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To solve the problem of the equation structure becoming more complex in the improved soil conservation service curve number (SCS- CN) model, a SCS- CN model with revised effective precipitation ( SCS- CN- REP) is proposed by introducing a revised coefficient after a comparison between the standard SCS-CN model and the improved model. Furthermore, for the complex area with low impact development (LID) in a city, a distributed SCS-CN-REP model was developed based on a hydrological response unit division in which the effects of the LID facility′s storage capacity on rainfall-runoff are also considered. Finally, taking the Shuangzi residential district in Beijing City as a study area, the rainfall-runoff is simulated and compared using the distributed SCS-CN-REP model. An analysis of the SCS- CN- REP model showed that when the revised coefficient is 1. 0, it is equivalent to the standard model, when the revised coefficient is smaller than 1. 0, it is equivalent to the improved model. In essence, the revised coefficient is a limit value of the runoff coefficient varied with the increase in precipitation. The distributed SCS-CNREP model application results demonstrated that the calculated runoff depth values are in good agreement with the measured values. The determination coefficients and Nash efficiency coefficient are 0. 91 and 0. 83 when the adopted value of the revised coefficient for permeable surfaces is 1. 0, and are 0. 92 and 0. 91 when the adopted value is less than 1. 0. The effects of the latter model are better than the former, indicating that the simulation effect can be effectively improved when the adopted value of the revised coefficient for permeable surfaces is less than 1. 0 in the distributed SCS-CN-REP model. [ABSTRACT FROM AUTHOR]

As a complex three-phase particle flow and the main carrier of non-point pollution,the coordinated transport processes and environmental effects of the runoff-sediment- pollutant systems on urban surfaces are very complicated. In this paper,the existing research on the transports of runoff-sediment-pollutant systems is summarized and analyzed from the perspectives of,the spatial-temporal distribution of urban surface sediment with absorbed pollutants,the hydrodynamic characteristics and simulation methods of urban surface rainfall-runoff,as well as the coordinated transport and reduction effects of runoff-sediment-pollutant systems. It is considered that the sediment dynamics theory can be used to study the urban surface sediment movement law during the rainfall-runoff process,and that the sediment deposition plays an important role in the reduction of particle pollutants due to the absorption effect. Finally,the following research actions should be carried out in the future: enlarging urban sample size; studying on dynamic characteristics of overland flow on different underlying surface; studying on incipient motion law for non-uniform sediment on urban surfaces, as well as sediment transport capacity for overland flow based on flow power theory. [ABSTRACT FROM AUTHOR]

Green roof is an important facility to mitigate urban flood resulted by increasing urbanization and impermeable surface. A thick substrate material layer with plants, grass, and/or trees, and extra structural support is one of main components of green roof. Due to the complexity of rainwater storage mechanism in the substrate material layer, the simulations results on rainfall-runoff on green roof are mostly unsatisfactory. In this study, the runoff reduction effect of green roof was simulated by considering the effect of substrate material layer on runoff. The green roof was compared with slope roof, plane roof and retention roof in order to understand the effect of substrate material layer on runoff. The experiment was carried out in Beijing Water Science and Technology Institute, China. The precipitation was measured by using a self-recording tipping bucket rain gauge. Runoff was monitored by using an equipment including water level gauges and triangular weir. The runoff coefficient and rainwater retention rate were calculated. A total of 11 rainfall-runoff events were monitored in 2015. The results showed that the change of the runoff coefficient was highly complex and it was influenced by many factors, e.g., precipitation, average/maximum rainfall intensity, and interval time between rainfall events. For all the monitored rainfall events, the average runoff coefficient values for plane roof, slope roof, green roof and retention roof were 0.68, 0.84, 0.41 and 0.43, respectively. The average rainwater retention rate values of green roof and retention roof were 58.9% and 57.2%, respectively. It indicated that the runoff reduction effects of green roof and retention roof are similar but both were better than the other two types of roofs. The runoff process of green roof was also similar with that of retention roof under the same rainfall conditions. Both the outflow processes from green roof and retention roof could be regarded as an unsteady orifice flow under the effect of accumulated water head on the roof-top. Thus, a unit hydrograph model to simulate runoff from green roof was proposed based on the saturated infiltration theory that included the thickness limitation of the substrate material layer and the influence of water accumulated on the surface. By using the proposed unit hydrograph model, the rainfall-runoff processes on green roof were simulated. The simulation results showed that the trends of the simulated and measured runoff were consistent well. The coefficient of determination and Nash-Sutcliffe efficiency were 0.85 and 0.84, respectively. This study will be helpful for further understanding the runoff reduction effect and the outflow mechanism of green roofs. [ABSTRACT FROM AUTHOR]

Based on the field data of sediment and water volume, the deposition process during 1960-2010 of the Inner Mongolia reach were calculated and studied by using the sediment discharge balance method. The results show that the deposition amount has an increasing trend of slow increase before 1986 and sharp increase after 1986 because of the influence of silt-discharge variations. By applying the delayed response model for fluvial process in which the deposition body was taken as a specific variable, the deposition process of the Inner Mongolia reach was simulated by using two calculation methods including the single-step analytical solution method and the multistep iterative method. The calculation results show that the calculated values of the deposition amount are basically in consistent with the measured values, the correlation coefficients for the single-step and the multistep method are 0.993 and 0.957 respectively. [ABSTRACT FROM AUTHOR]

For the Lower Yellow River,which has a major role of transferring sediment to the sea,the boundary condition has an important influence on the sediment transport efficiency. From the literature survey,this paper reviewed studies of the effects of boundary condition on sediment transport. An increasing number of studies have shown that the boundary condition and its evolutionary processes affect the spatial-temporal variation of the sediment transport efficiency. For different calculation methods of sediment transport,such as the hydrology method and hydrodynamics method,the influencing ways of boundary condition have both the difference and the relation. The mathematical comparison results show that the derivatives of sediment concentration of the two above mentioned methods are first order approximate. The key criterion used to check the effectiveness of simulation for sediment model is to determine whether the coupling effect between the sediment movement and bed deformation can be reflected. Seeing as how the sediment transport and bed deformation processes are very closely interlinked,it is proposed that the regulation of sediment transport efficiency can be studied from the aspect of the riverbed evolution process,potentially providing new insights and support for further studies. [ABSTRACT FROM AUTHOR]

The empirical power law relationship model and non-equilibrium sediment transport theory are two different methods used to describe the suspended sediment transport in alluvial rivers. The mathematical comparison results show that, for steady uniform flow, the derivatives of sediment concentration of the two above mentioned methods are first order approximate when sediment transport state is near equilibrium condition, and the variation of the saturation recovery coefficient is considered in power law relationship when sediment transport state is far away from the equilibrium condition. Based on the equivalence property, the calculation formula of exponent in power law function is established, showing that the value of exponent varies with the saturation recovery coefficient, sediment fall velocity, unit width discharge and longitudinal distance. Based on the derivative of power law function for the structural features of sediment concentration, the calculation expression of saturation recovery coefficient which is far away from the equilibrium condition is extracted and expressed. Finally, a new power law relationship model with changing exponent is proposed and applied to the sand basin. The application result revealed that the computed suspended sediment concentration along the distance of the sand basin is in suitable agreement with the measured values. [ABSTRACT FROM AUTHOR]