City of Des Moines SW 9th Street Bridge

Background

The City of Des Moines sought to replace the aging SW 9th Street bridge over Middle Creek. Built in 1971, the current structure was showing signs of significant deterioration on the pier pile encasements, with section loss on the exposed piles. Foth was tasked with evaluation of the bridge and development of replacement alternatives.

Approach

The impact of construction on traffic was a significant consideration when developing design alternatives to ensure prompt emergency response times for the fire department near the bridge’s south end. Preference was given to alternatives that allowed a staged approach to maintain traffic or used accelerated construction methods to limit road closure duration. Ultimately, a staged three-span continuous concrete slab bridge was selected as the preferred alternative, allowing one lane of traffic to be maintained throughout construction.

Our team completed HEC-RAS hydraulic modeling during preliminary design and prepared the Joint Application for project permitting. Because the project was located within a detailed Flood Insurance Study, we targeted and achieved a no-rise certification. We also performed wetland delineation and led environmental documentation efforts. Additional work included topographical, utility, and right-of-way survey and utility coordination.