Stream Channel Degradation and Aggradation: Causes and Consequences to Highways

摘要

Aggradation and degradation are long-term changes in stream channel elevation. The effects of gradation changes are not the same as local scour or erosion because they extend greater distances along the stream-bed. Degradation is a more common problem than aggradation and in general, has a more severe impact on highway crossings. Although gradation changes do occur naturally, human activities are responsible for the most severe cases. Channel alteration, stream-bed mining, and the construction of dams and control structures are the major causes of gradation problems. To aid in the anticipation of gradation changes the highway engineer should be aware of the principles of geomorphlogy. The simplest hydraulic analysis procedures predict the limiting slope of a gradient change based on critical shear stress of the bed material.