Assessing flash flood hazard in an arid mountainous region

Although flash floods are one of the major natural disasters that may hamper human development in arid areas, aspects of the process leading to their initiation remain uncertain and poorly understood. In the present study, wadi El-Alam Basin, one of the major basins in the Eastern Desert of Egypt that is frequently subjected to severe flash flood damage, is selected for investigation. Here, a hydrological modeling approach was used to predict flash flood hazard within the basin. Earlier work conducted for the same basin showed that such approach is successful and was able to accurately highlight the locations of historical flood damage. However, such work was based on one set of arbitrary model parameters. The present study has taking into account the rainfall as the excitation factor in the adopted hydrological modeling. The study aims to build on the earlier study by investigating impacts of variation of rainfall depth, areal coverage, and location on flash flood generation. Results demonstrate that the basin under study requires a rainstorm intensity of at least 40 mm in order to initiate surface runoff with a noticeable flood peak at its main outlet. The location of rainstorm has a major effect on the shape of the basin final hydrograph. Furthermore, in the study basin, the upstream flood appears to be of a magnitude and a peak flow that is much higher than those for downstream ones, which believes to be strongly attributed to the surface steepness and impermeability of the former. The used approach shows to be useful in the rapid assessing of flash flood hazard in mountainous desert and could be adopted, with appropriate modifications, elsewhere in arid regions.     

Decision support system based on the history of flood and flash flood events in Romania

A lightweight decision support system is presented, oriented also to statistics, useful for assisting weather forecasters and other parties interested in hazard assessment associated with extreme weather. The system can be used in enhancing the warning procedures, ahead of a flood or a flash flood whose probability of occurrence is based on the history of such events in a particular region. A software application has been built that integrates meteorological data with Geographical Information Systems procedures, in a unified informational aggregate. This system stores various types of data related to flood and flash flood events, so it is able to provide the user with any piece of information related to a documented event. It also catalogues any information that users provide it with, to further document a past, or an ongoing event. The system can be used to raise awareness of forecasters over a particular context, before a possibly hazardous situation, and it can also offer automatic warnings and suggestions to those interested in disaster mitigation.     

Grey- and rough-set-based seasonal disaster predictions: an analysis of flood data in India

Natural Hazards - In a globally competitive market, companies attempt to foresee the occurrences of any catastrophe that may cause disruptions in their supply chains. Indian subcontinent is prone...     

基于高分辨率卫星数据铀矿找矿信息提取——以巴什布拉克地区为例

论述了利用遥感技术提取砂岩型铀矿找矿信息的研究意义及研究内容,并选择我国新疆巴什布拉克地区作为研究区．利用快鸟（Quickbird）卫星遥感数据,通过多种图像处理方法的应用研究,提取控矿构造、含矿层和矿化蚀变信息等与铀成矿密切相关的找矿信息,探索高空间分辨率卫星数据在地质矿产资源勘查领域的实用性,拓宽在类似区域进行地质矿产勘查的研究思路。     

Urban landscape extraction and analysis based on optical and microwave ALOS satellite data

Accurate mapping of urban land cover from satellite data provides essential input to urban landscape analysis, modelling and urban ecosystem studies. Additionally, analysis of urban landscape metrics will provide a positive step towards comprehensive understanding of the features of urban landscape structure and further planning. In the present study, multi-spectral Advanced Land Observing Satellite (ALOS)/Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2) images and ALOS/Phased Array type L-band Synthetic Aperture Radar (PALSAR) dual-polarized (FBD) microwave images were used to extract urban land cover information by applying the decision tree method, and additional Advanced Space borne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER/GDEM) was used to reduce the effects of mountains in Synthetic Aperture Radar (SAR) images due to high backscattering from urban construction land. A set of landscape metrics, such as landscape diversity, edge density and landscape shape indices with supplementary ecological meanings, were chosen to quantitatively analysis urban landscape patterns in arid environments. The overall accuracy assessment result was 91.50%, and the experimental results demonstrate that synergetic use of optical and SAR ALOS data has the potential and advantages for Arid Urban Region mapping, while the decision tree method showed intuitive simplicity and computational efficiency. The quantitative analysis results of landscape metrics showed that distribution of landscape types in Urumqi city were inhomogeneous, the urban landscape dominated by a few classes. Urbanization in this region has resulted in dramatic increases in patch density (PD), edge density (ED) and landscape shape complexity.     

Modeling the effect of uncertainties in rainfall characteristics on flash flood warning based on rainfall thresholds

Natural Hazards - This study proposes a risk assessment framework for quantifying the reliability of the rainfall threshold used in flash flood warning, which should be influenced by the...     

基于Sentinel-1卫星数据的北极西北航道通航适宜性分析

北极西北航道对北极资源开发与世界贸易格局有重要影响。针对当前西北航道通航适宜性时空变化分析研究中时空分辨率低、时效性差等问题,利用2015—2019年每年9月及2019年8月1日至9月20日的Sentinel-1 SAR数据,基于k均值非监督分类方法反演了十米级高空间分辨率海冰密集度。通过长时序宏观跟踪和短时序精细分析西北航道全线通航窗口,并以70%的海冰密集度作为阈值,测算了西北航道经过重要海湾及海峡累计不可通航的次数。结果表明：西北航道的航情随冰情而变,通航能力尚不稳定。具体来说,西北航道的冰情呈现东轻西重、南轻北重的格局,不可通航节点个数东少西多、南少北多。2018年9月西北航道通航情况最差,高于可通航阈值的海冰覆盖面积占总航道面积的35.24%,共有10个不可通航节点。2016年和2019年9月的通航情况较好,阿蒙森湾—科罗内申湾—毛德皇后湾—维多利亚海峡—富兰克林海峡—皮尔海峡—巴罗海峡—兰开斯特海峡段航道（航道C）可实现全线通航。进一步通过小尺度时间窗口研究发现,西北航道的最佳通航窗口为8月下旬至9月上旬,期间共出现3条全线通航的航道;最佳通航路线为航道C,其连续通航时间长达30天。     

基于FloodArea模型的小流域山洪灾害临界雨量阈值初探

针对缺乏水位流量资料的山区小流域地区山洪临界雨量难以确定的问题,以四川省南江河上游流域作为研究区域,基于德国Geomer公司开发的二维非恒定流水动力模型"FloodArea ",利用流域逐时降雨资料,地形高程数据以及土地利用数据,重现南江" 6·28"山洪暴发的动态演进过程,对模拟得到的逐时淹没深度与1~24 h累积流域面雨量求相关,选取预警点淹没深度与累积面雨量的相关系数最高的时效作为预警点致灾临界雨量阈值的预报时效,通过建立预警点淹没深度与预报时效累积面雨量的回归方程,从而获取预警点不同风险等级的临界雨量阈值。结果表明：FloodArea模型能够较好地呈现出此次典型山洪的暴发过程,通过对不同地势预警点临界雨量阈值的对比,最终选取地势较低,位于河流汇口地带、风险等级较高的上两九义校作为南江河上游流域山洪风险预警点。     

Micro-scale flood risk analysis based on detailed 2D hydraulic modelling and high resolution geographic data

The paper presents a consistent micro-scale flood risk analysis procedure, relying on detailed 2D inundation modelling as well as on high resolution topographic and land use database. The flow model is based on the shallow-water equations, solved by means of a finite volume scheme on multi-block structured grids. Using highly accurate laser altimetry, the simulations are performed with a typical grid spacing of 2 m, which is fine enough to represent the flow at the scale of individual buildings. Consequently, the outcomes of hydraulic modelling constitute suitable inputs for the subsequent exposure analysis, performed at a micro-scale using detailed land use maps and geographic database. Eventually, the procedure incorporates social flood impact analysis and evaluation of direct economic damage to residential buildings. Besides detailing the characteristics and performance of the hydraulic model, the paper describes the flow of data within the overall flood risk analysis procedure and demonstrates its applicability by means of a case study, for which two different flood protection measures were evaluated.     

Impact of flash flood recharge on groundwater quality and its suitability in the Wadi Baysh Basin,Western Saudi Arabia: an integrated approach

An integrated approach was used to evaluate the impact of flash flood recharge on groundwater quality and its suitability for drinking, irrigation, livestock and poultry uses in the Wadi Baysh Basin, Western Saudi Arabia. Analyses of 182 groundwater samples, collected from the study area before and after a flash flood (FF) event, show that the average concentrations of TDS, Mg, Na, Cl, NO₃ and EC decreased significantly after the event. The major water types (mixed CaMgCl, NaCl and CaCl) indicate that the infiltration of surface water from FF recharge has a great influence on groundwater chemistry. Drinking water suitability maps, created using WHO standards, indicate that wells located in the upstream region are suitable for drinking despite their high TDS and total hardness (TH) values. Groundwater in the coastal region is unsuitable due to its high salinity, high TH and high concentrations of major ions. The suitability of groundwater for irrigational use was assessed using salinity, sodium adsorption ratio, bicarbonate hazard, residual sodium carbonate, Kelly’s ratio, magnesium hazard, sodium percentage and permeability index values, which indicated that groundwater in the study region is suitable for most soils and crops. After FF, groundwater quality is improved by dilution, especially in the downstream region. USSL classification shows that the majority of the water samples are in the C3S1, C4S2, and C3S2 classes and are therefore suitable for the irrigation of salt-tolerant crops. Irrigational suitability maps suggest that wells in the upstream region are suitable for irrigation, whereas wells located near to the coast are unfit for irrigation. This study implies that construction of check dams in the dry valleys (wadies) may improve the groundwater quality in the area.     

The socioeconomic impact of climate-related hazards: flash flood impact assessment in Kuala Lumpur,Malaysia

Small-scale flash flood events are climate-related disasters which can put multiple aspects of the system at risk. The consequences of flash floods in densely populated cities are increasingly becoming problematic around the globe. However, they are largely ignored in disaster impact assessment studies, especially in assessing socioeconomic loss and damage, which can provide a significant insight for disaster risk reduction measures. Using a structured questionnaire survey, this study applied a statistical approach and developed a structural equation model (SEM) for assessing several socioeconomic dimensions including physical impacts, mobility disruption, lifeline facilities, health and income-related impacts. The study reveals that respondents have experienced a stronger impact on direct tangible elements such as household contents and buildings as well as direct intangible elements with β coefficients 0.703, 0.576 and 0.635, respectively, at p?<?0:001 level. The direct intangible impacts affect mobility disruption with β coefficients equal to 0.701 at p?<?0:001 level which then further cause adversity to income-generating activities with β 0.316 at significant p?<?0:001 as well. The overall model fit indices show highly acceptable scores of SRMR 0.068, RMSEA 0.055 and PClose 0.092. Thus, the SEM has successfully incorporated the socioeconomic dimensions of disaster impact and explained the impact phenomena reliably. This modeling approach will allow inclusion of various variables from different disciplines to assess hazard impact, vulnerability and resilience.

     

Development of roughness updating based on artificial neural network in a river hydraulic model for flash flood forecasting

Flood is the worst weather-related hazard in Taiwan because of steep terrain and storm. The tropical storm often results in disastrous flash flood. To provide reliable forecast of water stages in rivers is indispensable for proper actions in the emergency response during flood. The river hydraulic model based on dynamic wave theory using an implicit finite-difference method is developed with river roughness updating for flash flood forecast. The artificial neural network (ANN) is employed to update the roughness of rivers in accordance with the observed river stages at each time-step of the flood routing process. Several typhoon events at Tamsui River are utilized to evaluate the accuracy of flood forecasting. The results present the adaptive n-values of roughness for river hydraulic model that can provide a better flow state for subsequent forecasting at significant locations and longitudinal profiles along rivers.     

Detection of hydrothermal alteration zones in a tropical region using satellite remote sensing data: Bau goldfield,Sarawak, Malaysia

Remote sensing for geology in tropical environments is very challenging, because of the dense vegetation cover and the problem of persistent cloud cover. In this research paper, we have investigated and demonstrated the detection of hydrothermal alteration zones and structural elements associated with intrusion-related gold mineralization using various types of remote sensing data in the Bau gold mining district in the State of Sarawak, East Malaysia, on the island of Borneo. The climate of Bau is tropical with persistent cloud cover and very dense vegetation ground. Geological analyses coupled with remote sensing data were used to detect hydrothermally altered rocks and structural elements associated with gold mineralization in the Bau area. Landsat Enhanced Thematic Mapper⁺ (ETM⁺), Hyperion and Phased Array type L-band Synthetic Aperture Radar (PALSAR) data were used to carry out lithological–structural mapping of the mineralized zones in the study area and surrounding terrain. Hydrothermal alteration zones were detected along the SSW to NNE structural trend of the Tai Parit fault that corresponds with the occurrence of other gold mineralization in the Bau Limestone. The results show that the known gold prospects and potential areas of mineralization are recognizable by the methods used, despite limited bedrock exposure. The approach used in this study is broadly applicable to the detection of gold mineralization using ETM⁺, Hyperion and PALSAR data in tropical/sub-tropical regions.     

Reconstruction and post-event analysis of a flash flood in a small ungauged basin: a case study in Slovak territory

Flash floods are one of the major natural hazards occurring in small streams with a negative effect on the country as well as on human lives. Heavy rainfall occurred on July 20, 2014 and July 21, 2014 and caused severe surface water flooding and a flash flood in the Malá Fatra National Park (Slovakia). The most affected was Vrátna Valley with the Varínka stream. This study presents a reconstruction and post-event analysis of a flash flood on small ungauged basin located in this protected area of Slovakia. The reconstruction included hydraulic terrain measurements on estimating the flood’s culmination and documenting the flood’s development. The measurements were taken at three cross sections of the Varínka stream. This paper is focused mainly on post-event analysis of the Varínka stream in two profiles: Strá?a (gauged profile) and Tiesňavy (ungauged cross section). Subsequently, the extremeness of the flash flood was preliminary evaluated. Results of the post-event analysis showed that the July 2014 flood was not the highest flood in this area despite its catastrophic consequences. By studying historical materials, we came to the conclusion that in the past (e.g. in 1848 or 1939) some devastating floods in this area had occurred, which had disastrous consequences for the population. The second part of the study is focused on comparing this flash flood with three major floods which have occurred in Slovak territory since 1998. The first flood occurred on the 20th of July, 1998 on the Malá Svinka stream, and the two others are floods which occurred on the 7th of June, 2011 in the Small Carpathian Mountains: on the Gidra stream in Píla village and on the Parná stream in Horné Ore?any village. Such comparison of flash floods from different geographical regions and different rainfall events can provide comprehensive information about their regimes, threats and disastrous effects.     

A comparative analysis of the loss of life during two recent floods in France: the sea surge caused by the storm Xynthia and the flash flood in Var

This paper aims to analyse and compare the loss of life that occurred during two recent floods in France. The first flood was due to a sea surge triggered by the storm called Xynthia that hit the Atlantic coast on 28 February 2010 (41 flood-related deaths). The second was a flash flood that struck the Var Department in the French Mediterranean region on 15 June 2010 (26 fatalities). After detailing the assumptions and expected outcomes of the study of disaster-related fatalities, the paper focuses on the characteristics of the victims and the circumstances of their deaths. In the first case, 71% of the victims were people aged over 60 (mainly women) who were surprised while they were sleeping and who died in or near their homes. In the case of the flash flood, the profiles of the victims were diverse as the flooding occurred in the afternoon and many people were trapped in open. The paper also highlights the factors that explain mortality. Physical factors such as water depth were determined. The relationship between the water depth and the age of victims was found to be relevant. In the case of the storm surge Xynthia, the correlation between age and water depth is positive. For the flash flood, the correlation between age and water depth was negative as male adults died in open. In the first case, the vulnerability of people was closely linked to human features such as type of housing and age that people are not directly responsible for. During flash floods, dangerous behaviour by people highlighted the role of risk-taking in loss of life. We also examined the particular case of the deaths of the children. The paper concludes by discussing the factors of vulnerability on frail population such as elderly people or marginalized. The lack of risk awareness and crisis preparedness were clearly a major factor of vulnerability.     

The Indus flood of 2010 in Pakistan: a perspective analysis using remote sensing data

The Indus flood in 2010 was one of the greatest river disasters in recent history, which affected more than 14 million people in Pakistan. Although excessive rainfall between July and September 2010 has been cited as the major causative factor for this disaster, the human interventions in the river system over the years made this disaster a catastrophe. Geomorphic analysis suggests that the Indus River has had a very dynamic regime in the past. However, the river has now been constrained by embankments on both sides, and several barrages have been constructed along the river. As a result, the river has been aggrading rapidly during the last few decades due to its exceptionally high sediment load particularly in reaches upstream of the barrages. This in turn has caused significant increase in cross-valley gradient leading to breaches upstream of the barrages and inundation of large areas. Our flow accumulation analysis using SRTM data not only supports this interpretation but also points out that there are several reaches along the Indus River, which are still vulnerable to such breaches and flooding. Even though the Indus flood in 2010 was characterized by exceptionally high discharges, our experience in working on Himalayan rivers and similar recent events in rivers in Nepal and India suggest that such events can occur at relatively low discharges. It is therefore of utmost importance to identify such areas and plan mitigation measures as soon as possible. We emphasize the role of geomorphology in flood analysis and management and urge the river managers to take urgent steps to incorporate the geomorphic understanding of Himalayan rivers in river management plans.     

Diagenetic mobility of trace elements in sediments covered by a flash flood deposit: Mn,Fe and As

The vertical distribution and concentrations of Fe, Mn, and As were measured in porewaters and sediments recovered with box-cores taken each year since the 1996 flood along the main axis of the Saguenay Fjord and in the Baie des Ha! Ha!. Time-series analyses reveal that Mn remobilization was not significantly affected by the accumulation of the flood deposit. Authigenic Mn oxi-hydroxides present at the original sediment–water interface and in the flood material were progressively reduced, and much of the Mn(II) diffused to the current interface, where it was oxidized and precipitated. First-order rate constants for the reduction and precipitation of the authigenic Mn oxi-hydroxides were estimated by fitting the time-series data to a diagenetic model. On the basis of these rate constants and given that the maximum reactive solid Mn remains concentrated in the thin, oxic layer near the sediment-water interface, an upper limit to the biodiffusion coefficient, D_B, was also evaluated. In contrast to Mn, Fe associated with the authigenic oxi-hydroxides at the original interface was mostly trapped as acid volatile sulfides (i.e., AVS) under the SO₄-reducing conditions established rapidly after the flood. Most of the As associated with the authigenic oxi-hydroxides at the original (buried) interface also appears to be trapped with the authigenic sulfides, thus limiting its diffusion through the flood deposit.