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12000 KiB

Open AccessArticle

A Hydrological and Geomorphometric Approach to Understanding the Generation of Wadi Flash Floods

by Mohammed Abdel-Fattah, Mohamed Saber, Sameh A. Kantoush, Mohamed F. Khalil, Tetsuya Sumi and Ahmed M. Sefelnasr

Water 2017, 9(7), 553; https://doi.org/10.3390/w9070553 - 24 Jul 2017

Cited by 55 | Viewed by 9734

Abstract

Abstract: The generation and processes of wadi flash floods are very complex and are not well understood. In this paper, we investigate the relationship between variations in geomorphometric and rainfall characteristics and the responses of wadi flash floods. An integrated approach was developed [...] Read more.

Abstract: The generation and processes of wadi flash floods are very complex and are not well understood. In this paper, we investigate the relationship between variations in geomorphometric and rainfall characteristics and the responses of wadi flash floods. An integrated approach was developed based on geomorphometric analysis and hydrological modeling. The Wadi Qena, which is located in the Eastern Desert of Egypt, was selected to validate the developed approach and was divided into 14 sub-basins with areas ranging from 315 to 1488 km2. The distributed Hydrological River Basin Environment Assessment Model (Hydro-BEAM) was used to obtain a good representation of the spatial variability of the rainfall and geomorphology in the basin. Thirty-eight geomorphometric parameters representing the topographic, scale, shape and drainage characteristics of the basins were considered and extracted using geographic information system (GIS) techniques. A series of flash flood events from 1994, 2010, 2013, and 2014, in addition to synthetic virtual storms with different durations and intensities, were selected for the application of this study. The results exhibit strong correlations between scale and topographic parameters and the hydrological indices of the wadi flash floods, while the shape and drainage network metrics have smaller impacts. The total rainfall amount and duration significantly impact the relationship between the hydrologic response of the wadi and its geomorphometry. For most of the parameters, we found that the impact of the wadi geomorphometry on the hydrologic response increases with increasing rainfall intensity. Full article

(This article belongs to the Special Issue Innovative Aspects in Flood Risk Evaluation, Mapping and Communication)

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6024 KiB

Open AccessArticle

Risk Analysis of Reservoir Operations Considering Short-Term Flood Control and Long-Term Water Supply: A Case Study for the Da-Han Creek Basin in Taiwan

by Wen-Ming Cheng, Chien-Lin Huang, Nien-Sheng Hsu and Chih-Chiang Wei

Water 2017, 9(6), 424; https://doi.org/10.3390/w9060424 - 12 Jun 2017

Cited by 20 | Viewed by 6360

Abstract

This study applies an integrated methodology to assess short-term over-levee risk and long-term water shortage risk in the Da-Han Creek basin, which is the most important flood control and water storage system in northern Taiwan. An optimization model for reservoir flood control and [...] Read more.

This study applies an integrated methodology to assess short-term over-levee risk and long-term water shortage risk in the Da-Han Creek basin, which is the most important flood control and water storage system in northern Taiwan. An optimization model for reservoir flood control and water supply is adopted, to determine reservoir releases based on synthetic inflow hydrographs during typhoons, which are generated by Monte Carlo simulations. The release is then used to calculate the water level at a downstream control point using a novel developed back-propagation neural network-based model, to reduce computational complexity and achieve automatic-efficient risk evaluation. The calculated downstream water levels and final reservoir water levels after a typhoon event are used to evaluate the mapped over-levee risk and water shortage risk, respectively. The results showed that the different upper limit settings for the reservoir have a significant influence on the variation of 1.19 × 10⁻⁵% to 75.6% of the water shortage risk. This occurs because of the insufficient inflow and narrow storage capacity of the Shih-Men Reservoir during drought periods. However, the upper limit settings have a minor influence (with a variation of only 0.149% to 0.157%) on the over-levee risk in typhoon periods, because of the high protection standards for the downstream embankment. Full article

(This article belongs to the Special Issue Innovative Aspects in Flood Risk Evaluation, Mapping and Communication)

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4998 KiB

Open AccessArticle

Vulnerability of Buildings on Coastal Dikes due to Wave Overtopping

by Xuexue Chen, Sebastiaan N. Jonkman, Sander Pasterkamp, Tomohiro Suzuki and Corrado Altomare

Water 2017, 9(6), 394; https://doi.org/10.3390/w9060394 - 02 Jun 2017

Cited by 10 | Viewed by 5959

Abstract

The vulnerability of buildings on coastal dikes due to overtopping wave impacts is difficult to assess. A method is developed in this paper to quantify the vulnerability of masonry buildings on a coastal dike exposed to wave overtopping. Using previous studies, the accidental [...] Read more.

The vulnerability of buildings on coastal dikes due to overtopping wave impacts is difficult to assess. A method is developed in this paper to quantify the vulnerability of masonry buildings on a coastal dike exposed to wave overtopping. Using previous studies, the accidental loads due to the extreme wave impacts are characterized. Using the approach from Eurocode 6, the strength of masonry buildings under these loads is assessed. Results from a case study in Belgium show that masonry buildings located 10–15 m away from the seafront would suffer from localized damage, such as windows being broken under a 1000 year storm. The building would collapse under a 10,000-year storm. The method can be used to assess the safety of existing buildings on coastal dikes and to design new buildings. Full article

(This article belongs to the Special Issue Innovative Aspects in Flood Risk Evaluation, Mapping and Communication)

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1741 KiB

Open AccessArticle

A Study on Coastal Flooding and Risk Assessment under Climate Change in the Mid-Western Coast of Taiwan

by Tai-Wen Hsu, Dong-Sin Shih, Chi-Yu Li, Yuan-Jyh Lan and Yu-Chen Lin

Water 2017, 9(6), 390; https://doi.org/10.3390/w9060390 - 01 Jun 2017

Cited by 34 | Viewed by 7671

Abstract

This study integrated coastal watershed models and combined them with a risk assessment method to develop a methodology to investigate the impact resulting from coastal disasters under climate change. The mid-western coast of Taiwan suffering from land subsidence was selected as the demonstrative [...] Read more.

This study integrated coastal watershed models and combined them with a risk assessment method to develop a methodology to investigate the impact resulting from coastal disasters under climate change. The mid-western coast of Taiwan suffering from land subsidence was selected as the demonstrative area for the vulnerability analysis based on the prediction of sea level rise (SLR), wave run-up, overtopping, and coastal flooding under the scenarios of the years from 2020 to 2039. Databases from tidal gauges and satellite images were used to analyze SLR using Ensemble Empirical Mode Decomposition (EEMD). Extreme wave condition and storm surge were estimated by numerical simulation using the Wind Wave Model (WWM) and the Princeton Ocean Model (POM). Coastal inundation was then simulated via the WASH123D watershed model. The risk map of study areas based on the analyses of vulnerability and disaster were established using the Analytic Hierarchy Process (AHP) technique. Predictions of sea level rise, the maximum wave condition, and storm surge under the scenarios of 2020 to 2039 are presented. The results indicate that the sea level at the mid-western coast of Taiwan will rise by an average of 5.8 cm, equivalent to a rising velocity of 2.8 mm/year. The analysis indicates that the Wuqi, Lukang, Mailiao, and Taixi townships are susceptive, low resistant and low resilient and reach the high-risk level. This assessment provides important information for creating an adaption policy for the mid-western coast of Taiwan. Full article

(This article belongs to the Special Issue Innovative Aspects in Flood Risk Evaluation, Mapping and Communication)

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4890 KiB

Open AccessEditor’s ChoiceArticle

Application of GIS-Interval Rough AHP Methodology for Flood Hazard Mapping in Urban Areas

by Ljubomir Gigović, Dragan Pamučar, Zoran Bajić and Siniša Drobnjak

Water 2017, 9(6), 360; https://doi.org/10.3390/w9060360 - 24 May 2017

Cited by 191 | Viewed by 14037

Abstract

Floods are natural disasters with significant socio-economic consequences. Urban areas with uncontrolled urban development, rapid population growth, an unregulated municipal system and an unplanned change of land use belong to the highly sensitive areas where floods cause devastating economic and social losses. The [...] Read more.

Floods are natural disasters with significant socio-economic consequences. Urban areas with uncontrolled urban development, rapid population growth, an unregulated municipal system and an unplanned change of land use belong to the highly sensitive areas where floods cause devastating economic and social losses. The aim of this paper is to present a reliable GIS multi-criteria methodology for hazard zones’ mapping of flood-prone areas in urban areas. The proposed methodology is based on the combined application of geographical information systems (GIS) and multi-criteria decision analysis (MCDA). The methodology considers six factors that are relevant to the hazard of flooding in urban areas: the height, slope, distance to the sewage network, the distance from the water surface, the water table and land use. The expert evaluation takes into account the nature and severity of observed criteria, and it is tested using three scenarios: the modalities of the analytic hierarchy process (AHP). The first of them uses a new approach to the exploitation of uncertainty in the application of the AHP technique, the interval rough numbers (IR’AHP). The second one uses the fuzzy technique for the exploitation of uncertainty with the AHP method (F’AHP), and the third scenario contemplates the use of the traditional (crisp) AHP method. The proposed methodology is demonstrated in Palilula Municipality, Belgrade, Serbia. In the last few decades, Palilula Municipality has been repeatedly devastated by extreme flood events. These floods severely affected the transportation networks and other infrastructure. Historical flood inundation data have been used in the validation process. The final urban flood hazard map proves a satisfactory agreement between the flood hazard zones and the spatial distribution of historical floods that happened in the last 58 years. The results indicate that the scenario in which the IR’AHP methodology is used provides the highest level of compatibility with historical data on floods. The produced map showed that the areas of very high flood hazard are located on the left Danube River bank. These areas are characterized by lowland morphology, gentle slope, sewage network, expansion of impermeable locations and intense urbanization. The proposed GIS-IR’AHP methodology and the results of this study provide a good basis for developing a system of flood hazard management in urban areas and can be successfully used for spatial city development policy. Full article

(This article belongs to the Special Issue Innovative Aspects in Flood Risk Evaluation, Mapping and Communication)

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11969 KiB

Open AccessArticle

Flood Loss Models and Risk Analysis for Private Households in Can Tho City, Vietnam

by Do Thi Chinh, Nguyen Viet Dung, Animesh K. Gain and Heidi Kreibich

Water 2017, 9(5), 313; https://doi.org/10.3390/w9050313 - 29 Apr 2017

Cited by 20 | Viewed by 11656

Abstract

Vietnam has a long history and experience with floods. Flood risk is expected to increase further due to climatic, land use and other global changes. Can Tho City, the cultural and economic center of the Mekong delta in Vietnam, is at high risk [...] Read more.

Vietnam has a long history and experience with floods. Flood risk is expected to increase further due to climatic, land use and other global changes. Can Tho City, the cultural and economic center of the Mekong delta in Vietnam, is at high risk of flooding. To improve flood risk analyses for Vietnam, this study presents novel multi-variable flood loss models for residential buildings and contents and demonstrates their application in a flood risk assessment for the inner city of Can Tho. Cross-validation reveals that decision tree based loss models using the three input variables water depth, flood duration and floor space of building are more appropriate for estimating building and contents loss in comparison with depth–damage functions. The flood risk assessment reveals a median expected annual flood damage to private households of US$3340 thousand for the inner city of Can Tho. This is approximately 2.5% of the total annual income of households in the study area. For damage reduction improved flood risk management is required for the Mekong Delta, based on reliable damage and risk analyses. Full article

(This article belongs to the Special Issue Innovative Aspects in Flood Risk Evaluation, Mapping and Communication)

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5000 KiB

Open AccessArticle

Assessment of Social Vulnerability to Flood in Urban Côte d’Ivoire Using the MOVE Framework

by Malan Ketcha Armand Kablan, Kouassi Dongo and Mamadou Coulibaly

Water 2017, 9(4), 292; https://doi.org/10.3390/w9040292 - 21 Apr 2017

Cited by 59 | Viewed by 10375

Abstract

Coupled with poor urban development, the increasing urban population of many Sub-Saharan African countries is subject to recurrent severe flooding episodes. In response to these flood events, while the focus is often put on slums and precarious urban settings, the social implications of [...] Read more.

Coupled with poor urban development, the increasing urban population of many Sub-Saharan African countries is subject to recurrent severe flooding episodes. In response to these flood events, while the focus is often put on slums and precarious urban settings, the social implications of these floods affect a variety of social classes. Presenting a case study of Cocody, a district of Abidjan, Côte d’Ivoire, known to have the country’s highest number of flood-impacted people, this paper evaluates the social vulnerability of urban Côte d’Ivoire to flooding using the MOVE framework. The MOVE framework (Method for the Improvement of Vulnerability Assessment in Europe) has successfully been used in European contexts to assess social vulnerability of urban areas to geo-environmental disasters such floods. It helped assess the major factors involved in the social vulnerability to urban flooding and to have a good appreciation of the spatial distribution of areas that are vulnerable to urban flood. By taking this framework to the local context, relevant indicators were developed and GIS applications were used to assess spatially the relative social vulnerability of Cocody sub-districts to urban flooding. The results revealed that many sub-districts of Cocody are highly vulnerable to urban floods. Exposure and susceptibility are components that are found to have high influence on vulnerability to flood hazard in the district of Cocody. Their respective indicators need to be addressed properly in order to increase residents’ resilience to urban flooding. The MOVE theoretical framework can be applied in Africa by contextualizing the vulnerability by using local indicators. Full article

(This article belongs to the Special Issue Innovative Aspects in Flood Risk Evaluation, Mapping and Communication)

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7219 KiB

Open AccessArticle

Optimal Operation Research of Flood Retarding in Plain River Network Region

by Zhenye Zhu, Zengchuan Dong, Wanhong Yang, Jie Zhou, Dayong Li, Xiaohua Fu and Wei Xu

Water 2017, 9(4), 280; https://doi.org/10.3390/w9040280 - 17 Apr 2017

Cited by 6 | Viewed by 4786

Abstract

The operation of flood retarding areas does not attract much attention, although they are important components of flood control systems. Poor operation of such areas restricts not only the socio-economic development of the flood retarding area, but also limits scientific flood control options. [...] Read more.

The operation of flood retarding areas does not attract much attention, although they are important components of flood control systems. Poor operation of such areas restricts not only the socio-economic development of the flood retarding area, but also limits scientific flood control options. As the second-largest flood retarding area in China, with more than 2000 km² and 300 polders, the Hongze Lake vicinity was taken as a case study of graded flood retarding. A one and two-dimensional coupled hydrodynamic model was established to simulate flood routing in the Hongze Lake area. Fifteen different schemes involving different flood magnitudes and flood retarding operations were simulated. The results show that (1) having a flood retarding area is essential; and (2) the “graded flood retarding” scheme is superior to “no grading flood retarding” scheme; and (3) a “two-grade flood retarding” scheme is recommended. Full article

(This article belongs to the Special Issue Innovative Aspects in Flood Risk Evaluation, Mapping and Communication)

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34184 KiB

Open AccessArticle

Paleohydraulic Reconstruction of Modern Large Floods at Subcritical Speed in a Confined Valley: Proof of Concept

by Patricio Bohorquez

Water 2016, 8(12), 567; https://doi.org/10.3390/w8120567 - 02 Dec 2016

Cited by 11 | Viewed by 5690

Abstract

The present study aims to show the accuracy of paleoflood reconstruction techniques based on two-dimensional (2D) hydraulic modelling of a large flood. Using this reconstruction technique, we determined trends in flood stages over time in a regulated river. A stretch of the Guadalquivir [...] Read more.

The present study aims to show the accuracy of paleoflood reconstruction techniques based on two-dimensional (2D) hydraulic modelling of a large flood. Using this reconstruction technique, we determined trends in flood stages over time in a regulated river. A stretch of the Guadalquivir River (Southern Spain) was selected as the study site. High-resolution orthophotos and LiDAR (Light Detection and Ranging) elevations were acquired just after modern floods. They were used for the identification and location of stage indicators. In addition, water gradients were estimated from gauging records, documentary information and paleostage indicators (PSIs) in two situations: (i) pre-vegetation encroachment; and (ii) post-vegetation encroachment due to upstream impoundment. Standard two-dimensional, flow depth-averaged equations over fixed beds were used in the hydraulic modelling. In a first stage, long records of instrumental data at gauging stations and documentary evidence of flood levels served to calibrate the input parameters of the hydraulic model. In a second stage, paleoflood signatures within sedimentary and botanical sequences served to verify the flood stages in the numerical simulations not only at the river reach where instrumental data exist but also in the downstream river reach. Interestingly, the rating curve obtained from the combined use of documentary information and imagery was nearly as accurate as gauging measurements. The thoughtful comparison of 2D modelled hydraulic variables against inferred values from PSIs and instrumental data supports the paleoflood reconstruction method over fixed beds. Vegetation encroachment provoked 10% deeper floods at the water discharge of 2000 m³

\cdot

s⁻¹, which implied an increase of Manning’s roughness coefficient from 0.04 to 0.055 s

\cdot

m^−1/3 in less than 15 years. Full article

(This article belongs to the Special Issue Innovative Aspects in Flood Risk Evaluation, Mapping and Communication)

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