Excess surface water on roadways due to storm events can cause hazardous scenarios for traffic. The design of efficient road and transportation facility drainage systems is a major challenge. Different approaches to limit excess surface water can be found in the drainage design standards of different countries. This document presents a method based on hydraulic numerical simulation and the assessment of grate inlet efficiency using the Iber model. The method is suitable for application to design criteria according to the regulations of different countries. The presented method facilitates sensitivity analyses of the performance of different scupper dispositions through the total control of the hydraulic behavior of each of the grate inlets considered in each scenario. The detailed hydraulic information can be the basis of different solution comparisons to make better decisions and obtain solutions that maximize efficiency.

Stochastic weather generators combined with hydrological models have been proposed for continuous synthetic simulation to estimate return periods of extreme floods. Yet, this approach relies upon the length and spatial distribution of the precipitation input data series, which often are scarce, especially in arid and semiarid regions. In this work, we present a new approach for the estimation of extreme floods based on the continuous synthetic simulation method supported with inputs of (a) a regional study of extreme precipitation to improve the calibration of the weather generator (GWEX), and (b) non-systematic flood information (i.e., historical information and/or palaeoflood records) for the validation of the generated discharges with a fully distributed hydrological model (TETIS). The results showed that this complementary information of extremes allowed for a more accurate implementation of both the weather generator and the hydrological model. This, in turn, improved the flood quantile estimates, especially for those associated with return periods higher than 50 years but also for higher quantiles (up to approximately 500 years). Therefore, it has been proved that continuous synthetic simulation studies focused on the estimation of extreme floods should incorporate a generalized representation of regional extreme rainfall and/or non-systematic flood data, particularly in regions with scarce hydrometeorological records.

Numerous studies have examined the complex relationship between factors like embankment downspout spacing, height, slope, and rainfall characteristics in the quest to find the best spacing for embankment downspouts. Defining the correct spacing between road drainage elements is of utmost importance in minimizing water flow on roadways. This paper presents a methodology based on numerical methods for the design of road drainage systems using the Iber model. The objective of the work is to propose a tool and criteria for analyzing the hydraulic behavior of runoff on highways, determine the appropriate drainage behavior, and apply the methodology in a case study. This case study is based on a straight highway section with slopes up to 5%, according to Spanish road design regulations. Different dimensions are considered for the chute, drainage channel, collection nozzle, and downspout over the embankment. Tests are carried out to evaluate the separation between downspouts, the longitudinal slope, and the size of the nozzles. The results show the suitable hydraulic performance of the model, besides providing the absorption capacity of each downspout. The influence of the nozzle size, the slope, and the width of the causeway on the draughts and velocities is analyzed. The influence of downspout spacing and nozzle type on road drainage design is determined. In summary, this article presents a methodology and criteria for the design of road drainage systems and shows the results obtained in a case study using the Iber model. The results help in understanding the influence of different variables on the hydraulic behavior of road runoff and provide relevant information for proper drainage design.

En la actualidad existe una gran incertidumbre de los efectos del cambio climático en la peligrosidad de las inundaciones. Estos caudales extremos dependen de las características de las cuencas y representan una respuesta local que, a menudo, no pueden interpretarse a partir de los modelos de clima. En la práctica, esta incertidumbre dificulta la adaptación a los riesgos futuros según el mandato de la Directiva Europea de Inundaciones (2007/60/EC). En un caso de estudio (Rambla de la Viuda, Castellón) se ha aplicado un análisis de caudales máximos (recurrencia de 100 años) en base a proyecciones de precipitación extrema (escenario RCP 8.5) realizadas con modelos de clima regionales (Eurocordex), y convertidos en caudal instantáneo mediante un modelo hidrológico distribuido (TETIS). El análisis muestra una elevada variabilidad en los resultados, siendo difícil determinar la bondad de los modelos de clima. Por otro lado se han analizado series largas de inundaciones obtenidas a partir de registros históricos y sedimentarios (paleoinundaciones), que permiten obtener los caudales máximos registrados secularmente. Esta información incorpora eventos de inundación que han ocurrido en periodos pasados de calentamiento relativo o de incremento de la actividad de las inundaciones, considerando que los eventos extremos que han acontecido alguna vez pueden repetirse en el futuro. Estos caudales del pasado se han analizado conjuntamente con registros instrumentales mejorando sustancialmente el cálculo de los cuantiles de inundación requeridos en los mapas de peligrosidad de la Directiva de Inundaciones. Los datos de extremos del paleocrecidas permiten validar los datos de los modelos de clima e hidrológicos para los cuantiles altos. Esta aproximación constituye una práctica beneficiosa (win-win actions), de relativo bajo costo, y que permite avanzar en la adaptación al cambio climático. Igualmente, esta información del pasado proporciona una evidencia” real” de sucesos de inundación que posibilitan la recuperación de la cultura del riesgo.

The combined use of weather generators (WG) and hydrological models (HM) in what is called synthetic continuous simulation (SCS) has become a common practice for carrying out flood studies. However, flood quantile estimations are far from presenting relatively high confidence levels, which mostly relate to the uncertainty of models’ input data. The main objective of this paper is to assess how different precipitation regimes, climate extremality, and basin hydrological characteristics impact the uncertainty of daily flood quantile estimates obtained by SCS. A Monte Carlo simulation from 18 synthetic populations encompassing all these scenarios was performed, evaluating the uncertainty of the simulated quantiles. Additionally, the uncertainty propagation of the quantile estimates from the WG to the HM was analyzed. General findings show that integrating the regional precipitation quantile ($X_{T,P})$ in the WG model calibration clearly reduces the uncertainty of flood quantile estimates, especially those near the regional $X_{T,P}$. Basin size, climate extremality, and the hydrological characteristics of the basin have been proven not to affect flood quantiles’ uncertainty substantially. Furthermore, it has been found that uncertainty clearly increases with the aridity of the climate and that the HM is not capable of buffering the uncertainty of flood quantiles, but rather increases it.

Study region: The proposed methodology has been applied in the Segura River basin (south-eastern Spain) whose hydrological regime has a high anthropic alteration and catastrophic floods have occurred at different times for centuries. The climate is generally semi-arid, with frequent droughts but also floods caused mainly by rainfall associated with mesoscale convective systems. Study focus: We present a methodology that exploits all available information to obtain reliable low-frequency flood quantiles through the integration of different methods. First, a Weather Generator (WG) was implemented with the results from a regional study of annual maximum precipitation. Second, a rainfall temporal disaggregation procedure was carried out to capture the sub-daily behavior of flood generating storms. Third, a fully-distributed Hydrological Model (HM) was implemented including the role of sediments in extreme events. Finally, the estimation of flood quantiles using plotting positions was validated with systematic and non-systematic information. New Hydrological Insights for the region The use of this process-based approach allows to reproduce the main hydrometeorological mechanisms associated with floods in the region studied. Accurate flood quantiles up to 200 years have been possible to obtain, which represents an important advance in the knowledge of the basin since reliable flood quantiles of only 20 years were adequately captured with the current observations. Finally, sediment yield has been proven to be an important factor for the region hydrographs’ reconstruction.