Showing papers in "Journal of Hydraulic Engineering in 1982"

Bedload and Size Distribution in Paved Gravel-Bed Streams

Abstract: Field data are used to study the size distribution of bedload in paved gravel-bed streams Similarity analysis yields the results that all grain size ranges are of approximately equal transportability when the critical condition for breaking the pavement is exceeded This result is only approximately correct due to deviations from similarity However, it is adequate to justify development of a method for calculating total bedload, which requires only the subpavement median grain size rather than the size distribution A method for calculating bedload size distribution that accounts for deviation from similarity is also developed

Calculation of Secondary Currents in Channel Flow

Abstract: A model is presented for calculating the flow in channels with turbulence-driven secondary motion, with an emphasis on open channel flow. Algebraic expressions are derived for the Reynolds stresses in the momentum equations for the secondary motion by simplifying modelled Reynolds stress equations. A simple eddy viscosity model is used for the shear stresses in the logitudinal momentum equation. The kinetic energy k, and the dissipation rate ϵ of the turbulent motion appearing in the algebraic and eddy viscosity expressions are determined from transport equations for these quantities. The restricting influence of a free surface on the length scale of turbulence is accounted for by a special free surface boundary condition for ϵ. The resulting set of equations is solved with a marching forward numerical procedure for three-dimensional boundary layers. The model is tested by application to developed two-dimensional closed and open channel flow, closed square duct flow, and flow in open channels of various width-to-depth-ratios. Most features of these flows are simulated well by the model, including the reduction of the eddy viscosity near the free surface and the depression of the velocity maximum below the surface.

Origin of Step-Pool Systems in Mountain Streams

Abstract: Mountain streams very often present a step-pool aspect. Antidune formation alone; dispersion and sorting theory or velocity reversal as advocated for the origin of riffle-pool sequences do not explain how steps and pools form. Experiments have been conducted to clarify their origin. It was found that the step-pool aspect appears after high flows had deformed the bed. During the presented tests a self armoring process occurred which resulted in a stabilization of the bed. When coarsening of the top layer was little classic antidunes resulted. An important coarsening was accompanied by a structuring of the bed into roughness elements whose spacing did correspond to maximum flow resistance. The substantial increase in resistance was an essential factor in bed-stabilization.

Discharge Assessment in Compound Channel Flow

Abstract: A series of laboratory tests were performed to measure the boundary shear stresses in a compound channel consisting of a main channel and associated shallow floodplains. Four different floodplain roughnesses were used. From these results apparent shear stresses across three different assumed main channel/floodplain interface planes (vertical, horizontal and diagonal) were calculated. The data was used with data from previous studies to derive a statistical relationship between the apparent shear stress on the vertical interface and several easily calculated parameters of the channel geometry and hydraulic characteristics. The accuracies of different methods of discharge calculation were shown to be dependent upon the assumptions they make regarding the magnitude of the apparent shear stress on the particular interface chosen. An apparent shear stress ratio was proposed which was found to be a useful yardstick in selecting the best method of discharge calculation for particular channel and flow conditions. Generally it was found that at low floodplain depths using the horizontal or diagonal interfaces gave better discharge results than the vertical.

Equivalent Roughness of Alluvial Bed

Abstract: The eguivalent roughness of a movable bed is considered. Relationships are given which can be used to determine the equivalent bed roughness from the bed material size and the bed-form dimensions. In the case of a plane bed the equivalent roughness is related to the D 9 0 of the bed material. Based on flume and field data, the equivalent roughness may vary from 1-10 D 9 0 . Similar values were reported by other research-workers. In the case of bed forms the equivalent roughness is related to the average height and length of the bed forms. Both flume and field data were used to determine a functional relationship. The proposed relationship yields values which are considerably smaller than other existing relationships.

Analytical Approach to River Regime

Abstract: Rational regime relationships for the width, depth and slope of a channel in equilibrium are developed using the Ackers and White sediment transport formulae and the White, Paris and Bettess friction relationships, together with the principle of maximum sediment transporting capacity. Favorable comparisons are made with data from sand and gravel channels and with existing empirical regime relationships.

Lateral Bed Load Transport on Side Slopes

Abstract: Lateral bed load transport is studied in laboratory flume and wind tunnel. Introduction of laterally inclinable wind tunnel permits accurate measurements of shear stress on side slope and of lateral bed load. The result of wind tunnel test was examined by an open channel experiment. A universal formula for the lateral bed load q* l is presented as a function of inclination of side slope, θ, and dimensionless shear stress τ*/τ* c ; and the expression is q* l /tanθ = α(τ*/τ* c )β. The numerical constants α and β are found to be 0.0039 and 1.5, respectively, for τ*/τ* c > 1.07. The formula may add some information to bank protection engineering, prediction of river meander, and to widening of braided river.

Incipient Motion of Sand Particles on Side Slopes

Abstract: Several criteria have been theoretically proposed for the critical shear stress of noncohesive sediment on side slopes. However, no laboratory work has ever been done on this problem. A theoretical study of the incipient motion of sediment particles on side slopes is presented, including the effects of viscous sublayer, turbulence and lift force. As a special case of level beds, the theory describes the experimental values reported by several workers. A specially designed rotary wind tunnel permits the evaluation of the critical shear stress on side slopes, and the experiment supports the theory. These works reveal that the lift force can be neglected in estimating the critical shear stress using the proposed theory if the averaged experimental values are concerned, but inclusion of the lift force in the theory is recommended for safety and for describing the lower limit of the possibility of incipient motion.

Shape and Dimensions of Stationary Dunes in Rivers

Abstract: The shape and dimensions (length, height) of sand dunes in rivers are calculated by use of the measured bed shear stress distribution downstream a rearward-facing step. The transport of sediment is split up into bed load and suspended load, which makes it possible to explain the transition to plane bed. The model can predict flow-resistance curves in alluvial streams.

Obtaining the Layout of Water Distribution Systems

Abstract: An essential first step in the design of a municipal water distribution system is the determination of the locational placement or layout of the links of pipe that will form the system. A two-level hierarchically integrated system of models is developed for the layout of both single and multiple source water distribution systems. The first level, a nonlinear programming model, selects an economical tree layout for the major pipe links. The second level, an integer programming model, chooses the loop- forming links to add to the first level tree layout in order to minimize the cost of providing a specified level of reliability in case of failure of the larger first level links. The system of models is applied to an example two-source water distribution system layout problem.

Routing Graded Sediments in Streams: Formulations

Abstract: 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.

Hydrothermal Analysis of Lakes and Reservoirs

Abstract: The impact of Hunter Rouse on the application of fluid mechanics to hydraulic engineering practice in the United States is reviewed. The development of physical and mathematical techniques for predicting the hydrothermal structure of lakes and reservoirs during the past fifteen years is discussed. Laboratory models have played a key role in the development and testing of early mathematical models based on the vertical diffusion concept. The sensitivity of these models to variations in turbulent diffusivity, internal heat absorption and vertical advection due to inflows and outflows is demonstrated. A wind-mixing model is proposed as an alternative to specifying temporal and spatial variations in the vertical diffusivity. The wind-mixing algorithm converts turbulent kinetic energy input by wind shear to potential energy through entrainment of hypolimnetic water across the thermocline. An iterative technique is used to achieve a heat balance based on meteorological inputs averaged over hourly or daily time steps. The temperature predictions of the numrical model are compared with field data for a number of lakes and reservoirs.

Sediment Transport and Unit Stream Power Function

Abstract: 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.

Asymptotic Solution for Dam-Break Problem

Abstract: The kinematic wave approximation is used to obtain a simple, closed-form solution for the catastrophic failure of a dam upon a dry, sloping channel. The solution validity is investigated by computing orders of magnitude for neglected terms in the equations of motion and by comparing the solution with the results of previously calculated numerical solutions and with experimental results. These calculations and comparisons suggest that the kinematic wave solution becomes asymptotically valid after the flood wave has advanced about four reservoir lengths downstream.

Erosion by Submerged Circular Jets

Abstract: An experimental study on the erosion of sand beds by impinging submerged circular water jets shows similarities between air-sand system and water-sand system. It is shown that there are significant differences between the two systems regarding the depth and radial extent of the scour hole.

Mathematical Model for Erodible Channels

Abstract: A mathematical model for erodible channels is formulated, developed and tested with field data. A significant feature of the model is its ability to account for changes in both channel width and channel-bed profile of aggrading and degrading streams. Since changes in channel width and channel-bed elevation are closely interrelated, this model represents an improvement in this direction. This model employs the techniQues for water and sediment routing; an additional condition based upon the concept of minimum stream power is used as the width predictor. Analysis using this model shows that the total stream power of a reach is reduced if the widths at all cross-sections are so adjusted as to reduce the variation in energy gradients at these sections. When this model is applied, a varied flow will eventually develop into a uniform flow for which the stream power is an eventual minimum.

Accuracy Criteria in Diffusion Routing

Abstract: An analysis of Muskingum diffusion model, in which routing parameters are calculated based on channel and grid characteristics, is carried out. Numerical experiments are performed to throw addition...

Bed material sorting in pools and riffles.

Abstract: When rivers flow in a series of riffles and pools during periods of low flow, bed material sizes change from coarser to finer in the riffle-pool sequence. The Froude Number also changes from high to low from riffle to pool. Larger particle sizes are therefore associated with higher Froude Number and vice versa. The sorting of bed materials, with coarser material at the riffles and finer materials at the pools, is mainly due to the high bed shear stress at the riffles, where the fine materials unable to withstand the high shear stress are washed away and deposited in the pools downstream where the bed shear stress is lower. The aforementioned process of sorting takes place during low discharges when the difference in velocity between that of a riffle and a pool are the greatest.

Distributed Model for Small Semiarid Watersheds

Abstract: A distributed model for estimation of runoff volumes and peak rates of flow from small semiarid watersheds is shown to produce reasonable estimates for mean runoff and flood frequency distributions. The model is simplified and constructed to require a minimum of observed data for calibration. The model simulates runoff volume and peak discharge rates for individual storm events. It can also be used to estimate water yield and a surface water balance incorporating transmission losses in ephemeral stream channels. Experimental data are compared with the simulation model predictions. Individual components of the model could be improved with further research and data. However, based on available information contained in soils and topographic maps and published sources, the distributed model can be used to estimate runoff rates and amounts from ungaged watersheds in semiarid regions.

Envelope Curves for Extreme Flood Events

Abstract: Maximum flood experience in a region can be depicted by a graph on which maximum known floods are plotted against drainage area. A smooth curve enveloping the plotted points provides the most concise description. such curves have been developed for 17 regions in the conterminous United States and are described by equations. The curves are not associated with specific probabilities or frequencies, but, within the region to which they apply, they give evidence as to the magnitude of flow that was occurred. Given similar basin characteristics, a peak lying close to the envelope curve might occur at other basins in the same region.

Computation of Flow Patterns in Rivers

Abstract: Quasisteady flow in a river with flood plains is considered with the objective of determining flood levels and flow patterns. The two-dimensional hydrodynamic equations are solved using a time-dependent, finite-difference method. Bottom and lateral friction are found to have an important influence. The mathematical model is calibrated and verified, using detailed laboratory measurements. A fair agreement is found, but the need of calibrating frictional parameters with field data is stressed.

Sedimentology of Erect Vegetal Filters

Abstract: In order to analyze sediment deposition in vegetated areas, it is necessary to develop relationships that define the steady-state sediment transport capacity of a given filter media. The development of these relationships was greatly facilitated by drawing an analogy between the flow in a narrow, deep channel and flow through closely spaced erect bodies. Based on the analogy, a dimensionless shear parameter is calculated using a spacing hydraulic radius as the characteristic length. Utilizing data collected with artificial media, this dimensionless shear is correlated to the bed load and total load parameters of Graf and Einstein with r² values ranging from 0.81 - 0.94. Neil's relationship was also analyzed and yielded a high r² value. Relationships based on the analogy were further examined by incorporating them into a model that predicted the sediment deposition wedge advance distance in actual vegetation. The agreement between the predicted and observed values was excellent. Thus, the sedimentology of grass filters presented herein is considered useful for design and research applications.

Bed Characteristics in Alluvial Channel Bends

Abstract: An approach to the description of the steady-state distributions of flow and bed characteristics in an alluvial channel bend is presented. The approach, which is based on a combination of the principle of moment-of-momentum flux and a critical-shear-stress analysis, is used to explain observed transverse variations of depth, depth-averaged velocity, and mean-grain size in a bend of the Sacramento River, California. The local transverse bed slope is found to vary linearly with d/r (the ratio of depth, d, to radius of curvature, r) and almost linearly with the bed-surface particle Froude number. It is established that the distributions of depth, depth-averaged velocity, and bed-surface sediment size depend on the variety of grain sizes in the bed sediment. Equations for the transverse variation of depth, depth-averaged velocity, and mean-grain size are developed, which can provide a guide to the depth of bed erosion and depth-averaged velocity near the outer banks of river bends.

Saltation in Water Dynamics

Abstract: An evaluation of the fluid forces exerted on a bed load particle is presented. The study used strobe photography to measure the kinematics of a sphere moving via saltation along the bed of an open channel flow. The experiment showed that the forces of bouyancy, added mass, and drag could predict the particle motion. The added mass force included an unusual component due to the mean shear of the open channel flow.

Stability of Armour Layers in Rivers

Abstract: The importance of both the overpassing and the embedding of river bed particles is demonstrated by experiments. When a single layer thick armouring layer of uniform d\d1 size particles on a bed of uniform finer d\d2 size particles is broken at one location the stability of the remainder of the armour layer depends on the tendency of the d\d1 particles to embed into the surface of d\d2 particles. If a d\d1 size particle is seated in the exposed position on the surface of the d\d2 sized bed sediment it may, by virtue of its exposure to the flow, be preferentially entrained and it may then overpass the finer bed sediment. Alternatively, the d\d1 particle may be too large for overpassing and it will become embedded. Armour layers composed of particles which embed, tend to be more stable.

Time Scale for Scour Downstream of Hydraulic Jump

Abstract: Scour downstream a hydraulic structure takes time to develop. Therefore, for a river in which peak flows are of short duration, the time history of scour development is of major importance. The paper briefly describes the work of Breusers on the time scale of local scour downstream of estuary closure structures and then extends it by reference to a program of experiments to the case of local scour downstream a hydraulic jump. The paper includes an example calculation of the determination of the time scale between a model and prototype overflow weir with plunge-type dissipator, subject to scour downstream.

Carrying Capacity of Flood Plains

Abstract: The field data of flood flows for several streams were analyzed to determine the distribution of flow in the main channel and in the flood plains The discharge carrying capacity of flood plains were found to vary from a few percent to more than 80 percent of the total flow The carrying capacity of flood plains depends upon many factors including the nature of the flood plain and the main channel, and the flood frequency In general, the carrying capacity of flood plains increases with the return period of the flood When the return period of the flood is about 40 years or more, the flood plain and the main channel appear to behave as a single unit

Dispersion in Three Dimensions: Approximate Analytic Solutions

Abstract: Solutions to three-dimensional convection dispersion equation under different boundary conditions are obtained by integrating the appropriate Green's functions. Two approximations are used during the integration. First, error function differences are approximated by exponential functions through Taylor expansion. Second, the time integral is approximated by Laplace method. The error introduced due to these approximations is analysed and discussed. The pollution source is assumed to be an arbitrary function of time and of finite size in space. The boundary conditions considered are of a stream in a horizontal flow field and a water table in a vertical flow field. Such solutions have potential use in quick preliminary analysis of groundwater pollution problems.