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Dimensionless ratios for surge waves in open canals Wu, Henry Jaw-Here

Abstract

This study investigates the propagation of a surge wave in a power canal following load rejection or reduction. Dimensionless relationships are derived to predict (a) the initial wave height, (b) the variation of the wave height along the canal and (c) the maximum stage of water depth at the downstream end for straight prismatic canals of rectangular, triangular and trapezoidal cross-sections. The effects of various parameters, such as velocity and depth of initial flow, frictional coefficients, bed slope, cross-section of the canal, distance of wave propagation and initial wave height of the surge are studied. A computer program is developed for the calculations required. It is found that, as a positive surge propagates along the canal, the wave height decreases linearly with distance for a short canal, according to an exponential function for a long canal. An approximate logarithmic relationship is also found between the variation of wave height of a positive surge and canal cross-sectional parameters. The variation of water depth at the downstream end of the canal is not linear with respect to time. An almost linear relationship between the maximum water depth at the downstream end of the canal and the length of the canal is noted. The dimensionless relationships derived in this study may be used to establish design criteria for crest elevations of the banks and walls of power canals to avoid overtopping.

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