Stream Cross Section Research Articles

Sentinel-2 MSI image time series reveal hydrological and geomorphological control of the sedimentation processes in an Amazonian hydropower dam

Monitoring sediment transport in a run-of-river hydropower dam was investigated to detect and quantify the siltation processes using Sentinel-2/MSI satellite images. We developed a method allowing us to assess the fate of sediment discharge in reservoirs and to map the locations of eroding and silting stream cross sections. This monitoring was achieved by retrieving the seasonal and interannual variation in suspended sediment concentration (SPM) longitudinally and by developing indices to detect local deviations from the overall SPM trend. A comparison between Sentinel-2 reflectance, processed for atmospheric and glint correction, and field measurements showed fine accuracy for the b8a/b4 band ratio (RMSE = 0.23 sr-1, N = 50) as well as a very good SPM retrieval performance for a wide range of concentrations [10–926 mg/L] with an RMSLE of 0.23 mg/L. SPM trend analysis demonstrated that significant (p < 0.001) sedimentation processes (i.e., decreases in SPM concentration upstream to downstream) occur for most parts of the hydrological cycle except during peak flooding when there was no significant SPM siltation. The overall rate of SPM decrease is −0.52 mg/L/km, varying from +0.11 mg/L/km down to −1.10 mg/L/km. We developed a deviation index to detect local anomalies from the overall upstream–downstream satellite-derived SPM trend. A satellite-derived map of eroding and silting reaches is produced evidencing the control of the sediment transport pattern by geomorphological features, such as rapids. Using independent bathymetric surveys, we showed that satellite data allow the locations of eroding and silting river reaches to be correctly mapped.

A comprehensive assessment and comparison of the impacts of storage parameters on solute transport in streams using a novel framework

Researchers must determine the storage parameter values to understand the storage processes and compare them across streams. These parameters are highly variable in time and space, making them challenging to measure. Individual studies of a single stream cannot characterize the interrelations among the processes involved in solute transport, hydraulic variables, and physical stream characteristics. Despite decades of research, a comprehensive framework is lacking. This study uses a simple and effective Monte Carlo approach to propose a general framework within which most solute transport models can undergo sensitivity analysis. This framework provides a comprehensive depiction of model performance under various scenarios, such as flow properties, stream geomorphology, and solute status. The relative and absolute sensitivities of three solute transport models, namely, the modified advection–dispersion equation (MADE), transient storage model (TSM), and variable residence time (VART), were evaluated and compared within the proposed framework. The main findings can be summarized as follows. In most conditions, storage models are more sensitive to the ratio of the storage zone cross-section to the stream cross-section than other parameters. Increasing the exchange rate between the stream and storage zones reduces the sensitivity to its indicative parameter and, consequently, its impact on the concentration time series. MADE's capability to identify modification parameters is higher for streams where dispersion dominates over advection, and their estimates have lower uncertainty. On the other hand, as advection becomes more dominant over dispersion in TSM and VART, estimated storage parameters have lower uncertainty.“

Spatiotemporal Variability Comparisons of Water Quality and Escherichia coli in an Oklahoma Stream

AbstractFecal indicator bacteria, Escherichia coli, for primary body contact recreation (PBCR) in Oklahoma waterbodies, is defined as the geometric mean of 10 samples from the recreation season, May 1 to September 30, with an impairment threshold of 126 colony forming units (cfu) per 100 mL. However, the water quality standards provide limited guidance on spatiotemporal and environmental factors that could influence samples collected and analyzed. In this study, two stream cross sections under baseflow conditions in a central Oklahoma urban perennial stream, Spring Creek, were densely sampled to investigate temporal and spatial variability of E. coli concentrations and water quality parameters across the stream channel. Water quality parameters (specific conductivity, temperature, dissolved oxygen, pH, turbidity, and total suspended solids (TSS)), stream discharge, and bacteria samples were collected simultaneously at equal intervals across the two cross sections in the morning and afternoon during one summer day with sunny, dry, and hot weather conditions. Results indicate a significant difference between time‐of‐day samples and water quality parameters and E. coli concentrations. Strong correlations between temperature, dissolved oxygen, and time versus E. coli concentrations were observed, while location, turbidity, and TSS were not significant or correlated to measured values. Furthermore, E. coli concentrations were highly variable spatially across each stream cross section, regardless of time of day or location. Results from this study provide an initial indication that stream water quality, spatial cross section sample location, and diurnal variations may be influencing factors on bacteria concentrations.

Lithological controls influence river form in contrasting sub‐catchments: The Scamander and Avenue Rivers, Tasmania

AbstractBedrock influence on river channel form is difficult to assess, with many catchments dominated by glacial erosion and with blanketing sediments from both pluvial and fluvial sources. The Scamander catchment in Tasmania lacks glacial history and features two bedrock‐confined sub‐catchments of similar area and maximum flow length, but one dominated by Mathinna Group sedimentary rocks, and the other with large areas in granite lithology. Lithology types, stream network parameters and near stream slope angles were analysed using geographical information systems, and results of stream cross sections, channel form and planforms were compared for each lithology. Results showed that granite features low gradient, shallow streams with channel slope cross sections of &lt;10°. Granite channels are irregular and dominated by large boulders that create channel roughness and resist incision. Weathering products of coarse quartz sand provide anchorages for in‐channel vegetation. By contrast, sedimentary Mathinna Group rocks feature steeply incised trough‐like channels, with near‐channel hillslope gradients mostly between 30° and 50°. Rectangular blocks disintegrate to gravel cobbles on the channel bed, providing poor anchorage for vegetation. Mathinna lithology influences steep, low roughness channels, and stable, incised recurved meanders formed by river interaction with vertical layers of resistant rock. The resistant bedrock lithology is demonstrated in this study to influence varied river planforms, near‐channel slope gradients, channel sediments and cross sections.

Discharge Monitoring in Open-Channels: An Operational Rating Curve Management Tool.

An aspect correlated with climate change is certainly represented by the alternation of severe floods and relevant drought periods. Moreover, there is evidence that changes in climate and land cover are inducing changes in stream channel cross-sections, altering local channel capacity. A direct consequence of a significant change in the local channel capacity is that the relationship between the amount of water flowing at a given point in a river or stream (usually at gauging stations) and the corresponding stage in that section, known as a stage-discharge relationship or rating curve, is changed. The key messages deriving from the present work are: (a) the more frequent and extreme the floods become, the more rapid the changes in the stream channel cross-section become, (b) from an operational point of view, the collection and processing of field measurements of the stage and corresponding discharge at a given section in order to quickly and frequently update the rating curve becomes a priority. It is, therefore, necessary to define a control system for acquiring hydrological data capable of keeping river levels and discharges under control to support flood early warnings and water management. The proposed stage-discharge management system is used by the Civil Protection Service of the Marche Region (east-central Italy) for the monitoring of river runoff in the regional watersheds. The Civil Protection Service staff performs stage-discharge field measurements using water level sensors and recorders (e.g., staff gauges, submersible pressure transducers, ultrasound and radar sensors) and a current meter, acoustic doppler velocimeter, acoustic doppler current profilers, portable mobile radar profiler and salt dilution method equipment, respectively. Power functions are fitted to the stage-discharge field data. Furthermore, extrapolation is performed to cover the full range of flow measurements; in general, extrapolation is not an easy task because of sharp changes in the stream cross-section geometry for very high or very low stages. In the present work, we also focused attention on the application problems that occur in practice and the need for frequent updating.

Field testing a High-Frequency acoustic attenuation system for measuring fine suspended sediments and algal movements

Acoustic measurements of suspended sediment have the potential to allow remote, autonomous monitoring of sediment movements at much higher temporal resolution than traditional manual sampling methods. Although suspended sands present a challenging measurement problem due to their logarithmic distribution with depth, fine clay sediments are distributed evenly throughout a stream cross section, making them amenable to point measurements. In order to improve measurement capabilities for fine sediments in stream channels, The National Center for Physical Acoustics at The University of Mississippi has developed a remote, autonomous acoustic system to monitor fine sediments transported in streams. The system was tested on the Middle Rio Grande near San Acacia, New Mexico, and in Goodwin Creek in Panola County, Mississippi. The acoustic instruments were compared to sediment concentrations from physical samples in both deployments. Diurnal patterns were found in the acoustic signals from the Middle Rio Grande, and a follow up experiment at The University of Mississippi Biological Field Station was used to investigate the potential effects of algal biomass on acoustic attenuation measurements. The results showed diurnal patterns in attenuation were associated with patterns in light, temperature, and dissolved oxygen. These results combined with information from the literature indicate diel movement of algal colonies in the water column of some water bodies may interfere with high-frequency acoustic measurements in natural environments and that acoustic methods have the potential to allow ecological researchers to evaluate mass algal movements in the field. Results from Goodwin Creek demonstrate that the acoustic system is able to provide measurements of sediment concentration with high temporal resolution that track well with expected sediment transport patterns in response to discharge hydrographs.

Streamflow Measurement Using Mean Surface Velocity

This study developed an efficient discharge measurement method that can be applied to estimate the streamflow of natural streams and artificial channels. The conventional methods that apply current meters to measure discharge are costly, time-consuming, and labor-intensive. Owing to a shortage of observers in streamflow measurement and for the safety of hydrologists and with advances in measurement techniques, many have strongly suggested the use of non-contact methods when determining streamflow. The non-contact methods that use floats or surface velocity radar to determine the streamflow are becoming more and more popular especially during periods of high water. However, it is not easy to estimate the surface velocity coefficient of each vertical directly for determining the mean velocity in each subsection. As the relationship between the mean surface velocity and mean velocity of a stream cross-section is constant, an efficient and accurate non-contact method of streamflow measurement could be further developed. Thus, streamflow can be estimated by the constant, the mean surface velocity, and cross-sectional area of a stream. The mean velocity of a cross-section, used for parameter calibration, is usually obtained from the discharge made based on the velocity-area principle and cross-sectional area. The surface velocity was measured at the vertical that is then used to estimate mean velocity of a subsection. Once the parameter is determined, streamflow can be obtained from the surface velocity. This approach was further applied to a natural stream and an artificial channel. Measurements were made to verify the reliability and accuracy of the proposed approach. The results show that the relationship between mean channel velocity and mean surface velocity is very stable in both a natural stream and an artificial channel because the streamflow differences, given by the proposed and the conventional method, are relatively insignificant. As a result, mean surface velocity can be used to determine the streamflow quickly and provides for a reliable and accurate measurement of streamflow.

Variability of E. coli in streambed sediment and its implication for sediment sampling

E. coli is the number one cause for water quality impairments in rivers and streams in South Dakota and the United States. Stream bottom sediments can be a reservoir for bacteria, including pathogenic organisms and fecal indicator bacteria (FIB), due to the favorable conditions provided by sediments for survival. Despite this, little is known about the variability of E. coli in sediments which should be considered when developing a sampling regime. This study examines the spatial variability of E. coli in sediment across the stream cross-section, the temporal stability of E. coli in sediment samples, and the implications for sediment sampling and processing. Five locations were sampled for sediment E. coli along two tributaries to the Big Sioux River in eastern South Dakota, four along Skunk Creek (Sk1, Sk2, Sk3, and Sk4), and one in Sixmile Creek (SM). In Skunk Creek, site Sk1 has direct cattle access where the other three sites (Sk2, Sk3, and Sk4) are under Seasonal Riparian Area Management (SRAM), a strategy that limits the cattle access to the stream. E. coli concentrations in the sediment ranged from 4 to 997 CFU g−1 (8.5 × 102 to 2.1 × 105 CFU 100 mL−1). The highest and lowest E. coli concentrations observed were at sites Sk1 and Sk4, respectively. The E. coli concentration decreased from the upstream cattle crossing site (Sk1) through the downstream SRAM sites. Analyzing the stream cross-section analysis revealed no significant difference in E. coli concentration between the edge and the middle of the stream. Sediment samples can be held up to 24 h after sample collection in refrigerated conditions (37 °F) in the majority of cases (80%) without significant changes in E. coli concentrations. The sample size analysis indicated the spatial variability of E. coli across the stream cross-section is high and a single grab sample may not be able to provide adequate representation of E. coli concentrations in sediment without substantial error. The findings provide insight for designing E. coli monitoring projects and promote the awareness of unconventional sources of microbiological water quality impairment which are often overlooked.

Flood analysis of Buntung River and the structural measures in Sidoarjo Regency

Sidoarjo Regency as one of the downstream areas of the Brantas River Basin is prone to flooding. This study aims to simulate the flood discharge and inundation in Buntung River, a river passes through Sidoarjo City area with several time return periods and to discuss its physical flood mitigation. Data needed in this study are Rainfall Data for 3 Rain Stations, topography map, cross section of river stream, and land use map. Based on these data, a flood flow analysis plan is then performed using the Nakayasu synthetic hydrographs method. The inundation is simulated using HEC-RAS with 10, 25, and 50 years return periods. Based on the calculation, Buntung River flood discharge with return period of 10, 25, and 50 years return periods is 151,342, 196,923, and 233,981 m3/s respectively. The inundation extend of 25 years return period is reaching 0,53 m height above the bank along Sta. P0 to P1. The study reveals that the existing cross section cannot accommodate the design flood for at least 25 years return period. Therefore, normalization is essential for river improvement. The channel is design with river cross-sectional shape of double trapezoidal. The size of the earth dike is 0.60 m above the flood water level with 3.0 m width and 1:2 channel slope. The designed river channel improvement increase the channel depth from -3,56 m to -4,07 m in Sta. P1. The normalized channel could accommodate the design flood and would be beneficial for increasing the urban area safety from flood disaster.

Monitoring ungauged watersheds for investigating the variability of flow and salinity to implement the possible removal of salt fill sites.

Salinity is a crucial environmental problem leading to profound consequences in wetland plants and aquatic habitats including the rapid development of Phragmites australis in the marshland. These Phragmites australis are extremely vulnerable to capture fire, which might eventually affect the overall ecosystem of the marsh. However, in order to restore the marsh, a hydrologic investigation is needed, which is possible if a watershed is gauged, and long-term data are available. In this study, a systematic approach has been presented to conduct hydrologic modeling and salinity prediction in an ungauged watershed in order to implement the possible removal of salt fill sites. The stage and electrical conductivity were measured continuously, whereas stream cross sections and velocity of the streamflow were recorded intermittently in the Blackbrook Creek to develop a rating curve and generate continuous streamflow data. The watershed model Soil and Water Assessment Tool (SWAT) was calibrated and validated to a monthly scale with good model performance. In the next step, critical sources of salinity were identified from the two tributaries in order to implement the removal of salt fill sites for the possible reduction of salinity in the marsh. While salinity loading was approximately 10 times higher from Marsh Creek (65.63tons to 2028.13tons per month) compared with Blackbrook Creek (10.23tons to 163.98 per month), the analysis suggested that salinity concentration was higher from Blackbrook Creek, which was particularly due to abandoned salt fill sites near the Creek. The salinity loadings were linearly correlated with streamflow on a monthly (R2 = 0.81) scale, which was utilized to generate the salinity loadings that were diverted due to the rerouting of the Creek through the new location in order to avoid salt fill sites and reduce salinity in the Mentor Marsh. Our analysis suggested that approximately 74kg/day salinity was being rerouted from the Marsh; however, the salt fill sites contribute salinity to the Marsh equivalent to 63kg/day, which still needs to be removed. The research findings are expected to be helpful for monitoring small ungauged watersheds.

Implications of Systemic Hematocrit on the Radial Distribution of Red Cells in Arterioles

It is well‐established that the tube hemacocrit (HctT) in blood vessels and glass tubes with an internal diameter less than 200‐microns is significantly lower than feed or discharge Hct (the Fahraeus Effect). Microscopic imaging of the flow stream reveals a decrease in Hct in the vicinity of the wall (the plasma layer, PL) but the mechanism of the effect is unclear. To address this question, we recorded high speed videos (3000 fps) of blood flow in 35‐micron diameter arterioles of the rat cremaster muscle at systemic Hct (HctS) levels of 20% to 72%. We found that the PL is an annulus bordering the wall that occupies 12% to 50% of the flow stream cross section, and that it is inversely related to HctS. In addition, results indicate that the Hct in the core region of the flow stream is not significantly different from HctS. The position of the PL coincides with the region of maximal shear stress in the flow stream, which may strip away the red cell monolayer adjacent to the wall, creating the PL while the monolayer moves toward the faster‐flowing center of the flow stream. In conclusion, while volumetric flow is related to the cross section of the flow stream, the PL is related to the circumference, thus reducing HctT as radius decreases.Support or Funding InformationThis work was supported by the NIH Heart Lung and Blood Institute under Grants R01HL126945 and R01HL138116.

Distribution of fire extinguishing powder fractions in simulated non-stationary gas stream

Introduction. The article presents the regularities of particles distribution of fire extinguishing powder fractions in the cross sections of the simulated unregulated non-stationary gas stream. The distance from the fire extinguisher cut which the stream is most stable in terms of the content of fire extinguishing powder particles is determined. There are works in which the physical and chemical properties of fire-extinguishing powders are considered, the movement of powder particles in the stream is modeled, the influence of the fractional composition of the powder on its fire-extinguishing capacity is determined. At the same time distribution of powder fractions during its movement in gas-powder stream is not considered. The purpose of the present work is to find ways to improve the efficiency of powder extinguishers by controlling the distribution of powder fractions in a non-stationary gas stream.Materials and methods. Experimental study installation consists of coordinate table oriented perpendicular to gas-powder stream direction. The table is equipped with collectors that allow to collect powder samples at control points of flow cross-section. Food sodium chloride (further — salt) was used in the experiment. Its characteristics correspond to GOST R 53280.4–2009 and allow to apply it as a model. The coordinate table was installed sequentially at a distance of 500, 750, 1000 and 1250 mm from the fire extinguisher cut. Next, a shot of salt with a known fractional composition was supplied with a fire extinguisher model to a coordinate table and the retained powder samples were taken. The mass and fractional composition of the samples collected by each collector were then determined. Stability of the particle distribution in the gas stream by statistical analysis (by Fischer’s criterion) was measured for their content.Conclusions. Regularities of different fire extinguishing powder fractions distribution in cross section of non-regulated non-stationary gas stream are established and analytically described. These regularities can be used in finding ways to regulate fire extinguishing powder fractions during fire extinguishing. The most representative and stable in accuracy (correctness and precision) results of powder fractions content in the section of non-stationary gas stream at a distance of 1000 mm from the fire extinguisher cut. This should be taken into account in further research.

Estimating the Frequency and Extent of Overbank Flow of a Baseflow‐Dominated Stream Flowing through a Wetland

AbstractRiver floodplains provide critical habitat for a wide range of animal and plant species and reduce phosphorus and nitrogen loads in streams. It has been observed that baseflow‐dominated streams flowing through wetlands are commonly at or near bankfull and overflow their banks much more frequently than other streams. However, there is very little published quantitative support for this observation. The study focuses on a 1‐km reach of Black Earth Creek, a stream in the Midwestern United States (U.S.). We used one‐dimensional hydraulic modeling to estimate bankfull discharge at evenly spaced stream cross sections, and two‐dimensional modeling to quantitate the extent of wetland inundation as a function of discharge. We then used historical streamflow data from two U.S. Geological Survey gaging stations to quantitate the frequency of wetland inundation. For the with‐sediment case, the frequency of overbank conditions at the 38 cross sections in the wetland ranged from 3 to 85 days per year and averaged 43 days per year. Ten percent of the wetland was inundated for an average of 35 days per year. For the without‐sediment case, the frequency of overbank conditions ranged from 2.6 to 48 days per year and averaged 14 days per year. Also, 10% of the wetland was inundated for an average of 25 days per year. These unusually high rates of floodplain inundation are likely due in part to the very low stream gradient and shallow depths of overbank flow.

Using Areal Composition of Riparian Vegetation Communities to Identify Thresholds in Prairie Streams

Riparian areas often have multiple plant communities that may change rapidly due to seasonal hydrological shifts, and variation of those plant communities may not necessarily indicate transitioning ecological status. Thus, while plant communities are often used to assess land ecological status in upland systems, applying that principle to riparian systems may not be appropriate. Geomorphic parameters may be better indicators of a transition in ecological status, but they cannot be understood separately from plant community dynamics. This research assessed stream geomorphology and riparian plant communities along 34 reaches of 8 streams in North Dakota. The area of three plant community components (PCCs) associated within riparian complexes were mapped, and stream cross-section and longitudinal profile data were collected to classify Rosgen stream channels into stable (E and C channels), stabilizing (B channels), and unstable (F and G channels) states. The area of PCC1, the community nearest the stream bank consisting of wetland obligate species, was similar among stable and unstable streams, but PCC2 and PCC3, transitional plant communities, had greater area along stable reaches than along unstable reaches. Thus, the proportion of PCC1 in stable reaches was much lower (≈25%) than in unstable reaches (≈75%). Entrenchment ratio was the only stream parameter that was a good predictor of PCC areas, likely due to its relationship with floodplain connectivity. These findings may be valuable in developing riparian complex ecological site descriptions, specifically identifying potential thresholds between the unstable and stable states.

Englacial Pore Water Localizes Shear in Temperate Ice Stream Margins

The margins of fast‐moving ice streams are characterized by steep velocity gradients. Some of these gradients cannot be explained by a temperature‐dependent viscosity alone. Laboratory data suggest that water in the ice‐grain matrix decreases the ice viscosity; we propose that this causes the strong localization of shear in temperate ice stream margins. However, the magnitude of weakening and its consequences for ice stream dynamics are poorly understood. Here we investigate how the coupling between temperate ice properties, ice mechanics, and drainage of melt water from the ice stream margin alters the dynamics of ice streams. We consider the steady‐state ice flow, temperature, water content, and subglacial water drainage in an ice stream cross section. Temperate ice dynamics are modeled as a two‐phase flow, with gravity‐driven water transport in the pores of a viscously compacting and deforming ice matrix. We find that the dependence of ice viscosity on meltwater content focuses the temperate ice region and steepens the velocity gradients in the ice stream margin. It provides a possible explanation for the steep velocity gradients observed in some ice stream shear margins. This localizes heat dissipation there, which in turn increases the amount of meltwater delivered to the ice stream bed. This process is controlled by the permeability of the temperate ice and the sensitivity of ice viscosity to meltwater content, both of which are poorly constrained properties.

Study on the Characteristics of the Hydraulic Environment in the Downstream Area According to the Discharge of Changnyeong-Haman Weir

Kim, T.W.; Kim, Y.J.; Cho, W.C.; Park, B.W., and Yoon, J.S., 2019. Study on the characteristics of the hydraulic environment in the down-stream area according to the discharge of Changnyeong-haman weir. In: Lee, J.-L.; Yoon, J.S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp.151-155. Coconut Creek (Florida), ISSN 0749-0208.This study refined the reproducibility of a stream cross section of the Nakdong River using the Modified EFDC model and examined the salt water flow from the external sea to the river upstream according to the changing gate open rate of Nakdong River estuary barrage and the influent flow and tide level conditions in the Changnyenong-Haman Weir using a numerical model. Furthermore, numerical simulations were conducted and the hydraulic characteristics were examined to investigate the flushing effect according to the changing discharge of the Changnyenong-Haman Weir in the event of a salt wedge.

A gas-discharge plasma focuser

A device is proposed for the formation of a gas-discharge plasma stream with a sinusoidal distribution of the charged-particle density over the stream cross section, which is achieved by using wavy shapes of the anode and cathode surfaces that are placed coaxially relative to each other at the distance λ e < h < 3λ e , where λ e is the mean free path of an electron in the gas-discharge plasma stream. The anode is a stainless steel grid with mesh dimensions of 1 × 1 mm. The aluminum cathode is 120 mm in diameter and 50-mm thick. The device provides a discharge current of up to 0.6 А at a controlled voltage at the electrodes in the range of 0.21–0.7 kV. In this case, plasma streams propagate to a distance of up to 50λ e beyond the limits of the electrodes.

Hillslope coupled stream morphology, flow conditions, and their effects on detrital sedimentology in Garnet Canyon, Teton Range, Wyoming

Characterizing stream erosion in any steep mountain landscape is arduous, but the challenge level increases when the stream flows through a glaciated catchment frequently modified by hillslope debris. Glacial landforms and stochastic mass wasting in alpine systems may interfere with sediment delivery to downstream sites where detrital sediments are often collected to represent upstream bedrock sources. To use detrital sediments as indicators of erosion, we need to understand potential sediment accumulation in flat glaciated reaches or behind rockfall barriers. This study investigates the stream channel in Garnet Canyon, a glaciated catchment located in the central Teton Range, to describe hillslope coupled channel morphology and the subsequent effects on sediment transport throughout the catchment. Stream cross-section surveys and sediment size measurements of the surface bedload were collected in the field within a glacially flattened segment of Garnet Canyon. Calculations of shear stress conditions allowed evaluation of the importance of mineral densities on potential grain entrainment. The length of the Garnet Canyon stream observed in this study was coupled with hillslope deposits. Critical shear stresses were sufficient to move gravel-sized sediments through all sections when calculated with quartz mineral density and through most sections when applying apatite mineral density. These results verify the application of detrital sediments to evaluate erosion rates or spatial bedrock sources because snowmelt stream flow efficiently moves entrained sediment past glacially reduced slopes and potential talus barriers.

Heat tracing to determine spatial patterns of hyporheic exchange across a river transect

Significant spatial variability of water fluxes may exist at the water-sediment interface in river channels and has great influence on a variety of water issues. Understanding the complicated flow systems controlling the flux exchanges along an entire river is often limited due to averaging of parameters or the small number of discrete point measurements usually used. This study investigated the spatial pattern of the hyporheic flux exchange across a river transect in China, using the heat tracing approach. This was done with measurements of temperature at high spatial resolution during a 64-h monitoring period and using the data to identify the spatial pattern of the hyporheic exchange flux with the aid of a one-dimensional conduction-advection-dispersion model (VFLUX). The threshold of neutral exchange was considered as 126 L m−2 d−1 in this study and the heat tracing results showed that the change patterns of vertical hyporheic flux varied with buried depth along the river transect; however, the hyporheic flux was not simply controlled by the streambed hydraulic conductivity and water depth in the river transect. Also, lateral flow dominated the hyporheic process within the shallow high-permeability streambed, while the vertical flow was dominant in the deep low-permeability streambed. The spatial pattern of hyporheic exchange across the river transect was naturally controlled by the heterogeneity of the streambed and the bedform of the stream cross-section. Consequently, a two-dimensional conceptual illustration of the hyporheic process across the river transect is proposed, which could be applicable to river transects of similar conditions.

Probe Positioning for the Exhaust Emissions Measurements

Emission of harmful compounds in the exhaust gases depends on the operating conditions of the engine and its technical condition. Therefore, the legislative activity is focused on the introduction of new diagnostic and research procedures. The preferred method is using probes with plurality of holes for multi-gas sampling from the entire cross-section of exhaust stream. This method appears to vitiated by an error caused by averaging dilution and sampling gas from the very beginning of the measurement path. The results of measurements contained in the article are related to changes in the concentration of harmful substances in exhaust gases depending on the distance from the axis of the jet. In the article the disadvantages of this the methods were highlighted and the single-point measurement method was proposed.