In this paper the new family of the stream routing curves was obtained on the basis of disparity in the "water stage vs water volume" curve on the rise and the recession of the flood wave. The paper ...contains the results of the numerical experiments with the different stream routing curves using the row data about the artificial outflows downstream from Novotveretskaya and Ivankovo dams.
A Simple Model of Flood Peak Attenuation Paiva, Rodrigo C. D.; Lima, Stefany G.
Water resources research,
February 2024, 2024-02-00, 20240201, Letnik:
60, Številka:
2
Journal Article
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A simple analytical model was developed for evaluating the attenuation of flood wave peak discharge. The physically‐based model represents the flood wave along its trajectory, based on the diffusive ...model. Relative peak discharge decreases along the downstream distance according to a power function. The distance is scaled by the attenuation factor related to river hydrodynamics (flow rating, hydraulic diffusivity, celerity, and floodplain storage) and input hydrograph (initial peak discharge, hydrograph volume, and its relative curvature). It also informs the attenuation length, which is a practical indicator of the river distance in which discharge decreases by a given factor. Sensitivity analyses indicate that initial peak discharge, volume, floodplain storage, and slope are the governing factors of attenuation. Model's validity and accuracy were demonstrated by reproducing data from (a) numerical solutions of the Saint‐Venant equations covering a wide range of conditions, (b) 29 observations from 11 historical dam‐breaks, (c) 15 observations of natural floods in seven rivers and (d) a detailed hydrodynamic model. The model errors were generally lower than 10% and not larger than the typical uncertainty of flood observations. The accuracy is higher than simplified empirical models and analogous to a detailed hydrodynamic model that is representative of current practice. The proposed flood attenuation model can be easily applied using a few common parameters and a simple equation in a basic spreadsheet. It is suitable for practical applications such as first assessments of natural and dam‐break floods, engineering design, and analyses of large river networks supported by remote sensing data.
Plain Language Summary
Floods are the most common and damaging natural disaster. Predicting how flood waves weaken while traveling along rivers is key to clarifying the risks of natural and dam‐break floods, in engineering design, reservoir operation, and environmental analysis. We developed a simple and innovative physical model of flood wave attenuation. This model was accurate when tested against observations from historical dam‐break and natural floods and sophisticated computer simulations covering a wide range of river types and flow conditions. Flood waves weaken more when their peak is large, their volume is low, and in low‐slope rivers with large floodplains. This simple and meaningful equation can be easily applied for practical applications and help with massive mapping of floods over large regions.
Key Points
A simple physically‐based analytical model of flood wave peak attenuation is developed
The model is validated using numerical solutions of the Saint‐Venant equations and observations of historical dam breaks and natural floods
Flood wave attenuation is governed mostly by initial peak discharge, volume, floodplain storage, and river slope
To study the hyporheic exchange driven by a single peak flood‐induced water level fluctuation (i.e., flood wave), a method combining numerical simulation with theoretical derivation was proposed ...based on the Inbuk Stream, Korea, where flooding occurs frequently. The hyporheic exchanges induced by different flood waves were investigated by varying amplitude (A), duration (T), wave type parameter (r), and rising duration (tp), which were adopted from the real‐time stream stage fluctuations. Additionally, the idea of constant upstream flood volume (CUFV) condition for flood waves was put forward, and the effects of “Botan” (T/A) and peak number (N) on hyporheic exchange were studied. The results showed that the hyporheic exchange flux (q) was controlled by the water level h (sine‐type) and its change rate v (cosine‐type), and was proportional to the polynomial of them q ∝ (ω∙h + v), where ω is the angular frequency of the flood wave. Based on this mechanism, the influence principles on hyporheic exchanges of the typical flood wave parameters (A, T, r and tp) as well as T/A and N under CUFV condition were clarified. The main characteristic variables of hyporheic exchange, which were maximum aquifer storage and residence time, were positively correlated. They also had positive relations to the integral of the flood wave over time, which increased when the wave became higher, wider, rounder and less skewed. However, when CUFV condition was imposed, the residence time was positively correlated with T/A, whereas the maximum aquifer storage was negatively correlated with T/A. With the increase in N, water exchanged more frequently and some water returned to the stream early, leading to the slight decrease in maximum aquifer storage and residence time. These findings enriched the theory of hyporheic exchange driven by surface water fluctuation and be of great significance to enhance pollutant degradation in the hyporheic zone downstream of reservoirs.
We reveal the influence mechanism of water level and its change rate on hyporheic exchange.
We clarify the influences on hyporheic change of parameters that characterize the height, width, roundness and skewness of a wave.
We put forward an idea of constant upstream flood volume condition for flood waves and its ecological significance.
In this study, a two-dimensional hydraulic routing model was applied to a sudden failure scenario for the Atasu Dam in Trabzon, Turkey. The goal was to simulate spreading and propagation of a dam ...break flood wave along a narrow valley into a downstream city center with many buildings. Flow properties along the downstream were routed according to diffusive and dynamic wave models represented by Saint–Venant equations. Maximum flow depth, maximum flow velocity, and time moment of the maximum flow depth maps are shown in a Geographic Information System environment. The results predict that flow depths could reach approximately 8 m in the residential area, and this would be achieved approximately 32 min after the dam-break event. Houses in a large section of the city center would be under the maximum flow depths. The results of this study demonstrate that these two approaches can determine potential risk areas of a floodplain due to natural hazards and facilitate preparation of emergency action plans.
Using river centerlines created with Landsat images and the Shuttle Radar Topography Mission digital elevation model, we created spatially continuous maps of mean annual flow river width, slope, ...meander wavelength, sinuosity, and catchment area for all rivers wider than 90 m located between 60°N and 56°S. We analyzed the distributions of these properties, identified their typical ranges, and explored relationships between river planform and slope. We found width to be directly associated with the magnitude of meander wavelength and catchment area. Moreover, we found that narrower rivers show a larger range of slope and sinuosity values than wider rivers. Finally, by comparing simulated discharge from a water balance model with measured widths, we show that power laws between mean annual discharge and width can predict width typically to −35% to +81%, even when a single relationship is applied across all rivers with discharge ranging from 100 to 50,000 m3/s.
Plain Language Summary
For years, scientists and engineers have been using aerial photography to study the shapes of rivers, how they change over time, and how they relate to other river characteristics, such as river width, the slope of the water surface, and flow. These studies served as basis for the development of theories describing erosion, sediment transport, the speed at which flood waves travel through a basin, and serving as guidance for the measurement of river flow. However, such studies were often conducted in person, or done by combining results from other authors, leading to a very limited coverage of world rivers, most of which were in North America. As images of world rivers obtained by satellites became available and adequate computational power became affordable, we were able to describe the shape of worldwide rivers and how other properties, such as slope, width, and flow relate to meander characteristics. We showed that although classical geomorphic studies had limited geographical coverage, their results could generally be applied to typical rivers over the world. Additionally, with our results, rivers with atypical meander characteristics can be better identified, allowing the advancement of our understanding of how rivers work.
Key Points
Using satellite imagery, meander wavelength and sinuosity were computed globally for the first time
Even when extended to global scales, classical relationships between river width and meander wavelength and discharge still hold
We found strong associations between sinuosity, width, meander wavelength, slope, and discharge
Tides are changing worldwide at rates not explained by astronomical forcing. Rather, the observed evolution of tides and other long waves, such as storm surges, is influenced by shelf processes and ...changes to the roughness, depth, width, and length of embayments, estuaries, and tidal rivers. In this review, we focus on processes in estuaries and tidal rivers, because that is where the largest changes to tidal properties are occurring. Recent literature shows that changes in tidal amplitude have been ubiquitous worldwide over the past century, often in response to wetland reclamation, channel dredging, and other environmental changes. While tidal amplitude changes are sometimes slight (<1%) or even negative, we identify two types of systems that are particularly prone to tidal amplification: (
a
) shallow, strongly damped systems, in which a small increase in depth produces a large decrease in effective friction, and (
b
) systems in which wave reflection and resonance are strongly influenced by changes to depth, friction, and convergence. The largest changes in amplitude occur inland, some distance from the coast, and can sometimes be measured in meters. Tide changes are a leading indicator that the dynamics of storm surges and river flood waves have also changed and are often associated with shifts in sediment transport, salinity intrusion, and ecosystem properties. Therefore, the dynamics of tidal evolution have major implications for coastal management, particularly for systems that are sensitive to changes in geometry induced by sea-level rise and anthropogenic development.
Dams have an important role in the industrial development of countries. Irrespective of the reason for dam break, the flood can cause devastating disasters with loss of life and property especially ...in densely populated areas. In this study, the effects of the vegetation on the flood wave propagation in case of dam break were investigated experimentally by using the distorted physical model of Ürkmez Dam. The horizontal and vertical scales of the distorted physical model are 1/150 and 1/30, respectively. The dam break scenarios were achieved by means of a gate of rectangular and triangular shape. The results obtained from experiments performed with vegetation were compared and interpreted with those obtained from experiments at which the vegetation configuration was absent. The analysis of the experimental data showed that the presence of vegetation causes a significant decrease in water depths as the flood wave propagates to the downstream and greatly reduces its impact on the settlements. It is also revealed that dam break shape plays an important role in temporal variation of flood wave.
An accurate comprehension of celerity (flood wave speed) dynamics is a key step for understanding flood wave propagation in rivers. We present the results of empirically estimated celerity values in ...12 Brazilian rivers, and analyse the behaviour of celerity-discharge relationships (CxQ). Celerity was estimated with a reach-scale (RS) method, based on the peak travel time between stations; and with a local-scale (LS) method, based on the derivative of discharge-cross-section area relationships surveyed at gauging stations. The results indicate that the magnitudes of celerity values obtained by the methods are reasonably comparable, and can rarely be considered constant, varying with river discharge. Three reaches presented differing CxQ relationships at local and reach scales, which suggests that in situ cross-sections at gauging stations should not be extrapolated as representative of the whole reach for flood routing studies, and that CxQ relationship assessments might provide relevant insights for hydrological modelling.
Large‐scale river models are being refined over coastal regions to improve the scientific understanding of coastal processes, hazards and responses to climate change. However, coarse mesh resolutions ...and approximations in physical representations of tidal rivers limit the performance of such models at resolving the complex flow dynamics especially near the river‐ocean interface, resulting in inaccurate simulations of flood inundation. In this research, we propose a machine learning (ML) framework based on the state‐of‐the‐art physics‐informed neural network (PINN) to simulate the downscaled flow at the subgrid scale. First, we demonstrate that PINN is able to assimilate observations of various types and solve the one‐dimensional (1‐D) Saint‐Venant equations (SVE) directly. We perform the flow simulations over a floodplain and along an open channel in several synthetic case studies. The PINN performance is evaluated against analytical solutions and numerical models. Our results indicate that the PINN solutions of water depth have satisfactory accuracy with limited observations assimilated. In the case of flood wave propagation induced by storm surge and tide, a new neural network architecture is proposed based on Fourier feature embeddings that seamlessly encodes the periodic tidal boundary condition in the PINN's formulation. Furthermore, we show that the PINN‐based downscaling can produce more reasonable subgrid solutions of the along‐channel water depth by assimilating observational data. The PINN solution outperforms the simple linear interpolation in resolving the topography and dynamic flow regimes at the subgrid scale. This study provides a promising path toward improving emulation capabilities in large‐scale models to characterize fine‐scale coastal processes.
Key Points
A data assimilation method is developed based on physics‐based deep learning
The method can be used to resolve the downscaled flow within the subgrid of a large‐scale river model by assimilating observational data
A new neural network architecture is proposed based on Fourier feature embeddings to address the periodic tidal boundary
The time-dependent bridge pier scour during flood waves is analysed. Scour experiments were conducted in a novel installation able to produce complex hydrographs with high precision. Experimental ...data were used to test scour formulas including a new mathematical model. Results confirm the reliability and superior performance of the proposed dimensionless, effective flow work based model under steady and unsteady hydraulic conditions. Analyses highlight the impact of different hydrographs on scour, demonstrating the strong control by the hydrograph shape of the temporal evolution of scour depth and scour rate, although final scour after a flood only depends on the total effective flow work exerted by the hydrograph on the sediment bed. Hysteresis between flow discharge and scour rate is reported and explained. Flow acceleration is shown to play a minor role in scouring. The proposed model is a promising alternative for computation of local scour under highly unsteady hydraulic conditions.
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