Detachment Rate Coefficients Research Articles

Mathematical modeling the transport of few-layer graphene in saturated porous media

This mathematical modeling study incorporates an existing set of effluent data for FLG-NPs transport through water-saturated quartz sand to estimate kinetic particle mobility parameters for a range of experimental ionic strengths (IS) and organic macromolecules (OMs) concentrations. Parameter estimation was done by implementing several NP filtration models in inverse analyses: (i) the clean-bed colloid filtration theory model (CFT, ii) maximum retention capacity model (MRC), and (iii) two subclasses of a two-attachment-site model (2S). It was found that as solution IS (1-100 mM NaCl) increased, the kinetic conditions for particle-collector attachment transitioned from unfavorable (i.e. fractional attachment) to favorable (i.e. diffusion-limited), and the unbounded subclass of 2S lost the better numerical performance compared to CFT and MRC; as the difference between the normalized sum of squared residuals (NSSR) of the unbounded subclass of 2S and CFT decreased from 20% at 1 mM to less than 1% at 100 mM NaCl suggesting the adequacy of CFT to estimate mobility parameters at high ionic strength. As the OMs concentrations increased from 0.8 to 50 total organic carbon (mg (TOC)/L) in the system, the unbounded subclass of 2S showed the best outcomes. Simulation results from all models predicted that attachment efficiency decreases with increasing OM concentration consistent with the observed enhancement of FLG mobility at higher OM levels. The FLG detachment rate coefficient slightly increased with an increase of OM concentration in the influent. The unbounded four-parameter subclass of 2S exhibited a numerical advantage in comparison with CFT and MRC models for estimating FLG mobility parameters at low IS (1 mM NaCl) and high OMs concentration (50 mg (TOC)/L). However, the CFT model yielded similar goodness of fit values very similar to 2S and MRC models at high IS (100 mM NaCl) and low OMs concentration (0.8 mg (TOC)/L).

Transport and removal of spores of Bacillus subtilis in an alluvial gravel aquifer at varying flow rates and implications for setback distances

To guarantee proper protection from fecally transmitted pathogen infections, drinking water wells should have a sufficiently large setback distance from potential sources of contamination, e.g. a nearby river. The aim of this study was to provide insight in regards to microbial contamination of groundwater under different flow velocities, which can vary over time due to changes in river stage, season or pumping rate. The effects of these changes, and how they affect removal parameters, are not completely understood. In this study, field tracer tests were carried out in a sandy gravel aquifer near Vienna, Austria to evaluate the ability of subsurface media to attenuate Bacillus subtilis spores, used as a surrogate for Cryptosporidium and Campylobacter. The hydraulic gradient between injection and extraction was controlled by changing the pumping rate (1, 10 l/s) of a pumping well at the test site, building upon previously published work in which tracer tests with a 5 l/s pumping rate were carried out. Attachment and detachment rate coefficients were determined using a HYDRUS-3D model and ranged from 0.12 to 0.76 and 0–0.0013 h−1, respectively. Setback distances were calculated based on the 60-day travel time, as well as a quantitative microbial risk assessment (QMRA) approach, which showed similar results at this site; around 700 m at the highest pumping rate. Removal rates (λ) in the field tests ranged from 0.2 to 0.3 log/m, with lower pumping rates leading to higher removal. It was shown that scale must be taken into consideration when determining λ for the calculation of safe setback distances.

Transport and targeted binding of Pluronic-coated nanoparticles in unsaturated porous media

The effectiveness of most in situ remedial technologies, including nanoremediation, lies on successful delivery of reagents to a subsurface target treatment zone. Targeted delivery of engineered nanoparticles (NPs) to treat petroleum hydrocarbons present in the unsaturated zone requires an understanding of their transport behaviour in these systems. A series of column experiments explored the effect of initial water saturation, flowrate, input dosage, and porous medium texture on the transport of iron oxide or cobalt ferrite NPs coated with an amphiphilic co-polymer, as well as their targeted attachment to a crude oil zone. As the initial water content increased with a concomitant reduction in air saturation, the degree of tailing present in the NP breakthrough curves (BTCs) reduced, and the mass of NPs recovered increased. Air saturation is positively correlated with the magnitude of air-water interfaces, which provide additional NP retention sites. At a lower injection flow rate, NP retention increased due to a longer residence time and comparatively high air saturation. NP transport behaviour was not sensitive to NP injection dose over the range tested. Increased retention and retardation of the NP BTC was observed in sediments with a higher clay and silt content. NPs coated with a lower concentration of a Pluronic block co-polymer to promote binding were preferentially retained within the crude oil zone. To simulate the asymmetrical NP breakthrough curves observed from the unsaturated systems required the use of a model that accounted for both mobile and immobile flow regions as well as NP attachment and detachment with nonlinear Langmuirian blocking. This model allowed examination of attachment and detachment rate coefficients which captured NP interaction with the porous medium and/or crude oil. It was found that the initial water saturation and flow rate did not have an appreciable impact on the NP attachment rate coefficient, while it increased by ~10× with increasing clay and silt content, and by ~100× in the presence of crude oil, indicating preferential NP attachment within the crude oil zone. As a result of the lower NP polymer concentration coating used to promote increased attachment to crude oil, higher retention was observed near the column inlet and was captured quantitatively by adding a depth-dependent straining term to the model. This retention behaviour represents a combination of irreversible attachment at the air-water interfaces and straining near the column inlet enhanced by the formation of NP aggregates. The detachment rate coefficient decreased with a lower initial water saturation and flowrate, but increased with higher clay and silt content. The findings from this study contribute to our understanding of the transport and binding behaviour of Pluronic-coated NPs in unsaturated conditions and, in particular, the role of initial water content, flowrate and porous medium texture. Demonstrated delivery of NPs to a target zone is an important step towards expanding the utility of NPs as treatment reagents.

Influence of flow rate on the transport of nTiO2 and phosphate and its modeling

We studied Zeta potentials of nanoparticles titanium dioxides （nTiO2） in different concentration of NaNO3 and phosphate (P) solutions. In addition, the effect of flow rate on the transport of nTiO2 in P was investigated at pH＝6.5. Experimental results show that the Zeta potential of nTiO2 is compressed with the increasing ion concentration (IC) of NaNO3 at pH＝6.5. The negative charge increases with the augment of P. Therefore, the high P and low NaNO3 induce the stabilization of nTiO2 aggregates. The transport experiments suggest that the rapid flow rate is favorable for the transportability of nTiO2 and soluble phosphate. The breakthrough transport curves (BTCs) of nTiO2 in sand columns can be fitted well with two-site kinetic attachment model. The modeling results suggest that the values of first-order attachment rate coefficients (k2) and detachment rate coefficients (k2d) on site 2 and first-order attachment rate coefficients (k1) on site 1 are responsible to the attaching efficiency of nTiO2 on sands and their transportability.

Multiscale Modeling of Uranium Bioreduction in Porous Media by One-Dimensional Biofilms

We formulate a multiscale mathematical model that describes the bioreduction of uranium in porous media. On the mesoscale we describe the bioreduction of uranium [VI] to uranium [IV] using a multispecies one-dimensional biofilm model with suspended bacteria and thermodynamic growth inhibition. We upscale the mesoscopic (colony scale) model to the macroscale (reactor scale) and investigate the behavior of substrate utilization and production, attachment and detachment processes, and thermodynamic effects not usually considered in biofilm growth models. Simulation results of the reactor model indicate that thermodynamic inhibition quantitatively alters the dynamics of the model and neglecting thermodynamic effects may over- or underestimate chemical concentrations in the system. Furthermore, we numerically investigate uncertainties related to the specific choice of attachment and detachment rate coefficients and find that while increasing the attachment rate coefficient or decreasing the detachment rate coefficient leads to thicker biofilms, performance of the reactor remains largely unaffected.

Identification of the discharge kinetics in the perfluoro-nitrile C4F7N with swarm and breakdown experiments

We follow up on our previous publication on C4F7N and investigate the ion kinetics influencing C4F7N discharges with a pulsed Townsend experiment. The measured current signals at pressures between 0.06 and 6.9 kPa, in the range of density-reduced electric fields E/N from 500 to 1050 Td, show evidence of three anions: one long-lived anion with a detachment rate coefficient in the order of , a presumably non-detaching anion, and a short-lived anion with a detachment rate coefficient in the order of . We obtain the corresponding rate coefficients for ionization, attachment and detachment in C4F7N. Using these results, we calculate a corrected value of the effective ionization rate coefficient , taking into account detachment from negative ions. It results in a corrected value of the density-reduced critical electric field strength Td, much lower than the previously obtained value of Td, which is valid only when electron detachment is negligible, i.e. for low pressure and small geometric distance. To find which value is most relevant for electrical insulation, we perform breakdown voltage measurements in homogeneous electric fields in C4F7N at 5–65 kPa. We compare the measured density-reduced breakdown field strength to that calculated using the streamer criterion with the presently obtained rate coefficients, including electron detachment. We find excellent agreement between the measured and calculated .

Experimentally derived rate coefficients for electron ionization, attachment and detachment as well as ion conversion in pure O2 and N2–O2 mixtures

We obtain rate coefficients for mixtures of and as well as pure , by fitting pulsed Townsend measurements over a large pressure range from 3 kPa to 100 kPa in a density-reduced electric field range from 40 to 110 Td (1 Td = 10−21 Vm2). The applied model includes ionization, dissociative attachment to and non-dissociative attachment to , and detachment, as well as charge transfer and ion conversion from to and . The results are compared to Bolsig+ and MAGBOLTZ simulations and experimental data, where available. The key novelty is the simultaneously obtained rate coefficients from a single pulsed Townsend experiment including several ion processes over the whole – mixing range.

Isotopic effects in the interaction of O− with D2 and H2 at low temperatures

The isotopic effects in reactions of ${\mathrm{O}}^{\ensuremath{-}}$ ions with ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ have been studied experimentally using a cryogenic 22-pole radio-frequency ion trap. The rate coefficients for associative detachment leading to ${\mathrm{H}}_{2}\mathrm{O}+{e}^{\ensuremath{-}}$ and to ${\mathrm{D}}_{2}\mathrm{O}+{e}^{\ensuremath{-}}$ and for atom transfer reactions leading to formation of ${\mathrm{OH}}^{\ensuremath{-}}$ and ${\mathrm{OD}}^{\ensuremath{-}}$ ions were determined at temperatures ranging from 15 to 300 K. The measured temperature dependencies of the rate coefficients for both channels of reactions of ${\mathrm{O}}^{\ensuremath{-}}$ with ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ are compared with the results of the classical trajectory Monte Carlo simulation of the ${\mathrm{O}}^{\ensuremath{-}}+{\mathrm{H}}_{2}$ and ${\mathrm{O}}^{\ensuremath{-}}+{\mathrm{D}}_{2}$ collisions using the newly calculated potential energy surfaces. The measured temperature dependencies of the reaction rate coefficients for associative detachment are in very good agreement with the calculated ones. Agreement between experimental and calculated temperature dependencies of the rate coefficients of atom transfer reactions is off at most by a factor of 3 and the isotope effect is reproduced.

Measurement of ionization, attachment, detachment and charge transfer rate coefficients in dry air around the critical electric field

We obtain pressure-dependent rate coefficients in dry synthetic air (79% , 21% ) by fitting Pulsed Townsend measurements over a pressure range from 10 to 100 kPa, around the critical density-reduced electric field from 86 to 104 Td. The physical processes are reviewed and set in relation to a suitable kinetic model. A procedure for fitting kinetic reaction rates, based on finite-volume simulations of charge carrier drift, is described. Rate coefficients are obtained for electron attachment, ionization and detachment, as well as for ion conversion. We find a quadratic pressure dependency in the conversion rate, consistent with three-body collisions, and observe a pressure dependency in the onset of electron avalanche growth in dry air.

The effect of seed electrons on the repeatability of atmospheric pressure plasma plume propagation. II. Modeling

One of the distinguishable features of plasma jets compared with the traditional streamers is their repeatable propagation. As an initial objective, the effect of seed electrons on the repeatability of plasma plume propagation is investigated numerically. Besides residual electrons left from previous pulses, the electrons detached from O2− ions could also be a significant source of the seed electrons to affect the repeatability of plasma plume propagation when an electronegative gas admixture is presented. In this investigation, a global plasma chemical kinetics model is developed to investigate the temporal evolution of the electron and O2− ions in the afterglow of a plasma plume driven by microsecond pulse direct current voltages, at a total gas pressure of 2 × 104 Pa or 4 × 103 Pa in helium or helium-oxygen mixtures with an air impurity of 0.025%. In addition, a Monte Carlo technique has been applied to calculate the O2− detachment rate coefficient. Accordingly, the seed electron density due to detachment from O2− ions for different percentages of oxygen is obtained. Finally, the minimum seed electron density required for the plasma bullets to propagate in a repeatable mode is obtained according to the critical frequency from the experiments. It is found that the order of minimum seed electron number density required for repeatable propagation mode is independent of oxygen concentrations in the helium-oxygen mixture. It is 108 cm−3 for 20 kPa and 107 cm−3 for 4 kPa. Furthermore, for the helium with an air impurity of 0.025%, the residual electrons left over from previous discharges are the main source of seed electrons. On the other hand, when 0.5% of O2 is added, the detachment of O2− is the main source of the seed electrons.

Dynamic properties of a continuous stirred tank biofilm bioreactor for aerobic processes

A dynamic analysis of a continuous stirred tank bioreactor with biofilm was performed. The existence of gas, liquid, and biofilm were taken into account. The proposed heterogeneous model of such bioreactor takes into account dynamic biofilm growth and interphase transfer of substrates and biomass for a double‐substrate aerobic process. Simulations were performed to investigate the influence of important process parameters, i.e., toxic substrate concentration in the feed stream, detachment rate coefficient, mean residence time of the liquid and aeration intensity, on dynamic properties of the bioreactor. Dynamic behavior at conditions of anoxia of microorganisms were shown. A method was proposed to reduce bioreactor start‐up time significantly. The paper presents a mathematical model of the bioreactor that uses a discrete model of biofilm growth based on the theory of cellular automata. Dynamics of the bioreactor based on the continuous and discrete biofilm model was compared. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1818–1829, 2017

Transport of Fecal Indicators from Beach Sand to the Surf Zone by Recirculating Seawater: Laboratory Experiments and Numerical Modeling.

Recirculating seawater is an important component of submarine groundwater discharge, yet its role in transporting microbial contaminants from beach sand to coastal water is unknown. This study investigated the extent to which recirculating seawater carries fecal indicators, Enterococcus and bird-associated Catellicoccus, through the beach subsurface. Laboratory experiments and numerical modeling were performed to characterize the transport of fecal indicators suspended in seawater through medium-grained beach sand under transient and saturated flow conditions. Enterococcus was measured both by culture (cENT) and DNA assay (tENT), and Catellicoccus (CAT) by DNA assay. There were differences between transport of tENT and CAT compared to cENT through laboratory columns containing beach sands. Under transient flow conditions, first-order attachment rate coefficients (katt) of DNA markers were greater (∼10 h-1) than katt of cENT (∼1 h-1), although under saturated conditions katt values were similar (∼1 h-1). First-order detachment rate coefficients, kdet, of DNA markers were greater (∼1 h-1) than kdet of cENT (∼0.1h-1) under both types of flow conditions. Incorporating the rate coefficients into field-scale subsurface transport simulations showed that, in this sand type, the contribution of recirculating seawater to surf zone contamination is likely to be minimal unless bird feces are deposited close to the land-sea interface.

A study of the deep-bed filtration of a suspension of ash particles

A new experimental approach to estimating the attachment and detachment rate coefficients of suspended particles in a filtering bed has been proposed. These coefficients are determined using the deepbed filtration of clarified power station water containing ash particles as an example to show how they could be used to calculate the contaminant-retention capacity of a filtering bed. The effect of the direction and velocity of filtration on the decontamination efficiency and contaminant-retention capacity of a filtering bed has been established.

Modeling the co-transport of viruses and colloids in unsaturated porous media

A mathematical model is developed to simulate the co-transport of viruses and colloids in unsaturated porous media under steady-state flow conditions. The virus attachment to the mobile and immobile colloids is described using a linear reversible kinetic model. Colloid transport is assumed to be decoupled from virus transport; that is, we assume that colloids are not affected by the presence of attached viruses on their surface. The governing equations are solved numerically using an alternating three-step operator splitting approach. The model is verified by fitting three sets of experimental data published in the literature: (1) Syngouna and Chrysikopoulos (2013) and (2) Walshe et al. (2010), both on the co-transport of viruses and clay colloids under saturated conditions, and (3) Syngouna and Chrysikopoulos (2015) for the co-transport of viruses and clay colloids under unsaturated conditions. We found a good agreement between observed and fitted breakthrough curves (BTCs) under both saturated and unsaturated conditions. Then, the developed model was used to simulate the co-transport of viruses and colloids in porous media under unsaturated conditions, with the aim of understanding the relative importance of various processes on the co-transport of viruses and colloids in unsaturated porous media. The virus retention in porous media in the presence of colloids is greater during unsaturated conditions as compared to the saturated conditions due to: (1) virus attachment to the air–water interface (AWI), and (2) co-deposition of colloids with attached viruses on its surface to the AWI. A sensitivity analysis of the model to various parameters showed that the virus attachment to AWI is the most sensitive parameter affecting the BTCs of both free viruses and total mobile viruses and has a significant effect on all parts of the BTC. The free and the total mobile viruses BTCs are mainly influenced by parameters describing virus attachment to the AWI, virus interaction with mobile and immobile colloids, virus attachment to solid–water interface (SWI), and colloid interaction with SWI and AWI. The virus BTC is relatively insensitive to parameters describing the maximum adsorption capacity of the AWI for colloids, inlet colloid concentration, virus detachment rate coefficient from the SWI, maximum adsorption capacity of the AWI for viruses and inlet virus concentration.

Interaction of O(-) and H2 at low temperatures.

Reactive collisions between O(-) and H2 have been studied experimentally at temperatures ranging from 10 K to 300 K using a cryogenic radiofrequency 22-pole ion trap. The rate coefficients for associative detachment, leading to H2O + e(-), increase with decreasing temperature and reach a flat maximum of 1.8 × 10(-9) cm(3) s(-1) at temperatures between 20 K and 80 K. There, the overall reaction probability is in good agreement with a capture model indicating efficient non-adiabatic couplings between the entrance potential energy surfaces. Classical trajectory calculations on newly calculated potential energy surfaces as well as the topology of the conical intersection seam leading to the neutral surface corroborate this. The formation of OH(-) + H via hydrogen transfer, although occurring with a probability of a few percent only (about 5 × 10(-11) cm(3) s(-1) at temperatures 10-300 K), indicates that there are reaction paths, where electron detachment is avoided.

Bacteriophage PRD1 batch experiments to study attachment, detachment and inactivation processes

Knowledge of virus removal in subsurface environments is pivotal for assessing the risk of viral contamination of water resources and developing appropriate protection measures. Columns packed with sand are frequently used to quantify attachment, detachment and inactivation rates of viruses. Since column transport experiments are very laborious, a common alternative is to perform batch experiments where usually one or two measurements are done assuming equilibrium is reached. It is also possible to perform kinetic batch experiments. In that case, however, it is necessary to monitor changes in the concentration with time. This means that kinetic batch experiments will be almost as laborious as column experiments. Moreover, attachment and detachment rate coefficients derived from batch experiments may differ from those determined using column experiments. The aim of this study was to determine the utility of kinetic batch experiments and investigate the effects of different designs of the batch experiments on estimated attachment, detachment and inactivation rate coefficients. The experiments involved various combinations of container size, sand-water ratio, and mixing method (i.e., rolling or tumbling by pivoting the tubes around their horizontal or vertical axes, respectively). Batch experiments were conducted with clean quartz sand, water at pH 7 and ionic strength of 20 mM, and using the bacteriophage PRD1 as a model virus. Values of attachment, detachment and inactivation rate coefficients were found by fitting an analytical solution of the kinetic model equations to the data. Attachment rate coefficients were found to be systematically higher under tumbling than under rolling conditions because of better mixing and more efficient contact of phages with the surfaces of the sand grains. In both mixing methods, more sand in the container yielded higher attachment rate coefficients. A linear increase in the detachment rate coefficient was observed with increased solid-water ratio using tumbling method. Given the differences in the attachment rate coefficients, and assuming the same sticking efficiencies since chemical conditions of the batch and column experiments were the same, our results show that collision efficiencies of batch experiments are not the same as those of column experiments. Upscaling of the attachment rate from batch to column experiments hence requires proper understanding of the mixing conditions. Because batch experiments, in which the kinetics are monitored, are as laborious as column experiments, there seems to be no major advantage in performing batch instead of column experiments.

Assessment of In Situ Scour Profile in Sand Using a Jet Probe

Abstract Work in this paper presents a device and a process for in situ assessment of erosion potential with depth. The proposed device is termed “in situ erosion evaluation probe” (ISEEP), and the process is developed based upon advancing a rod fitted with a truncated cone jet nozzle into the soil. As water exits the nozzle with controllable velocity and flow rate (induced by an external pump) the probe advances into the subsurface profile and the rate of advancement is measured. The jet flow velocity and the advancement rate of the probe are correlated with a stream power value, and used to estimate soil erodibility parameters. Results from laboratory testing show the feasibility of the concept. An approach for the estimation of a critical stream power and a detachment rate coefficient is presented. Numerical modeling and deployment of the device at a North Carolina barrier island site after hurricane Irene are used to demonstrate the applicability of the proposed concept. Correlations between scour magnitudes, estimated by ISEEP parameters, and those estimated through modeling and field observation are presented and illustrate the viability of ISEEP’s soil erosion parameters as defined by a critical stream power and a detachment rate coefficient.

Effect of dissolved calcium on the removal of bacteriophage PRD1 during soil passage: The role of double-layer interactions

The objective of this work was to investigate and obtain quantitative relations for the effects of Ca(2+) concentration on virus removal in saturated soil and to compare the experimental findings with predictions of the DLVO theory. In order to do so, a systematic study was performed with a range of calcium concentrations corresponding to natural field conditions. Experiments were conducted in a 50-cm column with clean quartz sand under saturated conditions. Inflow solutions were prepared by adding CaCl(2,) NaCl and NaHCO(3) to de-ionized water. Values of pH and ionic strength were fixed at 7 and 10mM, respectively. Bacteriophage PRD1 was used as a conservative model virus for virus removal. The samples were assayed using the plaque forming technique. Attachment, detachment and inactivation rate coefficients were determined from fitting breakthrough curves. Attachment rate coefficients were found to increase with increasing calcium concentration. Results were used to calculate sticking efficiency, for which an empirical formula as a function of Ca(2+) was developed. Numerical solutions of the Poisson-Boltzmann equation were obtained to evaluate the effect of Ca(2+) on the double-layer interactions between quartz and PRD1. Based on these results, the DLVO interaction energies were calculated. It turned out that the experimental findings cannot be explained with the distance profiles of the DLVO interaction. The discrepancy between theory and experiment can be attributed to underestimation of the van der Waals interactions, chemisorption of Ca(2+) onto the surfaces, or by factors affecting the double-layer interactions, which are not included in the Poisson-Boltzmann equation. When abruptly changing from inflow solution containing Ca(2+) to a Ca(2+)-free solution, pronounced mobilization of viruses was observed. This indicates virus removal is not irreversible and that chemical perturbations of the groundwater can cause a burst of released viruses.

Electron Attachment to C7F14, Thermal Detachment from C7F14–, the Electron Affinity of C7F14, and Neutralization of C7F14– by Ar+

Rate coefficients and branching fractions have been measured for electron attachment to perfluoromethylcyclohexane, C(7)F(14), along with thermal detachment rate coefficients for C(7)F(14)(-), from 300 to 630 K, using a flowing-afterglow Langmuir-probe apparatus. The attachment rate coefficient at room temperature is 4.5 ± 1.2 × 10(-8) cm(3) s(-1) and increases with temperature at a rate described by an activation energy of 50 ± 25 meV. Thermal electron detachment is negligible at room temperature, but measurable at 600 K and above, reaching 2300 ± 1300 s(-1) at 630 K. Analysis of the attachment-detachment equilibrium yields EA(C(7)F(14)) = 1.02 ± 0.06 eV, in agreement with the literature value while more than halving the uncertainty. Implications of the measurement for the electron affinity of SF(6) are discussed. The dominant product of electron attachment is the parent anion, but C(6)F(11)(-) and C(7)F(13)(-) are also observed at very low levels (<0.1%) at room temperature and increase in importance as the temperature is increased, reaching ~10% each at 630 K. In the course of this work we have also measured rate coefficients for the neutralization of C(7)F(14)(-) by Ar(+) at 300, 400, and 500 K: 4.8, 3.5, and 3.1 × 10(-8) cm(3) s(-1), respectively, with uncertainties of ±5 × 10(-9) cm(3) s(-1).

Development and Characterization of Soil Material Parameters for Embankment Breach

Despite the widespread use of earthen dams, the processes by which earthen embankments erode and fail when overtopped during extreme events are only imperfectly understood. Aging of these dams and the associated recent focus on dam rehabilitation has increased the need for new technology and tools for predicting the performance of earthen embankments during overtopping. Windows Dam Analysis Modules (WinDAM B) is a modular software application being developed to address this need for homogeneous earthen embankments. This software is being developed through joint efforts of the Agricultural Research Service, the Natural Resources Conservation Service, and Kansas State University. The computational model being incorporated into this software is the result of research including embankment overtopping tests conducted in the outdoor laboratory. The WinDAM B model is a simplified representation of the observed process of progressive erosion leading to embankment breach to be useful for field application the model has been developed to utilize soil parameters that may be reasonably obtained for the conditions to which the model is applied. This article presents the background for the material parameter input requirements for overtopping erosion and breach analysis including: 1) the detachment rate coefficient and critical stress parameters of the excess stress equation, 2) the total unit weight of soil, 3) the undrained shear strength, and 4) the headcut migration coefficient.