Geospatial products, such as digital elevation models (DEMs), are important topographic tools for tackling local flood studies. This study investigates the contribution of LiDAR elevation data in DEM generation based on fixed-wing unmanned aerial vehicle (UAV) imaging for flood applications. More specifically, it assesses the accuracy of UAV-derived DEMs using the proposed LiDAR-derived control point (LCP) method in a Structure-from-Motion photogrammetry processing. Also, the flood estimates (volume and area) of the UAV terrain products are compared with a LiDAR-based reference. The applied LCP-georeferencing method achieves an accuracy comparable with other studies. In addition, it has the advantage of using semi-automatic terrain data classification and is readily applicable in flood studies. Lastly, it proves the complementarity between LiDAR and UAV photogrammetry at the local level.
We compare two flood models applied to Riohacha. MODCEL, a conceptual model, had already been calibrated; IBER, a physically based 2D hydraulic model, has been calibrated and validated now with the same dataset used in MODCEL. MODCEL performs better according to several indicators. One cause of this difference is the low resolution of topography, a key input for IBER. Additionally, IBER is weak in representing hydraulic works, particularly concerning their real maintenance status, an information that MODCEL instead includes as the cells schematization is based on the actual flow directions reported by the people interviewed. This procedure however requires a deep insight into the actual behaviour of the physical system and a vast modelling experience. Furthermore, MODCEL software is less user-friendly than IBER. Both models, anyway, in the case at hand, capture sufficiently well the behaviour of urban flooding and the impact of interventions. Which is why they constitute key planning tools in the face of the flood problem in Riohacha and similar cases.
Palabras clave: trazador, tiempo de retención hidráulico, flujo disperso, mezcla completa, zona muerta RESUMEN La hidráulica, junto con los procesos bioquímicos tiene una importancia esencial en la eficiencia de los sistemas de tratamiento biológico, tales como los reactores anaerobios de flujo ascendente (RAFA). En esta investigación se evaluó el desempeño hidráulico en un RAFA de 518 L utilizando un modelo de dispersión axial. El reactor fue inoculado con 105 L de lodo (20 % v/v) y se alimentó con agua residual municipal del colector C de la ciudad de Maracaibo, Venezuela. Los ensayos fueron realizados al agregar una solución de LiCl de forma puntual en el efluente. El Li + fue cuantificado como trazador. Las muestras fueron recolectadas en el efluente y en un punto intermedio del reactor a tiempos de retención hidráulica teóricos (t o ) de 10, 8, 5, 4 y 3 h con tres entradas alineadas en el fondo del reactor y a t o de 5 h incrementando las entradas de forma impar hasta llegar a 15. El número de dispersión obtenido en la zona de lecho y manto de lodo (punto intermedio) fue mayor que en el efluente, obteniendo valores de 1.1842 < d < 1.7550 y 0.2911 < d < 0.7285 respectivamente. El modelo de dispersión axial con inyección y recolección en flujo (IRF) e inyección en flujo y recolección en el fluido residente (IFRFR), presentó buenos ajustes a los datos experimentales de concentración del trazador. El reactor se comportó como mezcla completa en el lecho y manto de lodo y flujo disperso en el sedimentador.Key words: tracer, hydraulic retention time, dispersed flow, complete mix, dead zone ABSTRACT Hydraulics along with biogeochemical processes have a remarkable value in the efficiency of wastewater treatment systems as upflow anaerobic sludge reactors (UASB). In this study the hydraulic performance was evaluated on a UASB of 518L volume capacity using an axial dispersion model. The reactor was inoculated with 105 L of sludge (20 % v/v) and was fed with a local municipal wastewater flowing at the collector C of the city Maracaibo, Venezuela. Assays were carried out using a solution with LiCl (Li + measured as tracer) incorporated at the influent as instantaneous injection. Samples were collected at the effluent and at a midpoint of the reactor. Different theoretical hydraulic retention times (t o )
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