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Using a 2D shallow water model to assess Large-Scale Particle Image Velocimetry (LSPIV) and Structure from Motion (SfM) techniques in a street-scale urban drainage physical model
Abstract
Link (before July 05, 2019):https://authors.elsevier.com/a/1Z3d152cuNCt7. Physically-based numerical modelling of surface processes in urban drainage, such as pollutant wash-off or the assessment of flood risks, requires appropriate calibration and terrain elevation data to properly simulate the overland flows and thus to achieve useful results. Accordingly, this study aims to obtain an accurate representation of the runoff generated by three different rain intensities, 30, 50 and 80 mm/h, in a full-scale urban drainage physical model of 36 m2. The study focuses firstly on applying the Structure from Motion (SfM) photogrammetric technique to carry out a high-resolution and accurate topographic survey. This topography was implemented in a 2D shallow water model and the results were compared with those obtained using traditional data point measured topography. Negligible differences were found when comparing the two models with measured discharges at the physical model gully pots. However, significant differences were obtained in the velocity distributions, especially in the shallowest flow areas where drainage channels of a few millimeters’ depth appeared in the high resolution topographic survey. Results from the numerical model were compared with overland flow velocities, determined by applying a modified Large Scale Particle Image Velocimetry (LSPIV) methodology using fluorescent particles. With the SfM topography, the 2D model was able to obtain a better representation of the experimental data, since small scale irregularities of the pavement surface could be represented in the model domain. At the same time, LSPIV was presented as a very suitable tool for the accurate measurement of runoff velocities in urban drainage models, avoiding the interference of raindrop features in the recorded images and with overland water depths in the order of few millimeters.
... Hydraulic data (surface depths, flows and velocities), wash-off tests (total suspended solids and particle size distribution) and rainfall intensities (30, 50 and 80 mm/h) were obtained using a full-scale physical model (This is schematically represented in Fig. 2.1.). Built in the Hydraulic Laboratory of CITEEC at the University of A Coruña Spain, this unique experimental facility has been used for multiple studies (Fraga et al., 2017;Naves et al., 2017Naves et al., , 2020aNaves et al., 2019a). The model comprises of a hypothetical full scale street profile which has an area of 36 m 2 . ...
... The generated rainfall drains into each gully and through a piped system to an outfall via an outflow channel. All the data files that were used in this project along with experimental details are fully open access and can be found in the WASHTREET dataset (Naves et al., 2019a(Naves et al., , 2019b. ...
... Structure (SfM) photogrammetric techniques were used to verify the surface elevations to raw data files such that the experiments could be replicated in the numerical modelling. More details can be found in the papers provided by Naves,et al., (2019a) and Naves et al., (2019b). ...
... Hydraulic data (surface depths, flows and velocities), wash-off tests (total suspended solids and particle size distribution) and rainfall intensities (30, 50 and 80 mm/h) were obtained using a full-scale physical model (This is schematically represented in Fig. 2.1.). Built in the Hydraulic Laboratory of CITEEC at the University of A Coruña Spain, this unique experimental facility has been used for multiple studies (Fraga et al., 2017;Naves et al., 2017Naves et al., , 2020aNaves et al., 2019a). The model comprises of a hypothetical full scale street profile which has an area of 36 m 2 . ...
... The generated rainfall drains into each gully and through a piped system to an outfall via an outflow channel. All the data files that were used in this project along with experimental details are fully open access and can be found in the WASHTREET dataset (Naves et al., 2019a(Naves et al., , 2019b. ...
... Structure (SfM) photogrammetric techniques were used to verify the surface elevations to raw data files such that the experiments could be replicated in the numerical modelling. More details can be found in the papers provided by Naves,et al., (2019a) and Naves et al., (2019b). ...
... A partir de la técnica SfM ha sido posible disponer de una topografía con una resolución de 5 mm, frente a los 500 mm de la topografía tradicional realizada, que permite modelizar con mayor precisión el flujo superficial. Los mapas de elevaciones resultantes se pueden consultar en Naves et al. (2019a), donde se analiza también el funcionamiento del modelo Iber (Bladé et al., 2014) para modelizar la escorrentía empleando cada una de las topografías. ...
... Dada su importancia en el lavado y transporte de sedimentos y su necesidad a la hora de calibrar con precisión modelos de drenaje, la caracterización hidráulica se completa con la medida de la distribución de velocidades en la superficie del modelo. En la Figura 7 se presenta en detalle las velocidades en las inmediaciones del imbornal 2 obtenidas mediante la técnica LSPIV para la lluvia de 50 mm/h, en donde se pueden observar los canales preferenciales de drenaje en dirección perpendicular a la cuneta detectados en Naves et al. (2019a) para todas las intensidades de lluvia. Estos canales tienen un ancho de unos 25 cm y se sitúan en las posiciones y=2.5, y=3.25, y=4.25, y=4.9 e y=5.75 m. ...
... En Naves et al. (2021) se presentan de forma detallada los resultados comparando las velocidades obtenidas usando diferentes técnicas de procesamiento de las imágenes y usando dos trazadores diferentes: partículas fluorescentes añadidas a la escorrentía y burbujas naturalmente presentes en el agua generadas por el impacto de las gotas de lluvia en la superficie del modelo. Ante las irregularidades del terreno que se han intuido a partir de estos resultados, se ha empleado la técnica fotogramétrica SfM para la determinación de forma precisa de las elevaciones de la superficie, que se hace imprescindible para modelizar adecuadamente la escorrentía generada (Naves et al. 2019a(Naves et al. , 2020a. En la Figura 8 se presentan los polutogramas de SST de las muestras tomadas en las dos arquetas y en el punto de vertido de la red de colectores para la intensidad de lluvia de 50 mm/h y las diferentes clases de sedimentos. ...
Ante la falta de datos experimentales precisos para el desarrollo y validación de modelos de lavado y transporte de sedimentos en la superficie de cuencas urbanas, en este estudio se presenta una serie de ensayos en los que los procesos involucrados son medidos con detalle en un modelo físico de drenaje urbano dual de 36 m2 a escala real. Durante los experimentos, se han analizado tres intensidades de lluvia y cinco clases de sedimento y se han medido calados y velocidades en superficie; calados en colectores; caudales, concentraciones de SST y distribuciones de tamaños de partícula en el flujo de entrada a las arquetas y en el punto de vertido de la red de colectores; y se han realizado balances de masas a partir del sedimento que queda depositado en las distintas partes del modelo. Todos los datos brutos y procesados obtenidos se encuentran disponibles en el repositorio de acceso abierto Zenodo (https://zenodo.org/communities/washtreet).
... In Naves et al. (2019a), a variation of the LSPIV technique was applied to measure the surface velocity fields generated by 60 three different rain intensities in a full-scale urban drainage physical model. That study used UV illumination and fluorescent particles as artificial tracers to satisfactorily address the problems caused by the presence of raindrops in the experiments, which are the interference of raindrops in the visualization of images and the disturbances generated in the flow because of https://doi.org/10.5194/hess-2020-136 ...
... Two types of configurations have been used to visualize overland flow: a) experiments using fluorescent particles and UV illumination; and b) using white-LED lamps without artificial particles to highlight air bubbles and water reflections generated by raindrops in the flow. While seeded videos were already used in the application of a modified LSPIV technique in Naves et al. (2019a) As seen in Fig. 1b, two Lumix GH4 cameras with 28 mm focal length recorded the first 2 m attached to the curb along 5 m of 100 the physical model. UV torches and LED lamps were installed next to the cameras 2.2 m above the pathway. ...
... These six sets of images considering both the experimental setup and the three rain intensities were used as the basis for the different imaging velocimetry techniques assessed in this study. A more detailed description of the physical model, the simulated rain, or the procedure to extract the images can be consulted in Naves et al. (2020bNaves et al. ( , 2020cNaves et al. ( , 2019a, respectively. 110 https://doi.org/10.5194/hess-2020-136 ...
Abstract. Although surface velocities are key in the calibration of physically based urban drainage models, the shallow water depths developed during non-extreme precipitations and the potential risks during flood events limit the availability of this type of data in urban catchments. In this context, imaging velocimetry techniques are being investigated as suitable non-intrusive methods to estimate runoff velocities, when the possible influence of rain has yet to be analyzed. This study carried out a comparative assessment of different seeded and unseeded imaging velocimetry techniques: Large Scale Particle Image Velocimetry (LSPIV); Surface Structure Image Velocimetry (SSIV); and Bubble Image Velocimetry (BIV), through six realistic but laboratory-controlled experiments where the runoff generated by three different rain intensities was recorded. First, the use of naturally-generated bubbles and water shadows and glares as tracers allows the unseeded techniques (SSIV and BIV) to measure extremely shallow flows, but these are more affected by raindrop impacts, which even lead to erroneous velocities in the case of the highest rain intensities. At the same time, better results were obtained with techniques that use artificial particles for high intensities and in complex flows. Finally, the study highlights the feasibility of these imaging techniques to be used in measuring surface velocities in real field applications and the importance of considering rain properties to interpret and assess the results obtained.
... First, an accurate hydraulic characterization was performed, measuring flows and depths generated by three different rain intensities, additionally obtaining runoff velocity distributions and elevations using visualization techniques. In Naves et al. 27 , these data have been used to assess Large-Scale Particle Image Velocimetry (LSPIV) and Structure from Motion (SfM) techniques to accurately represent overland flow obtaining surface velocity distributions and surface elevations respectively. The videos and images provided can be of reuse as a means of optimizing visualization techniques for hydraulic modelling purposes. ...
... Finally, the resulted velocity distributions that are provided correspond to the surface flow velocity and not to the depth-average velocities. Some authors use a flow velocity correction factor from 0.6 to 1 based on the log-law velocity profile 24,42 , and in Naves et al. 27 the classical value of 0.85 was applied. However, due to the very shallow flow conditions, this assumption is not expected to add significant uncertainties. ...
... In addition, the raw and processed data provided were used in Naves et al. 27 to assess LSPIV and SfM techniques, showing their usefulness for hydraulic modelling purposes. In this work, the topographic data obtained from the photogrammetric technique was used to represent overland flow with a 2D shallow water model. ...
This paper presents a dataset obtained from hydraulic and sediment transport experiments performed in a full-scale urban drainage physical model of 36 m². The study seeks to accurately measure sediment mobilization through the different parts of the model (surface, gully pots and pipe system), also obtaining a precise characterization of water flow and using realistic rainfall simulator to ensure the transferability of the results. Three different rain intensities and five sediment granulometries were tested in 6 hydraulic and 23 wash-off and sediment transport experiments. The following experimental data were produced: surface elevations and 2D runoff velocities measured by visualization techniques; surface and in-pipe water depths; flow discharges, total suspended solids concentrations and particle size distribution at the entrance of the gully pots and at the pipe system outlet; and sediment mass balances. This data is optimal for developing and validating wash-off and sediment transport formulations in urban drainage models, towards better treatment and management techniques for minimizing the impact of urban surface pollutants on the environments of towns and cities.
... Previous studies have shown the capacity of the model to adequately represent the spatial distributions of water depth and velocity under overland flow conditions and including rainfall-runoff transformation (Cea et al., 2010;Cea and Blade, 2015). The runoff model has also been validated for urban areas in the same laboratory facility described in this work (Fraga et al., 2015;Naves et al., 2019b) and also in field applications (Fraga et al., 2016). The input factors in the hydrodynamic equations are the rain intensity (R), the bed roughness Manning coefficient (n), and the surface initial losses (IL). ...
... A rainfall simulator is located 2.6 m over a concrete street surface, which is divided into a sidewalk and a roadway (Fig. 1). The detailed surface elevation data of the facility and the details of the rainfall simulator, which is able to generate rain intensities of 30 mm/ h, 50 mm/h and 80 mm/h with high spatial uniformity, were described in Naves et al. (2019b). The generated rainfall-runoff drains into two gully pots located along the curb and into a lateral outflow channel. ...
... In addition, a more detailed description of the physical model and those experimental results not included here, have been uploaded to the open-access repository Zenodo (Naves et al., 2019a). The hydraulics of the experiments has already been calibrated successfully, using the measured hydrographs with the 2D shallow water model in Naves et al. (2019b). ...
Physically-based urban wash-off models are a promising means of studying the transport of finer suspended solids and their associated pollutants during rain events, considering spatial and temporal heterogeneities. This study contributes to the understanding of these models through an in-depth sensitivity analysis to provide the necessary information to simplify the model and deal with parameter identifiability. First, based on twelve tailored high-resolution experiments, the accurate measurement of input variables was used to study the parameters of the Hairsine-Rose sediment transport model through a global sensitivity analysis. Using Standardized Regression Coefficients (SRC) and Extended Fourier Amplitude Sensitivity Test (EFAST) methods, the analysis showed that both the total washed-off mass and the TSS peaks concentration are highly sensitive to the critical mass, which considers the reduction in the detachment of particles when the sediment available decreases and is scattered over the surface. In addition, the rain- and flow-driven detachment parameters were presented as key for smaller and larger sediment particles, respectively. Then, those uncertainties that are associated in field studies with the determination of the model input variables were also considered by conducting a local sensitivity analysis. The initial load of sediment and the mean grain size were seen to be the most important variables, thus underlining the need for very accurate measurements here. Moreover, a precise definition of Harsine-Rose parameters is also necessary to achieve reliable results in order to work on treatment and management techniques to minimize the impact of urban surface contaminants on urban environments.
... Las técnicas de procesamiento de imágenes han mostrado un gran potencial en trabajos de estimación de velocidades, calados y elevaciones tanto en campo en tramos fluviales (Pearce et al., 2020) o en pozos de bombeo de sistemas de saneamiento (Moreno-Rodenas, 2021) como en laboratorio (Naves et al. 2019(Naves et al. , 2020(Naves et al. y 2021. Por lo tanto, estas técnicas basadas en visión artificial están proporcionando datos útiles y precisos que permiten incrementar el conocimiento sobre procesos relevantes, por lo que el desarrollo de sensores de bajo coste y asequibles en términos de complejidad, montaje e instalación es muy interesante para poder sacar el máximo partido a estas nuevas fuentes de datos y monitorización. ...
... Los primeros ensayos presentados se corresponden con la aplicación de la técnica LSPIV (Large Scale Particle Image Velocimetry) para la estimación de campos de velocidad en escorrentía urbana superficial de calados muy someros de escasos milímetros y con la presencia de lluvia. La técnica ha sido utilizada con anterioridad en una aplicación similar (Naves et al., 2019), por lo que la principal novedad es el uso del sistema basado en Raspberry Pi y las librerías de código abierto OpenCV y OpenPIV tanto para la grabación de los vídeos como para el procesado de estos, así como la utilización de hasta 8 cámaras al mismo tiempo para cubrir una superficie total de unos 40 m 2 con diferentes resoluciones tanto espaciales como temporales (ver Figura 1). Aunque los resultados preliminares han demostrado que las Raspberry Pi son capaces de poder llevar a cabo este tipo de análisis con una resolución temporal adecuada, el rendimiento se ve condicionado por la calidad del video, la frecuencia de adquisición, parámetros de la técnica PIV y otras variables que se están analizando para la optimización del sistema de medida. ...
... Datasets obtained in field campaigns are typically used to calibrate the model parameters in real urban basins, but usually introduce measurement errors such as uncertainties in the acquisition system or in the sensor calibration processes (Fraga et al., 2016). On the other hand, the use of experimental data obtained in laboratory facilities is more suitable for assessing the performance of numerical models, since tests are carried out under strictly controlled conditions, and hence there is far lower uncertainty in terms of the input and observed data (Naves et al., 2019;Addison-Atkinson et al., 2023). For this reason, in recent years a number of studies using urban drainage laboratory facilities have been conducted to better understand the relevant processes on urban hydrology and the hydrodynamics of urban flooding (Mignot et al., 2019). ...
... The Manning coefficient was set to 0.016 on the street surface (Naves et al., 2019), 0.025 on the roofs, and 0.008 in the pipes, since these latter are made of plastic and are completely clean. It is highlighted that no initial abstraction was defined on any surface, since the experiments were performed under wet antecedent conditions. ...
Numerical models are currently the main tool used to simulate the effects of urban flooding. The validation of these models requires thorough and accurate observed data in order to test their performance. The current study presents a series of laboratory experiments in a large‐scale urban drainage physical facility of approximately 100 m ² that includes roofs, streets, inlets, manholes and sewers. The facility is equipped with a rainfall simulator as well as a surface runoff and pipe inflows generators. The experiments were divided in two sets. In Set 1 the surface runoff was generated exclusively by the rainfall input, while in Set 2 the rainfall simulator was used in combination with the runoff generators. In all the tests the water discharge was measured at points on the inlets, roofs, and outfall. The water depth at different locations of the facility was also measured. The experimental tests were replicated numerically using the urban drainage model Iber‐SWMM. Experimental results show that, even in a relatively small catchment the peaks in the hydrographs generated at each element of the facility during intermittent rainfalls are significantly attenuated at the catchment outlet. The agreement between the experimental and numerical results show that there are some differences in the hydrographs generated at each element, but that these differences compensate each other and disappear at the outfall. The results generated provide the research community with a thorough and high‐resolution dataset obtained under controlled laboratory conditions in a large‐scale urban drainage facility, something which has not previously been available.
... The use of photogrammetric techniques to obtain elevations by the authors is noteworthy, especially on impervious surfaces and accumulation of sediments in sewer pipes. Further information regarding these applications can be found in Naves et al. (2019) and Regueiro-Picallo et al. (2020). ...
... In addition, the mean vertical error obtained for roof and paved surface topographies was less than 2 mm. These differences agree with the results in Naves et al. (2019) where a topography with a similar resolution was used and validated in a hydraulic numerical model. Therefore, no significant differences can be considered regarding DEM resolution and accuracy between both techniques for this research scope. ...
The investigation of rain gauge and radar-based runoff has become essential due to advantages and disadvantages of both types of rainfall measurement methods. A comparative analysis was made in this study based on both types of rainfall-based forecast using three different types of storm events. The rain gauge-based forecast performed better than radar with limited ability to capture spatial variation of rainfall in urban catchment. The radar-based forecast showed potential to simulate spatial rainfall dynamics but could not reasonably performed well, might be due to presence of uncertainties from multiple sources.
... The physical model consists of a full-scale street section of 36 m 2 with a sewer system and a rainfall simulator. This facility was used in previous studies [10,[35][36][37] to validate urban drainage models and to measure wash-off and sediment transport in urban environments. The street consists of a concrete roadway and a concrete pavement separated by a 15-cm high curb. ...
... The surface domain was discretized using an unstructured mesh with an average element size of 0.06 m and approximately 20,000 elements. From previous studies in this laboratory facility [36], the Manning coefficient was set to 0.016, and an initial abstraction of 0.6 mm was established in the whole surface. In the lateral plastic channel and in all the pipes of the sewer network, the Manning coefficient was set to 0.008 [10]. ...
Dual urban drainage models allow users to simulate pluvial urban flooding by analysing the interaction between the sewer network (minor drainage system) and the overland flow (major drainage system). This work presents a free distribution dual drainage model linking the models Iber and Storm Water Management Model (SWMM), which are a 2D overland flow model and a 1D sewer network model, respectively. The linking methodology consists in a step by step calling process from Iber to a Dynamic-link Library (DLL) that contains the functions in which the SWMM code is split. The work involves the validation of the model in a simplified urban street, in a full-scale urban drainage physical model and in a real urban settlement. The three study cases have been carefully chosen to show and validate the main capabilities of the model. Therefore, the model is developed as a tool that considers the main hydrological and hydraulic processes during a rainfall event in an urban basin, allowing the user to plan, evaluate and design new or existing urban drainage systems in a realistic way.
... Experiments were performed under controlled conditions to address the issue of sediment transport models in sewers, which were historically based on formulas proposed for alluvial sediments (Bertrand-Krajewski, 2006). The earliest attempts were carried out in pipe channels with non-cohesive materials (Perrusquia, 1992;May, 1993;Nalluri et al., 1994;Ackers et al., 1996). However, significant differences were shown between non-cohesive model approaches derived from experiments with uniform sands, and measurements performed in sewers (Arthur et al., 1996;De Sutter et al., 2003). ...
... This methodology was briefly introduced in Regueiro- Picallo et al. (2018) for the same purpose of measuring sediment accumulation and bed formations; prior to this, there seem to be no references in the literature to the application of such a technique in the sanitary system research field. Another recent example of the application of SfM in the urban drainage field can be found in studies by Naves et al. (2019aNaves et al. ( , 2019b, which used this technique to obtain the topography of a laboratory street model to simulate surface run-off and to calculate velocity map distributions. ...
The deposition and resuspension of sediments are issues of considerable concern in combined sewer systems management. Sediments can produce the loss of hydraulic capacity and odour generation in sewers, and are also considered the main source of pollution due to their occasional uncontrolled discharges into the environment via Combined Sewer Overflows (CSO). Sewer sediments contain granular and cohesive organic fractions that can have a significant influence on bed resistance. In order to address the relationship between sewer sediment composition and its erodibility, accumulation and erosion experiments were performed in a flume test facility fed with wastewater. The flume was placed in a Wastewater Treatment Plant (WWTP), in which different circular pipe geometries were set. Wastewater flow inlet conditions and bed structures were monitored during the experiments. The photogrammetric technique Structure from Motion (SfM) was applied to record the bed
deposit structures, providing accurate measurements of the accumulation rates. The SfM was also used to assess sediment transport and the characteristics of the bed forms after the erosion tests. In addition, velocity distributions and shear stress profiles were measured during the erosion tests to characterize flow resistance and sediment erosion. During both accumulation and erosion tests, sediments were sampled in order to analyse their physicochemical properties, thus highlighting the study of the biodegradability of the organic matter. Different deposition periods showed biological transformations in the bed deposit structure, which were seen to affect its cohesion, and in consequence, its erosion threshold. Tests with significant erosion rates agreed in broad terms with dimensionless sediment transport models derived from previous experimental studies performed with partly cohesive and organic materials in sewer pipes.
... The generated mesh consisted of 75,000 elements and 37,926 nodes ( Figure 3). Manning's coefficients, referenced from previous studies, were set to n = 0.016 for street surfaces [28,29], 0.025 for roofs, and 0.008 for pipes. No initial conditions for the surface were defined because of pre-existing rainfall conditions in the laboratory data. ...
Due to climate change, the frequency and intensity of torrential rainfall in urban areas are increasing, leading to more frequent flood damage. Consequently, there is a need for a rapid and accurate analysis of urban flood response capabilities. The dual-drainage model has been widely used for accurate flood analysis, with minimum time step synchronization being commonly adopted. However, this method has limitations in terms of speed. This study applied the hyper-connected solution for an urban flood (HC-SURF) model with fixed-time step flow synchronization, validated its accuracy using laboratory observation data, and tested its effectiveness in real urban watersheds with various synchronization times. Excellent performance was achieved in simulating real phenomena. In actual urban watersheds, as the synchronization time increased, the errors in surcharge and discharge also increased due to the inability to accurately reflect water level changes within the synchronization time; however, overall, they remained minimal. Therefore, the HC-SURF model is demonstrated as a useful tool for urban flood management that can be used to advantage in real-time flood forecasting and decision-making.
... El desarrollo de estos modelos requiere la utilización de datos observados de campo y/o laboratorio con la finalidad de validar su funcionamiento. Los datos experimentales obtenidos en instalaciones de drenaje urbano en condiciones controladas de laboratorio son los más adecuados para evaluar y validar los modelos numéricos (Fraga et al., 2017;Naves et al., 2019Naves et al., , 2020b, sin embargo, su disponibilidad es muy limitada y generalmente conlleva elevados costes de obtención. Por otra parte, disponemos de estudios que recogen ensayos sobre elementos aislados como sumideros (Russo et al., 2021), pozos de registro (Rubinato et al., 2022) o tejados (Sañudo et al., 2022), pero se evidencia una carencia en trabajos que analicen los procesos y elementos de forma integrada. ...
... El volumen de agua en el interior de las casas también se midió mediante sensores de presión conectados a un tubo de 10 mm conectado a un orificio en la parte inferior de 11 de las 25 casas. Por último, se instalaron cámaras alrededor de la plataforma para capturar vídeos desde distintos ángulos y obtener el campo de velocidades sobre la superficie mediante la técnica LSPIV a partir de la metodología desarrollada en Naves et al. (2019Naves et al. ( , 2021. Con este montaje experimental se han realizado ensayos en donde se combinan las intensidades de lluvia disponibles con una duración de 5 minutos y diferentes escenarios en los que se abren o cierran las puertas de los edificios para analizar el efecto en el hidrograma al variar la capacidad de almacenamiento de la ciudad modelada y su distribución espacial. ...
... La predicción de inundaciones generadas por la escorrentía en ciudades mediante el modelamiento numérico, es un factor clave para abordar esta problemática [9]. El modelamiento de los sistemas de drenajes basados en la física son herramientas comúnmente implementadas para predecir estos fenómenos y conocer el comportamiento de los sistemas de alcantarillado [10]. Sin embargo, los modelos existentes presentan retos importantes para representar el entorno y la hidrología urbana [11], necesitando la incorporación de datos de entrada rigurosos que permitan mostrar de forma correcta el flujo de escorrentía como información de salida [12]. ...
La modelización numérica de los sistemas de drenaje en ambientes urbanos basada físicamente de los procesos superficiales de escorrentía, como el análisis de zonas de inundación o la evaluación del peligro, requiere una calibración adecuada y precisa de los factores físicos para simular los flujos en la superficie y así lograr resultados que se asemejen a la realidad. Esta calibración en la mayoría de modelos es una fase difícil de conseguir debido a la escasez de datos de velocidad y profundidad de flujo medidos en campo cuando se está presentando inundaciones. El presente artículo tiene como objetivo dar a conocer los avances en el uso de técnicas de procesamiento digital de imágenes para la estimación semi-automática de los niveles de inundación en ambientes urbanos mediante la implementación en una primera fase a escala laboratorio. Para el estudio se utilizó un modelo experimental de prueba que consta de un canal rectangular de 250 centímetro (cm) de largo y una sección nominal de 5.35 cm de ancho y 12 cm de alto, el cual está conectado a un banco hidráulico volumétrico para el suministro de agua de forma permanente como condición de entrada al modelo. El canal permitió regular su pendiente longitudinal simulando una vía urbana por donde transcurre el agua de escorrentía. Se realizó la comparación de los datos medidos de forma manual y los valores de profundidad de flujo logrados bajo la técnica de procesamiento digital de imágenes, evidenciando un buen rendimiento en la determinación de las alturas del fluido para los diferentes caudales trabajados en el modelo experimental, con bajos valores del error cuadrático medio (ECM) y la raíz del error cuadrático medio (RECM), mostrando en cada medición desfases inferiores al milímetro (mm), con valores entre 0.1 y 0.6 mm. Finalmente, los resultados de la investigación pudieron evidenciar que la técnica presentada es una forma de medición no invasiva que, a diferencia de otras existentes, no genera perturbaciones en el flujo y por lo tanto resulta muy útil para flujos con profundidades muy pequeñas y altas velocidades.
... The authors stated that multiple CCTV cameras could improve the measurement of surface velocities by covering more regions to analyze the complex behavior of water flows in urban areas. In the same year, Naves et al. (2019) tested LSPIV at an urban drainage laboratory-scale experimental site for three rainfall intensities (30, 50, and 80 mm/h) using fluorescent particles. The SfM photogrammetric method was adopted to obtain high-resolution topography, which was used to estimate water depth and avoid interference from raindrops. ...
Floods are among the most common natural hazards in urban areas. To mitigate the problems caused by flooding, unstructured data such as images and videos collected from closed circuit televisions (CCTVs) or unmanned aerial vehicles (UAVs) have been examined for flood management (FM). Many computer vision (CV) techniques have been widely adopted to analyze imagery data. Although some papers have reviewed recent CV approaches that utilize UAV images or remote sensing data, less effort has been devoted to studies that have focused on CCTV data. In addition, few studies have distinguished between the main research objectives of CV techniques (e.g., flood depth and flooded area) for a comprehensive understanding of the current status and trends of CV applications for each FM research topic. Thus, this paper provides a comprehensive review of the literature that proposes CV techniques for aspects of FM using ground camera (e.g., CCTV) data. Research topics are classified into four categories: flood depth, flood detection, flooded area, and surface water velocity. These application areas are subdivided into three types: urban, river and stream, and experimental. The adopted CV techniques are summarized for each research topic and application area. The primary goal of this review is to provide guidance for researchers who plan to design a CV model for specific purposes such as flood-depth estimation. Researchers should be able to draw on this review to construct an appropriate CV model for any FM purpose.
... Extensive tables of the roughness coefficient n are available for different channel characteristics [63,64], natural channels, and flood plains [65]. More recently, distributed hydrological simulations have shown that Manning's resistance law is also plausible to predict the runoff dynamics in roads, urban floods and agriculture areas [32,[66][67][68]. ...
The frequency and magnitude of flash floods in the olive orchards of southern Spain have increased because of climate change and unsustainable olive-growing techniques. Affected surfaces occupy >85% of the rural regions of the Upper Guadalquivir Basin. Dangerous geomorphic processes record the increase of runoff, soil loss and streamflow through time. We report on ripple/dune growth over a plane bed on overland flows, deep incision of ephemeral gullies in olive groves and rock-bed erosion in streams, showing an extraordinary sediment transport capacity of sub-daily pluvial floods. We develop a novel method to design optimal solutions for natural flood management and erosion risk mitigation. We adopt physical-based equations and build a whole-system model that accurately reproduces the named processes. The approach yields the optimal targeted locations of nature-based solutions (NbSs) for active flow-control by choosing the physical-model parameters that minimise the peak discharge and the erosion-prone area, maximising the soil infiltration capacity. The sub-metric spatial resolution used to resolve microtopographic features of terrains/NbS yields a computational mesh with millions of cells, requiring a Graphics Processing Unit (GPU) to run massive numerical simulations. Our study could contribute to developing principles and standards for agricultural-management initiatives using NbSs in Mediterranean olive and vineyard orchards.
... The basic idea of non-intrusive methods is to measure the surface velocity and then provide a reasonable estimation of discharge for various flow conditions. To facilitate surveys in the field, image-based large-scale particle image velocimetry (LSPIV), which efficiently measures the motions of floating objects (e.g., bubbles) in a rectangular grid, has been developed [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Without tracking particles, it can effectively analyze the surface velocity through the ripple pattern on the river surface. ...
Large-scale particle image velocimetry (LSPIV) provides a cost-effective, rapid, and secure monitoring tool for streamflow measurements. However, surveys of ground control points (GCPs) might affect the camera parameters through the solution of collinearity equations and then impose uncertainty on the measurement results. In this paper, we explore and present an uncertainty analysis for image-based streamflow measurements with the main focus on the ground control points. The study area was Yufeng Creek, which is upstream of the Shimen Reservoir in Northern Taiwan. A monitoring system with dual cameras was set up on the platform of a gauge station to measure the surface velocity. To evaluate the feasibility and accuracy of image-based LSPIV, a comparison with the conventional measurement using a flow meter was conducted. Furthermore, the degree of uncertainty in LSPIV streamflow measurements influenced by the ground control points was quantified using Monte Carlo simulation (MCS). Different operations (with survey times from one to nine) and standard errors (30 mm, 10 mm, and 3 mm) during GCP measurements were considered. Overall, the impacts in the case of single GCP measurement are apparent, i.e., a shifted and wider confidence interval. This uncertainty can be alleviated if the coordinates of the control points are measured and averaged with three repetitions. In terms of the standard errors, the degrees of uncertainty (i.e., normalized confidence intervals) in the streamflow measurement were 20.7%, 12.8%, and 10.7%. Given a smaller SE in GCPs, less uncertain estimations of the river surface velocity and streamflow from LSPIV could be obtained.
... This experimental setup consists of a full-scale street section physical model of 36 m 2 with an impervious concrete asphalt surface retrofitted with the same porous asphalt used in the previous tests (Figure 2a). Surface topography was measured using a point gauge in a rectangular grid of 50 x 50 cm using the procedure defined in Naves et al. (2019). The error bounds of the measured horizontal coordinates were assumed to be approximately 1 cm for the horizontal coordinates, and about 1mm for the vertical coordinates. ...
... One of the few exceptions is the Storm Water Management Model (SWMM) (Rossman and Simon, 2022). However, SWMM can only apply to a local, small-city level due to its intensive computational demand and requirement for detailed MS4 data, which are typically not available to the public (e.g., Nanía et al., 2015;Meyers et al., 2021;Fraga et al., 2016;Naves et al., 2019;Yang et al., 2011). Moreover, some studies, instead of using the actual urban drainage network, generate synthetic networks based on probabilistic methods that can capture the hydrologic responses of urban watersheds (e.g., Seo and Schmidt, 2014;Kim et al., 2021). ...
Belowground urban stormwater networks (BUSNs) are critical for removing excess rainfall from impervious urban areas and preventing or mitigating urban flooding. However, available BUSN data are sparse, preventing the modeling and analysis of urban hydrologic processes at regional and larger scales. We propose a novel algorithm for estimating BUSNs by drawing on concepts from graph theory and existing, extensively available land surface data, such as street network, topography, and land use/land cover. First, we derive the causal relationships between the topology of BUSNs and urban surface features based on graph theory concepts. We then apply the causal relationships and estimate BUSNs using web-service data retrieval, spatial analysis, and high-performance computing techniques. Finally, we validate the derived BUSNs in the metropolitan areas of Los Angeles, Seattle, Houston, and Baltimore in the US, where real BUSN data are partly available to the public. Results show that our algorithm can effectively capture 59 %–76 % of the topology of real BUSN data, depending on the supporting data quality. This algorithm has promising potential to support large-scale urban hydrologic modeling and future urban drainage system planning.
... The Lagrangian particle movement model solves the Langevin equation illustrated as Eq. (1), which considers a dispersive component resulting from random processes, including molecular and turbulence diffusion in water, with a random walk numerical algorithm (Naves et al., 2019). The drifting-egg floating simulation model is defined by the superposition of two groups of motion vectors in the model, where the horizontal movement direction and speed of the eggs are defined as the horizontal flow direction and speed, respectively, and the vertical movement is determined by the minimum flow velocity required to keep the drifting eggs floating, below which the vertical settling speed of the eggs is defined as 0.0075 m/s Wan et al., 2021;Zeng et al., 2019). ...
The use of environmental flow (e-flow) regimes has been widely implemented to improve fish habitat quality in river restoration efforts. However, e-flow designs focusing only on one key life stage (e.g., spawning) without considering potential bottlenecks in other stages (e.g., hatching) can result in little to no improvement, especially when targeting the restoration of fish with drifting eggs. Few e-flow assessments are available that closely link the spatial-temporal dependence of the hydrodynamic effect of drifting eggs on hatching habitats. Moreover, an understanding of how to allocate e-flows to achieve the best possible outcomes for biological diversity conservation is still lacking. In this study, a new framework was developed to assess e-flows, aiming to satisfy the requirements of multiple fish species with different spawning patterns concerning streamflow requirements during spawning and hatching periods. In this framework, the final weighted usable area (FWUA) was proposed by linking the spawning demand to the hydrodynamic effect of drifting eggs to assess habitat quality for fish that produce drifting eggs, and water temperature was used to guide when and how to shift from fixed to moving protection targets in allocating e-flows. Here, we used the Xiangjiaba Reservoir, located in the lower Jinsha River, as a case study to design e-flows for the conservation of multiple fish species with different spawning patterns, which was beneficial for increasing the probability of restoration success. By testing scenarios with an absence of drifting passage, the ecological base flow considering only spawning habitat appears to be lower than that considering both quality of spawning habitat and hatching passage. The ecological benefits (FWUA) generated from the ecological base flow identified by traditional models represent only 64.91% of our framework and are thus anticipated to have cascading deviant effects on ecological patterns and processes in riverine ecosystems. This underlying difference in FWUA generated due to different ecological base flows determined from traditional models and our framework, however, has been overshadowed in previous research. We highlight that the highest fish population density recovery potential will be reached at only certain ratios for both sets of habitat benefits. This work provides a tool that can help managers evaluate e-flows and compare different river restoration scenarios to protect degraded rivers or develop strategies to build resilience to climate change.
... Kinect photogrammetric technology has been experimentally investigated by Masoudi et al. (2018) [27] for measuring and assessing riverbank variations. Naves et al. (2019) [28] focused on applying the SFM photogrammetric technique to carry out a high-resolution and accurate topographic survey of a shallow water model. Ruther (2019) [11] applied the SFM software (Agisoft PhotoScan) to study bed evolution in a physical fluvial model at high sediment transport containing complex flushing hydraulic structures. ...
Accurate measurements of sediment flushing cone geometry (SFCG) are essential for determining sediment removal efficiency in reservoirs. SFCG measurements are related to the point-to-point height that affects bathymetry accuracy, and they are used to develop a digital elevation model (DEM). Conventional bathymetry monitoring techniques require a longer time for data processing and output data with insufficient accuracy despite being inexpensive and simple. In the current research, a close-range photogrammetric method called the structure from motion (SFM) method was investigated to determine the SFCG in an experimental study. The regular geometric shape of a cube was used to verify the SFM. Additionally, measurements between model control points (MCPs) on the flushed sediment bed were compared with those from the SFM method. The results indicated that the calculated SFM values were consistent with the measured values. To determine the SFCG, two sets of images were captured with 70% average overlapping before and after the completion of each test. After processing and post-processing via the SFM tool AgiSoft Metashape, a georeferenced 3D model was achieved. The accuracy of the surveyed data in terms of the dimensions, cross-sections, and temporal developments of the sediment flushing cone was investigated to verify the SFM method. Finally, the results revealed good agreement (R2=0.99 and average error of 0.03–0.74 mm) between the DEMs created by the SFM method and the actual model.
... can only apply to a local, small-city level due to its intensive computational demand and requirement of detailed BUSN data, which typically are not available to the public (e.g., Nanía et al., 2015;Meyers et al., 2021; Fraga et al., 2016;Naves et al., 2019). Therefore, BUSN data sparsity remains a grand challenge in urban hydrology, preventing us from understanding and modeling below-ground urban hydrologic processes at the regional or larger scales that are compatible with the impacts of 30 urbanization and climate change. ...
Below-ground Urban stormwater networks (BUSNs) are critical for removing excess rainfall from impervious areas and preventing or mitigating urban flooding. However, available BUSN data are sparse, preventing modeling and analyzing urban hydrologic processes at regional and larger scales. We thus propose a novel algorithm for estimating BUSNs from existing, extensively available land surface data such as street network, topography, land use/land cover, etc. The rationale underpinning this algorithm are the causal relationships between the topology of BUSNs and urban surface features that we derive based on the Graph theory concepts. We implement this algorithm using web services for data retrieval and high-performance computing techniques for big-data analyses. Lastly, we validate this algorithm at a small portion of Los Angeles and Seattle, and the metropolitan areas of Houston and Baltimore in the U.S., where real BUSN data are available to the public. Results show that our algorithm can effectively capture 60–75 % of the topology of real BUSN data, depending on the supporting data quality. This algorithm has promising potential to support large-scale urban hydrologic modeling and future urban drainage system planning.
... In addition, it has been used in a LSPIV application as a post-processing software for velocity vectors produced by the PIVlab. Naves et al. [90] used the software in laboratory conditions on street-scale urban drainage physical model to study runoff using fluorescent seeding particles. ...
Sustainable water resources management plans require advanced instrumentation to measure accurately both the water velocity and the discharge of the aquatic bodies. An innovative way to achieve this goal is with the use of non-contact, cost-effective, and efficient image-based methods. A studied water surface can be captured by subsequent images while surface velocity can be estimated by the movement of tracers on the water’s surface. Various software have been developed in order to utilize such tracing algorithms and to monitor the surface velocity of fluids. The objective of this study was to present the current status of these software, describe the main parameters, and provide applied examples of image-based velocimetry application. To achieve this firstly, a comprehensive review was conducted that focused on the scientific publications that have utilized particle image and tracking velocimetry methods on water bodies. Secondly,
the main scope of this research was to record and analyze these publications based on the software that were used. This paper presents 30 software with their main features and few of their application examples. This should help other researchers choose the appropriate image-based velocimetry software to measure water velocity and discharge based on the needs of their study.
... The numerical solution was separately divided into advective transport and random components as described above. In this study, we disabled the random components for either the horizontal or vertical directions (Naves et al., 2019). ...
For shallow lakes, the water exchange process is a crucial factor that affects lake eutrophication, which can be solved by a water diversion project (WDP). However, the water exchange process in shallow lakes is complex and affected by hydrological characteristics (the water level and inflow stream) and external forcing (the wind field). It is of profound significance to evaluate the process of lake water exchange by combining dynamic and static methods. In this study, for hydrological characterization, a Morlet wavelet analysis was used for the periodic analysis of 24-year water level data. The monthly discharge of the main rivers over three hydrological years was calculated by a hydrological frequency curve and water balance theory. The external wind field was studied by the wind sheltering coefficient to simulate an uneven distribution. The water age model and particle tracking model were coupled to explore the water exchange process of Dianchi Lake with the influence of two major WDPs. The results show that in each scenario, the distribution of the water age presents a radial distribution and decreases in age from the centre of the lake to the shore, and the largest proportion of the oldest water occurs without exception at the centre of Dianchi Lake. Moreover, the water mass in Dianchi Lake generally circulates counter clockwise around a circle of a fixed size. When the Niulanjiang Water Diversion Project (NWDP) and the Dianzhong Water Diversion Project (DWDP) are combined for water diversion, the annual water diversion volume accounts for 76% of the lake water volume, which can reduce the water age of the lake centre by 38%-52%.
... Artificial rain has already been used to simulate various hyetographs to deal with lack of data associated with intense rain (Bengtsson 2005;Villarreal & Bengtsson 2005). Spatial uniformity of the simulated rainfall has been investigated in a certain number of studies (Naves et al. 2017;Naves et al. 2019). However, no research was found to apply the rainfall simulator to test different hyetographs on a full-scale green roof under changing initial climate conditions. ...
Rooftops cover a large percentage of land area in urban areas, which can potentially be used for stormwater purposes. Seeking adaptation strategies, there is an increasing interest in utilising green roofs for stormwater management. However, the impact of extreme rainfall on the hydrological performance of green roofs and their design implications remain challenging to quantify. In this study, a method was developed to assess the detention performance of a detention-based green roof (underlaid with 100 mm of expanded clay) for current and future climate conditions under extreme precipitation using an artificial rainfall generator. The green roof runoff was found to be more sensitive to the initial water content than the hyetograph shape. The green roof outperformed the black roof in terms of all performance indicators (time of concentration, centroid delay, T50 or peak attenuation). While the time of concentration for the reference black roof was within 5 minutes independently of rainfall intensity, for the green roof was extrapolated between 30 and 90 minutes with intensity from 0.8 to 2.5 mm/min. Adding a layer of expanded clay under the green roof substrate provided a significant improvement to the detention performance under extreme precipitation in current and future climate conditions.
... The experimental dataset obtained is described and openly available at the Zenodo [43] repository, where the quality of the experimental results obtained using this rainfall simulator can be confirmed. In addition, these experimental results were used to obtain a detailed representation of the overland runoff though a 2D shallow water model [44] and to analyze the performance of a novel physically-based urban wash-off model [45]. ...
Rainfall simulators are useful tools for controlling the main variables that govern natural rainfall. In this study, a new drop-forming rainfall simulator, which consists of pressure-compensating dripper grids above a horizontal mesh that breaks and distributes raindrops, was developed to be applied in wash-off experiments in a large-scale physical model of 36 m2. The mesh typology and size, and its distance to drippers, were established through a calibration where rain uniformity and distributions of raindrop sizes and velocities were compared with local natural rainfall. Finally, the rain properties of the final solution were measured for the three rain intensities that the rainfall simulator is able to generate (30, 50 and 80 mm/h), obtaining almost uniform rainfalls with uniformity coefficients of 81%, 89% and 91%, respectively. This, together with the very suitable raindrop size distribution obtained, and the raindrop velocities of around 87.5% of the terminal velocity for the mean raindrop diameter, makes the proposed solution optimal for wash-off studies, where rain properties are key in the detachment of particles. In addition, the flexibility seen in controlling rain characteristics increases the value of the proposed design in that it is adaptable to a wide range of studies.
Drainage modeling that accurately captures urban storm inundation serves as the foundation for flood warning and drainage scheduling. In this paper, we proposed a novel coupling ideology that, by integrating 2D-1D and 1D-2D unidirectional processes, overcomes the drawback of the conventional unidirectional coupling approach that fails to properly represent the rainfall surface catchment dynamics, and provides more coherent hydrological implications compared to the bidirectional coupling concept. This paper first referred to a laboratory experimental case from the literature, applied and analyzed the coupling scheme proposed in this paper and the bidirectional coupling scheme that has been widely studied in recent years, compared the two coupling solutions in terms of the resulting accuracy and applicability, and discussed their respective strengths and weaknesses to validate the reliability of the proposed method. The verified proposed coupling scheme was then applied to the modeling of a real drainage system in a region of Nanjing, China, and the results proved that the coupling mechanism proposed in this study is of practical application value.
This work presents an Adaptive Large Scale Particle Image Velocimetry method (ALSPIV), which measures surface velocity of a physical model experiment with complex flow pattern. In the experiment, the eleven low-cost, high-resolution surveillance cameras are adopted to achieve a large-scale flow field in real time. The lenses of them are shined perpendicularly on water surface to minimize perspective distortion. A camera calibration method is also designed to enhance measurement accuracy. In addition, an adaptive cross-correlation algorithm can contribute to cross-correlation and a lower signal-to-noise ratio. Finally, an experimental method is employed to verify the ALSPIV method’s accuracy, and the surface velocity distributions under three different steady flows are measured to demonstrate its applicability. Results show that the method is demonstrated to be a low-cost and automatic flow diagnostic tool and an accurate means of measuring surface velocities in the physical model experiments of flood propagation with complex flow patterns.
This paper presents two datasets obtained from laboratory experiments of urban flooding in a street network performed at the University of Liège. The experimental model represents a part of a synthetic urban district that consists of three inlets, three outlets and several three- and four- branches crossroads. The following experimental data was produced: (i) dataset 1: time-series of flow depths at model inlets and time-series of discharges at model outlets for a two-branch junction model, a two-branch bifurcation model and a district model. The datasets were generated by varying the upstream and downstream boundary conditions, i.e. flooding conditions; (ii) dataset 2 includes the same data type as dataset 1 complemented by 2D surface velocity measured using the non-intrusive LSPIV technique for eight urban form configurations in the district model. The collected data enable improving the understanding of the effect of urban forms on the urban flood processes. These two datasets are valuable for validating and improving numerical or analytical models of urban flooding and may contribute to flood risk management and flood-resilient urban design.
Water-sensitive urban design is an integral part of flood risk management. Based on computational modelling, we investigated the influence of various urban forms on flooding severity at the level of an urban block and for the case of long-duration urban flooding. The upstream flow depths, downstream discharge partition and flow exchange through the urban forms were examined. The results indicate that one urban characteristic has an overwhelming influence on the flow variables: the conveyance porosity in the main flow direction is by far more influential than the conveyance porosity in the normal direction or the number of streets. Such anisotropic effect was not pointed in recent similar studies, and it hints at practical guidelines for sustainable urban planning in practice. Moreover, the computational model was verified against laboratory observations, which constitute a novel valuable dataset for the validation of other urban flooding models.
Structure from motion (SfM) has been applied recently in fluvial sedimentology. This application is due to the availability of many low-cost unmanned aerial vehicles/drones, which can help overcome challenging terrain, provide efficient and reproducible and high-accuracy topographic images and data. The current study describes the application of SfM to build a geomorphological model and estimate the surface water velocity of the Way Semaka River in the Bandar Negeri Suoh (BNS) region in the West Lampung area. Way Semaka is a river type with an extensive meandering system and stable extension tectonic regime relatively. River morphology approximately 96.62 m width and 4 m depth in straight (relatively) area, whereas in channel area approximately 171.22 m width and 5 m depth. The velocity range between 0.39 – 1.56 m/s based on image analysis proven by current meter measurements onsite with an RMS error of 0.25. Manual geomorphic unit level 2 analysis revealed that 9% of the coverage consisted of basins for the channel's zone, 35% of the coverage consisted of convexity, 9% consisted of planar features, and 37% of the coverage consisted of the transition zone.
A three-axis accelerometer was combined with large-scale particle image velocimetry (LSPIV) to obtain nonintrusive and safe surface velocity measurements. Dual cameras were established at the Yu-Feng gauging station of Shimen Reservoir to capture near-field and far-field images and analyze the surface velocity of rivers. Surface velocity measurements were obtained with a flow meter, LPSIV with ground control points, and LSPIV with a three-axis accelerometer to compare the measurement accuracy. The results show that the relative root mean square error (RMSE) values for LSPIV with ground control points and with the three-axis accelerometer are 21% and 18%, respectively. The LSPIV technique with the three-axis accelerometer slightly improved the measurement accuracy of the surface velocity. However a three-axis accelerometer can be utilized to replace the traditional ground control points for yielding the camera pose parameters. Furthermore, the effects of the camera pose, three-axis acceleration, interrogation area (IA), and image resolution on surface velocity measurements were explored. The camera pose parameters, namely, roll (θ) and tilt (τ), and three-axis acceleration parameters, including Xa and Ya, influence surface velocity measurements. If the measurement error of the surface velocity is controlled within ±10%, the acceptable variational ranges of θ, τ, Xa, and Ya are 6.2°, 1.3°, 0.11 g, and 0.02 g, respectively. The IA size and image resolution also significantly affect the accuracy of surface velocity measurements. Therefore, the selection of a suitable IA size and image resolution is crucial for accurately measuring surface velocity.
In order to investigate the relationship between water surface velocity and breach hydrograph, a series of dam breach experiments with a generalised landslide dam were conducted in an open channel of 50 m × 4 m × 2 m. The large‐scale particle image velocimetry (LSPIV) technique was applied to measure the time history of water surface velocity during the dam breach process, and the hydrography was obtained by integrating the surface velocity along the water depth. The influence of different vertical velocity profile approximation and suspended sediment concentration on the peak breach discharge were analysed and discussed. The results showed that the water depth over the breach crest can be described as a function of water surface velocity using . A simple formula based on surface velocity and breach width for the estimation of breach discharge was further proposed and verified.
Although surface velocities are key in the calibration of physically based urban drainage models, the shallow water depths developed during non-extreme precipitation and the potential risks during flood events limit the availability of this type of data in urban catchments. In this context, imaging velocimetry techniques are being investigated as suitable non-intrusive methods to estimate runoff velocities, when the possible influence of rain has yet to be analyzed. This study carried out a comparative assessment of different seeded and unseeded imaging velocimetry techniques based on large-scale particle image velocimetry (LSPIV) and bubble image velocimetry (BIV) through six realistic but laboratory-controlled experiments, in which the runoff generated by three different rain intensities was recorded. First, the use of naturally generated bubbles and water shadows and glares as tracers allows unseeded techniques to measure extremely shallow flows. However, these techniques are more affected by raindrop impacts, which even lead to erroneous velocities in the case of high rain intensities. At the same time, better results were obtained for high intensities and in complex flows with techniques that use artificial particles. Finally, the study highlights the potential of these imaging techniques for measuring surface velocities in real field applications as well as the importance of considering rain properties to interpret and assess the results obtained. The robustness of the techniques for real-life applications yet remains to be proven by means of further studies in non-controlled environments.
This paper presents a cost-effective methodology to simultaneously measure mixing processes and surface velocity fields in shallow flows using low cost cameras and lighting. Velocity fields and depth averaged concentration of a soluble fluorescent tracer are obtained using the new techniques and the results verified against traditional point probe measurements in a laboratory flume. An example of simultaneous velocity/concentration measurement is presented for an instantaneous release of tracer into flow around an obstruction. The method will help to improve the understanding of mixing processes in shallow open channel flows. It is anticipated that the technique will be useful in physical modelling studies where the mixing and hydraulic length scales under investigation are in the order of 1-10 m, for example in compound channels and partially vegetated streams.
Within urban areas humans carry out a great diversity of activities, and some of them require the use of vehicles. Floods, especially in urban areas, can generate significant tangible direct damages to vehicles themselves and to the urban elements in case of loss of stability and collision, which cannot be dismissed. In this paper, after a state‐of‐the‐art review on damage curves for vehicles, a methodology to assess the direct economic impact for vehicles exposed to flooding has been described, and applied within a study carried out in the framework of the BINGO H2020 EU Project. Only three different studies focused on damages to vehicles in contact with floodwater have been found. Contrasting damage curves for vehicles are found when comparing the three approaches, however the ones proposed by the USACE offer a high level of completeness and accuracy. Moreover, USACE’s development is the most current research and all the steps for the development of the damage curves are comprehensively described. Finally, after the description of a detailed methodology for flood damage mapping for vehicles, a procedure to evaluate the Expected Annual Damage for vehicles is offered.
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This research is focused in the monitoring of sediments in circular sewer pipes with different diameters at a flume facility fed with urban wastewater. For this purpose, sediment physical and chemical characteristics, and sediment mobility were recorded. The Structure from Motion photogrammetric technique was used for the measurement of sediment bed evolution. In addition, sediment properties were determined in order to study the cohesiveness of the bed deposits. In particular, the chemical oxygen demand and the oxygen uptake rate of the sediment samples were analysed after different accumulation periods on the pipe inverts, resulting in a relation between these parameters and the mobility processes of solids.
Among the urban aquatic pollutants, the most common is sediment which also acts as a transport medium for many contaminants. Hence there is an increasing interest in being able to better predict the sediment wash–off from urban surfaces. The exponential wash-off model is the most widely used method to predict the sediment wash-off. Although a number of studies proposed various modifications to the original exponential wash-off equation, these studies mostly looked into one parameter in isolation thereby ignoring the interactions between the parameters corresponding to rainfall, catchment and sediment characteristics. Hence in this study we aim (a) to investigate the effect of rainfall intensity, surface slope and initial load on wash-off load in an integrated and systematic way and (b) to subsequently improve the exponential wash-off equation focusing on the effect of the aforementioned three parameters. A series of laboratory experiments were carried out in a full-scale setup, comprising of a rainfall simulator, a 1 m² bituminous road surface, and a continuous wash-off measuring system. Five rainfall intensities ranging from 33 to 155 mm/h, four slopes ranging from 2 to 16% and three initial loads ranging from 50 to 200 g/m² were selected based on values obtained from the literature. Fine sediment with a size range of 300–600 µm was used for all of the tests. Each test was carried out for one hour with at least 9 wash-off samples per test collected. Mass balance checks were carried out for all the tests as a quality control measure to make sure that there is no significant loss of sand during the tests. Results show that the washed off sediment load at any given time is proportional to initial load for a given combination of rainfall intensity and surface slope. This indicates the importance of dedicated modelling of build-up so as to subsequently predict wash-off load. It was also observed that the maximum fraction that is washed off from the surface increases with both rainfall intensity and the surface slope. This observation leads to the second part of the study where the existing wash-off model is modified by introducing a capacity factor which defines this maximum fraction. This capacity factor is derived as a function of wash-off coefficient, making use of the correlation between the maximum fraction and the wash-off rate. Values of the modified wash-off coefficient are presented for all combinations of rainfall intensities and surface slopes, which can be transferred to other urban catchments with similar conditions.
p class="Resumen">Las inundaciones urbanas pueden provocar importantes daños a vehículos que, en general, no son considerados en la mayoría de estudios sobre evaluación de riesgo por inundaciones. En este artículo se propone una metodología para la estimación de los daños a vehículos expuestos a inundaciones urbanas. Se presenta inicialmente el estado de la cuestión en lo que se refiere a curvas de daños para vehículos, escogiéndose las desarrolladas por el U.S. Army Corps of Engineers (USACE, 2009) por ser las más recientes, mejor justificadas y presentar mayor adaptabilidad al caso de estudio propuesto. La metodología propuesta se aplica al municipio español de Badalona, en el marco del proyecto europeo H2020 BINGO. Para llevar a cabo dicha metodología se definen y aplican conceptos como la distribución vehicular en toda el área estudiada. Finalmente, se evalúa el Daño Anual Esperado (DAE) relativo a coches a partir de los daños ocasionados por eventos sintéticos de 1, 10, 100 y 500 años de periodo de retorno.</p
This study analyses the mobilization of total suspended solids (TSSs) for different spatial distributions of sediment load located over the roadway surface of a full-scale street section physical model. At the sewer network outlet, flow discharges were measured and TSS pollutographs were determined with manual grab samples and inferred from turbidity records. In all the tests, the rain duration was five minutes and its averaged intensity was 101 mm/h. In addition, solids that were not washed off at the end of the experiments were collected from the street surface, gully pots and pipes and the mass balance error was checked. The experiments were configured to assess the influence of the initial load, spatial distribution method, distance from gully pot and distribution area dimensions on the TSSs washoff. The study showed that sediment initial load and distribution cannot explain completely pollutant washoff processes because other variables such as the spatial rainfall distribution or the runoff depth also affect to the outlet pollutographs and system mass balances.
The probability of the occurrence of urban flash floods has increased appreciably in recent years. Scientists have published various articles related to the estimation of the vulnerability of people and vehicles in urban areas resulting from flash floods. However, most published works are based on research performed using numerical models and laboratory experiments. This paper presents a novel approach that combines the implementation of image velocimetry technique (large-scale particle image velocimetry—LSPIV) using a flash flood video recorded by the public locally and the estimation of the vulnerability of people and vehicles to high water velocities in urban areas. A numerical one‐dimensional hydrodynamic model has also been used in this approach for water velocity characterization. The results presented in this paper correspond to a flash flood resulting on November 29, 2012, in the city of Asunción in Paraguay. During this flash flood, people and vehicles were observed being carried away because of high water velocities. Various sequences of the recorded flash flood video were characterized using LSPIV. The results obtained in this work validate the existing vulnerability criterion based on the effect of the flash flood and resulting high water velocities on people and vehicles.
Populations in urban environments are extremely mobile throughout the day and in various weather conditions; accounting for this pedestrian mobility and security becomes high importance. Research into the security and stability of the pedestrian environment under exposure to critical water flows provides an essential knowledge base with which the associated hazard unto them can be critically evaluated. This research seeks to analyse degrees of hazard in relation to persons exposed to high-volume rain events in urban areas. Several human trials of critical urban flows were conducted in order to determine the stability limits of pedestrians, crossing through a water flow in a real-scale physic model. Additionally, the critical first step from a dry footpath into fast-flowing water is considered and an assessment of the tested subjects’ emotional responses when entering and crossing flooded roadways was carried out. Results from this study are compared with various proposed human stability criteria as well as alternatives proposed in other written works. The presented study offers a stability threshold focused on shallow depths and high-velocity conditions, the most common urban flooding conditions.
Digital particle image velocimetry (DPIV) is a non-intrusive analysis technique that is very popular for mapping flows quantitatively. To get accurate results, in particular in complex flow fields, a number of challenges have to be faced and solved: The quality of the flow measurements is affected by computational details such as image pre-conditioning, sub-pixel peak estimators, data validation procedures, interpolation algorithms and smoothing methods. The accuracy of several algorithms was determined and the best performing methods were implemented in a user-friendly open-source tool for performing DPIV flow analysis in Matlab.
A mathematical model of suspended solids discharge from impervious surfaces during storm events has been developed. The model continuously simulates two major processes of different time scales; solids build-up at impervious surfaces between two storm events, and solids wash-off from the surfaces during storm events. Buildup is modelled using the Sartor and Boyd equation (21) in which the amount of' solids available on the surface is an exponential function of antecedent dry weather period duration. The spatial distribution of solid particles over the street surface is also modelled, which is an innovation. The wash-off process is divided into three subprocesses that are modelled consecutively. A kinematic wave model is used for overland flow modelling. The particle entrainment into suspension is estimated by two methods. In one, the rainfall and overland flow effects are not separated and the total shear stress is used to predict entrainment. In the other, the rainfall and overland flow effects are treated separately and then summed. An original equation was developed for this method. The model is applied on two small experimental catchments, one at Miljakovac-Belgrade, Yugoslavia and the other in Lund, Sweden. The description and verification of the model are presented and discussed in the paper.
The model of soil erosion on a plane slope introduced by Hairsine and Rose (this issue) is further developed by considering rill flow. The rills are considered to be parallel and incised in a homogeneous soil mass and have sediment and water flux contributed to them orthogonally. The erosive action of water flowing down these rills is described using the concept of stream power, which is assumed to be uniformly distributed around the wetted perimeter. The apportioning of the erosion and deposition processes within a rill is then considered to be influenced by the spatial extent of a deposited layer. The theory is developed for trapezoidal rills, with triangular rills and rectangular rills as special cases. Equations describing sediment continuity are presented, and numerical and analytical solutions are described for the entrainment-limited and transport-limited situations. The experiments of Meyer and Harmon (1985) are examined using this theory, and consistency of evaluated parameters is demonstrated within this data set.
A new method for detecting spikes in acoustic Doppler velocimeter data sequences is suggested. The method combines three concepts: (1) that differentiation enhances the high frequency portion of a signal, (2) that the expected maximum of a random series is given by the Universal threshold, and (3) that good data cluster in a dense cloud in phase space or Poincare maps. These concepts are used to construct an ellipsoid in three-dimensional phase space, then points lying outside the ellipsoid are designated as spikes. The new method is shown to have superior performance to various other methods and it has the added advantage that it requires no parameters. Several methods for replacing sequences of spurious data are presented. A polynomial fitted to good data on either side of the spike event, then interpolated across the event, is preferred by the authors.
Recent developments in flood modeling have led to the concept of coupled (sewer/surface) hydraulic models. In this paper two coupled models are examined; a one-dimensional (1D) sewer model coupled with a 1D surface network model (1D/1D) and a 1D sewer model coupled with a two-dimensional (2D) surface flow model (1D/2D). Flow over the terrain is better modeled by 2D models, whereas in confined channels 1D models provide a good approximation with less computational effort. This paper presents a comparison of the simulation results of 1D/1D model and a 1D/2D model. The methodology adopted for setting up the models is outlined and explained in detail as well as the 1D/1D modeling techniques used for reproducing the 1D/2D model results. The surface flow comparison clarifies the limitations of the 1D/1D model and indicates that the definition of the surface pathways, the linking elements sewer/surface, and inclusion of virtual manholes are key factors for setting up a more accurate 1D/1D model.
Low velocity and shallow-depth flow fields often are a challenge to most velocity measuring instruments. In the framework of a research project on reservoir sedimentation, the influence of the reservoir geometry on sediment transport and deposition was studied. An inexpensive and accurate technique for Large-Scale Particle Image Velocimetry (LSPIV) was developed to measure the surface velocity field in 2D. An Ultrasonic Doppler Velocity Profiler (UVP) and LSPIV techniques were used for verification and validation of the numerical simulations. The velocities measured by means of UVP allowed an instantaneous measurement of the 1D velocity profile over the whole flow depth. The turbulence large-scale structures and jet expansion in the basin have been determined based on UVP, LSPIV and numerical simulations. Vertical velocity distributions were defined to study the vertical velocity effect. UVP measurements confirm 2D flow map in shallow reservoir. LSPIV has potential to measure low velocities. The comparison between LSPIV, UVP and numerical simulation gives good agreements.
This paper describes benchmark testing of six two-dimensional (2D) hydraulic models (DIVAST, DIVAST-TVD, TUFLOW, JFLOW, TRENT and LISFLOOD-FP) in terms of their ability to simulate surface flows in a densely urbanised area. The models are applied to a 1.0 km x 0.4 km urban catchment within the city of Glasgow, Scotland, UK, and are used to simulate a flood event that occurred at this site on 30 July 2002. An identical numerical grid describing the underlying topography is constructed for each model, using a combination of airborne laser altimetry (LiDAR) fused with digital map data, and used to run a benchmark simulation. Two numerical experiments were then conducted to test the response of each model to topographic error and uncertainty over friction parameterisation. While all the models tested produce plausible results, subtle differences between particular groups of codes give considerable insight into both the practice and science of urban hydraulic modelling. In particular, the results show that the terrain data available from modern LiDAR systems are sufficiently accurate and resolved for simulating urban flows, but such data need to be fused with digital map data of building topology and land use to gain maximum benefit from the information contained therein. When such terrain data are available, uncertainty in friction parameters becomes a more dominant factor than topographic error for typical problems. The simulations also show that flows in urban environments are characterised by numerous transitions to supercritical flow and numerical shocks. However, the effects of these are localised and they do not appear to affect overall wave propagation. In contrast, inertia terms are shown to be important in this particular case, but the specific characteristics of the test site may mean that this does not hold more generally.
We provide corrections to several key formula by Hairsine and Rose (1992) for steady state flow driven sediment transport and at the same time generalize their solution for the case of entrainment limiting flow when the mass of sediment in each size class is arbitrary. Yes Yes
This practical guide provides comprehensive information on PIV. The third edition extends many aspects of Particle image Velocimetry, in particular the tomographic PIV method, high-velocity PIV, Micro-PIV, and accuracy assessment.
In this book, relevant theoretical background information directly support the practical aspects associated with the planning, performance and understanding of experiments employing the PIV technique. It is primarily intended for engineers, scientists and students, who already have some basic knowledge of fluid mechanics and non-intrusive optical measurement techniques. It shall guide researchers and engineers to design and perform their experiment successfully without requiring them to first become specialists in the field. Nonetheless many of the basic properties of PIV are provided as they must be well understood before a correct interpretation of the results is possible
Physically-based models are important tools for evaluating the hydraulic behaviour of urban drainage systems and, more specifically, assessing flood risk. While it is well known that such models should be calibrated and validated with monitoring data, overland runoff information is seldom available for this purpose. This study investigates the potential of using surveillance camera footage to measure surface flow velocity thanks to an LSPIV-based method called Surface Structure Image Velocimetry (SSIV). Seven real-scale experiments conducted in a specialized flood training facility were used to test the SSIV method under varied and challenging conditions. SSIV performance was evaluated by benchmarking bulk (mean) velocity against that measured by a conventional sensor array. In the best conditions tested, SSIV and conventional flow sensors differed by only 1.7% (0.1% standard deviation). While the method proved sensitive to light conditions, our results suggest that infrared lighting could be used to increase measurement consistency. Our study concludes that for measuring overland flow velocity in urban areas, surveillance and traffic cameras can be considered as a low-maintenance and easy-to-install alternative to conventional sensor systems.
The accurate characterisation of flow from urban surfaces to sewer/stormwater systems is important for urban drainage design and flood modelling/risk identification. However, the geometrical complexity and large variety of drainage structures (linking elements) available makes model calibration and verification difficult. In this study an extensive comparison between experimentally measured and numerically modelled flow characteristics in the vicinity of ten different designs of manhole grate was performed under drainage flow in sub‐critical conditions. Using a 2D surface PIV (sPIV) system the work presents the first detailed characterisation of velocity fields around these linking elements. In addition, it provides the first detailed verification of the ability of a 2D numerical model to describe both velocity fields and drainage flows. The overall comparison shows a close relationship between numerical and the experimental results with some higher inflows in the experimental results as a consequence of a localised transition from weir to orifice condition near the void areas of the grates. It was also noted that velocity differences decreased further from the manhole, due mainly to the more directional flow. Overall the work demonstrates the potential for further use of 2D numerical models to describe flow conditions at linking elements, either directly within modelling simulations or indirectly via the characterisation of energy loss coefficients.
Measurements, aiming at the investigation of pollution wash-off from a single asphalt area which is drained into one gullypot, have been carried out at two similar experimental urban catchments: in Lund, Sweden, and in Belgrade, Yugoslavia. At both sites the continuous measurements of rainfall intensity, storm runoff and four water quality characteristics (suspended solids, pH-factor, conductivity and temperature) were carried out, using a similar method and similar equipment. To reach the required level of process dynamics, the data were recorded at short time intervals (10 sec) during a storm event. Statistical analysis of reliably measured data showed the main factor that affect surface solids build-up and wash-off. Based on it, a new physically based mathematical model of suspended solids wash-off has been developed. The model was calibrated and verified for both catchments. The brief description of the measurements, statistical analysis of recorded data, and the model, is presented in the paper.
Waste-water channels or physical hydraulic models often convey shallow water flows with depths around 5 cm. Such free surface flows can in principle be measured using standard measuring flumes or thin-plate weirs, but proper employment of these is often practically impossible, e.g. due to limited space. To avoid this, various flow meters with contact probes (i.e. »area-velocity« probes) are employed instead, but in reality this often results in inaccurate measured values of discharge. This paper presents an effective way to determine discharge of very shallow flow without intruding the flow. Our approach is based on computer aided visualization, namely on the quantification of the field of vectors representing local velocities on the water surface of the flow. In contrast to other studies, this method does not require complex measuring equipment, special lights or special devices for the seeding of particles. Experiments were conducted in 0.5 m and 1.06 m wide rectangular channels, made of glass and concrete, respectively, and they show that this method could be employed both in hydraulic laboratories and in the field. Measurements showed that velocity on the surface of the shallow water flow differs from theoretical average mean flow velocity in the observed cross section, and further that this difference increases with the decrease of water depth. This suggests that the assumption, which states that in shallow water flows the surface velocity is similar enough to the mean flow velocity, is not necessarily correct.
This article presents an example for an image-based method to determine a small rivers’ surface velocity field, bathymetry, and its flow discharge derived thereof. While common river measurement techniques typically need to be in contact with the waterbody, at least to measure transects of water depths, the new approach is completely without direct contact to water. The scenery is recorded by an off-the-shelf action camera mounted to a low-cost quadcopter. During the analysis, image frames are orthorectified and georeferenced by an approach that combines structure from motion and multiview stereo algorithms. Particle image velocimetry based on tracer particles present in the river is utilized to compute flow velocities. Instantaneous surface flow velocity fields are used to compute the mean velocity field as well as to derive water depth estimates by turbulence metrics. The latter provide a basis to verify the bathymetry gained from the reconstructed subaqueous three-dimensional scenery. Finally, flow discharge is estimated based on the above findings. The new method will expand the scientific knowledge on river flows for diverse disciplines such as hydrology, biology, and river engineering. Due to the low cost of the measurement instrumentation being deployed, it has the potential to be applied by a broad user group.
In this article we investigate the influence of fine scale changes in the elevation of urban terrains on the dynamics and final distribution of flood inundation generated by intense rainfall. Numerical experiments have been performed combining 2D shallow-water model with extremely fine resolution (10 cm) terrain data. Our results reveal that localized, decimetric-scale alterations in the elevation of streets can lead to remarkable differences in the flood inundation. These results confirm the important role played by finely resolved and accurate terrain data in capturing flow patterns that have a central impact on model predictions of flood inundation. Also, we argue that the observed sensitivity of flood inundation to small-scale topographical features paves the way to new opportunities for flood risk management measures. In particular, engineering flood resilient urban surfaces using fine resolution models has a potential to considerably reduce flood impacts at a relatively low cost.
Current urban washoff models still rely on empirical catchment-scale functions, that have not been substantially updated during the last 40years. This paper introduce a new approach using the physical model FullSWOF to evaluate urban washoff process. The modelling approach is performed for a Parisian road catchment. Water flow simulation is validated by outlet discharge measurements and local observations of water depth. Water quality modelling of three classes of particles (d50=7μm, 70μm, and 250μm) is applied using the Hairsine-Rose model. Analysis of the washoff process at the catchment scale indicates that most (>90%) of the finest particles are removed at the beginning of a rainfall event, about 10%-20% of medium-sized particles are moved over the latest part of the event, and almost no coarse particles can be transferred into the sewer inlet. Spatial analysis of washoff process reveals that the concentration of suspended solids on road and sidewalk surface is more sensitive to rainfall intensities than that on gutter surface, while coarser particles tend to accumulate in the gutter over the later part of a rainfall event. Investigation of the driving force behind the detachment process indicates that rainfall-driven effects are two orders of magnitude higher than flow-driven effects. Moreover, it is observed that rainfall-driven detachment is considerably decreased with the rising water depth, while flow-driven detachment occurs only in gutter areas. Finally, several controversial arguments on the use of physical models for assessing the washoff process, and perspectives on development of physical urban washoff models are discussed.
Nowadays, the increasing use of vehicles is causing contaminated stormwater runoff to drain from roads. The detailed understanding of urban wash-off processes is essential for addressing urban management issues. However, existing modelling approaches are rarely applied for these objectives due to the lack of realistic input data, unsuitability of physical descriptions, and inadequate documentation of model testing. In this context, we implement a method of coupling monitoring surveys with the physically-based FullSWOF (Full Shallow Water equations for Overland Flow) model (Delestre et al., 2014) and the process-based H-R (Hairsine-Rose) model (Hairsine and Rose, 1992a, 1992b) to evaluate urban wash-off process on a road catchment near Paris (Le Perreux sur Marne, Val de Marne, France, 2661 m2). This work is the first time that such an approach is applied for road wash-off modelling in the context of urban stormwater runoff. On-site experimental measurements have shown that only the finest particles of the road dry stocks could be transferred to the sewer inlet during rainfall events, and most Polycyclic Aromatic Hydrocarbons (PAHs) are found in the particulate phase. Simulations over different rainfall events represent promising results in reproducing the various dynamics of water flows and sediment transports at the road catchment scale. Elementary Effects method is applied for sensitivity analysis. It is confirmed that settling velocity (_V__s_) and initial dry stocks (_S_) are the most influential parameters in both overall and higher order effects. Furthermore, flow-driven detachment seems to be insignificant in our case study, while raindrop-driven detachment is shown to be the major force for detaching sediment from the studied urban surface. Finally, a multiple sediment classification regarding the Particle Size Distribution (PSD) can be suggested for improving the model performance for future studies.
This paper presents a global sensitivity and uncertainty analysis of a dual drainage model applied to a 0.049km2 (4.9-ha) urban catchment based on generalized likelihood uncertainty estimation (GLUE). The model solves the nonlinear bidimensional (2D) and one-dimensional (1D) Saint-Venant equations to compute respectively the surface runoff and the flow in the sewer network. The sensitivity of the outlet hydrograph to the input parameters of the model was determined by using variance-based Sobol sensitivity indices. These indices highlight the great effect of the overland flow parameters on the model output, in contrast with the limited effect of the sewer-network parameters. The Manning coefficient of the impervious terrains was identified as the most influential model parameter. The effect on model calibration of two subjective factors of the GLUE methodology (the acceptability threshold and the shaping factor of the likelihood function) was analyzed. From this analysis, a NSE acceptability threshold of 0.6 and a shaping factor of 1 were adopted for model calibration. Greater values of these parameters resulted in very narrow uncertainty bounds and therefore in low coverage ratios. The results obtained after calibration and validation show a satisfactory performance of the model, with NSE values within 0.78 and 0.98 and coverage ratios of the 95% confidence intervals in the range 66-91%. The worst performances are obtained in the events with lowest rainfall depths, since in those cases the overland flow in the whole catchment is extremely shallow and the runoff propagation is not well captured by the model.
This paper presents a 1D-2D dual drainage model to compute the rainfall-runoff transformation in urban environments. Overland flow in major drainage systems is modelled with the 2D shallow water equations, whereas the flow in a sewer network is computed with the 1D Saint-Venant equations using the two-component pressure approach to model pressure-flow conditions. The surface and sewer network models are linked through manholes, which allow water interchange in both directions. A new series of rainfall–runoff experiments in a real-scale physical model of a street section is used to validate the model under unsteady part-full and pressure flow conditions. The experimental measurements of water depth and discharge at several locations in a drainage network show a very satisfactory performance of the numerical model.
Process variability in pollutant build-up and wash-off generates inherent uncertainty that affects the outcomes of stormwater quality models. Poor characterisation of process variability constrains the accurate accounting of the uncertainty associated with pollutant processes. This acts as a significant limitation to effective decision making in relation to stormwater pollution mitigation. The study undertaken developed three theoretical scenarios based on research findings that variations in particle size fractions <150μm and >150μm during pollutant build-up and wash-off primarily determine the variability associated with these processes. These scenarios, which combine pollutant build-up and wash-off processes that takes place on a continuous timeline, are able to explain process variability under different field conditions. Given the variability characteristics of a specific build-up or wash-off event, the theoretical scenarios help to infer the variability characteristics of the associated pollutant process that follows. Mathematical formulation of the theoretical scenarios enables the incorporation of variability characteristics of pollutant build-up and wash-off processes in stormwater quality models. The research study outcomes will contribute to the quantitative assessment of uncertainty as an integral part of the interpretation of stormwater quality modelling outcomes.
Copyright © 2015 Elsevier B.V. All rights reserved.
This paper presents the Decoupled Hydrological Discretisation (DHD) scheme for solving the shallow water equations in hydrological applications involving surface runoff in rural and urban basins. The name of the scheme is motivated by the fact that the three equations which form the two-dimensional shallow water system are discretised independently from each other and thus, the numerical scheme is decoupled in a mathematical sense. Its main advantages compared to other classic finite volume schemes for the shallow water equations are its simplicity to code and the lower computational cost per time step. The validation of the scheme is presented in five test cases involving overland flow and rainfall-runoff transformation over topographies of different complexity. The scheme is compared to the finite volume scheme ofRoe [1986], to the simple inertia formulation [Bates et al., 2010], and to the diffusive wave model. The test cases show that the DHD scheme is able to compute subcritical and supercritical flows in rural and urban environments, and that in overland flow applications it gives similar results to the second order scheme of Roe with a lower computational cost. The results obtained with the simple inertia and diffusive wave models are very similar to those obtained with the DHD scheme in rural basins in which the bed friction and topography dominate the flow hydrodynamics but they deteriorate in typical urban configurations in which the presence of supercritical flow conditions and small scale patterns boost the relevance of the inertial terms in the momentum equations. This article is protected by copyright. All rights reserved.
Pluvial flooding in urban areas drained by storm sewer networks is characterized by surcharge-induced inundation. Urban inundation models need to reproduce the complex interaction between the sewer flow and the surcharge-induced inundation to make reasonable predictions of the likely flood damage in urban areas. In the framework of the present work, the storm sewer model SWMM5 and a newly developed two-dimensional (2D) noninertia overland-flow model have been coupled to simulate the interaction between the sewer system and the urban floodplain. The solution of the 2D model is on the basis of an alternating direction implicit scheme that solves the 2D noninertia free-surface shallow-water equations. For accuracy reasons, the time step is limited and controlled by the use of iteration to home-in on an accurate solution at each sweep. The dynamic interaction between the two models is bidirectional, and the interacting discharges are calculated according to the water level differences between the flows in the sewer system network and aboveground flows. The paper presents details of the newly developed 2D model and describes the way in which the model was coupled with a one-dimensional (ID) sewer network model (SWMM5). The models were tested on one hypothetical case study and one real-life case study. DOI: 10.1061/(ASCE)HY.1943-7900.0000485. (C) 2012 American Society of Civil Engineers.
This paper presents a validation of a two-dimensional overland flow model using empirical laboratory data. Unlike previous publications in which model performance is evaluated as the ability to predict an outlet hydrograph, we use high resolution 2D water depth and velocity data to analyze to what degree the model is able to reproduce the spatial distribution of these variables. Several overland flow conditions over two impervious surfaces of the order of one square meter with different micro and macro-roughness characteristics are studied. The first surface is a simplified representation of a sinusoidal terrain with three crests and furrows, while the second one is a mould of a real agricultural seedbed terrain. We analyze four different bed friction parameterizations and we show that the performance of formulations which consider the transition between laminar, smooth turbulent and rough turbulent flow do not improve the results obtained with Manning or Keulegan formulas for rough turbulent flow. The simulations performed show that using Keulegan formula with a physically-based definition of the bed roughness coefficient, a two-dimensional shallow water model is able to reproduce satisfactorily the flow hydrodynamics. It is shown that, even if the resolution of the topography data and numerical mesh are high enough to include all the small scale features of the bed surface, the roughness coefficient must account for the macro-roughness characteristics of the terrain in order to correctly reproduce the flow hydrodynamics.
The time complexity of incremental structure from motion (SfM) is often known as O(n^4) with respect to the number of cameras. As bundle adjustment (BA) being significantly improved recently by preconditioned conjugate gradient (PCG), it is worth revisiting how fast incremental SfM is. We introduce a novel BA strategy that provides good balance between speed and accuracy. Through algorithm analysis and extensive experiments, we show that incremental SfM requires only O(n) time on many major steps including BA. Our method maintains high accuracy by regularly re-triangulating the feature matches that initially fail to triangulate. We test our algorithm on large photo collections and long video sequences with various settings, and show that our method offers state of the art performance for large-scale reconstructions. The presented algorithm is available as part of VisualSFM at http://homes.cs.washington.edu/~ccwu/vsfm/.
The work presented in this paper analyses the effect of water depth and rainfall intensity on the surface roughness coefficients used in overland flow models based on the shallow water equations. The relation between the Manning coefficient and the water depth and rainfall intensity has been quantified using different methodologies based on the analysis of two sets of experimental data. In the first set uniform overland flow conditions were generated, and the bed roughness coefficient was computed from direct measurements of the water depth and discharge. In the second set of experiments, unsteady rainfall-runoff transformations with different rainfall intensities were generated in a flume and computed with a shallow water model in which different bed friction formulations were implemented and calibrated. Results show that for very low water depth values there is a significant increase in the surface resistance, which is not captured by any standard bed friction formulation. Rainfall intensity also increases surface resistance especially as the water depth diminishes below a critical threshold. Using a Reynolds dependent formulation for the Manning coefficient improves model predictions.
Large-Scale Particle Image Velocimetry (LSPIV), as presented herein, is an extension of particle image velocimetry (PIV), which aims at providing velocity fields spanning large flow areas in laboratory or field conditions. Additional data, such as mappings of large-scale flow structures and discharges are readily obtainable using LSPIV. While the image- and data-processing algorithms are similar to conventional PIV, adjustments are required for illumination, seeding procedures, and pre-processing of the recorded images. This paper describes the implementation of video-based LSPIV in three hydraulic engineering applications covering surfaces from 4 m to 45,000 m. These applications are: gas-transfer processes downstream a model spillway, ice conveyance through a model river confluence, and flood plain flow in a full-scale river. The special problems encountered in each of these experiments, as well as the selection and adjustments of the parameters to properly solve them, are examined. LSPIV has proven to be a reliable, flexible, and economically efficient flow diagnostic tool that can be employed successfully in the surveillance planning, design, hazard warning, operation, and management in water-related activities.
Flood inundation modelling on urbanised floodplains has become more feasible due to the increased availability of high resolution digital terrain data and computer power. However, studies that validate simulations with spatially distributed measurements are rare, especially for large events. This paper reports one of the most comprehensive validation data sets available to date on an urban flood, collected in January 2005 after a major event in the city of Carlisle, UK. For the first time this case study collated distributed urban maximum water level and extent measurements with gauged hydrographs, LiDAR elevation data and digital Mastermap® data. These data were used to build and calibrate two 2D diffusion wave models at the whole city scale, based on digital elevation data with and without buildings. RMSE between measured and simulated maximum water level was 0.32 m and 0.28 m for the models with and without buildings, respectively, the latter being more accurate due to blockages on the floodplain when building heights were included in the topography. The magnitude of simulation errors compared well with other studies in the literature, and considering potential errors in the measurement data indicates that the diffusion wave approach was adequate to capture the first-order physics relevant here, although a global channel roughness parameter was unable to capture the full spatially-varying dynamics of the flood event.
The paper presents measurements acquired with Large-Scale Particle Image Velocimetry (LSPIV) during normal flows and floods in the Iowa River (U.S.A). For normal flows, comparison is made with measurements obtained with Acoustic Doppler Current Profilers (ADCP) in order to test LSPIV’s performance and to address concerns potentially affecting the accuracy of the measurements. The historic flood of the Iowa River during the summer of 2008 was captured for testing LSPIV capabilities during extreme flows. Lacking alternative measurements during the flood, the LSPIV measurements are compared to the rating curve extrapolated for high flows using a one-to-one discharge–stage relationship. The comparison reveals limitations of the single-values rating curve for providing discharge estimates during high flows. Finally, the paper summarizes lessons learned during these and previous LSPIV studies with the intent to chart the research needed to enhance this promising non-intrusive field measurement technique.
This paper presents an experimental validation of two widely used numerical models in urban flood inundation studies, the two-dimensional dynamic and diffusive wave models. Instead of using the common approach in flood inundation modelling, which consists of computing the water depth and velocity fields for a given water discharge, in this study the rainfall intensity is imposed directly in the model, the surface runoff being generated automatically. Both the dynamic and diffusive wave models are implemented in the same unstructured finite volume code, removing in such a way any differences in the numerical discretisation other than the wave approximation used to compute the water velocity. Two different methods for representing buildings are used and compared, the so-called building-block and building-hole approaches. Experimental validation of the models is presented in several simplified laboratory configurations of urban catchments, in which the surface runoff has been measured for different hyetographs. For this purpose, 72 experiments were undertaken in a rainfall simulator, including eight catchment configurations and nine hyetographs. Numerical results show that the dynamic wave model is able to predict the peak discharge and its arrival time, as well as the shape of the outlet hydrograph, while the diffusive wave model gives less accurate results. The experimental validation confirms that, when the geometry of the problem is well defined, depth-averaged dynamic wave models may be used to predict rainfall–runoff from direct precipitation data in urban environments.
Modeling flood inundation in an urban setting is increasingly relevant given the magnitude of potential loss and disruption associated with non-riverine, urban flooding. Both complexities in the urban environment and lack of high-resolution topographic and hydrologic data compromise the development and implementation of models of non-riverine flooding in urban areas. This paper describes a case study analysis of an urban university campus to develop and test a GIS-based urban flood inundation model (GUFIM). The model consists of two components: a storm–runoff model and an inundation model. Cumulative surface runoff, output of the storm–runoff model, serves as input to the inundation model. The storm–runoff model adapts the Green–Ampt model to compute infiltration based on rainfall characteristics, soil properties, and drainage infrastructure conveyance. The basis of the inundation model is a flat–water model. This effort uses publicly available elevation data, storm data, and insurance claim data to develop, implement and verify the model approach. GUFIM is an alternative to physical-based dynamic models characterized by accurate results, efficient performance, and reasonable input and hardware requirements. The University of Memphis in Memphis, Tennessee is the study location used here.
Keywords: Flash-flood Hydrometry Discharge measurement Image analysis LSPIV s u m m a r y Flash-floods that occur in Mediterranean regions result in significant casualties and economic impacts. Remote image-based techniques such as Large-Scale Particle Image Velocimetry (LSPIV) offer an oppor-tunity to improve the accuracy of flow rate measurements during such events, by measuring the surface flow velocities. During recent floods of the Ardèche river, LSPIV performance tests were conducted at the Sauze–Saint Martin gauging station without adding tracers. The rating curve is well documented, with gauged discharge ranging from 4.8 m 3 s À1 to 2700 m 3 s À1 , i.e., mean velocity from 0.02 m s À1 to 2.9 m s À1 . Mobile LSPIV measurements were carried out using a telescopic mast with a remotely-con-trolled platform equipped with a video camera. Also, LSPIV measurements were performed using the images recorded by a fixed camera. A specific attention was paid to the hydraulic assumptions made for computing the river discharge from the LSPIV surface velocity measurements. Simple solutions for interpolating and extrapolating missing or poor-quality velocity measurements, especially in the image far-field, were applied. Theoretical considerations on the depth-average velocity to surface velocity ratio (or velocity coefficient) variability supported the analysis of velocity profiles established from available gauging datasets, from which a velocity coefficient value of 0.90 (standard deviation 0.05) was derived. For a discharge of 300 m 3 s À1 , LSPIV velocities throughout the river cross-section were found to be in good agreement (±10%) with concurrent measurements by Doppler profiler (ADCP). For discharges rang-ing from 300 to 2500 m 3 s À1 , LSPIV discharges usually were in acceptable agreement (<20%) with the rat-ing curve. Detrimental image conditions or flow unsteadiness during the image sampling period led to larger deviations ranging 30–80%. The compared performances of the fixed and mobile LSPIV systems evi-denced that for LSPIV stations, sampling images in isolated series (or bursts) is a better strategy than in pairs evenly distributed in time.
Custom-produced fluorescent particles are presented and their use as tracers for particle image velocimetry is evaluated.
The fabrication procedure is explained and the main properties of the particles are described. The advantages of using fluorescent
particles over nonfluorescent ones are discussed, in particular, for applications involving large facilities, as those used
in hydraulic research. Images using the produced particles are also shown.
The 3D instantaneous velocity recorded with an acoustic Doppler velocimeter (ADV) in a highly turbulent free surface flow
is analysed using several filters in order to eliminate the corrupted data from the sample. The filters used include the minimum/maximum
threshold, the acceleration threshold, and the phase-space threshold. Following some ideas of the phase-space filter, a new
method based on the 3D velocity cross-correlation is proposed and tested. A way of computing the constants of the acceleration
threshold method is proposed, so no parameters need to be fixed by the us