The open water system of the Tielerwaard has been assessed to see if the area meets the flooding standards by 2015, for both the current climate and the W+ climate scenario for 2050. For this assessment, a stochastic model input was used to calculate decisive water levels for inundation- and bottleneck maps and flooding specifications, for both the current open water system and the open water system with measures implemented until 2015.
Open water system assessment of the Tielerwaard
Supervisors: Paul Torfs (WUR), Janneke de Graaf (HydroLogic)
The open water system of the Tielerwaard, the area between Tiel and Gorinchem, the Linge and the Waal, has been assessed according to the standard method for open water system assessment of STOWA. The previous assessment of the Tielerwaard was done in 2007, to assess the robustness of the open water system under various conditions, but the open water system should meet the flooding standards by 2015. Firstly, the current SOBEK model of the Tielerwaard has been calibrated and validated with data from 2009 to 2011.
Stochastic calculations, consisting of combinations of precipitation volume, shower type, groundwater levels and seasonal variables, and the chance of occurrence of the combination, determine the water level statistics of the area. With the calculated water levels, inundation maps, bottleneck maps and flooding specifications are created for both the current climate scenario and the future W+ climate scenario for 2050 of the KNMI. Also the open water system of 2015 was assessed, with all measures implemented until 2015.
The current system has most inundations in the western, drained area of the Tielerwaard. In the eastern, dammed area are hardly any inundations. The W+ climate scenario does not show new inundations, but expands and intensifies the current inundations. De flooding specification does show a water surplus in the eastern part, but the main surplus can be found in the western part of the Tielerwaard. The open water system of 2015 shows less inundations, especially around Heukelum and Oude Boutenstein, but the bottleneck maps don’t show clear differences. The measures reduce the current surplus by 9% and the surplus in 2050 by 6%. However, the maps also show a water surplus at new locations, due to the transportation of water within the system. Especially the broadening of waterways establishes fast transportation.