The changing rules of the composite roughness in drainage pipelines with sediments

Abstract The deposition of sediments with different roughness increases uncertainty in the prediction effective Manning's n (also known as composite roughness). In this paper, changing rules and influence on discharge capacity drainage pipes under flows slopes were studied by experimental measurement numerical simulation. When Froude number is less than 1, decreases gradually increase flow. more at first then It also showed that bed has a great roughness, which affects hydraulic characteristics pipe increases. water surface rises average velocity certain slope formulas for calculating are obtained analogy analysis, can provide theoretical support design pipeline.