Bed Material Size Research Articles

Velocity–bed-form–texture patterns of meander bends in the lower Wabash River of Illinois and Indiana

Meander bends in the lower Wabash River of Illinois and Indiana display coherent patterns of current velocity, bed topography, lower-regime bed forms, and bed-material size. The upstream reach of a bend is a zone of transition from the reversed hydraulic and sedimentologic conditions of the preceding bend. A downstream shift of the cross-sectional maximum velocity magnitude from the inner (point-bar side) bank to the outer bank defines a transitional zone for velocity magnitude in each bend; in this zone, current velocities are strongest and dunes and sand waves most prominently developed at near-bankfull and higher flows. Similar translations of the cross-sectional maxima of depth, mean size of bed material, and dune height and a reversal in the orientation of spiral flow define a transitional zone for each of these four other parameters in each bend. A given meander bend at any stream discharge shows the following sequence of increasing length of transition zones: spiral flow, depth, velocity magnitude, mean size of bed material, and dune height. Downstream from each transitional zone in a bend, the normal asymmetrical cross-sectional distribution of each parameter defines a fully developed zone for that parameter. Only in the fully developed zone does each parameter increase from the inner bank to the outer bank, as implied in the standard facies models for meandering streams. In both sharply curved and gently curved bends, fully developed zones for bed-material size do not exist. Sharply curved bends do not contain fully developed zones for velocity magnitude, which in other bends show the strongest velocities and largest dunes at near-bankfull or lower flows, especially if the zone is bypassed by overland flow during higher stream discharges. Available data from laboratory channels and from other meandering streams suggest that the above patterns of velocity magnitude, spiral motion, and bed-material size characterize freely meandering streams. The transitional zones of sedimentary and hydraulic parameters and the variations of these parameters through different flows and dissimilar bend curvatures introduce significant complications to present depositional models of meandering streams.

Channel gradient in relation to discharge and bed material characteristics

By relating channel gradient to the downstream behaviour of discharge and bed material size, a general explanation of profile from is obtained for a stream in which lithological complications are relatively small. Unlike previous studies of logarithmic profiles, bed material size decreases systematically in the downstream direction. Slope varies significantly with mean grain diameter and particularly with grain sizes in the pebble fraction. However, particles finer than 4 mm have a lesser influence on slope. Calculation of SHIELDS' entrainment function parameters indicates that the stream is competent to transport local bed material at higher flows. This competence apparently results largely from slope adjustment where debris is coarse and from the adjustment of other channel variables related to the downstream increase in discharge where debris is fine. Wenn man das Gerinnegefälle mit der Veränderung von Abfluß und Bettmaterialgröße flußabwärts vergleicht, erhält man eine generelle Erklärung der Profilform für Flüsse mit nur geringen lithologischen Komplikationen. Im Gegensatz zu früheren Studien mit logarithmischem Profil nimmt die Bettmaterialgröße systematisch in flußabwärtiger Richtung ab. Das Gefälle verändert sich signifikant mit dem mittleren Korndurchmesser, und zwar besonders der Geröllfraktion; Partikel unter 4 mm haben einen kleineren Einfluß auf das Gefälle. Abschätzungen der Parameter von SHIELDS' Belastungsfunktion zeigen, daß der Fluß kompetent ist, das lokale Bettmaterial bei höheren Hochwässern abzutransportieren. Diese Kompetenz resultiert bei grobem Schutt weitgehend aus Veränderungen im Bereich der Hänge und bei feinem Schutt aus Veränderungen anderer Gerinnebettparameter, die in Beziehung stehen zu der Abflußzunahme nach flußabwärts.

On the Problem of Meanders

The problem of meanders has been discussed for a long time, and yet there are many arguments and opinions on it.The term, meander, is derived from the name of a river in Turkey, the Büyük Menderes. Since it is a universally accepted term, it may be used in katakana in Japanese, but the Chinese character compound, dako, is preferable as an adverb or a verb.There are various theories about the origin of meanders, but there seems to be no established theory. Most theories explain the origin of meanders according to the phenomena associated with them. In the case of hydraulic geometry of stream channels, the study of meandering channels may be the most advanced field of research. There are many relationships between the geometry of meanders and hydrualic quantity; however, little is known quantitatively about the interrelationships among the parameters such as discharge, slope, size of bed and bank materials, etc.Two opposing views exist regarding the origin of incised meanders. One view recognizes the inheritance from free meanders, but it is not accpted by others. It is doubtful that meanders can develop on relatively “steep” slopes of 30° or so, judging from present surrounding landforms. Dury (1964, 1965) dealt intensively with meandering valleys and underfit streams, but he did not explain the origin of incised meanders specifically. However, there is a possibility in Dury's theory for considering meanders from the viewpoint of climatic geomorphology in responding to criticisms such as that of Hack (1965).

Bed Material Size Changes and Sediment Transport

Bed Material Size Changes and Sediment Transport

Determination of Some Paleohydraulic Parameters: ABSTRACT

New river measurements combined with existing laboratory evidence show that, in a river reach where traction motion as well as net sediment deposition take place, the mean applied bed shear stress is equal to the critical shear stress required to move particles of median bed material size. Consequently, application of Shields' relation between shear stress and material size permits the determination of mean applied shear stress at an ancient depositional site from the grain-size distribution of the sediment. Furthermore, by applying laboratory values for the friction factor, determined for the appropriate bed configuration, we can calculate the paleoflow velocity by the Darcy-Weisbach relation. This method for the determination of paleoflow velocity is generally applicabl to any sedimentary deposit if a reasonable estimate of the friction factor can be made. For rock units containing climbing ripple cross-lamination, we can go one step farther and determine the rate at which the sediments were accumulated. The rate of bedload transport has a known functional relation to the mean velocity of the overlying column of water as determined in the first part of this study. Very high rates of sedimentation are found to exist in nature. Late Pleistocene deltaic sediments in the Truckee Canyon of Nevada, locally contain climbing ripple cross-laminated units indicating a local rate of aggradation of 0.1 mm/sec or 36 cm/hr. End_of_Article - Last_Page 797------------

INFLUENCES OF A FOREST ON THE HYDRAULIC GEOMETRY OF TWO MOUNTAIN STREAMS1

ABSTRACT The influence of a forest on the formation of steps in two small streams of the Colorado Rocky Mountains was studied. Steps provided by logs fallen across the channel added to flow energy reduction. The streams required additional gravel bars to adjust to slope. Average step length between logs and gravel bars was strongly related to channel gradient and median bed material size. Based on the average number of log steps per 50 feet of channel, an average of 116 percent of gravel bars were added at Fool Creek and 60 percent at Deadhorse Creek. The latter had 52 percent more logs in the channel and therefore required less bed material movement than the former. Although these are “rushing mountain streams,” most flow velocities ranged between 0.5 and 2.5 f.p.s. Exponents of a function relating rate of change of depth or velocity to discharge indicated that dynamic stream equilibrium was attained. Implications for forest management are that sanitation cuts (removal of dead and dying trees) would not be permissible where a stream is in dynamic equilibrium and bed material movement should be minimized.

Longitudinal Profiles of Ephemeral Streams in Southeastern Arizona

Two longitudinal profile segments of different concavity in ephemeral streams heading in the mountains of southeastern Arizona are related to the longitudinal variation of drainage area (A) , bed-material size ( D mm ), and channel width: depth ratio (W/D) . These parameters approximate discharge, sediment load, and roughness, which have been found to control stream profiles in other regions, but were unavailable for this ephemeral-stream study. Inclusion of basin relief (R) and lithology allowed development of statistically significant equations for both segments of streams draining granitic and sedimentary terrains: Sedimentary concave: Sedimentary straight: Granitic concave: Granitic straight: Profiles of streams in two additional mountain ranges were predicted from the equations with an accuracy within the limits of accuracy of the field and map measurements. Precipitation-elevation relations have no apparent effect on the accuracy of the predictions or on stream-profile concavity.

Particle Size of River Sediments

The relationships between particle size of river sediments and the variation in stream discharge are studied. The results of a study carried out to determine the variation of both bed material and suspended sediment particle size for differing flow conditions is presented. A significant finding is presented which shows that the particle size of suspended and bed sediments remains relatively constant with variation in stream discharge. This condition was found from the analysis of results at four river sections on three rivers in Scotland and was also corroborated by results from research in the United States. Conclusions are presented which attempt to explain these findings in terms of the availability of material for transport by streams rather than on purely hydraulic considerations.

ON THE LONGITUDINAL PROFILES OF THE ASAKE, MITAKI AND UTSUBE RIVERS, MIE PREFECTURE

The Asake, Mitaki and Utsube Rivers rise in the Suzuka Mountains, run eastward through the alluvial plain and flow into the Ise Bay (Fig. 1). The geological conditions of the river basin in the mountainous areas present striking contrast each other. The Asake River basin, for instance, consists only of granite, while that of the Mitaki River contains Paleozoic rocks in addition to granite. And most portion of the Utsube River basin is composed of Paleozoic rocks. Meanwhile, the longitudinal profiles of the three rivers have a common characteristics : they have concave reaches in the upper stream and straight reaches in the lower. Among the upper stream, the Asake River has the greatest concavity and the Utsube River the smallest (Fig. 2, A. B). The purpose of this study is to investigate the cause that has created the difference in the concavity in the longitudinal profiles of the three rivers. Thus the observation is made not only on the particle size of the bed material but also on the grain lithology. The study of the relationship between the particle size of the bed material and the change of channel slope downstream as each rivers has led to the following findings : (1) The distribution of maximum size grains in the bed material of each river changes exponentially (Sternberg's law). However, it is subject to the grain lithology and is not corre-lated with the change of channel slope (Fig. 2, C). (2) The downstream change of channel slope-concavity-is closely correlated with the change in median size of bed material downstream (Fig. 2, B. D). (3) L, ithological separation of bed material, however, indicates that the change in the median size of bed material downstream does not correlated with the channel slope. The change in the size of bed material is characterized by the peculiarity in the distribution of each kind of rock involved. For instance, granite breaks up rapidly into mineral particles, 2-3mm in diameter, but the diminishing rate of the particle size, further on, is very small. The di-minishing rate of particle size of Paleozoic rocks is very small as compared with that of granite (Fig. 2, D). (4) Therefore, the downstream change of bed material size is influenced by its lithologic composition. And the lithological composition of bed material exactly reflects the geological conditions of each river basin in the mountainous area (Fig. 3). Reflecting the lithology of the mountainous part, the bed material of the Asake River is composed of granite, and the downstream change of the bed material size indicates that of granite debris, so the Asake River produces great concave profile in its upper reaches and the straight profile in its lower reaches. On the other hand, the Utsube River, mainly consists of Paleozoic rocks, has the bed material of Paleozoic rocks, so it produces small concave profile. The longitudinal profile of the Mitaki River has intermediate character of two other rivers, due to the lithology of her basin. Concludingly, it may be said, that the difference of the concavity of longitudinal profiles of these rivers are mainly due to the difference in the lithologic conditions of the mountainous part of each river basin. The more quickly the particle size of bed material diminishing down-stream, the more the longitudinal profile becomes concave. Then, it may be said, that the concavity of longitudinal profiles of alluvial rivers is one of good examples of the configura-tions formed under the influence of lithologic condition (ROCK CONTROLLED TOPOGRAPHY).

Similarity in Unlined Irrigation Canal Systems

Data from three irrigation canal systems are examined, and the observed variations in some relevant flow parameters are considered in relation to the conditions which apply in the case of completely similar movable bed channel flows. It can be seen that the canals flow with ripple, dune, or transitional bed regimes, and that the bed material size decreases in a downstream direction in such a way that the ratio of the mean velocity of flow to the fall velocity of the bed material tends to remain constant. It is shown that it is impossible for complete similarity to exist between the flows in real alluvial channels, and accordingly an attempt is made to define conditions of quasisimilarity based on the stage of development of the bed formation.

MEANDERING OF RIVERS

Abstract Among various factors that have influence on the meandering of an alluvial channel, the most significant are valley slope, discharge, bed material, and time. The necessary condition for the origin and development of meandering of an alluvial channel is the erosion of bed material and deposition of the eroded material downstream. The criterion for the development of the meandering is that the discharge must be equal to or greater than the critical discharge (i.e., discharge corresponding to critical shear velocity). The initial channel section has an effect on the development of meandering. The meandering in the V-shaped channels starts from the center (deepest point) of the channel and works inside the banks (inside meandering) before it windens the banks, While the meandering in the rectangular channels starts with the widening of the banks (outside meandering). Maender width increases with the increase in the increase discharge and slope, and decreases with the increase in size of bed material....

Stable Channels with Gravel-Paved Beds

The hydraulics of naturally gravel-paved channels are examined on the basis of field and laboratory data covering a discharge range from 1 cfs to 100,000 cfs and a bed-material-size range from 0.5 in. to 18 in. Natural gravel pavements appear to be closely associated with conditions of low bed-load transport. An equation relating tractive force to bed material size, an exponential flow formula, and a regime-type width-discharge relationship are combined to form a set of channel design rules. Some possible applications are stated. Methods for sampling gravel pavements are also mentioned briefly.

Observations on Unmeasured Rivers

An analysis of data on hydraulic parameters collected during a single boat trip down a river system is presented, plotted in form of the hydraulic geometry. A dimensionless rating curve is used to estimate bankfull and average discharge for basins of various sizes. When compared with gaging station data, estimates of bankfull discharge are as consistent and possibly equal in accuracy to estimates made from gaging station data. Estimates of average discharge are less consistent; within the range of drainage areas represented by the gaging stations, er- rors of estimate vary from 0 to 58 percent. Local variations of bed material size along the river are compensated mostly by changes in local channel slope and roughness and do not much affect the progres- sive downstream changes in width, depth, or velocity.

Practical Regime Analysis of River Slopes

To assess regime peculiarities of a river, for forecasting the effects of future human interference, and for general geomorphic analysis, a chart is required defining a zone in which the data of most unobstructed rivers with uniformly mobile beds will lie. Points deviating from the zone will indicate either that the measured conditions are not entirely those of self-formation in transported material, or that the regime parameters have unusual values. Theory indicates that a zoned graph plotting representative discharge against a parameter composed of breadth, slope, and the (that corresponds to vanishingly small bed-load charge) should be suitable. Such a graph is presented. It is recommended for tentative use as a regime analysis chart for all regime-type rivers under investigation. The prerequisite graph for estimating zero bed-factor from a practical measure of bed material size also is provided, together with an auxiliary one for applications involving known bed-load charge.