Abstract: : An alluvial river adjusts the dimensions of its channel to the wide range of flows that mobilize its boundary sediments. However, in man)' rivers it has been demonstrated that a single representative discharge can be used to determine a stable channel geometry. The use of a single representative discharge is the foundation of "regime" and "hydraulic geometry" theories for detennining morphological characteristics of alluvial channels and rivers. This representative discharge has been given several names by different researchers including dominant discharge, channel forming discharge, effective discharge, and bankfull discharge. This has led to some confusion. The channel forming discharge and the dominant discharge are equivalent and are defined as a theoretical discharge that if maintained indefinitely would result in the same channel geometry as the existing channel subiect to the natural range of flow events. Although conceptually attractive, this definition is not necessarily physically feasible, because bank line vegetation, bank stability and even the bed configuration would be different in a natural stream than in a constant discharge stream. Channel-forming discharge concepts are applicable to stable stream systems, i.e., streams that are neither aggrading or degrading. Channel-forming discharge can be estimated using one of three prescribed methodologies. One such deterministic discharge is the bankfull discharge, which is the discharge that fills the channel to the top of its banks. Another deterministic discharge used to represent the channel-forming discharge is a specified recurrence interval discharge, typically between the mean annual and five-year peak. This report focuses on a third approach to determine the channel-forming discharge, known as the effective discharge. The effective discharge transports the largest fraction of the bed material load. Because of this, the effective discharge can be a good estimator for channel-forming discharge.

Abstract: he present study describes field surveys of bed material, findings based on surveyed data and bed variation in a downstream reach, 0km to 37km, of the Kizu River. Field data realize that the river bed elevation changes longitudinally like riffle-pool bed profiles, coarse gravel are dominant in the riffle region, sand particles are deposited deep in the pool region, and sediment particles of pool region are transported from upstream as over-passing load or as selectively entrained sediment on riffle bed. The formula of grain size distribution which is employed in numerical simulation of river bed variation as the upper boundary condition of the study reach is proposed, taking account for the difference between grain sizes in riffle and pool regions as well as for characteristics of bed load transport such as over-passing load.

Abstract: Previous investigations of non equilibrium and equilibrium sediment transport are analyzed and a two dimensional mathematical model of non equilibrium sediment transport in river channels with non uniform bed material is presented. The concept of exchange rate of bed material is introduced, and a very short time step is used in the calculation. The main reason why the sediment recovering equilibrium distance for the non uniform bed material is far longer than that for uniform bed material is discussed. Because the size composition of surface bed material is coarsened, the scouring of finer sand is far less than that for the initial state and the distance of non equilibrium sediment transport becomes much longer. A slower exchange rate of bed material then leads to a longer distance of non equilibrium sediment transport.

Abstract: Based on the characteristics of sediment,the authors put forward that the coast with the sediment diameter between 0.03mm to 0.12mm is categorized as the silty sand coast,and its characteristics are studied by experiments.The results show that the characteristics of sediment in silty sand coast is related not only to the sediment diameter,but also to the size distribution.When it contains much more cohesive particles the overall characteristics are that of mud.When it contains less cohesive particles the overall characteristics are that of loose sand particles.The former is suspended load movement and the latter are suspended\|load and bed load movement.For the bed load movement,the rate of transport is related not only to the dynamic condition,but also to the sediment diameter.In the same dynamic condition,the finer the sediment,the smaller the rate of bed load transport will be.

Abstract: The experimental result on wash load transport is reported in this paper. It shows that not only the grain size and flow intensity, but also the concentration of fine material plays important role on its mutual transformation between wash load and bed material load. The experiment demonstrates that there exists a maximum trasport capacity of stream for wash load under which fine material keeps its fraction in bed as zero and plays no part in river evolution process. Based on the theory established in Part Ⅰ of this paper, formulas for stream's maximum transport capacity of stream wash load and criterion for distinguishing wash load from bed material load are proposed. Comparison between the calculation result of the formula and the field data shows that the agreement is satisfactory.

Abstract: According to the characteristics of non-uniform bed load with a wide size distribution, a new concept and the corresponding computation method of the armoring degree for the bed material with a wide size distribution are introduced to reflect the difference of sediment transport rate in the armoring process of bed material. Based on the field data of sediment particle exposure, a parameter, which changes with the armoring process, is used to describe the degree of armoring process. The influence of the armoring degree on the non-uniform sediment transport rate is discussed, and the corresponding computation method is also obtained.

Abstract: The movable bed phenomenon constitutes a complicated system in which the flow, the bed-material load and the bed shape interact with each other. In the present paper, a study onthis mutual interaction system has been performed. However, an interaction between turbulent flow and bed-material load has not been so investigated, because it is very difficult to conduct turbulence measurements in sediment laden flows. In the present study, turbulence measurements were conducted using LDA in sediment laden open channel flows, and bed-material load was also measured by PIV.

Abstract: Channel forming process under the condition of no sediment discharge was investigated with both flum experiments and numerical simulations. In addition to the degradation of bed -elevation, natural channel can change its width relatively within short time, in the process. The experimental results revealed that the relatively short time for channel widening firstly occurs, and then the bed-slope gradually adjusts to the static equilibrium condition with no significant change of the channel width. The numerical model to simulate the channel forming process, which is constituted by the depth-averaged 2-D flow model with the non-orthogonal boundary fitted grid system and the bed -deformation model taking into account the collapse of the bed -material on side banks, can reproduce the process observed in the experiment.

Abstract: Sand-bed rivers form deltas when they reach standing bodies of water such as lakes and reservoirs. Most sand-bed rivers carry much more mud as wash load than they do sand as bed material load. Deltas typically form so that the sand falls out fluvially in a low-slope topset deposit and avalanches to form a much steeper prograding foreset deposit. The mud deposits out in a low-slope bottomset on the bed the lake or reservoir. Here the case of a sand-mud delta with co-evolving parts is treated numerically using a moving-boundary technique. Although the results reported here are preliminary, the simulated morphology shows a striking resemblance to e.g. the delta of the Colorado River in Lake Mead.

Abstract: Detailed information concerning the rate and particle size distribution of bed material transport by streamflows can be very difficult and expensive to obtain, especially where peak streamflows are brief and bed material is poorly sorted, including some very large boulders. Such streams, however, are common in steep, arid watersheds. Any computational approach must consider that (1) only the smaller particle sizes present on the streambed move even during large floods and (2) the largest bed particles exert a significant form drag on the flow. Conventional methods that rely on a single particle size to estimate the skin friction shear stress acting on the mobile fraction of the bed material perform poorly. Instead, for this study, the skin friction shear stress was calculated for the observed range of streamflows by calculating the form drag exerted on the reach-averaged flow field by all particle sizes. Suspended and bed load transported rates computed from reach-averaged skin friction shear stress are in excellent agreement with measured transport rates. The computed mean annual bed material load, including both bed load and suspended load, of the East Fork Virgin River for the water years 1992-1996 was approximately 1.3×10 5 t. A large portion of the bed material load consists of sand-sized particles, 0.062–1.0 mm in diameter, that are transported in suspension. Such particles, however, constituted only 10% of the surface bed material and less than 25% of the subsurface bed material. The mean annual quantity of bed load transported was 1060 t/yr with a median size of 15 mm.

Abstract: Laboratory and river data has been analyzed in terms of applied power principles to determine the relationships between absolute roughness and bed deformation under steady state sediment transport conditions. It has been found that the full spectrum of bed conditions can be represented by simple relationships within a single system. As the bed forms grow, the unit stream power being applied along the bed decreases. The process of deformation continues until equilibrium is reached. Dynamic equilibrium is reached with the average rate of deposition of particles equal to the rate of re-suspension. By expressing the applied power in terms of the size of the boundary eddies i.e. the bed form sizes and comparing this with the power required to suspend the sediment particles, the link is obtained between absolute roughness and particle characteristics. Transition from lower regime conditions to upper regime conditions is initiated when the applied (laminar) power along the bed becomes greater than that which is ...