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Fluvial hydraulics is complex because the velocity, slope, depth, and channel roughness are all subject to change. The unit stream power, defined as the rate of potential energy expenditure per unit weight of water, required to transport a given sediment load is sensitive to water depth when the sediment concentration is low. The interdependence between unit stream power and water depth decreases as sediment concentration increases. A computer program is used to generate different combinations of velocity, slope, depth, and unit stream power for a given sediment load. The generated unit stream power in the lower flow regime either has a clear minimum value at a particular depth or approaches a minimum value for a given sediment load. These agreements suggest that an alluvial channel in the lower flow regime adjusts its velocity, slope, depth, and roughness in such a manner that a given sediment load can be transported with the minimum amount of unit stream power.

Basic fluid mechanics and turbulence theories are applied to show that suspended sediment concentration at a given depth of an open channel flow is a function of the turbulence energy production rate at that depth. Depth-averaged suspended sediment concentration can be obtained by integrating a function of the turbulence energy production rate over the depth of flow which in turn is a function of unit stream power. Total sediment concentration can also be expressed as a function of unit stream power following the foresaid and a procedure similar to that proposed by Einstein. Comparisons of seven total load equations indicate that equations derived from the concept that the rate of sediment transport should be related to the rate of energy dissipation of the flow are more accurate than other equations for both laboratory flumes and natural rivers.

Electronic computers are opening up the field of sedimentation engineering by permitting the analysis of problems which heretofore have required too much time and effort. Movable stream bed profiles are being calculated in addition to water surface profiles. The initial gradation of sediment material in the stream bed may be prescribed to facilitate the calculation of an armor layer. This gradation is continually changed by the computer program in response to sediment particles being deposited on the stream bed and material on the stream bed being removed to satisfy transport capacity. Hydraulic sorting of sediment by grain size is accomodated. The stream bed does not have to be represented by a single grain size. Retardance of motion because of armor layer is calculated.

Some difficulties arise in predicting the stream morphology and sediment runoff, in and from a sediment deposited area typical in mountain streams, because a stream channel often forms in the restricted region and changes its course. This paper describes the mechanism of a stream formation and the relation between the sediment runoff and the process of a stream change. A mathematical model, which is useful for a regime criterion of channel formation as well as for calculating the cross-sectional shape of a stream, is presented, and applies to the flume tests. Numerical predictions are made with modified one-dimensional model for the sediment runoff and channel variation, and compared with data obtained from a flume experiment.

The rate and extent of bed aggradation resulting from sediment overloading are determined by means of computer‐based numerical experiments. A nondimensional momentum equation, along with continuity equations for water and sediment of unsteady flow for a wide, prismatic channel, are solved numerically using recently developed relations for sediment discharge and friction factor. Numerical experiments are executed for a range of values of nondimensional input data. Principal dependent variables, such as changes in bed levels from equilibrium levels and the length of aggradation, determined from the computer experiments are correlated by multiple linear regression analysis to the independent nondimensional variables. Numerical results show that the sediment diffusion coefficient is a function of the rate of sediment overloading. The agreement between the numerical results and the available experimental data is satisfactory.

The behaviour and form of, and bedload sediment transport through, a 3.5 m wide forest stream have been monitored for nearly three years. Bedload transport is highly episodic and spatially variable, and is controlled less by water discharge than by sediment availability. Organic debris in the channel creates temporary base levels and sites at which coarse sediment may remain stored for long periods; collapse or disruption of log and debris jams makes sediment available for transport in only a small proportion of the runoff events that are actually competent to move the material. Even then, sediment travels only a short distance before being redeposited, frequently behind debris accumulations further downstream. Rates of sediment transport during a given runoff event can vary markedly over short distances along the stream, again depending on whether sediment was made available for transport by log jam collapse upstream. Organic debris is therefore a major constraint on the application of physical laws and theories to explaining sediment movement in, and the morphology of, this stream.

Channel patterns of sand-bed rivers have been analyzed using the concept of minimum stream power together with formulas for flow resistance and sediment transport. A diagram has been constructed, on the plane of water discharge vs. valley slope, dividing regime rivers into straight, meandering, and braided patterns in plan configuration. The analytical diagram is supported by river data and previous observations. For the given water discharge Q and sediment load Qs, the stable channel geometry and slope were obtained from the stream power analysis, wherein a stable configuration is assumed to correspond to a minimum stream power per unit channel length. For small values of Q and Qs, the analysis shows that a unique minimum exists, indicating a unique stable channel configuration and slope. With this unique stable channel slope equal to the valley slope, the channel pattern is straight. Above a certain threshold valley slope, the stream power actually has two minimums, indicating two possible stable channel configurations and slopes. Whenever multiple channel slopes exist on a uniform valley slope, the river must be sinuous. The reason for meandering development is attributed to minimum stream power per unit channel length for the river system, because with its multiple configurations and slopes, a meandering river may minimize its stream power expenditure as well as its sediment load for the river system subject to physical constraints. Analytical relations also predict that highly sinuous rivers which are small in width/depth ratio occur on flatter valley slopes and that they become more braided and less sinuous as the valley slope increases.

A numerical model for channel alteration is developed for sand-bed rivers and deltas. The unsteady river flow is computed using the continuity equation and momentum equation of flow with prescribed boundary conditions. Changes in cross-sectional area and delta growth are evaluated based upon the continuity equation for sediment and a sediment transport equation. Subject to certain physical constraints, the part of the river on the delta (delta stream) is assumed to adjust its width freely. To determine the variation in delta stream width, it is assumed to vary in such a way that the total stream power of the river flow is a minimum subject to the physical constraints. The analytical results substantiated with field data indicate that the width-depth ratio of the delta stream tends to increase with a decreasing velocity in an aggrading delta stream, while it tends to decrease with an increasing velocity in a degrading delta stream.

Equilibrium sediment transport experiments were made in two flumes, one with a 6‐m long by 0.15‐m wide channel and the other with an 11‐m long and either 0.74‐ or 0.53‐m wide channel. The sediment (0.1 to 32 mm, D50=3.03mm) was fed at the upstream end of the channel and was trapped in the sump at the downstream end. For the runs of this study the bed‐surface grain size became finer and the sediment transport rate increased as the total bed shear stress decreased slightly and then increased. This decrease in bed shear stress was probably caused by the varying coarseness of the bed surface. In the runs with higher transport rates the bed surface was finer, so bed shear stresses were lower. The difference in friction factors (determined from the Moody diagram for rough turbulent flow) for D65 of the bed surface sediment and D65 of the original sediment mix (or of the sediment in transport) was used to represent the extra friction factor due to roughness changes. Subtracting this quantity from the bed frictio...

A theory is developed to predict the bed material load for steady fluid and sediment flow. The theory is based on the fact that the total power of the fluid and sediment flow is constant. The power of the sediment flow increases as the power of the fluid flow decreases. A solution is obtained for the flow stage with maximum sediment transport. The theory is supported by results of field measurements.

Experimental research has been performed to determine the sediment pick-up by a uniform flow without initial sediment load. A sediment lift was designed by which the sediment particles were moved upwards at a constant rate through a circular opening in the flume bottom. Five types of bed material (sand) have been used with D\d5\d0-values in the range 130-1500μm. The mean flow velocities were in the range 9.5-1.0 m/s. The experimental results have been used to derive an empirical pick-up function. The results have also been used to evaluate several existing pick-up functions. Finally, the proposed empirical pick-up function has been applied to predict the bed-load and suspended load transport. In the latter application the proposed function has been used as a bed-boundary condition in a mathematical model for suspended sediment transport.

The basic assumptions used in the derivation of bedload or gravel transport equations are reviewed and examined to determine their validities. Laboratory data indicate that unit stream power is mor...

An analytical model has been developed to evaluate and improve our knowledge of steady-state flow of ground water toward a well near a stream. This model differs from others in that the direction of ambient ground-water flow (i.e., regional ground-water flow) does not have to be perpendicular to a gaining stream, but can be oriented in any direction. Without using measured water levels, flow directions and rates can be calculated, i.e. estimated flow nets can be drawn based on the pumping rate, the ambient ground-water flow rate and direction, and the location of the well and stream. The model can be used to help determine the minimum rate of pumping that will induce infiltration from a stream to a well, and the components of pumping that are derived from the stream and the aquifer. The areal distribution of flow includes: a zone of induced infiltration from a stream toward a pumping well denoted the stream capture zone, a zone that includes all ambient ground water captured by a pumping well called the aquifer capture zone, and a zone downstream of the stream capture zone where water flows from the stream into the aquifer and then back to the gaining stream called the zone of induced throughflow. Each zone could be distinct geo-chemically. The concepts elucidated by the model are useful for ground-water pollution studies and for planning purposes. Normalized curves are presented to quickly determine the estimated boundaries between the stream capture zone and the zone of induced throughflow. An example of induced streamflow from Albuquerque, New Mexico illustrates application of the model.

This study has involved a literature review and data analysis regarding suspended stream sediments in southern Ontario, highlighting knowledge and identifying gaps with reference to stream loadings, seasonal and areal variability, extreme events, sources of sediments, and sediment and water quality. The quantity of sediment transported in Ontario streams is generally not of major proportion or of major significance. Daily loads follow a distinctive seasonal pattern, the bulk being transported during the spring period; and sediment transport in the province is an event-oriented process, a large percentage of the load moving in a small percentage of time. Extreme events transport a significant portion of the total suspended load, but so also do annual peak events. The bulk of the load emanates from sheet and rill erosion in cropland areas, and areal variability in loads can be related to land use and surface soil conditions. Suspended sediment has been documented to be both a pollutant carrier or source of contamination and a sink or trap for pollutants such as phosphorus, organic compounds, pesticides, and heavy metals. Key words: suspended sediment, loads, temporal patterns, areal variability, extreme values, sources.

A one-dimensional numerical model is developed for simulating the movement of well graded sediments through a stream network. The model is based on the physical processes governing the mechanics of sediment movement in alluvial channels. It incorporates the effect of sediment gradation on the stream's potential transport capacity. It also accounts for the effect of particle exchange between the sediment load and the bed, while simulating aggradation, degradation and armoring of the bed. The applicability of the model is restricted to noncohesive materials and relatively stable channel geometries. Any valid water routing algorithm can be used in simulating the movement of water.

Since the majority of road drainage points in western Washington and Oregon enter small, often ephemeral streams rather than large, fish-bearing waters, impact of road-surface sediment on biota in permanent streams depends, to a large extent, on transport through these small watercourses. A series of experimental additions of road-surface sediment was made to two ephemeral streams to examine the downstream transport of this material as a function of discharge and channel characteristics. These small streams were found to store large amounts of sediment washed from road surface. In no instance did either stream transport more than 45 percent of the added material to their mouths, distances of 95 and 125 m. Larger-sized sediment particles were delivered at a lower rate than finer material. Added sediment

The sediment transport problem in shallow flows, such as furrow flows, in the upper flow regime is formulated based upon continuum mechanics principles. Considering the dynamics of the water flow as well as the dynamics of sediment flow, a mathematical expression which is a modification of the classical stability criterion of flow over a fixed bed is obtained for the case when a movable sediment layer is present near the bed of the channel. Coincident with this stability criterion, the amount of sediment being moved is defined as the transport capacity of the flow. The results suggest the dependence of the capacity on the sediment properties, active layer thickness, channel gradient and the hydraulic properties of the flow. Comparison of the theoretical results with experimental data revealed a general agreement. In particular, the theory predicted satisfactorily the transport capacity in models of steep croprow furrows.

This study describes the sediment transportation and its relating phenomena typical in mountain streams. In a stream with the step-pool system, the sediment transportation depends greatly on sediment storage in the pools. The destruction of armor coat results in the destroy of step-pool system, which causes a Change of stream morphology. In addition, a meandering channel, the characteristics of which accords with the degree of the flood, is formed.Stream channels do not change so much in the conditions the armor coat can not be destructed even if a flood comes. In such cases, the sediment transportation depend greatly on the sediment storage in the step-pool system. In the case that the destruction of armor coat occurs, stream channels change very much.Debris flow brings a great change to the stream channel in the areas of its running-out; deep erosion in the occurrence areas and rapid aggradation in the ceasing area. In the deposition area, a new stream channel is formed due to the eroding action of water flow after the event.

Movement of granular bed material near the critical shear stress exerted on a stream bed is important to hydraulic engineers. Experiments at low shear stress have been performed at Oak Creek near the Oregon State University campus and results are presented. The data in this paper indicate that sediment transport is possible at very low values of the Shields parameter. The work herein presented makes clear that some probability of sediment transport exists at all levels of bed shear stress and, in the words of Paintal, “this probability is never zero except in still water.”

The transport and yield of bed sediment in a small coastal stream is the focus of this study. Spatial and temporal variations of sediment characteristics have been simulated using a calibrated mathematical model for time-dependent fluvial process-response. The study illustrates how channel storage, a major factor affecting sediment yield, can be quantified by an erodible-boundary model. The mathematical model also accounts for the storage effects caused by the works of man, a task that cannot be easily accomplished by other methods. The model simulates the interrelated changes in channel-bed profile and channel width based upon the stream's tendency to seek uniformities in sediment discharge and power expenditure. Scour and fill of the channel bed are accompanied by significant changes in channel width, which may contribute more to sediment storage. Thus, sediment routing must be based upon an erodible-boundary model rather than an erodible-bed model. This study confirms field evidence of the significant variation in sediment yield that occurs along the stream reach.

Whenever the amount of sediment coming into a given reach of an alluvial stream is less than its sediment transport capacity, there is a general lowering of the stream bed-a process known as degradation. The most common occurrence of degradation is downstream of a large capacity reservoir on an alluvial stream. Earlier investigations on degradation have shown that composition of the bed material plays an important role in controlling degradation. If initial shear stress on the bed is such that the coarser fraction of the bed does not move, the material in the surface layer becomes progressively coarser, ultimately forming an armor coat that stops further lowering of the bed. In such a case the shear stress remains essentially constant. Under such condition, it is interesting to know the variation of characteristic size of surface layer with time at the given section.

Washload and fine sediment load should not be used synonymously. In streams with large concentrations of fines, the sediment size D\d1\d0 may be much smaller than 0.0625 mm. The fluid becomes very viscous at low concentrations of clays and the reduced settling velocity inhibits the exchange of sediment particles between the bed and the suspension. The sediment transport capacity under those conditions remains very poorly defined. In coarse bed streams, sands and fine gravel can be considered as washload as long as the sediment transport capacity remains larger than the availability of sediment. Intermittently, different conditions prevail when the upstream supply exceeds the transport capacity.

Variational formulations of the equations of motion applicable to irrotational, nonaccelerating, as well as gradually varied open channel flows are presented. It is shown that there exists a suitable functional, J, from which the equation of motion can be obtained as the condition of minimization with respect to the velocity profile. Minimization of J is shown to be equivalent to the minimization of the total rate of energy loss, E, providing that the discharge, Q, and the total head, H, at upstream and downstream ends of the river is known. Furthermore, if the speed of the movement of the river bed is small, then the total rate of energy loss is shown to be equal to the total stream power. Thus, under certain restrictive conditions the hydraulic problem reduces to the problem of minimizing total stream power. The minimization theory presented here is somewhat similar to the second writer's theory of minimum unit stream power.

Bed load transport in a small gravel-bedded stream on Chichagof Island, Alaska, was measured for 33 autumn storm flows during 1980 through 1985 to determine temporal and spatial trends within a riffle-pool-riffle sequence. The transport of fine sediment was more frequent than coarse sediment. Scouring of coarse material in the reach appeared to be triggered only by high flows with Tr ≥ 5 years. Within a given storm season, both antecedent storm history and cumulative flow (above the threshold for bed load transport, 0.25 m3 s−1) influenced bed load transport; however, the effects of these seasonal factors changed from year to year, presumably in response to storage and release of sediment around large organic debris upstream. Hysteresis loops existed in bed load transport versus flow plots for many storms. Fine bed load material was more subject to such differential transport over the storm hydrograph than was coarse material. During the 6-year period, both riffles scoured along most of the channel width while the middle portion of the pool filled.

Accumulations of stored sediments in a sub-alpine environment of a front range of New Zealand's Southern Alps closely resemble sieve deposits previously described from southeastern California. The locations of such deposits, within active river channels, has important implications for long term sediment yields from catchments where such deposits occur. The catastrophic failure of a sieve deposit in the Torlesse Stream catchment, the site of an earlier investigation of mountain stream sediments, resulted in a sediment yield equivalent to a third of the total yield recorded over an eight-year period. Derived bed-load transport rates represent, at a minimum, a four-fold increase over calculated average transport rates. Such deposits are only likely to fail during extreme low frequency events since their highly permeable gravels allow for the continuation of stream flow underneath the bulk of the deposit and restricts significant increases in moisture content within the deposit. The loss of water is responsible for the inhibition of flowage-type mass movement transport mechanisms wherein available water contributes to the maintenance of positive pore pressures. For the example studied here the percentage of silt and clay is less than 3 per cent of the total sample while sorting values (σ1) are generally less than 2.0ϕ. These values are approximately one-third and one-half respectively, of typical values obtained for these parameters from debris flow deposits. The feature described here is believed to have originated through failure of a higher altitude perched scree-field. This mode of origin would account for the distinctive sediment size parameters.

The accumulated volume of sediment in reservoris is investigated in this paper using a statistical method. Based on the fact that sediment load and river discharge are highly correlated, a relationship between them is established. With longer records of stream flows, this relationship will serve either as a data generation mechanism which produces a sediment S-sequence having the same length as the river discharge Q-sequence, or as a transformation of variables, by which the distribution of S is transferred from the distribution of Q. The mean and variance of the sediment volume accumulated in the design life of a reservoir are then derived, assuming the S- and Q-sequences follow the log-normal distribution. Finally, case studies are given for illustrating the proposed method.

Buffalo Bayou, a major stream in Houston, Texas, was the subject of a detailed water quality study. The stream is heavily stressed by domestic waste loads and has shown significant degradation in water quality since 1970. Currently, the stream reaches critically low DO values through much of its length during low flow, high temperature periods. The QUAL‐IITX model was calibrated, verified, and applied to simulate worst case conditions and to test a series of stream protection alternatives. A combined program of sewage plant regionalization, stream aeration, and flow augmentation was found to be the most cost‐effective solution.

Total stream power does not necessarily increase systematically in the downstream direction because of the conflicting influences of channel slope, width, and depth. Historical records and field data for arroyo systems of the northern Henry Mountains, south-central Utah, show that total stream power decreased in the downstream direction during a deposition period before 1896 and increased downstream during an erosion period thereafter. When total stream power declined in the downstream direction, channels were small and meandering, and the ten-year flood exceeded channel capacity, resulting in overbank deposition of sediment. After an especially erosive flood in 1896, total stream power increased in the downstream direction because channels were in the bottoms of arroyos that confined discharges, resulting in channel erosion and through-put of sediment. In 1980 deposition was occurring in the headward portions of the continuous arroyo system and in the large master stream, but not in mid-basin areas. Channels in the arid and semi-arid Henry Mountains do not exhibit mutual adjustment between form and process. Rather, at times of catastrophic system-wide events, fluvial processes control channel forms, whereas at other times channel forms control fluvial processes. Comparison of historical and modern conditions shows that mutual adjustment is unlikely to occur in the discontinuous operation of semi-arid fluvial systems.

A thorough study of the existing applicable data reveals the basic reason that previous equations often provide misleading predictions of the sediment transport rates. The error stems from the unrealistic assumptions made in their derivations. Unit stream power, defined as the time rate of potential energy expenditure per unit weight of water in an alluvial channel, is shown to dominate the total sediment concentration. Statistical analyses of 1,225 sets of laboratory flume data and 50 sets of field data indicate the existence and the generality of the linear relationship between the logarithm of total sediment concentration and the logarithm of the effective unit stream power. The coefficients in the proposed equation are shown to be related to particle size and water depth, or particle size and width-depth ratio. An equation generalized from Gilbert's data can be applied to natural streams for the prediction of total sediment discharge with good accuracy.

Solution is obtained for distribution of dissolved oxygen in polluted water of stream in which volume and velocity of flow are steady at any cross section, but not necessarily uniform at all cross sections; solution can account for added discharge and pollution along course of stream; in addition, unsteady distribution of dissolved oxygen due to unsteady initial oxygen content and BOD load can be computed.

A simulated stream channel was used in laboratory investigations to determine a rational expression relating stream variables and fluid properties which define the reaeration rate constant, k2. Direct measurement of the reaeration coefficient at controlled depths and stream velocities enabled the development of a dimensionally homogeneous expression for k2. The developed expression accounts for variations in k2 due to changes in temperature as well as changes in fluid flow conditions. For the rectangular cross section employed in these studies, the reaeration rate constant, k2, was found to be directly proportional to average stream Telocity, and inversely proportional to the average stream depth raised to the 3/2 power. The constant of proportionality was found to be 3.053. When the same analytical approach was applied to the best available natural stream data, the proportionality constant obtained was 3.739. Both analyses yielded highly acceptable correlation coefficients. It is believed that the difference in the values of the proportionality constant is due primarily to differences in channel geometry, i.e., smooth rectangular laboratory channel versus irregular-shaped natural river channels.

Turbulent flow in a sediment laden stream is described by a random walk model which simulates the behavior of sediment particles, fluctuating in depth near the surface of the stream down to the stream bed. The basic aspect of this model is the probability laws which govern the transfer of mass for both water and sediment from one level to another throughout the total depth. The downstream velocity at each level is introduced to convert mass to momentum. Three sources of momentum loss are taken into account. The downstream velocities at the various levels, which are unknown, are determined from a set of equations based on the assumption that the expected momentum at a given level equals the sum of the expected momentum contributed at time Δt previous from all levels and by gravity. The solution of these equations in the limit where the distance between levels goes to zero leads to the vertical velocity distribution of the sediment-water mixture which is dependent upon four parameters.

A description is given of modern techniques and equipment used to plan and make sedimentation measurements on natural streams. First typical examples are given of sedimentation characteristics of streams such as distribution of sediment with distance above the bed, variation of concentration with time and position in the stream cross section for the purpose of illustrating some of the problems of sediment measurement. Equipment available is then described for obtaining suspended load concentration, bed load discharge and bed sediment samples. Next, the planning is outlined for making measurements at a cross section to obtain the sedimenmt discharge of a stream and the procedure is presented for making the necessary calculations based on measured data. Finally the method of obtaining long-time records of sediment discharge is considered. This includes the determination of the frequency of making measurements in order to achieve the desired accuracy. The report is intended for the use of engineers not familiar with sediment measurement techniques on streams.

At least five alternative measures of fluid forces or fluid velocities may have usually dominant effects on the discharge of bed-material in a sand-bed stream. Interrelationships among most of these measures vary widely with changes in the resistance to flow. Approximately defined average relationships between discharge of bed-material per foot of stream width and each of four usually dominant measures (mean velocity, stream power, and two forms of effective shear on the bed sediment) are shown graphically as possible bases for practical computations of bed-material discharge. Such usually secondary factors as depth of flow, particle size of the bed sediment, water temperature, and concentration of fine sediment affect each defined relationship, generally by different amounts.

As to the lower stream (0-17km) of the Abe-kawa in Shizuoka Prefecture, the author estimated the amount of the degradation of river bed in recent years by considering (a) fluctuations in the mean heights of river bed and (b) quantities of deposition or scouring in the river bed. Regarding the causes of the degradation, he considered (a) the decrease of tractional loads to the construction of sand catch dams and (b) the effect of gravel mining in the river bed. Conclusions are summarized as follows: 1) The degradation of river bed in the lower stream of the Abekawa has been increasingly remarkable since about 1954, and the quantity of degradation during the past 10 years (1954-1964) is larger in the lower reaches below the 9km. point from the river mouth, the maximum being about 2 meters at the 6km. point. 2) The yearly records of total deposition or scouring in the river bed show a huge amount of scouring for every year since 1954 excepting 1957, and that of the last year (March 1963—March 1964) amounted to about 2×106m3 of scouring. 3) In the upper stream (above the 34km. point) of the Abe-kawa, four large sand catch dams were constructed between 1951 and 1958. From the quantity of gravels deposited in those dams, mean annual volume of the tractional loads at the 34km. point (Ogochi Dam) is calculated to be 2.5×105m3, corresponding to about 20% of the total sediment transportation. The effect of those dams to the river bed in the lower stream, however, is indirect and has a minor importance as compared with that of the gravel mining. 4) The relation between the degradation of river bed and the gravel mining is direct and decisive. Based on the analysis of data from 1952 to 1959, the author pointed out that there is a close correlation between quantities of scouring in the river bed and quantities of mined gravels, in the reaches of 1-6km. Moreover, there is a considerable correlation too in the reaches of 2-6km. between the lowering of river bed calculated from the quantity of mined gravels and the degradation -based on the actual measurement. Therefore, it is to be said that gravel mining has been definitely too excessively undertaken in recent years and the scale of operation is still expanding. If this trend is not reversed in the immediate future, serious social problems will be caused by the degradation of river bed.

A review of existing literature reveals some disadvantages of using Shields diagram as the criterion for incipient motion of sediment particles on an alluvial bed. A new criterion based on average flow velocity, fall velocity, and shear velocity Reynolds number is proposed herein with the supporting data collected by different investigators. This new criterion is used to calculate the dimensionless critical unit stream power in a dimensionless unit stream power equation for sediment transport. The dimensionless unit stream power is the ratio of the time rate of potential energy expenditure per unit weight of water and the terminal fall velocity of the sediment. More than 1,000 sets of data from both laboratory flumes and natural streams published by different authors are used to support this dimensionless equation for sediment transport.

Relationships proposed give both quantity and quality of total, suspended, and bed loads as functions of stream and sediment characteristics; in process of empirically defining relationships, encouraging correlation of laboratory and field data was obtained. (25 refs.)

This study examined the river sediment transport characteristics of the Ping River basin, which is one of the major river basins in Thailand. River surveys of the Ping River were carried out nine times between 2011 and 2013. Survey data included river cross sections, flow velocities, suspended sediment concentration, and bed load transport in the river. Analyzes of these data indicated that suspended transport rates in the Ping River during normal flow conditions in 2012-2013 ranged between 107 and 9,562 metric tons/day (mt/d), but increased to 35,300 mt/d during high flooding conditions (Thailand's Great Flood of 2011). The rate of bed load transport was 1,401 mt/d during the Flood of 2011. However, the measured bed load in 2012-2013 varied between 0 and 482 mt/d. The bed-to-suspended load ratio in the Ping River fluctuated in the broad range of 0-2.0. Estimates of total sediment transport in the Ping River were made using some of the classic equations from the hydrologic literature. The results obtained from the different methods show that the Laursen-Copeland formula gives the best estimate of total sediment transport rate of the Ping River compared to other methods. Results from this study also reveal that the Bhumibol Dam, constructed in 1964, has had a significant effect on suspended sediment load reduction downstream of the dam.

This paper proposes a method for establishing both the velocity profile and concentration profile for suspended sediment based on measured data consisting of average velocity and average suspended sediment concentration in the river and the irrigation channel. In addition, a numerical model for computing suspended load and bed load was also developed for computing bed load transport rate when measurable load is available. In this study, bed loads for published laboratory and field sediment data were computed using the presently developed numerical model based on four different bed layer thicknesses. The computed bed loads were found to be in reasonable agreement with the values from Einstein’s bed load function when the thickness of the bed layer was taken at 10θd or 0.05D. The numerical model developed in this study may be used to evaluate the validities of other bed load formulas.

Within a river basin, the streams can be classified by the Horton-Strahler stream order system. In 1945, Horton introduced the law of stream lengths and the law of stream slopes and found the average stream lengths and slopes as semilogarithmic functions of the stream order. In this study, paralleling Horton's development, the law of stream relief is proposed and the average stream relief is found also to be a semilog function of the stream order. Results from numerical analysis indicate that the riverbed profile can be described by a semilog equation expressing stream relief as a function of stream length. The F value in the stream relief equation may be considered as an indicator of the riverbed profile properties; however, more investigations are needed before any conclusive statements can be made.

There is an enormous variability in the flow equations which were proposed for mobile-bed channels, and which contain a term that purports to measure sediment load. J. W. Johnson compiled experimental data on sediment transport data that existed prior to 1948 to address this problem. The authors have expanded Johnson's work to include the more recent data collections and have analyzed the data to determine the scope of available experimental conditions.

Bed load transport rate was measured in ten self-formed small-scale gravel braided streams developed in a laboratory flume at several different values of steady discharge and flume gradient. The streams are approximate Froude models of typical prototype braided streams but of no particular river. Slight viscous effects may be present in the models because particle Reynolds numbers are close to 70. Total bed load discharge was measured every fifteen minutes throughout each 60 hour run. In addition, 80 channel cross-sections were measured in each run to establish the average channel geometry. Total bed load transport rate correlates well with total discharge and total stream power, although at a given stream power bed load discharge is greater when braiding is less intense and the width/depth ratio is lower. Analysis using unit stream power and cross-section average bed shear stress reveals that the laboratory data conform to existing empirical bed load transport relationships. However, comparison with field data from gravel-bed rivers shows discrepancies that may be due to differences in bed material size gradation and bed sediment structure. At constant discharge, wide fluctuations in bed load discharge occur with some regularity. Periods range from 2 to 10 hours in the models, which is equivalent to several tens of hours in a prototype. The presence of these long-period fluctuations compounds the problems of field measurement of bed load in braided streams.

Summary Sediment transport measurements have been made in the estuary of the Zaire river since 1968. The results show that bed and channel morphology is a predominant factor of the sediment distribution and transport. Vertical distribution of sediment transport near the bed reveals high rates in a layer of a thickness of a few decimeters, moving close to the bed, and a very erratic transport on the bed. At constant velocity, the influence of varying bottom shear stresses is shown in time series of bed load and suspended load. These observations could be related to the burst-sweep cycle. The successful application of Bagnold's approach for computation of sediment transport at single stations tends to prove the validity of power-related theories for large alluvial streams.