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Public Meeting Highlights

January 21 & 23 Public Open Houses- Summary & Materials

The Village contracted with Strand Associates for engineering services to re-evaluate the Village’s western drainage basins for creative, cost-effective westward looking improvements for storms ranging from the 10-year to the 100-year event, taking into account the Village’s flood-control goals and objectives. Strand took a holistic approach to this project, evaluating a variety of grey and green infrastructure approaches, conveyance, detention, retention, infiltration, property buyout or individual protection retrofit programs, and a host of other traditional and emerging stormwater management technologies.

On January 21 and 23, 2016 Strand Associates conducted the initial Awareness Phase Public Open Houses, focusing on communicating the results of model verification and the consultant’s early observations.  Strand also focused on listening to the community to solicit innovative ideas and receive public input on experiences in these flood-prone areas.

pw-picture-1-img-20190501Strand Associates made a brief introductory presentation, which outlined the study area, explained how the geography and topography of the area contributes to the Village’s flooding problems, and showed detailed flood modeling results. 

After this presentation, Strand Associates conducted breakout activity stations, where residents in each study sub-area viewed model predictions of flooding under current conditions, shared their flooding observations to help Strand confirm the hydraulic modeling, learned about the wide variety flood reduction techniques that might be considered for sub-areas, and provided comments and input for Strand. You can view flood model simulations of the July, 2011 flood event by clicking below:

Strand documented the input received at these meetings and began evaluating the feasibility and benefits of various approaches to flood reduction in the project areas.

March 3 & 5 Exploration Phase Open Houses- Materials & Summary

Review Exploration Phase Materials:pw-picture-1-img-20190501

Open House Summary:

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 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).  pw-target-level-service-img-20190501

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). 

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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.

Stormwater Storage

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.

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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-datepw-duke-childs-detention-img-20190501.  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.

Stormwater Conveyance

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. 

Public Involvement

Comments received from the public were 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.

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April 12 Vision Phase Workshop- Materials & Summary

Review Vision Phase Materials:

The April 12 Vision Phase Workshop built upon the preliminary opportunities identified and presented. Strand Associates presented and discussed a conceptual vision for stormwater and flood control. Over 125 people attended to hear the presentation and to ask questions, provide comments, and discuss the project with the Strand team. The presentation and Powerpoint can be viewed via the following links:

Presentation Summary and Highlights:

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 design storm event producing 4.85 inches of rainfall over a 3-hour period of time. 

Summary of Watershed Investigations

A number of opportunities wereidentified 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 is being assessed to create a final vision for stormwater and flood control in western and southwestern Winnetka. 

Green infrastructure opportunities being considered include homeowner-level improvements like rain barrels, rain gardens, and pervious driveways, and neighborhood-level improvements such as parkway rain gardens and infiltration areas. Potential opportunities for stormwater storage require identification of available open space and generally fall into two types of opportunities: neighborhood and watershed. 

Neighborhood opportunities include the Washburne-Skokie Play Field, which would entail providing underground stormwater storage and replacing the surface play fields. Other potential neighborhood storage opportunities are being explored, including Crow Island Woods, which poses one of the best storage opportunities and advances the Village’s water quality goals.

At the watershed level, Strand is evaluating storage on lands belonging to the 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 Forest Preserve 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. The current vision would also provide for increased access and use of these lands for passive and active recreational use.

Conversion of the lacrosse fields at Duke Childs Field, north of Willow Road (and owned by New Trier High School District), 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.

Integral to implementation of any identified stormwater storage location is the conveyance system that transports the stormwater away from private properties. Strand’s conveyance improvements include 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.

Overall Vision

Based on Strand’s modeling and evaluation to-date, they proposed a combination of conceptual projects that produces an advantageous balance of flood reduction benefit, cost-effectiveness, and phased implementation. Strand identified a series of projects that, if fully implemented, would significantly reduce the number of homes in the watershed that are at risk of floodwater intrusion for the design event. The proposed vision consists of 15 discrete stormwater storage and conveyance projects, water quality management improvements, and distributed green infrastructure improvements, in four phases. These elements are shown in Figure #1 (below).

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Phase 1

Phase 1 conceptual improvements consist of a large constructed wetland improvement on Cook County Forest Preserve property south of Willow Road west of Hibbard Road, and a wetland and stormwater storage facility on the Duke Childs Field property at Willow Road and Hibbard Road. The two lacrosse/soccer fields would be relocated to open space at the top of the Village’s landfill property. Phase I improvements would also include large stormwater conveyance pipes on Ash Street, Cherry Street, Oak Street, Pine Street, Spruce Street, and Hibbard Road to carry stormwater to the new storage areas.

The critical Phase 1 improvement is a restored, constructed wetland on Cook County Forest Preserve property located to the south and to the east of the Village’s landfill, along Hibbard Road and Winnetka Avenue. This improvement, which still requires significant additional cooperative evaluation with the Forest Preserve District staff, and ultimately Forest Preserve Board approval, provides wetland restoration, habitat and water quality improvements, and approximately 124.1 acre-feet (40.4 million gallons) of stormwater holding capacity. This conceptual improvement is illustrated in Figure #2 below.

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A second key improvement would be located in Duke Childs Field, at the northwest corner of Willow Road and Hibbard Road. This concept involves relocating the existing lacrosse and soccer fields to the top of the Village’s landfill, across Willow Road, and creating approximately 18.2 acre-feet (5.9 million gallons) of stormwater storage capacity as well as a water quality enhancement area. Preliminary evaluation indicates that with re-contouring, there is sufficient space on the landfill to safely accommodate the two fields, but many details remain to be worked out. It is important to note that Duke Childs Field is owned by New Trier High School and is valuable to their athletic programming. Any stormwater improvements at that location need to be coordinated with and approved by the New Trier Board of Education.

These two storage projects, and the associated larger storm sewer pipes under Ash Street, Cherry Street, Oak Street, Spruce Street, Pine Street, and Hibbard Road, will bring relief to areas north of Willow Road.

Phase 2

Phase 2 projects are focused on flood reduction for areas south of Willow Road, and consist of conveyance improvements along Sunset Road, the Skokie Ditch, Mount Pleasant Street, and the Chestnut/Hill intersection, and a water quality and stormwater detention project in the Crow Island Woods area. These projects are shown in Figure #3 below.

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The conceptual Crow Island Woods project would involve creating approximately 15.9 acre-feet (5.2 million gallons) of stormwater storage capacity along with a water quality enhancement wetland, in the currently wooded southern section of the park. The northern section, with the pavilion, Burnham Log Cabin, picnic areas, tribal council ring, and open fields would not be modified. This conceptual project is shown in Figure #4 below.

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The conceptual vision for Crow Island Woods includes a permanent pool and wetland environment, for water quality enhancement, as well as upland areas with walking paths and forested areas.

Phase 2 also requires construction of larger storm sewers (10-foot x 5-foot) underneath Sunset Road and along the Skokie Ditch to convey water to the Crow Island and Forest Preserve storage areas. The Phase 2 projects, in conjunction with the Forest Preserve project, will bring significant stormwater relief to areas south of Willow Road.

Phase 3

The Phase 3 projects call for new larger storm sewers on Oak Street, and an underground stormwater storage vault beneath the Skokie-Washburne athletic fields that provides 5.6 acre-feet (1.8 million gallons) of stormwater storage capacity. These projects, which would bring further relief to areas north of Willow Road, are shown in Figure #5 below. These fields belong to Winnetka School District 36 and any improvements in this location will require cooperation with and approval by the School District.

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Phase 4

Phase 4 projects are primarily conveyance projects – larger storm sewers – but also includes implementing some additional storage opportunities north of Willow Road.  These projects that bring flood relief to areas farther north and east in the study area are shown in Figure #6 below.

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Mitigation Zones

If all of these projects are implemented, the extent of flooding and number of at-risk residences will be significantly reduced. Under existing conditions, modeling has indicated that approximately 474 residences are at risk of flooding from the design event. If the full vision is implemented, this number would be significantly reduced, to approximately 61 properties that would need to be addressed by a process of individual property mitigation. Strand will evaluate individual homes or small areas to identify specific buildings with flood risk and to identify individual or group property protection activities to protect buildings against the design storm. These mitigation zones are shown in Figure #7 below.

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Mitigation measures might include things like protecting low entry points like basement doors or window wells, raising buildings, grading properties to provide flood protection, or other localized measures.

Green Infrastructure

Green infrastructure is a key part of the storage projects envisioned for the Cook County Forest Preserve, Duke Childs Field, and Crow Island Woods. Stormwater wetlands use natural biological processes to filter stormwater prior to discharge to waterways. A variety of neighborhood level green infrastructure improvements, such as parkway and intersection rain gardens, are critical to the Village’s vision as they provide water quality and storage benefits in key areas, for smaller storms. Sample green infrastructure installations are shown in Figure #8 below.

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Concept Level Cost Estimates

Strand has developed conceptual level costs estimates for all of the improvements outlined in the current Vision. These estimates were developed using current unit cost information. The total project cost estimate, for all four phases, is $57,717,000. Individual phases and component costs are shown in the following Figure #9.

It is important to note that this estimate includes approximately $10.9 million in total contingencies – accounting for the many uncertainties present at the current conceptual level of design. The total also captures $6.1 million for detailed final engineering and project permitting.

 

 

 

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