To provide support for scientific decision-making about scheduling to keep a water-conveyance project running safely in Beijing, China, a Web geographic information system (GIS)-based conveyance system (WGCS) is proposed. The development of WGCS involves three primary modules. First, the pipe-channel hydrodynamic model with various types of hydraulic structure (reservoir, sluice, and inverted siphon) control equations is established as the engine to simulate a variety of flow regimes and hydraulic responses for different conveyance scenarios. Then, a relatively lightweight Web GIS platform without expensive mature GIS packages is implemented through rendering vector map layers based on Silverlight painting technology for model setting, simulation and data visualization. Furthermore, the employment of an asynchronous refresh mechanism facilitates the performance of particle motion animation. Finally, the database platform is used to record initial information, configuration parameters, hydraulic structure parameters converted to the hydrodynamic model for computation, result data received from the hydrodynamic model for analysis, attribute data and spatial data for map publishing and visualization. WGCS represents an effective attempt to integrate large-scale hydrodynamic numerical calculations on the web. The functionality of WGCS is illustrated through two case studies on conveyance progress. Currently, this system is successfully operating in Beijing.