Warrenville, IL :: Floodplain

September 2008 Flood Event Investigation and Related City Follow-up:

Phase I Analysis:
In 2008 and 2009, the City conducted a comprehensive analysis to better understand the magnitude of the September 2008 flood event, why it occurred, and to identify any obvious issues or conditions that needed to be addressed to avoid any unnecessary flood impacts in the City of Warrenville in the future. On November 3, 2008, the Warrenville City Council unanimously approved the execution of a professional services agreement with Strand Associates, a civil engineering consulting firm from Joliet, Illinois, to assist in this phase I engineering analysis and to provide their professional opinions related to the September 2008 flood event. A copy of the October 30, 2008, Strand and Associates contract can be reviewed by clicking here. The detailed scope of services Strand Associates will provide to the City was defined by City staff based on input received from residents and the City Council prior to, during, and following the September 22, 2008, Community Development Committee of the Whole meeting discussion on the flood event. The scope of the Phase I analysis Strand Associates performed for the City is summarized as follows:

Fawell Dam impacts on Warrenville floodplain elevations: Independent determination of the impact the construction, DuPage County modification, and subsequent operation of Fawell Dam has on floodplain elevations in the City of Warrenville.
Operation of Fawell Dam during September 2008 flood event: Independent determination if Fawell Dam was operated in conformance with the State of Illinois approved Operations Plan during the recent September 2008 Flood event.
Magnitude of September 2008 flood event: Independent determination of the magnitude of the September 2008 Flood (100 year flood/500 year flood)
I-88 and Ferry Road Bridge impacts on flooding in Warrenville: Independent determination of what, if any, impact the I-88 bridge and the Ferry Road bridge had on increasing flood elevations in the City of Warrenville during the September 08 Flood.
McDowell Grove temporary construction bridge impacts on flooding in Warrenville: Independent determination of what, if any, impact the temporary bridge in the McDowell Grove Forest Preserve had on flood elevations in the City of Warrenville during the September 08 Flood.
Localized flooding in the River/Ferry Road - Bower School area: Provide qualified professional assistance to City staff in the evaluation of the localized flooding that occurred in the River Road/Bower School area and the identification of possible causes and potential recommendations to mitigate future such flooding.
Provide Input on scope of proposed DuPage County Watershed Plan Update: Review and provide recommendations on exactly what work and analysis would be performed by DuPage County as part of their update of the Watershed Plan for the West Branch of the DuPage River.

The total cost to the City for Strand Associates to complete this Phase I work was approximately $55,000. A copy of the final Project Summary Report Strand Associates prepared and presented to the City on the 2008 flood event can be viewed/downloaded by clicking at the following links:

September 2008 Flood Investigation Report

Phase II Analysis:
One of the key recommendations Strand made as part of their Phase I Analysis was for the City to continue to pursue the County to complete a Study of the West Branch of the DuPage River (WBDPR) watershed. The study would include updating the river FEQ hydraulic model and identify more accurately the conditions that cause flooding in Warrenville. This study would also evaluate the effectiveness of potential flood control projects that could help reduce flooding in Warrenville and more accurately predict river elevations and timing during sever rainfall events.
DuPage County has agreed to work in cooperation with the City to update the watershed plan and supporting FEQ hydraulic model for the WBDPR. The County's Summary of the purpose and process for this watershed study is available by clicking here.

The City has contracted Strand Associates to assist the City during this process and help insure that the County’s FEQ hydraulic model is updated and calibrated properly with all of the most current rainfall, land use, and stormwater infrastructure data for the WBDPR watershed. The City Council approved a $20,800 amendment to Strand Associates Phase I proposal/contract for this additional work. A copy of the detailed scope of work for Strand's additional Phase II work is available by clicking here. The County is working to complete the Watershed Plan Update Process by the end of the summer 2010.

Questions regarding this issue should be directed to City of Warrenville Community Development Director Ronald Mentzer at (630) 393-9050.