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This report presents experimental results on the conditions of initiation of an ice jam by a simple surface obstruction, on the equilibrium thickness of an ice jam formed by accumulation and submergence of ice floes, and on the compression strength of floating, fragmented ice cover. In the study on ice jam initiation, it was found that the minimum concentration of floes in the opening of the obstruction at which a jam occurs is nearly independent of the ratio of width of constricted passage to channel width, and is proportional to a negative power of the ratio of floe length to width of constricted passage. From energy analysis of floe submergence, a relationship relating the thickness of a jam formed by accumulation and submergence of floes to the approach flow characteristics was derived and found to fit satisfactorily the experimental data. In experiments on compression strength of floating, fragmented ice cover it was found that the compressive strength is inversely proportional to compression velocity and independent of cover length.

Closed-form mathematical models are formulated for the rate of development and strength of secondary current, and for bed topography in meandering, erodible-bed streams of arbitary plan form. The formulations utilize conservation of flux-of-moment-of momentum as the additional relation required to complete the formulation for the radial bed-shear stress. The secondary-flow-velocity calculation was uncoupled from the calculation of the radial mass-shift velocity and streamwise velocity distributions, which were obtained from the depth-integrated equations expressing conservation of mass and streamwise momentum. Numerical simulations were made for one laboratory flow and two Sacramento River flows with constant centerline curvature. Good agreement was obtained between measured and computed distributions of flow and depth-averaged streamwise velocity. (Author)

The principal features of the numerical model developed herein for calculation of flow and sediment-transport distributions in alluvial-river bends may be summarized as follows: i. The secondary-flow strength and the bed topography are uncoupled from the calculation of distributions of lateral shift velocity and streamwise velocity. This is accomplished by, first, calculating the secondary-flow strength on the basis of conservation of flux of moment-of-momentum, and, second, determining the bed topography on the basis of radial force equilibrium of the moving bed layer. ii. The distributions of lateral shift velocity and depth-averaged streamwise velocity are calculated, for the warped channel determined as described in step i above, from the depth-integrated equations expressing conservation of mass and momentum. It was concluded that for flows which satisfy (24), it is not necessary to include the third conservation equation, that for radial-direction momentum, or to iterate among three equations to obtain a solution. The numerical scheme utilizes the backward finite-difference method, and evaluates transverse and streamwise distributions of the radial mass-shift velocity and the depth-averaged streamwise velocity. Numerical simulations utilizing the model developed were made for one laboratory flow, two Sacramento River flows, and three different idealized channel bends. The principal conclusions obtained from the simulations are as follows: i. Generally satisfactory agreement between computed and measured results was obtained by utilizing error tolerances of E_U and E_V of 2% and 0.2%, respectively. In the absence of better information, it is recommended that alpha = 1.00 and beta = 3.50 be utilized. In instances where actual field data are available on the rate of development and equilibrium values of S_T, alpha and beta should be adjusted on the basis of the data. ii. The most cost-effective square-grid size is approximately equal to the mean flow depth. iii.

The principal features of the numerical model developed herein for calculation of flow and sediment-transport distributions in alluvial-river bends may be summarized as follows: i. The secondary-flow strength and the bed topography are uncoupled from the calculation of distributions of lateral shift velocity and streamwise velocity. This is accomplished by, first, calculating the secondary-flow strength on the basis of conservation of flux of moment-of-momentum, and, second, determining the bed topography on the basis of radial force equilibrium of the moving bed layer. ii. The distributions of lateral shift velocity and depth-averaged streamwise velocity are calculated, for the warped channel determined as described in step i above, from the depth-integrated equations expressing conservation of mass and momentum. It was concluded that for flows which satisfy (24), it is not necessary to include the third conservation equation, that for radial-direction momentum, or to iterate among three equations to obtain a solution. The numerical scheme utilizes the backward finite-difference method, and evaluates transverse and streamwise distributions of the radial mass-shift velocity and the depth-averaged streamwise velocity. Numerical simulations utilizing the model developed were made for one laboratory flow, two Sacramento River flows, and three different idealized channel bends. The principal conclusions obtained from the simulations are as follows: i. Generally satisfactory agreement between computed and measured results was obtained by utilizing error tolerances of E_U and E_V of 2% and 0.2%, respectively. In the absence of better information, it is recommended that alpha = 1.00 and beta = 3.50 be utilized. In instances where actual field data are available on the rate of development and equilibrium values of S_T, alpha and beta should be adjusted on the basis of the data. ii. The most cost-effective square-grid size is approximately equal to the mean flow depth. iii.