Flood hazard analysis in small catchments: Comparison of hydrological and hydrodynamic approaches by the use of direct rainfall

Abstract

The classical 'decoupled' approach for fluvial flooding makes use of hydrographs as input boundary conditions. The catchment hydrology is determined by empirical semi-distributed rainfall-runoff models, the flood processes by the use of hydrodynamic models. However, for urban floods, the distributed rainfall is set directly as input ('direct rainfall modelling'-DRM) to the elements of the 2D model. This 'integrated approach' aims to include hydrological and hydraulic processes in one single model. In this study, both modelling approaches are applied and evaluated for their suitability to determine flood hazards in small, rural catchments. The resulting flood maps and flow hydrographs are compared for selected rainfall-runoff events in a catchment located in Central Germany. In the first approach, the hydrological model (HEC-HMS) from the Hydrologic Engineering Center (HEC) is used to generate the inflow boundary hydrographs for the 2D model (HEC-RAS), which is then used to simulate the flow variables for the river network and its floodplains. For the second approach, the DRM is applied over the whole catchment by the use of HEC-RAS. Special focus is given for the integrated approach to the difficulties occurring during the model optimisation and calibration. The comparison of the results and modelling processes of both approaches give insights into the advantages, disadvantages and difficulties or limitations of each presented approach. K E Y W O R D S direct rainfall modelling (DRM), flash flood, flood inundation modelling (FIM), HEC-RAS, hydraulic modelling, hydrological modelling, pluvial flooding, small catchments

Evaluation of Design Storms and Critical Rainfall Durations for Flood Prediction in Partially Urbanized Catchments

“…Note that the channel network did not directly affect the hydraulic modeling and is illustrated here to better understand the catchment characteristics and anticipate the main flow paths. The overall catchment has an area of 3.08 km 2 . Nearly half of this area (1.36 km 2 ) belongs to the subcatchment of the largest drainage system that flows east of the city center and where the most damaging consequences of floods have been documented.…”

“…In the European Union (EU), a standardized procedure for flood mapping has been established by the EU Flood Directive (2007/60/EC) [1], which explicitly specifies which types of floods, flood parameters, and flood frequencies should be considered when assessing flood hazards. Due to a rising number of natural disasters, there is a growing interest in the EU regarding floods that occur directly from heavy rainfall, which are usually called pluvial floods [2]. Furthermore, because of a strongly interconnected rainfall-runoff process, as well as a rapid advancement of computational technology and the availability of high-resolution topographic data [3], pluvial floods are now simulated using integrated hydrological-hydraulic methods consisting of time-dependent 2D models and so-called rain-on-grid approaches [2,[4][5][6][7].…”

“…Due to a rising number of natural disasters, there is a growing interest in the EU regarding floods that occur directly from heavy rainfall, which are usually called pluvial floods [2]. Furthermore, because of a strongly interconnected rainfall-runoff process, as well as a rapid advancement of computational technology and the availability of high-resolution topographic data [3], pluvial floods are now simulated using integrated hydrological-hydraulic methods consisting of time-dependent 2D models and so-called rain-on-grid approaches [2,[4][5][6][7]. However, a reliable flood prediction in small ungauged catchments remains difficult because of the lack of field observations needed to calibrate models [8][9][10][11].…”

A Systematic Analysis of the Interaction between Rain-on-Grid-Simulations and Spatial Resolution in 2D Hydrodynamic Modeling

“…The DRM has, meanwhile, established itself and is included in the mainstream commercial and non-commercial 2D software packages for urban or river flooding. Examples of applications of DRM together with a hydrodynamic Rainfall-runoff Model (HDRRM) or "hydro-inundation model" [2] can be found for urban and rural areas in Zeiger & Hubbart, (2021) [3], Krvavica & Rubinić (2020) [4], David & Schmalz (2020) [5], Broich et al (2019) [6], Jia et al (2019) [7], Tyrna et al (2018) [8], Yu et al (2015) [2], Cea et al (2010) [9] or Hunter et al (2008) [10].…”

Computational advances and innovations in flood risk mapping

“…Nonetheless, these tools are now being investigated and enhanced to enable their application to open problems such as rainfall‐induced flooding (Caviedes‐Voullième, Fernández‐Pato, & Hinz, 2020) and pluvial urban and peri‐urban flooding and additional interactions with the environment, from objects (vehicles, street furniture, people) transported by the flow. In this special issue, David and Schmalz (2020) compare and analyse the performance of fluvial flooding tools in the context of pluvial flooding. They demonstrate that the applicability is constrained by proper calibration and computational costs, but a substantial amount of new information can be obtained in comparison to more traditional hydrological approaches.…”