Ravine Erosion Control
Lake County, IL

Grantee: City of Highland Park , IL
Basin Program Funds: $49,500 (phase I); $10,000 (phase II)
Non-federal Funds: $71,667
Project Duration: 05/1993 - 10/1997
Status: complete

Problem Statement
Highland Park storm sewers empty directly into ravines which then drain into Lake Michigan. During storm events they produce high speed runoff with short detention time that create heavy erosion from the ravines.

Background
The City of Highland Park, Illinois, population 34,000, has ten (10) separate ravines, totaling over eleven (11) miles of channel that drain the eastern third of the city into Lake Michigan. This watershed is highly urbanized and contains approximately 2,500 residential, commercial, and retail properties. The separate ravine drainage basins have impervious surface ratios (square footage of impervious surface divided by the total area square footage) of 20 percent to 48 percent. Sanitary sewers were installed in Highland Park 70 to 90 years ago to convey wastewater to Lake Michigan. Such sewers, along with a large interceptor sewer which receives and transports the conveyed wastewater to a treatment plant, are still in use. The construction of the sanitary sewers and other infrastructure improvements resulted in increased development of surrounding properties for residential, commercial and retail use. The result of this urbanization in and near the City of Highland Park has been storm sewers that directly discharge into the ravine channels at various locations, producing high runoff rates, short detention times, high peak flows and velocities. The energy produced from the high flows and velocity have substantially eroded the ravine channel, clay and silt banks and slope toe leading to slope failures and slumping.

The goal of this project was to construct an in-channel "Gabion" basket detention basin at a strategically located site to detain the selected ravine sub-watershed runoff up to a 10 year storm event. This in-channel detention basin was designed to restrict downstream flow and control erosion from a 3.5 square mile highly urbanized watershed that flows into Lake Michigan. Other goals of the one year project included verification of the success of the detention basin with respect to limiting ravine slope and bank erosion and developing criteria for future ravine stormwater detention projects.

Activities
This project was funded in two phases. The first phase was conducted from 1993 through 1995 and included the project design, site selection, and most of the treatment construction. The second phase, conducted from 1995 through October 1997, involved construction completion, follow-up measurement and testing, and publication and distribution of results.

Project personnel chose two ravine sites, Lake Bluff and Highland Park, which were susceptible to rapid erosion and exhibited various stages of renewed down cutting with associated bank slumping and structural rotary failures.

Lake Bluff Ravine – This ravine is about 3,000 feet long draining directly into Lake Michigan. The project focused on a 450 foot previously restored section and another 100 foot unrestored section upstream with an average slope 1:42. The intent was to augment or reestablish natural stream bed and stream bank armor. Project personnel graded out stream bed irregularities, laid down geotextile in slumped areas. These were then filled with quarried limestone cobble and concrete rubble. The slumps were covered with soil and hydro-seeded with temporary annual grass in order for natural vegetation to have an opportunity to reestablish itself.

Highland Park Ravine 10 – Interceptor sanitary sewers installed in some of the ravines appear to have added to increased erosion because their installation disturbed the natural stream bed armoring from cobble. The project focused on 900 feet of ravine beginning at its head with an average slope 1:53. Project personnel utilized several methods for remediating this ravine section. They built gabion baskets out of galvanized steel mesh, filled them with 3-6 inch quarried limestone and installed 3X3X9 and 3X3X12 units along the toes of ravine slopes where erosion was active. They also installed Reno Mattresses which were constructed like the gabion baskets except they were only 9 inches thick. The Reno Mattresses were installed over geotextile on the base of the ravine bed. A-Jacks are concrete or plastic structures shaped like a 6-arm toy jack. These were installed at the toe of the ravine slope on either or both sides of the ravine bed or adjacent to and downstream of a Reno Mattress. Project personnel then planted willow cuttings between the jacks. Finally geo-web, a plastic textile which holds cobblestones in place, was used in areas of actively eroding clay.

Results
Project personnel measured the effectiveness of ravine stabilization in three ways: sediment transport sampling stations, stream bed down cutting measured with rod and transit, and visual survey. The various techniques showed different rates of success. Least successful were the A-Jacks and willow plantings because there was too much erosion and not enough sunlight to enable the willows to grow. The restored stream bed armor in Lake Bluff exceeded expectations. Project personnel were able to demonstrate a savings of 13.2 ton/year/100 feet of restored ravine at the Lake Bluff site. They concluded that the installation of a continuous layer of streambed armor most closely mimics nature, is the least expensive solution and is less obtrusive than other methods.

Contact: James H. Johnson, (847) 926-1144