FLOOD10216

• County: Statewide
• Basin: Statewide
• Title: Method for Estimating the Magnitude and Frequency of Floods at Ungaged Sites on Unregulated Rural Streams in Iowa
• Date: 1/1/1987
• Prepared For: State of Iowa
• Prepared By: USGS
• Floodplain - Doc Type: Educational/Technical/Reference Information

CONTENTS

Abstract. . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .. . . . ., . . . . . . . .. . . . 1
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Regional analysis.................................................... 2
Region 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Region 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Region 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - . . . . . . . . . . . . . . 4
Region 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Region 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Floods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Floods at gaged sites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Regional flood frequency equations.... ... ..................... .... 6
Floods on mainstems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Maximum floods..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Method for estimating the magnitude and frequency of floods

at ungaged sites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15
Limits of application. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 16
Illustrative examples............................................. 16

Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 20

Figure 1.
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FIGURES

Map of Iowa showing location of hydrologic regions and
gaging stations used in this study. ..... .... .... ....... .... 3
Graphs showing flood discharges for indicated recurrence
intervals along mainstem of Turkey River from site 27 to

site 28.................................................... 8
Graphs showing flood discharges for indicated recurrence
intervals along mainstem of Wapsipinicon River from

site 54 to site 62..................... _ . . . . . . . . . . . . . . . . . . . 9
Graphs showing flood discharges for indicated recurrence
intervals along mainstem of Cedar River from site 116 to

si te 126................................................... 10
Graphs showing flood discharges for indicated recurrence
intervals along mainstem of Skunk River from site 140 to

site 143................................................... 11
Graphs showing flood discharges for indicated recurrence
intervals along mainstem of Little Sioux River from site

206 to site 211.......................................... - . 12
Graphs showing flood discharges for indicated recurrence
intervals along mainstem of West Nishnabotna River from
site 228 to site 238....................................... 13
Graphs showing flood discharges for indicated recurrence
intervals along mainstem of East Nishnabotna River from
site 236 to site 238....................................... 14
Graph of flood-frequency curve for Potato Creek. ...... ..... 18

TABLES

Table 1. Flood discharges for selected recurrence intervals at
gaging stations in Iowa. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2l
2. Regional flood-frequency equations.......................... 28
3. Characteristics of maximum floods at gaging stations

in Iowa. .. . . . . . . . . . ... . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . .. . " 29