The effects of low impact development on urban flooding under different rainfall characteristics.

Low impact development (LID) is generally regarded as a more sustainable solution for urban stormwater management than conventional urban drainage systems. However, its effects on urban flooding at a scale of urban drainage systems have not been fully understood particularly when different rainfall characteristics are considered. In this paper, using an urbanizing catchment in China as a case study, the effects of three LID techniques (swale, permeable pavement and green roof) on urban flooding are analyzed and compared with the conventional drainage system design. A range of storm events with different rainfall amounts, durations and locations of peak intensity are considered for holistic assessment of the LID techniques. The effects are measured by the total flood volume reduction during a storm event compared to the conventional drainage system design. The results obtained indicate that all three LID scenarios are more effective in flood reduction during heavier and shorter storm events. Their performance, however, varies significantly according to the location of peak intensity. That is, swales perform best during a storm event with an early peak, permeable pavements perform best with a middle peak, and green roofs perform best with a late peak, respectively. The trends of flood reduction can be explained using a newly proposed water balance method, i.e., by comparing the effective storage depth of the LID designs with the accumulative rainfall amounts at the beginning and end of flooding in the conventional drainage system. This paper provides an insight into the performance of LID designs under different rainfall characteristics, which is essential for effective urban flood management.

Qin HP ，Li ZX ，Fu G 《-》

Assessment of low impact development (LID) strategies under different land uses in an urban sub-catchment in the Philippines.

Lack of studies in developing countries with tropical climate such as the Philippines limit local LID adoption. This study compared the performance of different LID scenarios across different urban land use types at the sub-catchment level using peak flow, runoff volume and flood reductions as performance criteria. Results showed that the most effective strategies for each land use are: 1) combined green roof and bioretention for low-density residential (reduction up to 10% peak flow, 11% runoff volume and 33% flood volume); 2) green roof for high-density residential (8% peak flow, 6% runoff volume and 18% flood volume); 3) combined rain barrel, bioretention and permeable pavement for industrial (23% peak flow, 41% runoff volume and 56% flood volume), and 4) combined vegetative swale and detention pond for urban open spaces (81% peak flow, 8% runoff volume and 84% flood volume). While effective for most low intensity storms, the observed sharp decrease in LID performance with increased rainfall intensity poses a major challenge, especially in the context of the Philippines frequented by high intensity storms. This study also examined how differences in land use characteristics influence LID performance, unlike most studies that focused on LID type comparisons. It showed that low urban density setting positively affected peak flow and flood reduction performance of rain barrels and green roofs, while good drainage infrastructure quality positively affected peak flow and flood reduction performance of rain barrels and bioretention. Decision-makers may use these findings to conduct rapid assessments on LID selection and siting, provided similarities between land use characteristics described in this study and those at their localities are justified. This can lead to increased LID adoption towards building water resilient, and sustainable cities.

Boongaling CGK ，Sevilla-Nastor JB ，Espaldon MVO ，Sanchez PAJ ，Villanueva-Peyraube JD ，Jago-On KAB ... -  《-》

Study on the response analysis of LID hydrological process to rainfall pattern based on framework for dynamic simulation of urban floods.

Liu C ，Xie T ，Yu Q ，Niu C ，Sun Y ，Xu Y ，Luo Q ，Hu C ... -  《-》

A robust approach for comparing conventional and sustainable flood mitigation measures in urban basins.

An integrated methodological framework for assessing different flood mitigation measures in urban catchments is presented. The framework comprises hydrologic, hydraulic and economic indices aiming at quantifying the effect of different alternatives regarding flood hazard mitigation. The alternatives evaluated include both conventional drainage solutions and low impact development measures. The conventional drainage solutions were: (i) off-line detention tanks; and (ii) sewer enlargement. The low impact development measures included: (i) green roofs (GR); and (ii) permeable surfaces (PS). Each solution was modeled using SWMM5 with respect to flood reduction effectiveness, and the results were compared to those of the existing condition (i.e., no flood mitigation measures). All the examined solutions were also compared based on their construction and operation and maintenance costs for a typical lifespan (i.e., 30 years). The results of the simulation revealed that both low impact development measures and conventional drainage solutions were highly effective even for storm events with low probability of occurrence. However, sewer enlargement was found to be the best alternative from an economic perspective. Nevertheless, peak at the sewer exit increased and time to peak remained unchanged; as a result, local flooding problems are resolved but downstream flooding problems may be introduced. If other criteria are considered, i.e., traffic obstruction, noise, construction easiness, co-benefits and downstream impacts, low impact development measures become more attractive compared to conventional drainage solutions.

Kourtis IM ，Tsihrintzis VA ，Baltas E 《-》

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 ... -  《-》