To satisfy the needs of a variety of demand-responsive transport, the multimodal transportation problem appeared. This paper focuses on network modeling with a hierarchical structure. The relationship between different levels is described in detail, and dynamic segmentation and linear referencing techniques are used to solve the overlay problem in multimodal network. Furthermore, a shortest path algorithm is proposed to solve the transfer problem with several public vehicle modes. Finally, the results simulated by Geographic Information System (GIS) are given to demonstrate the effectiveness of the proposed model and algorithm.

Understanding the dynamics of water renewal in a reservoir is essential when the transport and fate of dissolved substances are evaluated. A three-dimensional hydrodynamic model was implemented to compute average residence time and water age in Dahuofang Reservoir in China. The model was verified for a one-year time period in 2006. A simulation reproduced intra-annual variation of mixing represented by the fall/winter mixing and the spring/summer stratification. The simulated variation of vertical thermal structures also matched observation. The spatially varying average residence times and age distribution were investigated through a series of numerical experiments using a passively dissolved and conservative tracer as a surrogate. Residence time estimations yield a broad range of values depending on the position. The average residence time for a tracer placed at the head of the reservoir under high-, mean-, and low flow conditions was found to be about 125, 236 and 521 days, respectively. The age simulation reveals that the age distribution is a function of the freshwater discharge. In the vertical direction, the age of the surface layers is larger than that of the bottom layers and the age difference between the surface and bottom layers decreases further downstream. The density-induced circulation plays an important role in the circulation in the reservoir, and can generate vertical age distribution in the reservoir. These findings provide useful information for understanding the transport process in Dahuofang Reservoir that can be used to assist the water quality management of the reservoir.Dahuofang reservoir, reservoir, three-dimensional model, residence time, age PACS: 92.40.qf, 92.40.Cy, 92.40.We, 47.85.Dh

A three-dimensional eutrophication model was applied to assist the management of Dahuofang Reservoir in China. Transport processes were obtained from the three-dimensional, finite volume hydrodynamic model. The hydrodynamic model was verified for a one-year time period in 2006. Our simulation reproduced intra-annual variation of stratification. The simulated variation of vertical thermal structures also matched observations. The water quality model included 8 state variables, including dissolved oxygen, phytoplankton as carbon, carbonaceous biochemical oxygen demand, ammonium nitrogen, nitrate and nitrite nitrogen, ortho-phosphorus, organic nitrogen, and organic phosphorus. Sensitivity of the parameters has been analyzed to decide which process would affect the water quality in the simulation. The water quality verification suggested the model successfully computed the temporal cycles and spatial distributions of key water quality components. The comparison between water quality components before and after the first phase of the water conveyance project suggests that the project has a slight effect on the reservoir ecosystem. The model could be used as a tool to guide physico-biological engineering design or management strategies for Dahuofang Reservoir.Dahuofang Reservoir, reservoir, water quality, hydrodynamic, three-dimensional model PACS: 92.40.qf, 92.40.qc, 92.40.Cy, 92.40.We, 47.85.Dh

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