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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Water resources and hydroinformatics : Surface roughness parameterization to account for subgrid scale topography in shallow water flow mod...
Surface roughness parameterization to account for subgrid scale topography in shallow water flow modeling
Author : ILHAN ÖZGEN(1), KATHARINA TEUBER(2), DONGFANG LIANG(3), REINHARD HINKELMANN(4)
ABSTRACT
This paper studies the usage of roughness formulations to account for subgrid-scale effects based on microtopographic
features in the context of upscaling overland flow models. The aim is to increase the cell size in order to reduce the
computational cost of shallow water models applied to surface runoff in small catchments. The integral discharge is the
primary function of concern, however velocity and water depth distributions in the domain are also considered. Two novel
roughness formulations are presented and compared. The first formulation has two calibration parameters and the second
one has three calibration parameters. Both formulations depend on the inundation ratio, i.e. water depth divided by the
characteristic roughness length (determined from microtopography). One formulation takes the slope of the cell as the
other free parameter. The formulations are implemented in the Hydroinformatics Modeling System. Upscaling capabilities
of the formulations are tested in three numerical cases with simplified geometries. The modelling accuracies are compared
by calculating the L2-errors of the results of the upscaled models with the high-resolution modelling results regarded as the
baseline. Additionally, the calibration effort of both models is compared by considering the effort of an automated
calibration algorithm. The computational time is given for each model to compare the speed up gained due to the cell size
increase. Overall, a good agreement is achieved between the results of the high-resolution model and the upscaled
models with roughness parameterization. As the number of calibration parameters increases, the accuracy of the model
results increases. However, the calibration process generally requires more effort. For the presented cases, the
simulations on a coarser resolution run about 50 times faster than the simulations on fine resolution meshes. It is
concluded that the increased accuracy of the three parameter roughness formulation outweighs its drawbacks associated
with the calibration effort.
File Size : 1,309,641 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Water resources and hydroinformatics
Date Published : 19/08/2015
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