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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shown on the FIRM are also tied to MSL datum. After careful evaluation, discrepancies
were found between the elevations shown on the 1971 Rock Rapids topographic map
and the FIS surveyed elevations. The differences were quite variable and could not be
attributed to a constant datum shift. Due to the elevation discrepancies found, it was
not feasible to determine proposed levee heights by taking ground profiles from the
1971 topographic map. A description of the process for levee sizing is discussed later in
this report.

It should also be noted that the HEC-2 cross-section locations and water surface
contours were not consistent between the work map and the published FIRM. It was
assumed that the provided work map shows preliminary results of the PIS analysis, and
the information shown on the FIRM was assumed to be the finaI and correct data.
HEC-2 cross-sections on the FIRM and on the work map do not represent all of the
cross-sections that are included in the provided FIS hydraulic model, and therefore it
was difficult to estimate the horizontal alignment of model cross-sections (i.e. bent
sections) that were not depicted on the maps.

Evaluation of Site U AU
Analyses for Site U AU included evaluation and conceptual design of proposed levee and
interior drainage facilities for the area located along the west side of the fairgrounds. In
addition, anticipated levee effects on existing flood boundaries were evaluated and
preliminary cost estimates for loo-year and 500-year levels of protection were
developed.

During the 1993 flooding, citizens of the City constructed an emergency sand bag levee
which meandered aIong the west side of the fairgrounds to protect the structures
located within the floodplain in that area. The sand bag levee was reported to be about
2 feet high, and the maximum flood water was reported to be at or near the top of the
emergency levee. The city has requested that the proposed permanent levee should be
located approximately 15 feet to the east of the sand bag levee alignment

The proposed l00-year and 500-year levee alignments for site U AU shown on plate 2 are
estimates of a possible alignments. However, without surveyed information regarding
the exact location of the sand bag levee, it was difficult to determine the City's

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