Ensemble Kalman filter versus ensemble smoother for assessing hydraulic conductivity via tracer test data assimilation

Abstract. Estimating the spatial variability of hydraulic conductivity K in natural aquifers is important for predicting the transport of dissolved compounds. Especially in the nonreactive case, the plume evolution is mainly controlled by the heterogeneity of K. At the local scale, the spatial distribution of K can be inferred by combining the Lagrangian formulation of the transport with a Kalman-filter-based technique and assimilating a sequence of time-lapse concentration C measurements, which, for example, can be evaluated on site through the application of a geophysical method. The objective of this work is to compare the ensemble Kalman filter (EnKF) and the ensemble smoother (ES) capabilities to retrieve the hydraulic conductivity spatial distribution in a groundwater flow and transport modeling framework. The application refers to a two-dimensional synthetic aquifer in which a tracer test is simulated. Moreover, since Kalman-filter-based methods are optimal only if each of the involved variables fit to a Gaussian probability density function (pdf) and since this condition may not be met by some of the flow and transport state variables, issues related to the non-Gaussianity of the variables are analyzed and different transformation of the pdfs are considered in order to evaluate their influence on the performance of the methods. The results show that the EnKF reproduces with good accuracy the hydraulic conductivity field, outperforming the ES regardless of the pdf of the concentrations

Effects of temperature on flood forecasting: analysis of an operative case study in Alpine basins

Abstract. In recent years the interest in the forecast and prevention of natural hazards related to hydro-meteorological events has increased the challenge for numerical weather modelling, in particular for limited area models, to improve the quantitative precipitation forecasts (QPF) for hydrological purposes. After the encouraging results obtained in the MAP D-PHASE Project, we decided to devote further analyses to show recent improvements in the operational use of hydro-meteorological chains, and above all to better investigate the key role played by temperature during snowy precipitation. In this study we present a reanalysis simulation of one meteorological event, which occurred in November 2008 in the Piedmont Region. The attention is focused on the key role of air temperature, which is a crucial feature in determining the partitioning of precipitation in solid and liquid phase, influencing the quantitative discharge forecast (QDF) into the Alpine region. This is linked to the basin ipsographic curve and therefore by the total contributing area related to the snow line of the event. In order to assess hydrological predictions affected by meteorological forcing, a sensitivity analysis of the model output was carried out to evaluate different simulation scenarios, considering the forecast effects which can radically modify the discharge forecast. Results show how in real-time systems hydrological forecasters have to consider also the temperature uncertainty in forecasts in order to better understand the snow dynamics and its effect on runoff during a meteorological warning with a crucial snow line over the basin. The hydrological ensemble forecasts are based on the 16 members of the meteorological ensemble system COSMO-LEPS (developed by ARPA-SIMC) based on the non-hydrostatic model COSMO, while the hydrological model used to generate the runoff simulations is the rainfall–runoff distributed FEST-WB model, developed at Politecnico di Milano

Modeling rainfall-driven transport of Glyphosate in the vadose zone of two experimental sites in North-East Italy

A vertical one-dimensional analysis of infiltration processes and mobility of a tracer (potassium bromide) and a glyphosate-based herbicide, both subjected to hydrological forcing, was performed. Glyphosate is a widespread herbicide whose potential harmfulness and mobility under hydrological forcing have not been fully understood yet. Here, the spatio-temporal evolution of the two compounds was monitored for one year in two experimental sites (Settolo - Valdobbiadene, Colnù - Conegliano), located within the production area of the Prosecco wine (Treviso, Italy). In each experimental site the activities were carried out on two 25 m2 plots located at distances of 50-100 m from each other. The interpretative analyses considered rainwater infiltration as the driving mechanism of the herbicide transport and allowed us to obtain the calibration of a one-dimensional hydrologic model in each monitored plot. Different scenarios of the tracer evolution were simulated considering the pedologic properties of the shallower soil layers, the status of the plant coverage and of the root apparati, leading to a satisfactory reproduction of the observations in both the experimental sites. Modeling the mobility of the herbicide, considering also the degradation to its metabolite AMPA, proved to be more challenging, due to the tendency of glyphosate to be adsorbed to the soil matrix rather than be dissolved in water and transported toward deeper soil layers. Nevertheless, the analysis of model results for tracer and herbicide, compared with in situ observations, suggests that the transport of the glyphosate can take place even when it is adsorbed to the soil, through the movement, triggered by intense precipitation events, of microscopic soil particles within preferential flow paths

Torino: A Tangible Programming Language Inclusive of Children with Visual Disabilities

© 2018, Copyright © 2018 Taylor & Francis Group, LLC. Across the world, policy initiatives are being developed to engage children with computer programming and computational thinking. Diversity and inclusion has been a strong force in this agenda, but children with disabilities have largely been omitted from the conversation. Currently, there are no age appropriate tools for teaching programming concepts and computational thinking to primary school children with visual disabilities. We address this gap through presenting the design and implementation of Torino, a tangible programming language for teaching programming concepts to children age 7–11 regardless of level of vision. In this paper, we: (1) describe the design process done in conjunction with children with visual disabilities; (2) articulate the design decisions made; and (3) report insights generated from an evaluation with 10 children with mixed visual abilities that considers how children are able to trace (read) and create (write) programs with Torino. We discuss key design trade-offs: (1) readability versus extensibility; and (2) size versus liveness. We conclude by reflecting upon how an inclusive design approach shaped the final result

Sviluppo di piastre dinamometriche per la misura in pista dei carichi su tavole da sci

Aim of the work was the development of dynamometric plates suitable for application to racing skis with the minimum mass and stiffening effect: commercially available dynamometric plates or customized systems presented in literature are still very heavy and in most cases based on the presence of a very stiff central plate preventing the ski from its free bending behaviour. The developed system is based on two independent plates enabling to measure three forces and one moment (with axis parallel to the ski) at the front-rear bindings: the plates correspond to the original behaviour of the racing plates. The system was calibrated and validated after laboratory tests

Comparison of coupled hydrogeophysical inversion techniques for salt tracer experiments

Evolutionary optimization algorithms are known as reliable optimization methods, but they are typically associated with a high computational effort. This is especially true for cases where a large number of model parameters are being optimized, as is the case with the application of electrical resistivity tomography (ERT) to infer the spatio-temporal state of the subsurface water or soil hydrological properties. Suitable alternatives are represented by Bayesian methods, such as the ensemble Kalman filter (EnKF). This is a Monte Carlo-based data assimilation approach that can be effectively used for combined state and parameter estimation. In this contribution, we compare a hierarchical approach for optimization using a genetic algorithm (GA), which was specifically developed to reduce the computational effort, with an EnKF-based approach. The test case for this comparison is focused on the determination of hydraulic conductivity from monitoring of salt tracer tests by ERT. We report on the retrieval performance of the two approaches for a two-dimensional synthetic experiment simulating the evolution of a saline tracer in a shallow aquifer and we discuss some of the strengths and weaknesses of the GA and EnKF optimization strategies

Assessment of local hydraulic properties from Electrical Resistivity Tomography monitoring of tracer test experiments

In recent years geophysical methods have been used increasingly as tools for subsurface transport process characterization. Time-lapse electrical resistivity imaging (ERT) represents a powerful tool for solute transport characterization since a full picture of the spatio-temporal evolution of the process can be obtained. This method can provide spatially and temporally highly resolved information on subsurface parameters which are closely linked to both structural and transport properties. However, a quantitative interpretation of solute tracer experiments is made difficult by the uncertainty related to the ERT data inversion as well as to the a priori unknown hydraulic properties (e.g. porosity, hydraulic conductivity, storativity, etc.) in heterogeneous natural formations. For a conservative solute, also the (arbitrary) initial state of the plume, as defined by its concentration field, controls the subsequent evolution of solute cloud. Here an approach based on the Lagrangian formulation of transport and the ensemble Kalman Filter (EnKF) data assimilation technique is suggested to analyze cross-hole ERT data. The data consist of 3D cross-hole ERT images generated for a synthetic heterogeneous aquifer. Under the assumption that the solute spreads as a passive tracer, for high values of the Peclet number the spatial moments of the evolving plume are dominated by the porosity and the spatial distribution of the hydraulic conductivity. The assimilation of resistivity measurements in terms of low-order spatial concentration moments allows the update of the system state vector, including information about the spatial distribution of hydraulic conductivity. Thus, the assessment of both the concentration evolution and the delineation of the local aquifer heterogeneity can be achieved at the same time by the new methodology proposed to interpret time-lapse electrical images from tracer test experiments. Moreover, the influence of inherent uncertainty in ERT inversion of the same synthetic tracer test experiment is investigated

Electrical resistivity tomography time-lapse monitoring of three-dimensional synthetic tracer test experiments

In recent years geophysical methods have become increasingly popular for hydrological applications. Time-lapse electrical resistivity tomography (ERT) represents a potentially powerful tool for subsurface solute transport characterization since a full picture of the spatio-temporal evolution of the process can be obtained. However, the quantitative interpretation of tracer tests is difficult because of the uncertainty related to the geo-electrical inversion, the constitutive models linking geophysical and hydrological quantities, and the a priori unknown heterogeneous properties of natural formations. Here a new approach based on the Lagrangian formulation of trans port and the ensemble Kalman filter (EnKF) data assimilation technique is applied to assess the spatial distribution of hydraulic conductivity K by incorporating time-lapse cross-hole ERT data. Electrical data consist of three-dimensional cross-hole ERT images generated for a synthetic tracer test in a heterogeneous aquifer. Under the assumption that the solute spreads as a passive tracer, for high Peclet numbers the spatial moments of the evolve ing plume are dominated by the spatial distribution of the hydraulic conductivity. The assimilation of the electrical conductivity 4D images allows updating of the hydrological state as well as the spatial distribution of K. Thus, delineation of the tracer plume and estimation of the local aquifer heterogeneity can be achieved at the same time by means of this interpretation of time-lapse electrical images from tracer tests. We assess the impact on the performance of the hydrological inversion of i) the uncertainty inherently affecting ERT inversions in terms of tracer concentration and ii) the choice of the prior statistics of K