Influence of elevation modelling on hydrodynamic simulations of a tidally-dominated estuary Ana Paula Falcão a,b,⇑ , Andrea Mazzolari a,c , Alexandre B. Gonçalves a,b , Maria Amélia V.C. Araújo a,c , António Trigo-Teixeira a,c a Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, Lisboa, Portugal b ICIST, Instituto de Engenharia de Estruturas, Território e Construção, Lisboa, Portugal c CEHIDRO, Centro de Estudos de Hidrossistemas, Lisboa, Portugal article info Article history: Received 18 August 2012 Received in revised form 6 May 2013 Accepted 26 May 2013 Available online 4 June 2013 This manuscript was handled by Andras Bardossy, Editor-in-Chief, with the assistance of Uwe Haberlandt, Associate Editor Keywords: Spatial interpolation Digital elevation model resolution Hydrodynamic simulation in estuary Satellite positioning High resolution geoid undulation model Wet and dry summary Hydrodynamic simulation of estuaries requires a single digital elevation model (DEM) resulting from merging of both topographic and bathymetric data. These two datasets are usually produced using differ- ent technologies, co-ordinate systems and datums. Intertidal data in particular are often lacking due to the difficulty of data acquisition using conventional survey techniques. This paper presents a fast, accu- rate and low-cost methodology to fill this gap and highlights the effect of the digital elevation model characteristics, such as the interpolation method and spatial resolution, on modelled water levels and flooded areas. The Lima river estuary, located in North-western Portugal, is used as a case study. Valida- tion tests for commonly available spatial interpolators showed ordinary kriging to be the most adequate interpolator. Digital elevation models with regular grids of 5 m and 50 m resolution were used, together with the original (not interpolated) elevation dataset, as input to a finite element hydrodynamic model for astronomic tide simulation. Results indicate that the larger differences between using different eleva- tion models occur at low tide during spring tide, marginally impacting the flood modelling. The effect of a vertical offset of the chart datum with respect to a part of the digital elevation model was finally inves- tigated, showing a limited influence in the determination of the water levels. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Floods in estuarine areas occur when the normal tidal level is exceeded. These are natural phenomena which are mainly linked to the surge of sea level caused by meteorological factors, such as low atmospheric pressure, high freshwater flow rates or the unusual entrance of water in the estuary due to high run-off events (McInnes et al., 2009). The study of flood events, including the esti- mation of the highest water level and the flooded area, has to rely on a model that has been previously validated for ordinary flow conditions: in the case of an estuary domain, these are represented by the astronomical tide forcing and the river flow. Simulations made by hydrodynamic models have limitations in considering physical and hydrodynamic conditions, such as the maximum number of elements used to describe the channel geom- etry and roughness (Merwade et al., 2008a), and these became more evident in estuarine areas, where a series of additional cir- cumstances influencing the flooding process have to be considered (shallow waters and intertidal areas, distinct flow directions and complexity of the drainage system). 2D/3D hydrodynamic models require an integrated continuous surface combining elevation from the river bed (bathymetry) with the topography from adjacent areas covering the floodplain. This may eventually be complemented by the inclusion of more de- tailed data representing features that influence the spread of flood- ing, such as dykes or roads (Poulter and Halpin, 2008). Results of the hydrodynamic modelling processes are known to be dependent on the properties of the elevation model (Ali et al., 2009; Weaver and Slinn, 2010; Cea and French, 2012). The channel bathymetry, namely the horizontal resolution, is known to affect the results of models, such as the rate, extent and timing in inun- dation mapping (Hardy et al., 1999; Omer et al., 2003; Horritt et al., 2006; Buttner, 2007; Raber et al., 2007; Poulter and Halpin, 2008; Merwade et al., 2008b). Despite these known effects, changes of scale, which result in distinct horizontal resolutions for the input elevation data, may be necessary to obtain files that do not over- load the hydrodynamic model. To create the digital elevation model (DEM) for the simulation stages, data from several sources, formats and acquisition and pro- cessing techniques, have to be combined: discrete bathymetry 0022-1694/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhydrol.2013.05.045 ⇑ Corresponding author. Address: Department of Civil Engineering, Architecture and Georesources, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal. Tel.: +351 218418328. E-mail address: afalcao@civil.ist.utl.pt (A.P. Falcão). Journal of Hydrology 497 (2013) 152–164 Contents lists available at SciVerse ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol