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Urban lakes are typically characterized by fragile ecological capacities and complex management of their hydrospheric ecosystems. The aims of this study are to establish a reliable hydrodynamic-water quality model for an urban lake, to investigate the responses of water quality to different extreme hydrological conditions associated with rainstorms, and to explore the results from different modeled scenarios surrounding the pollution threats associated with a sewage leak. A three-dimensional hydrodynamic water quality model was developed in this study. The model was calibrated and validated using observed data. The model results agreed well with the observed data, and the averaged relative root mean-squared error (RRMSE) for all of the compared variables was 33.3 %. The validated model was applied to analyze water quality responses for different extreme historical rainfall scenarios from January 1, 2012 to December 31, 2012. The model results indicate that for Lake Tianyinhu, rainstorms adversely affect water quality due to larger nutrient loads, generated by larger rainfall events, and the limited water storage capacity of the lake. Moreover, the responses of water quality to sewage leak events were studied through four scenarios with different leak intensities and durations. The model results indicate that sewage leaks have measureable negative effects on water quality and that it is vital to inspect and promptly eliminate any possible leaks within pipes surrounding the lake. This study may provide a useful tool for hydrological ecosystem protection and management techniques for similar urban lakes. [ABSTRACT FROM AUTHOR]

Combined with the basic characteristics of Suzhou plain river network, two modules are established, one of which is the hydrodynamic module using the water level node method involving gate operation, while the other is the water quality module based on the principle of WASP5 (water quality analysis simulation program5). These two modules were coupled and verified by the monitoring data of Suzhou River network. The results showed that calculation errors of NH-N and DO for the model were in the ranges of −15%-13% and −18%-16%, respectively. Despite of the deviations between the monitoring data and simulation result, the calculation accuracy of the model conforms to the practical engineering requirement. Therefore, the proposed coupling model may be useful for water quality simulation and assessment for river network under tidal influences. [ABSTRACT FROM AUTHOR]

A mathematical model is formulated to simulate dam-break transient debris flows, in which the debris and water mixture is assumed to be isotropic and continuous. In terms of its viscoelastoplasticity, a three-dimensional (3D) rheologic model for Bingham body is used to describe the relationship between the stress tensor and the rate of strain. Only the deformation caused by the deviatoric stress tensor is taken into account. Under the prior considerations, the governing equations for two-dimensional (2D) depth-averaged transient debris flows are obtained by integrating the equation of continuity and equations of motion over depth for 3D flows. To deal with the transient and high-speed features of dam-break debris flows, the derived governing equations are discretized and solved using the method of characteristics. The model is applied to simulate the dam-break debris flow of April 30, 1986, for the Jinshan debris reservoir in Anhui, China. The debris and water mixtures reach as far as 900 m downstream from the initial tailings dam site, with a depth of 1.7 m near the tailings dam and 1.0 m at 900 m downstream. These model results are in good agreement with the available observations. [ABSTRACT FROM AUTHOR]