Village of Winnetka Flood Risk Reduction Assessment October 11, 2011 Christopher B. Burke Engineering, Ltd. (CBBEL) Thomas T. Burke, Jr., PhD, PE David Buckley, PE, CFM
Introduction The September 2008 storm event prompted a flood risk reduction assessment of Western Winnetka. Results were presented in September 2009 Remaining portions of the Village were analyzed and presented in July 2011
Purpose of this Study July 23-24 th 2011 storm event produced widespread flooding and prompted the analysis of the Village for the 25-, 50-, and 100-year design storms for all 8 study areas Previous analyses were performed for the 10-year design storm for all 8 study areas
Purpose of the Meeting Present study findings Proposed improvements to reduce flood risk Identify regulatory and permitting requirements Identify intergovernmental partners Obtain Board s input and public comment Next steps Village of Winnetka
Scope of Flood Risk Reduction Assessment Analysis of all 8 study areas for the 25-, 50-, and 100-year design storms Identify drainage improvements to provide the required level of protection for each design storm Develop conceptual plans and cost estimates for drainage projects for each design storm Village of Winnetka
Design Level of Protection Storm sewers sized for 10-year design storm (10% chance of occurring in any given year) Runoff exceeding storm sewer capacity flows overland To obtain greater level of protection: Larger storm sewers, detention, outfalls and pumps 25 yr design = 4% probability of occurring in any given yr 50 yr design = 2% probability of occurring in any given yr 100 yr design= 1% probability of occurring in any given yr Village of Winnetka
Information Analyzed Field investigations by Village and CBBEL staff during and after storm events 857 flood questionnaires Information provided by Village Staff Village of Winnetka storm sewer atlas Cook County aerial topographic mapping Village of Winnetka
Information Analyzed Computer Modeling (XP-SWMM) Dynamic hydrologic / hydraulic analyses Critical duration Data included in modeling Tributary areas Runoff curve numbers Time of concentration Storm sewer network data Overland flow paths Streets and yards Depressional storage areas Village of Winnetka
Overall Drainage P P
North of Willow Road Study Area To Winnetka Avenue Pump
North of Willow Road Study Area 25-year Improvements = $13.0 Million 24 42 P 24 72 54 Underground Vault Underground Vault 10.2 AC-FT CCFPD Property Park District storage Village flood control 72 Underground Vault
North of Willow Road Study Area 50-year Improvements = $ = $14.8 Million 42 48 24 P 24 72 54 60 Underground Vault Underground Vault 10.2 AC-FT 31.2 AC-FT CCFPD Property 72 Park District storage Village flood control Underground Vault
North of Willow Road Study Area 50-year 100-year Improvements = $ = $17.5 Million 48 42 24 P 24 72 60 66 Underground Vault 48 42 42 Underground Vault 31.2 AC-FT 58.5 AC-FT CCFPD Property 72 48 48 Park District storage Village flood control Underground Vault
North of Willow Road Benefits CCFPD approval and land acquisition Park District IDOT MWRDGC Winnetka School District 36 Level of Protection Engineer s Estimate of Probable Cost (Millions) 10-year $6.8 25-year $13.0 50-year $14.8 100-year $17.5
South of Willow Road Study Area Area from North of Willow Road Study Area Mount Pleasant Road Pump P P P Winnetka Avenue Pump DeWindt Road Pump 178 Acres Off-site Area
South of Willow Road Study Area 25-year Improvements = $9.7 million Crow Island Park 15 AC-FT Underground vault P 60 Relocate Mount Pleasant Rd Pump 400 feet of ditch re-grading and lowering 60 Twin 48
South of Willow Road Study Area 50-year Improvements = $12.6 million Crow Island Park 15 AC-FT 40 AC-FT Underground vault P 60 72 Relocate Mount Pleasant Rd Pump 60 72 400 feet of ditch re-grading and lowering Twin 48
South of Willow Road Study Area 100-year Improvements = $17.8 million Crow Island Park 40 AC-FT 65 AC-FT Underground vault P 72 84 Relocate Mount Pleasant Rd Pump 72 84 400 feet of ditch re-grading and lowering Twin 48
South of Willow Road Benefits CCFPD approval and land acquisition MWRDGC US Army Corps of Engineers Level of Protection Engineer s Estimate of Probable Cost (Millions) 10-year $6.8 25-year $13.0 50-year $14.8 100-year $17.5 100-year (above ground storage) $9.6
Underpass Study Area 24 Under RR Main System Junction 18 at Underpass
Underpass Study Area Three Alternatives Alt 1: Increase pipe sizes for each design storm Does not benefit pedestrian underpass Alt 2: Underground storage along Green Bay Rd Benefits both underpasses Reduces required pipe sizes Alt 3: Underground storage at New Trier Does not benefit pedestrian underpass Reduces required pipe sizes Village of Winnetka
Underpass Study Area 25-year Improvements (Alt 1) = $2.9 Million 66 Water quality structure 54 54 High capacity inlets
Underpass Study Area 50-year Improvements (Alt 1) = $3.4 Million 66 84 Water quality structure 54 66 54 66 High capacity inlets
Underpass Study Area 100-year Improvements (Alt 1) = $4.4 Million 84 96 Water quality structure 66 84 66 84 High capacity inlets