Collier was tasked to review a deteriorated corrugated metal pipe (CMP) underneath Oakley Drive. The infrastructure was original to the development of the neighborhood and very much in need of repair. However, this was determined to be a structure for a probable stream and introduced Tennessee Department of Environment and Conservation (TDEC) and Army Corps of Engineers (ACOE) regulatory oversight to the project. This decision was made to bypass the task of determining if the conveyance was a stream, saving Metro dollars and accelerating the design process. State and federal permitting and watershed analysis were required to comply with these regulations. Collier stormwater design staff analyzed the regional hydrology of the associated 225-acre watershed to ensure that the proposed slab bridge would be properly designed. Collier personnel compiled the needed resources and documents for the Aquatic Resource Alteration Permit (ARAP) and the ACOE permit and collaborated with MWS personnel to complete the documents that were subsequently reviewed and approved.

This design required the simple upsizing of an undersized culvert; however, a more complicated slab bridge/culvert was recommended during the design process to alleviate flooding issues and maintenance requirements. Collier worked internally with our structural department to select the appropriate slab culvert design and footers.

As the project moved towards construction, it became imperative to coordinate with utility owners and the contractor to ensure this project's timely construction. The ARAP included time limits on the construction of a temporary stream diversion. Having coordinated with utility companies during and after design, Collier was able to mitigate construction issues, saving MWS time and money for that process's duration.

As is typical with many slab culverts, the presence of solid bedrock on which to set the footing is not known until construction begins. Therefore, our design solutions always incorporate multiple solutions to accommodate multiple field conditions. Collier once again provided prompt service to complement their design by coordinating, guidance, and field investigation to examine the geotechnical aspect of the civil engineering design. Collier’s in-house geotechnical staff reviewed the field conditions to determine the suitability of the foundation for the slab bridge, ultimately providing the contractor with a timely recommendation and direction for the construction of the slab bridge.

Client: Metro Nashville Water Services