Flood Inundation Simulation Research Articles

A hybrid shallow water solver for overland flow modelling in rural and urban areas

This study aims to present an accurate and efficient finite volume approach for overland flow modelling in rural and urban areas through solving the two-dimensional shallow water equations. The proposed approach introduces a hybrid procedure that utilizes the sharpness of discontinuity to identify flow conditions in the entire computational domain, and then a low-accuracy/high-efficiency scheme (the Rusanov scheme) is used in regular flows, whereas a high-accuracy/low-efficiency scheme (the HLLC scheme) is adopted in strong discontinuous flows. Regions that simultaneously adopt the two schemes are artificially specified to diminish numerical unbalances between the two schemes. Model calibration is carried out through three strong discontinuous flow cases with the exact solutions. Model verification is next described by three benchmark cases, including rainfall-runoff around buildings, flash floods towards buildings, and street junction flows. Model efficiency assessment is also conducted to present the numerical efficiency improvement of the proposed approach for various flow conditions. Technical attention is devoted to the numerical performances on local accuracy and global efficiency of the proposed approach. The simulated results indicate that the proposed approach can simulate as accurate as the HLLC scheme with significant reduction on its computational time. How efficient the proposed hybrid approach can reach depends on flow conditions involved. It is more efficient than the HLLC scheme as the portion of strong discontinuous flows in the computational domain is relatively smaller. The proposed approach has proved its accuracy and efficiency for overland flow modeling, and it can also be used together with other speed-up techniques, such as local time stepping and parallelization, to improve its efficiency. Other finite volume schemes can also be utilized to improve the efficiency and accuracy of the proposed approach. Therefore, the solver has considerable potentials as a useful tool in flood inundation simulations.

Simulation of Hurricane Harvey flood event through coupled hydrologic‐hydraulic models: Challenges and next steps

AbstractUsing the 2017 Hurricane Harvey flood event as a test case, this study set up a series of sensitivity analyses to highlight three challenges associated with large‐scale flood inundation modeling, including (a) model parameterization, (b) errors in digital elevation models, and (c) effects of reservoir retention. Driven by radar‐based hourly rainfall data, a series of hydrologic‐hydraulic models including the VIC hydrologic model, RAPID routing model, and Flood2D‐GPU hydrodynamic model are set up over Harris County, Texas, to simulate flood inundation and hazards. The results demonstrate the importance of hydrologic parameters in improving flood modeling. For a large flood event such as Hurricane Harvey, the effect of the initial water depths is insignificant. The Manning's n values may increase the peak water depth by ~1%, the flood extents by 65km2, and the high danger zone by ~6%. On the contrary, the bathymetry correction factors may reduce the flood extent by ~1.4% and the high‐danger zone by ~4%. Reducing the reservoir storage capacity to 1% may increase the flood extent by ~4% and the high‐danger zone by ~17%. This study may provide supporting information to guide and prioritize the development of future high‐performance computing hydrodynamic large‐scale flood simulations.

1D and 2D model coupling approach for the development of operational spatial flood early warning system

Main aim of the paper is to emphasise the advantage of 1 D and 2 D hydrodynamic models coupling in simulating flood inundations using high resolution Digital Terrain Models. The developed flood early warning model was calibrated and validated thoroughly at critical locations using historic observed discharge data and point rainfall data of about 350 stations. The flood inundation simulation model was prepared using flexible mesh approach and compared with the satellite imagery of Radarsat2. 1 D hydrodynamic model was integrated with 2 D hydrodynamic model by standard links for seamless hydrodynamic modelling. It is found that computational time has reduced drastically due to integration of 1 D and 2 D hydrodynamic models. Web-enabled spatial flood early warning system is developed to disseminate flood advisories in real-time. Computed peak discharge is found to be more than 87% accurate with forecast lead time of 52 hours when compared with field measurements subsequently.

A dynamic bidirectional coupled surface flow model for flood inundation simulation

Abstract. Flood disasters frequently threaten people and property all over the world. Therefore, an effective numerical model is required to predict the impacts of floods. In this study, a dynamic bidirectional coupled hydrologic–hydrodynamic model (DBCM) is developed with the implementation of characteristic wave theory, in which the boundary between these two models can dynamically adapt according to local flow conditions. The proposed model accounts for both mass and momentum transfer on the coupling boundary and was validated via several benchmark tests. The results show that the DBCM can effectively reproduce the process of flood propagation and also account for surface flow interaction between non-inundation and inundation regions. The DBCM was implemented for the floods simulation that occurred at Helin Town located in Chongqing, China, which shows the capability of the model for flood risk early warning and future management.

A GIS-Based Simulation Application to Model Surface Runoff Level in Urban Blocks

Simulation of flood inundation in urban areas longer important, given the magnitude of potential loss and disruption associated with non-river based, urban flooding. The complexity of the urban environment and lack of high-resolution topographic and hydrologic data compromise the development and implementation of models. Low impact development (LID) is technical know-how on a collection of sustainable practices that mimic natural hydrological functions including infiltration, evapotranspiration or use of surface runoff. Several studies have been carried out to discuss the impact of urbanization scenarios in reducing the urban flood risk in watershed scale in Sri Lanka. Yet, there is a gap remains in simulating the effectiveness of LID-based planning practices to reduce flood risk with the complex built form scenarios. In such a situation, this study attempts to make a significant contribution to simulate the variations of flood regulation functions under different high-intensive urban development scenarios, particularly focusing on the urban metropolitan regions. The analyses were carried out utilizing SWMM (Storm Water Management Model) which is open-source flood inundation simulation approach with the help of GIS in a more qualitative manner. The simulation results indicate that expanding built form scenarios increase the flood venerability for city functions, increasing inundation duration and LID scenarios able to reduce the surface runoff to reduce flood vulnerability at a significant level. The simulation results had been verified with the real ground situation (mean percentage change < 15.5%) which able to capture the thresholds of built form variation, as well as dynamic land uses and infrastructure supply which can be used as a tool for future planning practices and decision-making.

Unmanned Aerial Vehicle Utilization in Flood Monitoring and Simulation

Recently, the frequency of water disaster occurrence and the scale of damage have increased due to the climate change. However, technology for effectively monitoring the flooding situation and the damage aspect is still insufficient. Since various studies are actively conducted on utilizing unmanned aerial vehicle (UAV) in the field of geospatial information, the utilization of UAV is expected to improve the timeliness and accuracy of flood monitoring. This study conducted a flood situation monitoring at Gap River on July 30, 2020 using UAVs. The comparison between the water boundaries derived from UAV images and hydraulic model simulations (FLUMEN) were performed. Results showed that the water boundaries simulated using FLUMEN only resulted to 2.85% difference with UAV images derived water boundaries. Thus, verifying that the UAV images can be used to provide supplementary data in providing spatial extents of stream variables. This study aims to introduce the technology for performing quick flood monitoring and the possibility of its utilization in flood inundation simulation.

Flood Modelling of Pamba River Using MIKE FLOOD

Flood hazard mapping and flood risk zoning are very effective in the monitoring and risk management of floods. For this flood inundation maps are required. Different computational models are available, such as one-dimensional (1D), two-dimensional (2D) and 1D-2D-coupled model. In this study a coupled 1D-2D hydrodynamic model, MIKE FLOOD was used to simulate flood inundation extent, water levels at different location of the river. MIKE FLOOD is a platform that combines the MIKE 11 and MIKE 21 models into a single modeling framework that is dynamically coupled. Using a coupled approach makes it possible to use the best features of all two versions of software. The study area considered is Pamba river in Kerala which is most effected region in 2018 flood. So flood modelling of Pamba river is necessary. The time series of daily discharge and water level of different gauging station of Centre Water Commission at Kallooppara, Malakkara, Thumpamon and water level data of Thottappalli spillway are used for the study. The SRTM DEM was used to generate the flood model for the period June to August 2010. At the downstream of the river, the maximum water level obtained is 1.48 m in 1D model and water depth obtained is in the range of 0.6 to 1.2 in 2D modelling. The correlation coefficient values ranges 0.52 to 0.96. This study will assist policy makers in the field of water management to achieve effective mitigation step

Effects of the temporal resolution of storm data on numerical simulations of urban flood inundation

The temporal resolution of storm data plays an important role in constructing reliable inundation simulations. The effects of the temporal resolution of storms with different return periods, peak coefficients, and durations on the simulated flood inundation were investigated with a two-dimensional numerical model. After analysing the modelled inundation peak values and occurrence times, which are affected by the temporal resolution of a storm, the following conclusions were obtained: 1) the accuracy of the simulated inundation results in terms of the peak values and shift times of the storm increases as the temporal resolution of the storm increases; 2) for the same temporal resolution of storm, the accuracy of the simulated inundation in terms of the peak values and shift times increases as the storm return period increases, except for the shift time in the second test case investigated; 3) for the same temporal resolution of storm, the accuracy of the simulated inundation in terms of the peak values and shift times of the storm does not display an obvious correlation with the storm peak coefficient and storm duration; and 4) the most suitable temporal resolution of storm is 15 min for obtaining an accurate numerical simulation of urban flood inundation. These results can help researchers understand the key effects of the temporal resolution of storms on urban flood inundation and identify storm temporal resolutions that can produce relatively accurate simulated inundation results, even without high-temporal-resolution data.

Real-time error correction of two-dimensional flood-inundation simulations during rainstorm events

This study develops a real-time error correction model named RTEC_2DIS for two-dimensional (2D) flood-inundation simulations. Inundation depth and flooding area provided by a 2D numerical hydraulic modeling (SOBEK model) are corrected in accordance with real-time observations at specific road-based water-level gauges. The proposed RTEC-2DIS method can estimate the forecast error of inundation depths for various lead times at both gauged grids and ungauged grids within the watershed/basin. By doing so, the real-time correction of the resulting inundation area composed of corrected water-depth forecast at all concerned grids can be achieved by adding the water-depth forecasts to the corresponding forecast errors. In this study, the demonstration of the model is made in the Tainan district in Southern Taiwan under the consideration of the design rainstorm events of specific return periods with a central-peak storm pattern and a real rainstorm event from Typhoon Megi in 2016. The results from the numerical demonstration indicate that the RTEC-2DIS method can effectively reduce the uncertainty in the estimating inundation depth at gauged grids to enhance its correction performance with the percentage of error reduction of 42% in the case of the real rainstorm event. Furthermore, regarding the design events, through the proposed RTEC-2DIS method, the accuracy of the simulated inundation area can be improved by 55%. In summary, the proposed RTEC-2DIS method not only can correct forecasted inundation depths at gauged grids, but also facilitate the accuracy and reliability of the resulting inundation area in accordance with real-time observations recorded at road-based water-level gauges.

Special Issue on SATREPS Myanmar Project Part 2: Development of a Comprehensive Disaster Resilience System and Collaboration Platform in Myanmar

This special issue summarizes the main results of the latter half of a five-year project called SATREPS (Science and Technology Research Partnership for Sustainable Development) supported by Japan International Cooperation Agency (JICA) and Japan Science and Technology Agency (JST). The project title is “Development of a Comprehensive Disaster Resilience System and Collaboration Platform in Myanmar” and it is the first SATREPS project adopted in Myanmar. Yangon Technological University (YTU) is a major counterpart organization and both national and local governmental organizations are working together as strategic partners. In the first half of the project, a database was constructed, composed of important data for assessing urban safety and disaster risk, such as the ground properties, and distribution of buildings, people, and traffic. Using the database, city development model and evaluation models for flood and earthquake risks were developed. In the latter half of the project, combining these two evaluation models, a system was developed for discussing future damage differences due to different urban plans and countermeasures. Furthermore, regarding flood, near-real-time flood inundation simulation system was developed. Related to earthquake disaster, a support system was developed for implementation of efficient countermeasures for both pre- and post-disaster. For infrastructure maintenance, performance monitoring and maintenance methods were proposed. Finally, in order to continue research activities and promote a continuous utilization of project results, a consortium scheme in which industry, government, and academia can work together has been created. We hope that our SATREPS project activities can contribute to proper urban development and improvement of disaster management issues not only in Myanmar but also in other Asian countries.

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.

Temporal Pattern Analysis of Local Rainstorm Events in China During the Flood Season Based on Time Series Clustering

Similar to the rainfall depth, duration and intensity, the temporal pattern is also an important characteristic of rainstorm events. Studies have shown that temporal patterns will influence runoff modelling, flash flood warning thresholds as well as urban and infrastructure flood inundation simulations. In this study, a time series clustering method using dynamic time warping (DTW) as similarity measurement criteria is proposed to analyze rainfall temporal patterns. Compared with the existing approaches, it can better reflect the real rainfall processes. Based on this novel method, five representative temporal patterns were extracted from 13,299 rainstorm events during the flood season in China. Through the analysis of their statistical characteristics, the disaster-causing risks of each temporal pattern were compared. Furthermore, we found that for rainstorm events whose durations are less than 24 h, the rainfall is mainly concentrated in 3 to 6 h, which proposes higher requirements for the design of flood control and drainage projects compared with those using average intensities of 12 or 24 h as design standards. Finally, through regional analysis, we found that the rainfall depth, intensity and peak value are affected by the macroclimate. However, the temporal patterns are not strongly related to the macroclimate but are more likely to be affected by the local climate and topography, which needs further studies at smaller scales.

Damage assessment of infrastructure based on urban flood inundation simulation

Flood is a serious challenge that increasingly produce immense economical and ecological damages in worldwide. Flood simulation is gradually becoming a central focus of the hydrology in recent years. It is worthwhile to combine flood simulation with flood damage to infrastructure. The purpose of this study is to develop an approach for better urabn flood simulation at different return periods and assess the damage of flood to infrastructures in different return period. The approach is organized into four parts: design rainstorm event simulation, runoff simulation, flood inundation simulation and submerged infrastructures extraction. Base on the flood simulation, we draw the flood inundation map of Xuanwu-Qinhuai-Jianye-Gulou-Yuhuatai (XQJGY) region. Results indicated that the transportation infrastructures suffer the largest proportion of flood damage. This study simulates the inundated infrastructure at different return periods, provides a theoretical support for flood risk management.

Three-dimensional urban flood inundation simulation based on digital aerial photogrammetry

Intense storm surge can lead to severe coastal floods. Flood inundation simulation is useful to identify areas that are most vulnerable to severe storm surges and to address potential flooding hazards. In this paper, both 2D and 3D hydrodynamic models are built separately to quantify the flood danger to a coastal city. A digital city model is generated by integrating building information modeling (BIM) and geographic information systems (GIS) technology based on digital aerial photogrammetry for the 3D hydrodynamic model. The results reveal that 2D hydrodynamic assumptions and approximations weaken if the vertical fluctuations are enormous, especially in urban environments. In comparison, a 3D model coupled with high-resolution topographic data can provide a more realistic and accurate result for the complex flow field. Furthermore, a comparison between using the digital city model and a standard digital elevation model (DEM) in a 3D model has been conducted. The flood inundation is simulated step-wise using the standard DEM, while the wave front propagates in a more realistic manner based on high-resolution topography data. Thus, a 3D hydrodynamic model coupled with the digital city model is recommended for urban flood simulation, which is promising to improve the ability of flood prediction and prevention.

Numerical Simulation of Flood Inundation in a Small-Scale Coastal Urban Area Due to Intense Rainfall and Poor Inner Drainage

: This study presents the numerical simulation and analysis of the characteristics of the flood inundation in a small-scale coastal urban area due to the intense rainfall and poor inner drainage from the tidal level rise occurring during a typhoon. The employed numerical model is a two-dimensional finite volume model with a well-balanced HLLC (Harten–Lax–Van Leer contact) scheme. The target area is a coastal urban area downstream of the Gohyun river; which is located in Geoje City of Kyungsangnam Province, Korea. This area was significantly damaged by flood inundation due to the heavy rainfall and significant increase in the tidal level during Typhoon “Maemi”, which occurred in September 2003. The numerical model used in this study is verified using the flood inundation traces observed in the selected urban area. Moreover; the characteristics of the flood inundation based on the change in the river inflow due to the increase or decrease in the intensity of the possible heavy rainfall that may occur in the future are simulated and analyzed.

A Modified Particle Filter‐Based Data Assimilation Method for a High‐Precision 2‐D Hydrodynamic Model Considering Spatial‐temporal Variability of Roughness: Simulation of Dam‐Break Flood Inundation

AbstractThe particle filter‐based data assimilation method is an effective tool to adjust model states based on observations. In this study, we proposed a modified particle filter‐based data assimilation method with a local weighting procedure (MPFDA‐LW) for a high‐precision two‐dimensional hydrodynamic model (HydroM2D) in dam‐break flood simulation. Moreover, a particle filter‐based data assimilation method with a global weighting procedure (PFDA‐GW) for the HydroM2D model was also investigated. The MPFDA‐LW and the PFDA‐GW for the HydroM2D model, respectively, adopted spatially nonuniform and uniform Manning's roughness coefficients. The MPFDA‐LW considering spatial‐temporal variability of Manning's roughness coefficient could significantly improve the performances of the HydroM2D model in simulating water stages at all gauges simultaneously, whereas the PFDA‐GW considering temporal variability of Manning's roughness coefficient could only slightly improve the performances of the HydroM2D model in simulating water stages at a few gauges. The MPFDA‐LW is more suitable for improving the performance of 2‐D hydrodynamic models in flood inundation simulation than the PFDA‐GW.

Residential Flood Loss Assessment and Risk Mapping from High-Resolution Simulation

Since the patterns of residential buildings in the urban area are small-sized and dispersed, this study proposes a high-resolution flood loss and risk assessment model to analyze the direct loss and risk impacts caused by floods. The flood inundation simulation with a fine digital elevation model (DEM) provides detailed estimations of flood-inundated areas and their corresponding inundation depths during the 2016 Typhoon Megi and 2017 Typhoon Haitang. The flood loss assessment identifies the impacts of both events on residential areas. The depth-damage table from surveys in the impacted area was applied. Results indicated that the flood simulation with the depth-damage table is an effective way to assess the direct loss of a flood disaster. The study also showed the effects of spatial resolution on the residential loss. The results indicated that the low-resolution model easily caused the estimated error of loss in dispersed residential areas when compared with the high-resolution model. The analytic hierarchy process (AHP), as a multi-criteria decision-making method, was used to identify the weight factor for each vulnerability factor. The flood-vulnerable area was mapped using natural and social vulnerability factors, such as high-resolution DEM, distance to river, distance to fire station, and population density. Eventually, the flood risk map was derived from the vulnerability and flood hazard maps to present the risk level of the flood disaster in the residential areas.

Flood damage assessment on rice crop in the Stung Sen River Basin of Cambodia

In Cambodia, rice production is important for the majority of rural populations as the main source of income. However, historical extreme flood events, especially the 2011 flood, caused significant damage to rice production due to insufficient flood preparedness and mitigation. To reduce the risk of damage, flood damage assessment is critical for providing essential information about potential risks to support the decision-making process and policy development in flood risk management. In this study, a physically based rainfall–runoff–inundation (RRI) model was used to simulate flood inundation in the Stung Sen River Basin of Cambodia, and then damage to rice crops was estimated based on the simulated inundation depth and duration that resulted from the RRI model. The simulated river discharges were calibrated and validated for 2011 and 2009 flood events, respectively. Indeed, the simulated flood inundation areas were compared with flood maps derived from satellite imagery to check their accuracy. As a result, it was confirmed that these results were reasonable and adequate. In the case of the 2011 flood, a distribution map of rice crop damage was created to represent the potentially affected rice areas at various levels of damage. Furthermore, the total of estimated affected rice areas was found to be close to the reported damage data, with an overlap of 89%. Overall, the preliminary results from this study are expected to be useful for key stakeholders at all levels, especially decision-makers, in planning better risk reduction strategies, for instance, when choosing the appropriate flood control option to cope with future extreme flood events.

An automatic domain updating method for fast 2-dimensional flood-inundation modelling

Flood-inundation modelling is essential for understanding flood dynamics and implementing flood risk management. Despite its increasing demands, it remains computationally expensive to perform 2-D flood-inundation simulations at large scales or fine spatial resolutions. This study presents a simple and novel algorithm for 2-D flood-inundation modelling, called the Automatic Domain Updating method, which dynamically updates the simulation domain of a 2-D flood-inundation model. The method limits the simulation domain where governing equations are solved to flooded areas in each time step by tracking the location of wet and dry interfaces. The proposed algorithm was tested in an actual river basin for different types of flooding. The results show that the ADU method regulates the simulation domain to flooded areas and slashes the computational time for grid-based 2-D flood-inundation simulations typically by 5%–20%, with correspond to the ratio of flooded area to the whole simulation domain.

Flood Inundation Mapping of the Sparsely Gauged Large-Scale Brahmaputra Basin Using Remote Sensing Products

Sustainable water management is one of the important priorities set out in the Sustainable Development Goals (SDGs) of the United Nations, which calls for efficient use of natural resources. Efficient water management nowadays depends a lot upon simulation models. However, the availability of limited hydro-meteorological data together with limited data sharing practices prohibits simulation modelling and consequently efficient flood risk management of sparsely gauged basins. Advances in remote sensing has significantly contributed to carrying out hydrological studies in ungauged or sparsely gauged basins. In particular, the global datasets of remote sensing observations (e.g., rainfall, evaporation, temperature, land use, terrain, etc.) allow to develop hydrological and hydraulic models of sparsely gauged catchments. In this research, we have considered large scale hydrological and hydraulic modelling, using freely available global datasets, of the sparsely gauged trans-boundary Brahmaputra basin, which has an enormous potential in terms of agriculture, hydropower, water supplies and other utilities. A semi-distributed conceptual hydrological model was developed using HEC-HMS (Hydrologic Modelling System from Hydrologic Engineering Centre). Rainfall estimates from Tropical Rainfall Measuring Mission (TRMM) was compared with limited gauge data and used in the simulation. The Nash Sutcliffe coefficient of the model with the uncorrected rainfall data in calibration and validation were 0.75 and 0.61 respectively whereas the similar values with the corrected rainfall data were 0.81 and 0.74. The output of the hydrological model was used as a boundary condition and lateral inflow to the hydraulic model. Modelling results obtained using uncorrected and corrected remotely sensed products of rainfall were compared with the discharge values at the basin outlet (Bahadurabad) and with altimetry data from Jason-2 satellite. The simulated flood inundation maps of the lower part of the Brahmaputra basin showed reasonably good match in terms of the probability of detection, success ratio and critical success index. Overall, this study demonstrated that reliable and robust results can be obtained in both hydrological and hydraulic modelling using remote sensing data as the only input to large scale and sparsely gauged basins.