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Thesis

2012

M.Sc. Thesis Title: “Bed Stripped Roughness Effect on Flow Measurements in Trapezoidal Channels with Free Overfalls”.

2012-05-09
In the present investigation, the effects of side slopes, bed slopes and bed roughness on the flow over free overfalls in trapezoidal channels have been studied experimentally. For this purpose, three models of trapezoidal free overfall channels have been built and tested in a laboratory flume. These models had 0.1 m bed width and 3.7 m length with different values of side-slope (m = 0.268, 0.577, and 1). Each model had four different bed slopes (S = zero, 0.0033, 0.01, and 0.02). For each slope, the bed was roughened with artificial strips of 10 cm long and a square cross section 0.6 cm × 0.6 cm arranging eight roughness patterns with eight longitudinal centre to centre spacing between strips of (L =1.2 cm, 2.4 cm, 4.8 cm, 9.6 cm, 19.2 cm, 38.4 cm, 76.8 cm, and 153.6 cm). The experimental testing program included thirty-six series of experiments for each model. Four of them were for smooth beds and thirty￾two for rough beds. A total of one hundred and eight series of the experiments were tested for different ranges of Froude number. Experimental results of all models showed that the variations of ሺܳ݉ଵǤହȀඥܾ݃ହሻ with ሺ݉ݕ௕Ȁܾሻ for smooth and rough beds, different bed slopes and various roughness patterns are simple power equations. It was observed that the values of ሺܳ݉ଵǤହȀඥܾ݃ହሻ increase with the increase of ሺ݉ݕ௕Ȁܾሻ values. The correlations between ሺ݉ݕ௕Ȁܾሻ with ሺ݉ݕ௖Ȁܾሻ were found to be linear for smooth and rough beds of different bed slopes and roughness patterns. The ratio ሺݕ௕Ȁݕ௖ሻ decreases with the increase of slope (S) for smooth and rough beds with an average value of 0.729 for subcritical and supercritical flow on smooth beds of different slopes. Two main power empirical expressions were obtained one for the variation of (ܳ݉ଵǤହȀඥܾ݃ହሻ with ሺ݉ݕ௕Ȁܾሻǡ and (S) for the free flow over smooth beds and the second for the variation of (ܳ݉ଵǤହȀඥܾ݃ହሻ with ሺ݉ݕ௕Ȁܾሻ and (S/n) for the free flow over rough beds. The results of the present study have been compared with theoretical and experimental results obtained by other investigators showing well agreements. For all models of different bed slopes roughened with strips, it was observed that the maximum roughness appears to occur at roughness concentration equals to 0.125.

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