Stream Surface Research Articles

Estimating Watershed Subsurface Permeability From Stream Discharge Data Using Deep Neural Networks

Subsurface permeability is a key parameter in watershed models that controls the contribution from the subsurface flow to stream flows. Since the permeability is difficult and expensive to measure directly at the spatial extent and resolution required by fully distributed watershed models, estimation through inverse modeling has had a long history in subsurface hydrology. The wide availability of stream surface flow data, compared to groundwater monitoring data, provides a new data source to infer soil and geologic properties using integrated surface and subsurface hydrologic models. As most of the existing methods have shown difficulty in dealing with highly nonlinear inverse problems, we explore the use of deep neural networks for inversion owing to their successes in mapping complex, highly nonlinear relationships. We train various deep neural network (DNN) models with different architectures to predict subsurface permeability from stream discharge hydrograph at the watershed outlet. The training data are obtained from ensemble simulations of hydrographs corresponding to an permeability ensemble using a fully-distributed, integrated surface-subsurface hydrologic model. The trained model is then applied to estimate the permeability of the real watershed using its observed hydrograph at the outlet. Our study demonstrates that the permeabilities of the soil and geologic facies that make significant contributions to the outlet discharge can be more accurately estimated from the discharge data. Their estimations are also more robust with observation errors. Compared to the traditional ensemble smoother method, DNNs show stronger performance in capturing the nonlinear relationship between permeability and stream hydrograph to accurately estimate permeability. Our study sheds new light on the value of the emerging deep learning methods in assisting integrated watershed modeling by improving parameter estimation, which will eventually reduce the uncertainty in predictive watershed models.

Geostatistical based framework for spatial modeling of groundwater level during dry and wet seasons in an arid region: a case study at Hadat Ash-Sham experimental station, Saudi Arabia

Saudi Arabia (SA) lies in an arid region where groundwater is the main natural resource; therefore, it is essential to understand the groundwater dynamics for the best groundwater management practice in SA. In Hadat Ash-Sham Farm Experimental Station, SA, water table data from 11 wells and rainfall data were monitored for 16 months. The water table (WT) data is analyzed using the geostatistical method with the ordinary Kriging technique to generate the best WT spatial distribution map for each month and the expected flow direction. The cross-validation technique is used to evaluate the goodness of the developed WT maps. The Kriging maps show two regimes: weak spatial dependence (WSD, the ratio of the nugget to sill > 75%) and strong spatial dependence (SSD, the ratio of the nugget to sill < 25%). The WSD regime happens during dry seasons, while the SSD happens during wet seasons. The SSD gives better results and accuracy when compared to WSD. The root-mean-square error (RMSE) of WT varies between 0.26 and 3.4 m in the case of SSD, while it varies between 0.51 and 4.8 m in the case of WSD. WT maps show that the groundwater flow direction is from south-east to north-west during the wet season (SSD). This direction is in the orientation of surface stream with higher elevation (in the south) to the surface stream with lower elevation (in the north), where the study area is between these surface streams. While during the dry season (WSD), there is no preferred direction since there is almost no flow.

Investigation of correlation between surface runoff rate and stream water quality

Abstract The purpose of this study was to investigate the relationship between stream water quality and the surface runoff rate defined as the ratio of annual surface runoff to annual average precipitation. The surface runoff rate was first estimated in the Han River basin located in South Korea using the calibrated and validated HSPF model. Then a linear regression analysis was performed to investigate the correlation between the computed surface runoff rate and the observed water quality. It was found that there were statistically significant relationships between the surface runoff rate and concentrations of BOD, COD, and T-P and higher surface runoff rate led to the deterioration of water quality in streams. Finally, the applicability of the surface runoff rate as an indicator to measure the impact of land development on stream water quality was evaluated using a receiver operating characteristic (ROC) curve analysis. The ROC curve analysis indicated that the surface runoff rate could be utilized as a useful indicator to illustrate the degradation of stream water quality at the watershed scale. The results from this study also suggest that the surface runoff rate needs to be managed and controlled within about 15% to prevent the degradation of stream water quality.

High specific speed Francis turbine for small hydro purposes - Design methodology based on solving the inverse problem in fluid mechanics and the cavitation test experience

The paper is a result of a research and development project aimed at developing a series of types of high specific speed (90 < nsQ < 100) Francis turbines. The inverse flow analysis approach based on the hodograph theory has been employed in order to develop the blading geometry of quality high enough to minimize the subsequent CFD based optimization process. The three-dimensional turbine blades are developed on meridional stream surfaces determined using the VLM methodology. The mass and momentum conservation equations are written in a curvilinear coordinate system, which is adjusted to the streamlines by means of the Christoffel symbols. The solution is found using the method of characteristics. The developed geometry is optimized by means of the genetic algorithm implemented in CFD software. Model tests were conducted in the Institute of Fluid-Flow Machinery of the Polish Academy of Sciences. Satisfactory coincidence between design assumptions, the CFD based performance assessments and those based on the model test results attained, shows reliability of the methodology adopted. Critical cavitation numbers as established according to different criteria have been applied to plot the sigma permissible isolines on top of the efficiency hill diagram. Physical interpretation of some irregularities in diagnostic characteristics is provided.

The Status of Arsenic Pollution in the Greek and Cyprus Environment: An Overview

This study presents an overview about the arsenic (As) contamination and its sources in two European countries. Arsenic is a highly toxic element in its inorganic form and it is carcinogenic to human seven in low concentrations. The occurrence of As in surface water, stream and marine waters, groundwater, bottled water, sediment, soil, mines, and seafood, its environmental origin, and its impacts on human health are discussed. The classes of Geoaccumulation Index for As in Greece ranges from practically uncontaminated to extremely contaminated, and in Cyprus varies between practically uncontaminated and heavily contaminated. In many cases, the As contamination reaches very high concentrations and the impacts may be crucial for the human health and ecosystems. Physicochemical properties, regional climate and geological setting are controlling the occurrence and transport of As. In Greece and Cyprus, the geology, lithology, and ore-deposits are the most important factors for the variation of As contents in water, soil, and sediment. The dominant As species are also determined by the location and the redox conditions. The findings of this paper may be useful for scientists and stakeholders monitoring the studied areas and applying measures for protection of the human and terrestrial ecological receptors (plants, avian, mammals).

Accessibility of Selected Key Non-Metallic Mineral Deposits in the Environmental and Social Context in Poland

The increase in demand for mineral resources, the depletion of the resources (deposits) and numerous environmental and social limitations concerning their utilization led to research on the assessment of environmental and the social availability of compact raw material deposits classified as key raw materials. The methodology of the research is based on the proposed environmental and social assessment procedure for the availability of deposits, in which, based on the constraints resulting from legal, environmental and planning conditions, four deposit availability classes have been determined: class I—very well accessible deposit, class II—well accessible deposit, class III—accessible deposit and class IV—inaccessible deposit. Ultimately, seven variables influencing the availability of the deposit were selected for the assessment, i.e., forms of nature protection, forests with protective functions, zones of indirect protection of groundwater and surface water intakes, main groundwater reservoirs, surface water reservoirs, rivers, streams and canals, buildings and infrastructure and road and railway. The research was carried out for 244 deposits located in Poland (Central Europe) with total resources of over 7.6 billion tons. The availability of deposits was analyzed for two variants. The first one included all the variables. The second variant, on the other hand, excluded railway infrastructure due to the fact that 90% of the compact raw materials transport is carried out by trucks. Finally, in variant I of the assessment, three classes of deposit availability were obtained: class IV inaccessible deposits (146 deposits), class III available deposits (93 deposits), and class II well-accessible deposits (5 deposits). In variant II four classes of deposit availability were obtained: class IV inaccessible deposits (145 deposits), class III available deposits (68 deposits), class II well-accessible deposits (28 deposits) and class I deposits very easily accessible (3 deposits).

Repeated colonization of caves leads to phenotypic convergence in catfishes (Siluriformes:Trichomycterus) at a small geographical scale

AbstractAcross various animal groups, adaptation to the challenging conditions of cave environments has resulted in convergent evolution. We document a Neotropical cavefish system with ample potential to study questions related to convergent adaptation to cave environments at the population level. In the karstic region of the Andes of Santander, Colombia, cave-dwelling catfish in the genus Trichomycterus exhibit variable levels of reduction of eyes and body pigmentation relative to surface congeners. We tested whether cave-dwelling, eye-reduced, depigmented Trichomycterus from separate caves in Santander were the result of a single event of cave colonization and subsequent dispersal, or of multiple colonizations to caves by surface ancestors followed by phenotypic convergence. Using mitochondrial DNA sequences to reconstruct phylogenetic relationships, we found that caves in this region have been colonized independently by two separate clades. Additional events of cave colonization – and possibly recolonization of surface streams – may have occurred in one of the clades, where surface and cave-dwelling populations exhibit shallow differentiation, suggesting recent divergence or divergence with gene flow. We also identify potentially undescribed species and likely problems with the circumscription of named taxa. The system appears promising for studies on a wide range of ecological and evolutionary questions.

Development of a Throughflow-Based Simulation Tool for Preliminary Compressor Design Considering Blade Geometry in Gas Turbine Engine

Gas turbine engines are highly intricate machines, and every component of them is closely associated with one another. In the traditional engine developing process, vast experiment tests are needed. To reduce unnecessary trials, a whole gas turbine engine simulation is extremely needed. For this purpose, a compressor simulation tool is now developed. Considering the inherent drawbacks of 0D analysis and 3D CFD (Computational Fluid Dynamics) calculation, the 2D throughflow method is an indispensable tool. Based on the circumferential average method (CAM), 3D Navier–Stokes is transformed into a 2D method. One phenomenon arising is that the lack of description about circumferential motion leads to the need for the blade force modeling in compressor simulation. Previous models are based on the assumption that flow passes through the average stream surface without entropy increasing, which is not applicable in the CAM. An improved model is proposed based on the result analysis from CAM and NUMECA method in a linear cascade. Whereafter, the model is applied in a highly loaded and low-speed fan, which has been tested for its performance characteristics. Utilizing the new model, the error of the adiabatic efficiency between CAM and experiment decreases from 4.0% to 1.0% and the accuracy of the mass flow, and pressure ratio remains unchanged. The time involved in the CAM simulation is nearly 70 times faster than that of the 3D simulation.

Spatial Analysis of Base Flow and Stream Flow from the Abbay River Basin after Watershed Management Interventions

Recently, increasing concern in Africa has been registered on the potential impacts on base flow and stream flow due to the implementation of watershed management interventions. This research incorporates spatially monthly geographical hydrological data sets into a developed spreadsheet water balance model to estimate the changes in surface runoff, base flow and stream flow as a result of implementing watershed management interventions in the Abbay River Basin during the period (2010-2018). The model was implemented at sub-catchment level. Considering Year 2005 as a datum for watershed management intervention, results of the modeling and spatial analysis indicated that watershed management interventions relatively reduced surface runoff, increased deep infiltration to groundwater and accordingly increased base flow to the stream. Among the key results in the Abbay Basin that change from Year 2010 to Year 2018 was reduction of surface runoff from the Abbay Basin in the amount of 1,753 million m3/yr. As a result, an increase in annual base flow in the amount of 23 million m3/yr was estimated, leaving a reduction in annual mean flow of the Abbay River in the amount of 1,731 million m3/yr of the Abbay River at El-Diem site. It is expected that the flow of the Abbay River will continue to decrease due to the continuous implementation of the watershed management interventions and agriculture expansion in the Abbay Basin.

Multiple Times and the Stratigraphies of History

In this article one of the leading theorists of multiple historical time adopts the language of stratigraphy, which Krzysztof Pomian and Reinhart Koselleck used to refer to the layered time of history. It is obvious to the author that “world-time” now exists only as a set of “world-times.” However, unidirectional linear time continues be dominant in the culture, and therefore the main challenge is to come up with unconventional ways of conceptualizing multiple time. During the eighteenth and nineteenth centuries, the “temporalization of history” described by Koselleck took place in the form of “denaturalization” — an opposition between the orders of natural and human life. However, the author concludes that denaturalization today is no longer up to that previous task and calls for treating microbes, planets, rocks and human affairs as having various temporal regimes that permeate each other. The plurality of times is manifested both in practical matters and in branches of knowledge. Fernand Braudel suggested that historians turn to the longue durée of landscapes and climates in order to make history a nomothetic science, but today the task is to analyze the historical and natural worlds, studying their interweaving without reducing them to each other. The author sees the theory of multilayer time as a full-fledged alternative to the idea of linear unidirectional time. Nevertheless, there are phenomena that it cannot describe: how does the quickly streaming surface of everyday life dissolve away, and how do slowly formed events erupt on the surface as natural disasters? In conclusion, the author calls for the incorporation of historiography within a comprehensive theory covering many temporal scales, within which the historical life of people is intertwined with the historical life of rocks and geological deposits.

The impact of ventilation patterns on calcite dissolution rates within karst conduits

Erosion rates in streams vary dramatically over time, as differences in streamflow and sediment load enhance or inhibit erosion processes. Within cave streams, and other bedrock channels incising soluble rocks, changes in water chemistry are an important factor in determining how erosion rates will vary in both time and space. Prior studies in surface streams, springs, and caves suggest that variation in dissolved CO2 is the strongest control on variation in calcite dissolution rates. However, the controls on CO2 variation remain poorly quantified. Limited data suggest that ventilation of karst systems can substantially influence dissolved CO2 within karst conduits. However, the interactions among cave ventilation, air–water CO2 exchange, and dissolution dynamics have not been studied in detail. In this study, three years of time series measurements of dissolved and gaseous CO2, cave airflow velocity, and specific conductance from Blowing Springs Cave, Arkansas, were analyzed and used to estimate continuous calcite dissolution rates and quantify the correlations between those rates and potential physical and chemical drivers. We find that chimney effect airflow creates temperature-driven switches in airflow direction, and that the resulting seasonal changes in airflow regulate both gaseous and dissolved CO2 within the cave. As in previous studies, partial pressure of CO2 (pCO2) is the strongest chemical control of dissolution rate variability. However, we also show that cave airflow direction, rather than streamflow, is the strongest physical driver of changes in dissolution rate, contrary to the typical situation in surface channel erosion where floods largely determine the timing and extent of geomorphic work. At the study site, chemical erosion is typically active in the summer, during periods of cave downdraft (airflow from upper to lower entrances), and inactive in the winter, during updraft (airflow from lower to upper entrances). Storms provide only minor perturbations to this overall pattern. We also find that airflow direction modulates dissolution rate variation during storms, with higher storm variability during updraft than during downdraft. Finally, we compare our results with the limited set of other studies that have examined dissolution rate variation within cave streams and draw an initial hypothesis that evolution of cave ventilation patterns strongly impacts how dissolution rate dynamics evolve over the lifetime of karst conduits.

Environmental issues in karst terrain: an example from Central India

In this paper, an attempt has been made to highlight the nature of karst in central India and evaluate possible effects of environmental degradation of groundwater due to indiscriminate disposal of various types of wastes into karst terrains without subjecting them to any treatment before disposal. Karst features associated with carbonate rocks of the Proterozoic Vindhyan basin in central India and environmental issues related to the same area’s groundwater resources are briefly given. Based on the process of formation, karst may be categorized as True karst (holo-karst) and (ii) Fluvial karst. On the other hand, based on the types of cover, karsts are classified into three types: (i) Covered karst, (ii) Soddy karst, and (iii) Buried karst. Three types of karst landforms identified in carbonates rocks of the Vindhyans are (i) Superficial landforms (Karren), produced mainly by solution action on the rock surfaces, (ii) Landforms due to fluvial erosion, and (iii) Underground landforms, i.e., Caves. In a particular hydrogeologic setting, the groundwater system consists of minor secondary porosity modified by solution activities. Accordingly, two types of groundwater flow systems (diffuse and conduit) occur in carbonate rocks. Due to karstification, limestones constitute the most productive aquifer in the area. It is noted that untreated municipal and industrial wastes are disposed of directly in surface water bodies and streams and associated sinkhole depressions in limestone terrain. Secondary openings being interconnected with each other gradually carry these pollutants to groundwater reservoirs in karst aquifers. The continued influx of pollutants to groundwater reservoirs through interconnected secondary voids would cause severe groundwater pollution in the long run and degrade the groundwater quality in karst aquifers for various usages.

Carbon Dioxide Partial Pressure and Emission Throughout the Scandinavian Stream Network

AbstractStream networks transport and emit substantial volumes of carbon dioxide (CO2) into the atmosphere. We gathered open monitoring data from streams in three Scandinavian countries and estimated CO2 partial pressure (pCO2) at 2,298 sites. Most of the sites (87%) were supersaturated when averaged across the year with an overall mean pCO2 of 1,464 μatm (range: 17–15,646). Using remote sensing data, we modeled a realistic stream network including streams above ~2.5 m wide and calculated catchment averages of multiple variables associated with geomorphometry, stream network proximity, and land cover. We compared the ability of eight machine learning models to predict pCO2 and found that the Random Forest model achieved the highest accuracy, with a root‐mean‐square error of 0.22 (log10(pCO2)) and R2 of 0.66. Mean catchment elevation, slope, and permanent water cover were the most important predictor variables. We used the predictive model to create a high‐resolution (25‐m resolution) map with predicted stream pCO2 throughout the 268.807 km stream network in Denmark, Sweden, and Finland. Predicted pCO2 averaged 1,134 μatm (range: 154–8,174). We used surface runoff, air temperature, and stream channel slope to estimate gas transfer velocity and CO2 flux throughout the network. Mean stream CO2 fluxes ranged from 1.0 and 1.2 in Sweden and Finland, respectively, 3 to 3.2 g C m−2 day−1 in Denmark. Better‐performing models improve our ability to predict pCO2 in stream networks and reduce the uncertainty of upscaling estimates of carbon emissions from inland waters to countries and continents.

Особенности формирования водопритоков к месторождению алмазов им. В. Гриба (Архангельская область)

Введение: На кимберлитовом месторождении им. В. Гриба принят поверхностный способ отработки, при котором осушению подлежат все водоносные породы над рабочим горизонтом. Фильтрация воды в отработанное пространство осуществляется по бортам карьера по всему периметру, что затрудняет ведение горных работ и может привести к негативным инженерно-геологическим явлениям в карьере (прорыву воды, оползням, обвалам). Основная цель исследований заключается в изучении процессов фильтрации подземных вод при осушении месторождения им. В. Гриба с использованием численного метода моделирования. Методика: Кимберлитовая трубка прорывает осадочные докембрийские отложения и перекрыта толщей среднекаменноугольных и четвертичных отложений. В районе исследований расположены многочисленные реки и озера, сооружено хвостохранилище. Определение источников формирования водопритоков в карьер осуществлялось с помощью разработанной численной геофильтрационной модели, на которой учитывались все элементы дренажной системы, активная взаимосвязь подземных и поверхностных вод, геолого-гидрогеологические особенности месторождения. Расчетная модель состоит из четырех слоев: четвертичный и олмугско-окуневский, урзугско-воереченский, падунский и мезенский комплексы. Фильтрационная задача решалась по программе MODFLOW лицензионного пакета GMS. Результаты и обсуждение: В процессе идентификации модели выявлен характер гидравлической связи водоносной толщи с речными и озерными долинами, определены участки питания и разгрузки водоносных пластов, фильтрационные потери из хвостохранилища Верхотинского ГОКа, установлены источники формирования водопритоков к дренажной системе карьера. Установлено, что водопритоки в карьер формируются за счет подземных вод и атмосферных осадков в зоне с активной гидравлической взаимосвязью подземных и поверхностных водных объектов. Заключение: С использованием численной модели определены основные источники формирования водопритоков в карьер: водоносные комплексы, получающие дополнительное питание из поверхностных водоемов и водотоков, установлена взаимосвязь изучаемого водоносного массива с долинами рек и озер, выявлены места питания и разгрузки исследуемой водоносной толщи, оценены инфильтрационные потери воды из хвостохранилища Верхотинского ГОКа.

Quality aspects of the Doñana groundwater resources (SW-Spain) before the intensification of agriculture

This article presents the initial hydrochemical status of the Almonte-Marismas aquifer system in 1966 – before agricultural intensification. The investigated aquifer is of critical importance for the groundwater dependent Doñana wetland areas of the National and Natural park of Doñana (SW – Spain). The analytical database involves 158 samples collected in 1966 by the Food and Agriculture Organization (FAO) and the Geological Survey of Spain (IGME), including electrical conductivity, hardness, chloride, bicarbonate, sulphate, calcium, magnesium, sodium, and potassium in groundwater that generate information about the initial hydrochemical state before the intensification of agricultural activity. These historical data existed as hardcopy lab reports and were introduced into a MS Access database. The parameters EC, Cl, SO4 and K of the year 1966 show a variety of spatial patterns before intensification and suggest five different types of influence: (i) natural lagoon systems, (ii) creeks or rivers, (iii) irrigated areas, (iv) urban areas, and (v) marshes. The results suggest that anthropogenic activities such as fertilizer use, domestic activities and wastewater in surface streams downstream of urban areas are responsible for elevated parameter values in most of the observation points, although their specific contributions cannot be determined based on the available data of 1966. In the marshes (north) area, apart from fertilizer use elevated geogenic salinity may also contribute to high parameter concentrations for intensive irrigated crop cultivation and proximity to the Guadalquivir River.

Bubble Formation by Short Plunging Jet in a Continuous Casting Tundish

A short plunging jet technique was developed to produce small bubbles in continuous casting tundish, with argon sealing, in order to promote the removal of inclusions smaller than 50 μm. The liquid steel coming out of the ladle shroud is accelerated and vibrated by gravity, leading to gas entrainment. This novel approach is free from bubbles growing along the nozzle surface due to the poor wetting condition, which is applicable to producing small bubbles in liquid steel. Water modeling was carried out to investigate the impact of the free-fall length on gas entrainment by a short plunging jet. The results show that gas can be entrained into the liquid bath with a free fall longer than 15 mm. Part of the entrained gas is separated from the gas sheath by the rough surface of the inflow stream, forming initial bubbles. These initial bubbles are further refined into small ones of 0.4~2.5 mm due to the turbulent flow in the pouring region. The cylindrical shield can effectively isolate the surface fluctuation caused by the short plunging jet; thereby, a stable slag layer in the tundish can be maintained during gas entrainment.

Factors controlling discharge-suspended sediment hysteresis in karst basins, southwest China: Implications for sediment management

Assessment of river sediment sources, transport, and controlling factors in karst regions is critical to the development of effective soil erosion and sediment management strategies. This 2-year study used a hysteresis index of discharge and suspended sediment data, combined with the basin's inherent geological characteristics, to assess sediment sources and hydrological connectivity at six sites in an agricultural karst watershed of southwest China. Principal component analysis was further used to describe sediment control by rainfall (antecedent precipitation, precipitation duration, amount, and intensity) and stream hydrology (maximum and total discharge, flood intensity, and runoff coefficient). Results indicate that the annual sediment yield (0.8–6.6 Mg km2 a−1) is low and sediment transport in karst areas is dependent on continuous rainfall. Ground substance component (GSC) and geomorphology characteristics determine the hydrology connectivity and sediment availability. In a sub-basin (CQ) marked by a peak cluster depression with good vegetation, sediment mainly comes from the paddy land, and the surface stream shows clockwise hysteresis. During storms, surface water enters the underground system from sinkholes, resulting in Figure-8 hysteresis with multiple sediment peaks. In another predominantly agricultural sub-basin (HTP), the thick layers of paddy and loess soil surrounding the river channel provide an accessible sediment source, resulting in clockwise hysteresis. The surface outlet of the watershed (HZ) is affected by an upstream reservoir, but bank erosion and sediment activation are evident during storms. The subsurface outlet (MSK) of the watershed shows more anti-clockwise hysteresis due to the activation of the conduit network in the wet season, surface water draining into the underground river and the distant sediment sources. This study shows that discharge-suspended sediment concentration hysteresis analysis can provide a reference for soil and water conservation decision-making in karst areas.

Identifying the optimal spatial distribution of tracers for optical sensing of stream surface flow

Abstract. River monitoring is of particular interest as a society that faces increasingly complex water management issues. Emerging technologies have contributed to opening new avenues for improving our monitoring capabilities but have also generated new challenges for the harmonised use of devices and algorithms. In this context, optical-sensing techniques for stream surface flow velocities are strongly influenced by tracer characteristics such as seeding density and their spatial distribution. Therefore, a principal research goal is the identification of how these properties affect the accuracy of such methods. To this aim, numerical simulations were performed to consider different levels of tracer clustering, particle colour (in terms of greyscale intensity), seeding density, and background noise. Two widely used image-velocimetry algorithms were adopted: (i) particle-tracking velocimetry (PTV) and (ii) particle image velocimetry (PIV). A descriptor of the seeding characteristics (based on seeding density and tracer clustering) was introduced based on a newly developed metric called the Seeding Distribution Index (SDI). This index can be approximated and used in practice as SDI=ν0.1/ρρcν1, where ν, ρ, and ρcν1 are the spatial-clustering level, the seeding density, and the reference seeding density at ν=1, respectively. A reduction in image-velocimetry errors was systematically observed for lower values of the SDI; therefore, the optimal frame window (i.e. a subset of the video image sequence) was defined as the one that minimises the SDI. In addition to numerical analyses, a field case study on the Basento river (located in southern Italy) was considered as a proof of concept of the proposed framework. Field results corroborated numerical findings, and error reductions of about 15.9 % and 16.1 % were calculated – using PTV and PIV, respectively – by employing the optimal frame window.

A general alternate loading technique and its applications in the inverse designs of centrifugal and mixed-flow pump impellers

For the inverse designs of centrifugal and mixed-flow pump impellers, clarifying the generation process of secondary flows and putting forward corresponding suppression measures is an important approach to improve the impeller performance. In this paper, to provide a better qualitative insight into the generation mechanism of secondary flows in the impeller, a simple kinematic equation is derived based on the ideal assumptions, which indicates that the potential rothalpy gradient (PRG) is the most important dynamic source that actively induces secondary vortical flows. Induced by the natural adverse PRG on the S1 and S2 stream surfaces, two typical secondary flows, H - S and P-S secondary flows, are clearly presented. To specially suppress these typical secondary flows, a general alternate loading technique (GALT) is proposed, aiming to adjust the real blade loading δp to control the PRG features. At the blade fore part, the δp on the hub streamline should be slowly increased to avoid breakneck growth of the potential rothalpy to reduce adverse streamwise PRG on the S2 streamsurface. At the blade middle part, the δp should be moderately decreased to reduce adverse streamwise PRG on the S1 streamsurface. At the blade aft part, the difference in the δp between the shroud and hub streamlines should be decreased faster to control the exit uniformity. By applying the GALT to the impeller designs of three typical pump types in hydraulic engineering, the organizational effect of the PRG on fundamental flow structures is proven. The GALT can effectively control the PRG distributions and suppress the secondary flows, thereby widening the pump’s high-efficiency zone, improving flow uniformity and suppressing pressure fluctuations. Compared with the current Z-G method and the ALT, the GALT can meet the requirements of “de-experience” better, thereby enabling the designers to obtain good products explicitly and quickly.

Biodegradation and metabolic pathway of fenvalerate by Citrobacter freundii CD-9

Fenvalerate is a pyrethroid insecticide with rapid action, strong targeting, broad spectrum, and high efficiency. However, continued use of fenvalerate has resulted in its widespread presence as a pollutant in surface streams and soils, causing serious environmental pollution. Pesticide residues in the soil are closely related to food safety, yet little is known regarding the kinetics and metabolic behaviors of fenvalerate. In this study, a fenvalerate-degrading microbial strain, CD-9, isolated from factory sludge, was identified as Citrobacter freundii based on morphological, physio-biochemical, and 16S rRNA sequence analysis. Response surface methodology analysis showed that the optimum conditions for fenvalerate degradation by CD-9 were pH 6.3, substrate concentration 77 mg/L, and inoculum amount 6% (v/v). Under these conditions, approximately 88% of fenvalerate present was degraded within 72 h of culture. Based on high-performance liquid chromatography and gas chromatography-mass spectrometry analysis, ten metabolites were confirmed after the degradation of fenvalerate by strain CD-9. Among them, o-phthalaldehyde is a new metabolite for fenvalerate degradation. Based on the identified metabolites, a possible degradation pathway of fenvalerate by C. freundii CD-9 was proposed. Furthermore, the enzyme localization method was used to study CD-9 bacteria and determine that its degrading enzyme is an intracellular enzyme. The degradation rate of fenvalerate by a crude enzyme solution for over 30 min was 73.87%. These results showed that strain CD-9 may be a suitable organism to eliminate environmental pollution by pyrethroid insecticides and provide a future reference for the preparation of microbial degradation agents and environmental remediation.