S. J. van Andel

Integrated modelling for flood risk mitigation in Romania: case study of the Timis–Bega river basin

An integrated flood modelling approach has been applied in a demonstrator of a flood management system, which was developed within the framework of a collaborative project between Romania and the Netherlands. The developed demonstrator system had two objectives: (a) operational water management under extreme conditions when actions have to be taken quickly; (b) off-line analysis and design of flood mitigation measures and alternatives. This article presents the applied approach and the achieved results for meeting the second objective. The pilot basin for the development of the system was the Timis–Bega river basin, in which the rivers Timis and Bega were considered jointly. The system is based on modelling the flood generation and routing processes by combined development and application of hydrological and hydrodynamic models. The modelling system HEC-HMS was used for the hydrological model, HEC-RAS for the one-dimensional hydrodynamic model and SOBEK for the two-dimensional (2D) model used for downstream flood analysis and design of mitigation measures and alternatives. The 2D model includes alternatives of deliberate dike breaching as part of the analysis of the system response. The analysis presented is concentrated on a specific flood event that occurred in April 2005, which occurred due to dike breaches along the Timis river. The combination of models is first used for reconstruction of inundation patterns resulting during this flood event. Subsequently the models were used for testing flood mitigation alternatives of deliberate (planned) breaches of flood protection dikes located in the downstream part of the Timis river at the same location where they had occurred during the 2005 flood event, but at different times with respect to the arrival of the flood hydrograph. The demonstrated approach can enable decision-makers to analyse the behaviour of the physical system and design possible preventive and/or mitigation measures.

Data assimilation of satellite-based actual evapotranspiration in a distributed hydrological model of a controlled water system

Abstract Advances in earth observation (EO) and spatially distributed hydrological modelling provide an opportunity to improve modelling of controlled water systems. In a controlled water system human interference is high, which may lead to incorrect parameterisation in the model calibration phase. This paper analyses whether assimilation of EO actual evapotranspiration (ETa) data can improve discharge simulation with a spatially distributed hydrological model of a controlled water system. The EO ETa estimates are in the form of eight-day ETa composite maps derived from Terra/MODIS images using the ITA-MyWater algorithm. This algorithm is based on the surface energy balance method and is calibrated for this research for a low-lying reclamation area with a heavily controlled water system: the Rijnland area in the Netherlands. Data assimilation (DA) with the particle filter method is applied to assimilate the ETa maps into a spatially distributed hydrological model. The hydrological model and DA framework are applied using the open source software SIMGRO and PCRaster-Python respectively. The analysis is done for a period between July and October 2013 in which a high discharge peak followed a long dry-spell. The assimilation of EO ETa resulted in local differences in modelled ETa compared to simulation without data assimilation, while the area average ETa remained almost the same. The modelled cumulative discharge graphs, with and without DA, showed distinctive differences with the simulation, with DA better matching the measured cumulative discharge. The bias of simulated cumulative discharge to the observed data reduced from 14% to 4% when using DA of EO ETa. These results showed that assimilating EO ETa may not only be effective in the more common applications of soil moisture and crop-growth modelling, but also for improving discharge modelling of controlled water systems.