An improved method for evaluating the seasonal variability of total suspended sediment flux field in the Yellow and East China Seas

The suspended sediment flux field in the Yellow and East China Seas (YECS) displays its seasonal variability. A new method is introduced in this paper to obtain the flux field via retrieval of ocean color remote sensing data, statistical analysis of historical suspended sediment concentration data, and numerical simulation of three-dimensional (3D) flow velocity. The components of the sediment flux field include (i) surface suspended sediment concentration inverted from ocean color remote sensing data; (ii) vertical distribution of suspended sediment concentration obtained by statistical analysis ofhistorical observation data; and (iii) 3D flow field modeled by a numerical simulation. With the improved method, the 3D suspended sediment flux field in the YECS has been illustrated. By comparison with the suspended sediment flux field solely based on the numerical simulation of a suspended sediment transport model, the suspended sediment flux field obtained by the improved method is found to be more reliable. The 3D suspended sediment flux field from ocean colour remote sensing and in situ observation are more closer to the reality. Furthermore, by quantitatively analyzing the newly obtained suspended sediment flux field, the quantity of sediment erosion and deposition within the different regions can be evaluated. The sediment exchange between the Yellow Sea and the East China Sea can be evident. The mechanism of suspended sediment transport in the YECS can be better understood. In particular, it is suggested that the long-term transport of suspended sediment is controlled mainly by the circulation pattern, especially the current in winter.     

Distribution of Clostridium perfringens and fecal sterols in a benthic coastal marine environment influenced by the sewage outfall from McMurdo Station, Antarctica

The spatial distribution, movement, and impact of the untreated wastewater outfall from McMurdo Station, Antarctica, were investigated under early austral summer conditions. The benthic environment was examined to determine the distribution of Clostridium perfringens in sediment cores and the intestinal contents of native invertebrates and fish along a transect of stations. These stations extended ca. 411 m south of the outfall. The findings revealed that the concentration of C. perfringens decreased with depth in the sediment and distance from the outfall. High percentages of tunicates and sea urchins were colonized with this bacterium along the transect. Coprostanol concentrations were also measured in sediment samples taken from each of the transect stations, and a similar trend was observed. These results are in agreement with the findings of previous studies performed with the water column and collectively provide evidence that the disposal of domestic wastes deserves special consideration in polar marine environments.     

Development of Effluent Concentration Models for Sediment Scoured from Catchbasin Sumps

The ability of catchbasin sumps and hydrodynamic separators to remove sediment must be balanced with their ability to retain the previously captured material by preventing scour. The sediment scour process in these storm-water structures differs from the unidirectional scour and sediment transport process that occurs in pipes and channels. The hydrodynamics is affected by the particular characteristics of the hydraulic structure. The study of sediment scour in these devices requires incorporation of all the factors involved in the scour phenomenon and is best supported through computational fluid dynamic modeling (CFD) verified experimentally. Scour can be documented in the effluent as suspended sediment or total suspended solids concentration, a parameter of critical importance in storm-water quality management. This paper presents two simplified models for estimating effluent suspended sediment concentration attributable to scour of previously captured sediment. These models are based on results obtained from full-scale physical experimentation and calibrated and validated CFD modeling over a wide range of operating conditions where different particles sizes would be scoured. This paper also shows the effects of the armoring layer and of homogeneous and heterogeneous sediment sizes on the effluent concentration patterns.     

Drinking Water Treatment Plant Design Incorporating Variability and Uncertainty

Both inherent natural variability and model parameter uncertainty must be considered in the development of robust and reliable designs for drinking water treatment. This study presents an optimization framework for investigating the effects of five variable influent parameters and three uncertain model parameters on the least-cost treatment plant configuration (contact, direct, or nonsweep conventional filtration) that reliably satisfies an effluent particulate matter concentration constraint. Incorporating variability and uncertainty within the decision-making framework generates information for investigating: (1) impacts on total cost and treatment reliability; (2) shifts on the least-cost treatment configuration for providing reliable treatment; and (3) the importance of the individual variable and uncertain parameter distributions for reliably satisfying an effluent water quality constraint. Increasing the magnitude of influent variability and model parameter uncertainty results in a greater expected design cost due, generally, to increases in process sizing required to reliably satisfy the effluent concentration constraint. The inclusion of variability and uncertainty can also produce a shift in the locations of the least-cost configuration regions, which are dependent on the expected influent water quality and the magnitude of variability and uncertainty. The additional information provided by incorporating the variable and uncertain parameters illustrates that parameter distributions related to the primary removal mechanism are critical, and that contact and direct filtration are more sensitive to variability and uncertainty than conventional filtration.     

Sediment Discharge from a Storm-Water Retention Pond

A small storm-water retention pond is primarily designed to reduce the peak rate of surface runoff. From a water quality standpoint, that same pond may be irregular in shape and trap suspended sediment carried by the surface runoff generated upstream of the site. Considering different pond inlet locations, the writer’s numerical model is used to investigate the change in peak concentration of sediment discharge at the pond outlet. It has been found that the various hydraulic conditions can have a significant impact on sediment discharge. Three different cases are presented to show the flexibility of modeling changes in boundary conditions. The results may help designers evaluate sediment discharge to determine the most effective pond inlet locations.     

Monitoring of a Best Management Practice Wetland before and after Maintenance

The U.S. Environmental Protection Agency’s (USEPA) Urban Watershed Management Branch monitored a best management practice (BMP) wetland in the Richmond Creek (RC) watershed. This BMP, designated Richmond Creek #5 (RC-5), is owned and operated by the New York City Department of Environmental Protection’s as part of the Bluebelt program. During monitoring performed in 2003 and 2004, RC-5 was monitored for several water quality parameters including suspended solids (SS), chemical oxygen demand (COD), and phosphorous. Calculated SS loads demonstrated a 61% removal which is in line with the anticipated removals of 55%–57%, however, COD was not being removed from RC-5. Due to visible accumulation of sediment in the forebay and leaves throughout the BMP, maintenance activity was performed in the spring of 2005, to remove the sediment and organic matter (leaves) by vactor truck and physical labor. About four truck loads of sediment and leaf litter, estimated at 35?m3 (46 cubic yards), was removed from the site. Monitoring during the fall of 2005 measured the effects of this maintenance activity. The effluent concentrations of COD were significantly less and less variable after maintenance, and calculated influent and effluent COD loading indicated removals. The reduction in COD effluent coincided with drops in effluent phosphorous levels. Effluent SS concentrations were not significantly altered, implying RC-5 still had capacity to remove sediments before maintenance occurred. Indications are that the maintenance activity significantly reduced the COD effluent and may help communities manage phosphorous loadings.     

Prediction of Concerted Sediment Flushing

A proprietary one-dimensional numerical model was developed for predicting the amounts of sediment flushed and deposited in the reservoirs in series, the bed evolutions, and variations of the suspended solids concentrations along a river during the concerted sediment flushing events. The model consists of a flow movement module and sediment transport module in which the bed material load is taken as sediment mixture. The nonuniform property of the bed material load is modeled by the introduction of a mixing layer, transition layer, and deposition strata. The model was calibrated on the basis of the field data at Dashidaira and Unazuki reservoirs on the Kurobe River in Japan. The calculated results are in good agreement with the measurements. For the reservoirs out of Japan, the Ashida and Michiue bed load formula used in the model should be verified or replaced by other formulas.     

Compatibility of Reservoir Sediment Flushing and River Protection

In this paper, we propose a system of numerical models for the compatibility assessment of reservoir sediment flushing and protection of downstream river environments. The model system is made up of two simulation models. The first model simulates soil erosion in watershed slopes and sediment transport in the tributary of the reservoir by means of a weighted essentially nonoscillatory (WENO) method, which is conservative and fourth-order accurate in space and time. The second model simulates velocity and suspended solid concentration fields in the reservoirs. This model is based on the three-dimensional (3D) numerical integration of motion and concentration equations, expressed in contravariant form on a generalized boundary-conforming curvilinear coordinate system by using a conservative and higher-order accurate numerical scheme. The proposed system of models is applied to the Pieve di Cadore (Veneto, Italy) reservoir and to its catchment area. By comparing suspended solid concentrations that are discharged through the bottom outlets during flushing operations with suspended solid concentrations in the main river during natural flooding, we perform an assessment of the compatibility between sediment flushing and the protection of the river ecosystem downstream.     

Uncertainty Analysis of Conventional Water Treatment Plant Design for Suspended Solids Removal

An approach that links a Monte-Carlo simulation based reliability program with the water treatment process behavior and performance model is presented for uncertainty analysis of the conventional water treatment plant (WTP) design. The expected mass concentration of suspended solids (SS) in the effluent water is employed as a measurement of system reliability. The approach for uncertainty analysis of a WTP is illustrated with a hypothetical case study. The parameters contributing significantly to the variability of SS concentration in the effluent water are identified. From an operational viewpoint, the variability in effluent water quality resulting from uncertainty in the system parameters is investigated. Also, improvement in the reliability of WTP using modified design parameters is investigated along with its cost implications. From the results, a method to calculate a set of safety factors corresponding to various performance reliability levels is proposed.     

Three-Dimensional Modeling of Sediment Transport in a Narrow 90° Channel Bend

A three-dimensional numerical model was used for calculating the velocity and bed level changes over time in a 90° bended channel. The numerical model solved the Reynolds-averaged Navier-Stokes equations in three dimensions to compute the water flow and used the finite-volume method as the discretization scheme. The k-ε model predicted the turbulence, and the SIMPLE method computed the pressure. The suspended sediment transport was calculated by solving the convection diffusion equation and the bed load transport quantity was determined with an empirical formula. The model was enhanced with relations for the movement of sediment particles on steep side slopes in river bends. Located on a transversally sloping bed, a sediment particle has a lower critical shear stress than on a flat bed. Also, the direction of its movement deviates from the direction of the shear stress near the bed. These phenomenona are considered to play an important role in the morphodynamic process in sharp channel bends. The calculated velocities as well as the bed changes over time were compared with data from a physical model study and good agreement was found.     

Volumetric Filtration of Rainfall Runoff. II: Event-Based and Interevent Nutrient Fate

This study examines in situ phosphorus treatment using a combined unit operation and process, a volumetric clarifying filter (VCF). Urban rainfall-runoff transports phosphorus in dissolved and particulate phases with the latter phase distributed across the particulate matter (PM) gradation. From a clean initial condition, the VCF was monitored across 19 events without maintenance, to examine partitioning and phosphorus distribution on PM. For the monitoring period, site influent total phosphorus (TP) is 0.342 mg/L of which 0.081 mg/L is dissolved; and subsequently reduced to 0.095 and 0.031 mg/L, respectively, by the VCF. PM-bound phosphorus is categorized as suspended, settleable and sediment fractions based on PM size and separation behavior. Site influent PM-based concentrations (mg/g) are 0.22 for sediment, 0.42 for settleable and 3.27 for the suspended fraction with each fraction further enriched in the VCF, based on effluent monitoring. A categorical analysis and odds ratio testing of PM-based phosphorus specific capacities (mg/g) indicate that a significant fraction of phosphorus can bind to suspended PM preferentially over settleable and sediment PM as a PM-based concentration. At the end of the event-based monitoring the inter-event change in phosphorus and nitrogen, chemistry is examined as a function of runoff storage time. Runoff retention generates nitrate reduction and ammonia (NH3+NH4+) production; predominately as ammonium. Phosphorus partitioning is stable during runoff storage with a dissolved fraction between one fourth to one-third of TP. Predominant species are H2PO4? for a pH<7 and HPO42? for a pH>7.     

Modeling of Disinfection Contactor Hydraulics under Uncertainty

A study has been done to evaluate the predictive capabilities of computational fluid dynamics (CFD) models of disinfection contactor hydraulics under model input uncertainty. The study consists of modeling the transport of a chemical tracer in a full-scale reactor and predicting the effluent residence time distribution (RTD) curve. An uncertainty analysis using Monte Carlo probabilistic techniques was used to determine the sensitivity of the effluent RTD to uncertainty in the influent turbulent kinetic energy constant, the turbulent Schmidt number, the wall roughness height, the influent turbulent length scale, and the turbulence model selection. Kruskal–Wallis, Friedman, and Spearman Rho statistical tests were used to evaluate changes in T10/HRT and Morril index due to input uncertainties. The results show that there are some variations in the effluent RTD due to changes in the model input parameters. The effluent RTD variations increased with decreasing contactor hydraulic efficiency or increased mixing. The effluent RTD was most sensitive to uncertainty in the turbulent Schmidt number and the selected turbulence model.     

Volumetric Filtration of Rainfall Runoff. I: Event-Based Separation of Particulate Matter

As a unit operation, filtration generally requires flow equalization and primary clarification. This study examines the separation of runoff particulate matter (PM) in a volumetric clarifying filter (VCF). The VCF is a detention/retention vault integrating filtration after sedimentation. A paved source area (1,088?m2) directly loaded the vault (4.2?m3) with five radial filters (4?m2 of filtration surface area). PM separation was examined for 19 runoff events through monitoring of influent and effluent granulometric fractions. During the monitoring phase no maintenance was conducted and subsequent to the 19 events a measured material balance of the sedimentation vault and the radial cartridge filters generated a 94% recovery of PM. During 5 months of monitoring and PM mass, suspended sediment concentration (SSC) was reduced from 334 to 34 mg/L (90% reduction) with effluent sediment (>75?μm) of <3?mg/L, settleable of 14 mg/L, suspended PM (<25?μm) of 17 mg/L as event mean concentrations; with turbidity reduced from 96 to 23 NTU (76% reduction). Based on separate PM recovery from the vault and filters, 77% of the PM separation was sedimentation in the vault and 23% as filtration. Captured particle-size distributions are heterodisperse with a d50?m of 300 μm in the vault and a d50?m that ranged from 34 to 63 μm with filter depth. Filter forensics indicated PM capture was nonuniform, with the bottom and middle most heavily loaded by PM as compared to the upper third of the filter. While paired testing of automatic and manual sampling produced similar median effluent SSC, automatic sampling significantly misrepresented the median influent PM as SSC (p ? α = 0.05).     

Depth-Averaged Two-Dimensional Numerical Modeling of Unsteady Flow and Nonuniform Sediment Transport in Open Channels

A depth-averaged two-dimensional (2D) numerical model for unsteady flow and nonuniform sediment transport in open channels is established using the finite volume method on a nonstaggered, curvilinear grid. The 2D shallow water equations are solved by the SIMPLE(C) algorithms with the Rhie and Chow’s momentum interpolation technique. The proposed sediment transport model adopts a nonequilibrium approach for nonuniform total-load sediment transport. The bed load and suspended load are calculated separately or jointly according to sediment transport mode. The sediment transport capacity is determined by four formulas which are capable of accounting for the hiding and exposure effects among different size classes. An empirical formula is proposed to consider the effects of the gravity on the sediment transport capacity and the bed-load movement direction in channels with steep slopes. Flow and sediment transport are simulated in a decoupled manner, but the sediment module adopts a coupling procedure for the computations of sediment transport, bed change, and bed material sorting. The model has been tested against several experimental and field cases, showing good agreement between the simulated results and measured data.     

Two-Dimensional Total Sediment Load Model Equations

An unsteady total load equation is derived for use in depth-averaged sediment transport models. The equation does not require the load to be segregated a priori into bed and suspended but rather automatically switches to suspended load, bed load, or mixed load depending on a transport mode parameter consisting of local flow hydraulics. Further, the sediment transport velocity, developed from available data, is explicitly tracked, and makes the equation suitable for unsteady events of sediment movement. The equation can be applied to multiple size fractions and ensures smooth transition of sediment variables between bed load and suspended load for each size fraction. The new contributions of the current work are the consistent treatment of sediment concentration in the model equation and the empirical definition of parameters that ensure smooth transitions of sediment variables between suspended load and bed load.     

New Process Design Procedure for Dealing with Variable Trickling Filter Effluent Suspended Solids

Based on a survey which showed that seven of eight conventional trickling filter (CTF) plants exceeded the U.S. Environmental Protection Agency secondary treatment regulatory requirements, a new design procedure is proposed. It recognizes that bioflocculation within CTFs is poor and that most of the effluent violations seen in the survey could be related directly or indirectly to the level of effluent suspended solids. In past practice, process design focus has been on soluble or settled effluent biochemical oxygen demand (BOD5) rather than the effluent suspended solids. The principal focus in CTF process design should be on predicting effluent suspended solids (SS) after secondary clarification, rather than effluent carbonaceous BOD5. If the total organic loading (TOL) is set in the proper range, the effluent carbonaceous BOD5 is primarily determined by the effluent SS. A new design procedure has been developed that identifies the highest TOL that can be sustained without posing a constraint on effluent SS due to effluent CBOD5 limitations. This is coupled with the incorporation of additional design features that can control effluent SS.     

Pollutant Transport and Mixing Zone Simulation of Sediment Density Currents

Prediction of water column concentrations of suspended sediment is often necessary for environmental impact assessment of point source industrial discharges. For example, in “flow lane” or “open water” disposal, suction dredges discharge large volumes of suspended sediment into shallow water disposal locations. A sediment density current mixing model is presented here as part of the D-CORMIX expert system for hydrodynamic simulation of mixing zone behavior. This density current model extends the CORMIX decision support system to simulate continuous negatively buoyant discharges with or without suspended sediment loads on a sloping bottom with loss of suspended particles by sedimentation. Sedimentation is modeled using Stokes settling for five particle size classes. Density current width and depth, trajectory, total solids, tracer concentration, dilution, and particle size concentration are predicted. In addition, location and widths of sediment deposits, accretion rates, including particle size fractions within the spoils deposit, are predicted. The model results are in good overall agreement with available field and laboratory data.     

Simulations of Dye Releases off the Coast of New Jersey: Development and Validation of an Ocean Outfall Mixing Model

A kinematic mixing model has been developed to predict far field effluent distributions for ocean discharges. The model allows for complex outfall configurations and time varying discharge rates to be simulated. The model can use field observations or the output from a proven near field mixing model as input to this far field mixing model. The model uses observed or simulated horizontal currents at one location to advect the effluent plume and a scale-dependent “diffusion velocity” submodel to account for horizontal diffusive processes. To collect data to calibrate and verify the model, long-term continuous dye release experiments were conducted at two New Jersey ocean outfalls. Based upon the results of the dye release experiments, appropriate values for the diffusion velocity were determined for each outfall. Simulations using these diffusion velocities provided reasonable predictions of plume width and of average dye concentration at each transect for each outfall. This work demonstrates that an Eulerian velocity observed at one location in the coastal ocean off New Jersey may be used to predict Lagrangian transport over a distance of several kilometers.     

Simulated Moving Bed Form Effects on Real-Time In-Stream Sediment Concentration Measurement with Densitometry

This study evaluated fluctuations in the output signal of a densimeter, an in situ suspended-sediment measurement device based on a very sensitive differential pressure transducer. Although the densimeter produced accurate (less than 10% error) results in the laboratory for concentrations of 10–1,000?mg/L, there was a much larger fluctuation in the field test output signal. These fluctuations were hypothesized to have originated from fluctuations imparted by movement of bed material on the channel bottom. Measuring root mean square and mean velocities and corresponding pressure differences at locations in front of and behind a bluff body simulated movement of a body/bed form past a sampling point in a quasistatic manner. Position of the bluff body relative to the sample port resulted in differential pressure swings equivalent to 65,000?mg/L sediment concentration. Turbulent structure changed dramatically with position of the bluff body. Thus, pressure densitometry using a differential pressure transducer is likely not a reliable system for measuring sediment concentration under in-stream conditions, particularly near the channel bottom where bed forms and large objects may pass between the sample ports.