The simulation, regulation capacity assessment and coping strategy of rainstorm runoff waterlogging in Zhu pai-chong Basin of Nanning, China.

Currently, China is experiencing a phase of rapid urbanization. With the frequent occurrence of extreme rainfall events within the context of climate change, the problem of heavy rainfall and waterlogging in many cities is very prominent. In November 2020, China issued a proposal for the construction of sponge cities across the entire region to significantly enhance the rainfall flood prevention and drainage capacity of cities and effectively improve the resilience of sponge city systems for flooding management. Therefore, this paper selected the Zhu pai-chong watershed in Nanning with frequent waterlogging disasters as an example. Based on underlying surface information, We used a coupled SWMM-LISFOOD model to simulate runoff and waterlogging processes and analyze the spatial and temporal evolution characteristics of the basin under 10 designed rainstorm return periods (0.25a-50a). The results confirm the substantial spatial and temporal variabilities of the runoff coefficient in the study area; impermeability was the main factor contributing to high runoff coefficient values. The spatial distribution characteristics of inundation area was general dispersion and local linear aggregation. Furthermore, this study assessed the effect of the control rate of blue‒green‒gray facilities on the actual storms, and the value ranged from only 48.6% (0.25a)-24.05% (50a). This study quantified the two-dimensional distribution of rainfall storage volume thresholds with or without considering the discharged from the pipe network. Quantitative mapping between the elements of "rainfall-storage volume of blue‒green‒gray facilities-runoff-drainage capacity of the pipe network-waterlogging level" was conducted within the study area as an example. Finally, an overall technical process scheme for rainfall and waterlogging management was proposed. The scheme covered the hydrological‒hydraulic mechanism, storage function of sponge facilities, engineering control response, nonengineering measures and intelligent management of rainfall and waterlogging during sponge city construction, which could provide critical scientific support for effective promotion of the construction of sponge cities in China.

Li Q ，Yang Y ，Liao H ，Liu M ，Liao L ，Huang S ，Sun G ，Mo C ，Li X ... -  《-》

Urban rainstorm and waterlogging scenario simulation based on SWMM under changing environment.

Urban rainstorm and waterlogging occurred more frequently in recent years, causing huge economic losses and serious social harms. Accurate rainstorm and waterlogging simulation is of significant value for disaster prevention and mitigation. This paper proposed a numerical model for urban rainstorm and waterlogging based on the Storm Water Management Model (SWMM) and Geographic Information System (GIS), and the model was applied in Lianhu district of Xi'an city of China. Furthermore, the effects of rainfall characteristics, pipe network implementation level and urbanization level on waterlogging were explored from the perspectives of spatial distribution of waterlogging points, drainage capacity of pipe network and surface runoff generation and confluence. The results show that: (1) with the increase of rainfall recurrence period, the peak of total water accumulating volume, the average decline rate of water accumulating volume and the number of waterlogging nodes increase; (2) optimizing the pipe diameter can shorten the average overload time of the pipe network from the entire pipe network, but for a single pipe, optimizing the pipe diameter may lead to overloading of unoptimized downstream pipeline; (3) the lower the imperviousness, the less the number of waterlogging nodes and average time of water accumulating, and (4) the west, northwest and southwest areas are relatively affected by the imperviousness, only improving the underlying surface conditions has limited influence on waterlogging in the study area. This study can provide reference for urban waterlogging prevention and reduction and pipe network reconstruction.

Wang S ，Jiang R ，Yang M ，Xie J ，Wang Y ，Li W ... -  《-》

Hydrological reduction and control effect evaluation of sponge city construction based on one-way coupling model of SWMM-FVCOM: A case in university campus.

The exacerbation of global warming, the frequent incidence of extreme weather events, and the rapid urbanization have collectively contributed to the heightened prevalence of flooding in urban areas. As a result of this challenge, sponge city (SPC) has been adopted in China as an efficient means of preventing and controlling urban floods. To evaluate the hydrological reduction and control effect of sponge city construction (SPCC) within a university campus, a one-way coupled model integrating one-dimensional sewer hydrodynamic model (SWMM) and two-dimensional surface flow model (FVCOM), namely SWMM-FVCOM model, was established. The Nash-Sutcliffe efficiency (NSE) of the SWMM were greater than 0.75 under there rainfalls with different intensity, indicating the good reliability and stability of this model could be used in the subsequent simulation. An analysis of drainage capacity and the risk of urban flooding was conducted using this model before and after the implementation of SPCC, considering six rainfall scenarios. Implementing SPCC demonstrated an effective performance in mitigating surface runoff, regulating inspection well overflow, and reducing overflow volume in the study region. However, the efficacy of runoff control diminished proportionally with the escalation of rainfall return period. Simultaneously, the implementation of low impact development (LID) measures can significantly decrease the extent and magnitude of surface inundations. The reduction rate of SPCC on the area of waterlogging ranged from 55.84% to 72.50%. But the control rate decreased with increasing rainfall return periods, demonstrating that adopting SPCC can effectively mitigate the severity of urban flooding resulting from low rainfall return period events (Tr < 20 years). This study can provide scientific foundation for environment managers to evaluate the impact of urban flooding prevention and control on runoff pollution mitigation when adopting the implementation of SPCC.

Tan Y ，Cheng Q ，Lyu F ，Liu F ，Liu L ，Su Y ，Yuan S ，Xiao W ，Liu Z ，Chen Y ... -  《-》

Spatial simulation of the ecological processes of stormwater for sponge cities.

The ecological stormwater processes of a sponge city include the ecological processes of runoff and confluence, the thermal landscape and decontamination. In this study, elements of stormwater processes - short-duration heavy rainfall, rainstorm intensity, drainage networks, surface temperature, the scouring process and the cumulative process of pollutants (SS, COD, TP and NH3_N), and, finally, the low impact development (LID) facilities at different recurrence periods-are simulated using the rainstorm intensity model, the scoured exponential model and the split-window algorithm. Land-use types and LID facilities in sponge cities greatly influence the spatial distribution of ecological stormwater processes. Rainstorm intensity, cumulative volume, flow rate and drainage capacity all increase in the initial stage of rainfall and decrease in the later stage, with an increase in rainfall duration. Rainfall, infiltration amount, runoff and rainstorm intensity all increase; however, the runoff coefficient and infiltration proportion decrease with an increase in the rainfall recurrence period. LID facilities can increase rainfall, peak flood delay time, area of low temperature zone, annual runoff control rate and runoff pollutant reduction rate at the recurrence periods of 1 a, 3 a, 5 a, 10 a, 20 a, 30 a and 50 a, especially during short-duration rainfall. The paper concludes LID facilities of sponge cities play an important role in weakening the effects of rain-, heat- and pollution-islands.

Hou J ，Mao H ，Li J ，Sun S ... -  《-》

Performance evaluation of time-sharing utilization of multi-function sponge space to reduce waterlogging in a highly urbanizing area.

Urban waterlogging is a dilemma faced by many highly urbanizing areas. To solve the contradiction between the space requirement for waterlogging control and the scarcity of urban space, time-sharing utilization of the multi-function sponge space (MFSS) is promoted in some urbanizing areas. The MFSS is designed to have certain social or economic functions during dry or light rain events and detains stormwater on heavy rain events. However, there is lack of understanding on how to achieve the maximum benefit of multi-function. In this study, three time-sharing utilization modes are proposed to use MFSS to detain runoff: when the rain event begins (Mode A), when cumulative rainfall is greater than a specific threshold (Mode B), or when rainfall intensity is higher than a specific threshold (Mode C). A methodological framework based on the Storm Water Management Model (SWMM) is proposed to evaluate the waterlogging reduction performance of the three modes under different rainfall conditions and thresholds for enabling MFSS in an urbanizing catchment in Shenzhen, China. The performance is measured by comparing the total volume of overflow from manholes of the drainage system with and without MFSS during a storm event. The results indicate that: (1) Under Mode A, the performance is more effective under a light storm event with an early peak; (2) Under Mode B, as the cumulative rainfall threshold for enabling MFSS increases, the overflow first decreases and then increases. Different threshold values have to be set for different types of rainfall events to achieve the best performance; (3) Under Mode C, as the rainfall intensity threshold for enabling MFSS increases, the overflow also first decreases and then rapidly increases at a high threshold value. The mode has an identical range of optimal thresholds under different types of rainfall events. Furthermore, Mode C has higher efficiency in overflow reduction than the other two modes, no matter whether under design storms or historical storms. Therefore, Mode C is recommended as an efficient and stable utilization mode for MFSS.

Cheng M ，Qin H ，Fu G ，He K ... -  《-》