Ames Cedar Falls Cedar Rapids Charles City Clarksville Columbus Junction Decorah Des Moines Elkader Estherville Fort Dodge Greene Hills Humboldt Ida Grove Independence Iowa City Manchester Monticello Mason City New Hartford Ottumwa Palo Plainfield Rock Rapids Rock Valley Spencer Waterloo Waverly

Adel Ames Cedar Falls Cedar Rapids Charles City Clarksville Columbus Junction Decorah Des Moines Elkader Estherville Fort Dodge Freeport Greene Hills Humboldt Ida Grove Independence Iowa City Kalona Manchester Monticello Maquoketa Mason City New Hartford Ottumwa Palo Pool 11 Pool 12 Pool 13 Pool 14 Pool 15 Pool 16 Pool 17 Pool 18 Pool 19 Plainfield Red Oak Rock Rapids Rock Valley Spencer Waterloo Waverly

Lake Red Rock Reservoir Pool Des Moines River flood inundation mapping for Lake Red Rock pool is based on a water surface elevation. The inundation boundaries were generated using 3m Iowa LiDAR, and the edges were generalized for appearance. The upstream inundation limit was set at Highway 65. Downstream to Mouth Des Moines River flood inundation mapping downstream of Lake Red Rock is based on releases from Red Rock Reservoir. The releases correspond to annual chance exceedance events according to the USACE Des Moines River Regulated Flow Frequency Study, 2019 Regulation Plan Update. Tributary inflow was not accounted for during this analysis. Top of levee elevations from the National Levee Database were incorporated into levee systems along the Des Moines River. Saylorville Lake Downstream of Saylorville Des Moines River flood inundation mapping downstream of Saylorville is based on releases from Saylorville Reservoir. The releases correspond to annual chance exceedance events according to the USACE Des Moines River Regulated Flow Frequency Study, 2019 Regulation Plan Update. The only tributary inflow accounted for during this analysis was the Raccoon River. Top of levee elevations from the National Levee Database were ncorporated into levee systems along the Des Moines River. The downstream inundation extent was set at Highway 65. Coralville Lake Coralville to Columbus Junction Iowa River flood inundation mapping downstream of Coralville reservoir to Columbus Junction is based on reservoir releases. The discharges correspond to annual chance exceedance events according to the 2009 USACE Iowa River Regulated Flow Frequency Study Final Report. Top of levee elevations from the National Levee Database were incorporated into levee systems along the Iowa River. Tributary inflow was only accounted for during this analysis downstream of Iowa City. Releases at Columbus Junction Iowa River flood inundation mapping from Highway 70 to upstream of Wapello, IA is based on the stage at the Columbus Junction, IA gage. The stages correspond to annual chance exceedance events according to the 2009 USACE Iowa River Regulated Flow Frequency Study Final Report at the Wapello, IA gage. Tributary inflow was not accounted for during this analysis. Releases at Wapello Iowa River flood inundation mapping near Wapello, IA is based on the stage at the Wapello, IA gage. The stages correspond to annual chance exceedance events according to the 2009 USACE Iowa River Regulated Flow Frequency Study Final Report at the Wapello, IA gage. Tributary inflow was not accounted for during this analysis. Releases at Oakville Iowa River flood inundation mapping near Oakville, IA is based on the stage at the Oakville, IA gage. The stages correspond to annual chance exceedance events according to the 2009 USACE Iowa River Regulated Flow Frequency Study Final Report at the Wapello, IA gage. Flows on the Mississippi River were of the coincident frequency event on the Iowa River. Tributary inflow was not accounted for during this analysis.

50% (2 yr) - most likely 20% (5 yr) 10% (10 yr) 4% (25 yr) 2% (50 yr) 1% (100 yr) 0.5% (200 yr) 0.2% (500 yr) - less likely