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Rivers adjust towards an equilibrium condition, the stability of which depends upon a set of controlling factors expressed by the Froude number. As alluvial river channels approach stable conditions, the Froude number of the channel flow will tend to attain a minimum value which reflects minimum bed material motion and maximum channel stability, under the constraints imposed by water discharge, sediment load, and particle size. Computer simulations for sand bed rivers show that the Froude number of the flow tends to a minimum value when the equilibrium river tends to a certain hydraulic geometry. Evidence from 57 alluvial sand material rivers and stable canals shows that this simulated hydraulic geometry with minimum Froude number corresponds to the natural equilibrium state.

The long wave equations governing the flow in alluvial rivers and channels are considered. The linearized equations are re-cast in the form of a single equation of wave hierarchy type as discussed by Whitham (1974). The dynamic and kinematic waves are of third and second order respectively. Behaviour at the wave fronts is considered and a roll-wave type instability is revealed. For stable flow, the theory is used to make both qualitative and quantitative predictions in the areas of short and long term floods, tidal waves and channel dredging. The non-uniformity in the quasi-steady theory on bedform development [see, for example, Reynolds (1985)] as the Froude number, F, approaches unity is also discussed, and appropriate scalings are obtained to derive a theory which remains valid when F ∼ 1.

[1] Transient bed profiles in alluvial channels are generally modeled using diffusion (or dynamic) waves and assuming equilibrium between detachment and deposition rates. Equilibrium sediment transport can be considerably affected by an excess (or deficiency) of sediment supply due to mostly flows during flash floods or floods resulting from dam break or dike failure. In such situations the sediment transport process occurs under nonequilibrium conditions, and extensive changes in alluvial river morphology can take place over a relatively short period of time. Therefore the study and prediction of these changes are important for sustainable development and use of river water. This study hence developed a mathematical model based on the kinematic wave theory to model transient bed profiles in alluvial channels under nonequilibrium conditions. The kinematic wave theory employs a functional relation between sediment transport rate and concentration, the shear-stress approach for flow transport capacity, and a relation between flow velocity and depth. The model satisfactorily simulated transient bed forms observed in laboratory experiments.

Degradation in an alluvial river is generally in a state of non-equilibrium. The reservoir intercepts all sediments coming from the upstream, while holding up the water, and releases clear water to the downstream channel. River bed continues to lower as a result of more sediments leaving than entering. A determination of magnitude and rate of channel-bed degradation downstream of a dam or reservoir is important to understand the geomorphic response of the channel to the alterations imposed by reservoirs and other possible implications. This paper explains about channel degradation in Arkansas River, Oklahoma. The flowlines of Arkansas River in Oklahoma were observed for a long-term period. The channel degradation was observed below Keystone Lake dam to 80.5 miles downstream. It was also found that the Arkansas River in Oklahoma has experienced the greatest degradation of 12.2 feet in the past 27 years below 6.5 miles of Webbers Falls dam.

This contribution provides an overview of the nature of fluvial responses to short-term (mostly centennial to millennial scale) environmental forcing. Climate change is the dominant driver of such changes and can sometimes be highly abrupt. Fluvial systems may respond to climate change by adjustments of channel pattern (fluvial style) or by changes in the longitudinal profile by means of aggradation or degradation (incision). First, fluvial incision can manifest itself in different ways (i.e., channel-bed degradation vs. floodplain-surface degradation), and the distinction between the two is paramount. Second, a variety of complex responses to simple perturbations can occur, making the interpretation of fluvial stratigraphic records more challenging. In addition, the nature of the fluvial response within one region may vary considerably according to the size of the drainage basin. Different types of fluvial response to climatic forcing on annual to millennial timescales are illustrated by means of examples from a range of latitudes, indicating, among other things, that even some large fluvial systems are capable of transmitting climate signals, from source to sink, over relatively short time frames.

International audience; Macroinvertebrate assemblages of large alluvial streams are poorly documented. This study identified the physical characteristics affecting the macroinvertebrates community distribution in a large alluvial river devoid of major anthropogenic impacts. It was oriented towards the influence of the characteristics of the physical habitat (velocity, depth, grain-size classes of mineral substrates, macrophytes) on macroinvertebrates (richness, density, body size, feeding habits), with particular attention to the pollution-sensitive taxa. The study was carried out in June during a period of hydrological stability. The effects of water velocity, depth and substrates on taxa were evaluated with multivariate analyses. Mineral substrates were most abundant while macrophytes accounted for only 3% of sampled habitat. Invertebrates that were present were those characteristics of the transition zone between upper and middle life reaches. Among the 63 taxa sampled, 14 were abundant. In relation to the characteristics of the physical environment, the macroinvertebrate assemblages were discriminated by substrate, velocity, and depth. Habitat exploitation, however, appeared complex. The highest community richness, EPT richness, and density were found in various substrates where the velocity ranged between 30 and 120 cm s)1, depths ranged from 16 to 50 cm. The most pollution-sensitive taxa preferred riffle habitats with velocities >70 cm s)1 and substrate >64 mm. This suggest that rapid bioassessment programmes should be carried out in the mineral substrates of the geomorphological unit riffles where richness is high and density sufficient to represent the macroinvertebrate community, including pollution-sensitive taxa.

A large data set pertaining to water quality of an alluvial river was analyzed using multi-way data analysis methods with a view to extract the hidden information, spatial and temporal variation trends in the river water quality. Four-way data (8 monitoring sites x 22 water quality variables x 10 monitoring years x 12 sampling months) analysis was performed using PARAFAC and Tucker3 models. A two component PARAFAC model, although explained 35.1% of the data variance, could not fit to the data set. Tucker3 model of optimum complexity (2,3,1,3) explaining 39.7% of the data variance, allowed interpretation of the data information in four modes. The model explained spatial and temporal variation trends in terms of water quality variables during the study period and revealed that sampling sites in mid-stretch of the river were dominated mainly by the variables of anthropogenic origin. The results delineated the mid stretch of the river as critical from pollution point of view and also identified summer months as having high influence on river water quality in this stretch. The information regarding spatial and temporal variations in water quality generated by the four-way modeling of data would be useful in developing long-term water resources management strategies in the river basin.

The Upper Mississippi River basin drains Lake Itasca in the bog and spruce swamps of northern Minnesota and flows south to join the Ohio River as a 10 th order alluvial river to form the largest river in North America. The progression of the river from the lake outlet to the great river creates an impressive range of physical, chemical, and biological diversity throughout the basin. The basin encompasses five terrestrial ecoregions, three biomes, and three physiographic provinces. Despite the variability created by climate and geology, commonalities are evident among rivers at the physiographic province and terrestrial ecoregion levels. Climatic conditions change considerably from the northern extreme of the basin to its southern boundary at the confluence with the Ohio River. This chapter presents the rivers acting as a representative within each region and that reflect both the common threads among rivers in the Upper Mississippi River basin and their unique attributes. The Upper Mississippi River is the only bioregionally outstanding river. This is partly due to the fact that there is only one species of fish, one species of crayfish, and one freshwater mussel, which are endemic to the region.

[1] A graded river conveys its sediment load without net aggradation or degradation. Grade is thought to represent the equilibrium state of a river system subject to steady allogenic forcing. We address the concept of grade in linked depositional systems through a combination of mathematical modeling and flume experiments. We develop a moving boundary morphodynamic model of fluviodeltaic sedimentation and use it to quantify the conditions necessary for a state of sustained grade in an alluvial-deltaic system developing on a uniformly sloping shelf. To test our theory, we conducted a series of flume experiments in which we constructed laboratory-scale fluviodeltaic systems under specific relative sea level histories. On large spatiotemporal scales, our theoretical and experimental results suggest an alternative view of grade as an intrinsically nonequilibrium state that requires a fall in relative sea level. Under conditions of stillstand or rise in relative sea level, the equilibrium (graded) profile does not exist, and the alluvial river will always aggrade. With a steady sediment supply, alluvial grade can be sustained if relative sea level falls with a specific, square-root-of-time dependence. Common sequence-stratigraphic conceptualizations of alluvial river response to sea level change suggest that rivers aggrade and degrade in response to relative sea level rise and fall, respectively. We show that rivers can remain aggradational if the rate of sea level fall is sufficiently small. The boundary between aggradational and degradational states is the graded state described here: that associated with a relative sea level fall that varies with the square root of time.

Special issue: Sediment Management in River Systems: A Need to Assess Changing Processes in the Long Term and at a Large Scale; International audience; Hydrogeomorphic processes within alluvial river systems create, maintain and degrade riparian habitat. The dynamic interactions between water, sediment, aquatic-terrestrial landforms and biotic elements control the functional processes and biodiversity patterns within the riparian zone and, thus, contribute directly to their ecological integrity and societal value. Numerous researchers from different disciplines publish work on the physical, biological, economic and societal functions of the riparian zone within various physiographic areas. The present paper aims to review the hydrogeomorphic processes of unconfined alluvial channel-floodplain rivers within the temperate zone. These processes and their interactions with the biotic environment provide the basis for understanding the physical as well as the ecological functioning of fluvial hydrosystems. The review focuses mainly on the European context, but major advances in riparian research from other continents are also considered. Rehabilitation and management strategies for the riparian zone are summarized and recommendations for further research conclude this review. Copyright © 2005 John Wiley & Sons, Ltd.

GSTARS-1D, Generalized Sediment Transport model for Alluvial River Simulation – One Dimensional, is the latest development in the GSTARS series. GSTARS-1D is a hydraulic and sediment transport numerical model developed to simulate flows in rivers and channels with or without movable boundaries. It is able to compute water surface profiles in single channels, simple channel networks, and complex channel networks. It has both steady and unsteady flow models, many sediment transport equations, floodplain simulation, and computation of width changes using a minimization theory. Lateral inflows can be simulated along with internal boundary conditions, such as time -stage tables, rating curves, weirs, bridges, and radial gates. Two examples are presented in this paper. The first example shows the capability of the network channel simulation with sediment transport. The second example illustrates the use of the unsteady flow and unsteady sediment transport features of GSTARS-1D in real engineering problems with hydraulic structures.

Geomorphic approaches to describe and explain the equilibrium alluvial river channel form, and another approache porpuses to stable «regime» channel design, have relied on simple equations relating channel dimensions to sediment grain-size, gradient and discharge. These equations are either empirical «hydraulic geometry» equations, obtained from regression analysis of the main variables sampled in natural rivers, or «rational» regime equations derived from physical theory of hydraulics and sediment transport. In this work several theories and hypothesis on the river regime are shown in order to explain the dynamic adjustments of channels in connection with environmental changes: i) theory of unit stream power, ii) minimum energy dissipation rate , iii) dispersive-force model, iv) concepts of boundary shear stress and critical bank shear, v) other regime relationships. Finally, the last part is devoted to the application of the regime theories in arid and semi-arid environments, by considering it a complex aspect, of great interest in the hydro-morphologic context and until the moment little studied., Las aproximaciones geomórficas para describir y explicar la forma de equilibrio de un cauce fluvial y los métodos propuestos para el diseño de cauces de «régimen » estable han contado siempre con ecuaciones simples que relacionan las dimensiones del cauce con el tipo de sedimento, pendiente y caudal. Estas ecuaciones son ecuaciones empíricas de «geometría hidráulica», obtenidas a partir del análisis de regresión de variables relevantes muestreadas en cursos de agua naturales o ecuaciones «racionales » de régimen derivadas a partir de la teoría física sobre hidráulica y transporte de sedimentos. En este trabajo se muestran diferentes teorías e hipótesis de régimen para explicar el ajuste dinámico de los cauces aluviales en relación con los cambios ambientales: i) teoría de energía por unidad de corriente, ii) tasa mínima de disipación de energía, iii) modelo de fuerza dispersiva, iv) conceptos de fuerza tractiva límite y corte crítico de margen, v) otras relaciones de régimen. Finalmente, se dedica un apartado a la aplicación de las teorías de régimen en medios áridos y semiáridos, por considerarlo un aspecto complejo, de gran interés en el ámbito hidro-morfológico y hasta el momento poco estudiado.

A comprehensive model strategy is presented which enables the prediction of catchment hydrology and the dynamics of sediment transport within the alluvial river systems draining these catchments. The model is driven by AGCM-based weather predictions, generalised by using a stochastic weather generator, and by palaeo-climate and palaeo-environment reconstructions. The model consists of a lumped hydrological rainfall-runoff model, calibrated against modern daily discharge data and the AGCM control experiment, combined with simple modules for hillslope erosion, river channel geometry, sediment transport and fluvial planform type. We apply the model to a conceptualised climatic cycle, and investigate the response to brief climatic events. Model predictions are discussed and compared to reconstructed river behaviour. © 2003 Elsevier Ltd. All rights reserved.

A numerical model, which simulates the dynamics of alluvial river channels on geological (Quaternary) time scales, is presented. The model includes water flow, channel dimensions, sediment transport and channel planform type. A number of numerical experiments, which investigate the response of an alluvial river to imposed sequences of water and sediment supply, with special emphasis on the time lags between these controlling variables, as well as a downstream discharge increase, are presented. It is found that the influence of the time lags can be substantial, having major implications for the reconstructions of palaeo climate based on river channel behavior documented in the geological record. The model is further applied to both a conceptual warm - cold - warm cycle and a reconstructed evolution of the river Meuse, the Netherlands, during the Late Glacial-Holocene warming. Results show that the model is capable of explaining the response of this river, although better validation against palaeoenvironmental data remains necessary. © 2000 Elsevier Science B.V.

Alluvial river channels adjust readily to formative discharges of moderate magnitude and frequency. Bedrock river channels present various thresholds to effective channel adjustment, such that only relatively rare, high-magnitude flood discharges contribute to shaping their morphologies. Very high values of power per unit area of bed, exceeding 10 2 Wm -2 , result in high-energy erosional processes, including cavitation and macroturbulent plucking. Although these processes are best exemplified in the Channeled Scabland and other late Pleistocene cataclysmic flood channels, they also can be achieved in modern bedrock gorges where very resistant rocks are acted upon by unusually large floods. Examples include the Katherine Gorge, northern Australia, and various gorges of the Narmada and Tapi Rivers in central India. Distinctive scabland-like morphologies occur, including wide, shallow bedrock surfaces with inner channels and narrow, deep gorges. As in alluvial rivers, there may be an adjustment to energy expenditure, but at a much higher level of energy associated with rare floods.

Bed-load transport measurements of different grain-size fractions in a sand-bed river (bankfull discharge = 10 m 3 /s, width = 15 m, depth = 1.5 m, mean grain diameter = 0.5 mm) in southwest Denmark showed that the transport rate in the central grain sizes varies less than in all other fractions in the bed load. This is argued to be related to the role of point bars as sediment reservoirs. During net erosion the lower part of the point bar is eroded, and deposition takes place at the bar top, whereas the situation is reversed during net deposition. Thus, during their growth, point bars undergo repeated episodes of erosion and deposition. During these episodes the bed load is sorted. Measurements of input and output of size fractions from the studied meander bend showed that the overall effect of the size sorting is preferential deposition of fine and coarse fractions, whereas the central size fractions are preferentially transported through the bend. This type of sorting seems to be a general feature in sand-bed river bends and affects the often assumed condition of bed-load continuity for each size range in meander bends. The long-term effect of this is (1) bed load becomes better sorted during its down-valley passage through meander bends and (2) the central size fraction is less abundant in the bulk sediment of point bars than in the average bed load. Thus, during floods when point bars release sediment to the bed load, the size distribution of the bed load is preferentially supplied with sizes on each side of the central fraction.

River training comprises engineering measures and works on rivers aimed at various objectives, of which one may be defense against floods. In this chapter works on the main channel are considered insofar as they serve flood defense objectives, while the relationships between the main channel and the floodplain are discussed in another chapter by the same author1.

A sediment-transport model that simulates channel change was applied to a reach of Cuchillo Negro Creek at the Interstate 25 crossing near Truth or Consequences, New Mexico. A 5,340-foot reach extending upstream and downstream from the crossing was modeled using the Bridge-Stream Tube model for Alluvial River Simulation (BRI-STARS). The Federal Highway Administration has recommended that simulations of bed scour be based on extreme events such as the 500-year peak discharge. The 100-year peak discharge was estimated to be 6,290 cubic feet per second. The 500-year peak discharge was estimated to be 10,700 cubic feet per second for the Cuchillo Negro Creek site. The regional maximum-peak discharge was estimated to be 81,700 cubic feet per second, based on maximum-peak discharge data for 259 streamflow-gaging stations in New Mexico. A bed-material sample was collected at the bed surface and at 13 feet below the bed surface, which was a depth greater than the anticipated scour depth. The median diameter was 4.6 millimeters at the bed surface and 9.0 millimeters 13 feet below the bed surface. Bed-material particle-size distribution was determined for six size classes ranging from 1 to 30 millimeters. Bed-material discharge was estimated at 18,770 tons per day using hydraulic properties, water temperature, and Yang's equation. Channel-change simulations showed a maximum channel fill of 0.13 foot for a 500-year flood. Maximum contraction and channel scour of 1.38 feet were simulated for the regional maximum-peak discharge flood. Maximum total scour was simulated to be 5.72 feet for the 500- year flood and 8.74 feet for the regional maximum-peak discharge flood. The simulations showed about 10 feet of pile freeboard remaining after passage of the 500-year flood. Historically, degradation has occurred at the bridges and the simulations of present channel conditions did not show the prior degradation. A hypothesis that the channel thalweg was not at equilibrium during the prior gravel mining was evaluated. Representation of present channel conditions was modified to simulate an excavation extending from about 500 feet below the downstream bridge to the end of the study reach. Simulations of the 500-year flood showed that degradation occurs at the upstream end of the hypothetical gravel mining area. The simulations showed a degradation at the peak discharge and a continuation of degradation throughout the flow event. The simulations used to evaluate this hypothesis show that the channel thalweg was not at equilibrium during the gravel mining and that bed material was subject to transport into the excavated area.

Alluvial rivers at low land as in Bangladesh are highly dynamic in nature; where huge landloss due to severe bank erosion at high flood as well as repeated interruptions of navigation system due to rapid sedimentation at low flow are very common. Groynes, revetments etc. are typically used to overcome these problems, but the goals are not achieved as expected. This study investigates the optimum design of a groyne for its effective functioning. A 2D model, RIC-Nays is utilized in this study upon confirmation. The channel and flow parameters are based on conformity to a typical river of Bangladesh. Four orientations and three configurations of groynes are considered here. The performance of groynes is evaluated through three key indices erosion in channel bed (thalweg), deposition in groyne field, and scour near groyne-tip. Computations reveal that a modified groyne functions better over the straight ones through protection of channel bank from erosion and maintenance of navigation channel as well.

The Choctawhatchee River system, which originates in Alabama and flows through a little developed portion of the Florida panhandle, is a major alluvial river that is the third largest in Florida in terms of discharge. Water and sediment quality analyses and biological investigations over a 12-month period indicated that, overall, the Florida portion of the Choctawhatchee remains in relatively good condition. Periodic water quality decreases were noted in some of the tributaries, however, and there were some indications of adverse effects due to clear-cutting in one of the tributaries.

Florida’s high rainfall and low topographic relief combine to produce a surprising variety of low-gradient streams. The intent of this chapter is to describe physical attributes and processes associated with these lotic environments. I employ the definition of “stream” used by Beck (1965), which is, “a body of water with unidirectional flow of measurable velocity.” This inclusive definition allows the recognition of some unusual Florida stream environments.

Snow and glacier cover in the western Himalaya region are very important because four major rivers—the Indus, Ganga, Brahmaputra, and Yamuna—originate there. Changes in snow and glacier cover influence the discharge and flow of these perennial rivers, which together constitute one of the world's largest alluvial river basins, the Indo-Gangetic (IG) basin. This basin is agriculturally fertile and densely populated with 700 million people. In the past, the basin has experienced numerous floods due to snow melting and also due to excessive monsoon rainfall. However, in recent years the areal extent of snow has been declining, especially in the western Himalayan region that has a direct influence over the hydrological regime of the basin and that also plays an important role in the changing climatic conditions of the Indian subcontinent.

Studies on the interaction of tide and river flow are scarce, while studies on the simplified characteristics of tides in canals and gulfs are common. This study employs the perturbation method to solve analytically the interaction of tides and river flow, taking into account the nonlinear convective inertia and bottom friction. Appropriate characteristics of the interaction obtained from an analysis of five records along a river are used in the derivation and verification. The study finds that the interaction of the tide and the river flow is well-described by the analytical solution for implicit doppler shift. Exclusion of convective term yields an underestimation of the tidal damping. The river flow raises the mean water level but damps the tide and reduces its celerity. The raising of the mean water level during a high discharge is more than the damping of the tide, causing flooding at high water level. Application of the analytical solutions for any value of the river flow requires only the bottom condition of the river, which is found to be smooth for the large alluvial river.

A simple model is considered describing tidal effects in a plane alluvial river with a mean seaward flow. The effects of quadratic resistance and sediment transport are accounted for in the model. It is shown that quadratic resistance introduces exponential decay of tidal effects together with a phase change between the free surface and the fluid velocity. The dissipation length and the phase change are examined quantitatively.

The regime slope adjustment from an alluvial river to an underfit stream with markedly decreased discharge is analyzed. Underfit streams in ample river valleys are usually characterized by a distinct meandering pattern. Such a feature is explained by the development of a stream slope flatter than the river valley slope in response to the discharge reduction. A regime equation which relates channel slope to the discharge, bedload and bed sediment size is developed. From this equation, the bedload/discharge ratio (or bedload content) for an alluvial channel reach of constant slope and sediment size varies as a direct function of the discharge. The bedload/discharge ratio decreases more rapidly as the discharge decreases toward the threshold for bedload movement. A channel reach is usually supplied by tributaries of smaller discharges. Following a marked decrease in discharge, the bedload/discharge ratio in the water-sediment mixture supplied to the reach usually decreases faster than that required to maintain the constant slope. In response to the deficiency in bedload content, the underfit stream eventually develops a flatter slope, i.e. a meandering pattern, in addition to other adjustments.

Natural alluvial river channels, in contrast to most regime or equilibrium canals, are characterized by variable streamflows. This paper relates channel geometry to measures of streamflow variability as distinct from mean discharge or flow magnitude. A relationship between mean channel width and the mean and coefficient of variation of channel-forming discharges is derived. For the given mean discharge it is shown that the more variable the flow, the narrower the Channel is in the mean. To a great extent, this relationship is confirmed by data on alluvial channels in the Missouri River basin. Variability of water discharges proves to be an important factor influencing natural river geometry. This initial approach to the understanding of the dynamics of river geometry leads to the construction of a simple simulation model in which a series of channel forming discharges is generated and corresponding changing channel geometry is calculated. Results from the simulation indicate (1) the channel has, in effect, a kind of truncated memory; i.e., the impact of an existing channel exists so long as the prevailing discharge does not exceed the present channel capacity; (2) the effect of memory or the impact of the existing channel on the mean channel geometry is opposite to that of flow variability (i.e., the memory tends to keep the channel geometry larger in the mean); (3) the simulated channel width, as expected, increases abruptly at high discharges, declining over time along a die-away curve until the advent of a recorded high flow.

An unidimensional model of alluvial river is developed to take account of temporal and spatial evolutions of bed (and bed load) grain compositions. The set of equations is solved in a fully coupled manner; numerical coefficients of the implicit scheme allow to optimize the time step value. A bed load "loading law" is included in the model. Some examples derived from the general features of the "middle third" of the Rhone river make clear how the flow unsteadiness affects the bed evolutions, through grain sorting and bed armouring.

Uniform flow in curved, wide, erodible-bed channels is formulated on the basis of the conservation of flux of moment-of-momentum, to obtain relations for the vertical distributions of radial-plane velocity and radial shear stress. The expression for the radial stress exerted on the bed is utilized in a force-equilibrium analysis of the moving bed layer to obtain relations for the average transverse slope of the bed and for the radial bed profile. The reduction of primary bed shear stress due to the net radial transport of streamwise momentum toward the outer (concave) bank is then calculated, by introducing the derived expressions for the velocity components into the momentum equation for the primary-flow direction. It is found that the stress reductions in deep, narrow channels can exceed 50%. Bed profiles and velocity distributions measured in natural and laboratory streams are found to be in good conformity with those calculated from this moment-based theory.

The annual smartweeds Polygonum lapathifolium L., P. pensylvanicum L., and P. persicaria L. grow on alluvial river bars during the summer and autumn when their substrate is free of flood waters and physical disturbance. They are dependent upon dispersal for the annual recolonization of this habitat. Achenes are the only diaspores (dispersal units), and hydrochory (water dispersal) appears to be a major dispersal method.An experimental study of water dispersal of these species revealed several adaptive features. The coordination of fruit fall with the availability of the agent (flood water) ensures that the achenes are picked up. The duration of buoyancy is adequate for successful transport downstream. The presence and condition of the perianth, degree of water turbulence, and achene size are factors which determine the duration of buoyancy. Alteration of the degree of dormancy but no loss of viability occurs as a result of water transport. After deposition the achenes may remain dormant or germinate rapidly depending on environmental conditions. The deposition stage (and therefore, hydrochory) is unsuccessful for most achenes of P. persicaria, which rapidly lose viability in sites where deposition is likely to occur. The presence of this species on alluvial bars must be due to other means of dispersal.

The evolution of a localized disturbance imposed upon an otherwise uniform alluvial flow is considered. For small disturbances a linearized theory is developed which shows that the initial disturbance splits into two modes. One mode is stationary and purely diffusive while the other mode propagates. The propagating mode may exhibit diffusion or, for sufficiently high Froude numbers instability of the “roll-wave” type. The theory provides the relevant diffusion, propagation and instability time scales associates with the two modes.

Radioactive isotopes have been applied for determining the transport rate of bed load in an alluvial river on the basis of: centroid velocity of the tracer particles, size and material-transporting width of mobile layer. These parameters were found by detailed measurements in the field. Computed values were produced on the basis of Engelund and Fredsøe's model on sediment transport (1976) and on the propagation of bed forms. When comparing measured and computed values, the difference was about 25%. Finally, the applicability of tracer methods for solving practical problems is discussed.

The Lower Kama hydroelectric station on the Kama River, the foundation of which is composed of ancient alluvial river deposits, is a typical run-of-river hydrostation with respect to design and layout. The 486-mtong powerhouse, 71-m-long overflow dam, and earth dam form a single barrier. The powerhouse is combined with outlets and is divided into eight sections. Two vertical units are located in each section. The sections are separated by 30-cm-wide contraction joints. The cavity of the contraction joints between sections is sealed on the upstream and downstream sides by asphalt shaft waterbars Nos. 12 and 14, the design of which is shown in Figs. 1 and 2. The rooms of the powerhous along the joints are sealed by contour {elastic) waterbars. The shaft waterbars along the foundation slab of the sections are connected to horizontal asphalt waterbars of a U-shaped profile. On the upstreamside a spare shaft is made in the joint for the possibility of making asphalt waterbar No. 13. The cavity of the joint during normal operation is filled with water to elevations corresponding to the lower pool levels and elevation of the bypass (pipe d = 100 mm), which provides discharge of water seeping into the joint into the lower pool, bypassing shaft waterbar No. 14. The capacity of the bypass when k = 1 m is 1 ma/min. During temporary operation of the hydrostation at an intermediate reservoir elevation of 62 m considerable leaks into the joint were observed, in connection with which the water levels for a number of joints exceeded the design. This led to complications in operating the equipment, including flooding of the cable galleries. Attempts to heat the asphalt waterbars by an electrical heating system embedded in the waterbar structure did not yield positive results as a consequence of breaks in the circuit of the heating electrodes during Construction works. In 1983 the Kama Hydroelectric Station Construction Association {Kamges~nergostroi) turned to the Institute for Special Operations (Gidrospetsproekt) and the State All-Union Trust for Reinforcement of Foundations and Structures (Gidrospetsstroi) with the request to give recommendations and to perform repair and restoration works on the shaft waterbars in order to provide the design water level in the cavity ofthesectionjoin ts.

Formation of ripples and dunes on alluvial river bed is studied by river bed stability analysis, basing on two-dimensional shear flow equation and a Meyer-Peter and Wuller type bed load transport equation modified by the inclusion of the lag distance of bed load relative to local bed shear. Dominant dimensionless wave-numbers of sand wave are analyzed. The effect of sediment particle diameter and lag distance on the dominant wavenumbers is examined, and the difference between ripples and dunes, with respect to their cause of occurrence, is discussed.

In the Cambridge Gulf-Ord River region of Australia, an area that experiences a dry monsoonal climate and a high tidal range (5.9 m), a variety of tidal-plain and fluvial depositional environments were recognized. Near the coast, prograding shorelines are characterized by extensive mangrove successional sequences and scattered thin beach-ridge deposits. In the interfluve regions and farther inland along the coast, tidal-plain sedimentation has given rise to extensive flats that are bare of vegetation at approximately the high spring tide level. Evaporites, algal-layered silts and clays, and massive sandy deposits form the bulk of these tidal-flat sediments. Sinuous tidal channels, displaying low width/depth ratios and characterized by a progressive tide wave, are found throughout the coastal tidal-flat region. These channels migrate laterally, leaving preserved channel sand bodies isolated in tidal deposits. In the funnel-shaped channel of the Ord River, the major river in the region receiving freshwater ...

On the south side of the river Calder, at Mytholmroyd, is a plateau or terrace raised some 20 to 50 feet above the present banks of the river, from which it is separated by a narrow tract of alluvial holm land. This terrace is about half a mile long, by 300 to 400 yards wide, and is on the 330 to 360 feet Datum level. It is bounded on the west by Stubbs Clough and Hawks Clough, and on the east it extends to within about 100 yards of the Cragg Brook, near its junction with the Calder, whilst on the south it abuts against and is bounded by the rising valley sides. Although the Cragg Vale Brook has almost evidently cut through and worn back the eastern edge of this terrace, the stream is now seen running against a cliff of grit shales on its east bank, and there is no evidence of drift deposits on that side. To the casual observer this terrace has the appearance of a well-defined alluvial river terrace only. For many years, however, local geologists have known that the deposits forming the terrace contained more than the ordinary river alluvium and local rocks, and it appears somewhat strange that the Memoirs of the Geological Survey of the Burnley Coal Field, which include this district, make no allusion to the discovery of erratics here. Although these Memoirs were published so late as A.D. 1874, the authors say in reference to this area, “The only part ...

This paper covers building damage occurring in the area between Inangahua Landing (approximately 14 miles north of Reefton,) Reefton itself and down to Totara Flat (approximately 16 miles south-west of Reefton). Reefton is an old mining town on the upper reaches of the Inangahua River some 20 miles above and to the south of Inangahua itself. It is administered as a County Town. The township of Reefton and in fact practically all structures in the area were situated on alluvial river flats, a fact of some significance in the damage observed. Almost without exception every property owner in the area suffered some damage. The degree of damage was greatest in the Rotokehu area, north of Reefton, but the extent of damage was of course greatest in the Reefton Township. There were in all some 665 claims against the Earthquake and War Damage Commission totalling some $205,000. There were few structures of significance and most buildings in the area were old or very old, but a number of new structures have been built in the last few years. On account of age and arrears of maintenance many buildings in the area were in poor condition before the earthquake, although their age indicates they must have survived previous earthquakes.

Hydraulic model studies for investigation of channel stabilization problems on the Mississippi, Ohio, Middle Rio Grande, and Arkansas Rivers are summarized. Most of the studies were conducted with models of the movable-bed type for the purpose of predicting changes in channel regime, for determining causes of failure of channel stabilization works, and for the design of systems of channel stabilization works. There has been a steady trend toward the use of models of larger scale and with smaller distortion, and movable-bed model techniques have been improved and refined. During the past 35 yr, models have made significant contributions to the understanding of alluvial river phenomena and to the development of the design of bank stabilization works.

Two new specific projects show the development of the panels as permanent river training structures. New information and references concerning 6 yr. of progress in theory, scale models and experiments in situ are presented herein. The works on the Loire River in France are linked with the cooling system of a nuclear power plant; on the Chao Phya River, the project deals with the improvement of navigation over a 100-km long reach. After 14 yrs. of experiments on large and wide waterways in Africa and Asia, followed by training works on medium wide reaches in France and Thailand, the scope of bottom panels on alluvial river with a gentle slope has been broadly investigated. This comparatively inexpensive method has been quite well controlled, however, the feasibility of panels must always be studied very carefully under new hydraulic and economic conditions.

The distribution of Arianta arbustorum, Cepaea nemoralis and C. hortensis, and the variations in the shell polymorphism of the Cepaea species have been studied in an area of low chalk downland and alluvial river valleys near Rickmansworth, Hertfordshire. The distribution of A. arbustorum is restricted, the species being largely confined to the bottoms of river valleys, especially in hedgerows. Variations in dampness seem the most likely limiting factor. C. hortensis is widespread and found in many habitats, but C. nemoralis is largely confined to woods, and is especially common in beechwoods. The morph-frequencies of C. nemoralis and C. hortensis vary in such a way as to suggest the operation of climatic and visual selection. In C. hortensis there are area effects for the presence or absence of pink five-banded shells, and there is an overall linkage disequilibrium resulting in an excess of unbandeds in non-yellow shells. Reasonable evidence for the operation of random factors in determining the morph-frequencies of populations of Cepaea in the area has been found only for three very disturbed populations. It is suggested that the large number of selective forces known to act on Cepaea populations in this area will account for the variation in morph-frequencies in populations from the same area or habitat.