Multi-objective automatic calibration of hydrodynamic models utilizing inundation maps and gauge data

Abstract

Abstract. Automatic and multi-objective calibration of hydrodynamic models is -compared to other disciplines like e.g. hydrology -still underdeveloped. This has mainly two reasons: the lack of appropriate data and the large computational demand in terms of CPU-time. Both aspects are aggravated in large-scale applications. However, there are recent developments that improve the situation on both the data and computing side. Remote sensing, especially radarbased techniques proved to provide highly valuable information on flood extents, and in case high precision DEMs are present, also on spatially distributed inundation depths. On the computing side the use of parallelization techniques brought significant performance gains. In the presented study we build on these developments by calibrating a large-scale 1-dimensional hydrodynamic model of the whole Mekong Delta downstream of Kratie in Cambodia: we combined insitu data from a network of river gauging stations, i.e. data with high temporal but low spatial resolution, with a series of inundation maps derived from ENVISAT Advanced Synthetic Aperture Radar (ASAR) satellite images, i.e. data with low temporal but high spatial resolution, in an multiobjective automatic calibration process. It is shown that an automatic, multi-objective calibration of hydrodynamic models, even of such complexity and on a large scale and complex as a model for the Mekong Delta, is possible. Furthermore, the calibration process revealed model deficiencies in the model structure, i.e. the representation of the dike system in Vietnam, which would have been difficult to detect by a standard manual calibration procedure.Correspondence to: N. V. Dung (dung@gfz-potsdam.de)

Has dyke development in the Vietnamese Mekong Delta shifted flood hazard downstream?

“…The multi-objective calibration by Dung et al (2011) showed that the model could satisfyingly simulate the inundation extent only, if the model dyke levels were lowered by 20 %. This indicated that the dyke level data were not accurate.…”

“…2). A comprehensive description of how floodplain compartments are introduced by the "virtual" channels and wide cross sections can be found in Dung et al (2011). The model has been calibrated by Dung et al (2011) …”

“…The model domain includes the CFP, the Tonle Sap Lake and the majority of the channels and hydraulic structures in the VMD. The model was initially developed by Dung et al (2011) and refined by Manh et al (2014). It is a quasi-2-D model, and takes the complex hydraulic system of the VMD into account.…”

“…It accounts for more than 52 % of the national food production and more than 85 % of the annual rice export (GSO, 2015). Being a low-lying coastal region, the VMD is susceptible to both riverine and tidal floods, threatening agricultural production and the safety of people (Schumann et al, 2008;Kuenzer et al, 2013;Le et al, 2007;Dung et al, 2009;Dung et al, 2011;Van et al, 2012). Climate change and sea level rise are expected to increase the risk, not only due to flooding but also due to droughts and salinity intrusion (Wassmann et al, 2004;Khang et al, 2008;Toan, 2014;Hak et al, 2016).…”

“…To obtain a better understanding of the trends, changes in flood peak and flood duration are analysed, which in combination define the severity of floods in the Mekong Delta . To quantify the relative contribution of high-dyke development, we update the quasi-2-D flood model developed by Dung et al (2011) and Manh et al (2014) using the latest comprehensive dyke survey data and high-resolution topographical data from the newly available 5 × 5 m resolution lidar DEM for the VMD. Changes in delta inundation dynamics for the preand post-high-dyke development are investigated in different model setups, simulating the two recent, most severe flood events in 2000 and 2011.…”