Showing papers in "Journal of Hydraulic Engineering in 1979"

Flow Resistance in Gravel-Bed Rivers

Abstract: The resistance to uniform flow in straight gravel-bed rivers is basically dependent on the flow geometry, the cross-sectional variation in roughness heights, and the roughness height of the graded gravel bed sediment. The effect of these factors on the resistance to flow is evaluated and a general approach for the estimation of the Darcy-Weisbach friction factor is presented. Independent field data indicates that the method can be successfully applied to predict the resistance to uniform flow in gravel-bed rivers.

Inception of sediment transport

Abstract: Sediment transport inception curves corresponding to both laminar and turbulent flows are presented. Using these curves one can determine the critical bed shear stress (corresponding to the beginning of sediment transport) depending on the properties of the fluid and of the cohesionless bed material. The laminar flow curve has been revealed on the basis of laboratory measurements carried out by the writers. The curve corresponding to turbulent flows has been established mainly using the available data of previous researchers. It has been found that the laminar flow curve lies in the Shields' plane higher than the turbulent flow curve and thus it yields larger critical values of the dimensionless bed shear stress. Both curves tend to become indistinguishable from each other when the grain size Reynolds number decreases, i.e., when the influence of viscosity on the turbulent flow at the bed increases. For larger values of this number the turbulent flow curve can be identified with the classical Shields' curve.

Hydraulic geometry of active gravel rivers

Abstract: The hydraulic geometry of straight reaches of wide, active rivers with beds and banks composed of loose gravel is considered. Naive mechanistic formulations lead to the stable channel paradox; stable width is incompatible with an active bed. A resolution of the paradox based on bed stress redistribution due to turbulent lateral transfer of downstream momentum is outlined and is used to obtain three rationally derived regime relations.These dimensionless relations provide channel properties as functions of bed pavement size and two specified variables, e.g., water and sediment discharge, or water discharge and width. Reduction to relations for hydraulic geometry is shown to require information concerning watershed mechanics that is external to the river, and thus fluvially indeterminate. An empirical relation is determined for this purpose, allowing for derivation of dimensionless relations for hydraulic geometry.

Estimating Average Velocity in Gravel-Bed Rivers

Abstract: Basic data from 67 gravel-bed river reaches in Alberta, Canada, are used to test widely adopted equations for computing average velocity in natural channels for the case of relatively high in-bank flows. Relations proposed by Cowan, Strickler, and Limerinos to estimate Manning's n are tested. The equations of the form presented by Keulegan and Lacey for computing average velocity are also evaluated. Computations based on these methods indicate that the Limerinos-Manning equation is the most acceptable approach for estimating average velocity in gravel-bed river reaches. The Lacey equation provides satisfactory results if no bed material data are available. The basic data are also used to develop best-fit relationships for computing Manning's n and the friction factor for gravel-bed river reaches. Particular emphasis is placed on an evaluation of the significance of bed material data in equations used to compute average velocity in gravel-bed river reaches.

Secondary Flow and Shear Stress at River Bends

Abstract: Field measurements are presented to illustrate the pattern of secondary circulation at river bends, the effect of the circulation on boundary shear stress disbribution, and the way in which that effect changes with discharge. The field results show that, in addition to the classical main cell, there can be a small cell of opposite circulation close to the outer bank provided the bank is steep. The circulation distorts the primary isovel pattern and thereby affects the positions and relative magnitudes of the boundary shear stress peaks associated with regions of downwelling and high velocity. Secondary circulation appears to be weakest at low and high discharges and to be strongest, with its greatest effect on the shear stress distribution, at medium discharges. Generally the distribution of shear stress at a section becomes more uniform as discharge increases and at high discharges is determined mainly by primary flow effects.

Calculation of strongly curved open channel flow

Abstract: The paper describes the application of a finite-difference calculation procedure to the problem of simulating the three-dimensional, turbulent flow in a strongly curved, open, 180° bend with straight inlet and outlet reaches. The configuration can be considered to represent an element of a model meander, and the work presented here forms an important stage in efforts to simulate the flow in successive reverse-curvature bends. No restrictions other than the absence of flow separation and hydraulic jumps are imposed. Full account is taken of non-linear fluid-inertia and of turbulent diffusion terms. Effects of turbulence are represented by an eddy viscosity related to two parameters— the turbulent kinetic energy k and its rate of dissipation ϵ\N— for which related differential transport equations are solved. Predictions are presented for the transverse surface slope and velocity field in a configuration experimentally examined by Rozovskii. Agreement between predictions and experimental data is judged to be satisfactory on all major flow phenomena.

Side Weir in Rectangular Channel

Abstract: The discharge characteristics of a side weir at the head of a branch channel taking off at right angles to the main channel have been investigated. Both sharp-crested and broad-crested weirs are studied for the case of subcritical flow in the main channel. A procedure of design based on De Marchi's theory has been evolved. The De Marchi coefficient is empirically related to the Froude number at the upstream end of the weir and the ratio of the upstream depth (above the weir crest) to the length of the weir.

Theory of Minimum Rate of Energy Dissipation

Abstract: A general theory of minimum rate of energy dissipation for a class of open channel flows with or without the movement of sediment is proposed in this paper. This theory states that the rate of energy dissipation is a minimum under steady equilibrium or gradually varied flow conditions. The theory is derived from the Navier-Stoke's equations of motion for gradually varied open channel flow without sediment transport. It applies to turbulent and laminar flows as long as the inertia forces due to the time-averaged velocity distribution is small compared with the forces due to gravity and shear. The theory in different degrees of generality can be used to explain the fluvial processes from the movement of sediment to the change of velocity, slope, roughness, channel geometry, pattern, and profile of a river under an eqiulibrium condition or during the process of self-adjustment to reach an equilibrium condition.

Collie River Underflow into the Wellington Reservoir

Abstract: Field data gathered from a Western Australian reservoir are used to obtain an estimate for the entrainment coefficient of the underflowing river. By the use of a steady normal flow theory, the entrainment coefficient is related to the flow and river channel characteristics. By combination with a general turbulent entrainment law, it is shown that the entrainment coefficient and dilution may be directly related to the physical characteristics of the river channel, and thus may be estimated without recourse to a field experiment. In order to determine the initial underflow depth and the location of the plunge line, a simple theory using the concept of a normal flow depth is used, the results of which compare favorably with observation.

Approximate Flood Routing Methods: A Review

Abstract: Some well-known approximate flood routing models, including diffusion analogy models, kinematic wave models, and various extensions of the storage routing methods, are reviewed in the light of their theoretical background. A class of kinematic models is identified and close relationships among many superficially diverse models are demonstrated. Limits of application for different groups of models are indicated and some emphasis is placed on the analyses of parameter selection procedures. Attention is drawn to the kinematic model corrected for dynamic effects, a generalized model developed recently by Koussis. It covers the widest range of practical applications, excluding only cases where dynamic effects or downstream disturbances play a major role. Other features are reviewed which make the Koussis model an ideal framework for the development of generalized computer programs for approximate flood routing computations.

Gravel Size Analysis from Photographs

Abstract: Gravel sizes measured from photographs of river beds are biased estimates of size when compared to standard sieve analysis. Mean apparent short axis size (for gravel coarser than 8 mm) from photographs may be converted to sieve-equivalent mean size by subtracting 0.1 phi (if mean size in phi units) or multiplying by 1.07 (if mean size in mm). Percentile of the distribution also differ by the same factors. Measures of grain size standard deviation from photographs are approximately equivalent to sieve values. For sizes in phi units the photograph and sieve size frequency distribution curves have similar shape, but are offset by the same bias as the mean size.

Downstream Effects of Stormwater Management Basins

Abstract: Urbanization decreases the natural storage of a watershed, which changes the timing characteristics of the runoff. Stormwater management (SWM) basins are an attempt to put the storage lost through development back into the runoff process. While SWM basins provide the proper volume of storage, they fail to return the timing characteristics to those that existed prior to development. The changes in storage and timing characteristics may have adverse effects on flow rates and bedload transport in downstream channel reaches. A study of a 2.12-sq mile watershed in Montgomery County, Md., showed that a SWM basin increased both peak flows and bedload transport rates in the channel downstream from the facility. This results from both the change in timing characteristics and the increased duration of bankfull flow. These results indicate that SWM policies must require evaluation of SWM plans on a regional basis and not just using on-site control criteria. Also, methods that can evaluate storage and timing changes must be used in the design of SWM facilities.

Line Plume and Ocean Outfall Dispersion

Abstract: The three-dimensional flowfield created by a line plume of finite length in a steady unstratified current was investigated experimentally and theoretically. The results are applicable to ocean sewer outfall design. Even though the diffuser length may be much greater than the water depth, the flowfield cannot be considered to be two dimensional. The most important dynamic parameter is a Froude number, F, given by the ratio of the current speed cubed to the buoyancy flux discharged per unit diffuser length. Different mixing regimes can occur depending on the value of F and the plume can be attached to the lower boundary. Dilution depends on current speed and direction only for F>0.1. For F>0.1, dilution increases with current speed and diffusers perpendicular to the current will result in greater dilution than if parallel. The surface wastefield spreads rapidly in a parallel current, showing that Y or similarly shaped diffusers are not essential to produce a widely dispersed wastefield. The buoyant spreading of the surface wastefield is a complex phenomenon, having growth laws that change with distance downstream.

Hydraulic Resistance of Artificial Strip Roughness

Abstract: An experimental study of two-dimensional flow over non-uniform roughness is reported in which artificial strip roughness was employed. The roughness elements were square in cross section and placed at different relative spacings. A six-fold classification system is suggested based upon the ideas of Morris and Adachi. Resistance data from other investigators is also considered, and the variation of resistance coefficient with Reynolds number, relative spacing, and relative depth examined. The general resistance parameter, X, first introduced by Sayre and Albertson is found to be particularly helpful in synthesizing the various sets of resistance data. Logarithmic resistance equations involving X are validated over a wide range of roughness wavelength to height ratio. The relationship between roughness height and Nikuradse's equivalent sand roughness size is also examined.

Model for Suspended Sediment Transport

Abstract: A mathematical model for suspended sediment transport is described, which enables the investigation of certain effects of river works or geometrical changes, or both, in a river or estuary by morphological computations. The model is based on the two-dimensional diffusion-convection equation. This equation describes the distribution of the sediment concentrations in a two-dimensional flow field by diffusion and convection. For the local velocities in the vertical the logarithmic distribution is used, while for the sediment diffusion coefficient a new expression is applied. The diffusion-convection equation is solved by an implicit numerical method using a coordinate transformation, while the influence of the diffusion coefficient on the adaptation of the transport in the case of an overcapacity of sediment is presented. A dimensionless graph of the adaptation length of a uniform concentration vertical is given, the application of the model for tidal flow is described and for such conditions a prototype verification and a sensitivity analysis is given. The model is limited to situations with relatively small changes in lateral direction and nongraded bed.

Steepness of Sedimentary Dunes

Abstract: A family of curves is determined for the prediction of the steepness of dunes generated by rivers and open channel flows by using field and laboratory data from various sources. The dune steepness appears to be determined by two dimensionless variables: the ratio of the existing bed shear stress to the shear stress inducing the inception of sediment transport, and the ratio of the flow depth to the grain size of sediment. It has been found that with the increment of the former variable the dune steepness first increases, then reaches its maximum value and then progressively decreases as to vanish asymptotically. The increment of the second variable causes only the increment of the dune steepness up to a certain upper limit. The curves forming the family are normalized as to merge into a single curve which is formulated in an exponential form.

Geometry of Rivers in Regime

Abstract: An analytical method has been developed for computing the self-adjusted geometry of sand-bed rivers based upon a sediment discharge formula, a flow resistance relationship, and the concept of minimum stream power. Regime rivers with low values of discharge Q and slope S are characterized by small width-depth ratios (generally less than 30) that are not sensitive to the change in slope or discharge. Most regime canals belong to this category. But for larger values of Q or S, or both, the results show that regime rivers may have large width-depth ratios sensitive to the changes in Q or S. As Q or S increases the width-depth ratio of a regime river may become so large that it indicates a braided channel pattern. However, a much smaller width-depth ratio under this situation is also a possible stable geometry. The stable geometry was obtained from the stream power analysis wherein each stable configuration is assumed to correspond to a minimum stream power for the given constraints.

Interaction between Main Channel and Flood-Plain Flows

Abstract: The experimental results presented in this paper have demonstrated the transport of longitudinal momentum from the main channel to the flood plain. This transport increases the bed shear stress in the flood plain and produces the opposite result on the main channel. The velocity profiles in the region affected by this interaction have been found to be similar if viewed with respect to the undisturbed flow in the flood plain. The velocity and length scales have been correlated with mainly the ratio of the depth of flow in the main channel to that in the flood plain. In the present experiments, the main channel was narrow and thus the interaction extended inwards to the center line of the main channel. For the concepts introduced in this paper to be used in solving practical problems, further experiments should be conducted with wider main channels including the effects of bed roughness.

Experiments in Longitudinal Dispersion with Dead Zones

Abstract: A series of laboratory experiments is reported which lends support for the need to consider the effects of dead zone trapping on the longitudinal dispersion process in natural streams. This may offer an explanation for the apparent non-applicability of Taylor's theory in some rivers. The results of an experiment devised to test the frozen cloud hypothesis with dead zones are presented. Experiments show an increase in the dispersion coefficient and delay in arrival at the diffusive period due to the presence of dead zones. These results are used to verify a two-dimensional computer solution which has been previously reported by the authors.

Open Channel Flow with Varying Bed Roughness

Abstract: The distribution of velocity and boundary shear stress in a rectangular flume has been examined experimentally, and the influence of varying the bed roughness and aspect ratio assessed. The resistance of the channel bed was varied by means of artificial strip roughness elements, and measurements made of the wall and bed shear stresses. Dimensionless plots of both shear stress and shear force parameters are presented for different bed roughnesses and aspect ratios, and these serve to illustrate the complex way in which such parameters vary. The definition of a wide channel is also examined, and a graph giving the limiting aspect ratio for different roughness conditions is presented. The boundary shear stress distributions and isovel patterns are used to examine one of the standard side-wall correction procedures. One of the basic assumptions underlying the procedure is found to be untenable due to the cross channel transfer of linear momentum.

Probability Analysis of Historical Flood Data

Abstract: In addition to routinely collected hydrometric data, information on past river water levels at a site can often be gathered from various other sources such as residents and archives. However these sources generally have varying reliability, overlapping and broken periods of record, and no well-defined reference levels—features that have made the probability analysis of this data difficult. The paper describes a simple method of incorporating such data into probability analyses and illustrates it by application to the probability analysis of ice breakup stages on the Peace River at Fort Vermilion, Alberta, Canada. There is generally little standard hydrometric information on such water levels, yet they are often a very significant component of the annual maximum water levels in cold regions. In such situations the analysis of historical data is particularly important.

Flood Frequency Estimates on Alluvial Fans

Abstract: A uniform method has been presented for the determination of flood flow frequencies on alluvial fans. The method is based on geomorphologic principles, and has general applicability. There are three basic assumptions underlying the proposed method. The first assumes that a log Pearson III distribution applies to the distribution of flood flows at the apex. The second basic assumption is that each event forms a single channel and flow remains in that channel throughout the event. The third basic assumption is that flood channels are distributed uniformly across any contour. The concept is basically reasonable, but it ignores the fact that equally valid assumptions concerning placing of channels and placing of centers of channels would result in different probabilities, particularly within one stream width of the edge of an alluvial fan.

Kaolinite Resuspension Properties

Abstract: Limited experiments on the initiation of motion of sand grains in the annular channel-ring system showed a reasonable agreement with Shields. curve for incipient motion. The resuspension rates of stratified beds continuously decrease, and may even become zero, as the depth of erosion increases. On the other hand, the erosion rates of uniform beds remain constant. This is in agreement with earlier observations on natural bay deposits. The nondimensional plot of the erosion rate against the bed shear stress for uniform beds agrees with earlier results based on soils with drastically different mineralogical composition.

Radial Hydraulic Jump

Abstract: Radial hydraulic jump occurs in a stilling basin with diverging side walls. Experimental data is used to obtain the free-surface profiles and the floor-pressure profiles within the diverging basin. These profiles are used to develop generalized equations for the effective side wall forces for Froude numbers from 2 to 10. The momentum equation, which involves these forces, is then applied to develop an equation for the sequent depth ratio for the jump. For Froude numbers above 3, the sequent depth ratio is shown to be less than that for the rectangular jump. The length of the radial jump is about 70% of the length of a rectangular jump for the same initial Froude number. However, the volume of the jump is approximately the same as for the rectangular jump. The energy dissipation in the radial jump is approx 15% greater than for the rectangular jump.

Shear-Stress Distribution in Stable Channel Bends

Abstract: A theoretical and experimental investigation is made concerning the relationships between secondary flow phenomena in alluvial channel bends and boundary shear-stress distribution and related stable bed topography generated in the vicinity of same. The physical model, a wide rectangular channel system in which two-dimensional flow conditions were reproduced, incorporated an adjustable bend test section and bends having central angles of 45—, 60—, and 70? were adopted in the study. Particular emphasis was placed on an examination of the secondary circulation decay process along that portion of the straight channel reach immediately following the bend section. Observed stable bed topography within the bend and along the downstream decay zone related favorably to the steady-state boundary shear-stress distributions obtained from a numerical model of the flow field therein.

Simplified Muskingum Routing Equation

Abstract: The Muskingum method and its variations are well established in the flood routing literature. Traditionally, its parameters K and X have been determined by calibration using measured inflow and outflow hydrographs. An improved version is due to Cunge, who showed that parameters K and X could be related to the physical problem, thus eliminating the need for trial and error calibration while at the same time enhancing the predictive capabilities of the method.

Estimating Design Flows for Urban Drainage

Abstract: As an area urbanizes, peak runoff tends to increase. But the effects of urbanization on storm flows can be offset by a policy of requiring detention storage. A new method for computing design flows and storage volumes has been developed to prepare a master drainage plan for a municipality in Western Canada. The method involves use of a hydrologic model to analyze all the significant storms of record over the range of parameter values likely to apply in the area, a frequency analysis of the computed peaks, storage of the results in a large matrix in a computer, and subsequent interpolation of the stored data. By inputting estimated values of the parameters for any particular basin, the user can obtain peak flows for any desired return period and also the amount of detention storage required. Parameters can be specified either with single values or by ranges, taking into account parameter uncertainty.

Disaggregation of Streamflow Volumes

Abstract: A disaggregation model, which differs from those developed by Valencia and Schaake (VS) and Mejia and Rousselle (MR) (referred to as the HB model), was developed specifically to preserve correlations between seasons joining water years in addition to the properties preserved by the basic VS model. The HB model simultaneously disaggregates two consecutive annual flow volumes, then the next two, etc. The HB model is extended to be able to disaggregate skewed seasonal flows that follow three-parameter log-normal distributions (3PLN). Mixtures of skewed and nonskewed seasonal flow volumes are approximated by 3PLN distributions for operational convenience. Practical considerations concerning use of these models for multisite flow disaggregation are reviewed together with computational space requirements and limitations on model computability. A HB 3PLN model for single-site flow disaggregation is used in an example application where comparisons are made with the MR model.

Two-Dimensional Bubble Plumes

Abstract: The behavior of large and small-scale bubble plumes is compared with that of plumes in which the buoyancy is miscible with the surrounding fluid. It is found that the structure of bubble plumes is determined by the value of a Weber number based on the ratio of buoyant and surface tension forces at the source. At low Weber numbers the structure tends to be self-preserving and the current generating capability is otpimized.

Drifting Snow Similitude

Abstract: The problem of modeling the drifting of snow in a boundary layer wind tunnel is reviewed. The important dimensionless parameters that govern the drifting phenomena are introduced. Theoretical means such as the equations for mass transport rate of saltating material and the particle trajectory equations of motion are used to combine these dimensionless parameters into five similitude parameters. These final five parameters are analyzed as to their relative importance in the wind tunnel simulation of drifting snow. The properties of snow and of possible modeling materials are examined, and the final results of a previous study involving simulation of sand movement are presented. Use of a variety of model particles and the variation of vertical distortion of the modeled topography can aid in application of the results to full-scale conditions. Quantitative scaling can be achieved by measurement of the rate of accumulation of drifting material.