In producing flood inundation maps, especially in urbanized areas, the use of one-dimensional numeri-cal models may be inadequate because they cannot adequately represent all the features of flow complexity and resulting water surface elevations that occur in real cases. However, 1D models are still popular due to their reduced computational time, their ease of implementation and low resolution topographic data requirements. Limitation exists with 1D modeling approaches due to the tacit assumption of a horizontal surface at each given cross section and by the inability in detecting transverse changes of flow regime. Moreover the accuracy of flow simulations significantly depends on the choice of the resolution and alignment of cross-sections de-scribing the river reach. Nowadays, the use of techniques for the automatic extraction of cross-sections from DEMs, obtained by LIDAR data, allows one to obtain cross-sections with improved discretization and increased resolu-tion, providing a more accurate characterization of the river geometry. However, a challenging aspect is the application of the 1D modeling to accurately rep-resent water surface profiles near skewed bridge crossing. Indeed, a dearth in knowledge currently exists on how to reliably predict water surface profiles on skewed bridge crossings with piers using a 1-D approach. The problem addressed here concerns the most appropriate choice of the cross sections in a 1-D modelling environment leading to a representation as close as possible to that provided by a 2D model. In order to study this problem, in this paper 1D and 2D state-of-the-art unsteady flow models have been applied to river reaches characterized by skewed bridges crossing. Two real cases are presented in this paper. In the first case (Crati river), the skewed bridge deck stands on nine piers placed in the river bed. In the second case (Corace river), there are four bridges crossing the river: the first two skewed to the main flow direction while the other two pass over the river almost orthogonal to the principle direction of the flow. The results obtained in this article for two different study reaches show that the increased resolution of cross sections in the 1-D environment produces an accurate representation of local effects as far as the longitudinal profile of the flow. However in the 1D cases, the effects are averaged through cross-sections so that the maximum simulated surface levels are lower than those calculated with the 2D model. Indeed, in the 2D model, the presence of piers causes local effects resulting in a free-surface super eleva-tion within sub-regions of several cross sections. Maximum water level increases using the 1-D mod-eling results could be better predicted if the total head values were used at any given cross section rather than water surface elevations.
REPRESENTING SKEWED BRIDGE CROSSING ON 1-D AND 2-D FLOOD PROPAGATION MODELS:COMPARED ANALYSIS IN PRACTICAL STUDIES
COSTABILE, Pierfranco;MACCHIONE, Francesco;
2014-01-01
Abstract
In producing flood inundation maps, especially in urbanized areas, the use of one-dimensional numeri-cal models may be inadequate because they cannot adequately represent all the features of flow complexity and resulting water surface elevations that occur in real cases. However, 1D models are still popular due to their reduced computational time, their ease of implementation and low resolution topographic data requirements. Limitation exists with 1D modeling approaches due to the tacit assumption of a horizontal surface at each given cross section and by the inability in detecting transverse changes of flow regime. Moreover the accuracy of flow simulations significantly depends on the choice of the resolution and alignment of cross-sections de-scribing the river reach. Nowadays, the use of techniques for the automatic extraction of cross-sections from DEMs, obtained by LIDAR data, allows one to obtain cross-sections with improved discretization and increased resolu-tion, providing a more accurate characterization of the river geometry. However, a challenging aspect is the application of the 1D modeling to accurately rep-resent water surface profiles near skewed bridge crossing. Indeed, a dearth in knowledge currently exists on how to reliably predict water surface profiles on skewed bridge crossings with piers using a 1-D approach. The problem addressed here concerns the most appropriate choice of the cross sections in a 1-D modelling environment leading to a representation as close as possible to that provided by a 2D model. In order to study this problem, in this paper 1D and 2D state-of-the-art unsteady flow models have been applied to river reaches characterized by skewed bridges crossing. Two real cases are presented in this paper. In the first case (Crati river), the skewed bridge deck stands on nine piers placed in the river bed. In the second case (Corace river), there are four bridges crossing the river: the first two skewed to the main flow direction while the other two pass over the river almost orthogonal to the principle direction of the flow. The results obtained in this article for two different study reaches show that the increased resolution of cross sections in the 1-D environment produces an accurate representation of local effects as far as the longitudinal profile of the flow. However in the 1D cases, the effects are averaged through cross-sections so that the maximum simulated surface levels are lower than those calculated with the 2D model. Indeed, in the 2D model, the presence of piers causes local effects resulting in a free-surface super eleva-tion within sub-regions of several cross sections. Maximum water level increases using the 1-D mod-eling results could be better predicted if the total head values were used at any given cross section rather than water surface elevations.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
