Evaluation of One-dimensional and Two-dimensional HEC-RAS Models for Flood Travel Time Prediction and Damage Assessment Using HAZUS-MH PDF Download
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Author: Ekaraj Ghimire
Publisher:
ISBN:
Category : Flood damage prevention
Languages : en
Pages : 178
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Book Description
Even though flood damage cannot be fully controlled, its effect can be minimized to some extent by careful planning, flood mitigation measures, and an effective flood warning system. Therefore, flood warning systems with flood travel time and inundation area information, derived from accurate model prediction, can be very effective to reduce potential flood damage. While a one-dimensional (1D) model was developed in the former research for the flood warning system, there has not been many comparative assessment of model performance among 1D, two-dimensional (2D), and coupled one-dimensional and two-dimensional (coupled 1D/2D) models particularly in HEC-RAS. Therefore, this research is an extension of the prior research and was especially conducted to calculate and compare the predictive capability of 1D, 2D, and coupled 1D/2D HEC-RAS models for the computation of travel time of flood and extent of flooded area needed for a flood warning system. The research was carried out in the Grand River in Lake County, Ohio. The model performance of 1D, 2D and coupled 1D/2D models were evaluated and sensitivity analysis was conducted using the same set of flow conditions and geometric conditions. The analysis suggested that 2D model could incredibly improve the model performance compared to 1D and coupled 1D/2D models, which were evaluated through the model evaluation indicators for the observed and simulated model outputs. Additionally, sensitivity analysis of input parameters, including discharge and Manning's roughness, revealed that the 2D model was comparatively less sensitive to the changes in model inflow and Manning's roughness compared to the coupled 1D/2D and 1D models. Furthermore, the flood travel time computed using 1D model was more predicted than that of the 2D model, indicating that the 2D model would be most appropriate to provide a safe evacuation time for the community before flood events. The 1D model consistently over predicted than that of the 2D model, which was also true for the estimation of the inundation flood zone (4.1% higher). In addition, the appropriate assessment of flood damage in the aftermath of major flooding is crucial for flood management agencies, emergency responders, and insurance companies. Therefore, damage assessment is an important step in the evaluation of the flood mitigation measures, vulnerability analysis and flood risk mapping. This is particularly true in a context that the damage assessment so far has been primarily relying on either the coarse resolution, 30m digital elevation model (DEM), or 1D hydraulic model. As this researcher is not aware of any explicit incorporation of 2D HEC-RAS model for the damage assessment among the scientific communities, another major objective of this analysis is to outline the effects of some of the key factors including the mode of hydraulic simulation (1D vs 2D), the effect of inventory data, and the effect of topography on the flood loss estimation. This was accomplished using the 1D and 2D HEC-RAS models to produce the flood depth grids from the varying degree of topographic resolutions including 30m, 10m and LiDAR-derived DEM with and without incorporating actual field survey of the river in each case. The flood loss was estimated using Hazards United States Multi-Hazards (HAZUS-MH) loss estimation software developed by Federal Emergency Management Agency (FEMA) software, for each building within study area for flood events of various recurrence intervals from 10 to 500-year return periods. This was accomplished by updating the default-building inventory within Lake County to represent the actual building information in the model. The analysis indicated that 1D model consistently overestimated the loss in general by 61.48% for the default database and 86.12% for updated inventory. The estimation of the 1D model was consistently larger compared to the 2D model for different set of topographic resolutions and recurrence intervals. These loss estimations significantly increased when analyzed using a coarse resolution terrain, which was true regardless of selecting 1D or 2D models. Furthermore, the 2D model showed a lesser percentage increase (10.45% in 10m DEM, and 25.49% in 30m DEM), whereas the 1D model exhibited a larger increment (23.17% in 10m DEM and 76.81% in 30m DEM). This analysis suggested that the loss estimation would decrease in general by 76.21% after incorporating additional local building data into the HAZUS-MH database. More specifically, this analysis concludes that 2D model with high-resolution topographic data, including the additional incorporation of local data, in HAZUS-MH database are tremendously essential for appropriate flood damage assessment.
Author: Ekaraj Ghimire
Publisher:
ISBN:
Category : Flood damage prevention
Languages : en
Pages : 178
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Book Description
Even though flood damage cannot be fully controlled, its effect can be minimized to some extent by careful planning, flood mitigation measures, and an effective flood warning system. Therefore, flood warning systems with flood travel time and inundation area information, derived from accurate model prediction, can be very effective to reduce potential flood damage. While a one-dimensional (1D) model was developed in the former research for the flood warning system, there has not been many comparative assessment of model performance among 1D, two-dimensional (2D), and coupled one-dimensional and two-dimensional (coupled 1D/2D) models particularly in HEC-RAS. Therefore, this research is an extension of the prior research and was especially conducted to calculate and compare the predictive capability of 1D, 2D, and coupled 1D/2D HEC-RAS models for the computation of travel time of flood and extent of flooded area needed for a flood warning system. The research was carried out in the Grand River in Lake County, Ohio. The model performance of 1D, 2D and coupled 1D/2D models were evaluated and sensitivity analysis was conducted using the same set of flow conditions and geometric conditions. The analysis suggested that 2D model could incredibly improve the model performance compared to 1D and coupled 1D/2D models, which were evaluated through the model evaluation indicators for the observed and simulated model outputs. Additionally, sensitivity analysis of input parameters, including discharge and Manning's roughness, revealed that the 2D model was comparatively less sensitive to the changes in model inflow and Manning's roughness compared to the coupled 1D/2D and 1D models. Furthermore, the flood travel time computed using 1D model was more predicted than that of the 2D model, indicating that the 2D model would be most appropriate to provide a safe evacuation time for the community before flood events. The 1D model consistently over predicted than that of the 2D model, which was also true for the estimation of the inundation flood zone (4.1% higher). In addition, the appropriate assessment of flood damage in the aftermath of major flooding is crucial for flood management agencies, emergency responders, and insurance companies. Therefore, damage assessment is an important step in the evaluation of the flood mitigation measures, vulnerability analysis and flood risk mapping. This is particularly true in a context that the damage assessment so far has been primarily relying on either the coarse resolution, 30m digital elevation model (DEM), or 1D hydraulic model. As this researcher is not aware of any explicit incorporation of 2D HEC-RAS model for the damage assessment among the scientific communities, another major objective of this analysis is to outline the effects of some of the key factors including the mode of hydraulic simulation (1D vs 2D), the effect of inventory data, and the effect of topography on the flood loss estimation. This was accomplished using the 1D and 2D HEC-RAS models to produce the flood depth grids from the varying degree of topographic resolutions including 30m, 10m and LiDAR-derived DEM with and without incorporating actual field survey of the river in each case. The flood loss was estimated using Hazards United States Multi-Hazards (HAZUS-MH) loss estimation software developed by Federal Emergency Management Agency (FEMA) software, for each building within study area for flood events of various recurrence intervals from 10 to 500-year return periods. This was accomplished by updating the default-building inventory within Lake County to represent the actual building information in the model. The analysis indicated that 1D model consistently overestimated the loss in general by 61.48% for the default database and 86.12% for updated inventory. The estimation of the 1D model was consistently larger compared to the 2D model for different set of topographic resolutions and recurrence intervals. These loss estimations significantly increased when analyzed using a coarse resolution terrain, which was true regardless of selecting 1D or 2D models. Furthermore, the 2D model showed a lesser percentage increase (10.45% in 10m DEM, and 25.49% in 30m DEM), whereas the 1D model exhibited a larger increment (23.17% in 10m DEM and 76.81% in 30m DEM). This analysis suggested that the loss estimation would decrease in general by 76.21% after incorporating additional local building data into the HAZUS-MH database. More specifically, this analysis concludes that 2D model with high-resolution topographic data, including the additional incorporation of local data, in HAZUS-MH database are tremendously essential for appropriate flood damage assessment.
Author: Joan Flotats Palau
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Flooding may occur as an overflow of water from water bodies, such as a river, lake or ocean, in which the water overtops or breaks levees, resulting in some of that water escaping its usual boundaries. Floods also occur in rivers when the flow rate exceeds the capacity of the river channel. Floods represent the deadliest natural hazard in Europe, resulting in loss of life, damage to buildings, homes, business and structures such as bridges and roads. Since such consequences are highly undesirable for human beings, the need to avoid or at least control them has become obvious. This led to the appearance of hydrodynamic models, numerical tools able to simulate the flow movement, also in case of flooding. Those models would let us know how the flow behaves in certain situations and how to act in consequence in order to avoid those undesirable effects. In April 2016, the new two-dimensional version of HEC-RAS has been released, the so-called HEC-RAS 5.0. This version is especially interesting since all previous versions of HEC-RAS had never been able to simulate flows in two dimensions. The main motivation of this document is to analyse the functionality and workability of HEC-RAS 5.0 regarding two-dimensional river flooding. In order to do so, three different work approaches have been carried out, with further analysis of the correspondent results. First, a detailed intercomparison between the main hydrodynamic models available has been carried out in order to check the features of the new version of HEC-RAS next to another four computational programs. Second, the same case simulation has been performed at the same time for HEC-RAS 5.0 and for Delft3D. The aim of this is to check the reliability and functionality of HEC-RAS new version regarding to 2D river flood modelling next to an already developed two-dimensional model such as Delft3D is. For this simulation, an ideal created prismatic channel has been chosen in order to work in a basic scenario and two approaches have been analysed: steady nonflooding and unsteady flooding cases. Finally, and once its workability has been checked, a more complex case has been simulated with HEC-RAS 5.0. In this case, the scenario is a real case study, consisting in a river flood in the Fluvià River, in Catalonia, Spain, with real data of a return period of 50 years, obtained from Agència Catalana de l'Aigua (ACA) in 2009. The results led to very sensitive output, realistic and similar to the expected and contrasted. Thus, one can conclude that, despite small instabilities were found, HEC-RAS 5.0 is able to perform simple 2D river flood modelling simulations at a similar level of the most advanced two-dimensional programs, such as Delft3D. However, when it comes to very complex simulations, some features, such as combination with transport of substances and water quality or combination with sediment transport and morphological evolution, are not yet available in two dimensions for HEC-RAS 5.0, so one would rather choose a more advanced model.
Author: Abdulaziz Saeed Alzahrani
Publisher:
ISBN:
Category : Bear Creek (Ohio)
Languages : en
Pages : 83
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Book Description
Flood simulation models have a wide variety of approaches that are available to compute the water surface elevations associated with a flood event. Some of these models use a One-dimensional (1D) approach, others use a Two-dimensional (2D), and there are others allow the use of integrated 1D and 2D simulations. In 2015, the US Army Corps of Engineering Hydrologic Engineering Center (HEC) released HEC-RAS Version 5.0.3 which performs 1D steady and unsteady flow calculation, as well as 2D unsteady flow calculation. 2D modeling is likely to become more common due to HEC-RAS. This paper is the comparison of 1D and 2D models for a water level in the channel and the floodplain inundation. Two treatments of the problem are explored: (1) a 1D model based upon discretization of floodplain units into storage areas; (2) a 2D model for a channel and a floodplain surface. The two models were tested on the Great Miami River and Bear Creek. The models were assessed by comparison with measured inundation extent. Also, the study reviews the academic basis for modeling floodplain flow based on a two-dimensional analysis. The goal of the proposed research effort will be to include the application of 2D unsteady-state models in future releases of the HEC-RAS 2D model.
Author: Gary W. Brunner
Publisher:
ISBN:
Category : HEC-RAS (Computer program)
Languages : en
Pages : 16
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Book Description
Author: Megan L. Carlson
Publisher:
ISBN:
Category :
Languages : en
Pages : 104
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Book Description
By combining FEMA's HAZUS-MH (Hazards U.S. Multi-Hazard) flood-loss estimation software and the HEC-RAS hydraulic modeling package, this study was able to quantify potential beneficial and adverse impacts of flood-control and navigational structures along the Middle Mississippi River (MMR; between Mississippi-Missouri River confluence and Thebes, IL). The goal of this investigation was to assess changes in water-surface elevations and associated flood losses to: 1) quantify the potential exposure of flooding under different flood-control configurations along the Middle Mississippi River (MMR), and 2) assess the relative contributions of various engineered structures and flood-loss strategies to potential flood losses. Assessment of the impact of engineering structures was accomplished by modeling five scenarios for the 100- and 500-year floods: 1) current MMR levee configuration (levee protecting for [less than or equal to] 50-year flood); 2) removal of all flood-control structures on the MMR; 3) increasing the height of levees and floodwalls in metropolitan St. Louis to protect urban areas to the 500-year flood level while simultaneously removing all agricultural levees downstream; 4A) a less engineered MMR channel and floodplain with fewer flood control and navigation structures, simulating conditions from 65 years ago (1942-1947) with 1940's levees; and 4B) a less engineered MMR channel and floodplain with fewer flood control and navigation structures, simulating conditions from 65 years ago (1942-1947) with current levee configuration.
Author: Charles Noble
Publisher:
ISBN:
Category :
Languages : en
Pages : 18
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Book Description
The desirability of accurately predicting the extent and duration of flooding resulting from the partial or total breach of a dam has been emphasized recently. The most practical way to meet this need is the development and use of good computer-based models. In order to predict the routing of floods, several hydrograph routing and one-dimensional models have recently been developed. Among the better known models are those employed in the code DAMBRK, Fread (1980) and in HEC-1 (1973). These models have proved to be quite good in predicting the flooding in those cases which have been amenable to a one-dimensional treatment. The accuracy of these models in situations which are clearly two-dimensional in nature is suspect, however. It is thus desirable to develop two-dimensional flood routing models to properly handle those situations in which the one-dimensional models are inadequate. Energy Incorporated (EI) has developed a computer code, FLOOD, that describes the two-dimensional motion of a flood. An analysis of the hypothetical Mackay Dam failure was performed using FLOOD. In this paper are given the equations used by EI, the numerical algorithm used for their solution, and the results of the Mackay Dam analysis.
Author: Maryellen Hearn
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Evan C. Deal
Publisher:
ISBN:
Category :
Languages : en
Pages : 271
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Book Description
Computer models are used every day to analyze river systems for a wide variety of reasons vital to the public interest. For decades most hydraulic engineers have been limited to models that simplify the fluid mechanics to the unidirectional case. With the advent of higher quality data and greater computational power, two-dimensional hydrodynamic models have become practical for widespread use. Two such models are considered in this report: HEC-RAS v.5.0, v.5.0.1, and v.5.0.3, and SRH-2D v.3.0. These two-dimensional models were compared to the most common one-dimensional model (HEC-RAS). While the latest version of HEC-RAS is capable of both one- and two-dimensional analyses, previous versions were restricted to one-dimensional flow. Findings in this report include: differences in the flow divisions for multiple opening bridges for all three models, less subjectivity in the construction of the 2D models than for the 1D, differences in the sensitivity of each 2D model to the Manning's roughness coefficient, great similarity in the expansion and contraction rates at bridges for the 2D models when using the full momentum equations with HEC-RAS 2D, differences in the response of the two-dimensional models at steady state conditions to vortex shedding through bridge openings with cylindrical piers, shorter computation times for HEC-RAS 2D than SRH-2D using highly comparable model setups, and in general, higher depths predicted by SRH-2D than HEC-RAS 1D but the highest depths overall predicted by the HEC-RAS 2D full momentum model.
Author: Devinder Singh Dhillon
Publisher:
ISBN: 9781321015577
Category :
Languages : en
Pages :
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Book Description
Numerical modeling is the standard tool in determining floodplain areas for engineering and insurance purposes. For many years one-dimensional (1-D) models have been primarily used for these purposes, with HEC-RAS arguably the most widely used 1-D model. Relatively robust guidelines and specifications, as well as an industry standard of practice, currently exists for 1-D models. While 1-D models are relatively simple to apply and rather inexpensive to develop, they are based on several assumptions that do not always hold true in overbank flooded conditions. These shortcoming are particularly significant for models intended to simulate flow over levees or in very flat areas, such as the Central Valley of California.In recent years, 2-D models have been used as an additional tool in floodplain mapping to allow for more detailed analyses. Unfortunately, the assumptions behind these 2-D models are not fully understood by all users. 2-D models are even less understood by decision and policy makers. The Federal Emergency Agency (FEMA) has recognized the need for greater understanding and improved guidelines for applying 2-D models in flood studies and intends to widely disseminate the advantages and limitations of 2-D models examined. This work develops a) a literature review of 2-D modeling use for floodplain mapping; b) presents the Blue Ribbon Panel's (BRP's) results of the 46 issues; c) develop a question form for 2-D software vendors; and d) produce written guidelines that address limitations and capabilities of 2-D models to help practitioners, decision and policy makers use 2-D models more effectively.The decision on model complexity and dimensionality for a given case, can be based on two main ideas: a) the goal of the analysis, and b) the modeler. Thus, the steps to consider when facing a modeling task should be: a) define the goal of the study; b) select the adequate modeler for the task; c) chose the right tool for the goal of the study and the modeler; and d) perform the study considering all conditions.
Author: Samir Shrestha
Publisher:
ISBN:
Category :
Languages : en
Pages : 146
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Book Description
In this study, Hazus-MH (v 2.1 SP 2) flood-loss estimation tools were assessed for their sensitivity to an array of different building and model parameters. The purpose of this study is to help guide users of the Hazus-MH flood-loss modeling tool in the selection of most appropriate model parameters. Six model parameters (square footage of the building, building age, construction types, foundation types, first floor heights, and the number of stories in the building) were assessed for their impacts on flood losses using the Hazus-MH user defined and aggregate flood-loss models. Building stock databases for these analyses were developed using county assessor records from two Illinois counties. A validation assessment was also performed using observed flood-damage survey data collected after the 2011 Mississippi River Flood which inundated the Olive Branch Area in Alexander County, Illinois. This analysis was performed to assess the accuracy of the detailed Hazus-MH User Defined Facility (UDF) flood-loss modeling tool. The foundation types and its associated first floor heights and number of stories in the building were found to substantially impact flood-loss estimates using the Hazus-MH flood-loss modeling tool. The model building parameters square footage, building age and construction type had little or no effect on the flood-loss estimates. The validation assessment reveled Hazus-MH UDF flood-loss modeling tool is capable of providing a reasonable estimate of actual flood losses. The validation assessment showed the modeled results to be within 23% of actual losses. The validation study results attained in this study using the detailed UDF flood-loss modeling tool where more realistic (within 23% of actual losses versus > 50% of actual losses) than previous Hazus-MH flood-loss validation assessments. The flood-loss estimates could be further improved by modifying or choosing a more region specific depth-damage curve, using higher resolution DEM and improving the flood-depth grid by incorporating more detailed flood elevation data or estimates using detailed hydraulic models that better reflects the local inundation conditions.
