FLOOD06759

• County: Statewide
• Community: Rock Rapids, Iowa
• Basin: Statewide
• Title: Technical Assistance Report Rock River at Rock Rapids Iowa
• Date: 9/1/1995
• Prepared For: US Army Corps of Engineers
• Prepared By: Greenhorne & O'Mara, Inc.
• Floodplain - Doc Type: Project

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HYDRAULIC ANALYSIS

For the purposes of this study, it was decided that the water surface elevations
published in the Rock Rapids FIS and shown on the Rock Rapids Flood Insurance Rate
Map (FIRM) would be used for evaluating existing and proposed facilities. The
differences are minimal between the computed water surface elevations (using the
regression equation peak discharges) and the FIS water surface elevations. Within the
areas of interest for evaluation of existing and proposed levees, the FIS elevations were
within 0.2 feet of the computed elevations. The small differences in water surface
elevations are attributed only to the differences in peak discharges, which were
previously presented in table 1.

DffiCIDWTIONOFEVALUATIONSANDCON~ALPLANS

General
For this Technical Assistance study, existing and proposed levee structures were
evaluated at three distinct sites as described previously in this report. For convenience,
the three sites will be referred to as follows:

Site A:
SiteB:

Proposed levee on the west side of the fairgrounds.
Existing levee located on the north side of the city near North 4th
Avenue and Boone Street.
Existing private ring levee around two homes along the Rock River
near East Street.

Site C:

Mapping
Available mapping which was used for this study includes four topographic maps and
one aerial photo. A description of each map is outlined below.

TQpOe-rl\Pbic Map of Rock Rltpids. Iowa
. Developed from aerials taken by Great Plains Aerial Surveys, Inc., on July 19, 1965.
. Map Date: May 1971
. Contour interval: 5 feet
. Scale: 1 inch = 400 feet
. Datum: none listed and noDe could be obtain through verbal confirmation

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