To implement the generation and decay of secondary flow in steady or quasi-steady nearly-horizontal flow models an approximative method is proposed which takes account of the convection of momentum of secondary flow in streamwise direction. The method is employed both for the effects of Coriolis acceleration and curvature. It is shown that both effects are almost equivalent. The method is verified by comparison with results obtained in various flumes of rectangular or almost rectangular cross-section. The agreement between theory and experiments for the intensity of the secondary flow is quite satisfactory, although the theory presented cannot reproduce each detail. RESUME Afin d'incorporer la generation et Pamortissement des courants secondaires dans les modèles d'écoulement quasi-horizontaux en régime permanent ou quasi-permanent, une methode approximative est proposée qui prend en compte la convection de la quantité de mouvement de l'écoulement secondaire dans la direction principale de l'écoulement. La methode est appliquée a la fois aux effets de l'accélcration de Coriolis et de la courbure. Il est montré que les deux effets sont pratiquement equivalents. La methode est vérifiée par comparaison a des résultats expérimentaux obtenus dans divers canaux de section rectangulaire ou quasirectangulaire. On constate un accord satisfaisant entre theorie et experiences pour l'intensité du courant secondaire, bien que la theorie proposée ne puisse reproduire chaque détail du phénomène.

SummaryThe mathematical model presented describes the flow in rivers of which i the depth~s small compared with the width,ii the width~s small compared with the radius of curvature,

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In the present investigation the influence of bottom slope on mass transport by progressive waves was investigated, both theoretically and experimentally. Theoretical considerations based on linear wave theory show the greatest influence of the slope on the bottom drift velocities for relatively long waves and steep slopes. The numerical values, however, remain rather small (influence less than 20%). In addition, the experiments show that the bottom drift velocities are more determined by the local parameters than by the magnitude of the bottom slope m the cases examined. Considering the net bottom velocities, the discrepancy between the horizontal bottom theory (Longuet- Higgms) and experimental results is considerable. Taking into account the first harmonic of the local wave form and the small slope effect for relatively small depths in horizontal bottom theory does show, however, the same tendency as the experimental results.

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