United States Department of Transportation
i
Stream channel degradation and aggradation : analysis of impacts to highway crossings.
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1981-03-01
[PDF-23.54 MB]
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OCLC Number:820578699
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Abstract:"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, streambed mining, and the construction of dams and control structures are the major causes of gradation problems. Every alluvial river in the U.S., has a potential for gradation change. The prevalence of human activities as chief cause of gradation changes means many rivers suffer to some degree. To aid in the anticipation of gradation changes the highway engineer should be aware of the principles of geomorphology and river mechanics. Analysis procedures for predicting aggradation and degradation can be simple or complex. The simplest techniques are qualitative in nature, involving the application of geomorphic concepts. The most complex techniques involve the analysis of entire drainage systems using detailed dynamic computer modeling of water and sediment transport processes. Between these two extremes are numerous quantitative techniques involving geomorphic and basic engineering relationships as well as some simpler modeling techniques."
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