Seepage and Piping through Levees and Dikes using 2D and 3D Modeling Codes

Abstract

Abstract : The purpose of this Technical Report (TR) is to evaluate the benefits of three-dimensional (3D) modeling of common seepage and piping issues along levees and dikes over traditional two-dimensional (2D) models. To facilitate the evaluation, one 3D model, two 2D cross-sectional models, and one 2D plan-view model were developed in this study to simulate a simplified real-world situation. This simplified model includes the main channel of a large river, a smaller tributary feeding this river from the north, and levees between the tributary and the river to protect low-lying inland area of concern from flooding. A set of extreme hydrologic conditions was applied to the models, and results from steady-state simulations were compared. Four scenarios, including Existing Condition, Cutoff Wall Only, Relief Wells Only, and Cutoff Wall and Relief Wells, were considered for model comparison. The 2D model results were compared to 3D model results to determine whether they may be sufficient for specified purposes. The results of this analysis indicate several strengths and weakness of both the 2D and 3D modeling approaches. The 2D models are easier to construct and require much less computational time for each simulation. Because a 2D model is assumed to be cut parallel to the flow path, however, complex geologic and topographic features in the real world are likely to result in complex 3D flow fields, which makes it difficult or impossible to define an appropriate 2D cross-sectional model accurately. Moreover, the changes of flow field under project conditions may further limit the usage of 2D models. While a 2D model may be acceptable for a screening level analysis, a 3D model may be deemed informative for a design level analysis.