Route P over Maple Slough

Route P over Maple Slough was a small three-span, one-lane bridge with a deteriorating super and substructure. The traffic demand on the structure is very low and the District wanted to replace the structure with a cost effective option that maintains the needed waterway opening.  Oates developed a HEC-RAS model using the hydraulic survey completed by MoDOT and supplemented by a LiDAR survey for the overbank areas.  Our initial investigation determined that the drainage area and channel flow pattern had changed since the bridge was originally built in 1939.  The new calculated drainage area was only 25% of the area shown on the 1939 plans.  The change in drainage area was confirmed during our field check when a local maintenance worker indicated the railroad bridge upstream was removed and the water was diverted to a different channel.  This finding allowed Oates to reduce the roadway profile and shorten the replacement structure.