Railway Bridge. Norwalk, Connecticut
The State of Connecticut Department of Transportation contracted HNTB Corporation to design and engineer alternatives for the replacement of the Walk Bridge Railroad Bridge across the Norwalk River in Norwalk, Connecticut.
HNTB commissioned e4sciences to perform surface, underwater, and subsurface measurements to support these engineering and design alternatives. The objectives were to a) make measurements in the vicinity of the swing bridge to characterize the bathymetric and geologic configuration and b) locate any obstructions to construction of the replacement bridge.
e4sciences performed single-beam bathymetry, side-scan sonar imaging, sub-bottom reflection seismology, magnetic field surveys, and waterborne LiDAR surveys. Side-scan data indicate that, north of the bridge, a point bar on the eastern side of the river is accumulating soft sediment. Under the bridge, the reflectivity of the acoustic signal increases in the channels east and west of the turntable pier, indicating that the soft sediment has been scoured. There are wooden pilings on the channel floor in the western channel. Other debris was found close to the Walk Bridge.
The side-scan images reveal cables along the shore and across the channel. The sub-bottom reflection seismic data shows that rock is around 75 to 90ft deep. Pipelines and cables cross the channel north and south of the bridge. The magnetic field density map is complicated by the presence of many steel structures in the channel. The LiDAR data mapped the bridge superstructure, pilings, docks, and structures along the shore.