Flood Hazard Areas Research Articles

Mapping flood inundation areas using GIS and HEC-RAS model at Fetam River, Upper Abbay Basin, Ethiopia

Flood occurs due to rapid population growth, land degradation, and climate change, and causes harmful damages to human beings and properties. This can be minimized by giving attention to flood risk measures. One of these measures is inundating flood hazard areas. Therefore, this study was conducted to map flood inundation areas along the Fetam River using GIS and HEC_RAS. Flood inundation mapping is used to define the zones which are more susceptible to flood along the river when the release of a stream surpasses the bank-full stage along the river. Using the past data on river banks and the release of earlier floods besides topographic data, maps were made to illustrate areas predictable to be covered with the flood for different releases. The flooded areas on Fetam River have been represented depending on 5% incidence peak flows for different reoccurrence eras using the HEC-RAS model, GIS for spatial data handling, and HEC-GeoRAS for interfacing among HEC-RAS and GIS. These critical floods were damaging the areas around Fetam River, which is hazardous to social and economic growth due to loss of lives and destruction of properties. Built-up areas and agricultural fields are located along the river banks and are highly susceptible to flooding. The inundated areas were particularly high from Abaya Kalo, Achigi, and Denbun kebeles for all return periods. These flooded areas along the side of the Fetam River are 27.31, 24.85, 20.47, 17.34, and 13.78 km2 for 100, 50, 25, 10, and 5 years return periods, respectively. Generally, this study discovered that flooded areas in the upstream and middle parts of Fetam River are high as related to the downstream parts.

Designation of Flood Risk Zones Using the Geographic Information System Technique and Remote Sensing Data in Wasit, Iraq

Floods are a great concern for people and infrastructure, and this is an issue which has increased in several regions around the globe in recent years. This study aims to evaluate flood risk areas and create a flood risk map using integrated remote sensing data and a geographic information system (GIS) in the Wasit governorate – eastern Iraq. Specifically, GIS‑based multi‑criteria analysis (MCA) was used to map flood hazard areas using a four‑criteria layer which is as follows: flow accumulation, slope, rainfall, and elevation. These four layers are standardized and combined using the overlay approach in ArcGIS software and a final map was produced. The study area was divided into five zones based on the results map, namely: very low, low, medium, high, and very high, according to the flood risk area. The resulting map indicates that over 60% of the study area is likely to experience a high and very high level of propensity of flooding. This study could be useful for government planners and decision‑makers to predict potential flooding areas and enhance flood management plans.

Assessment of flood hazard areas and its management using Remote Sensing and GIS Techniques: A Case Study of Tigris River - Salah Al-Din Governorate, Iraq

Flood is one of the most widely distributed hazards around the world and its management is an important concern for all decision maker this phenomenon. In Iraq, especially in Salah Al-Din Governorate, during the Spring 2019, the amount of water flowing has been increased into Tigris River, this led to a rise in the river level as a result of rains in close range and snow melting, as well as an increase in the drainage of the Small Zab, which is flowed into Tigris River at Salah Al-Din Governorate. Therefore, the flood hazard mapping and flood shelter analyses have been accomplished through the assessment of damage and determination the optimal location to make flood escape for mitigation the flood hazard processing. The Remote Sensing (R.S) technique and Geographic Information System (GIS) have been utilized to assess the damage by using the NDVI and NDWI indices. Arc Hydro tool in GIS software with the hydraulic model HEC-Ras software have been also utilized to find the flood escape and modeling the flood shelter. The result shows that the damaged areas at Salah Al-Din Governorate for agriculture land and flood inundation map.

Flood hazard areas assessment at a regional scale in M'zi wadi basin, Algeria

Located in the semi-arid areas of Algeria, M'zi wadi basin experienced severe floods that pose a potent threat to the present day. In order to reduce and mitigate flood damage there is a need to develop tools for effective flood hazard management at basin scale, the paper aims to mapping of flood hazard potential areas in M'zi wadi basin, using Analytic Hierarchy Process (AHP) approach coupled with Geographic Information System (GIS), based on several parameters that are relevant to flood hazard which has been weighted depending to their contributions. The Rainfall-Runoff-Inundation (RRI) model was also used in this study to understanding the hydrological behavior of M'zi wadi basin and to evaluate the efficiency of structural measures in downstream areas of basin.The results show a reasonable agreement with the inundated areas detected by Sentinel-2 imagery. The result of the flooding hazard in M'zi wadi basin reveals that 3%, 0.84%, 67%, 29%, and 0.16% of the catchment is high, very high, moderate, low, and very low flooding hazard areas respectively. The results show also that urban areas and agricultural areas surrounding of the lower portion of M'zi wadi are extremely exposed to flooding. The RRI model simulation results shows that the new dam -under construction-can reduce the magnitude of peak storm runoff only by 7%, and the widening of wadi near to outlet of basin can help to reduce the water level at this segment by 22% compared with results of simulation of naturalized conditions.Flood hazard areas assessment at M'zi wadi basin level can be used by concerned government's department as an excellent supporter of decision-makers during extreme and intense rainfall events in making floodplain management decisions.

To appeal and amend: Changes to recently updated Flood Insurance Rate Maps

AbstractFlood Insurance Rate Maps (FIRMs) are produced for the National Flood Insurance Program to depict and manage flood hazard in the United States. While past research has portrayed FIRMs as static maps, property residents and community representatives can propose changes to flood zones on FIRMs. These changes add and remove buildings from flood zones on FIRMs, which raises an important question: are there discernable trends or patterns in these alterations to FIRMs? We use Geographic Information Systems FIRM layers and building footprints to quantify the number of buildings moved in and out of the Special Flood Hazard Area (SFHA) for recently updated FIRMs. Our analysis of building additions and removals from SFHAs at county and census tract scales shows there has been a net change of over 20,000 buildings removed from these SFHAs between preliminary and present FIRM iterations. We also find that SFHAs are more frequently altered in places where median home values are higher, buildings are newer, and percentage of white populations are higher. These findings suggest changes to flood zones on FIRMs occur more often where people have greater socioeconomic means, raising questions of equity for future FIRM appeals and revisions.

Flood Hazard Assessment Mapping in Burned and Urban Areas

This study proposes a simple method to produce a flood hazard assessment map in burned and urban areas, where primary data are scarce. The study area is a municipal unit of Nea Makri, a coastal part of the eastern Attica peninsula (central Greece), which has been strongly urbanized and suffered damage from urban fires in 2018. Six factors were considered as the parameters most controlling runoff when it overdraws the drainage system’s capacity. The analytical hierarchy process (AHP) method and a geographical information system (GIS) were utilized to create the flood hazard assessment map. The outcome revealed that the areas with highest flood hazard are distributed in the eastern and southern parts of the study area, as a result of the combination of lowlands with gentle slopes, torrential behavior of the streams, streams covered by construction, increasing urbanization and burned areas. The uncertainty and the verification analyses demonstrate a robust behavior for the model predictions, as well as reliability and accuracy of the map. Comparing the existing urban fabric and road network to the potential flood hazard areas showed that 80% of the urban areas and 50% of the road network were situated within areas prone to flood. The method may be applied to land use planning projects, flood hazard mitigation and post-fire management.

The Integrated Spatial Assessment of The Flood Hazard Using AHP-GIS: The Case Study of Gorontalo Regency

Mapping of potential flood hazards is an important element in ensuring proper planning of development and implementing flood disaster mitigation efforts for flooded areas. Therefore, this study was conducted to assess the regional-scale flood hazard areas in Gorontalo District using an AHP-GIS integration technique with the focus on factors such as annual rainfall, elevation, slope, soil type, distance to the water bodies, and land-use. The flood hazard was divided into five classes, ranging from very low to very high, and 13.61% of the total area in Gorontalo Regency is classified as either high or very high. Moreover, the distribution of the hazard was verified and 65 events were recorded to have a level of 90.7% and this indicates the model is reliable to assess flood hazard. The results showed GIS-AHP integration is a promising method to accurately predict flood-hazard areas, especially in those with limited data.

Multi-geospatial flood hazard modelling for a large and complex river basin with data sparsity: a case study of the Lam River Basin, Vietnam

Mapping flood hazard becomes a basic and crucial requirement to cope with and to mitigate flood risks. However, it is a big challenge to accurately construct a flood hazard map in the large and sparsity data basin. Here, we present a new approach to make a flood hazard map in a large and complex river basin with data sparsity based on a comprehensive analysis of the relationship between previous flood records and hydrometeorological and geographical features coupled with holistic knowledge. The results show that the AHP-GIS approach (an integrated GIS-based Analytic Hierarchy Process method) can produce more accurate and reliable flood hazard map in basins with complex geological and hydrometeorological features such as the Lam River Basin (LRB). The LRB was a high vulnerability to flooding with approximately more than 90% of the total area in this river basin was classified into moderate, high, and very high hazard of flooding. More specifically, high, and very high flood hazard area occupied nearly 30% of the total area and affected nearly 45% of households living in the basin. More noticeable, these high flood hazard areas were in small valleys along the rivers and streams running from high mountains in the southwest to the coastal region. Moreover, the study indicated that rainfall and slope were the main factors that influence mapping flood hazard and assessing flood risk in the steep slope areas.

Design process in the urban context - Mobility and health in Special Flood Hazard Area

Resume In developing countries, unplanned urban growth, lack of infrastructure services, pollution, diseases, and flooding generate urgent needs. Floods cause diseases and damage to countries at all levels of development because they usually lack the preparedness for current climate variability. In Brazil, Municipal Civil Defense (JMCD) – in a 600,000 inhabitants city-, together with other city agencies, established a safe route (SRP) to be implemented during flood occurrences. This map is available for download as a PDF. This work aims to present the developed methodology, tools, and ways to design, in a collaborative way, a conceptual, innovative system model capable of bringing together needs like resilience, safety and sustainability, contributing to urban resilience, mobility, risks communication and health. Different design processes: design thinking, wayfinding system, signage, norms, and laws were used to create a dynamic conceptual design in the urban development. As a result, visual identity, pictograms icons, totems and luminous panels are presented. Luminous system is projected to be linked to rivers height (measured in hydrological gauging stations) to guide users to safe routes. The information technology which can link water height in rivers, to the different levels of flood in the designed system is not among the objectives of this study. Developing strategies to face the potential effects of climate change in the transportation sector poses a major significant challenge. Proper tools are required to prepare to change and provide meaningful environmental, health, social, and security solutions with the quickness the modern cities demand.

Flood hazard assessment in large plain basins with a scarce slope in the Pampean Plain, Argentina.

Floods are one of the most common natural phenomena and represent a serious hazard when they affect human activities. Structural measures are commonly used to mitigate them; however, these do not always give good results, mainly in plain areas with scarce slope. In this sense, the generation of a flood hazard map contributes to adequate hazard management and disaster prevention. The aim of this work is to evaluate the flood hazard areas in hydrological plain basins with scarce slope, taking as a case study the Samborombón river basin located in the Pampean Plain, Argentina. For this, a flood hazard map was made based on the analytical hierarchy process and using a GIS, taking into account physical aspects of the terrain, observations, and field measurements. Likewise, the map was validated using satellite images and the inhabitants in danger in the basin were quantified. The results show that the flood hazard areas correspond mainly to the floodplain of rivers and tributaries, while the main and secondary divide zones have low flood hazard sectors. On the other hand, numerous urban settlements were identified within flood hazard areas, these being urban settlements in the vicinity of old urban centers and new gated communities with high value homes, quantifying 1961 inhabitants at flood hazard and showing poor territorial planning. The methodology proposed gives to the management agencies the possibility of generating land use maps, as well as designing mitigation and contingency plans after a large rainfall event.

Quantification of continuous flood hazard using random forest classification and flood insurance claims at large spatial scales: a pilot study in southeast Texas

Abstract. Pre-disaster planning and mitigation necessitate detailed spatial information about flood hazards and their associated risks. In the US, the Federal Emergency Management Agency (FEMA) Special Flood Hazard Area (SFHA) provides important information about areas subject to flooding during the 1 % riverine or coastal event. The binary nature of flood hazard maps obscures the distribution of property risk inside of the SFHA and the residual risk outside of the SFHA, which can undermine mitigation efforts. Machine learning techniques provide an alternative approach to estimating flood hazards across large spatial scales at low computational expense. This study presents a pilot study for the Texas Gulf Coast region using random forest classification to predict flood probability across a 30 523 km2 area. Using a record of National Flood Insurance Program (NFIP) claims dating back to 1976 and high-resolution geospatial data, we generate a continuous flood hazard map for 12 US Geological Survey (USGS) eight-digit hydrologic unit code (HUC) watersheds. Results indicate that the random forest model predicts flooding with a high sensitivity (area under the curve, AUC: 0.895), especially compared to the existing FEMA regulatory floodplain. Our model identifies 649 000 structures with at least a 1 % annual chance of flooding, roughly 3 times more than are currently identified by FEMA as flood-prone.

Evaluation of lahar flood hazard management policy using participatory planning in Putih watershed, Magelang regency, central java, Indonesia

The occurrence of Lahar floods after Merapi Volcano eruption in 2010 still continue to be a concern for the government and the community. Kali Putih is one of the rivers that originates in Merapi Volcano and is one of the Lahar flood hazard area. Non-structural mitigation efforts have been carried out by the government. Until now, there are still community activities in the forbidden hazard area. Regulations regarding to spatial planning regulation in the hazard area need to be evaluated. The aim of the study is to evaluate the Lahar flood hazard mitigation based on participatory mapping and Focus Group Discussions (FGD). The research area is Jumoyo Village, which is the highest Lahar hazard flood area. The results indicate that there are still residential areas and community activities in the Lahar flood hazard area. The community does not want to lose their livelihood or relocation of their homes. The community expect that the government is able to revive the economic activities of the community through the establishment of new economic centres without relocation of their homes. The community also expect that the government able to creating new employment.

Changes in the spatial development of flood hazard areas in Poland between 1990 and 2018 in the light of legal conditions

The study presented herein focuses on determining the relationship between changes in the scale of economic losses between 1990–2018 which occurred in areas of high (10 %) and medium (1%) probability of flood occurrence as well as flood hazard areas due to the destruction of a stopbank, and changes in legislation affecting the spatial development of such areas within the said period. The analysis of changes in the development of flood hazard areas was conducted by means of the Corine Land Cover database. The results of the analysis were later used to evaluate potential economic losses on flood plains, and then spatiotemporal analysis was applied to identify areas with clusters of high and low loss values and the trends regarding their transformations. In consequence, the identification of municipality (Polish: gmina) clusters allowed us to verify the dependence of such transformations on those factors that could impact their intensity. For that purpose, we analysed the coverage of local spatial development plans for individual clusters. On the basis of the conducted studies, we concluded that the implemented legal solutions are not entirely effective, which has also been stated by the legislator. Nevertheless, the introduced legislative changes were beneficial, as the example of Poland shows. The implementation of the Floods Directive has, to a certain degree, decelerated the process of land use and its development in flood hazard areas.

Flood susceptibility mapping using a geomorphometric approach in South Australian basins

Watershed characteristics and their hydrological responses can have severe effects on the occurrence and extent of floods. Therefore, this study focuses on the integration of geospatial techniques and remote sensing data to identify watershed terrain characteristics and evaluate the influence of these characteristics on flood susceptibility in South Australia. Data from the Shuttle Radar Topography Mission (SRTM) and geologic and topographic maps and a geographic information system (GIS) were used to delineate drainage basins, measure morphometric parameters and link different parameters to evaluate the degree of flood vulnerability. Depending on their relations to the flood hazards, the morphometric parameters were categorized into two groups; then, a rank score was assigned to each group. Finally, the flood susceptibility of the basins was visualized, and the basins were classified into low, intermediate and high flood hazard areas. The results show that approximately 45.7, 44.7 and 9.7% of the study area is at risk of high, medium and low degrees of flooding, respectively. The results were validated through secondary data relating to historic floods. The causes of flooding were analysed using rainfall and road density data, while the consequences of flooding were verified by the population distribution across the study area. The findings of this study can be used to support decision-makers in planning and investing in mitigation measures, especially in highly susceptible areas of South Australian basins.

Flood vulnerability assessment using GIS at Fetam watershed, upper Abbay basin, Ethiopia

Flood is a danger to human beings and their properties because less consideration is given for risk analysis and assessment of risk areas. The main aim of this study was to assess the flood vulnerability areas of Fetam watershed. For analyzing this issue, flood generating factors: slope, elevation, land use/land cover, drainage density, rainfall, and soil types were rated and collected to mark out flood vulnerability zones using a multi-criteria evaluation technique within the Geographic Information System (GIS). Maps were constructed using past data on river banks and discharge of earlier floods along with topographic data to illustrate areas susceptible to flood for various discharges. The influences of all overflow distribution factors were calculated using pair-wise evaluation techniques for decisive weighted-overlay investigation of each factor in flood vulnerability assessment. The flood vulnerability valuation map showed that 67.54, 634.11, 280.89, 121.28, and 2.81 km2 areas correspond to very high, high, moderate, low, and very low flood vulnerabilities respectively. Residential areas and farming fields are located along with the flood hazard areas, which are susceptible to flooding. Hence, these areas are vulnerable to social and economic development due to loss of life and damage to properties of resident people. The main result of this study showed that the upstream and center part of Fetam watershed is highly sighted than the downstream part.

A rapid flood inundation model in the floodplain area due to an extreme rainfall event

Extreme rainfall in East Jakarta on February 19, 2021 caused flooding in a number of subdistricts. The research was conducted in the central part of Kali Sunter, which flows through three subdistricts, namely Cipinang Melayu, Cipinang Muara, and Pondok Bambu. The purpose of the study was to do flood hazard modeling and analyze the characteristics of flood-affected areas based on land use and topography. Inundation and flood hazard maps is done by: calculating the flood discharge using the SCS-CN method, flood inundation modelling using HEC-RAS, and analyzing the characteristics of the inundated area. This combination is effective for rapid modeling during extreme rainfall events. Based on the research, the distribution of the highest flood hazard area is in RW 004 Cipinang Melayu, with the widest inundation affecting small and medium-sized houses. The characteristics of the affected area are that there is green and empty land which reduces the potential for water to inundate buildings or other land uses. Buildings located in low-hazard housing areas tend to be more organized and relatively medium to large in size. While the types of housing in the Cipinang Melayu with a high level of danger tend to be dense and small to medium in size, but the majority have two floors as a form of flood adaptation.

Application of an Index-Based Approach in Geospatial Techniques for the Mapping of Flood Hazard Areas: A Case of Cape Coast Metropolis in Ghana

Floods remain one of the disasters that destroy properties, livelihoods, and in extreme situations, take lives. As a way of prevention, geospatial applications have been employed in many cities to map flood zones and predict floods. For a country such as Ghana, floods have been ranked as the second fatal disaster after epidemics leading to several kinds of research to resolve them. To date, the Cape Coast Metropolis (CCM) has received little attention in terms of research, though flood cases in the area continue to escalate. This study, therefore, examines the use of geospatial techniques as tools in addressing flood problems in the CCM of Ghana. From a Digital Elevation Model, hydrologic variables were generated using the ArcGIS software (Esri, Redlands, CA, USA). The soil drainage classification for the study was generated from a downloaded African Soil Grid Drainage map, while other important factors that influenced flooding in the CCM were obtained from Landsat 8 imagery. Over 21% of the CCM was classified as high flood hazard zones with areas around the river Kakum estuary being flood hotspots. It is, therefore, recommended that the CCM Assembly fund dredging of streams/rivers and promote afforestation along river banks to reduce the risk of flooding within the metropolis.

Deductible Choice in Flood Insurance: Who Chooses the Maximum?

Although some have proposed eliminating the National Flood Insurance Program (NFIP) to reduce government expenditures, other alternatives exist that could reduce the cost of the program and increase its viability, such as increasing deductibles, which may increase participation and revenue. The​ recently released FIMA NFIP Redacted Policies Data Set provides unprecedented opportunities to examine homeowner deductible choices for flood insurance policies using policy-level data. The menu of deductibles currently ranges from $1,000 to $10,000 in Special Flood Hazard Areas (SFHAs), but until April 1, 2015, the maximum deductible was $5,000. Using a matched sample of 252,280 SFHA policies that were active for the 2013–2019 time period, we provide insight regarding characteristics of homeowners who chose the maximum deductible as well as those who switched from the $5,000 to the new $10,000 deductible. Consistent with nudge theory and stickiness, we show that the majority of the homeowners accept the default deductible option. Individuals in high-income and high-premium areas were more likely to select the maximum dedu​ctible. Level of education and past flood events do not impact whether people decide to select the maximum deductible option.

Enhanced flood hazard modelling using hydraulic, analytical hierarchical process and height above nearest drainage models in Ogunpa river basin, Ibadan, Southwestern Nigeria

Flood risk mapping and analysis have gained much attention globally due to the increasing rate of flood disasters in most coastal and riverine areas. As a key element of flood risk study, mapping and delineation of flood hazard areas are very important for risk management and disaster reduction. We analysed potential flood hazards zones in Ogunpa river basin using integrated hydraulic modelling, the height above nearest drainage (HAND) model and multi criteria decision analysis (MCDA). An event-based flood simulation using FLO-2D model was done for the 28 h of the flooding event, while HAND model was employed in modelling the terrain to delineate inundation extent in the basin. In addition, seven flood causative factors were integrated using the Analytical Hierarchical Process (AHP) to delineate potential hazard zones in the study area. Flood inundation model result from FLO-2D revealed inundation depths between 0 and 5.24 m, an indication of intense flood hazards capable of causing lots of damages. MCDA results were classified into least, low, moderate, high and extreme flood hazard zones, while the classified HAND model include none, very low, low, moderate and high flood hazard zones. The MCDA results revealed that the downstream portions of the basin are mostly susceptible to moderate flood hazard compared to low vulnerability observed majorly in the upriver parts of the catchment. The comparison between the estimated flood depths ranges of 0.3–5.2 m by the FLO-2D model and the HAND model value range of 0–5 m (high flood hazard zone) revealed a strong similarity. In all, areas closed to the river course are highly vulnerable to flooding. The output of this study can serve as policy and decision-making tools for future flood hazard analysis, prevention and reduction plans at the research location.

Understanding coastal flood risk prevention by combining modelling and sketch maps (Mediterranean coast, France)

ABSTRACT An interdisciplinary approach combining modelling and sketch maps was adopted in order to study coastal flooding risk in the town of Leucate on the French Mediterranean coast. Hydrodynamic modelling was used for reference maps. This innovative approach proposed three types of sketch mapping, covering historical coastal flooding, flood hazard areas, and no-flood hazard areas. Only 55% of the respondents agreed to draw at least one sketch map, demonstrating the difficulty of the exercise, and respondent maps show a global underestimation of the risk. The respondents mainly identify the risk of coastal flooding along the seafront (overtopping), but do not take into account potential overflowing on the lagoon side. Locally, experience of recent flooding in a district impacts on the perception of the coastal flooding hazard. The sketch maps were also analysed by considering two variables: district of residence and residential profile. As expected, the results highlight that the people living in the most exposed areas have a better perception of the hazard than those who are less exposed or who do not live in these areas. First- and second-home residents show very similar hazard mapping, however.