Orland Grassland South Wetland Mitigation

Orland Park, Illinois

The Orland Grassland south addition mitigation site was selected by the Illinois Tollway to offset wetland impacts associated with the Jane Addams Tollway (I-90) expansion. This lane widening and traffic modernization project caused impact to 13 acres of regulatory wetlands, one acre of Waters of the US and seven acres of non-federal wetlands under the jurisdiction of the Illinois Department of Natural Resources. The mitigation requirements for this project totaled 33 acres. The final mitigation plan for the Orland Grassland south addition site includes more than 65 acres of wetland mitigation credits through re-establishment of historic wetlands, enhancement of existing wetlands and prairie buffer establishment. In addition, approximately six acres of stream mitigation credits were achieved through the hydrologic restoration and re-meandering of a headwater swale at the beginning of the unnamed tributary to Marley Creek.
This project included wetland restoration planning, design and permitting of 160 acres of preserve area within the ownership of the Forest Preserve District of Cook County and adjacent to the Orland Grassland Preserve. V3 evaluated the existing wetland and soil conditions to assess the feasibility of restoring the historic hydrology to the hydric soils on the preserve and enhancing existing wetlands. To determine the potential for wetland restoration, V3 classified and mapped the extent and location of hydric soils present on the site and completed a hydrologic and hydraulic assessment to evaluate surface water conditions after the drain tiles were removed.
The rolling site topography and headwaters drainage conditions made hydrologic restoration a unique challenge on this property. Water control structures and minor depressional berming was used to control the surface water flow down the steep slopes of the site. The top of the berms were used for an aggregate trail system that was desired by the Forest Preserve District of Cook County to provide public access to the wetlands habitats created on this unique property. Water control structures and drainage systems were designed to safely control drainage across these walking paths.
Hydrologic and hydraulic modeling was performed on the headwaters of the unnamed tributary of Marley Creek to evaluate off-site impacts of the re-meandering design of this headwaters swale. The existing flood storage on the property was expanded through wetland creation and swale re-meandering through the site. Therefore off-site impacts to upstream or downstream property owners, due to drainage modifications on the project, were avoided.

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