Kittur G. Ranga Raju

Estimation of temporal variation of sediment yield using GIS

Abstract A GIS-based method is proposed for computation of temporal variation of sediment yield during isolated storm events. Data from three Indian catchments, namely Karso and Nagwa in Jharkhand and Kharkari in Rajasthan, have been used. The Integrated Land and Water Information System (ILWIS) GIS package was used for (a) catchment discretization into cell areas using grid networks, (b) evaluation of the spatial variation in catchment topographical characteristics and land use, and (c) presentation of the results obtained. The process of sediment delivery from grid cells to the catchment outlet is represented by the topographical characteristics of the cells. Unit sediment graphs for the catchments are derived by translation of the sediment yield from the grid cells and routing through a linear storage reservoir. The proposed method is found to provide satisfactory estimates of the temporal variation of sediment yield during isolated storm events. The total sediment yield of a storm event may also be computed using the proposed method.

Rapidly varying transient flows in alluvial rivers

Extensive changes can occur in alluvial river morphology over relatively short time periods due to such extreme events as a flash flood or flood resulting due to dam break or dike failure. In the present paper the results obtained through the application of a fully coupled one-dimensional alluvial river model are presented for simulation of such sharp hydraulic and bed transients in an alluvial river. Here the governing system of partial differential equations was discretized by making use of the generalized Preissmann finite difference scheme. The resulting set of non-linear partial difference equations was solved by using Newton Raphson iterative procedure in which the solution for banded matrix of Jacobians was obtained through a hexa-diagonal solution algorithm. The model presented herein has been validated through a number of proofs of the concept tests and by simulating the Quail Creek Dike failure which occurred on 31 December 1988 and 1 January 1989 in Washington County, Utah, USA. The present model was further extended to simulate the processes of grain sorting, wash load transport and non-equilibrium sediment transport. The results obtained from these simulations are presented in this paper.

Suspended Wash Load Transport of Nonuniform Sediments

The results of an experimental study on transport of suspended wash load through a coarse-bed stream are presented. The experiments were conducted under different concentrations of fine suspended sediment (wash load of uniform size, 0.064 mm diameter) and with three different coarse-bed sediments: two having uniform sizes and one with nonuniform size distribution. For any equilibrium concentration of wash load in suspension, a definite proportion of the wash material was observed to be present within the bed material. No difference is found in this regard between wash load and suspended load transport. Therefore, the relationship, as stated by Samaga et al., for the parameter representing sheltering—exposure and interference effects in the suspended load transport of nonuniform sediments was applied in a modified form by using the present data and the data collected from the literature.

Experimental and mathematical investigation for infiltration of fine suspended sediments into surface layer of bed material

Abstract Fine sediment coming to the channels from the catchment during period of heavy rainfall flows in suspension and interacts with the channels’ bed material and gets deposited into the pores of the bed. Experiments have been carried out to study this process by using a 30 m long, 0.20 m wide and 0.5m deep tilting laboratory flume. Two uniform and one non-uniform sediments were used as bed material. The deposition of fine suspended sediment of size 0.064 mm within the pore space of the surface layer of coarse sediment of the channel bed was studied under different equilibrium concentrations of suspended load in the flow. The bed material was moving as bed load only under the hydraulic conditions of the experiments. The porosity of surface layer of stream bed material got reduced due to deposition and subsequent sheltering of fine sediment within the pores of the coarse bed material. A basic mathematical model to quantify the reduction in porosity of bed material due to the process of deposition is developed and applied to compute the porosity of the bed material for different equilibrium concentration of fine sediment in the flow.