Showing papers in "Journal of Hydraulic Engineering in 1975"

Analysis of Flow through Vegetation

Abstract: The Manning n value is quantitatively evaluated for flow in heavily vegetated channels. Momentum analysis shows that the composite n value as a function of flow depth is dependent on the bottom roughness and the density of vegetation. In some cases, the vegetation density can be evaluated directly from physical measurements of the vegetation. However, in most situations, it must be evaluated indirectly from limited field data. The results show that the n value increases in proportion to two-thirds power of the hydraulic radius for conditions where the vegetation density is a constant over the flow depth. Field application of the flow resistance model are described for projects concerned with flood routing, backwater computations, extension of rating curves, channel improvement work, and erosion control.

Rainfall Temporal Patterns for Design Floods

Abstract: The rainfalls used in the practical estimation of design floods are generally based on frequency-duration relationships derived from recorded intense burst of rainfall of various durations rather than from complete storms These recorded intense bursts are therefore used in the derivation of the temporal patterns The method produces patterns that incorporate average variability of intense rainfall and also the most likely sequence of intensities Use of these patterns should minimize the introduction of joint probabilities into the design flood model and aid in estimation of a flood with the same frequency as the design rainfall The method provides patterns with average or typical variations in intensity, in contrast to simple averaging which is shown to be generally unlikely yield satisfactory patterns Frequency distributions of rainfall during various periods immediately antecedent to the recorded intense bursts are also derived, and these antecedent rainfalls in flood estimation are considered

Sediment Transport in Smooth Fixed Bed Channels

Abstract: Incipient motion of discrete particles resting on a fixed smooth channel bed is investigated in different conveyance shapes. The results are compared with incipient motion studies in conveyances with movable beds. Higher critical velocities and shear stresses are obtained for smooth rectangular channels than for circular ones, but a single equation for all tested conveyance shapes is derived. The experimental results suggest that for normal sand as well as gravel much lower values of critical velocites are needed to avoid deposition than ususally adopted in sewer design. An analysis of the sediment transport parameter phi and flow parameter psi results in a relationship enabling the computation of sediment concentration C sub v for any conveyance for sediment transport as bed load without tendency for deposition. The results are again compared with similar functions for conveyances with movable beds. /ASCE/

Resistance to flow in alluvial channels

Abstract: A direct method of predicting flow resistance and uniform velocity in alluvial channels is developed. The method covers all known bed-form regimes and not only eliminates trial-and-error computations and use of rigid-boundary channel flow formulas but also avoids the difficulties associated with the use of the various existing alluvial channel flow computation techniques. The study shows that the Darcy-Weisbach friction factor can be expressed as a unique function of the ratio of the bed form and grain shear stress components for any anticipated discharge and flow geometry, the bed-form shear component being uniquely determinable from the flow and channel material characteristics. The results confirm that the friction factor is nonconstant but varies with the bed-form regime. The applicability of the method to laboratory flumes, field canals, and natural rivers is illustrated.

Boundary shear in channel with flood plain

Abstract: Shear stress distributions were measured around the periphery of a channel of complex cross section using Preston tube. The complex section consists of a deep channel and a flood plain. The measurements were carried out in the laboratory for flow in the full cross section and when the flow was confined to the deep section. In this way it was possible to compare shear stress distributions under both isolated and interacting conditions. This has revealed that the presence of the interaction between a channel and its flood plain has significantly altered the values and distributions of boundary shear.

Temperature Dynamics in Dimictic Lakes

Abstract: Daily water temperature profiles in temperature lakes are predicted from time-variable meteorological conditions and lake morphology. A total energy concept which includes wind energy is used. The method of analysis is derived and illustrated through case studies. Agreement of predicted and measured water temperatures in two lakes throughout the summer season is good. The prediction of daily water temperature distributions in temperate lakes under the effect of variable meteorologic conditions throughout a season is possible using the total energy concept. Heat energy input (or output) into a lake includes shortwave (solar) radiation, long wave (atmospheric) radiation, back radiation, evaporation, and convection. Mechanical energy input is by wind. Although energy inputs and losses are computed separately, step by step, the method of analysis recognizes and incorporates the mutual interdependence (feedback) between different forms of energy input. In the sample computations conducted, the sequence was found to be irrelevant if a time step of 1 day was used.

Soil Erosion and Sediment Transport from Gullies

Abstract: Field observations of four gullied watersheds, 74 acres to 150 acres (30 ha-61 ha) in size, showed that gully erosion was one-fifth of the total sediment yield during a 9-yr period. Erosion rates were dependent upon mass wasting of loessial gully banks and headcuts. For the nonconservation watersheds, tractive forces exerted by runoff on the channel boundary did not detach appreciable amounts of undisturbed soil but were more than adequate to entrain the soil debris yielded by mass-wasting processes. Gully erosion was minimal on conservation watersheds; the runoff was generally below the levels required for gully debris removal, and the degree of slope was reduced to a stable value. Soil mechanics principles, applied to strength/stability aspects of gully banks in western Iowa, indicate that the height of the water table, soil cohesive strength, and rate of water infiltration are controlling factors. Initial field and laboratory model experiments have provided insight into variables that affect the mass-wasting process.

Local erosion caused by rapid forced infiltration

Abstract: Examination of the stream bed over a water intake buried beneath it revealed a scoured hole with a dune downstream. Laboratory experiments result in the same kind of feature, providing the bed material is too penetrative to ripple. Theoretical treatment based on momentum changes in the suction zone and limited to two dimensions reproduces, with reasonable success, the behavior of beds of medium sand in a narrow laboratory flume. Grains move faster in the suction zone than elsewhere and their increased reluctance to settle is offset by increased stability of the stationary grains. A stable bed feature is arrived at when these two effects are so balanced that the transport rate of bed load is the same in the suction zone as elsewhere.

Nonequilibriun River Form

Abstract: In the absence of man-induced changes and climatic changes and in the engineering time scale, the form of many rivers is primarily a result of the flood history of the river. Evidence of the effects of floods on river channel width is found in the scientific literature. The extreme event flood is the erosional agent that widens the river channel; in some cases the entire river valley has been gutted by the extreme event flood. Succeeding floods of lesser magnitude result in channel deposits that narrow the river channel. The problem is to recognize river systems that are changing form or are susceptible to change in form. If the ratio of each individual flood-peak discharge to the average annual peak-flood discharge is small, the river form can be in equilibrium or “in regime.” If the ratio of some individual peak discharges to the average annual peak discharge is large, the river channel can exhibit nonequilibrium river form, i.e., the form will change with time.

Sediment inertia as cause of river antidunes

Abstract: The formation of antidunes on riverbeds is explained in terms of sediment inertial effects. Due to inertia, bed sediment in transport cannot respond immediately to flow changes. To quantify the effect, a simple equation for sediment momentum balance is derived. A stability analysis indicates that riverbeds are unstable for a specific range of Froude numbers and that the instability leads exclusively to antidune formation. The instability, which is scaled by a dimensionless number representing the ratio of sediment inertia to friction, is a result of a spatial lag of bed load behind bed stress. An analytical relation for spatial lag is obtained, and the lag is estimated for some experimental data. The limits of antidune formation are compared with data.

Fundamental Aspects of Erosion of Cohesive Soils

Abstract: This paper presents new and correct data on the critical shear stresses required to initiate erosion as a degree of dispersion as influenced by ion exchange. Data on the relationship between water uptake and critical shear stresses are also reported to support the fact that the mechanism causing erosion is due to the local swelling developed in clays.

Implicit Numerical Modeling of Unsteady Flows

Abstract: A numerical model based on the equations of unsteady flow in open channels is used to compute unsteady flows in rivers and reservoirs. The cross sections of the waterways range from uniform to highly irregular, the type of flow ranges from slowly varied to abrupt changes in discharge, and nearly all combinations of boundary conditions are encountered. The model uses an implicit finite difference method. The versatility, accuracy, stability, and efficiency of the method is demonstrated by field measurements.

Removal of Air from Water Lines by Hydraulic Means

Abstract: Air is introduced into water transmission lines through vortices at intakes, pumps, vents, and other causes. This results in loss of capacity, surges and blow backs, difficulties in filtering operations, corrosion of lines, and reduction of pump efficiency to name a few. The best solution to air problems is to prevent the introduction of air at the intake. Other means of air removal are air relief valves and by the inertia of the flowing water. No conventional similitude exist to study the time of clearance of isolated air pockets and results of Froudian scale model tests are very conservative. For pipe sizes below 1 ft. (0.30m) the clearance of isolated pockets may require higher than practical velocities.

Dynamic Behavior Model of Ephemeral Stream

Abstract: Ephemeral stream hydraulic features are dynamic and respond to the variable streamflow available to move sediment. Streamflow varies both from the runoff-producing storms and transmission losses that decrease the runoff volume and peak. The channel profile in an ephemeral stream tends to be concave up because of the transmission losses and concave down because there is more flow downstream due to tributary inflow. These phenomena were modeled for the main channel of the Walnut Gulch Experimental Watershed using a geomorphic approach to describe the channel and its tributaries and a hydraulic-hydrologic model for the runoff-sediment movement. Runoff and sediment transport were synthesized using the Diskin-Lane stochastic runoff model with a deterministic sediment transport relationship using the Manning and Laursen equations.

Shallow Laminar Flows over Rough Granular Surfaces

Abstract: Several investigations have established that at high values of relative roughness mean depths of liquid in laminar shear flow over rough surfaces are greater than the corresponding depths on a smooth surface. In this investigation the nature of the flow field in the vicinity of isolated roughness elements fixed to a smooth base is demonstrated using a flow visualization technique. Velocity profiles measured with an optical velocity meter are shown to be governed by the Nusselt equation, but surface velocity is a function of relative roughness and is less than the corresponding value for a smooth surface. An analytical model is proposed to explain an empirical relationship between friction coefficient, relative roughness, and Reynolds number. The equation developed is used to calculate the product of the coefficient of drag of a sphere resting on a plane surface and the tip Reynolds number and also to demonstrate the influence of velocity distribution on the drag coefficient.

Water Waves Generated by Landslides in Reservoirs

Abstract: A hydraulic model investigation has been conducted to ascertain the magnitude of wave height and runup to be expected from potential landslides in Lake Koocanusa at Libby Dam, Montana. Although this investigation is of a particular site, it furnishes valuable information and insight into general problems of waves resulting from landslides that might be pertinent to other areas. The model study results show the wave heights and runup to be expected at various pool elevations as well as the effect and corrective measures proposed to reduce wave heights to an acceptable level. This paper presents the Libby prototype problem, model concepts, some experimental data, and conclusions pertinent to the prediction of landslide generated water waves.

Aquifer Parameter Identification

Abstract: This paper presents an analysis of the inverse problem of parameter (or parameters) identification in unsteady ground-water flow. The response of the system is governed by a typical nonlinear second-order partial differential equation for which there exists no closed-form solution. Identification is an inverse process whereby the parameters embedded in a differential equation are determined from observations of the system’s input and output along with appropriate initial and boundary conditions. These parameters are usually not physically measurable. In this paper, a simple but illustrative inverse problem is analyzed by quasilinearization, maximum principle, gradient method, the influence coefficient method, and linear programming. A comparison is made between these methods. The problem of convergence and stability is examined and demonstrated by numerical experimentation.

Use of Satellite Data in Urban Hydrologic Models

Abstract: The study investigates the use of computer-aided analysis of LANDSAT multispectral data in estimating percentage of imperviousness and associated land uses needed in urban hydrologic modeling. An interactive computer was used to delineate seven land use classifications in the 132-sq mi (342-sq km) Maryland portion of the Anacostia River Basin from LANDSAT data. The land-use distributions compared favorably with those of an earlier study which obtained the same information through analysis of aerial photographs having a scale of 1:4800. The LANDSAT data were used to estimate the basin imperviousness as 25.1% while the aerial photographic study had given 23.5%. Comparisons between the photographic and LANDSAT imperviousness estimates are made for subareas within the Anacostia Basin as small as 0.14 sq mi (0.36 sq km). Approximately 94 man-days were required to complete the land-use analysis using the aerial photographs while less than 4 man-days were required to accomplish similar tasks using the LANDSAT data.

Sparsity Oriented Analysis of Large Pipe Networks

Abstract: Water distribution systems of large metropolitan centers contain several hundred nodes and pipes and a number of pumping stations and reservoirs. The size and complexity of these networks require v...

Wall Jet Analogy to Hydraulic Jump

Abstract: Hydraulic jump on horizontal bed of a rectangular channel is treated as a plane turbulent wall jet of an incompressible fluid of finite width in adverse pressure gradient. Momentum integral techniques have been applied to determine the longitudinal variations of the parameters characterizing the assumed mean velocity distribution. The kinematic constraint arising from the requirement of continuity has been imposed. The idealized wall jet has been modified to take into account the mean velocity distribution ahead of the jumps that is typical of most of the experimental situations. The mean flow properties of jumps at high Froude numbers, e.g., the maximum velocity, surface velocity and depth profile, are predicted and compared with experimental results.

Design of Conduit System with Diverging Branches

Abstract: The capability of a dynamic programming conduit design technique was expanded to cover systems with diverging branch pipelines. An interactive computer programming approach was used in optimization. Optimization design is valid with little restriction. Design applies to complete turbulent, transient, as well as laminar, flow conditions. The decision variable, pipe size, assumes only pipe sizes that are available on the market.

Fluid-Dynamic Excitation Involving Flow Instability

Abstract: Most flow-induced structural vibrations can be traced to shear-layer instability. They are generated by feedback mechanisms through which disturbances to the free shear layer are self-generated and amplified with an inherent dominant frequency and pressure fluctuations are produced over any portion of the body surface near the free shear layer. The range of flow conditions within which such vibrations may occur for given mechanical and geometrical properties of the structure is predicted by means of a kinematic analysis based on some results of stability theory and experiments. Verification of the validity of the analysis is provided by a comparision with tests for a typical hydraulic structure: a high-head gate with downstream lip. The results give support to the general applicability of this method for the determination of flow conditions under which structural vibrations can be excited.

Predicting Cavitation in Sudden Enlargements

Abstract: In recent years incipient, critical, and choking cavitation levels have been introduced as design criteria for orifices and valves in pipelines. Recent studies have evaluated a fourth level, incipient cavitation damage, for orifices that is applicable to the design of sudden-enlargement energy dissipators. Design data for these four levels are included in the paper. Since cavitation in prototype structures can differ from that predicted by model studies, research has also been directed toward evaluation of scale effects. The existence of scale effects due to pressure, size, and geometry for four levels of cavitation are examined herein and methods and equations for adjusting reference test data to structures of other sizes operating under different pressure conditions are presented. The location and distribution of cavitation pitting on the pipe wall downstream from the sudden enlargement are identified. The pitting is a function of expansion ratio and cavitation intensity.

Water Hammer in Coaxial Pipe Systems

Abstract: Transporting fluids involves the use of coaxial pipe systems in which water hammer may occur due to pump failure or valve operation. Investigations into the behavior of water hammer phenomena in such pipe systems of several different flow sections are reported. The solution of the differential equations covering nonstationary fluid flow in pipe systems of several different flow sections by means of the method of characteristics is sketched. The wave propagation as well as the transmission and reflection of waves at changes in diameter or density, and at pipe junctions, are expressed by the simplest possible formulas.

Prediction of Flow Development on Spillways

Abstract: A mathematical model for the flow development upstream of the region of air entrainment on a spillway is presented. The model is based on numerical solutions of the time-averaged two-dimensional form of the Navier-Stokes equations. Predictions from the model of mean velocity distributions, boundary layer growth, and water surface profiles are compared with experimental data, both model and prototype. Excellent agreement is obtained. Furthermore, it is shown conclusively that self-aeration in a spillway flow commences at the point where the bed induced turbulence reaches the free surface.

Review of models of tidal waters

Abstract: Approximately 100 models of water and waste movement in tidal bays and estuaries have been reviewed and their predictive capability and limitations have been examined. The review provides the detailed analysis of different models within the same classification. By using this review in conjunction with the classification scheme and the sequence of selection questions given in Proc. Paper 11643, the most appropriate model for a particular task may be selected.

Solid particle settlement in open-channel flow

Abstract: A random walk is formulated to describe the settlement of solid particles in open-channel flows Both uniform and mixed-size sediment particles are tested Results from simulations indicate that the probability density function of the settling length can be a lognormal distribution The mean settling length can be estimated by the ratio of the unit-width discharge to the fall velocity of particles The coefficient of variation is determined to be a power function of the ratio between flow shear velocity and fall velocity of solid particles The simulation results are generally in agreement with measured data The procedure for the design of settling basins is presented

Aspects of Hydrological Effects of Urbanization

Abstract: Urbanization both alters and complicates the natural hydrologic cycle. However, the effects are often not consistent, but depend on the nature and magnitude of the urban influence. The effects of urbanization on four aspects of the hydrologic cycle are examined: (1) Low flow; (2) total runoff; (3)infiltration; and (4) ground-water recharge. Both supporting data and a selected bibliography are provided. Inherent in the alteration of the hydrologic cycle by urbanization is the contamination by urban wastes, and the consequent pollution of the water resource.

Classification of Models of Tidal Waters

Abstract: A classification scheme is presented for numerical models of water and waste movement in tidal bays and estuaries. This classification is based on the number of spatial dimensions, the reference frame used, temporal resolution obtainable and the degree to which hydrodynamic processes are included. Newly developed models can easily be fitted into the scheme. With this classification scheme, different models may be assessed and compared on the basis of their theoretical assumptions. To select a model for a particular task, a sequence of questions may be answered and from the answers the appropriate type of model may be selected. The classification table then indicates the models available to meet the requirements of the particular physical situation.

Comparison of Warm Water Evaporation Equations

Abstract: Two methods of calculating the evaporation and, using the Bowen ratio, the sensible heat flux from warm water bodies are presented and their results compared. One method is empirical in that free convective and forced convective terms are simply added. The other method is a fluid mechanical approach combining the effects of free and forced convection in a nonlinear way by the use of the Monin-Obukhov similarity theory. The comparison of results depends on the value of roughness length. A specific roughness length allows the results of the two methods to compare within several percent.