Tracer Study of Mixing and Transport in the Upper Hudson River with Multiple Dams

In October 2001, ～ 0.2?mol of SF6 was injected into the upper Hudson River, a modified natural channel with multiple dams, at Ft. Edward, N.Y. The tracer was monitored for 7 days as it moved ～ 50?km downriver. The longitudinal evolution of the tracer distribution was used to estimate one-dimensional advection (9.0±0.2?km?d?1) and dispersion (17.3±4.0?m2?s?1) along the river axis. Comparison of these results to tracer studies on channels without dams suggests that dams reduce longitudinal dispersion below the value expected in a natural channel with the same discharge. SF6 loss through air–water gas exchange along the river and at two dams (10.7?m combined height) was estimated by observing decay in peak concentration. Losses at dams (approximately 50% per dam) were dominant. The estimated gas exchange at dams was compared to a simple model adapted from those available in literature. Small amounts of tracer were trapped in a canal segment ( ～ 5?km long) that parallels the river, where advection and dispersion were sharply reduced.     

Comparison of SF6 and Fluorescein as Tracers for Measuring Transport Processes in a Large Tidal River

We present the first large-scale comparison of a fluorescent dye [fluorescein (C20H10O5Na2)] and a gas [sulfur hexafluoride (SF6)] as tracers of advection and longitudinal dispersion from a dual tracer release experiment conducted in the tidal Hudson River. At the beginning of the experiment, 36?kg of fluorescein and ～ 4.3?mol of SF6 were injected into the Hudson River at an averaged depth of 9.5?m, ～ 1?m above the bottom, near Hyde Park, N.Y. After injection, fluorescein distributions were surveyed for 4 days (until it became undetectable) and SF6 distributions were surveyed for 10 days. The dye resolves initial vertical mixing on the day of injection, and then net advection and longitudinal dispersion, whereas SF6 provides information on net advection and longitudinal mixing on larger spatial scales and longer time scales. Quantitative estimates of transport processes (net advection and longitudinal dispersion) calculated from the two methods are consistent for the first three days, and start to deviate on the fourth day when the signal-to-noise ratio of the dye deteriorated.     

Agroecological Impacts from Salinization and Waterlogging in an Irrigated River Valley

Extensive field data and calibrated flow and salt-transport models characterize the spatial and temporal patterns of salinity and waterlogging in an irrigated western river valley. Over three irrigation seasons, average seasonal aquifer recharge from irrigated fields in a 50,600?ha study area ranges from 0.59?to?0.99?m, including contribution from precipitation. The salinity of irrigation water varies from 618?to?1,090?mg/L. The water table is shallow, with 16 to 33% of irrigated land underlaid by an average water table less than 2?m deep. Average water table salinity ranges from 2,680?to?3,015?mg/L, and average soil salinity from 2,490?to?3,860?mg/L. Crop yield reductions from salinity and waterlogging range from 0 to 89% on fields, with regional averages ranging from 11 to 19%. Annual salt loading to the river from subsurface return flows, generated in large part by dissolution from irrigation recharge, averages about 533?kg/irrigated?ha?per?km. Upflux from shallow water tables under fallow ground contributes to about 65?million?m3 (52,600?acre-ft) per year of nonbeneficial consumption. Beyond problem identification, the developed database and models provide a basis for effectively addressing these problems through a systematic and comparative assessment of alternative solutions.     

Case Study: Equivalent Widths of the Middle Rio Grande, New Mexico

Successive reaches of the Rio Grande have maintained equivalent channel widths of 50 and 250?m, respectively, over long periods of time. It is hypothesized that alluvial channels adjust bed slope to match the long-term changes in channel width. Analytical relationships show that wider river reaches develop steeper slopes. A modeling approach using daily water and sediment discharges simulates the transient evolution of bed elevation changes. The analytical and numerical models are in very good agreement with the longitudinal profile measurements of the Bosque del Apache reach of the Rio Grande, NM, from 1992 to 1999. The slope of the 50?m wide reach was 50?cm/km and the slope of the 250?m wide reach of the same river increased to 80?cm/km. This unsteady daily transient model compares well with a steady transient solution at a constant discharge close to the mean annual flow. The transient slope adjustments can also be approximated with an exponential model. Accordingly, it takes about 20–25?years for the Rio Grande to achieve about 90% of its slope adjustment.     

Imaging of metastatic melanoma utilising a technetium-99m labelled RGD-containing synthetic peptide

Genetic structure of bank vole populations in linear river bank habitat in southeast Norway was determined from analyses of DNA sequences for the mitochondrial D-loop. Animals were sampled at sites separated by 1 km, along two forested river banks separated by approximately 100 m of open water. Twenty-six distinct haplotypes were found among 120 voles. The voles showed significant deviation from panmixis on both sides of the river. Animals from the same site or from sites 1 km apart were more likely to share haplotypes than animals 2 km apart or more. Common haplotypes were widespread on both river banks, and had a wider distribution than relatively rare haplotypes. Some rare haplotypes were found on both banks, but most were restricted to a single bank. The results suggest that short-term gene flow may be restricted for female bank voles in linear habitats. Female territorial behaviour may vary with habitat geometry. In the linear habitat described here, females defend only two territorial borders and may effectively limit female dispersal. Results were compared to a previous study of bank voles from this region in a two-dimensional habitat. Gene flow in the linear habitat was much more restricted than gene flow in the two-dimensional habitat. Probable mechanisms underlying this difference are discussed.     

Subsurface Characterization Using Artificial Neural Network and GIS

A method for characterizing the subsurface is developed using an artificial neural network (ANN) and geographic information system (GIS). Data on the distribution of aquifer materials from monitoring well lithologic logs are used to train a multilayer perceptron using the back-propagation algorithm. The trained ANN predicts using an appropriate prediction scale, the subsurface formation materials at each point on a discretized grid of the model area. GIS is then used to develop subsurface profiles from the data generated using the ANN. These subsurface profiles are then compared with available geological sections to check the accuracy of the ANN-GIS generated profiles. This methodology is applied to determine the aquifer extent and calculate aquifer parameters for input to ground-water models for the multiaquifer system underlying the city of Bangkok, Thailand. A selected portion of the model domain is used for illustration. The integrated approach of ANN and GIS is shown to be a powerful tool for characterizing complex aquifer geometry, and for calculating aquifer parameters for ground-water flow modeling.     

Air Permeability of Waste in a Municipal Solid Waste Landfill

The permeability of compacted municipal solid waste in a landfill with respect to air (or gas) flow was estimated using a short-term air injection test. Air was added to 134 vertical wells installed at three different depths at flow rates in the range of 0.14?–1.4?m3?min?1 and the corresponding steady state pressures were recorded. The permeability of the waste with respect to airflow (described here as the air permeability) was estimated for different anisotropy ratios (kr/kz = 1, 10, and 100) using a steady state, two-dimensional, axisymmetric analytical fluid flow model in conjunction with the measured flow and pressure data. The air permeability of landfilled municipal solid waste modeled as an isotropic medium was found to range from 1.6×10?13 to 3.2×10?11?m2. The estimated air permeability results were on the low end of values previously applied to model landfill gas flow. Estimated air permeability decreased significantly with increasing waste depth. The lower permeability encountered in the deeper layers was primarily attributed to the lower porosity of the waste caused by higher overburden pressures and higher moisture content of waste in deeper layers of the landfill than in shallow layers. The results suggest that multiple wells screened at different depths provide greater control of air distribution within the landfill. Leachate recirculation was documented to impact the ability to add air. In addition to limitations posed by standing water in many of the deeper wells, waste exposed to leachate recirculation was found to be significantly less permeable to air when compared to original conditions.     

Percolation Induced Heat Transfer in Deep Unsaturated Zones

Subsurface temperature data from a borehole located in a desert wash were measured and used to delineate the conductive and advective heat transfer regimes, and to estimate the percolation quantity associated with the 1997–1998 El Ni?o precipitation. In an arid environment, conductive heat transfer dominates the variation of shallow subsurface temperature most of the time, except during sporadic precipitation periods. The subsurface time-varying temperature due to conductive heat transfer is highly correlated with the surface atmospheric temperature variation, whereas temperature variation due to advective heat transfer is strongly correlated with precipitation events. The advective heat transfer associated with precipitation and infiltration is the focus of this paper. Disruptions of the subsurface conductive temperature regime, associated with the 1997–1998 El Ni?o precipitation, were detected and used to quantify the percolation quantity. Modeling synthesis using a one-dimensional coupled heat and unsaturated flow model indicated that a percolation per unit area of 0.7 to 1.3 m height of water in two weeks during February 1998 was responsible for the observed temperature deviations down to a depth of 35.2 m. The reported study demonstrated quantitatively, for the first time, that the near surface temperature variation due to advective heat transfer can be significant at a depth greater than 10 m in unsaturated soils and can be used to infer the percolation amount in thick unsaturated soils.     

大方坯连铸42CrMoAH钢皮下夹杂物控制

 针对苏钢42CrMoAH钢大方坯（260mm×340mm）浇注存在的铸坯皮下夹杂物问题,分析了夹杂物的主要类型及其来源,研究了精炼渣组成对钢洁净度的影响,同时讨论了连铸工艺条件对铸坯皮下40mm以内的夹杂物数量、尺寸、组成的影响。研究表明：铸坯中的夹杂物主要来源于以A12O3为主的脱氧产物及以MnO·Cr2O3,FeO·Cr2O3等尖晶石类为主的二次氧化产物;由于精炼渣吸收A12O3夹杂物能力不足,再加上拉速低等因素导致结晶器内钢液上循环流弱,不利于脱氧及二次氧化产生的微小夹杂物在结晶器内碰撞聚合后上浮、排除,以致铸坯中尺寸为20~50μm的夹杂物达到总量的45%左右;采取提高精炼渣炉渣碱度、w(CaO)/w(Al2O3)值,及采用双侧孔型水口以加强结晶器内上循环流等措施后,铸坯皮下20~50μm的夹杂物降低了64%。     

Removal of Dissolved- and Free-Phase Benzene Pools from Ground Water Using In Situ Air Sparging

This paper presents the results of a laboratory investigation performed to study the use of air sparging to remediate dissolved-phase and free-phase [or non-aqueous-phase liquid (NAPL)-phase] benzene pools from ground water. The specific objectives of the study were (1) to assess how air injection rate affects the mass transfer and transport of dissolved- and NAPL-phase pools; and (2) to determine the effect of ground-water flow on the removal of dissolved- and NAPL-phase pools during the application of air sparging. A total of five 2D physical model tests were performed in a homogeneous coarse sand profile subjected to both static ground water and ground-water flow conditions. Three different air injection rates were used in a static ground-water condition, and two different air flow rates were used in soil profiles subjected to ground-water flow (hydraulic gradient = 0.011). All tests were performed with similar initial dissolved- and NAPL-phase benzene conditions. Injected air traveled within a parabolic zone of influence (in channel mode) when subjected to both static ground water and ground-water flow conditions, indicating that ground-water flow (for the ground-water velocities tested) did not affect the injected air zone of influence. An increase in air injection rate led to faster contaminant removal; however, at higher air injection rates, a threshold rate of removal was reached above which further increases in injection rate are a waste of effort. Additionally, air injected into the soil profile reduced the hydraulic conductivity within the zone of influence. This in turn led to lower ground-water flow rates, allowing for effective interception and treatment of a migrating NAPL plume. Higher air injection rates led to further reductions in hydraulic conductivity, allowing for substantial control of the NAPL plume in the downgradient direction. Overall, this study showed that air sparging can be used to effectively remediate dissolved- and NAPL-phase benzene.     

Effect of Flow Pulses on Degradation Downstream of Hapcheon Dam, South Korea

The changes in channel geometry downstream of Hapcheon Dam, South Korea, are closely examined. Daily pulses of water from peak hydropower generation and from sudden sluice gate operations affect the 45-km reach of the Hwang River between the Hapcheon Reregulation Dam and the Nakdong River. From 1983 to 2003, the median bed-material size, d50, increased from 1.0 to 5.7 mm, and the bed slope of the reach decreased from 94 to 85 cm/km. The vertical riverbed degradation averaged 2.6 m for a distance of 20 km below the reregulation dam. A simple analytical model is developed to predict the increase in sediment transport and the river bed adjustments from flow pulses in comparison with steady flow discharges. Numerical model simulations confirm the theoretical prediction that sediment transport rates from daily pulses are 21% higher than for steady flow discharges. Unsteady sediment transport simulations indicate that the channel bed degradation should extend mostly 20–25 km below the reregulation dam and should not change much after 2013.     

Simulation of Ground-Water Flow in Steep Basin with Shallow Surface Soil

A coupled ground-water∕channel flow distributed model has been developed for continuous simulation in a 123-km2 basin. The aim was to analyze the streamflow generation processes in natural vegetated environments. Finite-difference schemes have been used to solve conservation equations of the 2D saturated subsurface flow and the 1D kinematic surface flow. Because of the high hydraulic conductivity of the surface soil, only the saturation excess mechanism of runoff production has been considered. Parameter sensitivity analysis showed the overriding influence of soil storage capacity and conductivity. A grid discretization >100 m produces a hydraulic conductivity greater than physically meaningful, which considerably increases as the space-grid step increases. Results indicate that the model can satisfactorily simulate the water-flow behavior of the catchment after fitting the three parameters of surface hydraulic conductivity, effective porosity, and evapotranspiration losses. These are done after calculating the conductivity as a function of the height of the water table. The simulation efficiency has varied from 87% in the first 5-year calibration period to 85.8% in the subsequent 5-year validation period.     

Retention and Removal of Suspended Solids and Total Phosphorus from Water by Riparian Reeds

Riparian reeds in rivers may be able to remove contaminants such as phosphorus. In this study, a selected river section was surveyed to investigate the effects of riparian reeds on the suspended solids (SS) and total phosphorus (TP) in the water. Six observation periods over two years showed that in the reed zone (the upstream 8.1?km of the river), the SS deposition rates per unit of concentration were between 0.025 and 0.031 1/km, and the TP concentration was decreased from 0.28–0.62?to?0.165–0.31?mg/L with decreasing rate of 41–50%, while in the nonreed zone (the downstream 8.1?km), the SS deposition rates were only between 0.0073 and 0.0092 1/km and the TP concentration was reduced from 0.15–0.30?to?0.12–0.24?mg/L with decreasing rate of 20% or so. The presence of riparian reeds could result in a SS deposition rate four times higher than that in a reed-free area, and the TP removal rate for the nonreed zone was only 40–48.78% of that for the reed zone. Water SS content was significantly lower in the reed zone than the surrounding water area. For the reed zone, water TP concentration was positively correlated to water SS content, but this relation disappeared in the nonreed zone. In both reed and nonreed zones, water dissolved reactive phosphorus concentration showed a significant negative relation to water SS content. Furthermore, water SS content and TP concentration appeared to be linked to reed density, and high reed density reduced the water flow velocity, resulting in lower water SS content and TP concentration.     

Structure of Flow Upstream of Vertical Angled Screens in Open Channels

This paper presents the results of a laboratory study of the structure of flow in a diversion structure with a vertical angled wedge-wire fish screen. This screen had a 10×25?mm mesh and was tested at three angles of 10.4, 17.5, and 26.8°, to the direction of the approaching flow, for two mean velocities of 0.5 and 0.8?m/s, with a depth of flow of about 0.75?m. In this water and fish diversion (channel or) structure, it was found that the depth of flow at any section is approximately constant with a drop at the screen on the side of the canal and decreased towards the bypass located at the downstream end. The distribution of the velocity component u in the direction of the approaching flow as well as the perpendicular component w and the resultant velocity V was uniform in the vertical direction. The depth averaged mean velocity for different verticals at any section in the diversion structure increased with the longitudinal distance x and was correlated with the relative width, bs/b (in the diversion structure) for all five experiments. Correlations have been found for the depth averaged transport velocity and the impinging velocity on the screen in terms of the approach velocity U. A general relation has also been developed for the attack angle of the flow on the screen. The downstream part of the screen carried more flow into the canal compared to the upstream part as a result of the uniform mesh size used in this study. The results of this hydraulic study should be useful, particularly for freshwater adult fish, in designing screens in irrigation canals and for micro-hydro sites that use diversion canals.     

EDTA, NTA, Alkylphenol Ethoxylate and DOC Attenuation during Soil Aquifer Treatment

Removals of dissolved organic carbon (DOC), ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA) and carboxylated alkylphenol polyethoxylate metabolites (APECs) were studied at the Sweetwater (Tucson, Ariz.) soil aquifer treatment site that treated chlorinated secondary effluent. The site was operated in a first phase by flooding irregularly for weeks interrupted by days of drying and in a second phase by a regular schedule of flooding for 3 days and drying for 4 days. The average hydraulic loading rates were 0.13 and 0.17?m/day in the first and second phases, respectively. During drying, oxygen intruded at least 3?m deep into the unsaturated subsurface causing nitrification of the ammonium that was retained in the top layer during flooding. Nitrification increased nitrate concentrations to >200?mg/L but most was removed to <10?mg/L during transport to 38?m depth. At 38?m depth, removals of DOC, EDTA, NTA, and APECs during the first phase were 85, 80, 90, and 98%, slightly higher (<7%) than during the second phase. Most of the DOC removal occurred during transport to 3?m and most of the trace organics removal occurred during transport from 3 to 38?m depth.     

Effects of Electroosmosis on Natural Soil: Field Test

A unique configuration of horizontal sheet-like electrodes was used in the field at a site in Ohio that was underlain by silty clay glacial drift to induce electroosmotic flow and to characterize the effects of electroosmosis on soil properties (e.g., electrical conductivity and pH). The lower electrode was created at a depth of 2.2 m by filling a flat-lying hydraulic fracture with granular graphite, and the upper one was a metallic mesh placed at a depth of 0.4 m and covered with sand. The electrodes were attached to a DC power supply, creating an electrical gradient of 20–31 V∕m and a current of 42–57 A within approximately 20 m3 of soil. Total energy applied was 5,500 kW?h during approximate 4 months of operation. Electroosmotic flow rates of 0.6–0.8 L∕h were observed during tests lasting several weeks, although total flow rate (electroosmotic plus hydraulic) was strongly influenced by fluctuations of the ground-water table. The ratio of applied current to voltage decreased from 0.9 to 0.6 A∕V and was mainly due to a decrease in electrical conductivity of the soil. A low pH front developed at the anode and migrated toward the cathode. The velocity of the pH front per unit voltage gradient was 0.014 (cm∕day)/(V∕m). This was 40 times slower than what has been reported from laboratory experiments using kaolinite as a medium. These results confirm the feasibility of using horizontal electrodes at shallow depths, but they also underscore some important differences between the geochemical effects observed during field tests in natural soils and those seen in laboratory tests using ideal materials.     

River Dissolved Oxygen Model with Zebra Mussel Oxygen Demand (ZOD)

The development, calibration, and application of a dynamic two-dimensional mass balance model for dissolved oxygen (DO) for rivers are documented for the first time accommodating the oxygen demand associated with zebra mussels. The test system is a short (2.3 km) phytoplankton-rich section of the Seneca River, N.Y., which is believed to represent an upper bound of the impact of this exotic invader on oxygen resources because of the unusually high population densities and limited turbulent mixing that prevail. Model calibration is supported by comprehensive measurements of DO, which resolve diurnal and seasonal patterns, and various forcing conditions over a four-month period. Wide temporal variations in the areal consumption rate of DO by zebra mussels [zebra mussel oxygen demand (ZOD), g?m?2?day?1] were determined through model calibration. These determinations are supported by closure with earlier estimates based on simple DO budget calculations, and with laboratory biomass-specific oxygen consumption rates published in the scientific literature. Values of ZOD at times (e.g., >50 g?m?2?day?1) were an order of magnitude greater than the sediment oxygen demand associated with organically enriched deposits. The model performs well in simulating important features of the complex patterns of DO observed, including (1) DO depletion across the study section; (2) vertical DO stratification; and (3) diurnal changes. ZOD was the dominant sink for DO over the river study section; it was entirely responsible for the substantial observed DO depletion, and it was the major cause of the DO stratification during periods of low flow. A preliminary extension of the model is demonstrated to be successful in simulating the persistence of DO depletion 15 km downstream. The model is expected to have management utility for this and other phytoplankton-rich rivers that have been, or will be, invaded by zebra mussels.     

Hydrodynamics of Mesotidal Estuary in Winter

In this article, we quantify the effects of a standing ice cover on the hydrodynamics of a mesotidal estuary. The Portneuf Estuary, Québec, is 5.9?km in length and has a 3-m-deep thalweg. According to our numerical model simulations (using an adapted version of Environment Canada’s ONE-D model) and field measurements, the midwinter 50-cm-thick ice cover produced an attenuation of the neap tidal range (1.9?m) and spring tidal range (4.0?m) of 17 and 37%, respectively, near the upstream end of the estuary. The arrival of low water was also delayed by about 90?min at this location. At the mouth, the cover attenuated peak ebb tide flow (200?m3/s) and flood tide flow (500?m3/s) by approximately 18 and 13%, respectively. Here the peak flood flow was normally delayed by 41?min, while the ebb tide was usually advanced by 8?min. In general, the ice cover attenuated peak velocities by 12 to 20%, although at certain times and locations the ice cover could induce higher velocities than would be present under open water conditions. The ice cover also retarded and diminished the salt wedge intrusion and is expected to dramatically reduce the sediment transport processes, although its presence could cause some sporadic local increases in erosion.     

Considerations for Monitoring Permeable Ground-Water Treatment Walls

Permeable ground-water treatment walls (PTWs) have been implemented as a means by which innovative ground-water treatment technologies can be applied in-situ. Though not widely addressed in the technical literature, the ground-water monitoring program for a PTW at a commercial site should consider several factors including: (1) design elements of the PTW; (2) the remediation process to be implemented through the PTW; (3) the distribution of contaminants in the affected aquifer; (4) ground-water sampling methods; and (5) regulatory issues. Also, the compliance monitoring well network within the PTW and sampling plan should be designed to assure that (1) design ground-water residence time goals within the PTW are achieved prior to sampling; (2) the uniformity of ground-water flow through the PTW is accounted for; and (3) ground-water samples are collected using techniques (e.g., micropurging) that reduce the potential for collecting nontreated ground water from down- or upgradient of the PTW. A case study illustrates the concepts used to develop a ground-water monitoring program for a PTW that was accepted by regulatory agencies for a commercial site.     

Nitrate Removal with Sulfur-Limestone Autotrophic Denitrification Processes

Nitrate removal using sulfur and limestone autotrophic denitrification (SLAD) processes was evaluated with four laboratory-scale fixed-bed column reactors. The research objectives were (1) to determine the optimum design criteria of the fixed-bed SLAD columns; and (2) to evaluate the effects of biofouling on the SLAD column performance. A maximum denitrification rate of 384 g NO3?-N/(m3?day) was achieved at a loading rate between 600 and 700 g NO3?-N/(m3?day). The effluent nitrite concentration started to rise gradually once the loading rate was above 600 g NO3?-N/(m3?day). A loading rate between 175 and 225 g NO3?-N/(m3?day) achieved the maximum nitrate-N removal efficiency (～95%). Biofouling was evaluated based on tracer studies, the measured biofilm thickness, and modeling. The porosities of the columns fluctuated with time, and the elongation of the filter media was observed. Biofouling caused short-circuiting and decreased nitrate removal efficiency. A SLAD column will require backwashing after 6 months of operation when the influent is synthetic ground water but will foul and require backwashing within 1–2 months when the influent is real ground water.