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Nigerian Journal of Technology

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The Effects of Off Take Angle on the Velocity Distribution and Rate of Siltation of Canals

JC Agunwamba, CC Nnaji

Abstract


The problem of excessive siltation in canals (navigation, irrigation, water supply, etc) was tackled by the Schwarz-Christoffel transformation, neglecting gravity and assuming a constant depth of flow. This implies that large off take angles will encourage more intake of sediments by the canal. In addition, it was also observed that large off take angles exhibit higher and lower (wider range) velocities. That is, near the stagnation point, a large off take angle will posses lower velocities than small off take angles thus encouraging siltation, while near the point of infinite velocity, a large off take angle will posses higher velocities thereby increasing sediment intake by canal. It is therefore recommended that canals off take angles should be as small as possible but not too small. If the off take angle is too small, the bank between the branch canal and the main canal will be eroded gradually leading to flooding and eventual destruction of the canal. The results obtained can be applied to navigation, irrigation and water supply canals. The results obtained show that the larger the off take angle, the higher will be the off take discharge as well as the off take entrance velocity distribution. The results were found to agree with both laboratory data obtained using a model and field data, giving correlation coefficients of 0.76, 0.77 and 0.62.



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