GABIONS USED IN STREAM GRADE-STABILIZATION STRUCTURES: A CASE HISTORY

Streams in western Iowa have been degrading since the turn of the century and this entrenchment has endangered many highway and railroad bridges. Although grade-stabilization structures have been effective in controlling this erosion, the cost of reinforced-concrete structures has risen to the point that less expensive materials need to be considered. In an effort to evaluate alternative materials for this purpose, a gabion drop structure was designed and built and its performance monitored for 2 years after completion. The demonstration structure has performed satisfactorily with minimal differential settling and minor erosional problems downstream of the structure. Sedimentation occurred upstream of the structure during construction but little additional sediment has accumulated since. A cost analysis that normalizes several variables is used to compare the gabion structure with concrete structures and indicates that the cost of building the gabion structure was about 20 percent of that of a comparable-size concrete structure. It is concluded that this type of structure is an effective and economic alternative.