Ottawa Township High School Floodwall

Firm:Klingner & Associates, P.C.

Other Consultants: Poundstone Engineering & Surveying, D Construction Company, Inc., R&R Landscaping & Irrigation, Inc.

Owner:Ottawa Township High School

Description:Ottawa Township High School (OTHS) sits at the confluence of the Illinois and Fox Rivers in Ottawa, IL. For over 100 years, the school’s position in the watershed has posed a continuous threat to the property. Flow frequency profiles were updated after the 2008 flood, revealing that the school’s flood protection system was 1.5’ lower than the new 100-year surface profiles. Though the levee continuously passed USACE-RI inspection, the system lost its FEMA accreditation in 2011.

As the lead firm for this project, Klingner provided all permitting; levee certification reports; and water resources, civil / site, environmental, geotechnical, and structural engineering. Klingner’s water resources experts worked with OTHS to design system enhancements that will restore full FEMA accreditation. Extensive modeling by the Klingner team determined the necessary levee height increase and analyzed a full range of loading conditions to weigh the impacts of each design option. These complex hydraulic models of the Fox and Illinois Rivers — which showed impacts within 1/100 of a foot — were critical to the development of a design that would protect the school and minimize adverse effects on neighboring properties.

Working closely with the school, Klingner designed an 18” vertical extension of the existing concrete floodwall south of East Main Street and tying into an earthen berm. Addressing flood concerns north of E Main Street involved the development of a new permanent floodwall. Built atop an earthen berm lining the Ottawa East Side Historic District (OESHD), this new floodwall uses removable gates and an innovative combination of sheet pile and sheet pile clad with stamped concrete to protect neighbors’ property values and the district’s historic character. Combining materials significantly reduced the need for excavation — expediting construction, saving a third of the initial projected cost, and creating a consistent appearance for the finished system.

A drainage capture system — including trench drains, collection points for portable pumps, and a canal gate that opens when there is a higher head condition on the dry side of the floodwall — was also designed to protect school property and residents from interior flooding.

The new flood protection system requires no additional equipment or personnel, eliminating the need for costly sandbagging efforts and constant monitoring. Major flooding tested the system in May 2020. This floodfighting effort cost OTHS only $4,932.55 — a savings of over $20,000 as compared to their last major flood (April 2013). Restoring FEMA accreditation will also reduce the school’s annual flood insurance.

As of October 2020, this was the first levee height improvement permitted by USACE-RI in the state of Illinois and the only one executed by a Consultant.

Ottawa Township High School

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