Field Tracer Experiments Research Articles

Representation of Plot‐Scale Soil Heterogeneity in Dual‐Domain Effective Flow and Transport Models with Mass Exchange

Core Ideas The heterogeneity of soil hydraulic properties can be described with effective parameters. Increasing model complexity can be used to represent plot‐scale soil heterogeneity. One‐dimensional dual‐domain flow models are used to reproduce 2D preferential transport. Local subscale variability effects are included as mass transfer in an effective model. Agricultural soils are characterized by a structure that is strongly dependent on farming practices like tillage and trafficking. These practices can create compacted zones in the soil, thus initiating preferential flow. Two‐ or three‐dimensional models can be used to account for the spatial variability of the soil hydraulic and transport properties. Since it is challenging to obtain such data, it is logical to find simpler approaches. Our objective was to design a one‐dimensional (1D) modeling approach that effectively accounts for plot‐scale soil structure variability. A 1D dual‐permeability model was tested in which compacted soil was represented by a matrix domain and uncompacted soil by a fracture domain and eventually by assuming an additional immobile water region (MIM) in the fracture domain representing compacted clods embedded within the uncompacted soil. Models (1D) were compared with two‐dimensional single‐porosity (2D_SP) modeling results for water flow and Br− transport based on a previously performed field tracer experiment. Results indicated good agreement between 1D dual‐domain approaches (1D_DPERM and 1D_DPERM_MIM) and the 2D_SP representative model simulation results with high model efficiency and with respect to the field observations. This implied that a 1D vertical model description was sufficient to represent plot‐scale variability if smaller scale soil structure heterogeneities could be accounted for as effective parameters in dual‐domain models. Variation in the mass transfer term had a large effect on the vertical Br− profile distribution. The parameters describing the sizes and shapes of the domains were most relevant for estimating mass transfer between soil structural features in heterogeneous agricultural fields. Still, the calibration of the upscaling approach of two‐domain interactions in larger scale models remains challenging.

Incorporation of Numerical Plume Rise Algorithms in the Lagrangian Particle Model LAPMOD and Validation against the Indianapolis and Kincaid Datasets

This paper describes the methodology used to incorporate two numerical plume rise algorithms, one by Janicke and Janicke and another by Webster and Thomson, into the Lagrangian particle model LAPMOD. LAPMOD is fully interfaced with the diagnostic meteorological model CALMET, which is part of the widely used CALPUFF modeling system. LAPMOD can also use the meteorological input files produced with the AERMET meteorological processor of the US-EPA recommended model AERMOD. This paper outlines the theory behind the two plume rise algorithms and the details of their implementation in LAPMOD. The paper also provides the results of the evaluation of LAPMOD and its included plume rise algorithms against the well-known Indianapolis and Kincaid SF6 and SO2 field studies and tracer experiments. The performance of LAPMOD is successfully evaluated with the Model Evaluation Kit and compared with that of other air quality models.

Inverse uncertainty characteristics of pollution source identification for river chemical spill incidents by stochastic analysis

Identifying source information after river chemical spill occurrences is critical for emergency responses. However, the inverse uncertainty characteristics of this kind of pollution source inversion problem have not yet been clearly elucidated. To fill this gap, stochastic analysis approaches, including a regional sensitivity analysis method, identifiability plot and perturbation methods, were employed to conduct an empirical investigation on generic inverse uncertainty characteristics under a well-accepted uncertainty analysis framework. Case studies based on field tracer experiments and synthetic numerical tracer experiments revealed several new rules. For example, the release load can be most easily inverted, and the source location is responsible for the largest uncertainty among the source parameters. The diffusion and convection processes are more sensitive than the dilution and pollutant attenuation processes to the optimization of objective functions in terms of structural uncertainty. The differences among the different objective functions are smaller for instantaneous release than for continuous release cases. Small monitoring errors affect the inversion results only slightly, which can be ignored in practice. Interestingly, the estimated values of the release location and time negatively deviate from the real values, and the extent is positively correlated with the relative size of the mixing zone to the objective river reach. These new findings improve decision making in emergency responses to sudden water pollution and guide the monitoring network design.

Prediction of the wind speed probabilities in the atmospheric surface layer

Abstract Accurate prediction of the wind speed probabilities in the atmospheric surface layer is very important for wind energy assessment studies and many other practical applications such as the design and operation of wind turbines and human exposure to wind extremes. In a recent study, an optimized beta distribution was developed for the prediction of the wind speed probabilities in the atmospheric surface layer. Various uncertainties arise in real scenarios due to the composite atmospheric variability, the topography of the terrain, nearby obstacles, orographical features, and other synoptic conditions. Thus, in the first part of this study, the beta distribution is validated further with the wind speed database of the FUSION Field Trial 2007 (FFT-07) tracer field experiment for various atmospheric stability conditions. The model is applied without any change in its constants and a high degree of agreement with the field experiment is achieved. One main advantage of the proposed beta distribution is that it can be incorporated in computational models that are able to predict the mean, the variance and the integral time scale of the wind speed. The second part of the paper includes the incorporation of the beta distribution in the Reynolds Averaged Navier Stokes (RANS) methodology. Initially, the “RANS-beta” model is validated against wind speed measurements performed in a wind tunnel over a rough ground. The wind speed 25th, 50th and 75th percentiles were found to be highly dependent on the height and the model gave comparable results with the experiment. Then, the wind speed database of the field experiment JU2003 is used to examine the “RANS-beta” model's performance. The 25th, 50th, 75th and 95th model percentiles at 20 sensors located inside the complex urban area were found to be in good agreement with the experimental ones (FAC2 = 0.8).

Formulation of the Lagrangian particle model LAPMOD and its evaluation against Kincaid SF6 and SO2 datasets

This paper presents the Lagrangian particle model LAPMOD for modeling time-variable emissions in atmosphere of inert and radioactive gases and aerosols. LAPMOD is fully interfaced with the meteorological model CALMET (Scire et al., 1999a), part of the US-EPA recommended CALPUFF modeling system (EPA, 2017), and can also use the meteorological input files produced with the AERMET meteorological processor of US-EPA recommended model AERMOD (EPA, 2004).The paper outlines the theory on which LAPMOD is based and provides the results of the evaluation of LAPMOD against the Kincaid SF6 and SO2 classical field studies and tracer experiments. The performance of LAPMOD is successfully evaluated with the Model Evaluation Kit (Olesen, 2005) and compared with that of other air quality models.

Ensemble-based release estimation for accidental river pollution with known source position

Dispersion model is an important tool for decision makers to accurately assess risks and effectively plan countermeasures during river pollution accidents, but their applications suffer from significant modeling uncertainties, primarily due to the scarce information of the source. A fully sequential inverse estimation method is proposed to reconstruct the temporal release for accidental river pollution. The method is based on a one-dimensional advection-dispersion model in conjunction with the augmented ensemble Kalman filter method. Detailed analysis of the ensemble background error covariance (BEC) matrix is conducted to elucidate the “flow-dependent” mechanism, which enables the inversion method to simultaneously take into account the uncertainties in the hydrological parameters (mean flow velocity and longitudinal dispersion coefficient). The method is evaluated with six field tracer experiments with various mean flow velocities, ranging from 0.085 to 0.889ms−1, and also compared with the commonly used Tikhonov regularization inverse estimation method to demonstrate its performance improvement. The results indicate that it successfully reconstructs the temporal release and reduces the relative errors of the total release estimation by about 12.4% on average compared with the Tikhonov method, since the errors caused by the uncertainties in mean flow velocity and longitudinal dispersion coefficient are effectively alleviated.

A forward-backward coupled source term estimation for nuclear power plant accident: A case study of loss of coolant accident scenario

Source term information of radioactive release in a nuclear accident is important for emergency response. Two major categories of source term estimation techniques are forward method based on the status data of nuclear power plant and backward method based on environmental monitoring data. Both data contain considerable uncertainties which can propagate through estimation and result in a biased estimate. To solve the problem, a coupled estimation method is proposed in this study, which combines forward method (Response Technical Manual, RTM-96) and backward method (ensemble Kalman filter). The coupled method builds an evolution model based on a forward estimate and uses it to constrain the temporal correlation of estimates in the backward part, so that the propagation of uncertainties is reduced. Numerical experiments and sensitivity analysis are performed to verify the proposed method, based on a hypocritical loss-of-coolant (LOCA) accident process and the records of a tracer field experiment for Sanmen nuclear power plant. The results demonstrate that the coupled method provides the most accurate estimate in all tests and is more robust to uncertainties in various parameters than both RTM-96 and ensemble Kalman filter.

Modeling of sorption and degradation of selected pharmaceuticals: Case study of Belgrade groundwater source

The application of a mathematical model that analyzes the transport of selected pharmaceuticals from the Sava River to a corresponding radial collector well at Belgrade?s groundwater source is assessed. The occurrence of the selected pharmaceuticals in surface water and the corresponding well was monitored from 2009 to 2015. The pharmaceuticals selected for the present study are carbamazepine, trimethoprim, and metamizole metabolites 4-AAA and 4-FAA. Transport is analyzed based on experimental data (sorption isotherms) and a field tracer experiment that includes injection of the selected pharmaceuticals. The analysis shows that sorption of carbamazepine is relatively low and that this pharmaceutical does not degrade under the studied conditions, so it is not possible to accurately determine the degradation half-life. Trimethoprim is detected in the Sava River with an average concentration 8.5 ng/L, but there is no positive detection in well Rb-16. The average concentration of 4-AAA in the surface water is 34 ng/L and of 4-FAA 13 ng/L. The average concentrations of 4-FAAand 4-AAA in the groundwater are in the range from 1 and 1.85 ng/L. The objective of the research is to use an existing hydrogeologic model and apply a transport model to determine the minimum degradation half-life of the investigated pharmaceuticals.

Application of the Approximate Bayesian Computation methods in the stochastic estimation of atmospheric contamination parameters for mobile sources

In this paper the Bayesian methodology, known as Approximate Bayesian Computation (ABC), is applied to the problem of the atmospheric contamination source identification. The algorithm input data are on-line arriving concentrations of the released substance registered by the distributed sensors network. This paper presents the Sequential ABC algorithm in detail and tests its efficiency in estimation of probabilistic distributions of atmospheric release parameters of a mobile contamination source. The developed algorithms are tested using the data from Over-Land Atmospheric Diffusion (OLAD) field tracer experiment. The paper demonstrates estimation of seven parameters characterizing the contamination source, i.e.: contamination source starting position (x,y), the direction of the motion of the source (d), its velocity (v), release rate (q), start time of release (ts) and its duration (td). The online-arriving new concentrations dynamically update the probability distributions of search parameters. The atmospheric dispersion Second-order Closure Integrated PUFF (SCIPUFF) Model is used as the forward model to predict the concentrations at the sensors locations.

A Case Study of the Weather Research and Forecasting Model Applied to the Joint Urban 2003 Tracer Field Experiment. Part 2: Gas Tracer Dispersion

The Quick Urban & Industrial Complex (QUIC) atmospheric transport, and dispersion modelling, system was evaluated against the Joint Urban 2003 tracer-gas measurements. This was done using the wind and turbulence fields computed by the Weather Research and Forecasting (WRF) model. We compare the simulated and observed plume transport when using WRF-model-simulated wind fields, and local on-site wind measurements. Degradation of the WRF-model-based plume simulations was cased by errors in the simulated wind direction, and limitations in reproducing the small-scale wind-field variability. We explore two methods for importing turbulence from the WRF model simulations into the QUIC system. The first method uses parametrized turbulence profiles computed from WRF-model-computed boundary-layer similarity parameters; and the second method directly imports turbulent kinetic energy from the WRF model. Using the WRF model’s Mellor-Yamada-Janjic boundary-layer scheme, the parametrized turbulence profiles and the direct import of turbulent kinetic energy were found to overpredict and underpredict the observed turbulence quantities, respectively. Near-source building effects were found to propagate several km downwind. These building effects and the temporal/spatial variations in the observed wind field were often found to have a stronger influence over the lateral and vertical plume spread than the intensity of turbulence. Correcting the WRF model wind directions using a single observational location improved the performance of the WRF-model-based simulations, but using the spatially-varying flow fields generated from multiple observation profiles generally provided the best performance.

Coarse bedload routing and dispersion through tributary confluences

Abstract. Sediment routing fundamentally influences channel morphology and the propagation of disturbances such as debris flows. The transport and storage of bedload particles across headwater channel confluences, which may be significant nodes of the channel network in terms of sediment routing, morphology, and habitat, are poorly understood, however. We investigated patterns and processes of sediment routing through headwater confluences by comparing them to published results from lower-gradient confluences and by comparing the dispersive behavior of coarse bedload particles between headwater confluence and non-confluence reaches. We addressed these questions with a field tracer experiment using passive-integrated transponder and radio-frequency identification technology in the East Fork Bitterroot River basin, Montana, USA. Within the confluence zone, tracers tended to be deposited towards scour-hole and channel margins, suggesting narrow, efficient transport corridors that mirror those observed in prior studies, many of which are from finer-grained systems. Coarse particles in some confluence reaches experienced reduced depositional probabilities within the confluence relative to upstream and downstream of the confluence. Analysis of particle transport data suggests that variation in the spatial distribution of coarse-sediment particles may be enhanced by passing through confluences, though further study is needed to evaluate confluence effects on dispersive regimes and sediment routing on broader spatial and temporal scales.

An analysis of error propagation in AERMOD lateral dispersion using Round Hill II and Uttenweiller experiments in reduced averaging times

ABSTRACTDispersion modelling was proved by researchers that most part of the models, including the regulatory models recommended by the Environmental Protection Agency of the United States (AERMOD and CALPUFF), do not have the ability to predict under complex situations. This article presents a novel evaluation of the propagation of errors in lateral dispersion coefficient of AERMOD with emphasis on estimate of average times under 10 min. The sources of uncertainty evaluated were parameterizations of lateral dispersion (), standard deviation of lateral wind speed () and processing of obstacle effect. The model’s performance was tested in two field tracer experiments: Round Hill II and Uttenweiller. The results show that error propagation from the estimate of directly affects the determination of , especially in Round Hill II experiment conditions. After average times are reduced, errors arise in the parameterization of , even after observation assimilations of , exposing errors on Lagrangian Time Scale parameterization. The assessment of the model in the presence of obstacles shows that the implementation of a plume rise model enhancement algorithm can improve the performance of the AERMOD model. However, these improvements are small when the obstacles have a complex geometry, such as Uttenweiller.

Performance evaluation of inertial pumps used for sampling groundwater from small-diameter wells

Sampling water from small-diameter wells using narrow access tubes is a challenging problem in field research efforts. In this study, a simple, easy-to-use embedded inertial pump is used for sampling groundwater from small-diameter wells. Performance of the embedded inertial pumps with different designs was demonstrated at a high-resolution field tracer experiment site near Beijing, China. Tests on the effects of primary pump design variables (stroke frequency, amplitude and diameter of pump tube) and secondary variable (ball valve diameter, the distance between hollow cylinders, and slot depths) were conducted. A linear equation is set up to describe the relationship between flow rate and primary pump design variables. The data show that a motion frequency value of 1–4 Hz and amplitude around 20 cm could satisfy effective groundwater sampling for both manual and automotive operations. The ball valve diameter should be designed to accommodate the delivery tube and hollow cylinders, because it determines the overall effective cross-sectional area; higher sectional area implies higher flow rate. The distance between hollow cylinders is recommended as 1.5–2 times of ball valve diameter. The proposed pump design is a low-cost approach for sampling from multi-channel wells, which are used for conducting three-dimensional tracer tests or groundwater monitoring that requires sampling at high temporal and spatial resolution.

A Case Study of the Weather Research and Forecasting Model Applied to the Joint Urban 2003 Tracer Field Experiment. Part 1: Wind and Turbulence

Numerical-weather-prediction models are often used to supply the mean wind and turbulence fields for atmospheric transport and dispersion plume models as they provide dense horizontally- and vertically-resolved geographic coverage in comparison to typically sparse monitoring networks. Here, the Weather Research and Forecasting (WRF) model was run over the month-long period of the Joint Urban 2003 field campaign conducted in Oklahoma City and the simulated fields important to transport and dispersion models were compared to measurements from a number of sodars, tower-based sonic anemometers, and balloon soundings located in the greater metropolitan area. Time histories of computed wind speed, wind direction, turbulent kinetic energy (e), friction velocity ( $$u_*$$ ), and reciprocal Obukhov length (1 / L) were compared to measurements over the 1-month field campaign. Vertical profiles of wind speed, potential temperature ( $$\theta $$ ), and e were compared during short intensive operating periods. The WRF model was typically able to replicate the measured diurnal variation of the wind fields, but with an average absolute wind direction and speed difference of $$35^\circ $$ and $$1.9\hbox { m s}^{-1}$$ , respectively. Using the Mellor-Yamada-Janjic (MYJ) surface-layer scheme, the WRF model was found to generally underpredict surface-layer TKE but overpredict $$u_*$$ that was observed above a suburban region of Oklahoma City. The TKE-threshold method used by the WRF model’s MYJ surface-layer scheme to compute the boundary-layer height (h) consistently overestimated h derived from a $$\theta $$ gradient method whether using observed or modelled $$\theta $$ profiles.

Power law breakthrough curve tailing in a fracture: The role of advection

summary We offer an explanation of the strongly tailed solute breakthrough curve typically observed when a tracer test is conducted in fractured bedrock. In this example, we limit the model to a single planar fracture of varying aperture. Flow heterogeneity derives from variable fracture aperture, which implies variable transmissivity (T). The analysis employs a physically based model well-suited to strong heterogeneity and relies only upon advective transport. The purely advective model is able to explain a power-law trend of magnitude � 2t o� 3 in the breakthrough curve tail; a range that has been found in field tracer experiments. The principle cause of this trend is the comparatively slow transport in zones of small transmissivity (tight aperture). Slow advection occurs when either heterogeneity (variance of ln T )i s strong or when the assumed heterogeneity distribution is non-Gaussian. Thus, we link breakthrough tailing to the statistical parameters for the transmissivity field.

Pollutant Spreading in a Small Stream: A Case Study in Mala Nitra Canal in Slovakia

The Water Framework Directive requires as an obligatory goal to achieve and to keep “good water quality” status within the defined period (for Slovakia—up to the year 2015). For surface waters, the main criterion is the ecological and chemical status of the water. Mathematical and numerical modelling allows evaluating various situations of contaminants spreading in rivers (from everyday wastewater disposal through fatal accidents and discharges of the toxic substances) without immediate destructive impact to the environment. Determination of longitudinal and transverse dispersion coefficient values, as the main hydrodynamic characteristics of the dispersion, has the highest extent of uncertainty for hydrodynamic models simulating pollutant transport in streams. This paper deals with the determination of dispersion coefficients based on field tracer experiments performed in a small modified stream (basic hydrodynamic parameters during the experiments were: discharge Q = 0.138–0.553 m3.s−1, depth h = 0.29–0.48 m, width B = 5.2–5.9 m). During the experiments, various conditions and situations were taken into account, e.g., continuous and instantaneous pollution source, as well as various positions of pollution source along the river width, among others. Field measurements were evaluated using three different methods for dispersion coefficient determination: based on statistical evaluation, based on analytical solutions of advection–dispersion equation, and using numerical models. The dimensionless dispersion coefficients values were determined, which can be used for numerical simulation of pollutant transport in similar types of streams.

방사능 확산 검증을 위한 악기상 조건에서의 추적자 야외확산 실증실험

방사능 확산 검증을 위한 악기상 조건에서의 추적자 야외확산 실증실험

Characteristics of Groundwater Recharge on the North China Plain

Groundwater recharge is an important component of the groundwater system. On the North China Plain (NCP), groundwater is the main water supply. Because of large-scale overexploitation, the water table has declined, which has produced severe adverse effects on the environment and ecosystem. In this article, tracer experiment and watershed model were used to calculate and analyze NCP groundwater recharge. In the tracer experiment, average recharge was 108 mm/year and recharge coefficient 0.16. With its improved irrigation, vegetation coverage and evapotranspiration modules, the INFIL3.0 model was used for calculation of groundwater recharge. Regional modeling results showed an average recharge of 102 mm/year and recharge coefficient 0.14, for 2001-2009. These values are very similar to those from the field tracer experiment. Influences in the two methods were analyzed. The results can provide an important reference for NCP groundwater recharge.

Characterizing Heterogeneous Processes of Water Flow and Solute Transport in Soils Using Multiple Tracer Experiments

It is important yet challenging to adequately describe heterogeneous flow processes in soils. The objectives of this study were to “visualize” heterogeneous processes of water flow and solute transport in soils by using multiple tracers and to quantify heterogeneities of soil water flow and solute transport by using a discrete random cascade model. Field tracer experiments on two soils were conducted with sequences of iodine–nitrate and iodine–bromide mixtures. On the basis of the experimental data, a random cascade model, an annular histogram, and a similarity index were applied to characterize the heterogeneous flow and transport processes in the soils. Results showed that water and solute penetrated into deep soil preferentially mainly because of the macropore flow. At the beginning of infiltration, the solute transport heterogeneity was mainly related to the saturation process of soil macropores. As more water infiltrated into the soil, the solute transport heterogeneity was mainly attributable to the change of flow paths. After the macropores were saturated, unstable infiltration fronts resulted in the transport heterogeneity. The experimental data and analyses of the random cascade model demonstrated that the solute transport process included more heterogeneous information than the heterogeneous water flow, which was related to the soil heterogeneity, water flow heterogeneity, and the heterogeneity of the solute transport itself.

Displacement characteristics of coarse fluvial bed sediment

AbstractPrevious work highlights the need for data collection to identify appropriate models for temporal evolution of tracer dispersal in rivers. Results of 64 gravel‐bed field tracer experiments covering a wide range of flow and sediment supply regimes are compiled here to determine the probabilistic character of gravel transport. We focus on whether particle travel distances and waits are thin‐ or heavy‐tailed. While heavy‐tailed travel distance distributions are observed between successive monitoring events in different hydrological and sediment supply regimes, heavy‐tailedness does not persist through total travel distance over multiple monitoring events, suggesting that individual monitoring events occur before particle travel distance exceeds the characteristic correlation length for the channel (such that particles that start in fast paths remain in fast paths and particles in slow paths remain in slow paths). After a large number of transport events, super‐diffusive spreading was not observed at any of the gravel bed streams. Continuous‐time tracking of x, y, z coordinates of tracers in natural streams is necessary to capture exact step and waiting time distributions.