Flood Types Research Articles

Comparison of fluvial and pluvial flood risk curves in urban cities derived from a large ensemble climate simulation dataset: A case study in Nagoya, Japan

Flood disasters are caused by two types of flooding: pluvial and fluvial flooding. The different hydrodynamic characteristics of these two types have been intensively discussed in a literature. However, their impact and the resulting damage have not yet been examined in a comprehensive manner due to the lack of extreme rainfall data and/or computational costs of flood simulations. Recently, an increasing number of ensemble climate simulation data has become available, providing long-term rainfall data based on numerical climate simulations. This is a case study of a flooding in an urban area set in Nagoya City, Japan. We applied a large ensemble climate simulation database, d4PDF, to a pluvial and fluvial flood model and derived the flood risk curves for each type of flooding. The results indicated that pluvial flooding presents comparable economic risk to fluvial flooding (only 16% and 17% lesser damage at 50- and 100-year return periods, respectively) despite its significantly shallower flood depths (area with flood depth over 45 cm was only 10.5% and 5.4%, respectively). The significant impact of pluvial flooding is attributable to its wider flood area (despite shallower depths), impacting major economic assets sprawled over the city, including areas further away from the river. Furthermore, fluvial flood risk was managed by settling the Nagoya Castle (now the central economic district) on higher altitudes. The results suggest that pluvial flooding could have comparable economic risks to fluvial flooding in urban areas where major economic assets are not concentrated around streams as well as historical countermeasures are installed against fluvial flooding.

A local-scale analysis to understand differences in socioeconomic factors affecting economic loss due to floods among different communities

Investigation of the relationships between socioeconomic factors and water-related disasters, such as floods, is rather complex. The general practice is to undertake a qualitative analysis of the impact of socioeconomic factors on economic loss in disasters, while climate and structural impacts are investigated quantitatively. As such, an integrated approach is timely for understanding socioeconomic influences on economic loss due to floods. This paper is an attempt to understand the influence of different factors on economic loss, in different types of floods, among different economic groups, using a quantitative approach. Data was collected using a questionnaire survey delivered to randomly selected households in Rathnapura, Sri Lanka, in September 2017. Path analysis was used to analyze the influence of socioeconomic status on economic loss due to floods, using an effective sample of 231 households after subdividing the sample into poor and non-poor subcategories, based on socioeconomic condition. The results suggest that flood characteristics and household income level have a direct impact on economic loss in severe floods for both economic groups, with more significant impacts among poor households. Even for minor floods, inundation depth is the most significant factor affecting relative loss, irrespective of the economic group. Further, the absolute loss difference between poor and non-poor households is 48% of the loss experienced by non-poor households in severe floods, and 10% of the loss due to minor floods. These results indicate that severe floods increase the economic gap between the poor and non-poor cohorts. Through this analysis, it is concluded that floods exacerbate the economic gap between poor and non-poor communities, while the factors affecting economic loss due to floods differ among the different economic groups.

Quantifying Extreme Precipitation Forecasting Skill in High-Resolution Models Using Spatial Patterns: A Case Study of the 2016 and 2018 Ellicott City Floods

Recent historic floods in Ellicott City, MD, on 30 July 2016 and 27 May 2018 provide stark examples of the types of floods that are expected to become more frequent due to urbanization and climate change. Given the profound impacts associated with flood disasters, it is crucial to evaluate the capability of state-of-the-art weather models in predicting these hydrometeorological events. This study utilizes an object-based approach to evaluate short range (<12 h) hourly forecast precipitation from the High-Resolution Rapid Refresh (HRRR) versus observations from the National Centers for Environmental Prediction (NCEP) Stage IV precipitation analysis. For both datasets, a binary precipitation field is delineated using thresholds that span trace to extreme precipitation rates. Next, spatial metrics of area, perimeter, solidity, elongation, and fragmentation, as well as centroid positions for the forecast and observed fields are calculated. A Mann–Whitney U-test reveals biases (using a confidence level of 90%) related to the spatial attributes and locations of model forecast precipitation. Results indicate that traditional pixel-based precipitation verification metrics are limited in their ability to quantify and characterize model skill. In contrast, an object-based methodology offers encouraging results in that the HRRR can skillfully predict the extreme precipitation rates that are anticipated with anthropogenic climate change. Yet, there is still room for improvement, since model forecasts of extreme convective rainfall tend to be slightly too numerous and fragmented compared with observations. Lastly, results are sensitive to the HRRR model’s representation of synoptic-scale and mesoscale processes. Therefore, detailed surface analyses and an “ingredients-based” approach should remain central to the process of forecasting excessive rainfall.

Naïve Bayes Anomaly Detection System Design On Openflow Network

One of the generally launched attacks is Distributed Denial of Service that renders its target unable to provide its service. Gaussian Naïve Bayes Classifier is one out of several techniques used in detecting those attacks by classifying network traffic in a window as an attack or a normal traffic based on normal distribution previously calculated from normal and attack traffic datasets. This research focuses on mitigating SYN Flood Type DDoS attacks on OpenFlow Network using Zodiac FX as a switch. The developed system utilizes OpenFlow Protocol to apply flow rule in switch’s flow table in order to detect and mitigate SYN Flood attacks in real-time. Applied mitigation procedure is to divert incoming packets into SYN Proxy so that only legitimate TCP packets are able to reach the server. The results show that the system has a bandwidth of up to 60Mbps under normal condition and 5,03Mbps under attack. Maximum malicious packets that could reach server before it is diverted to SYN Proxy is estimated to be 400 packets and not affected by the number of attacks, assuming that the flow rule sent by the controller are enacted immediately.

SEL AFETLERİ HAKKINDA GENEL BİR DERLEME

The main aim of this study is to prepare a review by conducting a general literature review on flood disasters and its devastating consequences. In this study, which was prepared by examining a large number of publications, necessary definitions were made by considering disaster, flood and flood types, risk concept and flood risk, and studies on these subjects were compiled and gathered. In this context, literature information has been scanned in terms of social, economic and other effects caused by the flood disaster, which is one of the natural disasters that are common in the world and cause loss of life and property. Finally, it is aimed to be a preliminary study for scientific studies on this subject.

The Influence of Tidal on Fe Distribution at Tidal Swamp Rice-Farming in Barito River Area, South Kalimantan, Indonesia

Iron (Fe) poisoning can cause problems on growth, the formation of saplings, and the filling of grains. These problems lead to and plant death or decrease in productivity. The inhibition of growth and production is increasingly higher in susceptible varieties. The distribution of iron concentration varies in different regions and locations of swamp rice farming. Various adverse effects of iron poisoning on rice have been widely reported, but the spatial distribution of iron in tidal fields is still rare. Iron distribution in various soil profile depths has not been widely investigated and data availability to avoid Fe poisoning in tidal swamps has not been widely reported. Spatial distribution of Fe concentrations is needed as a reference for rice cultivation in tidal swamps. This study has been conducted in November 2015 until August 2017 using the survey method in the Barito River area, South Kalimantan, Indonesia. The use of thematic maps such as tidal height difference (Δ), tidal flood type, and thickness of mud map. The results showed that the spatial concentration of Fe is highest in the zone I which has the highest difference (Δ) of high tide maximum and low tide maximum. While on the soil profile, the highest of Fe concentration is in layer 1 and the lowest concentration is in layer 3. Based on the overflow type, the highest Fe concentration is typed A and type B especially close to the estuary. To prevent iron poisoning, rice seedlings should reach layer 2 (> 10 cm) and choose the safe zone that is zone II, III, or IV to produce optimal rice production.

Reliability check of flash-flood in Central Bohemia on May 25, 1872

Abstract The flash flood occurring on May 25, 1872 ranks among the most extreme events recorded within the Czech Republic. The causative torrential rain affected mostly the area between Karlovy Vary, Plzeň and Prague of approximately 2000 km2. A corresponding intensity of precipitation observed incidentally at two sites exceeded 200 mm in 3–8 h. The consequent flood caused tremendous damages to ponds, houses, and infrastructure and resulted in a temporary collapse of transport especially due to a total break of trains operation. The flood led to approximately 240–300 fatalities according to various sources. An extent of the total area affected reached approximately 2000–3000 km2 representing an unusually large scale for such a type of flood. The intensive rain and inflow caused the biggest rupture of a water reservoir in Mladotice so far. The respective Mladotický pond held very likely 3–4 million cubic meters of water before its rupture. With a delay of 2 to 3 days, a substantial saturation triggered a massive landslide blocking the Mladotický water stream and creating a new water body named the Odlezelske Lake. The flood event motivated elaboration of at least 3 scholarly papers already between 1872 and 1875. Accordingly, this flood presents for Czech hydrologists an outstanding example of such an extreme magnitude until now. The flood in 1872 and drought in 1874 led directly to establishing the Hydrological service of the Czech Kingdoms in 1875. Hitherto, we have no comparison for such extreme flood including recent floods occurring in 2002, 2010 and 2013. The flood peaks exceeded other historical or recent floods by at least 1–2 m. There is only one similar flood event, the flood of July 31, 1714 at the Sazava River catchment. As there were no regular hydrological observations including precipitation measurements available for the affected areas before 1883, the prevailing data source comprise documentary sources and their relevant interpretations. The aim of our study is to explain in a more detail the course of this flood and a number of indeterminate circumstances during the flood. An important question was an effect of the collapse of approximately 100 ponds and a role of the collapsed sizeable Mladotický pond. These phenomena were partly explained by newspapers and chronicles describing an incredibly rapid increase of water level (2–3 m in a few minutes) at a relatively large number of sites. We have completed a hydraulic estimation of peak discharges at major profiles. In our research we used the Aqualog hydrological modelling system. The hydrological modelling enabled us to complete and check the reliability of observed causative precipitation for the affected area and peak flow rates at the Beroun and Prague municipalities. An important point was the reconstruction of a flow hydrograph at Prague with very intricate shape and two likely local peaks. Second local maximum could be attributed to the collapse of the Mladotický pond. This flood is of crucial importance for the Prague flood protection system. The main reason being a short time span of 22 h between the beginning of causative rainfall and occurrence of maximum flood flow rate at Prague.

Detecting Saturation Attacks Based on Self-Similarity of OpenFlow Traffic

As a new networking paradigm, Software-Defined Networking (SDN) separates data and control planes to facilitate programmable functions and improve the efficiency of packet delivery. Recent studies have shown that there exist various security threats in SDN. For example, a saturation attack may disturb the normal delivery of packets and even make the SDN system out of service by flooding the data plane, the control plane, or both. The existing research has focused on saturation attacks caused by SYN flooding. This paper presents an anomaly detection method, called SA-Detector, for dealing with a family of saturation attacks through IP spoofing, ICMP flooding, UDP flooding, and other types of TCP flooding, in addition to SYN flooding. SA-Detector builds upon the study of self-similarity characteristics of OpenFlow traffic between the control and data planes. Our work has shown that the normal and abnormal traffic flows through the OpenFlow communication channel have different statistical properties. Specifically, normal OpenFlow traffic has a low self-similarity degree whereas the occurrences of saturation attacks typically imply a higher degree of self-similarity. Therefore, SA-Detector exploits statistical results and self-similarity degrees of OpenFlow traffic, measured by Hurst exponents, for anomaly detection. We have evaluated our approach in both physical and simulation SDN environments with various time intervals, network topologies and applications, Internet protocols, and traffic generation tools. For the physical SDN environment, the average accuracy of detection is 97.68% and the average precision is 94.67%. For the simulation environment, the average accuracy is 96.54% and the average precision is 92.06%. In addition, we have compared SA-Detector with the existing saturation attack detection methods in terms of the aforementioned performance metrics and controller’s CPU utilization. The experiment results indicate that SA-Detector is effective for the detection of saturation attacks in SDN.

Barium Sulfate Scaling and Control during Polymer, Surfactant, and Surfactant/Polymer Flooding

SummaryBarium sulfate (BaSO4) scale is a serious problem that is encountered during oilfield production and has been studied mainly for fields undergoing waterflooding. Chemical enhanced oil recovery (cEOR) processes involve interactions between the injected brine and the formation brine, rock and oil. Very little work has appeared in the literature on how cEOR processes can influence the severity of the mineral scaling problem that occurs in the field and how this can be managed. This study investigates barium and sulfate coproduction behavior, the deposition of BaSO4 in the formation and in the producer wellbore, and its inhibition during polymer, surfactant, and surfactant/polymer (SP) flooding cEOR processes. To aid the cEOR economic decision, assessment of the impact of cEOR flooding type on both scale management and oil recovery is performed.Reservoir simulation has been used in this study, employing homogenous and heterogeneous two-dimensional (2D) areal and vertical models. Data from the literature are used to define the parameters controlling the physical and chemical functionality of anionic surfactant and partially hydrolyzed polyacrylamide (HPAM) polymer [e.g., oil/water interfacial tension (IFT), IFT, polymer viscosity, and SP adsorption]. Assessment is made of the minimum inhibitor concentration (MIC) required to control the scale that is predicted to occur due to the changes in brine composition induced by the water and chemical flooding processes. The expected retention and release of a phosphonate scale inhibitor (SI) during squeeze treatments in the production wells is modeled.The high viscosity and more stable HPAM polymer slug reduces the mixing between the injected and the formation brines, especially with low-salinity low-sulfate (SO42−) make-up brine, reducing BaSO4 scale precipitation in the formation, delaying and reducing the potential scale risk in the producer wellbore compared to normal waterflooding. During surfactant flooding, from an oil recovery perspective, the optimal phase type and salinity can be any of the three microemulsion (ME) phase types, depending on the system multiphase parameters. However, the scaling risk can be different to that in the waterflooding case, depending on the IFT, ME phase type, the injected salinity, and sulfate concentration. In SP flooding, low-salinity make-up brine is preferred to enhance oil recovery, and it also delays and reduces scale risk. The impact of the injection brine salinity, SO42− concentration, and changing brine composition due to ion reactions affects the produced water rates, the number of required squeeze treatments and MIC values over time. This, then, impacts the inhibitor retention and release, which influences the treatment volumes and cost required to control scale over field life. Considering the economic impact of cEOR flood type on both oil recovery and scale management, low-salinity SP flooding is demonstrated to be the most viable option, showing the highest positive net present value (NPV).The study shows that barium and sulfate coproduction and the evolving scale risk depend on the mobility ratio (which is determined by the injected brine and oil viscosities) on the oil/water IFT, on the level of chemical adsorption, and on the selected brine salinity. The severity of the scale risk is also impacted by the flood techniques used, with the extent of reservoir reactions having an effect on the MIC required to control scale and the squeeze treatment volumes required to maintain production after breakthrough.

Sediment and nutrient deposition in different riparian forests and floods of the Middle Paraná River

AbstractSedimentation processes are important to the dynamics of lowland fluvial systems and depend on the characteristics of floods and of riparian ecosystems. The few known studies for the Paraná River system analysed only summer floods without considering the context in which the sedimentation occurred. This study focuses on sedimentation in three riparian forests during one summer and two winter floods of the Paraná River, quantifying the amount of deposited sediments, determining their texture, and measuring the associated quantities of Total Phosphorous (TP) and Total Nitrogen (TN). This study takes into account the elevations, floristic attributes, and geomorphologic context of the three forests, as well as water and sediment transport during floods. Differences in the floods' water discharge, wash load, and duration determined differences in the total amounts of drained water and mobilized sediments. The amount of sediments ranged from 0 to 510 kg m‐2 in the different floods and riparian forests studied. The texture was statistically different between the two winter floods, and between some riparian forests. The analysis of nutrients showed that 1 to 4919 kg ha‐1 of TP and 4.2 to 1152 kg ha‐1 of TN were deposited during the three floods in all forest types. Our results show that the amounts from winter floods can be as important as those from summer floods. These results provide insight not only into the importance of winter floods in the deposition processes, but also into the role of both types of floods as natural instruments of fertilization for floodplain–river ecosystems.

What is a bad flood? Local perspectives of extreme floods in the Peruvian Amazon.

The annual flood cycle is integral to rural life and livelihoods in riparian Amazonia. Livelihoods are built around the flood cycle, which facilitates transportation and affects soil fertility and fish migrations. Flood extremes, however, can have devastating impacts for riverine populations, yet there is minimal understanding of what distinguishes a 'normal' flood from a 'bad' flood, or flooding as integral to riverine settlement from flooding as environmental hazard. We address this limitation by drawing upon hydrograph data and field data collected in a riverine village in the Peruvian Amazon. We define four extreme flood types based on height, duration, and timing of onset, and illustrate how they each create a unique combination of negative and positive implications. We discuss the integral role of fishing to floodplain livelihoods during the flood season, and the implications of flood extremes for health, safety, and food provision. The article proposes a more nuanced conceptualization of flooding in riverine Amazonia to better inform policies and practices aimed at supporting local populations during extreme floods.

Assessment of Runoff and Drainage Conditions in a North Banat Sub-Catchment, North-Eastern Serbia

Abstract The lowland area of the southeastern part of the Carpathian Basin is exposed to extreme hydrological conditions. The monitoring and analysis of the excess inland water are necessary in order to understand the scope and direction of the development of this type of flooding. When solving the problem of the drainage of an area and dimensioning drainage systems, one of the most important steps is to calculate the rate of runoff. Before calculating the rate of runoff, it is necessary to perform various analysis such as: hydrological, hydrogeological, pedological and land use analysis. The use of empirical formulas by different authors is one of the methods for determining the rate of runoff. These formulas can be of regional character, while some are applicable in different parts of the world. In this paper, the runoff coefficient and rate of runoff were calculated as indicators of the efficiency of the area drainage, employing the formulas by Nemet and Turazzo. The emphasis was put on the usage of modern tools and databases of soil characteristics while using a “traditional” method to determine rate of runoff. The obtained results demonstrate that the rate of runoff which reflects the current state of the drainage basin is very similar to the rate of runoff used for dimensioning of drainage system. The problem of retaining smaller amounts of water that remains even after the anticipated drainage deadlines can be solved with the regular maintenance of amelioration canals and additional ameliorative measures.

Structural Durability Assessment of Stilt Houses to Flash Flooding: Case Study of Flash Flood-Affected Sites in Thailand

The ‘stilt house’ is found in many flood-prone areas and represents local wisdom regarding building construction to coexist with floodwaters. Most academic research projects have studied stilt houses based on two types of flood: inundation and coastal flooding. The study of pillar houses in flash floods is very limited. This research investigated whether the main structure of a stilt house could withstand strong water current to determine the suitability of the stilt house for flash flood sites. The study explored the physical appearance of stilt houses in five flash flood areas in Thailand. The styles of stilt houses in each area were simplified to generate models and to then test their tolerance toward moving water. The main findings were: 1) the main structure of the stilt house can resist flood loads at 1.00 m depth with a waterflow speed at 3.05 m/s; 2) the most vulnerable points on the main structure if struck by more rapid, deeper flows of water are the base of the column and the joint between the column and beams; and 3) the horizontal or diagonal bracing members perpendicular to the flow and not above the flood level become water blockades that increase the reactive force to the main structure.

Numerical analysis of viscous fingering and oil recovery by surfactant and polymer flooding in five-spot setup for water and oil-wet reservoirs

Surfactant and polymer are used to improve oil recovery. The micro-emulsion phase composition, viscosity and interfacial tension vary with salinity and injection concentration of chemicals. The viscosity contrast which is very large for heavy oil reservoirs, results in various types of viscous instabilities. There is no comprehensive field-scale modelling on the viscous fingering affecting the oil recovery for different types of surfactant-polymer (SP) flooding. We numerically simulated the above phenomena for different types of SP flooding in five-spot wells setup for both water-wet and oil-wet reservoirs. We have observed that many saturation shocks and banks of micro-emulsion, water and polymer are formed. The viscous fingering at the interface of these banks depend on the reservoir wettability, micro-emulsion phase behaviour and injection concentration of chemicals. Fingering can be suppressed by changing the duration of injection and concentration of surfactant and polymer. We have shown that Type II(+) flooding produces more oil than Type II(−) and Type III. But the oil production by Type II(−) can be increased by adopting better injection strategies. We have made a quantitative comparison of output, i.e., oil recovery vs inputs such as injected mass of chemicals, injection duration and pumping energy, which is of interest to industry. The pumping energy requirement is higher for Type II(−) flooding irrespective of wettability. Our results show that short duration injection of surfactant with multistep reduction of polymer concentration suppresses viscous instabilities and produce more than 90% OOIP.

Timescale-based flood typing to estimate temporal changes in flood frequencies

ABSTRACTThe flood peak is the dominating characteristic in nearly all flood-statistical analyses. Contrary to the general assumptions of design flood estimation, the peak is not closely related to other flood characteristics. Differentiation of floods into types provides a more realistic view. Often different parts of the probability distribution function of annual flood peaks are dominated by different flood types, which raises the question how shifts in flood regimes would modify the statistics of annual maxima. To answer this, a distinction into five flood types is proposed; then, temporal changes in flood-type frequencies are investigated. We show that the frequency of floods caused by heavy rain has increased significantly in recent years. A statistical model is developed that simulates peaks for each event type by type-specific peak–volume relationships. In a simulation study, we show how changes in frequency of flood event type lead to changes in the quantiles of annual maximum series.

The role of floods and droughts on riverine ecosystems under a changing climate

AbstractFloods and droughts are key driving forces shaping aquatic ecosystems. Climate change may alter key attributes of these events and consequently health and distribution of aquatic species. Improved knowledge of biological responses to different types of floods and droughts in rivers should allow the better prediction of the ecological consequences of climate change‐induced flow alterations. This review highlights that in unmodified ecosystems, the intensity and direction of biological impacts of floods and droughts vary, but the overall consequence is an increase in biological diversity and ecosystem health. To predict the impact of climate change, metrics that allow the quantitative linking of physical disturbance attributes to the directions and intensities of biological impacts are needed. The link between habitat change and the character of biological response is provided by the frequency of occurrence of the river wave characteristic—that is the event's predictability. The severity of impacts of floods is largely related to the river wave amplitude (flood magnitude), while the impact of droughts is related to river wavelength (drought duration).

Aplikasi Jenis Pupuk organik terhadap Kadar Hara NPK dan Produksi Kedelai (Glycine max (L.) Merril) pada Jarak Tanam yang Berbeda di Lahan Pasang Surut

Marlina N, Aminah IS, Amir N, Rosmiah R. 2019. Application of organic fertilizer types to NPK nutrients levels and soybeans production (Glycine max (L.) Merril) at different planting spaces in tidal land. Jurnal Lahan Suboptimal: Journal of Suboptimal Lands. 8(2):148-158. Tidal lowlands flood type C is suboptimal land and very potential in cultivating soybean, but it has problems in soil fertility, macro and micro nutrient poor, therefore to increase soil fertility can be given various types of organic fertilizers, including cow manure organic fertilizer, chicken manure organic fertilizer and biofertilizer. All types of organic fertilizers are composted, and specifically biofertilizers are made with their own formula. It is expected that the organic fertilizer provided can increase soil fertility and nutrient availability for soybean plants. This study aimed to get the best type of organic fertilizer on the availability of nutrient levels of NPK and soybean production at different spacing in tidal land. This research was conducted in Jaya Agung Village, Lalan District, Musi Banyuasin Regency, South Sumatra Province, and was carried out in March 2018 - June 2018. The method used was the experimental method. The design used is a split-plot design. with 9 treatment combinations and repeated 3 times. As the main plot treatment is plant spacing (20 cm x 20 cm, 20 cm x 30 cm and 20 cm x 40 cm), and treatment of subplots are: types of cow manure organic fertilizers 10 ton/ha, chicken manure organic fertilizer 10 ton/ha, and biofertilizer 400 kg/ha. The results showed that the combination treatment of plant spacing of 20 cm x 30 cm with the type of biofertilizer 400 kg/ha could increase soybean production by 9.11 g/plot or equivalent to 2.43 ton/ha.

Major flood events recorded in the Holocene sedimentary sequence of the uplifted Ladiko and Makrisia basins near ancient Olympia (western Peloponnese, Greece)

Detailed palaeoenvironmental studies were conducted in the Ladiko and Makrisia basins near the Alpheios River and ancient Olympia (western Peloponnese, Greece) to assess major landscape changes during the Holocene. Previous studies and literature data document that the area experienced crust uplift of minimum 13 m to 30 m since the mid-Holocene. Geological archives were sampled along a vibracore transect connecting the Ladiko and Makrisia basins. Sediment cores were analyzed using sedimento-logical, geochemical and micropalaeontological methods. Geochronological reconstruction of major landscape changes is based on a set of 24 radiocarbon dates. Geophysical studies were carried out using electrical resistivity tomography (ERT) and Direct Push-Electrical Conductivity (DP-EC) measurements to detect stratigraphic changes and subsurface bedrock structures. The stratigraphic record of the uplifted lake basins of Ladiko and Makrisia revealed two major lithostratigraphic units. Unit I, predominantly composed of clay, silt and silty fine sand, reflects prevailing low-energy sedimentary conditions typical of quiescent (fluvio-)limnic waterbodies. Unit II is made out of fine to coarse sand and documents repeated interferences of unit I associated with abrupt and temporary high-energy flood type (= heft) events. We found signals of four different heft events (H1 to H4) showing strong stratigraphic and geochronological consistencies along the vibracore transect. The following age ranges were determined: H1 – between 4360 – 4330 cal BC and 4320 – 4080 cal BC; H2 – be- tween 2830 – 2500 cal BC and 2270 – 2140 cal BC; H3 – between 1220 –1280 cal AD and 1290 –1390 cal AD; H4 – between 1640 –1800 cal AD and 1650 –1800 cal AD. Different hypotheses concerning the characteristics, potential trigger mechanisms and causes of the flood events were tested against the background of strong Holocene crust uplift and using a variety of different methodological approaches: Geomorphological and granulometric aspects, micropalaeontological contexts, geochronological data sets, numerical simulation of flooding events, local tectonic uplift, and the palaeoclimate background were taken into account. We hypothesize that, during the mid-Holocene, the study area was affected by tsunami events, namely between 4360 – 4330 cal BC and 4320 – 4080 cal BC (H1) and between 2830 – 2500 cal BC and 2270 – 2140 cal BC (H2). These ages are very well consistent with the supra-regional and regional tsunami event signal retrieved from many coastal archives in large parts of western Greece. The timing of flood events H1 and H2 is highly consistent with ages of (supra-)regional tectonic events known from literature and is not consistent with increased flood indices of palaeoclimate data available for western Greece. Tsunami inundation scenarios based on numerical simulation are highly consistent with vibracoring and geophysical (ERT, DP-EC) data. In contrast, heft events H3 and H4 are possibly related to phases of increased precipi- tation and flooding activity in the Mediterranean or to land-based geomorphological processes triggered by regional tectonic events (RTE). Neolithic, Chalcolithic as well as Early and Middle Helladic human activities documented at ancient Olympia were most probably affected by tsunami heft events H1 and H2. Sandy deposits of tsunami event H2, covering the prehistorical tumulus, seem to have been used as a higher and dry base to construct the apsidal houses in the center of the later sanctuary at Olympia. The site, already abandoned, must have again been subject to major flood events during the 13/14th cent. AD and the 17–19th cent. AD associated with heft events H3 and H4.

The use of watershed geomorphic data in flash flood susceptibility zoning: a case study of the Karnaphuli and Sangu river basins of Bangladesh

The occurrence of heavy rainfall in the south-eastern hilly region of Bangladesh makes this area highly susceptible to recurrent flash flooding. As the region is the commercial capital of Bangladesh, these flash floods pose a significant threat to the national economy. Predicting this type of flooding is a complex task which requires a detailed understanding of the river basin characteristics. This study evaluated the susceptibility of the region to flash floods emanating from within the Karnaphuli and Sangu river basins. Twenty-two morphometric parameters were used. The occurrence and impact of flash floods within these basins are mainly associated with the volume of runoff, runoff velocity, and the surface infiltration capacity of the various watersheds. Analysis showed that major parts of the basin were susceptible to flash flooding events of a ‘moderate’-to-‘very high’ level of severity. The degree of susceptibility of ten of the watersheds was rated as ‘high’, and one was ‘very high’. The flash flood susceptibility map drawn from the analysis was used at the sub-district level to identify populated areas at risk. More than 80% of the total area of the 16 sub-districts were determined to have a ‘high’-to-‘very-high’-level flood susceptibility. The analysis noted that around 3.4 million people reside in flash flood-prone areas, therefore indicating the potential for loss of life and property. The study identified significant flash flood potential zones within a region of national importance, and exposure of the population to these events. Detailed analysis and display of flash flood susceptibility data at the sub-district level can enable the relevant organizations to improve watershed management practices and, as a consequence, alleviate future flood risk.

Computational Bottom-Up Vulnerability Indicator for Low-Income Flood-Prone Urban Areas

This study presents the implementation of a methodology for the formulation of a vulnerability indicator for low-income urban territories in flood-prone areas, for two flood types: Sudden and slow. The methodology developed a computational assessment tool based on the Multiple Correspondence Analysis and the framework for vulnerability analysis in sustainable science. This approach uses participatory mapping and on-site data. The data collection was easily implemented with free software tools to facilitate its use in low-income urban territories. The method combines the evaluation of experts using the of the traditional approach for the qualification of the variables of vulnerability in its three components (exposure, susceptibility, and resilience), and incorporates a computational method of the correspondence analysis family to formulate the indicators of vulnerability. The results showed that the multiple correspondence analysis is useful for the identification of the most representative variables in the vulnerability assessment, used for the construction of spatial disaggregated vulnerability indicators and therefore the development of vulnerability maps that will help in the short term in disaster risk management, urban planning, and infrastructure protection. In addition, the variables of the susceptibility component are the most representative regardless of the type of flooding, followed by the variables of the exposure component, for sudden flood-prone territories, and the resilience component for slow flood-prone territories. Our findings and the computational tool can facilitate the prioritization of improvement projects and flood risk management on a household, neighborhood, and municipal level.