Consideration of Stream Morphology in Culvert and Bridge Design

In 1992, the Maryland State Highway Administration (SHA) initiated new design procedures to limit the impact of constructing culverts and bridges in streams. Elements of the new procedures included studies to define the characteristics of Maryland streams regarding bankfull widths, depths, and discharges; training of engineers in basic and advanced courses in stream morphology presented by David Rosgen; and updating the SHA culvert design manual to address consideration of stream morphology, fish passage, and other environmental features. The revised design procedure emphasizes the need to identify all appropriate objectives at the start of the design process so the best overall solution can be determined. The design concept is to construct a stream system that is stable and that neither scours nor aggrades. Elements of this approach include maintaining the consistency of dimension, pattern, and profile of the stream with particular attention given to maintaining bankfull width and width/depth ratio. Flood plain culverts are provided where appropriate to relieve the hydraulic load on the main channel culvert to limit downstream scour and erosion. Several culverts recently were constructed by using the stream morphology concepts discussed. These initial efforts have been quite successful and indicate that it is practical to consider stream morphology concepts in culvert design.