20180925 Ver 1_Justification for replacing Bridge 416 Randolph with a culvert_20180703

Justi�cation for replacing Bridge 416 Randolph with a culvert submitted by Galen Cail PE
The existing 100 Yr storm event overtops the road and the stream is in a Flood Hazard zone
(Detailed). There are houses just upstream located in both the 100 Yr floodplain and floodway. (see
attached). We could not increase backwater on any of these structures or would have to purchase the
structures. The use of a bridge here would be anticipated to be problematic, likely getting longer
resulting in additional overtopping blockage due to new bridge rail. Most likely resulting in an
increase. A culvert allows the grade to stay as low as possible and guardrail does not have to be
accounted for as blockage to flow. Culvert hydraulically is more efficient than similar bridge opening
area. Smoother concrete walls, etc.
-Small drainage area of 0.84 sq miles (540 acres) is a culvert sized drainage area. Existing bridge
functions more like a culvert than a bridge. Existing short span with timber abutments (ie does not span
channel with any overbank flow).
-An RCBC will last longer with less maintenance relative to a bridge.
Thanks
Galen