Accurately quantifying and assessing the flood risks is critical for flood hazard mitigation and prevention. This study proposed a new integrated flood risk assessment framework to map flood risk, ...hazard and vulnerability by coupling the HEC-HMS hydrological model, the HEC-RAS 1D and 2D hydraulic models, and a bottom-up hazard vulnerability analysis. The Old Brahmaputra River floodplain of Bangladesh, a flood-prone region, was chosen as a case study. The coupled hydrological-hydraulic model shows a comparable robust performance in both calibration and validation periods with Nash-Sutcliffe efficiency coefficient = 0.93 (0.81), coefficient of determination = 0.95 (0.89), and percent bias = −1.17% (2.40%) for the calibration (validation) period. Our results indicate that the assessed risk levels are roughly consistent with the overall property distribution and flood-hazard potential in the study area. The proposed framework and associated findings are valuable for developing adaptation strategies and early-warning systems to reduce flood impacts in the future.
•Developed an integrated flood risk assessment framework to map flood risk, hazard and vulnerability.•Coupled the HEC-HMS hydrological model, the HEC-RAS hydraulic models, and a bottom-up hazard vulnerability analysis.•Mapped flood risks of the flood-prone Old Brahmaputra River floodplain of Bangladesh.•Provided a used modeling system for flood adaptation and early-warning.
Alluvial rivers that exhibit multi-thread patterns are common in nature and can be the dominant channel morphology in large rivers. However, their ecological properties in response to diverse and ...dynamic channel morphology has gained limited attention and remained poorly understood. In this study, we adopted an eco-hydraulic model by integrating a hydrodynamic, a sediment-transport, and a habitat-suitability model to assess habitat quality for fish species (Schizopygopsis pylzovi and Platypharodon extremus) in three anabranching reaches with each exhibiting a distinct anabranching morphology in the Upper Yellow River, eastern Qinghai-Tibet Plateau. Based on the hydrologic data and actual channel morphology, we modeled the hydrodynamic and sediment-transport conditions for a period spanning ten years, and simulated habitat conditions under a potentially changing environment with different flow magnitudes and frequencies. The results indicated that the average flow velocity in the low and mid-order anabranching reaches is higher than that in the high-order, complex anabranching reaches. Meanwhile, the bedload transport rate was higher in the high and mid-order anabranching reaches than that in the low-order anabranching reach, demonstrating a greater transport efficiency of multi-thread systems with a greater multiplicity. Consequently, the habitat suitability shows a deteriorating trend over the ten-year modeling period and Schizopygopsis pylzovi shows better habitat status than Platypharodon extremus. The flow magnitudes and frequency also have a significant impact on the distribution of high habitat suitability index among the different river patterns in Upper Yellow River. This study can provide valuable information to optimize ecological outcomes and provide valuable insights for future dam operation strategies and consideration efforts aimed at preserving and restoring riverine ecosystems.
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•Multi-thread river habitat status under different degrees of multiplicity was investigated.•The habitat maps of multi-thread rivers and two fish species were drawn.•Habitat quality degraded over the modeling period.•Flow magnitudes and frequencies influenced high habitat suitability distribution of multi-thread rivers.
Urbanization increases regional impervious surface area, which generally reduces hydrologic response time and therefore increases flood risk. The objective of this work is to investigate the ...sensitivities of urban flooding to urban land growth through simulation of flood flows under different urbanization conditions and during different flooding stages. A sub-watershed in Toronto, Canada, with urban land conversion was selected as a test site for this study. In order to investigate the effects of urbanization on changes in urban flood risk, land use maps from six different years (1966, 1971, 1976, 1981, 1986, and 2000) and of six simulated land use scenarios (0%, 20%, 40%, 60, 80%, and 100% impervious surface area percentages) were input into coupled hydrologic and hydraulic models. The results show that urbanization creates higher surface runoff and river discharge rates and shortened times to achieve the peak runoff and discharge. Areas influenced by flash flood and floodplain increases due to urbanization are related not only to overall impervious surface area percentage but also to the spatial distribution of impervious surface coverage. With similar average impervious surface area percentage, land use with spatial variation may aggravate flash flood conditions more intensely compared to spatially uniform land use distribution.
•Efficient simulation model for district heating and cooling pipes.•Copes with highly variable mass flow rates and temperature profiles.•Good correspondence between simulations and various ...measurements.•Simulation time decreased substantially.
Simulation and optimisation of district heating and cooling networks requires efficient and realistic models of the individual network elements in order to correctly represent heat losses or gains, temperature propagation and pressure drops. Due to more recent thermal networks incorporating meshing decentralised heat and cold sources, the system often has to deal with variable temperatures and mass flow rates, with flow reversal occurring more frequently. This paper presents the mathematical derivation and software implementation in Modelica of a thermo-hydraulic model for thermal networks that meets the above requirements and compares it to both experimental data and a commonly used model. Good correspondence between experimental data from a controlled test set-up and simulations using the presented model was found. Compared to measurement data from a real district heating network, the simulation results led to a larger error than in the controlled test set-up, but the general trend is still approximated closely and the model yields results similar to a pipe model from the Modelica Standard Library. However, the presented model simulates 1.7 (for low number of volumes) to 68 (for highly discretized pipes) times faster than a conventional model for a realistic test case. A working implementation of the presented model is made openly available within the IBPSA Modelica Library. The model is robust in the sense that grid size and time step do not need to be adapted to the flow rate, as is the case in finite volume models.
Large‐scale river models are generally discretized by relatively large mesh cells resulting in bathymetry discretization errors and numerical effects. These hydraulic models are generally calibrated ...by altering the bed roughness to compensate for these errors and effects. Consequently, the calibrated roughness values are mesh‐dependent while generally local mesh refinements are executed after model calibration to study the effects of river interventions. This study shows both the errors caused by bathymetry discretization and numerical effects for locally refined meshes. First, schematised river meanders with a flat bed in the transverse flow direction are analysed to isolate the induced numerical effects by the mesh. Afterwards, a case study is considered to verify if similar mesh influences are found in natural river meanders. Curvilinear, triangular and hybrid (combination of curvilinear and triangular cells) meshes are used with different resolutions. The analysis shows that in the schematised river meanders lower depth‐averaged flow velocities and larger water depths are simulated with coarser meshes. In the case study, substantial differences in hydrodynamics between the meshes are obtained suggesting that the bathymetry discretization is more influential than the numerical effects. Finally, it was found that triangular meshes, and rivers with narrow meander bends, are most sensitive to mesh resolution. Especially in these cases, it is desirable to refine the mesh at the desired locations before model calibration.
•A segmentation framework combining rule-based simulation and optimization is proposed.•The method of identifying segmentation points based on rule-based simulation is applied.•The optimization time ...can be effectively reduced by segmented optimization method.
With the urban water resources becoming increasingly scarce, the optimal control engineering has emerged as a promising approach to improve the efficiency of water use in the environment. A hydraulic model is capable of accurately modeling and predicting the complex hydrodynamic processes occurring within a channel. However, its optimization and simulation time are often prolonged by the complexity of the channel system, resulting in poor real-time performance. This study presents a segmented hydraulic real-time optimization approach that combines rule-based simulation (RS) with real-time optimization (RTO). The aim of the proposed method is to reduce hydraulic model complexity and improve optimization time by dividing the full hydraulic model (FHM) into optimized segmented hydraulic model (SHMO) and non-optimized segmented hydraulic model (SHMN). The approach presents two main improvements: (1) a segmentation point recognition method based on RS is used to obtain SHMO from the FHM; and (2) a segmented optimization framework is employed to enable RTO based on SHMO. We demonstrate the effectiveness of the approach using a case study of China's Qing River. The results indicate that FHM can be successfully divided into SHMO and SHMN with similar simulation effect (R > 0.88 and RMSE < 0.1) by using the segmentation point recognition method, and the segmented hydraulic real-time optimization approach can reduce optimization time (average 68%) of hydraulics model. The case study indicated that the proposed method is a computationally efficient and feasible approach for real-time regulation of urban channel gate control based on hydraulic model.
•We derive global flood hazard maps at 30′′ resolution for several return periods•The mapping procedure is based on a hydrological and hydraulic modelling chain•Maps are evaluated using official and ...satellite-derived flood extent maps
Nowadays, the development of high-resolution flood hazard models have become feasible at continental and global scale, and their application in developing countries and data-scarce regions can be extremely helpful to increase preparedness of population and reduce catastrophic impacts.
The present work describes the development of a novel procedure for global flood hazard mapping, based on the most recent advances in large scale flood modelling. We derive a long-term dataset of daily river discharges from the hydrological simulations of the Global Flood Awareness System (GloFAS). Streamflow data is downscaled on a high resolution river network and processed to provide the input for local flood inundation simulations, performed with a two-dimensional hydrodynamic model. All flood-prone areas identified along the river network are then merged to create continental flood hazard maps for different return periods at 30′′ resolution. We evaluate the performance of our methodology in several river basins across the globe by comparing simulated flood maps with both official hazard maps and a mosaic of flooded areas detected from satellite images. The evaluation procedure also includes comparisons with the results of other large scale flood models. We further investigate the sensitivity of the flood modelling framework to several parameters and modelling approaches and identify strengths, limitations and possible improvements of the methodology.
Hot dry rock is one of the huge reserves of clean energy sources, and enhanced geothermal system is the effective utilization. Darcy's law is widely employed to describe the fluid flow in geothermal ...reservoirs. However, when Darcy's law is applied to describe supercritical flow in geothermal reservoir, there will be the deviation of temperature and pressure because of the high sensitivity of thermal physical properties. To compare Darcy's law with non-Darcy's law, Darcy's law is replaced by the non-Darcy’ law to establish the coupled numerical model. The results show that there is little difference for the temperature distribution of geothermal reservoir between the two assumptions. The pressure drops of geothermal reservoirs with different mass flow rates have a significant impact on power generation through the heat loss in production well. The heat preservation in production well is indispensability when the flow rate is small. Through the comparison between the two assumptions of Richardson number and Prandtl number, the buoyancy effect under non-Darcy's law is more significant than that of Darcy's law. When power generation, net work output, payback period and exergy efficiency are considered, mass flow rate of 50 kg/s is the optimal in EGS under the actual engineering conditions.
Observations show vulnerability segmentation between stems and leaves is highly variable within and between environments. While a number of species exhibit conventional vulnerability segmentation ...(stem P
50
< ${P}_{50}\lt $ leaf P
50 ${P}_{50}$), others exhibit no vulnerability segmentation and others reverse vulnerability segmentation (stem P
50
> ${P}_{50}\gt $ leaf P
50 ${P}_{50}$). We developed a hydraulic model to test hypotheses about vulnerability segmentation and how it interacts with other traits to impact plant conductance. We do this using a series of experiments across a broad parameter space and with a case study of two species with contrasting vulnerability segmentation patterns: Quercus douglasii and Populus trichocarpa. We found that while conventional vulnerability segmentation helps to preserve conductance in stem tissues, reverse vulnerability segmentation can better maintain conductance across the combined stem‐leaf hydraulic pathway, particularly when plants have more vulnerable P
50 ${P}_{50}$s and have hydraulic segmentation with greater resistance in the leaves. These findings show that the impacts of vulnerability segmentation are dependent upon other plant traits, notably hydraulic segmentation, a finding that could assist in the interpretation of variable observations of vulnerability segmentation. Further study is needed to examine how vulnerability segmentation impacts transpiration rates and recovery from water stress.
Summary statement
Using a hydraulic model, we examine how vulnerability segmentation interacts with other traits to impact plant conductance loss. We show that vulnerability segmentation impacts depend on other traits, which potentially helps explain variable observations of vulnerability segmentation.
Where high‐resolution topographic data are available, modelers are faced with the decision of whether it is better to spend computational resource on resolving topography at finer resolutions or on ...running more simulations to account for various uncertain input factors (e.g., model parameters). In this paper we apply global sensitivity analysis to explore how influential the choice of spatial resolution is when compared to uncertainties in the Manning's friction coefficient parameters, the inflow hydrograph, and those stemming from the coarsening of topographic data used to produce Digital Elevation Models (DEMs). We apply the hydraulic model LISFLOOD‐FP to produce several temporally and spatially variable model outputs that represent different aspects of flood inundation processes, including flood extent, water depth, and time of inundation. We find that the most influential input factor for flood extent predictions changes during the flood event, starting with the inflow hydrograph during the rising limb before switching to the channel friction parameter during peak flood inundation, and finally to the floodplain friction parameter during the drying phase of the flood event. Spatial resolution and uncertainty introduced by resampling topographic data to coarser resolutions are much more important for water depth predictions, which are also sensitive to different input factors spatially and temporally. Our findings indicate that the sensitivity of LISFLOOD‐FP predictions is more complex than previously thought. Consequently, the input factors that modelers should prioritize will differ depending on the model output assessed, and the location and time of when and where this output is most relevant.
Key Points
Sensitivity of flood inundation predictions to different input factors shown to be more complex than previously thought
The most influential model input factor for predicting flood extent changes during the flood event
Spatial resolution is much more influential for localized predictions of water depth than for flood extent
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