Moses Wheeler Bridge Hydraulics
I-95 over the Housatonic River – Milford/Stratford, CT

GM2 prepared a hydrologic, hydraulic, and scour susceptibility study relating to the reconstruction of the Moses Wheeler Bridge, carrying I-95 over the Housatonic River between Stratford and Milford in the state of Connecticut.

Due to the close proximity of the Moses Wheeler Bridge and the Metro-North Railroad Bridge ("Devon Bridge"), plus the existing scour susceptibility of the Devon Bridge, a detailed hydraulic analysis of this reach of the river was required. This analysis involved the use of the ACOE computer program HEC-RAS to evaluate and compare water surface profiles and velocities for the existing, proposed, and temporary (during construction) conditions. The unsteady flow component was used to perform a basic one-dimensional tidal hydraulic analysis of the daily tide cycle and the associated possible storm surges.

In order to perform the required detailed hydraulic analysis in the vicinity of the two bridges, a two-dimensional tidal hydraulic analysis needed to be employed. This was possible with the Surface Water Modeling System (SMS Platform) running Finite Element Surface Water Modeling Software (FESWMS). The boundary conditions for this two-dimensional hydraulic analysis were developed with unsteady flow analysis with the HEC-RAS program.

Scour evaluations for both bridges were prepared with recommendations for foundation design for the Moses Wheeler Bridge. The scour evaluation was completed in accordance with HEC-18 "Evaluating Scour at Bridges" and followed the mechanics of evaluating scour for complex piers in relation to the pier stem (single or multiple), pile cap or foundation and the pile group.

Based on the results of the study, a determination of the impacts of the proposed Moses Wheeler Bridge on the existing Devon Bridge with regards to the stage, velocities and predicted scour depths (with a discussion of scour countermeasures) was presented in a detailed technical report.

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