Bed material load

Abstract: CONTENTS Page Introduction. 1 Approach to the problem. _ 3 Limitation of the bed-load function _ _ _ 4 The undetermined function 4 The alluvial stream. 5 The sediment mixture 6 Hydraulics of the alluvial channel. 7 The friction formula 7 The friction factor 8 Resistance of the bars 9 The laminar sublayer 10 The transition between hydraulically rough and smooth beds_ 12 The velocity fluctuations 13 Suspension 14 The transportation rate of suspended load 17 Integration of the suspended load. _ 17 Numerical integration of suspended load 19 Limit of suspension. 24 The bed layer 24 Practical calculation of suspended load___ ____ 25 Numerical example 26 Page Bed-load concept 29 Some constants entering the laws of bed-load motion: 31 The bed-load equation 32 The exchange time 33 The exchange probability 34 Determination of the probability V 35 Transition between bed load and. suspended load 38 The necessary graphs 40 Flume tests with sediment mixtures.. 42 Sample calculation of a river reachl 44 Choice of a river reach 45 Description of a river reach_____ 45 Application of procedure to Big Sand Creek, Miss 46 Discussion of calculations 60 Limitations of the method____ 65 Summary. 67 Literature cited 68 Appendix 69 List of symbols. 69 Work charts _ 71

Abstract: A method is presented which enables the computation of the suspended load as the depth-integration of the product of the local concentration and flow velocity. The method is based on the computation of the reference concentration from the bed-load transport. Measured concentration profiles have been used for calibration. New relationships are proposed to represent the size gradation of the bed material and the damping of the turbulence by the sediment particles. A verification analysis using about 800 data shows that about 76% of the predicted values are within 0.5 and 2 times the measured values.

Abstract: The relationship of sediment transport to fluid flow is considered. Physical reasoning leads to dimensionless groupings of the variables which are different for coarse sediment and for fine sediment, because of dissimilar modes of transport. This concept provides a basis for a new analysis of data from flume experiments, and a method for dealing with transitional sizes of sediment is suggested. The analysis of experimental data supports the theory put forward and predictive equations are derived which relate total sediment flux to measurable properties of flow. A preliminary comparison is made with observations from other sources, including natural rivers.

Abstract: Stripping of the vegetation and soil from a 13-hectare site in Virginia underlain by coastal plain sediments created a rapidly evolving badland topography. Two types of channels developed: (1) sand-bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff, but they also generally eroded their beds slowly, and (2) steeper, bedrock-floored channels incised rapidly. In bedrock channels the erosion rate was proportional to the 4/9ths power of drainage area and the 2/3rds power of gradient. These exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows. Due to rapid mass wasting and reduced runoff, the alluvial channels became as much as 50% steeper during the winter than the summer, with an attendant yearly cycle of winter aggradation and summer entrenchment. The gradients, their seasonal variability, and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads. The hydraulic geometry of alluvial channels in the Virginia badlands were similar to that on the Morrison Formation in the western United States.