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Investigation of the Effect of Manning Roughness on Froude Number in Subcritical Flow

Aqeel Al Adili

Abstract


Knowing of flow resistance in channels is necessary for many purposes such as the estimation of stage-discharge relationship. All relationships between Froude number (Fr ) and Manning’s roughness coefficient (n) lead to obtain useful information in design, implementation, minimisation of the construction cost, and design the economical section. The goalnof the present work is to investigate experimentally the effect of Manning roughness on Froude number in open channel in subcritical flow, as well as, to establish some relations between different parameters. Three different cases have been adopted in this study. The first one is experimental tests on open channel laboratory flume, the second is to predict relationships from the concrete lining irrigation canal and the third procedure conducted in a selected reach of a natural stream main outfall drain (MOD) project as a case study. In the experimental tests on open channel laboratory flume, the relationship between Fr and n gave a good relationship and a good agreement with the observed values. Also, the results showed that the values of Manning’s roughness coefficient in the channel sides are greater than in the middle of channel. In the lined irrigation canal, the relationship between Fr and n appears as a polynomial relation of the fourth degree and a moderate relationship between them. However, Fr and n gave a significant relationship in the two regions in MOD, and gave a good agreement with the observed value. This study reveals a general equation that can correlate the Froude number with friction factor.

Keywords


froude number, manning’s roughness coefficient, concrete irrigation canal, main outfall drain, subcritical flow

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References


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