Rainfall Return Period Research Articles

Flood risk assessment of Kemang Area as a central business in South Jakarta

This paper presents a flood risk assessment of Kemang area which around 80 Ha as central business at South Jakarta, DKI Jakarta, Indonesia. It is crucial to asses this area as it well-known as central business that has high damaged due to affected by flooding. The objective of this study to know the current level flood risk in the area and then how structural interventions through improving drainage pumps capacity with 2 m3/s contribute to the its level. The rational method, HEC-RAS 2D, and GIS have applied for methods flood risk analysis in two years return period of rainfall (138 mm/day). Flood risks calculated based on hazard index, vulnerability index and capacity index in scale of 20 RT (neighbourhood associations). As the result, flood risk map show that the Kemang area has 65 % highly risk of flooding, 10 % in moderate level and the rest is low level risk of flooding. The current planning of structural intervention not significant to reduce risk level. Therefore, it needs more actions to reduce the flood risk level through both structural and non-structural measures such as normalization of drainage system, policy, social and private engagement.

Rainfall characteristics during pre- and post-onset of local climate change in Aceh Besar District, Indonesia

Climate change caused by global warming, which is characterized by increasing temperatures on the earth’s surface, is the biggest problem in the world today. This study attempts to examine how local climate change has affected the characteristics of rainfall in Aceh Besar District, which is situated in the far north of Indonesia’s Sumatra Island. 2001 was assumed to be the onset of local climate change in the region. Using EasyFit, probability distribution that best fits the rainfall data during the pre- and post-onset of climate change is chosen. The results indicated that the annual rainfall amount has increased over the past decade. The probability of receiving an annual total rainfall exceeding the long-term average (1700 mm) has increased significantly after the local climate change. Meanwhile, although the lowest and highest amounts of annual maximum daily rainfall for pre- and post-onset periods remain the same, the frequency of the maximum daily rainfall in a year greater than 140 mm/day was doubled during the post-onset period. Consequently, local climate change has increased the expected amount of annual maximum daily rainfall for return periods of 2, 5, and 10 years.

The impacts of rainfall and soil moisture to flood hazards in a humid mountainous catchment: a modeling investigation

Floods pose a significant threat to the safety of countries with severe societal, economic, and environmental consequences, especially the flash floods in mountainous regions. Previous studies have shown that many floods were caused by intense rainfall with highly saturated soil. In this study, we applied a physically-based distributed hydrological model (Integrated Hydrology Model, InHM) to a warm humid mountainous catchment in Southwest China, the Shouxi River. The main objective of our research is to investigate the relative importance of rainfall and antecedent soil moisture on flood generation in our study region. Our results show that an increase in rainfall return period and antecedent soil saturation ratio significantly increased peak flow and shortened peak time. There is a correlation between the ratio of antecedent soil saturation ratio to rainfall (SPR) and peak flow. When SPR <1, there is a positive correlation; when SPR >1, there is a negative correlation. Additionally, with the increase in drainage area, the relative importance of rainfall tends to decrease, while the relative contribution of soil saturation ratio tends to increase. The findings could provide support for the determination of the dominant factors influencing runoff generation in humid regions, offering scientific support for the timely and effective flood prevention and mitigation measures in mountainous regions.

Dynamic probabilistic analytical modeling for estimating rainfall–runoff transformation rates in drylands

Abstract Precipitation-runoff changes used in the development of precipitation-runoff models depict general runoff mechanisms in physical precipitation-runoff processes. For this purpose, it must be able to adequately express the characteristics of the physical system. Similar to other water resources management models, analytical-probabilistic models may be developed with different levels of complexity according to different types of rainfall–runoff developments. In this research, a log-normal probabilistic model was used to estimate the return period of rainfall and Soil and Water Assessment Tool (SWAT) software was used to convert rainfall values into discharge and runoff height in agricultural lands. The slope and the level of plant shade cover were considered the two basic factors in the estimation of the subsurface flow used in agriculture. Slopes of less than 0.015 and land cover level of more than 70% of extreme points were obtained to ensure subsurface water sources and prevent erosion.

Development of an integrated model for assessing landslide susceptibility on vegetated slopes under random rainfall scenarios

Physically-based landslide susceptibility analysis has been extensively employed to predict the likelihood of landslides owing to its remarkable predictive capability. However, due to an insufficiently comprehensive analysis of the vegetation-disaster connection, this approach may face limitations in its application to regions where there is significant variation in vegetation diversity and topography. An integrated model was thus proposed for predicting landslide susceptibility with the consideration of the positive and negative effects of vegetation on slope stability. However, to accurately implement the slope failure process under the influence of vegetation, it is important to have a high temporal resolution rainfall scenario for simulating the interception process of vegetation crowns on rainfall. Analysis of vegetation hydrological processes is associated with difficulties in a regional area because of limited data availability. The stochastic simulation method for extreme rainfall scenarios, adopted in this study, is known to be effective in dealing with uncertainty caused by insufficient data. The method, which comprises the Gumbel model and Bounded Random Cascade Model (BRCM), was used to overcome the difficulties in integrating the comprehensive effects of vegetation, the results of which provide refined rainfall scenarios for landslide susceptibility prediction from the perspective of the failure mechanism of vegetated slopes. The application of the proposed method for landslide susceptibility zoning was validated using a confusion matrix and ROC curve analysis in a practical case. Results showed that the method performed effectively and reliably. Furthermore, this study investigated the influence of different extreme rainfall scenarios on slope stability. Results revealed that as the return period of extreme rainfall increased from 50 to 150 years, the overall proportion of susceptible areas for different rainfall durations exhibited an upward trend. Additionally, the study found that increasing vegetation biomass had a positive impact on slope stability in the study area. The findings of this study are significant for disaster prevention and mitigation in mountainous regions, providing scientific support for risk management strategies.

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.

Comprehensive Performance Assessment for Sponge City Construction: A Case Study

Sponge City Construction (SCC) can effectively solve urban areas’ water problems. Green infrastructure (GI), the core of SCC, exhibits a multifaceted capacity to deliver many co-benefits, while grey infrastructure primarily serves the single function of controlling rainfall runoff. However, existing assessment indicator systems fail to either consider or evaluate comprehensive impacts. In this work, a comprehensive indicator system has been established to assess the co-benefits of five different GI measures. The system includes twelve indicators from four aspects, i.e., disaster reduction, economic, environmental, and social benefits. This newly established assessment system is applied to Jinan as a case study. Six out of twelve indicators are evaluated using the self-developed Flood Risk Analysis Software and empirical equations. The results show that the inundation reduction ratios are 11.02%, 9.32%, and 8.02% under the 24-h design rainfall with a 5-year, 10-year, and 20-year return period, respectively. In addition, the corresponding direct flood loss reduction rates are 13.86%, 4.28%, and 4.09%. That is, as the rainfall return periods increase, the disaster reduction benefits become less pronounced. On the contrary, other benefits, e.g., groundwater recharge volumes, are more obvious. The corresponding groundwater recharge volumes are 2.23 million m3, 2.86 million m3, and 2.87 million m3, respectively. The proposed indicator system can be adopted to assess the performances of the different GI combinations, which provides effective support and reference to decision-makers in SCC at the planning and design stages.

Stochastic Model of the Annual Maximum Rainfall Series Using Probability Distributions

Rainfall is a natural process that is often characterized by significant variability and uncertainty. Stochastic models of rainfall typically involve the use of probability distributions to describe the likelihood of different outcomes occurring. This study aimed to model the annual maximum of daily rainfall in Makassar City, Indonesia for the period 1980–2022, specifically focusing on the rainy season (November to April) using probability distributions to estimate return periods. The study used the Generalized Extreme Value (GEVD) and Gumbel distributions. The Kolmogorov-Smirnov test was used to determine the suitability of each distribution, and the likelihood ratio test was employed to determine the best-fit model. The Mann-Kendall test was used to detect any trends in the data. The results indicated that the Gumbel distribution was the best-fit model for data in November, December, January, March, and April, while GEV was appropriate for February. No trends were observed in any of the months. The study then estimated the maximum rainfall for various return periods. January produced the highest maximum rainfall estimates for the 2, 3, and 5-year return periods, while February produced the highest maximum rainfall estimates for the 10 and 20-year return periods. Information about maximum rainfall can be valuable for the government and other stakeholders in developing flood prevention strategies and mitigating the effects of heavy rainfall, particularly during the peak months of the rainy season in Makassar City, which are December, January, and February.

Climatic-Geomorphological Investigation of the World's Wettest Areas around Cherrapunji and Mawsynram, Meghalaya (India)

This research paper comprehensively examines the climate and geomorphological features of Cherrapunji and Mawsynram, aiming to understand the factors and environmental implications of their extreme precipitation. The study investigates climatic patterns, identifies geomorphological characteristics, and explores the factors influencing the occurrence of heavy rainfall in these areas, and displays unique rainfall patterns with high precipitation levels and notable spatio-temporal variation influenced by topographic interactions. Trend analysis reveals stable rainfall conditions over the past 122 years. The shift of the world's wettest place from Cherrapunji to Mawsynram in recent decades have been attributed to various factors such as geographical location, geomorphology-local topography, LULC-human influence, rain shadow effect, and orographic lifting effects. Cherrapunji recorded maximum rainfall of 24.55 thousand mm, while Mawsynram received 26 thousand mm of rainfall in the last century. The analysis of long-term rainfall data indicates distinct dry and wet seasons, with recent trends (2000-2020) suggesting a decline in rainfall for both locations. Furthermore, extreme value analysis techniques are employed to estimate maximum rainfall for different return periods, offering insights into extreme rainfall events. The return period of one day's highest rainfall of 1340.82 mm is about 100 years. The findings contribute to our understanding of climate change impacts, support sustainable development practices, and inform strategies for water resource management and erosion mitigation in similar geographic contexts. This research enhances our knowledge of these unique regions and their significance within the broader context of global climate systems.

Rainfall extremes under future climate change with implications for urban flood risk in Kathmandu, Nepal

Increased rainfall extremes cause severe urban flooding in cities with adverse socio-economic consequences, and Kathmandu city is no exception. Rainfall events are projected to become more intense and frequent in a warm and wet future, and they pose a major challenge to the sustainable development of Kathmandu city. This paper analyses historical extreme rainfall patterns across the city and uses these as the basis for future projections in combination with a range of General Circulation Models. Future projections of extreme rainfall are then fed into the numerical flood model HAIL-CAESAR (Lisflood), using a high-resolution digital elevation model of Kathmandu. We show that rainfall intensity, such as the annual maximum 1-day rainfall (RX1day), is projected to increase by up to 72% in the future, and the historical 100-year return period rainfall will become a 20 or 25-year return period rainfall. The flood modelling results show that the future flood hazard (magnitude and extent) will increase. The historical 100-year return period flood discharge will correspond to a 25-year return period future flood. A 100-year period flood discharge is likely to increase up to 72% (37% median) in the future. Area of land inundated by more than 1 m in a 100-year return period flood event could increase from 11.7 km2 to 23 km2 in the future. Furthermore, the location and timing of rainfall maxima affect the peak, timing, and location of flood hazards. This analysis can serve as a scientific basis to assess future flood-induced risk in Kathmandu in response to climate change.

Evaluation of urban flooding and potential exposure risk in central and southern Liaoning urban agglomeration, China

Urban flooding is an important natural hazard that affects urban security in the context of global climate change and urbanization. The simulation of stormwater inundation and risk assessment in urban environments is critical for the sustainable development of urban agglomerations. However, few studies have focused on rainstorm flooding at the urban agglomeration scale. In this study, the Central and Southern Liaoning Urban Agglomeration (CSLN) was selected a case study. A method was proposed to assess the urban flooding and potential exposure risk. The urban flooding of CSLN was characterized by the average flooding depth (AFD) of each sub-catchment, and exposure risk was indicated by potential regional and population exposure risk. The results illustrate that the AFD increased with an increase in the rainfall return period, especially in the urban core. The AFD of each city in the CSLN ranged from 10 to 80 mm, and there were strong differences among cities. The spatial distribution of urban flooding in the nine cities presented aggregation characteristics, and hotspots were mainly concentrated in the old urban districts. The potential regional exposure risk tended to increase as the rainfall return period increased from 10 to 100 years; however, there were significant differences among cities. Among them, the area of potential regional exposure risk in Shenyang was the largest, increasing from 365 km2 under a 10-year rainfall return period to 463 km2 under a 100-year rainfall return period. The largest proportion of potential regional exposure risk was in Anshan, which increased from 3% under 10-year to 13.8% under 100-year rainfall return periods. Most cities had some potential population exposure risk. More residents in populous cities, such as Shenyang and Dalian, were subject to higher exposure risks. However, Benxi, Anshan, and Tieling had a high proportion of severely affected areas, although the size of their cities is much smaller than that of Shenyang and Dalian. Urban flooding and potential exposure risk were apparently higher in the business and government zones than in the industrial and greenspace zones. These methods and results may provide references for rainstorm flooding mitigation through urban planning in urban agglomeration areas.

Risk analysis of rainfall erosion on upland adjacent to riparian zone of the Three Gorges Reservoir

The Three Gorges Reservoir (TGR) is an artificial riparian ecosystem and influenced on its soil erosion. However, the probability and magnitude of the erosion on upland adjacent to riparian zone and its impacts on the TGR are still unclear. In this research, we determined the relationship between minute-scale rainfall erosivity and soil erosion from three replicated upland bare plots (5 m × 20 m for each) in Zhong County, southwest of China, from 2017 to 2019 (short-term), and estimated the rainfall erosion based on the daily-scale rainfall erosivity from 1992 to 2015 (long-term). We performed generalized extreme value (GEV) modeling to quantify three risk elements (scenario, probability-magnitude relation, consequences) and predicted the erosion risks. The results indicated that, over the short-term, wet season increased the average runoff depth and soil loss by a factor of 1.6 (p < 0.01) and 1.4 (p < 0.01), respectively. Low and rare rainfall erosivity (5 years < return period ≤ 20 years) caused the erosion event with relative low occurrence probability (return period > 5 years) to dominantly contribute the total erosion (>65%) in dry season. Common and normal rainfall erosivity (return period ≤ 5 years) caused the common erosion events (return period ≤ 2 years) to contribute nearly 50% of the total erosion in wet season. Over the long-term, extreme rainfall erosivity (1621 MJ·mm·ha−1·h−1) in dry season was predicted to be more effective on upland erosion, but a uniform pattern of erosion contribution of incremental rainfall return periods was estimated in wet season. Our findings improve the understanding of the uncertainty of upland-surface hydrologic processes in the TGR, and could provide useful risk management or ecological restoration strategies for the soil and water conservationists.

Urban rainfall-runoff flooding response for development activities in new urbanized areas based on a novel distributed coupled model

The development and construction activities of new urbanized areas lead to drastic changes in land use, resulting in severe flood disasters. The main purpose is to systematically reveal the response process to urban stormwater under different urban development degree (DD) and low-impact development (LID) implementation. A novel distributed hydrological and hydrodynamic coupled model (DHHCM), consisting of a sub-catchment-based hydrological method for plot areas and a grid-based hydrodynamic method for road areas was developed in this study. The Fengxi New Town, China was applied as the research object, a total of 11 combined events of DDs (0%, 20%, 40%, 60%, 80% and 100%) and LID deployment were simulated under five rainfall return periods (P = 2a, 5a, 30a,50a and 100a) to explore their impact on the flood process. The results indicated that the DD and the LID implementation have no obvious impact on road flood when P ≤ 5a. However, the road flood increases significantly with the increase of DD when P ≥ 30a. The peak discharge of the drainage system significantly increases with the increase in DD under different return periods, and the average peak discharge increases the most obviously (2.62 m3/s) under P = 30a. The implementation of LID measures has significantly improved the mitigation effect of surface inundation, drainage system discharge and runoff control, and its effect has increased with the DD increase. It is with great significance to accurately control the flood disaster evolution process in urban development activities, and provide data and technical support for quantifying the risks and losses in policy making.

HydroPol2D — Distributed hydrodynamic and water quality model: Challenges and opportunities in poorly-gauged catchments

Floods are one of the deadliest natural hazards and are exacerbated by changes in land-use and climate. Urban development decreases infiltration by reducing pervious areas and increases the accumulation of pollutants during dry weather. It also decreases infiltration by reducing pervious areas and increases the accumulation of pollutants during dry periods. During rainy events, there is an increase in pollution concentrations and runoff that may be a source of water supply during drought periods. Modeling the quantity and quality dynamics of stormwater runoff requires a coupled hydrodynamic module capable of estimating the transport and fate of pollutants. In this paper, we evaluate the applicability of a distributed hydrodynamic model coupled with a water quality model (HydroPol2D). First, the model is compared to GSSHA and WCA2D in the V-Tilted catchment, and the limitation of the critical velocity of WCA2D is investigated. We also applied the model in a laboratory wooden board catchment, focusing on the validation of the numerical approach to simulate water quality dynamics. Then, we apply HydroPol2D in the Tijuco Preto catchment, in São Carlos - Brazil, and compare the modeled results with the full momentum solver of the HEC-RAS 2D. This catchment shares similar characteristics with many poorly-gauged and human-impacted catchments worldwide. The implementation of the model, the governing equations, and the estimation of input data are discussed, indicating the challenges and opportunities to scale HydroPol2D into the reality of data scarcity of larger poorly-gauged catchments. For a 1-yr return period of rainfall and antecedent dry days, and assuming an uncertainty of 40% in the water quality parameters, the results indicate that the maximum concentration of total suspended solids (TSS), the maximum load and the mass of the pollutant washed in 30% of the volume are, 456±260 mgL-1km-2, 2.56±0.4 kgs-1km-2, and 89%±10%, respectively.

Assessing runoff control of low impact development in Hong Kong's dense community with reliable SWMM setup and calibration

Low impact development (LID) is a sustainable practice to managing urban runoff. However, its effectiveness in densely populated areas with intense rainfall, such as Hong Kong, remains unclear due to limited studies with similar climate conditions and urban patterns. The highly mixed land use and complicated drainage network present challenges for preparing a Storm Water Management Model (SWMM). This study proposed a reliable framework for setting up and calibrating SWMM by integrating multiple automated tools to address these issues. With a validated SWMM, we examined LID's effects on runoff control in a densely built catchment of Hong Kong. A designed full-scale LID implementation can reduce total and peak runoffs by around 35–45% for 2, 10 and 50-year return rainfalls. However, LID alone may not be adequate to handle the runoff in densely built areas of Hong Kong. As the rainfall return period increases, total runoff reduction increases, but peak runoff reduction remains close. Percentages of reduction in total and peak runoffs decline. The marginal control diminishes for total runoff while remaining constant for peak runoff when increasing the extent of LID implementation. In addition, the study identifies the crucial design parameters of LID facilities using global sensitivity analysis. Overall, our study contributes to accelerating the reliable application of SWMM and deepening the understanding of the effectiveness of LID in ensuring water security in densely built urban communities located near the humid-tropical climate zone, such as Hong Kong.

Distribution System Dewatering in Coal Mining at PIT Sena Sungai Lilin District, Musi Banyuasin Regency, South Sumatra Province

The purpose of this research is to calculate the total design discharge of water entering the mining site in the sena pit of PT Putra Muba Coal (PMC), design the appropriate shape and dimensions of the sump to accommodate the amount of water entering the mining site and calculate the number of pumps needed to remove water entering the mine to the settling pond. The source of water entering the mine area comes from rainwater entering the mine opening, water runoff from the rainwater catchment area in the area around the mine opening, and groundwater rise. Based on the results of the analysis of rainfall data for 2013-2022, a rainfall plan of 77, 225 mm/day, rainfall intensity of 9.714 mm/hour with a rainfall return period of 2 years was obtained. The rainfall catchment area at the research site is 72,936 m2 with a discharge generated of 0.03 m3 / second and groundwater discharge of 0.00812 m3 / second. To remove the water entering the mine, it is flowed naturally into the sump with dimensions of 50 m length, 14 m top width, 13 m bottom width, and 5 m depth. The dimensions of the open channel are planned with a channel width of 32 cm, a flow depth of 28 cm, a wet cross-sectional area of 13.6 cm2, a wet circumference of 97 cm, a hydraulic radius of 9.25 cm, and a channel length of 233m. The water in the sump is pumped into an open channel. The pump used has a maximum discharge of 150 m3 / hour and a total pump head of 11.8712 m with a pipe diameter of 6 inches.

DESAIN KOLAM PEREDAM ENERGI BENDUNG PLAOSAN KABUPATEN SEMARANG

Hydraulic aspect of the weir is important factors in planning a stilling basin. Remaining energy on the stilling basin is expected to be as minimal as possible so that scour does not occur on the river bed. Plaosan Weir does not yet have a stiiling basin structure. Therefore it is necessary to recommend the design of stiliing basin.The analysis carried out hydrological analysis, including calculating return period rainfall, flood discharge (Q) using the Haspers method, and calculating Froude number (Fr) to determine pond type. Based on the recommendations for the type of stilling basin, a building design is carried out and also stability of design..From the results of calculation it is obtained that 50-year return period rainfall is 108.68 mm. Planned discharge for 50 years is 186.06 m3/s, and froude number : 4. The appropriate type of stilling basin is USBR Type IV. The pond is planned to have a length of L = 17 m, with a block face width of 0.68 m, height of 1.36 m, distance between front blocks of 1.69 m and total of 13 pieces. The results of stability control analysis during normal water conditions and flood water conditions produce values above the safety factor so that it can be concluded that the design is planned qualify.

Global transportation infrastructure exposure to the change of precipitation in a warmer world

Transportation infrastructures are generally designed to have multi-decadal service lives. Transport infrastructure design, however, is largely based on historical conditions. Yet, in the face of global warming, we are likely going to experience more intense and frequent extreme events, which may put infrastructure at severe risk. In this study, we comprehensively analyze the exposure of road and railway infrastructure assets to changes in precipitation return periods globally. Under ~2 degrees of warming in mid-century (RCP 8.5 scenario), 43.6% of the global transportation assets are expected to experience at least a 25% decrease in design return period of extreme rainfall (a 33% increase in exceedance probability), which may increase to 69.9% under ~4 degrees of warming by late-21st century. To accommodate for such increases, we propose to incorporate a safety factor for climate change adaptation during the transportation infrastructure design process to ensure transportation assets will maintain their designed risk level in the future. Our results show that a safety factor of 1.2 would work sufficient for most regions of the world for quick design process calculations following the RCP4.5 path.

Analysis of a landfill cover without geomembrane using varied particle sizes of recycled concrete

Previous studies have demonstrated the effectiveness of a novel three-layer landfill cover system constructed with recycled concrete aggregates (RCAs) without geomembrane in both laboratory and field. However, no systematic investigation has been carried out to optimize the combination of the particle sizes for fine-grained RCAs (FRC) and coarse-grained RCAs (CRC) that can be used for the three-layer landfill cover system. The aim of this paper is to assist engineers in designing the three-layer landfill cover system under a rainfall of 100-year return period in humid climate conditions using an easily controlled soil parameter D 10 of RCAs. The numerical study reveals that when D 10 of FRC increases from 0.05 mm to 0.16 mm, its saturated permeability increases by 10 times. As a result, a larger amount of rainwater infiltrates into the cover system, causing a higher lateral diversion in both the top FRC and middle CRC layers. No further changes in the lateral diversion are observed when the D 10 value of FRC is larger than 0.16 mm. Both the particle sizes of FRC and CRC layers are shown to have a minor influence on the percolation under the extreme rainfall event. This implies that the selection of particle sizes for the FRC and CRC layers can be based on the availability of materials. Although it is well known that the bottom layer of the cover system should be constructed with very fine-grained soils if possible, this study provides an upper limit to the particle size that can be used in the bottom layer ( D 10 not larger than 0.02 mm). With this limit, the three-layer system can still minimize the water percolation to meet the design criterion (30 mm/yr) even under a 100-year return period of rainfall in humid climates.

Assessment of urban flood resilience based on a systematic framework

Urban flooding can seriously threaten urban ecological security and human life, and therefore urban flood resilience (UFR) is important for urban safety and stability. To comprehensively evaluate urban system performance during the entire process of rainfall, runoff, flooding, and drainage, we developed a systematic framework for UFR assessment covering runoff simulation, flood estimation, and resilience assessment, which broadly corresponded to the phases of resistance, adaptation, and recovery. The UFR in the phases of resistance, adaptation, and recovery was simulated and assessed using a system performance curve (SPC) and technically combining with the hybrid flood model while mainly considering the total simulation time and inundated urban proportion in SPC. Because the extent of urban flooding can be influenced by climate change and the rate of urbanization, we chose the corresponding representative factors of precipitation and infiltration rate and considered 21 simulation scenarios (seven rainfall return periods and three infiltration rates) for which UFR was quantified according to urban system performance. The effectiveness of this framework was demonstrated in application to a typical highly urbanized area (i.e., Dongguan, China). The following results were derived: (1) The inundated area under the pessimistic scenario (i.e., S19) would be nearly four times greater than that under the optimistic scenario (i.e., S3); (2) The values of UFR in Dongguan were 0.9494–0.9863, locating at the high and very high level; (3) The lowest UFR value was 0.6552 in the Shuixiang New City district; and (4) The rainfall return period was the main factor influencing UFR under relatively short rainfall return periods (i.e., S1–S9), while infiltration rate was the principal influencing factor under relatively long rainfall return periods (i.e., S10–S21). The proposed systematic framework could be applied in other cities and large-scale regions like urban agglomerations and provinces.