Cellular automata based framework for evaluating mitigation strategies of sponge city.

Urban surface water flooding is increasing because of climate change and urbanization, and brings great challenges to urban sustainable development. It is, therefore, most important to develop urban flood management approaches to alleviate the consequences of floods. China is implementing a "sponge city" initiative to tackle urban surface water flooding and improve urban water management. There is, however, limited cost-effectiveness evaluation to support the choice of economically efficient mitigation strategies. To address this gap, this study developed an evaluation framework based on cellular automata and cost-benefit analysis to assess the performance of mitigation strategies in sponge city construction. This approach is demonstrated with a case study of Siergou (Dalian, China), which has a total area of 10.1 km2. The mitigation measures of green roofs, permeable pavements and bio-retention were used to generate mitigation scenarios. A two-dimensional cellular automata-based model was used to simulate urban surface water flooding. The results obtained from the case study indicate that the framework can achieve cost-effective mitigation strategies for sponge city construction, which can support robust decision making. The distribution of mitigation strategies has great impacts on the effectiveness of alleviating urban flood risk. This study provides new insight into the development of cost-effective mitigation strategies for sponge city construction.

Wang Y ，Liu Z ，Wang G ，Xue W ... -  《-》

Integrated assessments of green infrastructure for flood mitigation to support robust decision-making for sponge city construction in an urbanized watershed.

Green Infrastructure (GI) has become increasingly important in urban stormwater management because of the effects of climate change and urbanization. To mitigate severe urban water-related problems, China is implementing GI at the national scale under its Sponge City Program (SCP). The SCP is currently in a pilot period, however, little attention has been paid to the cost-effectiveness of GI implementation in China. In this study, an evaluation framework based on the Storm Water Management Model (SWMM) and life cycle cost analysis (LCCA) was applied to undertake integrated assessments of the development of GI for flood mitigation, to support robust decision making regarding sponge city construction in urbanized watersheds. A baseline scenario and 15 GI scenarios under six design rainfall events with recurrence intervals ranging from 2-100 years were simulated and assessed. Model simulation results confirmed the effectiveness of GI for flood mitigation. Nevertheless, even under the most beneficial scenario, the results showed the hydrological performance of GI was incapable of eliminating flooding. Analysis indicated the bioretention cell (BC) plus vegetated swale (VS) scenario was the most cost-effective GI option for unit investment under all rainfall events. However, regarding the maximum potential of the implementation areas of all GI scenarios, the porous pavement plus BC + VS strategy was considered most reasonable for the study area. Although the optimal combinations are influenced by uncertainties in both the model and the GI parameters, the main trends and key insights derived remain unaffected; therefore, the conclusions are relevant regarding sponge city construction within the study area.

Mei C ，Liu J ，Wang H ，Yang Z ，Ding X ，Shao W ... -  《-》

Assessing catchment scale flood resilience of urban areas using a grid cell based metric.

Urban flooding has become a global issue due to climate change, urbanization and limitation in the capacity of urban drainage infrastructures. To tackle the growing threats, it is crucial to understand urban surface flood resilience, i.e., how urban drainage catchments can resist against and recover from flooding. This study proposes a grid cell based resilience metric to assess urban surface flood resilience at the urban drainage catchment scale. The new metric is defined as the ratio of the number of unflooded grid cells to the total grid cell number in an urban drainage catchment. A two-dimensional Cellular Automata based model CADDIES is used to simulate urban surface flooding. This methodology is demonstrated using a case study in Dalian, China, which is divided into 31 urban drainage catchments for flood resilience analysis. Results show the high resolution resilience assessment identifies vulnerable catchments and helps develop effective adaptation strategies to enhance urban surface flood resilience. Comparison of the new metric with an existing metric reveals that new metric has the advantage of fully reflecting the changing process of system performance. Effectiveness of adaptation strategies for enhancing urban surface flood resilience is discussed for different catchments. This study provides a new way to characterize urban flood resilience and an in-depth understanding of flood resilience for urban drainage catchments of different characteristics, and thus help develop effective intervention strategies for sustainable sponge city development.

Wang Y ，Meng F ，Liu H ，Zhang C ，Fu G ... -  《-》

Water Sensitive Urban Design (WSUD) Spatial Prioritisation through Global Sensitivity Analysis for Effective Urban Pluvial Flood Mitigation.

Water Sensitive Urban Design (WSUD) has attracted growing attention as a sustainable approach for mitigating pluvial flooding (also known as flash flooding), which is expected to increase in frequency and intensity under the impacts of climate change and urbanisation. However, spatial planning of WSUD is not an easy task, not only due to the complex urban environment, but also the fact that not all locations in the catchment are equally effective for flood mitigation. In this study, we developed a new WSUD spatial prioritisation framework that applies global sensitivity analysis (GSA) to identify priority subcatchments where WSUD implementation will be most effective for flood mitigation. For the first time, the complex impact of WSUD locations on catchment flood volume can be assessed, and the GSA in hydrological modelling is adopted for applications in WSUD spatial planning. The framework uses a spatial WSUD planning model, the Urban Biophysical Environments and Technologies Simulator (UrbanBEATS), to generate a grid-based spatial representation of catchment, and an urban drainage model, the U.S. EPA Storm Water Management Model (SWMM), to simulate catchment flooding. The effective imperviousness of all subcatchments was varied simultaneously in the GSA to mimic the effect of WSUD implementation and future developments. Priority subcatchments were identified based on their influence on catchment flooding computed through the GSA. The method was tested for an urbanised catchment in Sydney, Australia. We found that high priority subcatchments were clustering in the upstream and midstream of the main drainage network, with a few distributed close to the catchment outlets. Rainfall frequency, subcatchment characteristics, and pipe network configuration were found to be important factors determining the influence of changes in different subcatchments on catchment flooding. The effectiveness of the framework in identifying influential subcatchments was validated by comparing the effect of removing 6% of the Sydney catchment's effective impervious area under four WSUD spatial distribution scenarios. Our results showed that WSUD implementation in high priority subcatchments consistently achieved the largest flood volume reduction (3.5-31.3% for 1% AEP to 50% AEP storms), followed by medium priority subcatchments (3.1-21.3%) and catchment-wide implementation (2.9-22.1%) under most design storms. Overall, we have demonstrated that the proposed method can be useful for maximising WSUD flood mitigation potential through identifying and targeting the most effective locations.

Wu W ，Jamali B ，Zhang K ，Marshall L ，Deletic A ... -  《-》

Urban flooding resilience evaluation with coupled rainfall and flooding models: a small area in Kunming City, China as an example.

Xu T ，Xie Z ，Jiang F ，Yang S ，Deng Z ，Zhao L ，Wen G ，Du Q ... -  《WATER SCIENCE AND TECHNOLOGY》