Integrated modeling of multi-scale hydrodynamics, sediment and pollutant transport

Modeling hydrodynamics, sediment and pollutant transport over a wide range of spatial scales and hydrological events (e.g., inland flood and storm surges) remains a fundamental impediment to flood risk prediction, water resources management, and environmental protection. In addition, forecasting of extreme hydrologic events caused by severe weather and climate change [Milly et al., 2002] is a growing challenge. The goal of this study is to develop a modeling system appropriate to predict the multiple scale hydrodynamics, sediment and pollutant transport as well as extreme hydrological events for rivers, floodplains, coastal areas and their watersheds.;Two major contributions are made in this dissertation. First, a two-dimensional (2-D) finite volume model (PIHM-Hydro) was developed to fully couple the hydrodynamics, pollutant transport, and sediment transport at the scale of river, floodplain, and coastal area. This is the first 2-D high-order model to fully couple shallow water flow and sediment transport in the successful simulation of a real flow field. The model is based on standard upwind finite volume methods using Roe's and HLL approximate Riemann solvers on unstructured triangular grids. A multidimensional linear reconstruction technique and multidimensional slope limiter were implemented to achieve second-order spatial accuracy. Model efficiency and stability are treated using an explicit-implicit method for temporal discretization with operator splitting.;The advantages of the present model are that (1) it can handle complicated geometry by using the Delaunay triangulation based on Shewchuk's algorithm; (2) it is capable of producing accurate and stable solutions over a wide range of spatial scales and hydrological events such as discontinuous flow and wetting/drying process by using the approximate Riemann solver and the semi-implicit time integration technique based on the CVODE; and (3) it can accurately simulate the interactions of hydrodynamics, sediment transport and pollutant transport by fully coupling these processes physically and numerically. These advantages of PIHM-Hydro have been illustrated by its successful application on the test cases where multiscale physical processes are dominant over a wide range of spatial scales.;The second contribution of this dissertation is to develop a spatially-distributed physically-based sediment transport modeling component at the watershed scale (PIHM-Sed) which is fully coupled with the hydrological processes within the Penn State Integrated Hydrologic Model system (PIHM) [Qu and Duffy, 2007]. This is the first spatially-distributed physically-based model to "fully-couple" hydrology and sediment transport in terms of physical and numerical coupling. It integrates the hillslope and channel processes, and is capable of predicting major surface/subsurface hydrological processes, sediment yield as well as spatial distribution of erosion/deposition. For the hillslope, the erosion processes of rain splash and sediment transport by overland flow are simulated; for the channel, it simulates the erosion of bed material and sediment transport by channel flow. An algorithm for bed armoring was also implemented in the channel component. In the model system, all hydrological and sediment transport processes are defined on discretized unit elements as a fully-coupled system of ordinary differential equations (ODEs) using a semi-discrete finite volume method (FVM) on unstructured grids. The implementation of the model has been performed on a hypothetical storm event at the Shale Hill watershed for demonstrating the capability of the model in multi-process simulation at watershed scale.