R. J. Garde

Resistance Of Two Dimensional Triangular Roughness

Measurements of shear and pressure distribution on smooth and sand coated two-dimensional triangular elements, simulating ripples and dunes, have been reported. Relations have been derived for the local and average skin shear coefficients in terms of the geometry of the elements and the flow Reynolds number. The local pressure coefficient and the form drag coefficient have been related to the relative roughness and the geometry of the elements. Analysis of the data has shown that the grain resistance of undulated beds calculated by the existing methods is generally greater than the measured average grain resistance of the bad. A large amount of alluvial channel data show agreement with the relation for form drag of the two-dimensional triangular roughness.

Experimental study on characteristics of flow past porous fences

Abstract The drag coefficient of a two-dimensional porous fence placed in a turbulent boundary layer is shown to be a function of the porosity and the ratio of the fence height to a parameter characterising the roughness of the approach boundary. A similarity approach has been employed to analyse the data of the turbulence velocities on the leeside of the fence.

Live-bed scour around cylindrical bridge piers

Considering the primary vortex in front of the pier to be the prime agent causing scour at bridge piers, a scheme has been proposed for computation of the temporal variation of scour depth during live-bed condition. An equation has also been developed for the computation of maximum scour depth around circular bridge piers in uniform sediments during live-bed condition. The equation follows logically from the scheme proposed for the computation of the temporal variation of scour. The effect of unsteadiness of flow on scour depth has been also studied.

Design of settling basins

Experiments have been carried out in the laboratory concerning the efficiency of settling basins. The data indicate that the existing methods of their design are not satisfactory. Analysis of all t...

Criterion for Deposition of Sediment Transported in Rigid Boundary Channels

Lined channels are used in irrigation and hydropower systems with the object of minimising seepage losses and conserving the available head. Concrete tunnels are also used in sediment excluders and extractors to carry flows with high sediment concentrations. When sediment-laden water enters such channels, an important design requirement is that the sediment entering the channel should not deposit on the bed. This means that the sediment transporting capacity of such channels should be greater than or equal to the rate at which the sediment is entering the channel. Although the laws of sediment transportation for alluvial channels are fairly well known,enough information is not available concerning the sediment carrying capacity of rigid boundary channels. Since wash load transport involves negligible exchange of sediment particles at the bed, the problem of determination of maximum wash load transport without objectionable deposition is closely related to the above problem. There is thus need to study the sediment transport capacity of rigid boundary channels.

Concentration distribution of sediment mixtures in open-channel flow

Rouses equation and some of the recently developed equations for concentration distribution in the case of flow in an open channel have been checked for their accuracy with the help of data ofsuspended-sediment concentration-distribution of the individual fractions in a mixture. The agreement between predictions and measurements is not found to be satisfactory. It is found that the sediment distribution exponent for any size in the mixture is not constant over the whole depth of flow. A two-layer model is accordingly suggested herein to describe the sediment distribution in the vertical. A predictor for the reference concentration at 0.2D is also suggested. The model showed satisfactory agreement with the measurements on the Rhine river and the Middle Rio Grande river.

Velocity distribution in alluvial channel flow

The velocity distribution equations which have been developed recently on the basis of data of sedimentladen flow over a rigid plane bed are checked with experimental data of flow over alluvial beds of sediment mixtures and found to be unsatisfactory for this case. Making use of the present set of data and the data collected by other investigators, a two-layer model of velocity distribution over alluvial beds has been developed. The model shows good agreement with field measurements of the Rhine and the Middle Rio Grande.