Case Study Project June 2, 2016 A project by the Alliance for the Great Lakes, Chicago Lake Blu Ravine Restoration Botanic Garden, The Field Museum, and for Control Openlands. Historical Context Overview The subject ravine in which the project was performed, known Ravine Park Ravine as the Ravine Park Ravine in the Village of Lake Blu , has a Village of Lake Blu , IL watershed of 375 acres. 2010-2013 Land use within the watershed is a fully developed suburban Funded by 2010 Great Lakes Restoration area. Due to high ows through the ravine during Initiative (USEPA) - $788,900 signicant rain events, (modeled at 122 cubic feet per second for the two year event), severe erosion problems existed. Over Project Management the project reach it was estimated that there was an average Village of Lake Blu of 3 to 4 feet over a 30 year period. The downcutting of the ravine streambed was triggering side Project Partners slope failures. Hey and Associates (Project Design, 100% of the ravine streambed was raw and unvegetated. As a Construction Management and Final Report) result of the erosion, extensive quantities of were Lake Blu Park District (Provided Easements for Work Access) being transported to Lake Michigan during each major rainfall V3 Companies, Woodridge, Illinois event. Prior to the project, soil erosion in the ravine was (Construction) estimated to be contributing several hundred tons of sediment annually into Lake Michigan. This was primarily due to scouring of the clay ravine streambed and adjacent lower Project Summary ravine side slopes by streamwater ows piped to the ravine The project primarily involved the from an urbanized watershed of 375 acres. placement of approximately 6,100 tons of Class RR-4 and RR-5 (IDOT Gradation Classication) rock rip rap along a 2,200 foot segment of a ravine streambed and adjacent lowest portions of the ravine side slopes. Project Concerns

Goal: Reduce Ravine Bed Erosion

The primary goal of the project was to signicantly reduce the rate of erosion or downcutting of the ravine streambed and as a result to reduce Key Project Themes sediment loading to Lake Michigan. ravine bed downcutting, rip rap, stormwater volumes Case Study Case Study Project Project June 2, 2016 Lake Blu Ravine Restoration Criteria for Success Obtaining funding for the project was critical. Of the estimated 19,000 linear feet of ravine streambed in the for Village the segment of ravine that was selected for this project was one of the areas of most signicant erosion, and was the most easily accessible due to a large part of the ravine area within the project owned by the Lake Blu Park District and the Village of Lake Blu . Public Village Roadways were located immediately adjacent to nearly the entire length of the project, making access relatively easy, and without the need for any private easements. When 375 acres of watershed carves out a ravine

Toe Scouring Slope Failure

Fallen Trees Bed Scouring Action Strategies

1) Obtain easement access from Lake Blu Park District for construction 2) Model potential impcts. Hydrologic and Hydraulic modeling was utilized to develop a riprap ll section which would be stable and could convey 100-year through the ravine. 3) Stabilize ravine bottom and toe of side-slope areas. Aeas were graded and lled with RR-4 and RR-5 Rock Riprap to re-establish streambed elevations two to four feet above existing conditions. 4) Protect roadway from slope failure. A steel sheetpile wall was utilized to stabilize a portion of the ravine side-slope that was failing and in danger of impacting an adjacent roadway. 5) Improve drainage from tableland stormwater inputs near ravine (roadway) 6) Implement stormwater erosion controls at outfalls Case Study Project June 2, 2016 Lessons Learned To date the project has conrmed our belief that sometimes hard armoring is the best and most cost e ective Community Engagement solution when stormwater ows are too high for vegetative solutions.

Lasting Impact The project completed 3 years ago. The installed rock rip rap has remained in position along the entire project length. No new ravine slope slides have been observed within the project limits.

The general conclusion is that the project has been very e ective in reducing the rates of erosion and that very little follow-up maintenance will be necessary in future decades. bed and toe stabilization

End-of-pipe erosion control 2 Years after Completion

Many thanks to George Advice to Ravine Communities Russell and Je Hansen for sharing this project While the short term impacts of this type of construction project are with the ravine region. 1 signicant, these impacts are outweighed by the long term benets. For More Information: Signicant erosion in many ravines is occurring and over time, if the erosion Je Hansen, Village 2 rates are not reduced, this erosion will lead to very signicant side slope Engineer at Village of Lake failures within the ravines, leaving the side slopes raw and unvegetated. Blu at Eventually tableland will be lost if the streambed erosion remains. jhansen@lakeblu .org