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April 2016 Workshop

April 12 Vision Phase Workshop- Materials & Summary

Review Vision Phase Materials:

The April 12 Vision Phase Workshop builds upon the preliminary opportunities identified and presented during the March 2016 Open Houses (those materials can be reviewed at the 2016 Open Houses page). 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 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 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 have proposed a combination of conceptual projects that produces an advantageous balance of flood reduction benefit, cost-effectiveness, and phased implementation. Strand has 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.

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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.

Public Involvement

Comments received from the public at open house forums and through electronic communications are being reviewed, and to-date, have been heavy influences to evaluate the potential stormwater opportunities and to develop a phased approach and vision. Moving forward, Strand will continue to analyze and refine 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 through the Vision Phase. Additional public engagement opportunities will be available to review and comment on the conceptual vision, see renderings of the recommended improvements, understand the anticipated costs and timeline for implementation of the vision, and provide comments for consideration before the vision is transmitted to the Village Council for deliberation.

 

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