Flood Inundation Area Research Articles

Quantitative assessment of flood risk with evaluation of the effectiveness of dam operation for flood control: A case of the Bago River Basin of Myanmar

Because property damage and loss of life owing to floods have increased in many countries in recent years, accurate assessment of flood risk is urgently needed for effective flood management. Improving the assessment of flood risk requires considering the impact of dam operation for flood control because dams and reservoirs play important roles in the assessment of flood hazards and associated damage. However, the impact of dam operation on flood hazards and associated damage was not considered well in previous assessments of flood risk. This paper focused on the quantitative assessment of flood hazard and risk, including the effectiveness of dam operation for flood prevention. The grid-based approach integrating the following was applied for analysis: (i) a hydrological–hydraulic model, (ii) a method considering the dam operation for flood control, and (iii) an assessment of flood damage. To assess the risk, flood characteristics were computed using the rainfall–runoff–inundation hydrological–hydraulic model, and flood damage was estimated by integrating the flood characteristics, flood damage curves, exposure characteristics, and property values. The risk was assessed by focusing on flood damage to residential buildings and assets and agricultural sectors for the largest recent floods and flood events with different return periods. This study considered the Bago River Basin of Myanmar. Results show that the dam operation for flood control in the study area reduces the flood inundation area by approximately 10% and flood damage to buildings, assets, and agriculture by approximately 40%, 60%, and 10%, respectively.

Applicability Analysis of 2-D Model for Evacuation Map to Establish Dam Emergency Action Plan

Recent instances of “excessive disasters,” which can be characterized as unprecedented and catastrophic, cause great damage and loss of life. One such incident is dam failure, which significantly affects downstream regions. Therefore, it is imperative to select flood inundation areas and establish EAP in advance. In addition, to prevent possible damage due to dam failure, flood wave analysis and evacuation map should be based on accurate hydraulic analysis. Accordingly, this study highlights the challenges in existing hydraulic analysis and suggests a method of establishing EAP by applying the 2-D model. Further, it compares the applicability of establishing EAP between 1-D and 2-D models using the Sandae reservoir incident, the actual collapse case. Consequently, it found that compared to the 1-D model, flood inundation analysis using the 2-D model can accurately reflect on topography such as roads and buildings and provide a wide range of information such as flood depth and flood velocity distribution. Thus, this study is expected to recommend an efficient method of selecting flood inundation areas and establishing informative EAP.

Inundation Analysis of the Oda River Basin in Japan during the Flood Event of 6–7 July 2018 Utilizing Local and Global Hydrographic Data

During the first week of July 2018, widespread flooding caused extensive damage across several river basins in western Japan. Among the affected basins were the Mabicho district of Kurashiki city in the lower part of the Oda river basin of the Okayama prefecture. An analysis of such a historical flood event can provide useful input for proper water resources management. Therefore, to improve our understanding of the flood inundation profile over the Oda river basin during the period of intense rainfall from 5–8 July 2018, the Rainfall-Runoff-Inundation (RRI) model was used, with radar rainfall data from the Japan Meteorological Agency (JMA) as the input. River geometries—width, depth, and embankments—of the Oda river were generated and applied in the simulation. Our results show that the Mabicho district flooding was due to a backwater effect and bursting embankments along the Oda River. The model setup was then redesigned, taking into account these factors. The simulated maximum flood-affected areas were then compared with data from the Japanese Geospatial Information Authority (GSI), which showed that the maximum flood inundation areas estimated by the RRI model and the GSI flood-affected area matched closely. River geometries were extracted from a high-resolution digital elevation model (DEM), combined with coarser resolution DEM data (global data), and then utilized to perform a hydrological simulation of the Oda river basin under the scenarios of backwater effect and embankment failure. While this approach produced a successful outcome in this study, this is a case study for a single river basin in Japan. However, the fact that these results yielded valid information on the extent of flood inundation over the flood-affected area suggests that such an approach could be applicable to any river basin.

New Empirical Model Using Landscape Hydric Potential Method to Estimate Median Peak Discharges in Mountain Ungauged Catchments

Designing hydraulic structures, such as culverts, bridges, weirs, and check dams, while planning new flood inundation areas, needs correct assessment of design discharges. In gauged catchments with long time series of discharges, statistical methods are commonly used based on fixed theoretical distributions and on empirical distributions. However, in ungauged catchments, this approach is not possible. In addition to more advanced methods, which are used today, e.g., rainfall–runoff models, much more simple approaches are still needed based on regionalization and empirical models. Thus, the objective of this work is to develop a new empirical model for calculating peak discharge expressed as the median of annual peak discharge (QMED). The innovative aspect of this paper is the use of a new parameter, named landscape hydric potential (LHP), as a descriptor of water storage in catchments. LHP has a crucial role as the descriptor of water storage in catchment and, thus, it has an influence on forming discharges. The work was done in the Upper Vistula basin in the Polish Carpathians. This study was carried out in mountain catchments located in the Upper Vistula basin, in the south part of Poland in in the Polish Carpathians. Results show that the proposed model could provide appropriate calculations in changing climate conditions, as well as when land use is changed. The proposed model is simple and effective; for calculating QMED, it needs only two parameters: catchment area and LHP. Since the model has a significant and high correlation coefficient, it could be used for assessing of QMED in ungauged mountain catchments. The determined form of the empirical equation finds application in the entire Upper Vistula basin, for catchments with a surface area from 24 km2 up to 660 km2.

Developing Flood Inundation Map Using RRI and SOBEK Models: A Case Study of the Bago River Basin, Myanmar

The Bago River Basin in Myanmar is highly flood-prone. To develop a flood forecasting system, an inundation map of the Bago River Basin is required. This study applied the Rainfall-Runoff-Inundation (RRI) model and SOBEK model to simulate flood discharges and inundation to determine the model most suitable for analysis of the study basin in terms of user friendliness, cost, type of output, and correlation between simulated and observed data. In this study, five flood events were selected to calibrate and validate the models, using discharge data measured at Bago station. The Nash–Sutcliffe efficiency (ENS) and coefficient of determination (R2) were used to evaluate the performance of the models. The simulated flood inundation area was validated with satellite images. According to the comparison, the SOBEK model is more accurate than the RRI model, and the simulated and observed discharges are closely related. However, when the calculation time and cost are included in the consideration, the RRI model is preferable, as it is faster and freely available. For the Bago River Basin, the RRI model is efficient in predicting the potential flood duration and areas of inundation in near-real time, whereas the SOBEK model is useful for floodplain management. This study shows that the RRI and SOBEK models are applicable to any basin in Myanmar that is similar to the Bago River Basin.

Effect of the Nanjung tunnel construction against flood inundation in Dayeuhkolot

Floods that occur in the Upper Citarum River Basin are generally caused by flood discharge that exceeds the capacity of the Citarum River. Dayeuhkolot is one of the areas that is often flooded in the Upper Citarum River Basin. The Citarum River Authority has made efforts to handle floods in Upper Citarum by constructing the Nanjung Tunnel. When floods occur, Nanjung Tunnel will function to divide the water partially into the tunnel and through the Curug Jompong. SOBEK Model was utilized to find out the effect of the Nanjung Tunnel against flood inundation in Dayeuhkolot. This flood modelling also accommodates other efforts that have been made by BBWS Citarum such as the Cieunteung Pond and Cisangkuy Floodway. A 20-year return period was used for modelling. From the results of the modelling, it was found that difference in flood inundation area with and without the Nanjung Tunnel was 12.5 Ha or 3.5 %, with the duration of the overall inundation being reduced by 4.9 hours. Nanjung Tunnel does not have a great influence on the area of inundation, but it has an effect on reducing the duration of floods that occur in Dayeuhkolot.

Flood Inundation Mapping of Cempaka Tropical Cyclone Effect in Gunung Sewu Karst Landscape Using Sentinel 1

Cempaka Tropical Cyclone (TC) occurred on November 27, 2017, at the Indian Ocean and induced high rainfall leading to flooding in the southern part of Java island. One of the most affected areas is the karst landscape of Gunung Sewu. This study aims to identify flood inundated areas caused by the Cempaka TC in the Gunung Sewu karst landscape through satellite imagery of Sentinel 1B. Sentinel 1B imageries were used to extract the flood inundation area through the processing of random forest (RF) and the thresholding value (TV). A significant difference in flood inundated area was obtained between RF and TV, where RF shows a result of 526.07 ha of the total inundated area while the TV shows a result of 105.46 ha. However, both methods show the same sequence for three regencies with the highest total flood inundated area (Gunungkidul, Pacitan, and Wonogiri) and show the same range of each flood inundated area (0-0.5 ha). This distribution of flood inundated area can be used by policymakers as a basis for spatial planning in Gunung Sewu karst landscape.

A Fundamental Study on the Effect of Flood Evacuation Plan with the Primary Goal of Evacuating from Flood Inundation Area

A Fundamental Study on the Effect of Flood Evacuation Plan with the Primary Goal of Evacuating from Flood Inundation Area

The prediction of flood damage in coastal urban areas

The increase of impervious surfaces in the urban area triggers a flood. A flood occurs area with a dense population that will result in a lot of damage. The flood simulation itself is not adequate to calculate the flood damage, as it only shows the flood depth and extent. It needs the capability of mapping software to map the vulnerable area. Accordingly, the research study’s aim is to propose the methodology to predict the flood damage on the coastal urban area by combining the flood simulation model with GIS mapping software. MIKE FLOOD and ArcGIS were used to represent the flood simulation model and mapping software. The flood depth and inundation area were calculated with MIKE FLOOD; meanwhile, the residential house was mapped using ArcGIS. Both of MIKE FLOOD and ArcGIS were then combined to obtain the flood depth in each residential house. Moreover, to value the flood damage in monetary terms, the depth-damage curve and average house prices were applied. The result shows that the majority of the inundation caused by riverine flood and coastal area is the place where the largest inundation area occurs. As the flood appears in a residential area, the flood damage of the residential building in terms of annual average damage (AAD) was obtained with the amount of $8,716,227.67 calculated from six AEPs (50%, 20%, 10%, 5%, 2%, and 1%).

Flood Plain Mapping and Hazard Assessment of Muga River by Using ArcGIS and HEC-RAS Model Upper Blue Nile Ethiopia

Flood happens repeatedly and is a common phenomenon in Ethiopia causing a lot of losses to human lives as well as damage to property. The majority of flood disasters’ victims are people living in and nearby stretch of floodplains. It results direct or indirect loss of agricultural productivity, infrastructure, and disruption of transportation access and services. The objective of this study was to analyze flood inundation area mapping and Hazard Assessment of Muga River. Flood generating factors, i.e. slope, elevation, rainfall, drainage density, land use, and soil type were rated and combined to delineate flood hazard zones using a multi-criteria evaluation technique in an ArcGIS environment. The flooded areas along the Muga River have been mapped based on highest flows for different return periods using the HEC-RAS model, ArcGIS for spatial data processing and HEC-GeoRAS for interfacing between HEC-RAS and ArcGIS. The areas along the Muga River simulated to be inundated for 5, 10, 25, 50 and 100 years return periods. The flooded areas along the Muga River are 18 km2, 21 km², 26 km², 34 km² and 43 km² for 5, 10, 25, 50 and 100 year return periods, respectively. Proper land use management and afforestation, is significant to reduce the adverse effects of flooding particularly in the low-lying flood prone areas. The result of this study will helps the concerned bodies to formulate develop strategies according to the available flood plain mapping and hazard to the area.

Change in Population within Estimated Flood Inundation Areas in Japan and its Prefectures

Change in Population within Estimated Flood Inundation Areas in Japan and its Prefectures

SIMULASI KERUNTUHAN BENDUNGAN BILI-BILI KABUPATEN GOWA PROVINSI SULAWESI SELATAN

The extreme weather that occurred on January 22-24, 2019 in the Makassar city and surrounding areas caused massive flooding in the downstream area of ​​the Bili-Bili DAM which covered 5 districts and cities, namely Gowa Regency, Makassar City, Jeneponto Regency, Maros Regency, and Selayar Regency. There 6757 people were displaced and tens of hectares of rice fields and housing were inundated. As a form of evaluation in the context of disaster mitigation efforts if similar or larger events occur in the future, it is very important to do a floods simulation to mapping which areas will be affected by flood inundation if the Bili-Bili DAM collapses. The software used to simulate flooding in this study is HEC-RAS 2D. The object of research is focused in the city of Makassar which is a densely populated city center and other vital objects. The parameters analyzed are the distribution of flood inundation area and the depth of flood inundation. Simulation results that have been calibrated will be used as a reference for disaster mitigation planning.

Assessment of Flood Hazard and Agriculture Damage Under Climate Change in the Bagmati River Basin of Nepal

Assessment of flood hazard and damage is a prerequisite for flood risk management in the river basins. The mitigation plans for flood risk management are mostly evaluated in quantified terms as it is important in decision making process. Therefore, analysis of flood hazards and quantitative assessment of potential flood damage is very essential for mitigating and managing flood risk. This study focused on assessment of flood hazard and quantitative agricultural damage in the Bagmati River basin including Lal Bakaiya River basin of Nepal under climate change conditions. Flood hazards were simulated using Rainfall Runoff Inundation (RRI) model. MRI-AGCM3.2S precipitation outputs of present and future climate scenarios were used to simulate flood hazards, flood inundation depth, and duration. Flood damage was assessed in the agricultural sector, focusing on flood damage to rice crops. The flood damage assessment was conducted by defining flood damage to rice crops as a function of flood depth, duration, and growth stage of rice plants and using depth-duration-damage function curves for each growth stage of rice plants. The hazard simulation and damage assessment were conducted for 50- and 100-year return period cases. The results show that flood inundation area and agricultural damage area may increase in the future by 41.09 % and 39.05 % in the case of 50-year flood, while 44.98 % and 40.76 % in the case of 100-year flood. The sensitivity to changes in flood extent area and damage with the intensity of return period was also analyzed.

STUDI PEMETAAN DAERAH GENANGAN BANJIR DAS SEI KAMBING DENGAN SISTEM INFORMASI GEOGRAFIS

<p><em>Sei Sikambing River Basin is one of the Sub Das of Deli River which has an important role in water requirement in Medan City. Rainfall with high intensity is supported by changes in land use causing floods which reach 0.6 m to 1 m from river banks. The purpose of this study was to map the Sei Kambing River basin flood inundation area as information to the public in disaster mitigation efforts. The scope of this research is to analyze the maximum daily rainfall with a return period of 2 to 100 years, analyze flood discharge with a return period of 2 to 100, analyze flood water levels with HECRAS software, and spatially map flood inundation areas with GIS. The results showed that the return flood rate of the Sikambing watershed with a 25-year return period of 211.94 m<sup>3</sup>/s caused the flood level of the Sikambing watershed to be between 1.7 m to 3.7 m. The Sikambing watershed flood inundation area reached an area of 1.19 Km<sup>2</sup> which resulted in the impact of flooding on 5 sub-districts in Medan, namely Medan Selayang District, Medan Sunggal, Medan Petisah, Medan Helvetia, and West Medan.</em><em></em></p>

LONG TERM CHANGES IN FLOODING AROUND GIFU CITY

Abstract. Heavy rainfall within a short period and consequent high river discharge are results in floods which subsequently creates huge infrastructure problems for areas, such huge economic deficits in production as well as damages to existing property and goods, even loss of human lives. In about hundred years ago the flat-land around the Kiso Three Rivers system (the catchment areas of the Kiso River, Nagara River, and Ibi River are called the Kiso Three River system) included Gifu City, Gifu Prefecture of Japan, was frequently damaged by inundation after heavy rainfall. Our research aims to evaluate flood risk changes by river improvement in the Kiso Three River system fin the past hundred years. For that reason, we simulated in several times on flood inundation in the large, medium and low scale case in the urban area of Gifu city with 2D flood inundation model, and compared the distribution of flood depth. The results, the flood inundation area in urban area for small scale flood disaster dramatically is reduced from 3.82 km2 in the past time to 0.48 km2 in the current time with the progress of river infrastructure improvement. However flooded area in urban area for large and middle scale disaster show the almost same. It is suggested that flood risks in urban area are dramatically improved for only small disaster.

GIS-BASED MAPPING OF ESTIMATED FLOOD INUNDATION AREA, GEOMETRICAL ASPECT

Abstract. A full processing chain for inundation modelling/mapping is implemented in different specialised software like HEC-RAS or Flood Modeller. Alternatively, inundation water level can be estimated separately, and then can be mapped in desktop (universal) Geographic Information System (GIS) software. Last approach can be demanded in a complex already-formed GIS-based mapping processing chains, when inundation area mapping appears only as a step of analysis and mapping technology. This context is usual for cadastral accounting of inundation areas. However, such a processing chain have a lack of computation tools, as currently used desktop GISs (e.g., QGIS, ArcGIS, etc.) capable originally to map only a lake-type inundation areas (certainly, in the case of regular software assembly), while along-the-river inundation should have water surface sloping along the river body. Addressing to the filling the gap of along-the-river inundation mapping in desktop GIS software, we have developed an approach to mapping of river-type inundation area, and implemented it in a test mode to support cadastral accounting of river flood inundation areas. The approach is based upon geometrical modelling of the water surface only, and is not concerned with consideration of hydrogeological conditions and ground water regime. Being simplified, this technique may be rough tool for the cases when hydrogeological aspect have to be respected, however it is simple for implementation and is useful when estimating topography impact only.

QUANTITATIVE ASSESSMENT OF RICE CROP DAMAGE POST TITLI CYCLONE IN SRIKAKULAM, ANDHRA PRADESH USING GEO-SPATIAL TECHNIQUES

Abstract. Mapping the extent of damage due to natural calamities remains one of the thrust areas in monitoring resource inventory through geo-spatial techniques. The effect of the cyclone ‘Titli’ and heavy rains during first fortnight of October 2018 in Srikakulam district, Andhra Pradesh State has been demonstrated using geo-spatial technology in terms of flood inundated rice area and corresponding yield and production loss. The pre- and post-cyclone (5 and 13 October 2018) flood inundation maps were generated using Sentinel-1A and TerraSAR-X Synthetic Aperture Radar (SAR) data respectively. The pre-cyclone rice area estimates were derived from multi-temporal Sentinel-1A SAR data, while yield forecast is based on the combination of satellite observations and yield simulation using ORYZA crop growth model. An intensive ground truth data collection had been carried out for the validation of satellite-derived rice area estimation of pre-cyclone event. An accuracy assessment has been carried out for district, mandal and village level. An overall accuracy of 96% with kappa coefficient 0.92 has been achieved. With the help map flood inundation and rice area maps, mandal-wise flood affected rice area and corresponding yield loss have been estimated. The post-cyclone ground truth data had been collected for quantitative assessment of crop damaged area. An overall accuracy of the flood affected rice map was 85% with kappa coefficient 0.70. It was estimated that rice crop damage assessment with SAR data indicated 53312 ha out of 205174 ha were affected and corresponding estimated yield as well as production are 0.8 t/ha and 189160 t respectively.

MODIS-Based Investigation of Flood Areas in Southern Cambodia from 2002–2013

In Cambodia and the Vietnamese Mekong Delta, floods commonly occur during the rainy season, and a better understanding of their spatio-temporal distribution is important for both disaster prevention and the improvement of agricultural production. This study investigated spatio-temporal flood inundation and land cover change from 2002 to 2013 in the southern part of Cambodia using Terra satellite on-board Moderate Resolution Imaging Spectroradiometer (MODIS) images. The algorithm for flood inundation detection, WFFI (Wavelet-based Filter for detecting spatio-temporal changes in Flood Inundation) was used, and the parameters were modified to fit the present study. The estimated inundation areas were validated using eight Landsat images. In a comparison between the original and modified WFFIs, the modified WFFI (70–96%) exhibited better accuracy than the original WFFI (30–70%). Overall, the temporal change in the flood inundation area presented a decreasing trend, and a link to the in-situ observed water level showed a decreasing trend during the rainy season. Furthermore, the estimated flood inundation exhibited a significant delay since 2008. Based on the yearly land cover MODIS product, the permanent water body and wetland areas decreased, whereas the cropland areas increased. This was as a result of increased agricultural productivity. However, water shortage was the major obstacle to increasing agricultural productivity, and it also had a negative impact on aquatic ecology, such as fish spawning grounds.

Interaction of a dam-break wave with an obstacle over an erodible floodplain

Abstract Because of climate change, flood-prone areas are more and more frequently exposed to potential casualties and damage. The capability of the flow to carry relevant quantities of sediments during these critical events adds to the further complexity of the resulting scenarios. The interaction between the flow and the obstacles in flood-inundated areas contributes to an increase in the hazard level and constitutes a relevant concern in the framework of risk analysis. Despite this relevance, the existing literature on the topic is relatively scarce, especially for the estimation of the forces acting on rigid obstacles in the presence of a mobile bed. In the present paper, a recent two-phase shallow-water morphodynamical model, particularly suited for the analysis of fast geomorphic transients, is applied for the numerical simulation of the propagation of a dam-break wave over an erodible floodplain in the presence of a rigid obstacle. The geometry of the test-case is inspired by a recent fixed-bed study reported in the literature, for which extensive experimental and numerical data concerning the flow field and the dynamic loading against the obstacle are available. Results of the numerical simulations contribute to highlight the effects of the obstacle on the changes in the bottom topography.

Assessing flood disaster impacts in agriculture under climate change in the river basins of Southeast Asia

This study focused on flood damage assessment for future floods under the impact of climate change. Four river basins of Southeast Asia were selected for the study. They included the Pampanga River Basin (PRB) in the Philippines, the Solo River Basin (SRB) in Indonesia, the Lower Mekong River Basin (LMRB) in Cambodia and Vietnam, and the Chao Phraya River Basin (CPRB) in Thailand. Flood damage to rice crops was assessed by flood damage functions considering flood depth and duration and the growth stage of rice plants. Flood characteristics such as flood depth, duration, and distribution were computed using the rainfall–runoff–inundation model to assess flood hazards under the present and future climatic conditions produced by MRI-AGCM3.2S. The damage assessment methodology for rice crops employed in this study was verified using data on past flood events. Then, flood damage assessment was conducted for both the present climate (1979–2003) and future climate (2075–2099) conditions, using MRI-AGCM3.2S precipitation datasets. Flood damage was assessed for worst cases chosen from each climate period and for floods of 50- and 100-year return periods with different rainfall patterns chosen from each climate scenario. The results of flood hazard and damage assessment show that the flood inundation area for a 100-year flood may increase in the future by 20% in PRB; by 66% in SRB; by 27% in LMRB; and by 27% in CPRB. The flood damage area of paddy fields for a 100-year flood may also increase in the future by 16% in PRB; by 55% in SRB; by 23% in LMRB; and by 13% in CPRB.