FLOOD07698

• County: Statewide
• Community: Rock Rapids, Iowa
• Basin: Statewide
• Title: Problem Identification Report Rock River at Rock Rapids Reconnaissance Study Section 205
• Date: 4/1/1995
• Prepared For: US Army Corps of Engineers
• Prepared By: Greenhorne & O'Mara, Inc.
• Floodplain - Doc Type: Project

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with the Dempster series is greater than 5 feet. The Kennebec series

soils consist of clay, are silty and fine grained, are medium plastic,

and are black to very dark gray in color from the surface to a 2.5-foot

deep level with a permeability ranging from 0.6 to 2.0 inches per hour.

Soils in the Kennebec series that are present below 2.5 feet consist of

silt, are sandy and fine grained, are low plastic, and are very dark

gray to brown in color. The permeability for this soil also ranges

between 0.6 to 2.0 inches per hour. The water table depth for the

Kennebec series soils ranges from 2 to S feet deep. The Colo series

soils are mostly silty clay loam which consists of clay, are fine

grained, are low to medium plastic, and are black to dark grayish-brown

in color. The permeability for this soil ranges from 0.2 to 6.0 inches

per hour and the water table is assumed to be between 1 and 3 feet deep.

The alluvial soils vary so much that they are not classified; however,

alluvial soils could have the potential for containing sands and gravels

which are highly permeable materials. Therefore, the alluvial soils are

not generally suitable for levee embankment material.

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In conclusion, a majority of the materials in the direct vicinity of

the proposed levees consist of clay except for the Dempster series soils

that are below the 3-foot depth and the alluvial soils. These soils have

permeabilities which range between 0.6 and 2.0 inches per hour which may

be suitable for levee construction. Based on preliminary findings, the

proposed levees can be constructed with side slopes of 3 (horizontall to

1 (verticall with a 10 foot minimum top width. Although groundwater was

estimated to be over 5 feet deep, except for the Kennebec and the Cola

series which have groundwater estimated to be less than 5 feet, grading

considerations shall be taken to minimize the costs associated with

dewatering and to minimize the chances of using the sands and gravels

below the 3-foot depth of the Dempster series in the levee embankments.

Levee design details should be finalized based on a detailed feasibility-

level geotechnical investigation.

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