Village of Winnetka
On March 3 and 5, a series of Open Houses were held at which the potential opportunities for stormwater and flood control were presented and discussed.
Flood Protection Goals
The Village has established flood protection goals to prevent home and structure flooding, reduce surface flooding on private property, and provide for passable flood depths in streets from a target storm event producing 4.85 inches of rainfall over a 3-hour period of time, as reflected in Figure #1 (below).
A number of opportunities have been identified that achieve these goals, including a mix of distributed homeowner-level green infrastructure improvements, neighborhood stormwater management and conveyance, and watershed-based stormwater storage. No single improvement will reach the Village’s goal, so a combination of improvement opportunities are being assessed to create a final vision for stormwater and flood control in western and southwestern Winnetka, as displayed in Figure #2 (below).
The opportunities that make-up this vision must be technically feasible, cost-effective, and community supported.
Distributed Green Infrastructure
Green infrastructureopportunities being considered include homeowner-level improvements like rain barrels, rain gardens, and pervious driveways. These opportunities alone are not able to address the target 100-year storm event, but they do provide relief during more frequent, less intense rainfalls. Additionally, these opportunities are instrumental in providing water quality improvements, which is an important aspect of the Village’s final stormwater management vision. The effectiveness of these opportunities is based on participation by property owners and would probably be implemented over an extended period of time.
Distributed green infrastructure also includes local neighborhood improvements such as street curb bump outs (Figure #3, below), rain garden parkways, and green intersections.
These improvements also provide benefit during smaller intensity rainfall events and add another valuable layer of water quality improvements. Challenges to be considered with these opportunities include changes to traffic patterns, permanent closing of streets, and loss of mature parkway trees.
A limitation to all of the green infrastructure opportunities are local soil conditions. Winnetka is underlain by stiff clay soils (Class D Soils) which have very limited infiltration capability. So the green infrastructure opportunities are generally intended for slowing down and cleansing of stormwater runoff rather than significantly reducing the total volume of runoff.
Potential opportunities for stormwater storage require identification of available open space and generally fall into one of two types: neighborhood opportunities and watershed opportunities. Potential neighborhood opportunities include the Washburne-Skokie Play Field, which would entail providing underground stormwater storage and replacing the surface play fields.
Other potential storage opportunities are being explored, including West Elm Street Park, Crow Island Park, and Indian Hill Golf Course. Stormwater storage at West Elm Street Park would require significant tree removal and change the character of the park. Strand’s model analysis shows that during significant rain events, portions of the Indian Hill Golf Course become inundated, affecting playability and course conditions. The potential exists to find ways to manage stormwater inundation so that both course recovery times and neighborhood flood risk would be reduced. Obviously, any improvements will have to be worked into the playability of the golf course and the requirements of the club. Crow Island Park (Figure #4, below) poses one of the best storage opportunities and would entail restoration of this area to its historical wetland and wet prairie conditions. Crow Island Park also represents a great water quality opportunity.
Another potential neighborhood storage opportunity would be to purchase vacant parcels or buy-out existing home sites. However, often the available vacant parcels are not connected to the areas that flood and provide limited benefit. Buying out existing home sites is very challenging, and in Winnetka’s case, may not be cost-effective.
Numerous potential watershed opportunities have been identified including the lands of Forest Preserve District of Cook County, New Trier High School, and Park District. Historical research has revealed that the Forest Preserve lands were lowland wet prairie and wetlands prior to development of the Skokie Lagoons and the Skokie River levee system. Conversion of the lands east of the Skokie River and south of the Skokie Lagoons back to these historical conditions would result in significant stormwater storage volumes, restoration of native habitat, and removal of invasive species while also providing for increased access and use of these lands for passive and active recreational use.
The Skokie Lagoons have also been considered for stormwater storage, but the elevation of the lagoons is actually higher than some of the flood prone areas in Winnetka. In addition to regulatory concerns and potential impacts to lagoon ecology, significant pumping—over 10 times the Village’s current pumping capacity—would be required to transfer flood waters to the Lagoons, making this alternative far more expensive and less feasible than the other identified opportunities.
Potential watershed storage opportunities on Duke Childs Field north of Willow Road, owned by the New Trier High School District, range from use of the existing lacrosse field along Hibbard Road to use of the entire field, including the baseball fields. Conversion of the lacrosse field to a wet or wetland pond represents one of the best stormwater storage and water quality opportunities identified to-date. In order to maintain current activities and levels of use for the High School, the lacrosse fields could be relocated to the top of the landfill south of Willow Road with modifications for public use, access, and parking. Additional storage could be realized by lowering the baseball fields to provide storage during large storm events with a system to drain the fields when flood waters recede. If an alternate location can be identified that provides sufficient land and logistics for the baseball fields, the entire Duke Childs Field could be converted to stormwater storage. Figure #5 (above) shows storage opportunities at this site.
Integral to implementation of any identified stormwater storage opportunity is the conveyance system that transports the stormwater away from private properties. Among the conveyance opportunities identified are new large diameter storm sewers and box culverts. The size of the conveyance infrastructure will require significant work in roadways and may require dedication of easements from private property owners. But the benefit of these new systems could result in removal of many of the Village’s existing pumping stations—reducing the Village’s dependence on pumping and elimination of reliability issues from pump or power failures.
Comments received from the public are being used to evaluate the potential stormwater opportunities and to develop the Village’s final vision for stormwater management and flood control. Figure #6 (below) presents a summary of feedback the Village has received via comment cards from March 3 and 5.
Moving forward, Strand will identify the combination of opportunities that together make up the Village’s recommended stormwater management and flood control vision. Public input is welcome as this process proceeds to the Vision Phase Workshop at the Washburne School Theater at 7:00 p.m. on Tuesday, April 12. Please note there will be no Village Council meeting that night. At that time, the public will have the chance to hear about the process used to develop the final vision, see renderings of the recommended improvements, understand the anticipated costs and timeline for implementation of the vision, and provide comments for consideration in finalizing the Vision for Village Council deliberation.
Study materials, concepts, cost estimates and feedback forms are available at: http://www.villageofwinnetka.org/residents/stormwater-alternatives-evaluation/.
510 Green Bay Rd. Winnetka, IL 60093
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