Digital Elevation Models (DEMs) play a significant role in hydraulic modeling and flood risk management. This study initially investigated the effect of Unmanned Aerial Vehicle (UAV) DEM resolutions, ...ranging from 1 m to 30 m, on flood characteristics, including the inundation area, mean flow depth, and mean flow velocity. Then, the errors of flood characteristics for global DEMs, comprising ALOS (30 m), ASTER (30 m), SRTM (30 m), and TDX (12 m) were quantified using UAV DEM measurements. For these purposes, the HEC-RAS 2D model in steady-state conditions was used to simulate the flood with return periods of 5- to 200 years along 20 km reach of Atrak River located in northeastern Iran. Results indicated when UAV DEM resolution decreased from 1 m to 30 m, inundation area and mean flow depth increased 17.0% (R2 = 0.94) and 10.2% (R2 = 0.96) respectively, while mean flow velocity decreased 16.8% (R2 = −0.94). Validation of the hydraulic modeling using the modified normalized difference water index demonstrated that the HEC-RAS 2D model in conjunction with UAV DEM simulates the flood with ⁓92% accuracy. Comparing the global DEMs with UAV DEM showed that the root mean square error (RMSE) values of the flow depth for ASTER, SRTM, ALOS, and TDX DEMs were 1.77, 1.12, 1.02, and 0.93 m, and the RMSE values of the flow velocity for the same DEMs were 0.81, 0.66, 0.55, and 0.47 m/s, respectively. Furthermore, TDX DEM with a 6.15% error in the inundation area was the nearest to UAV measurements. Overall, TDX DEM revealed a better performance in hydraulic modeling of the fluvial flood characteristics. Hence, it is recommended for environments where high-resolution topography data is scarce. The results of this study could potentially serve as a guideline for selecting global DEMs for hydraulic simulations.
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•An Unmanned Aerial Vehicle (UAV) DEM with 1 m resolution was used to simulate the flood with different return periods.•UAV DEM measurements were used as reference data for the accuracy assessment of global DEMs.•HEC-RAS 2D model in conjunction with UAV DEM simulates the flood with ⁓92% accuracy.•TDX DEM indicated higher accuracy for modeling fluvial flooding among other global data sources.
•A suite of low-complexity models was compared with a hydrodynamic model.•39 model configurations with three flood events and four terrain setups were tested.•National Water Model data were processed ...to generate boundary conditions.•All models produced nearly similar inundation extents with few discrepancies mostly in steep areas.•Depth simulations by low-complexity models were sensitive to levee or bathymetry.
The objective of this study is to compare two new generation low-complexity tools, AutoRoute and Height Above the Nearest Drainage (HAND), with a two-dimensional hydrodynamic model (Hydrologic Engineering Center-River Analysis System, HEC-RAS 2D). The assessment was conducted on two hydrologically different and geographically distant test-cases in the United States, including the 16,900 km2 Cedar River (CR) watershed in Iowa and a 62 km2 domain along the Black Warrior River (BWR) in Alabama. For BWR, twelve different configurations were set up for each of the models, including four different terrain setups (e.g. with and without channel bathymetry and a levee), and three flooding conditions representing moderate to extreme hazards at 10-, 100-, and 500-year return periods. For the CR watershed, models were compared with a simplistic terrain setup (without bathymetry and any form of hydraulic controls) and one flooding condition (100-year return period). Input streamflow forcing data representing these hypothetical events were constructed by applying a new fusion approach on National Water Model outputs. Simulated inundation extent and depth from AutoRoute, HAND, and HEC-RAS 2D were compared with one another and with the corresponding FEMA reference estimates. Irrespective of the configurations, the low-complexity models were able to produce inundation extents similar to HEC-RAS 2D, with AutoRoute showing slightly higher accuracy than the HAND model. Among four terrain setups, the one including both levee and channel bathymetry showed lowest fitness score on the spatial agreement of inundation extent, due to the weak physical representation of low-complexity models compared to a hydrodynamic model. For inundation depth, the low-complexity models showed an overestimating tendency, especially in the deeper segments of the channel. Based on such reasonably good prediction skills, low-complexity flood models can be considered as a suitable alternative for fast predictions in large-scale hyper-resolution operational frameworks, without completely overriding hydrodynamic models’ efficacy.
Abstract
Open‐source, satellite‐based digital elevation models (DEMs) are widely used for flood modeling. However, studies on effectiveness of these DEMs in depicting local‐level flood processes are ...limited. This study generated a high‐resolution digital terrain model (DTM) based on unmanned aerial vehicle (UAV) photogrammetry and used in a two‐dimensional (2D) hydrodynamic model (HEC‐RAS) to simulate the flood processes in a floodplain environment of the Jamuna River in northern Bangladesh. The effectiveness of a few satellite‐based DEMs was also compared with this DTM by using the DEMs in the same hydrodynamic model. Field data for two flood seasons were collected to develop the model. The results indicate that the 2D model with UAV‐based DTM provides the flood parameters, such as flood arrival time, depth, duration and extent, better than those from the satellite‐based DEMs. Of the open‐source DEMs, the FABDEM and the WorldDEM™ have the least errors and provide better results compared to the SRTM30, ALOS PALSAR, and ASTER DEMs. The UAV technique with ground control points and field measurements for the tree‐canopy and water areas is very useful in generating a fit‐for‐purpose DTM. The findings of this study would be useful for terrain generation and DEM selection for local‐level flood modeling elsewhere.
Jakarta is prone to pluvial, fluvial, and coastal flooding due to its geographical location and topography. In response to this problem, the Indonesian government has implemented several master ...plans, including the National Capital Integrated Coastal Development (NCICD). This ongoing program encompasses the construction of coastal and river embankment that stretch all over the coast of Jakarta. Since many coastal areas in Jakarta are residential or industrial, evaluating this performance of embankment has become crucial for effective flood management. The findings of this research can also support the development of other locations where NCICD embankment plan and enhance coastal resilience. Therefore, this research assessed the effectiveness of coastal and river embankment at Cengkareng Drain, a vital floodway in Jakarta, during extreme events that occur simultaneously. To simulate flooding events, two-dimensional HEC-RAS features were used to numerically calculate the area and depth of inundation. The simulation required geometry, terrain, land cover, and unsteady flow data. For the flow boundary conditions, a 100-year design rainfall, HHWL (Highest High Water Level), and 100-year design wave were considered to represent estuary conditions accurately. The simulation result showed that the maximum water level influenced by these factors was +3.145 mMSL, while the planned embankment top elevation was +3.40 mMSL. Furthermore, without the NCICD embankment, the simulation showed an inundation area of 1212.37 ha, which was reduced to 1111.22 ha after their implementation, leading to a decrease of 101.15 ha. This reduction significantly decreases potential damage to property and infrastructure, particularly in densely populated areas. The simulation also showed a reduction of 86.49 hectares or 66.22% in the inundation area with a depth exceeding 1 meter. These findings demonstrate the effectiveness of embankment in reducing the inundation area without any overtopping incidents.
Flood simulation with two-dimensional hydrodynamic models is subject to different sources of uncertainties in model configuration, boundary conditions, and model parametrization. HEC-RAS 2D is a ...widely used hydrodynamic model. Here, we assess the sensitivity of the HEC-RAS 2D to its configuration factors and parameters. We evaluate the impacts of different model configuration factors, including the floodplain and channel roughness coefficients, terrain and mesh size, as well as river boundary conditions on the dynamic of water levels, maximum water level, and flood extent, and determine the importance of these contributing factors for reliable flood inundation modeling using both variogram and variance-based analyses. For our case study, we found that depending on the perturbation scale, the performance measure, and the predicted output, the sensitivity to input factors changes. While for simulation of water level dynamics, the DEM and mesh resolutions are the most important factors, for flood extent mapping the floodplain roughness coefficient and the upstream boundary condition are the key factors. In addition, our analyses indicated that for a reliable simulation of maximum flood water level, modelers need to spend resources on the calibration of floodplain roughness coefficient while using fine DEM and mesh resolutions. Here, we also investigate the role of computational time interval and mesh resolution on the model's run time and accuracy. Our results suggested that reducing the computational time interval has minimum impact, as it increases the model run time without much improving the model accuracy.
•Variance and Variogram-based Global Sensitivity Analyses of the HEC-RAS 2D model are presented.•For simulations of water level dynamics, DEM resolution and Mesh Resolution are identified to be the most influential factors.•Floodplain roughness coefficient and boundary condition play a significant role in flood extent prediction.•DEM resolution, Mesh Resolution, and Floodplain roughness coefficient are the key factors in the maximum water level prediction.
A simulation was carried out in the Santa Catarina River watershed, located in the State of Nuevo Leon, Mexico, to study flood patterns and velocity maps during the occurrence of Hurricane Alex in ...June-July 2010. To conduct this simulation, a two-dimensional model of the Santa Catarina River Watershed was employed using the HEC-RAS software. The model was driven by Multisensor grid precipitation data as input. Land cover and soil layers were utilized in order to obtain various parameters within the watershed, such as Curve Number, Manning Number, Abstraction Ratio, Infiltration Rate, and Percent of Impervious Land. The simulated water levels were calibrated by comparing them with observed values at the Cadereyta Hydrometric Station, which is located near the city of Monterrey. The utilization of the HEC-RAS two-dimensional model combined with Multisensor grid precipitation demonstrates that this particular model is easy to set up and is user-friendly. Moreover, the model exhibits stability and possesses the ability to accurately simulate flood patterns and velocity maps within the watershed.
Keywords: Floodmap, HEC-RAS 2D, Mexico, Monterrey, MRMS-QPE.
As one of the most devastating tropical storms, 2017 Hurricane Harvey caused severe flooding and damage in Houston, Texas. Besides enormous rainfall amount, land subsidence might be another ...contributing factor to the Harvey flood. However, few studies have numerically quantified the evolvement of land subsidence over decades, largely due to the lack of reliable methods to realistically estimate land subsidence both continuously and at high spatial resolution. Therefore, this study aims to investigate retrospective changes of regional topology due to 117 years (1900 to 2017) of land subsidence and the consequent impacts on flood inundation. Based on continuous land subsidence, we conduct a series of simulations on the 2017 Hurricane Harvey in Brays Bayou, Texas using a hydrodynamic/hydraulic model. The results indicate that the overall change of flood depth caused by land subsidence is relatively minor with the flood water deepened by six centimeters per one meter of subsided land at the worst impacted location. The impact from land subsidence on flood depth exhibits strong nonlinearity in time, where effects from previous land subsidence hotspots could be altered by later continuing land subsidence. Spatially, changes in flood depth due to the land subsidence are not only heterogeneous but mixed with coexisting increased and reduced flood depths. The results of this study improve the understanding of the dynamic evolvement of flood inundation due to continuous land subsidence so that better planning can be initiated for sustainable urban development for coastal communities, which is imperative under ongoing climate change and sea level rise.
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•Retrospective land subsidence of 117 years is investigated with respect to the impact on flood inundation.•Hydrodynamic simulation reveals the impacts from land subsidence regarding flood depth, inundation extent, and flow velocity.•The effects of land subsidence on flooding are not only heterogeneous but even mixed with both positive and negative impacts.
The sustainable development of coastal peri-urban areas is associated with the awareness of the local vulnerability to natural disasters, such as flood hazards. In ungauged basins, statistical and ...modelling approaches combined with geographic information systems have been widely used for the evaluation of different scenarios. In the current study, a multicriteria decision analysis (MCDA) simulated the response of the floodplains to the variations of the most dominant criteria, which affected the flood susceptibility of the area. An index of flood susceptibility is proposed to compare the simulated outcomes of the different scenarios. We provide a thorough discussion about improving the accuracy of the MCDA method through calibration and validation procedures, in association with the HEC-RAS 2D model. Observed and simulated inundation depths were compared for the validation process. The derived maps effectively revealed the flood susceptibility of the area upon the criteria variation, particularly the elevation and the rainfall.
Floods are among the most devastating and recurring natural hazards and have caused extensive economic losses to human lives and infrastructures around the world. Swat valley in northern Pakistan is ...prone to frequent floods and was severely affected by the Flood2010 in the recent past. Flood hazard assessment is a non-structural strategy for flood mitigation in addition to the structure measure. In this study, 60 km long reach of the River Swat (Khwazakhela Bridge–Chakdara Bridge) was modeled using the HEC-RAS 2D model and high-resolution 12-m WorldDEM. The model was calibrated and validated for only historical maximum flood event, i.e., Flood2010 using Manning’s ‘n’ values, flood stage at the Chakdara Bridge and satellite imagery-based Flood2010-observed extent. In addition, flood model sensitivity to the DEM was carried out and simulated maximum depth was 12, 13, 14, and 25 m for the 12-m WorldDEM, 30-m SRTM, 30-m ALOS and 30-m ASTER DEMs, respectively. Designed hydrographs were prepared for 2, 5, 10, 25, 50, and 100-year return periods based on the Flood2010-observed hydrograph. Finally, the model was simulated for 2, 5, 10, 25, 50, and 100-year return periods with full momentum equation as the calculation method. Simulated extents based on the 12-m WorldDEM were used for the preparation of flood hazard maps. Landcover exposure to the designed flood events shows that agriculture including orchards is the major potential affected class with affected areas up to 55 Km
2
. The developed flood hazard maps will enable the policy makers to mainstream flood hazard assessment in the planning and development process for mitigating flood hazard in Swat Valley.
