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15 figures, 2 tables., In this study, a 2D shallow water flow solver integrated with a water quality model is presented. The interaction between the main water quality constituents included is based on the Water Quality Analysis Simulation Program. Efficiency is achieved by computing with a combination of a Central Processing Unit (CPU) and a Graphics Processing Unit (GPU) device. This technique is intended to provide robust and accurate simulations with high computation speedups with respect to a single-core CPU in real events. The proposed numerical model is evaluated in cases that include the transport and reaction of water quality components over irregular bed topography and dry–wet fronts, verifying that the numerical solution in these situations conserves the required properties (C-property and positivity). The model can operate in any steady or unsteady form allowing an efficient assessment of the environmental impact of water flows. The field data from an unsteady river reach test case are used to show that the model is capable of predicting the measured temporal distribution of dissolved oxygen and water temperature, proving the robustness and computational efficiency of the model, even in the presence of noisy signals such as wind speed., This work was funded by the Spanish Ministry of Science and Innovation under the research project PGC2018-094341-B-I00. Additionally, Mario Morales-Hernández was partially supported by the U.S. Air Force Numerical Weather Modeling Program.

15 figures, 1 table., Coupled 1D2D models emerged as an efficient solution for a two-dimensional (2D) representation of the floodplain combined with a fast one-dimensional (1D) schematization of the main channel. At the same time, high-performance computing (HPC) has appeared as an efficient tool for model acceleration. In this work, a previously validated 1D2D Central Processing Unit (CPU) model is combined with an HPC technique for fast and accurate flood simulation. Due to the speed of 1D schemes, a hybrid CPU/GPU model that runs the 1D main channel on CPU and accelerates the 2D floodplain with a Graphics Processing Unit (GPU) is presented. Since the data transfer between sub-domains and devices (CPU/GPU) may be the main potential drawback of this architecture, the test cases are selected to carry out a careful time analysis. The results reveal the speed-up dependency on the 2D mesh, the event to be solved and the 1D discretization of the main channel. Additionally, special attention must be paid to the time step size computation shared between sub-models. In spite of the use of a hybrid CPU/GPU implementation, high speed-ups are accomplished in some cases., This work is part of the PGC2018-094341-B-I00 research project funded by the Ministry of Science and Innovation/FEDER. Additionally, Mario Morales-Hernández was partially supported by the U.S. Air Force Numerical Weather Modeling Program.

This work presents a vision of future water resources hydrodynamics codes that can fully utilize the strengths of modern high-performance computing (HPC). The advances to computing power, formerly driven by the improvement of central processing unit processors, now focus on parallel computing and, in particular, the use of graphics processing units (GPUs). However, this shift to a parallel framework requires refactoring the code to make efficient use of the data as well as changing even the nature of the algorithm that solves the system of equations. These concepts along with other features such as the precision for the computations, dry regions management, and input/output data are analyzed in this paper. A 2D multi-GPU flood code applied to a large-scale test case is used to corroborate our statements and ascertain the new challenges for the next-generation parallel water resources codes.

In this work, a one-dimensional (1D) finite volume numerical model for the unsteady simulation of the flow hydrodynamics and water quality is developed. The water dynamics is formulated with the 1D shallow water equations, and the water quality evolution is described by the Water Quality Analysis Simulation Program (WASP) model, allowing us to interpret and predict the transport and fate of various biochemical substances along any river reach. This combined system is solved with an explicit finite volume scheme based on Roe's linearization for the advection component of both the flow and the solute transport equations. The proposed model is able to consider temporal variations in tributaries and abstractions occurring in the river basin. This feature is transcendent in order to predict the chemical composition of natural water bodies during winter and summer periods, leading to an improvement in the agreement between computed and observed water quality evolutions. The combined model has been evaluated using literature tests in a steady state and a real-field case of the Ebro river (Spain), characterized by a marked unsteady regime. In the real case, we found that the water temperature was very sensitive to both the solar radiation and the average air temperature, requiring a careful calibration of these parameters. The numerical results are also demonstrated to be reasonably accurate, conservative and robust in real-scale field cases, showing that the model is able to predict the evolution of quality parameters as well as hydrodynamic variables in complex scenarios.

Studying rotational variability of young stars is enabling us to investigate a multitude of properties of young star-disk systems. We utilise high cadence, multi-wavelength optical time series data from the Hunting Outbursting Young Stars citizen science project to identify periodic variables in the Pelican Nebula (IC5070). A double blind study using nine different period-finding algorithms was conducted and a sample of 59 periodic variables was identified. We find that a combination of four period finding algorithms can achieve a completeness of 85% and a contamination of 30% in identifying periods in inhomogeneous data sets. The best performing methods are periodograms that rely on fitting a sine curve. Utilising GaiaEDR3 data, we have identified an unbiased sample of 40 periodic YSOs, without using any colour or magnitude selections. With a 98.9% probability we can exclude a homogeneous YSO period distribution. Instead we find a bi-modal distribution with peaks at three and eight days. The sample has a disk fraction of 50%, and its statistical properties are in agreement with other similarly aged YSOs populations. In particular, we confirm that the presence of the disk is linked to predominantly slow rotation and find a probability of 4.8$\times$10$^{-3}$ that the observed relation between period and presence of a disk has occurred by chance. In our sample of periodic variables, we also find pulsating giants, an eclipsing binary, and potential YSOs in the foreground of IC5070., Comment: 25 pages, 14 figures, 5 tables, accepted for publication in MNRAS

This study shows the energy potential of pine wood waste for the production of solid biofuels, and was carried out in an indigenous community in the state of Michoacán. One of the main economic activities of this community is the production of handcrafted furniture, which generates a large amount of wood waste. The most relevant results obtained in this research show that the community generates approximately 2268 kg of sawdust and 5418 kg of shavings per week, and the estimated energy potential per year for both sawdust is 1.94 PJ and for shaving is 4.65 PJ. Based on the particle size observed, the wood residue can be used to generate pellets or briquettes. Other average results in sawdust and (shavings) are the following: initial moisture content 15.3% (16.8%), apparent density 169.23 kg/m3 (49.25 kg/m3), ash 0.43% (0.42%), volatile material 84.9% (83.60%), fixed carbon 14.65% (15.96%), hemicelluloses 12.89% (10.68%), cellulose 52.68% (52.82%), lignin 26.73% (25.98%), extractives 7.69% (10.51%), calorific value 17.6 MJ/kg (17.9 MJ/kg). The major chemical elements in the ash were Al, K. Fe, Ca, P, Na, and Mg. Finally, the results obtained indicate that this biomass can be used to generate pellets or briquettes in this indigenous community.

This study presents a prospective study for the potential exploitation of pelagic Sargassum spp. as a solid biofuel energy source. It was carried out in three stages. First we conducted a morphological, physical-chemical, and structural characterization using scanning electron microscopy (SEM), infrared spectroscopy (FTIR), and X-ray diffraction (DRX), respectively. Second we evaluated the material&rsquo, s functional properties as a solid biofuel based on its calorific value and the quantification of polymeric components like hemicellulose, cellulose, and lignin, as well as thermogravimetric and differential analysis to study the kinetics of its pyrolysis and determine parameters like activation energy (Ea), reaction order (n), and the pre-exponential factor (Z). Third we analyzed the energetic potential considering the estimated volume of pelagic Sargassum spp. that was removed from beaches along the Mexican Caribbean coast in recent years. Results of the kinetic study indicate that Sargassum spp. has an enormous potential for use as a complement to other bioenergy sources. Other results show the high potential for exploiting these algae as an energy source due to the huge volumes that have inundated Caribbean, West African, and northern Brazil shorelines in recent years. As a solid biofuel, Sargassum spp. has a potential energy the order of 0.203 gigajoules (GJ)/m3. In the energy matrix of the residential sector in Mexico, its potential use as an energy source is comparable to the national consumption of firewood. The volume of beachcast Sargassum spp. that was removed from ~8 km of coastline around Puerto Morelos, Mexico in 2018&ndash, 2019, could have generated over 40 terajoules/year of solid biofuel.

32 figures, 7 tables., Culverts allow roads to safely traverse small streams or drainage ditches, and their proper design is critical to ensure a safe and reliable transportation network. A correct modelization of these hydraulic structures becomes crucial in the assessment of flood footprints or discharge peak estimation in a risk evaluation plan. The question of how to include culverts comes up frequently when assembling a hydraulic model that requires the presence of as many singular elements as possible. In this work, three different culvert integrations with the surface domain are studied and compared in the context of a 2D shallow water (SW) model. All of them are based on the Federal Highway Administration (FHWA) formulation for the culvert discharge estimation but differ in complexity and in the interaction with the numerical model for surface flow, some of them as internal boundary conditions. Several steady and unsteady validation test cases are presented and the numerical results are compared with the predictions from HEC-RAS 1D and HY-8 software. The culvert area, shape and their sensitivity to the 2D computational mesh is also analyzed., The present work was partially funded by the Aragón Government through the Fondo Social Europeo. It has also been supported by the Research Project PGC2018-094341-B-I00 funded by the Spanish Ministry of Science, Innovation and Universities (MICINN). Additionally, Mario Morales-Hernández was partially supported by the U.S. Air Force Numerical Weather Modeling Program.

19 Pags.- 10 Figs.- 3 Tabls., River floods can be simulated with the 2D shallow water system of equations using finite volume methods, where the terrain is discretized in cells that form the computational mesh. Usually a proper treatment of wet/dry fronts is required. River levees can be modelled as part of the topography by means of sufficiently small cells of higher elevation than the rest of the bed level in locally refined meshes. This procedure is associated with a large computational time since the time step depends directly on the cell size. The alternative proposed in this work includes the levees as internal boundary conditions in the 2D numerical scheme. In particular, levees have been defined by a weir law that, depending on the relative values of water surface levels on both sides, can formulate the discharge for different situations (i.e. free flow and submerged flow). In addition, having identified numerical difficulties in cases of low discharge under free flow conditions, a novel procedure to avoid oscillations has been developed and called volume transport method. The validation and comparison between methods has been carried out with benchmark test cases and, in addition, with a real flood event in the Ebro River (Spain), This work was partially funded by the MINECO/FEDER under research Project CGL2015-66114-R and by Diputacion General de Aragon, DGA, through Fondo Europeo de Desarrollo Regional, FEDER. The third author also wants to thank to the MINECO for his Research Grant DI-14-06987.

42 Pags.- 4 Tabls.- 11 Figs. The definitive version is available at: https://www.sciencedirect.com/science/journal/03783774, Zebra mussel (Dreissena polymorpha) colonies are becoming a real problem in pressurized irrigation networks. The zebra mussel infestation of the 45 Water Users Associations (WUAs) of the Riegos del Alto Aragón (RAA) irrigation project (121 thousand hectares located in northeastern Spain) was assessed during the period of 2013–2017. Maps of WUA infestation stages were produced. A survey of the WUAs made it possible to assess the relevance of certain structural and management practices in the control of zebra mussels. A method to monitor zebra mussel colonization of pressurized collective irrigation networks was presented. The method is based on the combination of pressure measurements at network hydrants and hydraulic simulations. Normalized pressure, estimated as the difference between simulated and observed pressure, should approach zero in all hydrants in a properly characterized, non-infested network. A positive normalized pressure can indicate the presence of zebra mussel colonies. The methodology was validated using two different test cases located in two RAA WUAs: the first case involved a discrete chemical treatment, while the second case was based on the analysis of three years of telemetry pressure data and remote operation of network hydrants. The existence of an infested reservoir upstream of the WUAs was the most likely source of zebra mussel colonization of the WUA pressurized networks in the RAA project. The desiccation and chemical treatment of the small WUA reservoirs was associated with pest control. The hybrid (measurement-simulation) methodology is able to characterize the presence of zebra mussel colonies in specific reaches of pressurized irrigation networks., This work was supported by the European Agricultural Fund for Rural Development (EAFRD) and by the Government of Aragón. Both institutions funded the IRRIZEB (Programa integral para el control y mitigación del impacto de la plaga de Mejillón Cebra en sistemas de regadío) grant of the Plan de Desarrollo Rural (PDR).

A new open source multi-GPU 2D flood model called TRITON is presented in this work. The model solves the 2D shallow water equations with source terms using a time-explicit first order upwind scheme based on an Augmented Roe's solver that incorporates a careful estimation of bed strengths and a local implicit formulation of friction terms. The scheme is demonstrated to be first order accurate, robust and able to solve for flows under various conditions. TRITON is implemented such that the model effectively utilizes heterogeneous architectures, from single to multiple CPUs and GPUs. Different test cases are shown to illustrate the capabilities and performance of the model, showing promising runtimes for large spatial and temporal scales when leveraging the computer power of GPUs. Under this hardware configuration, communication and input/output subroutines may impact the scalability. The code is developed under an open source license and can be freely downloaded in https://code.ornl.gov/hydro/triton .

In this work, a Large Time Step (LTS) explicit finite volume scheme designed to allow CFL > 1 is applied to the numerical resolution of 2D scalar and systems of conservation laws on triangular grids. Based on the flux difference splitting formulation, a special concern is put on finding the way of packing the information to compute the numerical solution when working on unstructured grids. Not only the cell areas but also the length of the interfaces and their orientation are questions of interest to send the information from each edge or interface. The information to update the cell variables is computed according to the local average discrete velocity and the orientation of the edges of the cells involved. The performance of these ideas is tested and compared with the conventional explicit first order and second order schemes in academic configurations for the 2D linear scalar equation and for 2D systems of conservation laws (in particular the shallow water equations) without source terms. The LTS scheme is demonstrated to preserve or even gain accuracy and save computational time with respect to the first order scheme.

The shallow water equations have been extensively studied and used to model unsteady open channel flows in different applications. They belong to the category of hyperbolic partial differential equations and their treatment has recently been benefited from many numerical contributions leading to robust, accurate and well-balanced solutions. The correct formulation of external and internal boundary conditions is required to achieve a useful model in practical application. Control of internal boundary conditions may be useful in water distribution facilities. Therefore, development of a control strategy based on the fully dynamical mathematical model becomes attractive and justified. This work is devoted to the implementation of an adjoint based sensitivity analysis for the control of sluice gates in open-channel flow, formulated as internal boundary conditions. This is one of the most complex tasks in multiple regulated water delivery situations. Based on gradient method optimizers, the control of ...

34 Pags.- 14 Figs.- 2 Algorithms. The definitive version is available at: http://jh.iwaponline.com/, The calibration of parameters in complex systems usually requires a large computational effort. Moreover, it becomes harder to perform the calibration when non-linear systems underlie the physical process, and the direction to follow in order to optimize an objective function changes depending on the situation. In the context of shallow water equations (SWE), the calibration of parameters, such as the roughness coefficient or the gauge curve for the outlet boundary condition, is often required. In this work, the SWE are used to simulate an open channel flow with lateral gates. Due to the uncertainty in the mathematical modeling that these lateral discharges may introduce into the simulation, the work is focused on the calibration of discharge coefficients. Thus, the calibration is performed by two different approaches. On the one hand, a classical Monte Carlo method is used. On the other hand, the development and application of an adjoint formulation to evaluate the gradient is presented. This is then used in a gradient-based optimizer and is compared with the stochastic approach. The advantages and disadvantages are illustrated and discussed through different test cases., This research has been partially funded by the Spanish MINECO/FEDER through the Research Project CGL2015-66114-R and by Diputación General de Aragón, DGA, through FEDER funds. The first author was also supported by the Spanish Ministry of Economy and Competitiveness fellowship BES-2012-053691.

In this work, an implicit method for solving 2D hyperbolic systems of equations is presented, focusing on the application to the 2D shallow water equations. It is based on the first order Roe’s scheme, in the framework of finite volume methods. A conservative linearization is done for the flux terms, leading to a non-structured matrix for unstructured meshes thus requiring iterative methods for solving the system. The validation is done by comparing numerical and exact solutions in both unsteady and steady cases. In order to test the applicability of the implicit scheme to real world situations, a laboratory scale tsunami simulation is carried out and compared to the experimental data. The implicit schemes have the advantage of the unconditional stability, but a quality loss in the transient solution can appear for high CFL numbers. The properties of the scheme are well suited for the simulation of unsteady shallow water flows over irregular topography using all kind of meshes.

18 Pags.- 11 Figs.- 2 Tabls., The numerical modelling of 2D shallow flows in complex geometries involving transient flow and movable boundaries has been a challenge for researchers in recent years. There is a wide range of physical situations of environmental interest, such as flow in open channels and rivers, tsunami and flood modelling, that can be mathematically represented by first-order non-linear systems of partial differential equations, whose derivation involves an assumption of the shallow water type. Shallow water models may include more sophisticated terms when applied to cases of not pure water floods, such as mud/debris floods, produced by landslides. Mud/debris floods are unsteady flow phenomena in which the flow changes rapidly, and the properties of the moving fluid mixture include stop and go mechanisms. The present work reports on a numerical model able to solve the 2D shallow water equations even including bed load transport over erodible bed in realistic situations involving transient flow and movable flow boundaries. The novelty is that it offers accurate and stable results in realistic problems since an appropriate discretization of the governing equations is performed. Furthermore, the present work is focused on the importance of the computational cost. Usually, the main drawback is the high computational effort required for obtaining accurate numerical solutions due to the high number of cells involved in realistic cases. However, the proposed model is able to reduce computer times by orders of magnitude making 2D applications competitive and practical for operational flood prediction. Moreover our results show that high performance code development can take advantage of general purpose and inexpensive Graphical Processing Units, allowing to run almost 100 times faster than old generation codes in some cases., This work was partially funded by the MINECO/FEDER under research project CGL2015-66114-R and by Diputacion General de Aragon, DGA, through Fondo Europeo de Desarrollo Regional, FEDER. The third author also wants to thank to the MINECO for his Research Grant DI-14-06987.

29 Pags.- 17 Figs.- 2 Tabls. The definitive version is available at: https://link.springer.com/journal/40314, We address the problem of inverse design of linear hyperbolic transport equations in 2D heterogeneous media. We develop numerical algorithms based on gradient-adjoint methodologies on unstructured grids. While the flow equation is compulsorily solved by means of a second order upwind scheme so to guarantee sufficient accuracy, the necessity of using the same order of approximation when solving the sensitivity or adjoint equation is examined. Two test cases, including Doswell frontogenesis, are analysed. We show the convenience of using a low order method for the adjoint resolution, both in terms of accuracy and efficiency. An analytical explanation for this fact is also provided in the sense that, when employing higher order schemes for the adjoint problem, spurious high frequency numerical components slow down the convergence process., This work was done while the first author was a postdoctoral fellow of the team of the Advanced Grant NUMERIWAVES/FP7-246775 of the European Research Council. The second author was partially supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement NO: 694126-DyCon), the Grant MTM2017-92996-C2-1-R COSNET of MINECO (Spain), the ELKARTEK project KK-2018/00083 ROAD2DC of the Basque Government, the Air Force Office of Scientific Research under Award NO: FA9550-18-1-0242, the Marie Curie Training Action “ConFlex” SEP-210412102 and the ICON project of the French ANR.

Coupled 1D–2D numerical strategies are presented in this work for their application to fast computation of large rivers flooding. Both 1D and 2D models are built using explicit upwind finite volume schemes, able to deal with wetting-drying fronts. The topography representation is described via cross sections for the 1D model and with quadrilateral/triangular structured/unstructured meshes for the 2D model. The coupling strategies, free of hydraulic structures and tuning parameters, are firstly validated in a laboratory test dealing with a levee break and its flooding into a lateral plane. The numerical results are compared with a fully 2D model as well as with measurements in some gauge points giving satisfactory results. The simulation of a real flooding scenario in the Tiber river near the urban area of Rome (Italy) is then performed. A lateral coupling configuration is provided, in which the flood wave propagation in the main channel is simulated by means of a 1D model and the inundation of the riverside is simulated by means of a 2D model. On the other hand, a frontal coupling, in which the flood wave is simulated in a 1D model first and then it is propagated into a 2D model, is also performed. The flooding extension is almost well captured by all the schemes presented, being the 1D–2D lateral configuration the most confident with speed-ups of around 15x.

This study describes the exploitation of wood waste (Pinus spp.) in the form of sawdust and shavings generated during the production of furniture and artisanal items in a community in the state of Michoac&aacute, n, western Mexico. A process is described to densifying this raw material, to produce solid-type biofuel briquettes that can be used to satisfy the need to generate low-power heat for residential sectors. Briquette production involved six stages: (a) gathering samples of sawdust and shavings from artisanal workshops in the community, (b) proximal characterization of the samples, (c) elaborating the briquettes, (d) physicochemical characterization of the briquettes, (e) evaluation of the physical-thermal combustion of the briquettes, and (f) an economic evaluation of briquette production to determine viability. Finally, we performed a comparative analysis of the energy, economic, and environmental indicators of the briquettes produced and conventional pine and oak firewood (Pinus spp., Quercus spp.) in the study community. The results show the viability of using biomass residues to make briquettes, which are efficient, economic and easy to make and use.

The challenge of finding a compromise between computational time and level of accuracy and robustness has traditionally expanded the use simplified models rather than full two-dimensional (2D) models for flood simulation. This work presents a GPU accelerated 2D shallow water model for the simulation of flood events in real time. In particular, an explicit first-order finite volume scheme is detailed to control the numerical instabilities that are likely to appear when used in complex topography. The model is first validated with the benchmark test case of the Toce River (Italy) and numerical fixes are demonstrated to be necessary. The model is next applied to reproduce real events in a reach of the Ebro River (Spain) in order to compare simulation results with field data. The second case deals with a large domain (744 km2) and long flood duration (up to 20 days) allowing an analysis of the performance and speed-up achieved by different GPU devices. The high values of fit between observed and simulated results as well as the computational times achieved are encouraging to propose the use of the model as forecasting system.

18 Pags.- 8 Figs.- 3 Tabls., The 2D solute transport equation can be incorporated into the 2D shallow water equations in order to solve both flow and solute interactions in a coupled system of equations. In order to solve this system, an explicit finite volume scheme based on Roe’s linearization is proposed. Moreover, it is feasible to decouple the solute transport equation from the hydrodynamic system in a conservative way. In this case, the advection part is solved in essence defining a numerical flux, allowing the use of higher order numerical schemes. However, the discretization of the diffusion–dispersion terms have to be carefully analysed. In particular, time-step restrictions linked to the nature of the solute equation itself as well as the numerical diffusion associated to the numerical scheme used are question of interest in this work. These improvements are tested in an analytical case as well as in a laboratory test case with a passive solute (fluorescein) released from a reservoir. Experimental measurements are compared against the numerical results obtained with the proposed model and a sensitivity analysis is carried out, confirming an agreement with the longitudinal coefficients and an underestimation of the transversal ones, respectively., This work was partially funded by the MINECO/FEDER under research project CGL2015-66114-R and by Diputación General de Aragón, DGA, through Fondo Europeo de Desarrollo Regional, FEDER.

Zero-Inertia (ZI) models are used in overland flow simulation due to their mathematical simplicity, compared to more complex formulations such as Shallow Water (SW) models. The main hypothesis in ZI models is that the flow is driven by water surface and friction gradients, neglecting local accelerations. On the other hand, SW models are a complete dynamical formulation that provide more information at the cost of a higher level of complexity. In realistic problems, the usually huge number of cells required to ensure accurate spatial representation implies a large amount of computing effort and time. This is particularly true in 2D models. Hence, there is an interest in developing efficient numerical methods. In general terms, numerical schemes used to solve time dependent problems can be classified in two groups, attending to the time evaluation of the unknowns: explicit and implicit methods. Explicit schemes offer the possibility to update the solution at every cell from the known values but are restricted by numerical stability reasons. This can lead to very slow simulations in case of using fine meshes. Implicit schemes avoid this restriction at the cost of generating a system of as many equations as computational cells multiplied by the number of variables to solve. In this work, an implicit finite volume numerical scheme has been used to solve the 2D equations in both ZI and SW models. The scheme is formulated so that both quadrilateral and triangular meshes can be used. A conservative linearization is done for the flux terms, leading to a non-structured matrix for unstructured meshes thus requiring iterative methods for solving the system. A comparison between 2D SW and 2D ZI is done in terms of performance, efficiency and mesh requirements, in which both models benefit of an implicit temporal discretization in steady and nearly-steady situations.

Numerical modeling of bed-load transport in shallow flows, particularly oriented toward environmental flows, is an active field of research. Nevertheless, other possible applications exist. In particular, bed-load transport phenomena are relevant in urban drainage systems, including sewers. However, few applications of coupled two-dimensional (2D) shallow-water and bed-load transport models can be found, and their transfer from environmental applications-usually river and floodplain-into sewer applications requires some adaptation. Unlike to river systems, where there is a thick layer of sediment that constitutes a movable riverbed, sewer systems have thin layers of sediment that need to be removed, thus exposing a rigid, nonerodible surface. This problem requires careful numerical treatment to avoid generating errors and instability in the simulation. This paper deals with a numerical approach to tackle this issue in an efficient way that allows large-scale studies to be performed and provides empirical evidence that the proposed approach is accurate and applicable for sewage and channel-flushing problems. (C) 2017 American Society of Civil Engineers.

[EN] A study of measures oriented to flood mitigation in the mid reach of the Ebro river is presented: elimination of vegetation in the riverbed, use of controlled flooding areas and construction or re-adaptation of levees. The software used is RiverFlow2D which solves the conservative free-surface flow equations with a finite volume method running on GPU. The results are compared with measurements at gauge stations and aerial views. The most effective measure has turned out to be the elimination of vegetation in the riverbed. It is demonstrated that not only the maximum flooded area is narrower but also it reduces the water depth up to 1 m. The other measures have local consequences when the peak discharge is relatively high although they could be useful in case the discharge is lower, [ES] En este trabajo se presenta un estudio de medidas orientadas a la mitigación de avenidas en el tramo medio del río Ebro: limpieza de vegetación del cauce, uso de zonas de inundación controlada y construcción o re-adaptación de motas. Para ello se utiliza el software RiverFlow2D que resuelve las ecuaciones conservativas del flujo de superficie libre con un método de volúmenes finitos realizando los cálculos sobre GPU. Se comparan los resultados con medidas en estaciones de aforo e información extraída de ortofotos. La medida más efectiva, de las analizadas, ha resultado ser la eliminación de la vegetación en el cauce. Se demuestra que no sólo el área máxima inundada es menor en todo el tramo sino que también reduce la altura de agua hasta en 1 m. El resto de medidas tienen consecuencias locales y de poca entidad cuando los caudales pico son altos, aunque podrían resultar de utilidad para avenidas con caudales más bajos., Este trabajo se encuentra en el marco del proyecto de investigación CGL2015-66114-R financiado por el Ministerio de Ciencia e Innovación/FEDER. Los autores quieren agradecer también a la Confederación Hidrográfica del Ebro por su disponibilidad de consulta y gestión de datos.

This paper analyzes the Girona River (Spain) flash flood, occurred on the 12th of October 2007, combining hydrological and hydraulic modeling with geomorphologic mapping and post-flood survey information. This research aims to reproduce the flood event in order to understand and decipher the flood processes and dynamics on a system of prograding alluvial fans. The hydrological model TETIS was used to characterize the shape and dimension of the October 2007 Girona River hydrograph. Subsequently, the flood event was reproduced using the free surface flow module of the model RiverFlow2D. The combination of hydrological and hydraulic models was evaluated using post-flood surveys defining maximum flooded area and flood depths. Then, simulations with different peak discharges were carried out to estimate the hydro-geomorphologic response of the Girona River floodplain, through the identification of the activation thresholds in different geomorphic elements. Results showed that the unit peak discharge of the October 2007 flood event (5 m3 s−1 km−2) was among the largest ever recorded in the area, according to the existing literature. Likewise, the hydraulic model showed a good performance in reproducing the flood event (FitA = 76%, RMSE = 0.65 m and NSE = 0.6), despite the complexity of the case, an ephemeral and ungauged river. The model simulation revealed the existence of an activation pattern of paleochannels and alluvial fans, which was altered by the presence of some anthropogenic disturbances. This multidisciplinary approach proved to be a useful strategy for understanding flash flood processes in ungauged catchments. It allowed understanding the mechanisms governing floods in alluvial fans systems and it represented a solid contribution for early warning plans and risk mitigation policies., This collaborative research was financed with the projects CGL2013-44917-R and SLWAMED CGL2014-58127-C3-2, of the Ministry of Economy and Competitiveness of the Spanish Government. Both projects were co-financed with FEDER funds. The observed rainfall and water discharge records were provided by "Sistema Automatic de Information Hidrologica (SAIH)", which belongs to the CHJ (Spain). This work was also possible due to the kind cooperation of the members of the Plataforma Ciutadana Riu Girona and several anonymous farmers interviewed during the field works. We also thank two anonymous reviewers for their useful and thought-provoking comments.