The Third Avenue Bridge over the Moccasin Creek in Aberdeen, SD, was first built in 1975 and was one of the highest-volume bridges in the city. The structural integrity of the bridge had declined over several years, and the city had to restrict loads on the bridge due to concerns about the integrity of the structure, heavy loads, and increased traffic. IMEG was selected for the project based on a long-standing relationship with the city.

Plans for a replacement began by submitting applications for funding. IMEG assisted the city with this process and provided design for the new bridge and plans for closing the street during construction. IMEG also provided a traffic control plan for Third Avenue and Wilson Street, as well as a pedestrian traffic control plan for the pedestrian trail and sidewalk.

To keep silt out of the creek during construction, IMEG proposed floating silt curtains on each side around the new bridge bents, or piers. This allowed the creek flow to continue downstream in the center area of the new bridge while trapping silt within the construction area. Engineers also proposed riprap around the new bridge bents/piers to protect against scour from creek flow.

Since the bridge is located in a flood-sensitive area on Moccasin Creek with a detailed floodplain in place, IMEG evaluated the impacts of the proposed structure on the 100-year floodplain. IMEG evaluated the performance of the proposed bridge in a copy of the FEMA flood model to ensure it would cause no impacts to the floodplain.

The new bridge resolves the concern for increased traffic and accommodates pedestrian traffic along both sides. In addition, vehicular traffic and pedestrians are protected by guardrail and chain-link fencing. These were installed where necessary in locations adjacent to the bridge, where hazards such as steep slopes and riprap exist below.