Hydraulic Loss Coefficients for Culverts (2012) / Chapter Skim
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From page 68... ...
68 8.1 Summary Composite roughness in open channel flow describes a condition where different roughness materials line different parts of a channel cross-section. Some examples of composite roughness channels include concrete rectangular or trapezoidal channels where the channel invert has been covered with sand and/or gravel as a result of sediment transport; vegetation can also be present in the channel invert.
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From page 69... ...
69 8.2 Introduction It is not uncommon in open channel flow field applications for the wetted perimeter of a cross-section to be made up of more than one roughness material [e.g., concrete channels with the invert covered in sediment, gravel, and/or vegetation or buried-invert culverts (see Chapter 2)
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From page 70... ...
70 In Equation 8-1, V is the mean velocity, Kn = 1.49 (1.0 SI units) , Rh is the hydraulic radius [the ratio of the flow area (A)
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71 Composite Manning's n (ne) Equations The 16 ne relationships listed in Table 8-1 are divided into four groups based on the main assumption used in their derivation.
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72 The experimental composite channel results were compared with the predictive ne relationships. Pillai (1962)
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73 Four boundary roughness materials were used in this study: • Acrylic flume walls and floor used as a smooth surface (see Figure 6-2) , • A commercially available metal lath sheeting material measuring ¹⁄8-in.
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From page 74... ...
74 a constant ni value for each material that corresponds to the large-Rh constant ni values shown in Figure 8-1 instead of the average ni value as used by Flintham and Carling (1992)
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latoT SMR rof seulav ne snoitauqe ni * dohtem yticoleV naeM ecroF latoT egrahcsiD latoT yticoleV raehS latoT sllaW roolF notroH hctabeloC iiksvolvaP latoT 2F latoT 3F latoT 4F rettoL rettoL II latoT Q latoT 2Q latoT 3Q DAL MDH latoT *
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From page 76... ...
Figure 8-4. Examples of experimental and Horton relationship ne versus Rh data for Type I, II, and III composite roughness channels along with the corresponding experimental ni versus Rh data: (A)
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From page 77... ...
iiksvolvaP hctabeloC notroH .gifnoC latoT 2F latoT 3F latoT 4F rettoL rettoL II Q latoT latoT 2Q latoT 3Q MDH DAL latoT 1* U latoT 2*
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From page 78... ...
78 Based on the total RMS values for Channel Type I, on average the LAD, Horton, Colebatch, Pavlovskii, Total F3, Total F4, Total U* 2, and Total U*
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