Stream Cross Section Research Articles

Fluvial morphology and dynamics of the Godavari Khola, southeast Kathmandu, Central Nepal

The Godavari Khola flowing from the south to the north contributes the Hanumante Khola, which is one of important tributaries of the Bagmati River, flowing from the eastern part of the Kathmandu Basin. Recently, the Godavari Khola has been suffering from human encroachments due to rapid urbanization. Studying nature and dynamics of the stream are important works if the stream has to be made less affected and well managed. The present study aims to establish fluvial morphology and stability status of the Godavari Khola. For these purposes, the watershed was analysed for morphometric parameters and planform fluvial morphology, and thirteen representative segments were surveyed from upstream to downstream of the Godavari Khola for recording and analysing sediment properties, stream cross-sections and profiles, and hydraulic parameters, river dynamics and stability.The Godavari River is a fifth order stream, the two upstream segments of which are bedrock channels, and the rest of the segments are alluvial channels. The segments are classified into six kinds such as C4-, C5-, B3-, B4-, E4- and F4-type streams. The upstream segments are of B4-, B3- and ‘F4’-types which show entrenched, steep, gravel to cobble grade streams. The downstream segments are of C4-, C5-, E4- and F4-types showing non-entrenched to low entrenched streams with gentle slopes, high sinuosity and gravel to sand grade bed materials. The stability status of the Godavari Khola shows that the stream segments 1, 2, 11 and 13 lie in the degrading condition whereas the remaining nine segments lie in the aggrading condition. Because of the huge width/depth ratio in majority of the downstream channels, bank erosion is relatively prone in the downstream segments of the Godavari Khola, whereas bed incision is prone in segments 11 and 13.Bulletin of the Department of Geology, Vol. 19, 2016, pp. 15–28

Rapid ice flow rearrangement induced by subglacial drainage in West Antarctica

AbstractIce streams are corridors of rapid ice flow draining the ice sheets. They can exhibit astonishing spatial variability on annual to centennial time scales. We propose that changes in the subglacial drainage of meltwater could induce these sudden rearrangements of ice streams. We develop a two‐dimensional, thermomechanical model representing an ice stream cross section and couple it to a plastically deforming bed with spatially variable meltwater influx. We find that where ice flows over deformable sediments and lacks significant topographic control, the efficiency of subglacial water drainage exerts direct control on the velocity, location, and width of ice streams. This implies that meltwater percolation at the meter scale could have a significant effect on the short‐term variability in ice loss from a continental‐scale ice sheet. We verify our model against previous analytical results and validate it against surface observations from the Siple Coast of West Antarctica.

An Investigation Concerning the Effect of Canal width Contraction that May be Needed in the Location of Constructing Some Irrigation Works

AbstractThe compatibility between the needed structural designed dimensions of the irrigation works and the dimensions of the water stream or the canal in which the irrigation work will be located has a great importance from more than one point of view. As it is well known, the main aim of the designer of such works is to reach the optimum design for maximum performance efficiency with economical cost, and minimize negative technical impacts that may be harmful to the safety of the whole work. Since the complete suitability between the obtained designed dimensions of the different construction elements of the work, and the original properties and dimensions of the canal in which the work will be constructed, is rarely occurring. The designer always has to make some changes in the original engineering properties and dimensions of canals, such as bed width, bed level, and/or inside side slope, to reach the needed suitable compatibility between the structural design and the natural original canal cross section. For the economical purposes, the design always needs less width of the work, than the width of the bed of the original stream cross section, so a contraction may be needed where the work will be constructed; the literature indicated that, such a contraction must not be less than 0.6 of the original bed width. That contraction, of course, has a direct impact on the different hydraulic parameters, such as water depth, velocity, and flow regime in the location of the work. Changes of such hydraulic parameters may exceed their safe permissible values, and so the whole structure may face some dangerous situations, which must be overcome. In this paper, we present a technical survey of the previous research concerning canal width contraction, with the needed technical comments, and comparisons as a logical approach for a master-thesis under the same title.

Effect of the Molten Metal Stream’s Shape on Particle Size Distribution of Water Atomized Metal Powder

The current knowledge indicated that water pressure, molten metal temperature, water flow rate and water jet configuration are very important factors which affect on the particle size distribution and shapes of atomized powder. This study aimed to investigate whether the shape of molten affects the particle size of atomized powder. The experiments were the production of copper powder with the fixed atomization process conditions, but varied the shape of molten metal by using two different shapes of tundish nozzle’s orifice to make the round and rectangular cross section of molten metal stream. There were three sizes for each orifice shape to determine the rate of production (metal flow rate) at 13 kg/min, 19 kg/min and 26 kg/min. The results showed that at the same flow rate of molten metal the production of flat metal stream from rectangular orifice made higher yield of finer particle, smaller median size (D50) and narrower range of size distribution than the production with the round cross section orifice for every production rates.

A device for monitoring the distribution of particles of off-electrode high-voltage gas-discharge plasma over the stream cross section using the curved-cavity method

A device for monitoring the particle distribution over the cross section of a low-temperature offelectrode plasma stream, which is produced by a gas discharge, is proposed. Particles are collected with a stack of metallic tubes, which are bent at an angle of 0 < β < 90° and are linearly arranged over the plasmastream cross section. The inner (D) and outer (d2) diameters of the tubes correspond to the conditions d1 < D < d1 + 0.4L, d2 < d1 + L, which allow a significant decrease in the fraction of plasma particles reflected from the end surfaces of tubes (d1 is the diameter of the holes in the plate that form microstreams of charged particles, and L is the distance between these holes). The fulfillment of the above conditions and manufacturing of the ends of the curved tubes in the form of a cone completely eliminate the possibility of ionizing atoms of the residual gas in the volume of the tube cavities. The practical application of the proposed design in measurements of the current density over the cross section of the off-electrode gas-discharge stream showed that the density-distribution uniformity of negatively charged plasma particles was at least 98%.

Spatial interpolation of point velocities in stream cross-section

Abstract The most frequently used instrument for measuring velocity distribution in the cross-section of small rivers is the propeller-type current meter. Output of measuring using this instrument is point data of a tiny bulk. Spatial interpolation of measured data should produce a dense velocity profile, which is not available from the measuring itself. This paper describes the preparation of interpolation models. Measuring campaign was realized to obtain operational data. It took place on real streams with different velocity distributions. Seven data sets were obtained from four cross-sections varying in the number of measuring points, 24-82. Following methods of interpolation of the data were used in the same context: methods of geometric interpolation arithmetic mean and inverse distance weighted, the method of fitting the trend to the data thin-plate spline and the geostatistical method of ordinary kriging. Calibration of interpolation models carried out in the computational program Scilab is presented. The models were tested with error criteria by cross-validation. Ordinary kriging was proposed to be the most suitable interpolation method, giving the lowest values of used error criteria among the rest of the interpolation methods.

Flow and sediment size variability near gravel bars in the Beskidy Mountains in the Polish Carpathians

The purpose of the paper is to identify differences in hydraulic conditions in the areas closest to already-developed gravel bars situated in a small, mountain stream in the area of the Polish part of the Carpathian Mountains. Basic hydraulic parameters of flowing water, including velocity, shear stress, Froude number, Reynolds number and flow resistance coefficient were examined within the region of two different gravel bars in a mountain stream. At the same time, sediment samples were drawn from the riverbed in the area in which the hydraulic measurements were taken. After analysing the data, several conclusions were presented concerning sedimentation of gravel and hydraulic parameters within the cross section of a mountainous stream. The study was undertaken on Skawica-Jalowiecki Stream in the Polish part of the Carpathian Mountains called the Beskidy Mountains.

산지하천의 전자파 표면유속 측정에 기반한 유량 및 유속 관측 오차 분석

Abstract Fixed Electromagnetic Wave Surface Velocimetry (Fixed EWSV) has been started to be used to measure flood discharge in the mountain stream, since it has various advantages such that it works well to continuously measure stream discharge even in the night time as well as very strong weather. On the contrary, the Fixed EWSV only measures single point surface velocity, thus it does not consider varying feature of the transverse velocity profile in the given stream cross-section. In addition, a conventional value of 0.85 was generally used as the ratio for converting the measured surface velocity into the depth-averaged velocity. These aspects could bring in error for accurately measuring the stream discharge. The capacity of the EWSV for capturing rapid flow velocity was also not properly validated. This study aims at conducting error analysis of using the EWSV by: 1) measuring transverse velocity at multiple points along the cross-section to assess an error driven by the single point measurement; 2) figuring out ratio between surface velocity and the depth-averaged velocity based on the concurrent ADCP measurements; 3) validating the capacity of the EWSV for capturing rapid flow velocity. As results, the velocity measured near the center by the fixed EWSV overestimated about 15% of the cross-sectional mean velocity. The converting ratio from the surface velocity to the depth-averaged velocity was 0.8 rather than 0.85 of a conventional ratio. Finally, the EWSV revealed unstable velocity output when the flow velocity was higher than 2 m/s.

EVALUATION WITH STREAM CHARACTERISTICS OF DOWNSTREAM FLOOD PROBLEMS AFTER DAM CONSTRUCTION

The food may cause serious loss of life and property. The evaluation of food events is necessary for the planning and design of engineering projects. In a dam, food problems should be considered for both upstream and downstream conditions. The characteristics of food problems can be derived from observation of dam sites. Tis paper aims to evaluate the impact of food hazards from spillway based on downstream conditions after dam construction. Also, the paper discusses downstream food problems depending on stream characteristics in an example dam site. In results, three reasons are determined for downstream foods problems: control problems of spillway gates, the naturally developing vegetation through channel flow line and incompetence of stream cross-section for carrying of food flows. Therefore, downstream conditions should be investigated before dam construction. Tis investigation can be considered in the planning phase. In addition, the cross-section and longitudinal profile of stream should be controlled via maintenance of stream after dam construction. In stream cross-section problems (such as vegetation, incompetence and irregularities), some modifications (e.g. straighten, deepen, and widen) can be applied with engineering works.

DETERMINING THE CHARACTERISTICS OF DIRECT RUNOFF FROM REAL RAIN USING GIS ENVIRONMENT / STANOVENIE CHARAKTERISTÍK PRIAMEHO ODTOKU Z REÁLNEHO DAŽĎA S VYUŽITÍM PROSTREDIA GIS

Abstract The selected SCS-CN method is used worldwide and adapted to the conditions of Slovakia. GIS environment provides an opportunity to simulate changes in land use, and then to calculate the total volume of water from the river and peak water flow in the river bed of the stream. The simulation was done for two rainfall events, 72 mm and 42.6 mm, which were measured in precipitation station in Jelenec (a village situated next to the area of interest). The calculation was made for 4 possible scenarios - current land use, forest, arable land and grassland and pasture. Culmination discharge and time of outflow from rainfall 72 mm for current land use were calculated using the NRCS method. The calculation of water runoff volume showed that similar values were measured for the rainfall of 72 mm and rainfall 42.6 mm in case of AMC-III. The highest values of water runoff volume were marked in the case of arable land in all calculations, the lowest one for forest. Comparison of designed stream cross section and calculated culmination discharge allowed us to determine the point of outflow from the river bed of the Drevenica stream.

Combustion performance of eccentrically rotated flames

Experimental/computational work highlighted the combustion performance with eccentric blockage rotation in the reactive flow passage to augment the turbulence production rates in the flame for acquiring high power to weight ratios and effective heat transfer in industrial applications. The temporal/spatial velocity gradients stimulated around the reactive stream boundaries enhanced the turbulence development in both premixed and non-premixed flames. The eccentric shapes included circular, elliptical, squared and triangular shafts as well as a triple/straight blade rotor. The design was further developed to incorporate simultaneous rotation of the eccentric blockage around its axis via a planetary gear assembly to duplicate the vortical structure. While the premixed flames responded to such cyclic action by having a mixture velocity of 16.8 m/s, the non-premixed flames acquired an increase of 341% in the largest eddy size and a flame length reduction by 42%. Increasing the Strouhal number to 0.94 and the swirl ratio to 0.78 increased the turbulent kinetic energy to 9.1 m2/s2. By controlling the drag coefficient and wake vorticity for the solid shapes, the triangular rotor enhanced the combustor outward heat flux to exhibit a heater efficiency of 36.8% in the premixed flame mode and reduced the HC and CO emissions, respectively, to 0.1% and 513 ppm for non-premixed flames. Decreasing the reactive stream cross-section favorably increased the flow shearing effects, while the elliptical shape showed the highest sensitivity to axes’ orientation with respect to the direction of rotation. Due to the reduction in peak temperatures via increasing the turbulence intensity and heat transfer rate from the flame, the NO x exhaust concentrations decreased to a minimum value around 10 ppm. The combustion efficiency of diffusion flames was optimized with the fuel port central positioning in the burner, where the planetary gear design provided a turbulence intensity of 13.7% by the triple blade rotor.

Assessment of GeoEye-1 stereo-pair-generated DEM in flood mapping of an ungauged basin

A very high resolution (VHR) digital elevation model (DEM) is produced from a GeoEye-1 0.5-m-resolution satellite stereo pair and is used for floodplain management and mapping applications such as watershed delineation and river cross-section extraction. For this purpose, a 2 m × 2 m resolution terrain surface is produced from the stereo pair by using the Leica Photogrammetry Suite (LPS) enhanced Automatic Terrain Extraction (eATE) algorithm. DEM accuracy is assessed by comparison with measured individual ground control points (GCPs), stream cross-sections and other landscape features. Results show that the produced DEM is in good agreement with ground truth and superior to products of lower resolution, such as 90 m NASA Shuttle Radar Topography Mission (SRTM) and 1:5,000 topographical maps. One- and two-dimensional hydraulic models are used to simulate rainfall–runoff characteristics and flood wave kinematics of the flash flood event of 17 October 2006 that occurred in the ungauged basin of Almirida, using the 2 m VHR-DEM as an input. Results show that the hydraulic simulation based on the generated VHR-DEM, calibrated and validated via field data, produces an accurate extent and water level of the flooded area. Remote sensing stereo reconstruction is a promising alternative to traditional survey methods in flood mapping applications.

Bed coarsening, riffle shortening, and channel enlargement in urbanizing watersheds, northern Kentucky, USA

Stream systems naturally respond to watershed land use dynamics, particularly in urban developments with unmanaged impervious areas. Such urban-provoked alterations to channel morphology cause water quality impairments, have adverse effects on aquatic biota, and pose risks to adjacent public infrastructure. Over the past four years we have collected detailed hydrogeomorphic data at 40 unique stream locations throughout northern Kentucky, with at least two rounds of annually repeated surveys at 70% of the sites and three rounds of surveys at 50% of the sites. Analysis of this time-series data encompassed measured rates of instability across three distinct dimensions including (1) channel cross sections, (2) longitudinal profiles, and (3) bed material particle composition. Regression analyses between geomorphic change and 2011 watershed imperviousness indicated stream cross sections in urban/suburban watersheds tend to be getting larger—their overall shape is both deepening and widening. Additionally, stream riffle lengths are shrinking and their pools are becoming both longer and deeper; and finally, their bed material composition is coarsening, particularly in streams in the early stages of watershed development. By documenting fluvial geomorphologic dynamics in such detail, this study highlights the process by which unmitigated urbanization homogenizes stream habitat and degrades aquatic ecosystems. This improved, process-based understanding of the urban-induced channel response sequence has clear implications to both stormwater management and stream/ecosystem restoration, particularly in stream systems where headcut migration is a primary driver of channel instability.

A LiDAR-Based Analysis of Stream Channel Cross Section Change Across an Urban–Rural Land-Use Boundary*

Little is known about the downstream propagation of stream channel alterations initiated by urban flow regimes. In this study, freely available Light Detection and Ranging (LiDAR) data were combined with ground survey data to derive information on changes in stream cross sections in a North Carolina watershed, moving downstream across an urban-to-rural land-use boundary. Regression analyses relating LiDAR model and ground survey data exhibit poor relationships for all channel morphometric measurements except reach-average channel capacity. Application of the channel capacity regression reveals a negative power function pattern of downstream decline in channel enlargement. The largest declines occur before streams enter the rural landscape, with more gradual declines afterward. The largest declines in channel size might be attributable to reservoir effects along reaches with wide floodplains. Model results indicate no discernible enlargement once rural land covers and percentage impervious areas of about 60 percent and 16 percent of watershed area, respectively, are reached.

Non-LTE modeling of narrow emission components of He and Ca lines in optical spectra of classical T Tauri stars

Using LTE calculations of the structure of T Tauri stellar atmospheres heated by radiation from an accretion shock (Dodin and Lamzin 2012), we have calculated the spectrum of the hot spot emerging on the stellar surface by taking into account non-LTE effects for He I, He II, Ca I, and Ca II. Assuming the pre-shock gas density N 0 and velocity V 0 to be the same at all points of the accretion stream cross section, we have calculated the spectrum of the star+circular spot system at various N 0, V 0, and parameters characterizing the star and the spot. Using nine stars as an example, we show that the theoretical optical spectra reproduce well the observed veiling of photospheric absorption lines as well as the profiles and intensities of the so-called narrow components of He II and Ca I emission lines with an appropriate choice of parameters. The accreted gas density in all of the investigated stars except DK Tau has been found to be N 0 > 1012 cm−3. We have managed to choose the parameters for eight stars at a calcium abundance in the accreted gas ξ Ca equal to the solar one, but we have been able to achieve agreement between the calculations and observations for TW Hya only by assuming ξ Ca to be approximately a factor of 3 lower than the solar one. The estimated parameters do not depend on interstellar extinction, because they have been determined from the spectra normalized to the continuum level. The calculated intensity of Ca II lines has turned out to be lower than the observed one, but this contradiction can be eliminated by assuming that, in addition to the accreted gas with a high density N 0, a more rarefied gas also falls onto the star. The theoretical equivalent widths and relative intensities of the subordinate He I lines disagree significantly with the observations. This is apparently because non-LTE effects should be taken into account when calculating the structure of the upper layers of the hot spot, the accuracy of the cross sections for collisional processes from upper levels is insufficient, and the spot inhomogeneity should probably be taken into account.

Measurement of stream cross section using ground penetration radar with Hilbert–Huang transform

AbstractThis study presents a new method to measure stream cross section without having contact with water. Compared with conventional measurement methods which apply instruments such as sounding weight, ground penetration radar (GPR), used in this study, is a non‐contact measurement method. This non‐contact measurement method can reduce the risk to hydrologists when they are conducting measurements, particularly in high flow period. However, the original signals obtained by using GPR are very complex, different from studies in the past where the measured data were mostly interpreted by experts with special skill or knowledge of GPR so that the results obtained were less objective. This study employs Hilbert–Huang transform (HHT) to process GPR signals which are difficult to interpret by hydrologists. HHT is a newly developed signal processing method that can not only process the nonlinear and non‐stationary complex signals, but also maintain the physical significance of the signal itself. Using GPR with HHT, this study establishes a non‐contact stream cross‐section measurement method with the ability to measure stream cross‐sectional areas precisely and quickly. Also, in comparison with the conventional method, no significant difference in results is found to exist between the two methods, but the new method can considerably reduce risk, measurement time, and manpower. It is proven that the non‐contact method combining GPR with HHT is applicable to quickly and accurately measure stream cross section. Copyright © 2013 John Wiley &amp; Sons, Ltd.

A thermodynamic view of tracer plume evolution: Complete mixing condition evaluation

One of most controversial issues of modern tracer theory is the “complete mixing condition” because of its importance in evolution of hazardous solutes in natural flows. This condition named also as “Mixing length” measures the distance from pouring point when tracer particles have spread uniformly on cross section of stream. The point is that until now there is no rational, complete and easy to use formula to calculate it. Rather, this condition is evaluated mostly by means of empirical relationships; among them Ruthven's is one of current usage. Also there are statistical methods that applied by software packages allow to characterize this condition. However a new focus on this issue is important, because is necessary to tie together, generality, easiness and accuracy. This paper puts on discussion a thermodynamics method to understand when a tracer is in this remarkable condition. Herein it is developed the conditions when this method may be applied. It is shown also how the resulting formula is convergent with Ruthven's equation. An experimental demonstration is presented.

Experimental investigation on the injection of an urea–water solution in hot air stream for the SCR application: Evaporation and spray/wall interaction

In automotive application, Selective Catalytic Reduction (SCR) system is used to control the NOx emissions from Diesel engines. The reducing agent, ammonia NH3, is produced by urea decomposition in spraying Urea–Water Solution (UWS) in hot exhaust gas. UWS evaporation is a crucial step in SCR system process. The effects of turbulence and spray/wall interactions are of paramount importance for the SCR process, not taken into account in the quiescent environment conditions usually considered in experiments related in the literature. In this work, UWS spray is investigated in a hot air stream. Test bench was designed to reach conditions similar to Diesel exhaust conditions in term of dimensions, temperature, air mass flow rate and injection strategies. UWS was sprayed in hot air stream canalized in transparent duct to enable optical access. Promising experimental techniques were performed to study the spray/wall interaction and spray evaporation in hot stream. An adapted backlight imaging technique was used to visualize the formation and development of liquid film caused by the impaction of spray on the duct wall. The variation of the area of the formed liquid film is quantified for several working conditions. UWS spray in the hot stream is examined with the Laser light Sheet Imaging (LSI) technique. The principle of this technique is to illuminate liquid drops with a laser sheet and to record the scattered-light at 90° with a CCD camera. Such measurements allow determining a 2D distribution of liquid that indicates the distribution of the liquid phase in a stream cross-section. We show that the evolution of 2D liquid distribution contains global information on the UWS drops evaporation and an evaporation rate can be estimated considering the Mie-scattered-light theory and D-square evaporation law. The experimental work is completed with a theoretical work that leads to the calculation of evaporation time of UWS drop in different aerothermodynamic conditions. Finally, this study promises interesting perspectives for the investigation of UWS spray evaporation in hot gas stream.

Use of heat as tracer to quantify vertical streambed flow in a two‐dimensional flow field

Analytical solutions to the heat transport equation in porous media have been developed in the past to estimate surface water‐groundwater interactions. These solutions, however, are based upon simplifying assumptions that are frequently violated in natural systems. A nonvertical flow field, inherent to most field settings, can violate the one‐dimensional (1‐D) flow assumption and lead to erroneous velocity estimates. In this study, we have developed a 2‐D heat and mass transport finite element‐based numerical model for a stream aquifer cross section experiencing flow‐through. Synthetic multilevel streambed temperature time series were generated with the model using a sinusoidal temperature boundary. The temperature data was used to quantify the vertical flow velocity with a 1‐D analytical solution based on the amplitude decay and phase shift of temperature with depth. Results demonstrate that erroneous vertical components of fluid velocity can be obtained by the 1‐D analytical solution when the true vertical velocity approaches zero and the flow regime becomes almost horizontal. The results also illustrate that the amplitude ratio method performs quite poorly on the gaining side of the stream where the only reliable method is phase shift. On the losing side of the stream, both methods can be employed but a better estimation is obtained from the amplitude ratio method. In general, amplitude ratio and phase shift data should be used in conjunction to maximize the information of the system.

Fluorescent particle tracers for surface flow measurements: A proof of concept in a natural stream

In this paper, a new particle tracer for surface hydrology is proposed. The approach leverages the complementary advantages offered by particle‐tracking velocimetry and traditional tracing technologies, such as dyes and chemicals, toward a practically feasible and low‐cost measurement system. Specifically, the proposed methodology is based on the detection and tracking of buoyant fluorescent microspheres through an experimental system that incorporates ultraviolet lamps to elicit the fluorescence response and a digital camera to record the particle transit. This low‐cost measurement system can be used in a variety of natural settings ranging from small‐scale streams to rills with scales on the order of a few centimeters in hillslopes. The use of insoluble buoyant particles reduces the amount of tracing material for experimental measurements. Further, particles' enhanced fluorescence allows for noninvasive flow characterization, that is, for nonintrusively detecting the tracer without deploying probes and samplers in the water. A proof of concept experiment for the proposed methodology is conducted on the Rio Cordon, a natural mountainous stream in the Italian Alps. Flow measurements at selected stream cross sections and travel time experiments on varying stream reaches are performed to ascertain the feasibility of fluorescent particle tracers. Such experimental findings demonstrate that the particles are visible in complex natural streams and are effective in estimating flow velocities and travel times.