Mingfu Guan

2D Process-Based Morphodynamic Model for Flooding by Noncohesive Dyke Breach

AbstractInundation models based on the shallow water equations (SWE) have been shown to perform well for a wide variety of situations even at the limit of their theoretical applicability and, arguably, somewhat beyond. One of these situations is the catastrophic event of floods induced by dyke breach and consequent dyke erosion. The dyke collapse is often not sudden—as assumed by many flood simulations in which the dyke boundary is treated as a “dam-break.” The dyke erosion is a gradual and complex process that delays the onset of the flood, affecting the hydrograph of the flow. To simulate correct temporal passage of a flood, it is important to understand the rate at which these dykes collapse. In this paper, an overtopping flood event combined with dyke erosion is simulated. The model is built upon the two-dimensional (2D) shallow water equations together with sediment-flow interactions and incorporates a sediment transport equation. The model is solved using a second-order Godunov-type finite volume me...

Multimode Morphodynamic Model for Sediment-Laden Flows and Geomorphic Impacts

AbstractSediment-laden flows are a complex solid-fluid interaction process. This study presents a multimode morphodynamic model system combined with shallow water theory and a nonequilibrium assumption for sediment transport. The model system aims to simulate the morphological change caused by sediment-laden flows with various sediment transport modes. It involves three modules: a hydrodynamic module, a sediment transport module, and a morphological evolution module. The hydrodynamic model is governed by modified shallow water equations considering the interaction effects of flow and sediment. A flexible sediment transport model is presented that incorporates a weight coefficient. The model can adaptively choose an appropriate transport mode according to local, real-time flow conditions. Bedload, suspended load, and total mixed sediment load are all involved. The model is solved by a second-order Godunov-type finite-volume method that is robust and accurate. Validation is demonstrated through a series of ...

Assessment of LID practices for restoring pre-development runoff regime in an urbanized catchment in southern Finland

This study quantifies the effects of common stormwater management techniques on urban runoff generation. Simulated flow rates for different low impact development (LID) scenarios were compared with observed flow rates during different urban construction phases in a catchment (12.3 ha) that was developed from natural forest to a residential area over a monitoring period of 5 years. The Storm Water Management Model (SWMM) was calibrated and validated against the observed flow rates in the fully developed catchment conditions, and it was then applied to parameterize the LID measures and produce scenarios of their hydrological impacts. The results from the LID scenarios were compared with the observed flow rates in the pre-development and the partially developed catchment conditions. The results show that LID controls reduce urban runoff towards the flow conditions in the partially developed catchment, but the reduction effect diminishes during large rainfall events. The hydrographs with LID are still clearly different from the observed pre-development levels. Although the full restoration of pre-development flow conditions was not feasible, a combination of several measures controlling both volumes and retention times of storm runoff appeared to be effective for managing the stormwater runoff and mitigating the negative impacts of urban development.

The Influence of Floodplain Restoration on Flow and Sediment Dynamics in an Urban River

This article is freely available via Open Access. Follow the DOI to read the whole article on the publishers website.

A two-dimensional hydro-morphological model for river hydraulics and morphology with vegetation

This work develops a two-dimensional hydro-morphological model which can be used to simulate river hydraulics and morphology with various vegetation covers. The model system consists of five modules, including a hydrodynamic model, a sediment transport model, a vegetation model, a bank failure model and a bed deformation model. The secondary flow effects are incorporated through additional dispersion terms. The core components of the model system solve the full shallow water equations; this is coupled with a non-equilibrium sediment transport model. The new integrated model system is validated against a number of laboratory-scale test cases and then applied to a natural river. The satisfactory simulation results confirm the models capability in reproducing both stream hydraulics and channel morphological changes with vegetation. Several hypothetical simulations indicate that the model can be used not only to predict flooding and morphological evolution with vegetation, but also to assess river restoration involving vegetation. We developed a novel coupled flow-sediment-vegetation model.The model was tested against both laboratory-scale cases and a natural river.The model is capable of reproducing river hydraulics and morphology with vegetation.Vegetation affects localised stream hydraulics, river planform and ecological diversity.

Physical complexity to model morphological changes at a natural channel bend

This study developed a two-dimensional (2-D) depth-averaged model for morphological changes at natural bends by including a secondary flow correction. The model was tested in two laboratory-scale events. A field study was further adopted to demonstrate the capability of the model in predicting bed deformation at natural bends. Further, a series of scenarios with different setups of sediment-related parameters were tested to explore the possibility of a 2-D model to simulate morphological changes at a natural bend, and to investigate how much physical complexity is needed for reliable modeling. The results suggest that a 2-D depth-averaged model can reconstruct the hydrodynamic and morphological features at a bend reasonably provided that the model addresses a secondary flow correction, and reasonably parameterize grain-sizes within a channel in a pragmatic way. The factors, such as sediment transport formula and roughness height, have relatively less significance on the bed change pattern at a bend. The study reveals that the secondary flow effect and grain-size parameterization should be given a first priority among other parameters when modeling bed deformation at a natural bend using a 2-D model.