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Assessment of 1D and 2D model choices on model accuracy and computation time in D-Hydro

Mooijaart, Jan Berend (2023) Assessment of 1D and 2D model choices on model accuracy and computation time in D-Hydro.

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Abstract:Hydraulic models are used for different purposes, such as real-time flood forecasting, flood risk mapping, and flood damage assessment. Over the years, hydraulic models’ performance has improved because of better computers, improvement in details of the input data, and the possibility to couple 1D models with 2D models. However, the computation time can still be high for a large study area. This study investigates the effect of model choices on model accuracy and computation time in D-Hydro. The goal of this study is to understand the effect of mesh properties on breach discharge and to what extent line elements can compensate for a lower grid resolution. Dike ring area 49, located in Gelderland, the Netherlands, with an area of 12000 ha is used as a realistic case. Model accuracy is measured in three different ways; mean absolute error (MAE) of water depth, a measure of fit of inundation extent, and flood arrival times. The breach discharge is compared in two different ways, the peak discharge, and the cumulative discharge. The study shows that grid size and grid schematization affect the breach outflow hydrographs. Models with a coarser grid have a higher peak discharge and cumulative breach discharge. A model with a coarser grid has a peak breach discharge of up to 70% higher than a model with a fine grid resolution and the cumulative breach discharge is up to 50% higher from 3 days after the dike breach. Models with a coarse grid resolution artificially remove local backwater effects near the breach, easing throughflow to the hinterland and increasing breach inflow. The second part of the study is related to the schematization of higher line elements. Higher line elements, such as roads, are relatively small compared to the cell size and might not be correctly schematized in the 2D grid. For this analysis, roads are schematized as fixed weirs, and the breach outflow hydrograph of the reference model is used as a boundary condition. The study shows that schematizing roads as fixed weirs improves model accuracy significantly. If roads are not schematized correctly, the area will be flooded faster and a larger area inundates. Adding roads as fixed weirs increases model accuracy even in models with a fine grid resolution.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
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