ABSTRACT
A follow-on case study revisits the site of a small highway bridge crossing an ephemeral stream in an arid area of Texas with little hydrologic information. The bridge has presented chronic problems and maintenance issues for years because of stream instability. The bridge is at US Highway 62—180 where it crosses Guadalupe Arroyo in Culberson County. Texas.
Bed load sediment transport through the reach adjacent to the bridge appears inhibited. The authors originally concluded that the inhibition of bed load sediment movement through the bridge reach must be addressed for any solution to be effective; sediment accumulated since construction in 1959 must be allowed to disperse downstream, and sediment arriving at the site in the future must pass the reach without further accumulation upstream of the bridge. The authors conjectured engineered solutions that failed to address the inhibition of sediment movement through the reach by restoring stream geometry to a condition favorable to bed sediment movement would doom conventional approaches such as bank armoring to continued failure. Despite these recommendations, a construction project intended to stabilize the situation using only conventional bank armoring took place in 2009. This continued case study involves revisiting the site as it exists in 2017, and documenting the performance of those measures under conditions of extreme bed load sediment movement. The original case study was presented at the 7th TRB International Bridge Engineering Conference in San Antonio, Texas.
The authors find that this provides a unique opportunity to examine both the performance of bank armoring in areas of extreme bed sediment load, and document the stability state of the stream at another point in time, eight years after the original data was collected. A more complete understanding the interaction of roadway bridges with the geomorphic environment in which they exist is essential for their long-term performance and survival.
