Rainfall Return Period Research Articles

Catastrophic, rainfall-induced debris flows in Andean villages of Tarapacá, Atacama Desert, northern Chile

In March 2012, during the rainy season in the Altiplano plateau, a >100-year return period rainfall event affected the deeply incised valleys of the Precordillera of the Tarapaca Region, northern Chile. This extreme event in a very arid region triggered a number of debris and mud flows that caused severe damage and destruction in several small villages along the Camina and Tarapaca valleys. The highly vulnerable location of the villages on top of alluvial fans due to socioeconomic and cultural reasons is a key factor to explain the level of destruction in most villages. In this paper, this unusual, remarkable landslide event is described, and the hazard faced by these settlements for future rainfall episodes and possible mitigation measures are discussed.

An evaluation of enhanced geotextile layer in permeable pavement to improve stormwater infiltration and attenuation

This paper reports on an evaluation of the properties of a novel structure known as OASIS® which was designed at Coventry University as an enhancement of the commercially available geotextiles when incorporated in the permeable pavement system (PPS). The impact on the hydraulic behaviour of a PPS was analysed through the study of infiltration rate, throughout the PPS and time required to reach the steady-state stage behaviour of the water within the PPS, under extreme rainfall intensities of 100 mm/hr, 200 mm/hr and 400 mm/hr, corresponding to a 100-year return period rainfall over a duration of 15 min in different parts of the world. The result indicated that the novel structure provides an extra benefit when incorporated in PPSs, delaying peak flow of a rainfall event by retaining and storing great volumes of water within its structure. These additional benefits are especially important under extreme rainfall events.

Modelling the impact of increasing soil sealing on runoff coefficients at regional scale: a hydropedological approach

Abstract Soil sealing is the permanent covering of the land surface by buildings, infrastructures or any impermeable artificial material. Beside the loss of fertile soils with a direct impact on food security, soil sealing modifies the hydrological cycle. This can cause an increased flooding risk, due to urban development in potential risk areas and to the increased volumes of runoff. This work estimates the increase of runoff due to sealing following urbanization and land take in the plain of Emilia Romagna (Italy), using the Green and Ampt infiltration model for two rainfall return periods (20 and 200 years) in two different years, 1976 and 2008. To this goal a hydropedological approach was adopted in order to characterize soil hydraulic properties via locally calibrated pedotransfer functions (PTF). PTF inputs were estimated via sequential Gaussian simulations coupled with a simple kriging with varying local means, taking into account soil type and dominant land use. Results show that in the study area an average increment of 8.4% in sealed areas due to urbanization and sprawl induces an average increment in surface runoff equal to 3.5 and 2.7% respectively for 20 and 200-years return periods, with a maximum > 20% for highly sealed coast areas.

Selection of the Optimal Design Rainfall Return Period of Urban Drainage Systems

The aim of this work is to define a methodology to identify the optimal rainfall return period for the design of urban drainage systems. The choice of the optimal return period is made minimizing the total costs of the system: the sewer network is dimensioned for a set of possible design rainfall return periods, and the corresponding construction, maintenance and operation costs are evaluated. For each scenario, the total expected damage from flooding caused by rainfall events with return period greater than the design one is then estimated by hydraulic simulation. This methodology has been applied to a small urban catchment in Palermo (Italy).

Modelling hydrology of a single bioretention system with HYDRUS-1D.

A study was carried out on the effectiveness of bioretention systems to abate stormwater using computer simulation. The hydrologic performance was simulated for two bioretention cells using HYDRUS-1D, and the simulation results were verified by field data of nearly four years. Using the validated model, the optimization of design parameters of rainfall return period, filter media depth and type, and surface area was discussed. And the annual hydrologic performance of bioretention systems was further analyzed under the optimized parameters. The study reveals that bioretention systems with underdrains and impervious boundaries do have some detention capability, while their total water retention capability is extremely limited. Better detention capability is noted for smaller rainfall events, deeper filter media, and design storms with a return period smaller than 2 years, and a cost-effective filter media depth is recommended in bioretention design. Better hydrologic effectiveness is achieved with a higher hydraulic conductivity and ratio of the bioretention surface area to the catchment area, and filter media whose conductivity is between the conductivity of loamy sand and sandy loam, and a surface area of 10% of the catchment area is recommended. In the long-term simulation, both infiltration volume and evapotranspiration are critical for the total rainfall treatment in bioretention systems.

URBFEP Model for Basin Scale Simulation of Urban Floods Constrained by Sewerage's Size Limitations

Rain drainage in urban catchments is highly complex and depends on numerous and widespread restrictions to water flows caused by the layout of urban areas and building morphology, as well as by the size of sewers which are usually designed for low return period values (2÷10 years). The higher the rainfall return period, the higher the influence of such limitations and the correspondent hydrographs show reductions in peak values due to the reservoir effect generated by flood waters. The modelling of such processes is based on mathematical algorithms of transients associated with rainfall-runoff phenomena and with 1D/2D flow routing processes that, during more intense rainfall, occur simultaneously in the sewer and on the surface (dual drainage systems). However, when flood risk planning relates to the catchment scale for a vast territory with many urban areas, the model no longer focuses on a detailed simulation of what happens inside each urban area, but rather on an estimate of the main characteristics of the urban floods and of the hydrographs discharged into the receivers. In this case, it is necessary to use simpler models, but which are still able to provide a reliable representation of such phenomena. For such purpose, the conceptual model URBFEP (URBan Flood Equivalent Pipe) has been developed in order to obtain a reliable representation of these restricted urban flood processes. This model is presented here, demonstrating its ability to represent the real behaviour of urban sub-catchments in comparison to the results obtained in physically based simulations in a set of real urban areas selected as pilot cases.

Analysis of Emission Reduction Measures of City Stormwater Runoff and Facility Size

This paper analyzes the urban runoff reduction measures facilities scale. Analyze and conclude the relationship data between existing-pipeline-controlled rainfall return period and runoff coefficient, by using source control. Calculate and conclude the design scale of ecological measures and storage pools, draw the corresponding generalized model, by using peak flow reduction, volume reduction and flow reduction measures.

Herbicides runoff in vegetative filter strips: evaluation and validation of a recent rainfall return period model

Vegetative filter strips reduce herbicide runoff from cultivated fields owing to the ability of vegetation to delay surface runoff, promote infiltration, and adsorb herbicides. Previous research has shown that the annual runoff of each herbicide is typically less than 1 g ha−1. A model for the detection of the return period of rainfall events was recently proposed for a site in the north-eastern Po Valley, Italy. The return period model suggested that most of the herbicide loss by runoff (about 98%) is caused by a few, or even just one, extreme rainfall event with a return period of about 25–27 years, whereas ordinary events (4–5 each year) account for the rest. The present study aims to validate that model by comparing model predictions with the experimental results obtained in the 2010–2011 sampling season (independent test data), and to evaluate the effectiveness of the VFS. In addition, a 7-yr dataset of metolachlor and terbuthylazine concentration in real runoff events is summarised in order to highlight the medium-term magnitude of the pollution. Results show that on the Po Valley plain, 3–4 runoff events of low intensity are expected in spring–summer and that the consequent annual runoff of the herbicides metolachlor and terbuthylazine is about 0.5–0.7 g ha−1 yr−1. A summary shows that, owing to their chemical-physical properties, concentrations of the two herbicides are similar, both varying from about 0.01–300 μg l−1, with a potential pulse-like exposure risk for aquatic communities in waterways. This study showed that vegetative filter strips can reduce herbicide transfer to surface water by 90–98%, and should be suggested for environmental schemes at field and catchment scale.

설계 강우량의 재현빈도 변화에 따른 도시유역의 침수특성 분석

Abstract This study aims to investigate inundation characteristics such as inundated area, inundation depth according to variation in return period of design rainfall and to draw a comparison between the inundation characteristics by adapting design storm using dual-drainage model. Lidar data is used to construct terrain data with 1m × 1m resolution in Cheongju. The designed storm by return periods(10year, 30year, 50year and 200year) are acquired from Intensity Duration Frequency curve, which are distributed in 5 minutes interval using Huff’s method. As a results, the inundation volume is linearly increased, but inundated area is gradually increased in accordance with swell of return period for design storm. On the other hands, as a result of calculating discharge capacity for each points, deficit of discharge capacity is not observed using designed storm of 10 year return period at every points. If the return period is increased up more than 10 years, both the deficit of discharge capacity for each PT and entire study area are enlarged drastically.

Generation of intensity duration frequency curves and intensity temporal variability pattern of intense rainfall for Lages/SC

The objective of this work was to analyze the frequency distribution and intensity temporal variability of intense rainfall for Lages/SC from diary pluviograph data. Data on annual series of maximum rainfalls from rain gauges of the CAV-UDESC Weather Station in Lages/SC were used from 2000 to 2009. Gumbel statistic distribution was applied in order to obtain the rainfall height and intensity in the following return periods: 2, 5, 10, 15 and 20 years. Results showed intensity-duration-frequency curves (I-D-F) for those return periods, as well as I-D-F equations: i=2050.Tr0,20.(t+30)-0,89, where i was the intensity, Tr was the rainfall return periods and t was the rainfall duration. For the intensity of temporal variability pattern along of the rainfall duration time, the convective, or advanced pattern was the predominant, with larger precipitate rainfalls in the first half of the duration. The same pattern presented larger occurrences in the spring and summer stations.

Impact of Damaging Geo-Hydrological Events and Population Development in Calabria, Southern Italy

Damaging geo-Hydrogeological Events (DHEs) are defined as the occurrence of destructive phenomena (such as landslides and floods) that can cause damage to people and goods during periods of bad weather. These phenomena should be analyzed together as they actually occur because their interactions can both amplify the damage and obstruct emergency management. The occurrence of DHEs depends on the interactions between climatic and geomorphological features: except for long-term climatic changes, these interactions can be considered constant, and for this reason, some areas are systematically affected. However, damage scenarios can change; events that occurred in the past could presently cause different effects depending on the modifications that occurred in the geographical distribution of vulnerable elements. We analyzed a catastrophic DHE that in 1951 affected an area 3700 km2 wide, located in Calabria (southern Italy), with four-day cumulative rainfall exceeding 300 mm and return periods of daily rain exceeding 500 Y. It resulted in 101 victims and 4500 homeless individuals. The probability that a similar event will happen again in the future is assessed using the return period of the triggering rainfall, whereas the different anthropogenic factors are taken into account by means of the population densities at the time of the event and currently. The result is a classification of regional municipalities according to the probability that events such as the one analyzed will occur again in the future and the possible effects of this event on the current situation.

Estudo das precipitações para diferentes períodos de retorno no municipio de São João do Jaguaribe/CE

The knowledge of the probable maximum rainfall is of great importance in the development of hydraulic engineering projects and agricultural. The objective of this workwas to determine the city of São João do Jaguaribe-CE the maximum precipitation for return periods of 2 , 5 , 10 , 20 , 50 and 100 years through the Gumbel distribution . To estimate the parameters of Gumbel used the method of moments, which is a technique of resolutions of complex integral equations by reducing these to a simple system of linear equations . The results obtained for the maximum rainfall return periods of 2, 5 , 10 , 20 , 50 and 100 years were 41,71 ; 112,17 ; 158,82 ; 203,57 ; 261,50 and 304,91mm . The Gumbel method was suitable in the estimation of maximum rainfall , which represents an alternative in determining the maximum rains project . The results are meaningful and useful work for soil conservation, proper sizing of roads, spillways of dams, urban drainage and choice of crops to be planted.

Accelerative Genetic Algorithm-Based Parameter Optimization in Storm Intensity Formula

The genetic algorithm is an effective method to optimize model parameters, and to improve it, will accelerate the genetic algorithm is applied to the optimization of the return period storm intensity and rainfall parameters in the relationship with the traditional regression method and preferred-dregression optimization results are analyzed and compared. An example shows that: accelerative genetic algorithm for parameter estimation in storm intensity formula accuracy than traditional regression method and preferred regression parameters meter accuracy.

Integrated Flood Management for Beiyun River, China

Abstract Beiyun River Basin is holistically suffering a water shortage and relatively concentrated flood risk. The current operation (level-control) of dams and floodgates, which is in passive defense mode, cannot meet the demands of both flood control and storm water resources. An integrated flood forecasting and management system is developed by the connecting of the hydrological model and hydrodynamic model and coupling of the hydrodynamic model and hydraulic model for dams and floodgates. Based upon the forecasted runoff processes, a discharge-control operation mode of dams and floodgates is proposed to be utilized in order to well regulate the flood routing in channels. The simulated water level, discharge, and water storage volume under different design conditions of rainfall return periods and floodgates operation modes are compared. The results show that: (1) for small floods, current operation modes can satisfy the objectives, but discharge-control operation can do better; (2) for medium size floods, since pre-storing of the floods affects the discharge of follow-up floods by floodgates, the requirement of flood control cannot be satisfied under current operations, but the discharge-control operation can; (3) for large floods, neither operation can meet the requirement because of the limited storage of these dams. Then, the gravel pits, wetlands, ecological lakes and flood detention basins around the river must be used for excess flood waters. Using the flood forecasting and management system can change passive defense to active defense mode, solving the water resources problem of Beijing city and Beiyun River Basin to a certain extent.

Quantifying uncertainties associated with depth duration frequency curves

Uncertainty in depth–duration–frequency (DDF) curves is usually disregarded in the view of difficulties associated in assigning a value to it. In central Iran, precipitation duration is often long and characterized with low intensity leading to a considerable uncertainty in the parameters of the probabilistic distributions describing rainfall depth. In this paper, the daily rainfall depths from 4 stations in the Zayanderood basin, Iran, were analysed, and a generalized extreme value distribution was fitted to the maximum yearly rainfall for durations of 1, 2, 3, 4 and 5 days. DDF curves were described as a function of rainfall duration (D) and return period (T). Uncertainties of the rainfall depth in the DDF curves were estimated with the bootstrap sampling method and were described by a normal probability density function. Standard deviations were modeled as a function of rainfall duration and rainfall depth using 104 bootstrap samples for all the durations and return periods considered for each rainfall station.

The 2011 Thailand flood: climate causes and return periods

Thailand is one of the wealthiest and most developed countries in southeast Asia. However, its tropical location and the influence of seasonal monsoon rains and local topography make it prone to floods. The floods in 2011 were especially severe, causing estimated losses of US $30 billion (economic; Swiss Re, 2012) and US $12 billion (insured; Swiss Re, 2012). The insured loss ranks easily as the highest-ever worldwide from a freshwater flood disaster (Swiss Re, 2012). The primary reason for the floods was record rainfall: over Thailand as a whole, annual rainfall in 2011 was the highest in the country’s 61-year precipitation record (Thai Meteoro logical Department, 2011). In this article we first review the nature, impacts and historical ranking of the 2011 Thailand floods. We then examine the 2011 rainfall totals and anomalies across Thailand and use these with other data to discuss the climate causes for the exceptional rainfall. We then estimate the rainfall return period for this flooding event and compare this with satellite-derived return periods for the 2011 river flow. Finally, we bring together the different estimated return periods to provide a firmer assessment of how likely it is that a flood of the magnitude of 2011 will happen again.

Utilizing GIS and Infoworks RS in Modelling the Flooding Events for a Tropical River Basin

The large-scale atmospheric circulations and anomalies have been shown to have asignificant impact on seasonal weather over many parts of the world including Malaysia. Malaysia is located in the South East Asia with Southwest and Northeast Monsoons, experiences numerous flooding from year 1926 to 2012.Flood has become a regular disaster in Malaysia which happens every year in different states especially during the northeast monsoon. In December 2006 and January 2007, the Northeast Monsoon brought heavy rain through series of continuous extreme storms that caused devastating floods in the southern region of Peninsular Malaysia particularly to Kota Tinggi, Johor. The storms had occurred in two separate phases in late December 2006 and early January 2007 with atotal precipitation in four days exceeding twice of the monthly rainfall in which some places recorded a higher number. Johor River originates from Mt. Gemuruh and flows through the southeastern part of Johor and finally into the Straits of Johor. The 2006 average rainfall return period is 50-years while the 2007 gives more than 100-years return period. The objective of this study is to perform a flood simulation of the river basin using InfoWorks RS. The rainfall and stream flow data have been used as the hydrological input for the model. There are over 140 nodes representing the cross section throughout the length of the river. From the study, the main finding from the flood mapping process is that the simulated flood depth and flood risk map. Comparison between the simulated flood depth and observed flood depth has been done and shown a reasonable agreement.

台風に伴う将来の降水量極値の推定-高知市鏡川の治水計画への利用-

Heavy precipitation induced by a typhoon often causes a severe disaster. In this study, we aim to propose a statistical method to project extreme precipitation caused by typhoons in the future. Our method is a combination of a stochastic typhoon model, statistical precipitation analysis, climate model outputs, and a physical basis for changes in precipitation. Our method was applied to the Kagami river basin of Kochi. While the number of typhoon approaching Kochi is projected to slightly decrease or unchanged, 2-day extreme precipitation induced by typhoon is projected to increase in the last twenty first century (2081-2100). The projected values are widely different according to a method to estimate changes in precipitation. We also estimated the future return period of heavy rainfall causing the largest recorded flood of the Kagami River.

Probabilistic Modelling of Hourly Rainfall Data for Development of Intensity-Duration-Frequency Relationships

The rainfall Intensity-Duration-Frequency (IDF) relationship is commonly required for planning and designing of various water resources projects. The IDF relationship is a mathematical relationship between the rainfall intensity, duration and return period. This relationship is determined through statistical analysis of recorded rainfall data. In this paper, annual n-hourly maximum rainfall for different duration of 'n' such as 1-hour (hr), 2-hr, 3-hr, 6-hr, 12-hr, 18-hr, 24-hr, 48-hr and 72-hr are extracted from hourly rainfall data recorded at Hissar and Kalingapatnam; and further used for estimation of rainfall for different return periods. Order statistics approach is applied for determination of parameters of Gumbel distribution. Regional IDF relationships to estimate rainfall intensity for different return periods for Hissar and Kalingapatnam regions are developed and presented in the paper.

Rainfall spatial organization and areal reduction factors in the metropolitan area of Barcelona (Spain)

The rainfall spatial organization in the metropolitan area of Barcelona (Spain) has been studied from records of an urban rain gauge network in the period 1994–2009. Using statistical and regional analysis techniques, correlation between data recorded by the different rain gauges has been calculated, and the effective number of independent stations (n eq) equivalent to the used network has been determined. It has been found out that for durations longer than 20 min, the areal rainfall return period observed for a storm registered by the network approximately decreases by a factor of 1/n eq in relation to the current point rainfall intensity–duration–frequency relationships for the metropolitan area of Barcelona. Using objective analysis techniques, continuous precipitation fields have been generated on a regular grid with a spatial resolution of 300 × 300 m for the storms registered by the rain gauges from 1994 to 2009, for durations from 10 min to 24 h. The precipitation fields obtained have been useful to estimate the characteristic areal reduction factors in the metropolitan area of Barcelona. A direct relationship has been found between the areal reduction factor for all the area corresponding to the urban rainfall network of Barcelona and the effective number of n eq for every duration considered.