Stream Geometry Research Articles

The West Dapto flood of February 1984: rainfall characteristics and channel changes

Summary This paper describes the distribution, magnitude and areal pattern of recurrence intervals for a very severe rainstorm centred over the West Dapto area of Wollongong in February 1984. It also examines the impact of this storm on the channel geometry of streams draining the Illawarra escarpment. The storm was the largest 24 hour rainfall ever recorded in temperate Australia, and was very likely in excess of the 200 year event for the Dapto area. However, the localised nature of such storms in the region suggests that Wollongong can expect a major flood (in excess of the 100 year event) somewhere within the city every 25–50 years. Similarly, because the catchment of Lake Illawarra is usually larger than the areal distribution of these very high‐intensity storm centres, the frequency of severe flooding in the lake is bound to be greater than the frequency of any individual storm event. The most pronounced channel erosion (up to a fourfold increase in channel size) resulting from the 1984 storm occurr...

Estimation of Advection-Dispersion Characteristics of a Stream From Two-Point Time-Series Data

Detailed time series records on conductivity at two stations along the Nederrijn River (The Netherlands) are used to estimate the advection and dispersion parameters in the time variable advection-dispersion equation. River gauge data and stream geometries are used to yield a time variable, deterministic value for the flow velocity between the two points. Dispersion is modelled as a process proportional to flow velocity. Least squares estimation yields a proportionality factor of about 2.3 km, but the variance of the estimate is large. Although the level related flow velocity results in good predictions even under extreme discharge conditions, its deterministic definition must be| abandonned if a more accurate dispersion estimate is to be obtained

A Field Method to Determine Unsaturated Hydraulic Conductivity Using Flow Nets

A practical new field method is proposed to evaluate hydraulic conductivity in partially saturated media near a water impoundment. The new method is an inverse procedure which utilizes a flow net constructed from the steady state total hydraulic head distribution around the water source. In the vicinity of constant head sources and downstream along any stream tube, wetness and conductivity generally decrease. Knowing the stream tube geometry and hydraulic gradient from the flow net, Darcy's law is used to determine unsaturated hydraulic conductivities within the stream tube relative to some segment of the stream tube where conductivity is known. This approach was used successfully to predict the unsaturated hydraulic conductivity which was input to two variably saturated numerical models, utilizing total hydraulic head fields generated by the models. This procedure is also applied to pressure head and water content data collected in the field surrounding a constant head borehole infiltration test originally designed to determine only saturated hydraulic conductivity above the water table. For practical purposes the new procedure compares very favorably with (1) results of a field experiment to obtain unsaturated hydraulic conductivity in situ using the instantaneous profile method and (2) values of unsaturated conductivity calculated from field and laboratory measurements of water content and pressure head.

Geometry of Gravel Streams

A rational method has been developed to predict the regime geometry of straight active gravel streams. The analytical model is based upon a resistance equation, a bed load equation, and the condition of minimum stream power for gravel streams in equilibrium. The analytical channel geometry so obtained is in general agreement with previously established relations and observations. The analytical channel width is proportional to Q 0 . 4 7 , in which Q is the bank full discharge. Except for steep slopes, the width is essentially only a function of the discharge. The analytical depth increases with the discharge but decreases with the slope. On steep slopes, the width increases rapidly with the slope. This rapid increase in width accompanied by a decrease in depth indicates braiding tendency for steep gravel streams. As the bed load approaches zero at the lower boundary, this model for active streams reduces to the threshold theory.

Awards presented at the Spring Annual Meeting: First Presentation Robert E. Horton Medal to Walter B. Langbein for Outstanding Contributions to the Geophysical Aspects of Hydrology

The man that we are honoring has distinguished himself both as a specialist and a generalist in the field of geoscience. Few can match his breadth and depth of understanding in the science of water and especially its role in water resources planning and management. His recognition as one of the greatest hydrologists today is well deserved.Walter B. Langbein, born in 1907 and graduated as a civil engineer from Cooper Union in 1931, has spent most of his career with the U.S. Geological Survey. First as a hydraulic engineer and later as a senior research hydrologist, he has become the hidden conscience and soul of our hydrologic profession. Not only is the science of hydrology indebted to his innovative research over a wide range of subjects (including flood frequencies, sediment transport, geochemistry, evaporation, reservoir storage, river meanders, and the hydraulic geometry of streams, just to mention a few), but also the public at large, for his work in floodplain regulation, water management, and hydrologic education, which has helped the establishment of many national water policies and programs.

AO Cassiopeiae - Phase-locked polarization and the geometry of the gas stream

view Abstract Citations (35) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS AO Cassiopeiae: phase-locked polarization and the geometry of the gas stream. Rudy, R. J. ; Kemp, J. C. Abstract Variable linear polarization in this O-star close binary has been found to be accurately synchronous with the orbital motion over a span of 20 cycles. The polarization is explained by light scattered from a gas stream. Our analysis indicates that the main scaterring region is on the advancing side of the secondary star. Publication: The Astrophysical Journal Pub Date: July 1976 DOI: 10.1086/182194 Bibcode: 1976ApJ...207L.125R Keywords: Eclipsing Binary Stars; O Stars; Polarization Characteristics; Stellar Mass Ejection; Astronomical Models; Flow Geometry; Gas Streams; Light Scattering; Astrophysics full text sources ADS | data products SIMBAD (2)

Rates of fuel conversion and heat release in turbulent combustion of methane-air mixtures in tunnel burners

The experimental results presented in this paper deal with fuel conversion and heat-releaserates in experimental and commercial tunnel burners. Methane was used as fuel, and was premixed with air before entering the combustion chamber. Measurements of radial and axial distributions of temperature, concentration of stable components, and fluid velocity were used to calculate local conversion rates of combustibles and local heat-release rates. The effect of burner geometry, fuel throughput, air-fuel ratio, and turbulence intensity of the inlet mixture stream were also studied. The results show that the maximum local fuel-conversion rates and local heat-release rates occur in regions of large velocity gradients. The maximum heat-release rates obtained are much lower than in a homogeneous reactor. When the fuel throughput exceeds certain limits, unburned gases escape from the burner, resulting in lower mean combustion efficiencies. Combustion efficiencies close to 1 can only be achieved for an excess of air of more than 20 per cent stoichiometric. Conclusions for the optimum design of tunnel burners are drawn.

Stochastic methods in hydraulics and hydrology of streamflow

Stochastic methods in hydraulics and hydrology of streamflow are presented. The hydraulics part consists of mechanics of streamflow and sediment transport. A technique presented herein enables one to analyze a limited amount of field data to determine the stochastic structure of irregular stream geometry so that cross-sections and slopes of a stream may be simulated wherever, or as many as, needed. It provides the rational basis of efficient use, interpolation, and extrapolation of field data of irregular stream geometry for any studies to understand and control transport processes in streams. Stochastic modelings of motion of a single sediment particle, either in suspension or on the stream bed, help in understanding the complex mechanism governing sediment transport and, hence, improving techniques for calculating the spatial distribution and transport rate of sediment. For practical applications, however, the technique combining the stochastic and deterministic methods should be most effective.

FACTORS CONTROLLING THE GEOMETRY OF FLUVIAL MEANDERS

Abstract The geometry of a meandering stream depends strongly on the relative stream size (Q 2/5 / g 1/5)/D, on the valley slope, Sv, and on the charge, Q s/Q, where Q and Q s are the fluid and sediment discharges respectively, g is acceleration due to gravity and D is the mean sediment size. The geometry depends less strongly on the relative settling size of sediment, D/(v 2/3 / g 1/3), where v is the kinematic viscosity. For constant values of Q, S v and D, the effect of increase of charge reduces the meander length, M L, and the mean channel surface width, B, whereas meander width, M B, bend radius, R M, and mean channel depth, H, increase, For a constant value of (Q 2/5 / g1/5)/D the values of M L, M B, R M and B increase with the increase of valley slope but the value of H tends to decrease.

Downstream variations in the hydraulic geometry of streams; special emphasis on mean velocity

The equation for the relation of downstream increase in discharge to downstream changes in hydraulic geometry is a power function in which the exponents for width, depth, and velocity have been determined by Leopold and Maddock to be 0.5, 0.4, and 0.1, respectively. The least squares solution for the mean exponent in ten analyzed river basins is width = 0.461, depth = 0.383, and velocity = 0.155. The most common relationships on long segments of rivers is a nearly constant velocity; however, many smaller streams may increase or decrease velocity downstream because of geological influences present at the mean annual discharge level. Large rivers accomodate downstream increase in discharge principally through increase in depth, and smaller streams through increase in width.

Hydraulics and Stream Geometry

Hydraulics and Stream Geometry

THE GULF STREAM AS A GRADED RIVER1

The Gulf Stream flowing north through the Straits of Florida and across the Blake Plateau has many of the characteristics of a graded river. As a graded river, it transports water and sediment in such a manner that it neither erodes nor aggrades its channel. The delicate balance between erosion and deposition is emphasized by the presence of scour depressions and aggradational banks side by side on the bottom, and the well‐sorted Globigerina sand being winnowed over a bottom partly encrusted with manganese nodules. The hydraulic geometry of the Gulf Stream is also comparable to large rivers on land.

A REVIEW OF THE ORIGIN AND CHARACTERISTICS OF RECENT ALLUVIAL SEDIMENTS

SUMMARYRecent alluvial sediments are reviewed with respect to their geometrical, textural, structural and biological characteristics. These properties are related to the physiographic occurrence and hydraulic geometry of streams and to the dynamics of flowing water as controlling sediment transport‐deposition and stream morphological activities. Based on this data, three‐dimensional facies models are presented as an aid to the identification of ancient alluvial sediments, which are briefly reviewed also.

Experiments on Small Streams in Alluvium

An experimental study of small streams in alluvium indicates correlations between stream geometry and discharge. These are compared with established regime equations, with some areas of disagreement. Results have been analyzed on the basis of sediment transport, channel roughness, and width-depth ratio. These three physical relationships can be used to predict the geometrical functions.

New Studies of the Arc Discharge

The equation V = A + B/I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sup> which correctly represents all normal arc characteristics is used as the starting point for a general discussion of arc phenomena and industrial applications. Tests of this equation are applied to iron arcs in various gas atmospheres to obtain a series of values for A and B, making possible certain deductions about arc voltage variations and significance of the characteristics. In limiting the current exponent n, the anode temperature must exert considerable influence on the discharge as a whole. Suggestions are given why this may be so. A value of n is predicted from the arc stream geometry, and is compared with actual values of n for various arcs. From energy considerations of this equation new concepts of the ``minimum energy'' and the ``excess energy'' requirements in the arc conduction process are gained. Some applications to arc problems prove these concepts valuable. On this basis high temperature arcs are shown to be the most efficient. Light intensity and probe measurements on the arc stream suggest a new physical picture of high current arcs. Some difficulties are removed in accounting for energy equilibrium at the welding arc cathode.

New studies of the arc discharge

THE equation V = A + B/I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sup> which represents correctly all normal arc characteristics is used as the starting point for a general discussion of arc phenomena and industrial applications. Tests of this equation are applied to iron arcs in various gas atmospheres to obtain a series of values for A and B making possible certain deductions about arc voltage variations and significance of the characteristics. In limiting the current exponent n, the anode temperature must exert considerable influence upon the discharge as a whole. Suggestions are given why this may be so. A value of n is predicted from the arc stream geometry, and is compared with actual values of n for various arcs.