Comparative evaluation of 1D and quasi-2D hydraulic models based on benchmark and real-world applications for uncertainty assessment in flood mapping Panayiotis Dimitriadis, Aristoteles Tegos ⇑ , Athanasios Oikonomou, Vassiliki Pagana, Antonios Koukouvinos, Nikos Mamassis, Demetris Koutsoyiannis, Andreas Efstratiadis Department of Water Resources and Environmental Engineering, School of Civil Engineering, National Technical University of Athens, Heroon Polytechneiou 5, 15780 Zographou, Greece article info Article history: Received 4 October 2015 Received in revised form 8 December 2015 Accepted 9 January 2016 Available online 15 January 2016 This manuscript was handled by Konstantine P. Georgakakos, Editor-in-Chief, with the assistance of Jennifer Guohong Duan, Associate Editor Keywords: Flood inundation Uncertainty Sensitivity analysis Monte-Carlo simulation summary One-dimensional and quasi-two-dimensional hydraulic freeware models (HEC-RAS, LISFLOOD-FP and FLO-2d) are widely used for flood inundation mapping. These models are tested on a benchmark test with a mixed rectangular–triangular channel cross section. Using a Monte-Carlo approach, we employ extended sensitivity analysis by simultaneously varying the input discharge, longitudinal and lateral gradients and roughness coefficients, as well as the grid cell size. Based on statistical analysis of three output variables of interest, i.e. water depths at the inflow and outflow locations and total flood volume, we investigate the uncertainty enclosed in different model configurations and flow conditions, without the influence of errors and other assumptions on topography, channel geometry and boundary condi- tions. Moreover, we estimate the uncertainty associated to each input variable and we compare it to the overall one. The outcomes of the benchmark analysis are further highlighted by applying the three models to real-world flood propagation problems, in the context of two challenging case studies in Greece. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction Flood forecasting and impact assessment is a multidisciplinary topic of high importance, spanning over meteorological, hydrolog- ical, hydraulic and environmental sciences and associated technologies. Preliminary attempts to explain the related to floods physical phenomena originate from ancient civilizations (Koutsoyiannis et al., 2007). The EU Directive 2007/60 on the assess- ment and management of flood risk requires establishing flood hazard and flood risk maps showing the potential adverse conse- quences to human health, the environment, cultural heritage and economic activities. These should be accompanied by measures to manage floods and mitigate the frequency of potential flood dam- ages. In this context, it is essential to explain the multivariate effects of the development of societies to floodplain dynamics, as well as their feedbacks (Di Baldassarre et al., 2009, 2013). This is a far from challenging task, influenced by several uncertain factors, such as climatic variability, hydro-morphological conditions, land use alterations and demographic changes. The literature has numerous investigations on the effects of changing model inputs to the uncertainty induced in flood risk assessment (e.g., Kundzewicz et al., 2014). On the other hand, less attention is put to the uncertainty derived from modelling assump- tions and simplifications. Typically, flood modelling comprises two components, i.e. the hydrological simulation, which quantifies the size, duration and probability of the flood event, and the hydraulic simulation, employing the propagation of the flood wave across the river channel and the mapping of inundated areas. Inherent uncertainties are present in multiple aspects of the above approaches, involving the model structure, model parameters, boundary conditions and input data. However, most of such uncer- tainties that may be surprisingly large, even in small basins (e.g., Lazaridou et al., 2004), are usually ignored. In fact, in most applica- tions, particularly of the everyday engineering practice, flood mod- els are considered as fully deterministic tools, in which the unique expression of uncertainty is the return period of rainfall (Efstratiadis et al., 2014). A thorough investigation of the role of hydrological inputs in flood hazard mapping is provided by Grimaldi et al. (2013). In this article we focus on the hydraulic simulation component and the associated sources of uncertainty. Flood routing models have http://dx.doi.org/10.1016/j.jhydrol.2016.01.020 0022-1694/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Journal of Hydrology 534 (2016) 478–492 Contents lists available at ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol