Surface Flow Type Research Articles

Classification of River Sediment Fractions in a River Segment including Shallow Water Areas Based on Aerial Images from Unmanned Aerial Vehicles with Convolution Neural Networks

Riverbed materials serve multiple environmental functions as a habitat for aquatic invertebrates and fish. At the same time, the particle size of the bed material reflects the tractive force of the flow regime in a flood and provides useful information for flood control. The traditional riverbed particle size surveys, such as sieving, require time and labor to investigate riverbed materials. The authors of this study have proposed a method to classify aerial images taken by unmanned aerial vehicles (UAVs) using convolutional neural networks (CNNs). Our previous study showed that terrestrial riverbed materials could be classified with high accuracy. In this study, we attempted to classify riverbed materials of terrestrial and underwater samples including that which is distributed in shallow waters where the bottom can be seen using UAVs over the river segment. It was considered that the surface flow types taken overlapping the riverbed material on images disturb the accuracy of classification. By including photographs of various surface flow conditions in the training data, the classification focusing on the patterns of riverbed materials could be achieved. The total accuracy reached 90.3%. Moreover, the proposed method was applied to the river segments to determine the distribution of the particle size. In parallel, the microtopography was surveyed using a LiDAR UAV, and the relationship between the microtopography and particle size distribution was discussed. In the steep section, coarse particles were distributed and formed riffles. Fine particles were deposited on the upstream side of those riffles, where the slope had become gentler due to the dammed part. The good concordance between the microtopographical trends and the grain size distribution supports the validity of this method.

The fate of microplastics from municipal wastewater in a surface flow treatment wetland

Microplastics (MPs) are an anthropogenic pollutant of emerging concern prominent in both raw and treated municipal wastewater as well as urban and agricultural run-off. There is a critical need for the mitigation of both point- and diffuse sources, with treatment wetlands a possible sustainable nature-based solution. In this study, the possible retention of MPs in treatment wetlands of the widely used surface flow (SF) type was investigated. In- and outflow water, as well as atmospheric deposition, at a full-scale reed-based SF wetland (operating as a polishing phase of municipal wastewater treatment) was analyzed for MPs in a size range of 25–1000 μm. FPA-based μFT-IR spectroscopic imaging was used in combination with automated data analysis software, allowing for an unbiased assessment of MP numbers, polymer types and size distribution.Inflow water samples (secondary treated wastewater) contained 104 MPs m−3 and 56 MPs m−3 in sampling campaigns 1 and 2, respectively. Passage through the SF wetland increased the MP concentration in the water by 92 % during a rain intense period (campaign 1) and by 43 % during a low precipitation period (campaign 2). The MP particle numbers, size and polymer type distribution varied between the two sampling campaigns, making conclusions around the fate of specific types of MPs in SF wetlands difficult.Atmospheric deposition was measured to be 590 MPs m−2 week−1 during the rain-intense period. Our findings point towards atmospheric deposited MPs as an important factor in the fate of MPs in SF wetlands, causing an increase of MP concentrations, and potentially explaining the variations observed in MP concentrations in wetland effluent and removal efficiency. Furthermore, atmospheric deposition might also be a reason for the considerable inter-study variation regarding MPs removal efficiency in SF wetlands found in the available literature.

Smoothed particle hydrodynamics method for free surface flow based on MPI parallel computing

In the field of computational fluid dynamics (CFD), smoothed particle hydrodynamics (SPH) is very suitable for simulating problems with large deformation, free surface flow and other types of flow scenarios. However, traditional smoothed particle hydrodynamics methods suffer from the problem of high computation complexity, which constrains their application in scenarios with accuracy requirements. DualSPHysics is an excellent smoothed particle hydrodynamics software proposed in academia. Based on this tool, this paper presents a largescale parallel smoothed particle hydrodynamics framework: parallelDualSPHysics, which can solve the simulation of large-scale free surface flow. First, an efficient domain decomposition algorithm is proposed. And the data structure of DualSPHysics in a parallel framework is reshaped. Secondly, we proposed a strategy of overlapping computation and communication to the parallel particle interaction and particle update module, which greatly improves the parallel efficiency of the smoothed particle hydrodynamics method. Finally, we also added the pre-processing and post-processing modules to enable parallelDualSPHysics to run in modern high performance computers. In addition, a thorough evaluation shows that the 3 to 120 million particles tested can still maintain more than 90% computing efficiency, which demonstrates that the parallel strategy can achieve superior parallel efficiency.

건물 밀집도에 따른 도시협곡 풍환경 평가

In this study, based on conditions observed for different building densities, the conditions for changing the width between buildings around the reference building were assigned. Accordingly, a sensitivity test for changes in wind conditions in urban canyons was performed, and the pattern and changes in wind formed under different test conditions were compared and analyzed. In addition, the characteristics of the wind environment occurring in the canyon, the wind speed variability, and wind velocity components were considered. The results showed that the wind speed in urban canyons increased or decreased according to the density of the buildings. In particular, it was confirmed that some vortex flow occurred in the canyons (y/H = 1.5), and various surface flow types were observed depending on the experimental conditions regarding the vertical and horizontal wind velocity components. In the case of horizontal flow, it was confirmed that the wind speed strength of the wall increased as the x/H ratio increased, regardless of the y/H condition. However, the simulation of the characteristics differed depending on the canyon. Therefore, changes in wind field and wind velocity components that occur due to building density centered on the reference building were confirmed.

System construction based on a wire-mesh sensor for flow analysis

Wire-mesh sensor (WMS, mesh sensor) is a device for invasive imaging of vertical and horizontal flows of liquids and gases. Visualisation of the measurement results does not require any complicated software reconstruction. The device consists of two parts: the wire-mesh acquisition module and the wire-mesh sensor. The device allows for testing of multiphase flows as well as air bubbles in air-lift reactors. The sensors are also suitable for testing various types of surface flows and the movement of bulk materials along the bottom of a pipeline. This paper describes the goals and results of construction of the system for flow analysis based on a wire-mesh sensor.

Design of Self-Assembling Molecules and Boundary Value Problem for Flows on a Space of <i>n</i>-Simplices

Self-assembling molecules are ubiquitous in nature, among which are proteins, nucleic acids (DNA and RNA), peptides and lipids. Recognizing the ability of biomolecules to self-assemble into various 3D shapes at the nanoscale, researchers are mimicking the self-assembly strategy for engineering of complex nanostructures. However, the general principles underlying the design of self-assembled molecules have not yet been identified. The question is “How to obtain a well-defined shape with desired properties by folding a chain of subunits (such as amino acids and nucleic acids)”, where properties are determined by the precise spatial arrangement of the subunits on the surface. In this paper, we consider the question from the viewpoint of the discrete differential geometry of n-simplices. Self-assembling molecules are then represented as a union of trajectories of 3-simplices (i.e., tetrahedrons), and the question is rephrased as a “boundary value problem” for flows on a space of tetrahedrons. Also considered is a characterization of two types of surface flows of n-simplices. It is a rough classification of surface flows, but may be essential in characterizing important properties of biomolecules such as allosteric regulation. The author believes this paper not only provides a new perspective for the engineering of self-assembling molecules, but also promotes further collaboration between mathematics and other disciplines in life science.

Flow and Turbulence driven Water Surface Roughness and Gas Exchange Velocity in Streams

Gas exchange velocity in streams and rivers controls fluxes of atmospheric gases across the air-water interface and is commonly related to the turbulence at the water side. Similarly, river flow hydraulics influences the water surface roughness, which is frequently used (in terms of surface flow types) for eco- and morphological mapping of spatial variations of hydraulic conditions. We investigated the relationships between gas exchange velocity, water surface roughness and flow hydraulics for different surface flow types in a low-mountain stream. We used the flux chamber-method to estimate exchange velocity, a freely floating sphere (equipped with acceleration sensors) to measure water surface roughness, as well as a field-particle image velocimetry system for flow and turbulence measurements. The results demonstrate that the gas exchange velocity in smooth and rippled flows followed the same universal dependence on turbulent dissipation rates (with an empirical scaling coefficient at the upper limit) as observed in wind-driven systems. More rough flows were anisotropic and gas exchange velocity was stronger related to vertical components of turbulence parameters. We further explored the potential of using surface flow type evaluations and water surface roughness measurements for estimating gas exchange velocities at the reach scale and beyond.

The Accuracy and Reliability of Traditional Surface Flow Type Mapping: Is it Time for a New Method of Characterizing Physical River Habitat?

Surface flow types (SFT) are advocated as ecologically relevant hydraulic units, often mapped visually from the bankside to characterise rapidly the physical habitat of rivers. SFT mapping is simple, non-invasive and cost-efficient. However, it is also qualitative, subjective and plagued by difficulties in recording accurately the spatial extent of SFT units. Quantitative validation of the underlying physical habitat parameters is often lacking, and does not consistently differentiate between SFTs. Here, we investigate explicitly the accuracy, reliability and statistical separability of traditionally mapped SFTs as indicators of physical habitat, using independent, hydraulic and topographic data collected during three surveys of a c. 50m reach of the River Arrow, Warwickshire, England. We also explore the potential of a novel remote sensing approach, comprising a small unmanned aerial system (sUAS) and Structure-from-Motion photogrammetry (SfM), as an alternative method of physical habitat characterisation. Our key findings indicate that SFT mapping accuracy is highly variable, with overall mapping accuracy not exceeding 74%. Results from analysis of similarity (ANOSIM) tests found that strong differences did not exist between all SFT pairs. This leads us to question the suitability of SFTs for characterising physical habitat for river science and management applications. In contrast, the sUAS-SfM approach provided high resolution, spatially continuous, spatially explicit, quantitative measurements of water depth and point cloud roughness at the microscale (spatial scales ≤1m). Such data are acquired rapidly, inexpensively, and provide new opportunities for examining the heterogeneity of physical habitat over a range of spatial and temporal scales. Whilst continued refinement of the sUAS-SfM approach is required, we propose that this method offers an opportunity to move away from broad, mesoscale classifications of physical habitat (spatial scales 10-100m), and towards continuous, quantitative measurements of the continuum of hydraulic and geomorphic conditions which actually exists at the microscale.

Removal efficiencies of constructed wetland and efficacy of plant on treating benzene

Abstract Leaking underground petroleum storage poses human and environmental health risks as it contaminates the soil and the groundwater. Of the many contaminants, benzene – a major constituent of gasoline, is of primary concern. It is an identified carcinogen with a permissible limit set at a low level of 0.005 mg L−1. This poses technical and regulatory challenge to remediation of contaminated sites. Various specialized treatment methods are available, but despite of the high removal efficiencies of sophisticated treatments, the residual level still poses health risks. Thus, additional alternative ways that are cost effective and require minimum technical expertise are necessary, and a constructed wetland (CW) is a potential alternative. This study evaluates the performance of a surface flow type CW for the removal of benzene from the contaminated water. It further determines the efficacy of a common reed plant Phragmites karka in treating benzene. Planted and unplanted CW were acclimated with benzene for 16 wk and tested for an 8-d hydraulic retention time at benzene levels of 66 and 45 mg L−1. Results indicate that the planted CW performed better and gave reliable and stable results.

Evaluation of treatment efficiencies of pollutants in daecheong lake juwon stream constructed wetlands

This study focused on evaluating the efficiency of the removal of non-point source pollution by Daecheong Lake Juwon Stream constructed wetlands. The constructed wetland system is a surface flow type designed in the year 2007 for purifying eutrophic water of Daecheong Lake Juwon Stream. The value of conductivity, suspended solids(SS), chemical oxygen demand using a potassium permanganate(CODMn), five-day biochemical oxygen demand(BOD5), total nitrogen(T-N), total phosphorous(T-P), and pH in inflow averaged 220.2, 2.46, 3.33, 1.34, 2.00, 0.04 mg/L and 7.24, respectively and in outflow averaged 227.9, 1.12, 3.34, 0.87, 1.16, 0.02 mg/L and 7.45, respectively. The average removal efficiency of constructed wetlands was 30 % for SS, 22 % for BOD5, 45 % for T-N and 31 % for T-P. The removal rates of SS, BOD5 and T-N in the spring, summer and autumn were higher than those in winter. The removal rate of T-P was not significant different in all seasons. The amounts of pollutants removal in the constructed wetlands were higher in the order of 3rd ‹ 2nd ‹ 1st wetland for SS and T-P, 2nd ‹ 3rd ‹ 1st wetland for BOD5 and T-N. Therefore, our findings suggest that the constructed wetlands could well treat the eutrophic Daecheong Lake Juwon Stream waters.

Visually determined stream mesohabitats influence benthic macroinvertebrate assessments in headwater streams.

Mesohabitat components such as substrate and surface flow types are intimately related to benthic macroinvertebrate assemblages in streams. Visual assessments of the distribution of these components provide a means of evaluating physical habitat heterogeneity and aid biodiversity surveys and monitoring. We determined the degree to which stream site and visually assessed mesohabitat variables explain variability (i.e., beta-diversity) in the relative abundance and presence-absence of all macroinvertebrate families and of Ephemeroptera, Plecoptera, and Trichoptera (EPT) genera. We systematically sampled a wide variety of mesohabitat arrangements as they occured in stream sites. We also estimated how much of the explanation given by mesohabitat was associated with substrate or surface flow types. We performed variation partitioning to determine fractions of explained variance through use of partial redundancy analysis (pRDA). Mesohabitats and stream sites explained together from 23 to 32% of the variation in the four analyses. Stream site explained 8-11% of that variation, and mesohabitat variables explained 13-20%. Surface flow types accounted for >60% of the variation provided by the mesohabitat component. These patterns are in accordance with those obtained in previous studies that showed the predominance of environmental variables over spatial location in explaining macroinvertebrate distribution. We conclude that visually assessed mesohabitat components are important predictors of assemblage composition, explaining significant amounts of beta-diversity. Therefore, they are critical to consider in ecological and biodiversity assessments involving macroinvertebrates.

An evaluation of surface flow types as a rapid measure of channel morphology for the geomorphic component of river condition assessments

Riverine assessments of channel morphology and fluvial processes typically involve a time-consuming survey of channel cross sections and longitudinal profiles, expensive aerial imagery, and/or require specialised knowledge. As a result, geomorphic input is not widely included in multiparameter river condition assessments. We were interested in determining if surface flow type observations can be used as a rapid measure of channel morphology and then subsequently be used in river condition assessments to monitor channel change over time. We examined the relationship between flow types (e.g., rippled flow, no perceptible flow) and channel morphology. Two aspects of channel morphology were assessed: (i) within-reach depth variability and (ii) cross section geometry (e.g., width, area, Froude number). In a two-part study, each of these was correlated with flow type diversity for a range of study sites from upland and lowland environments in Victoria, Australia. We found that an increased diversity of flow types correlated with greater depth diversity, based on the coefficient of variation of depth along a reach. Flow types also correlated well with the cross-sectional Froude number, but less so with other geometric parameters. The proportion of flow types present was also notably sensitive to discharge within the low flow range examined (70–99% flow exceedance). Three ‘geo-topes’ — cross section units of a dominant flow type — were found to be the most physically distinct units at this cross section scale; no perceptible flow (deadwater), smooth boundary turbulent (glide), and rippled flow (run/riffle). Rippled flow is a revision to previous run/riffle classifications and is identified by the presence of unbroken waves of any size with crests moving in a general downstream direction. Our findings indicate that flow types can provide indicative information on channel morphology along a reach. When assessed at low flow levels, the diversity of flow types reflects the variability of cross-sectional geometry and also the diversity of the channel bed (depth). On this basis, the inclusion of flow type observations in river condition assessments can provide meaningful information on channel morphology, in a rapid and repeatable way. With repeat surveys, flow types could be used as a geomorphic metric to track changes in morphologic diversity over time, including changes associated with processes of sediment transport, scour, and deposition at a reach.

Surface flow types, near-bed hydraulics and the distribution of stream macroinvertebrates

Abstract. Spatial variation in hydraulic conditions in streams often results in distinct water surface patterns, or surface flow types. Visual assessments of the distribution of surface flow types have been used to provide rapid assessment of the habitat heterogeneity. The efficacy of this approach is predicated on the notion that surface flow types consistently represent a distinct suite of hydraulic conditions with biological relevance. This study tested this notion, asking three specific questions. First, do surface flow types provide a characterisation of physical habitat that is relevant to macroinvertebrates? Second, how well do near-bed hydraulic conditions explain macroinvertebrate distributions? Third, what components of near-bed hydraulic conditions exert the strongest influence on macroinvertebrate distributions? Results show that hydraulic conditions (incorporating direct measurements of near-bed velocity and turbulence in three dimensions) and substratum character (incorporating estimates of particle size distribution, and biofilm and macrophyte cover) within each surface flow type were largely distinct and that macroinvertebrate assemblages differed across flow types in taxon richness and assemblage composition, thus supporting the notion that rapid assessments of surface flow type distributions provide biologically relevant information. Macroinvertebrate assemblages were most strongly correlated with water depth, size of a flow type patch, near-bed velocity in the downstream direction, turbulence in the transverse direction, % pebble, % sand, % silt and clay and macrophyte cover. This study suggests that surface flow type mapping provides an assessment of physical habitat that is relevant to macroinvertebrates. The strong relationship detected between macroinvertebrate assemblages and transverse turbulence also highlights the value of directly measuring near-bed hydraulics. Further investigations are required to test the mechanisms underlying this relationship.

Towards an ecologically meaningful classification of the flow biotope for river inventory, rehabilitation, design and appraisal purposes

Recent research into the physical and ecological status of rivers has focused upon rapid field-based assessments of mesoscale habitat features in order to satisfy international regulatory requirements for habitat inventory and appraisal. Despite the low cost and time efficient nature of rapid field surveys, the robustness of such techniques remains uncertain. This paper uses data from over 4000 surveyed UK river reaches in the UK River Habitat Survey (RHS) database in order to seek linkages between surface flow conditions (flow biotopes), local channel morphology (physical biotopes) and biologically distinct vegetative and minerogenic habitat units (functional habitats). Attempts to identify one-to-one connections between surface flow types, units of channel morphology and functional habitats oversimplify a complex and dynamic hydraulic environment. Instead, a nested hierarchy of reach-scale physical and ecological habitat structures exists, characterised by transferable assemblages of habitat units. Five flow biotopes show strong correlations with functional habitats, and differing combinations of three of these account for over 60% of the distribution for all functional habitats. On this basis, a classification of environments for ecological purposes is proposed. Principal components analysis and agglomerative hierarchical clustering analysis are employed to objectively validate the proposed classification. Flow biotope assemblages may also represent reach-scale channel morphologies (step-pool, riffle-pool and glide-pool), although functional habitats exhibit differing ‘preferences’ for rougher or more tranquil environments within these. While the data and analysis are specific to the UK RHS, the methods and findings have wider application in situations, where rapid field appraisal methods and associated databases are deployed in water resource inventory and river rehabilitation design.

Managing river flows for hydraulic diversity: an example of an upland regulated gravel‐bed river

AbstractThe establishment of ecologically responsive environmental flow regimes is a challenge for river managers. Biological communities in river environments are partly constrained by hydraulic characteristics such as water depth, flow velocity and turbulence, so a key step in understanding the links between discharge and biotic response is to relate discharge and hydraulic character. This paper explores the nature of the relationship observed between discharge and hydraulic character in the Cotter River, Australia. Surface flow types or hydraulic patches, expressing a variety of hydraulic characteristics, were mapped in six reaches in this upland gravel‐bed river, during 18 different flow releases ranging from 8 to 260 ML per day. The distributions of these hydraulic patches were variable, both spatially and over time. The patches represent hydraulic habitats (of varying depth, flow velocity and turbulence) the diversity of which may contribute to in‐stream biodiversity. The study identified a range of flow releases that produce the greatest in‐stream diversity of hydraulic habitats, which, if included in managed release strategies, potentially benefits in‐stream biodiversity. Copyright © 2006 John Wiley & Sons, Ltd.

The habitat-scale ecohydraulics of rivers

This paper establishes the link between ‘functional habitats’ (biologically defined habitat units) and flow ‘biotopes’ (hydraulically defined habitat units) using Froude number. Froude number has been shown to be the hydraulic variable that best describes surface flow type (flow biotope). The approach used was to examine the relationship between functional habitat occurrence and Froude number, with the aim of developing ‘habitat preference curves’. Fifteen of the 16 functional habitats were found to be distributed with Froude number in a non-random fashion (‘woody-debris’ being the only exception). Eight functional habitats were most likely to occur in the lowest Froude number class. These were ‘silt’, ‘roots’, ‘trailing vegetation’, ‘marginal plants’, ‘leaf-litter’, ‘emergent macrophytes’, ‘floating-leaved macrophytes’, and ‘submerged broad-leaved macrophytes’. The remaining habitats occurred at higher Froude numbers, with a gradient of increasing Froude number going from ‘sand’, to ‘gravel’, to ‘moss’ to ‘macroalgae’ to ‘cobbles’ to ‘submerged, fine-leaved macrophytes’. This information can be applied to river rehabilitation projects. Hydraulic variables, such as Froude number, can be manipulated through changes to channel morphology, to maximise habitat heterogeneity and therefore biodiversity.

Hydrodynamics and mass transfer in an absorber under controllable interface disturbance

The hydrodynamics and kinetics of CO2 absorption by water when the interface is disturbed by partially immersed disks that execute torsional oscillations or uniform unidirectional motion (rotation) was studied. It is shown that interface disturbance and generated surface flows enhance mass transfer by a factor of 2.5 and lead to extremum dependences of the mass transfer coefficient on the area and thickness of the insoluble film covering the water surface. The surface flows generated by disks at the gas-liquid interface were examined. Two types of surface flows that differ by their direction and the nature of driving forces are revealed. The role of these flows in enhancing mass transfer at small Re numbers was elucidated.

Towards the assessment of ‘ecological integrity’ in running waters of the United Kingdom

The development of methods to assess ecological integrity of running waters requires integrating physical and chemical parameters, as well as their effects upon biological structure, diversity and processes. River management in the UK has seen the development of a series of quality assessment methodologies with little integration between them. Methods which assess habitat structure in a biologically meaningful way offer the best approach to integrating measures of the effects of physical and chemical processes upon the river environment. Simultaneous measurement of surface flow types (‘flow biotopes’) and habitat structure (‘functional habitats’) showed clear links. These links could form the first stage in the development of a rapid, cost-effective measure of ecological integrity in rivers of the UK

A cost-effective approach for linking habitats, flow types and species requirements

1. This paper explains the background to concepts of instream physical habitat incorporated in River Habitat Surveys. Two independent research threads—physical biotopes and functional habitats—are described representing, respectively, ‘top down’ and ‘bottom up’ attempts to describe the use of instream physical environment by biota. 2. Physical biotopes are observed in the field by identification of surface flow types, each of which has been proved as distinctive by hydraulic study; these have been incorporated in River Habitat Surveys. Functional habitats have been derived from invertebrate sampling and statistical analysis. 3. Reconciling the two approaches is now an urgent research requirement so that RHS databases can be used predictively and the quality of habitat evaluated as the basis of rehabilitation and restoration. 4. The current practical uses of the two approaches are described. © 1998 John Wiley & Sons, Ltd.

Application of the hydraulic biotope concept to the classification of instream habitats

Abstract A simple matrix developed by a small group of ecologists, geomorphologists and an hydraulic engineer at a workshop in February 1995 was proposed as a standardised classification tool for the recognition of hydraulic biotopes, instream flow environments recognised on the basis of surface flow type and substrate class. Research was carried out in the Buffalo River, South Africa, to test the validity of this classification with respect to measurable hydraulic attributes. Hydraulic biotopes were classified at a number of sites representing a range of stream morphologies, channel scale and discharge. The hydraulic attributes at each sampling point were measured. Using simple measures of flow depth, velocity and bed roughness, hydraulic indices were calculated to describe both the near bed conditions (shear velocity and ‘roughness’ Reynolds number) and the mean flow in the water column (Froude number and Reynolds number). Results indicate that hydraulic biotope classes can be considered as significantly different in terms of flow hydraulics. Hydraulic characteristics appear to be consistent within classes across different spatial scales. An assessment of the influence of discharge showed that differences are recognised in the classes of the lower energy environments (pool and run) but despite considerable within class variability, no significant differences were observed across discharges in the higher energy environments. The hydraulic biotope classification and associated hydraulic biotope matrix shows good potential as a standardised method for classifying instream environments over a range of channel scales and discharges.