TERRA was selected to perform engineering services that included hydrologic and hydraulic analysis of the 585-acre tributary watershed utilizing HEC-HMS, generation of both design and construction documents, and construction inspection for the removal and replacement of an existing culvert under Main Street in Elmwood, Illinois.

The existing corrugated metal pipe (CMP) culvert under Main Street was old and in poor condition. Additionally, the area near the downstream end of the watershed at the culvert has experienced flooding due to the inadequate size of the existing culvert. This project involved removing the existing single 72” pipe culvert and replacing it with dual 60” RCP pipe culverts. This solution alleviated much of the potential for flooding upstream, but an existing single 72” CMP culvert just downstream of the Main Street culvert under a railroad embankment created design difficulties. TERRA analyzed several design alternatives using HEC-HMS and recommended that the City coordinate with the railroad to add a second pipe culvert under the railroad embankment to increase flow capacity and alleviate potential flooding of properties near the railroad culvert.

In addition to the culvert itself, TERRA designed a grading plan for approximately 1,000-ft. of ditch re-grade both upstream and downstream of the culvert. Erosion control was an important factor in this project due to the steep slopes near the culvert and the high flow rates carried by the ditch. Turf reinforcement mats, temporary erosion control blankets, and special plantings were used to help control erosion around the culvert and within the ditch limits.

TERRA assisted the City with the bidding process. This included fielding questions from contractors, handling the bid submittals and making a contractor recommendation to the City.

TERRA also acted as the resident engineer during construction of the culvert as well. A professional was on site during all major construction activities to make timely decisions and work with the contractor to resolve any issues that arose.


City of Elmwood