The existing discharge pipe was undermined by more than seven feet due to the erosive velocity of stormwater exiting the discharge pipe at the existing headwall. A large volume of soil and earth that was behind the headwall had washed out due to erosion, forming a large and deep void. This void has caused approximately 40 feet of 48-inch CMP to break away from the main storm sewer and headwall. The headwall has also been undermined by erosion and is slowly being washed downstream toward Thorn Creek.
TERRA has analyzed the storm sewer watershed to determine the velocity exiting the 48-inch CMP for the 2-, 10-, 25-, 50- and 100-year storm events. This analysis formed the basis for the design of the storm sewer repair and both temporary and long-term erosion control measures. Temporary erosion control measures included silt fence around the construction limits, an erosion control blanket, and a temporary 12-foot-wide and 705-foot length gravel construction road. Permanent erosion control measures include a rip-rap apron at the proposed 48-inch CMP Flared End Section (FES), native seeding to mitigate the erosive velocity of stormwater discharge, and a permanent turf reinforcement matt that lines the bottom of the channel from the proposed 48-inch FES to Thorn Creek.
Approximately 700 feet of existing 48-inch CMP storm sewer, the existing discharge pipe, and headwall are located within the Forest Preserve District of Cook County’s property. Both TERRA and the Village of Glenwood worked with, and obtained permits from the Forest Preserve District of Cook County.
Village of Glenwood
Forest Preserve District of Cook County