bench mark; TBM, temporary bench mark; RP, refertioning System; T, township; R, range; N, north; W, west; S, south; E, east; RM, reference mark; a number in parentheses following the quarter-section designation indicates the TBM, or RP in that particular quarter section; an RM designation with a number in parentheses following a Mark description indicates the RM is located at a U.S. Geological Su
Public Land Survey 

System (township, range, 

section, quarter section)

Mark 

classification Location Mark

Elevation 

in feet 

(NGVD 192

T79N R21W 04 NE (2) RP About 2 miles west of Colfax, on Interstate 80 bridge over the South 

Skunk River (downstream bridge), at 4th drain hole from right downstream end of bridge.

Chiseled square 812.69 

T80N R22W 15 NE (1) BM About 4 miles northeast of Bondurant, on U.S. Highway 65 bridge over 

the South Skunk River (upstream bridge), on left upstream guardrail.

Iowa Department 

of Transportation bench mark

826.72 

T80N R22W 15 NE (2) RP About 4 miles northeast of Bondurant, on U.S. Highway 65 bridge over 

the South Skunk River (downstream bridge), at 4th drain hole from left downstream end of bridge, on curb.

Chiseled square 826.38 

T81N R22W 30 SW (1) TBM About 3 miles east of Elkhart, on County Road S14/F22/NE Yoder Drive 

bridge over the South Skunk River, on right downstream abutment, 0.7 feet below road.

Chiseled square. 835.20 

T81N R22W 30 SW (2) TBM About 3 miles east of Elkhart, on County Road S14/F22/NE Yoder Drive 

bridge over the South Skunk River, on left downstream abutment.

Penny in concrete 835.13 

T81N R22W 30 SW (3) RP About 3 miles east of Elkhart, on County Road S14/F22/NE Yoder Drive 

bridge over South Skunk River, at 3d downstream guardrail post left of center pier, on top of right side of post.

Chiseled arrow 839.23 

T82N R23W 34 NE (1) BM About 1.6 miles southeast of Cambridge, on U.S. Highway 210 bridge 

over the South Skunk River, on right downstream wingwall.

Iowa Department 

of Transportation bench mark

857.04 

T82N R23W 34 NE (2) RP About 1.6 miles southeast of Cambridge, on U.S. Highway 210 bridge 

over the South Skunk River, between 2d and 3d drain holes from left downstream end of bridge, on concrete guardrail.

Chiseled square 857.40 

T83N R23W 30 SE (1) BM About 4.5 miles southeast of Ames, on Interstate 35 bridge over the 

South Skunk River (downstream bridge), on top of right downstream wingwall.

Iowa Department 

of Transportation bench mark

879.53 

T83N R23W 30 SE (2) RP About 4.5 miles southeast of Ames, on Interstate 35 bridge over the 

South Skunk River, at 3d drain hole from left downstream end of bridge, on concrete guardrail.

Chiseled square 880.18 

T83N R24W 13 NW (1) TBM About 2 miles southeast of Ames, site of streamgage 05471000 South 

Skunk River below Squaw Creek near Ames, on U.S. Highway 30 bridge over the South Skunk River, on right upstream wingwall.

Chiseled square 

(RM9)

891.19 

T84N R24W 23 SW (1) BM At northern edge of Ames, site of streamgage 05470000 South Skunk 

River near Ames, on West Riverside Road bridge over the South Skunk River, on right upstream wingwall.

Iowa Department 

of Transportation bench mark (RM16)

914.53 

Table 1–1. Bench marks and reference points used in the August 11–16, 2010, South Skunk River flood profile.—Continued[Bench marks and reference points are listed in upstream order. NGVD 29, National Geodetic Vertical Datum of 1929, BM, bench mark; TBM, temporary bench mark; RP, refertioning System; T, township; R, range; N, north; W, west; S, south; E, east; RM, reference mark; a number in parentheses following the quarter-section designation indicates the TBM, or RP in that particular quarter section; an RM designation with a number in parentheses following a Mark description indicates the RM is located at a U.S. Geological Su
Publishing support provided by the: 

Denver and Rolla Publishing Service Centers 

For more information concerning this publication, contact:

Director, USGS Iowa Water Science Center

P.O. Box 1230

Iowa City, IA 52244

(319) 337–4191

Or visit the Iowa Water Science Center Web site at:

http://ia.water.usgs.gov

Printed on recycled paper

Barnes and Eash—Flood of August 11–16, 2010, in the South Skunk River Basin, Central and Southeast Iowa—Open-File Report 2012–1202