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•River discharge has two scaling regimes.•High correlation between complexity and 1/f fractal fluctuations.•New extension for the information/complexity metrics for flood analysis.
...The availability of distinctly interpretable assessments to characterize and describe river discharge for mountainous rivers for different climatic events can improve our understanding of the various dynamics related to hydrological processes. Furthermore, information and complexity metrics can reveal invaluable information about the unseen processes that occur within a system. In this study, hourly streamflow records obtained from five gauging stations of a mountainous river were analyzed to quantify different patterns and characterize system states at both low and high frequencies using increasing aggregation lengths. In addition, we propose a new extension for the information and complexity theory, allowing it to be customized for flood assessment. Moreover, we clarify how a pattern (i.e., a word length) can be suitably defined by means of information and complexity metrics. Regarding low-frequency analyses, our results related to information and complexity metrics indicate two scaling regimes for river discharge, one of which may describe river memory characteristics. Regarding high-frequency analyses, our findings indicate the presence of an additional scaling regime that occurs along an hourly scale, captured by streamflow data, and is obtained using a novel hydroacoustic system. Additionally, power spectral density results confirmed our findings. A further significant result from our study is the clear correlation between complexity and fractal fluctuations, which should be addressed in future studies. In summary, this research focuses on new aspects of information and complexity metrics to be customized for the detection and understanding of temporal structures of streamflow patterns during both standard and extreme events.
Understanding of flood dynamics forms the basis for the leading water resource management and flood risk mitigation practices. In particular, accurate prediction of river flow during massive flood ...events and capturing the hysteretic behavior of river stage-discharge are among the key interests in hydrological research. The literature demonstrates that data-driven models are significant in identifying complex and hidden relationships among dependent variables, without considering explicit physical schemes. In this regard, we aim to discover the extent to which data-driven models can recognize the hidden relationships among different hydrological variables, in order to generate accurate predictions of the river flow. A secondary aim involves the detection of whether data-driven models can digest the internal features of training inputs to extrapolate severe flood records beyond the training domain. To achieve these aims, we developed a recurrent neural network (RNN) model of two hidden layers to capture the hidden relationships among the inputs, and investigated the model’s predictive capability using quantitative and qualitative analyses. The quantitative analysis comprised of a comparison between model predictions, and another set of precise independent records obtained through an advanced hydroacoustic system for reference. A qualitative approach was adopted to visualize the hysteretic behavior of the stage-discharge relations of the model records, with the high-resolution records of the hydroacoustic system. The findings display the potential of data-driven models for accurately predicting river flow. Consequently, the qualitative analysis revealed moderate correlations of stage-discharge loops as compared to the reference records. Additionally, the model was tested against severe destructive flood records generated from the East Asian monsoon and tropical cyclones. Its findings suggest that data-driven models cannot extrapolate new features beyond their training dataset. Overall, this study discusses the competence of RNNs in providing reliable and accurate river flow predictions during floods.
Accurate streamflow measurements are often challenging for extremely shallow rivers within complex bathymetries. In this study, a new version of the fluvial acoustic tomography (FAT) system operated ...by high-frequency 53-kHz underwater acoustic transducers was used to measure the discharge of a shallow mountainous river. The system was placed under a stringent site condition that was challenging for receiving pure underwater acoustic signals and hence, resulted in low-quality estimates of the river discharge. To overcome this challenge, the shortest path graph method was adopted to capture the desired hydroacoustic data, which can improve the discharge measurements significantly. The results showed that the discharge estimated by the FAT was in very good agreement with that estimated by the rating curve method, suggesting that the FAT was capable of measuring the river discharge for shallow streams when the minimum water depth for a given cross-section was greater than 28 cm. In addition, the findings of this study indicated that under the low-flow condition, the temperature variations during the daytime and nighttime along the acoustic cross-section can play an important role in reducing the signal-to-noise ratio, hence leading to sparse and weak signals of the arrival time, as recorded by the acoustic transducers.
Applying the fluvial acoustic tomography (FAT) system to shallow tidal junctions for studying the flow division and spatiotemporal difference of velocity and salinity is vital to understand the tidal ...hydrodynamics in multi-channel networks. To the best of our knowledge, this is the first study that monitors continuous 2D current and salinity distributions at a shallow tidal junction using six FATs for ~34.4 days. The horizontal distribution and spatiotemporal variation of the currents and salinity were efficiently estimated by the inverse method. These results demonstrate that FAT is a potential tool for the continuous mapping of variable 2D currents and salinity at shallow tidal junctions. The reciprocating patterns of the current and salinity during the spring tide at the junction responded well to the tide. High salinity occurred around high water, whereas salinity was negligible at low water. During flood tides, significant landward currents flowed with the maximum speed of ~0.4 m/s, and significant seaward currents with the maximum speed of ~0.55 m/s occurred during ebb tides. During neap tides, the salinity pattern began to develop landward from the low water and reached a mature phase around the high water; salinity at the ebb slack remained high. Inverted FAT results indicated a counter-clockwise circulation around the low water during neap tide; some of the currents continuously flowed landward at the downstream of the junction (S4–S5), whereas others continuously flowed to the Tenma River. The behaviors of the currents varied slightly with the tide. The behaviors of the current and salinity during the neap tide mostly resulted from the density-driven current phenomenon. Furthermore, tidal harmonic analyses of the reconstructed currents were performed to clarify the river-tide interactions at the tidal junction. The results reflected the increased tidal wave deformation that occurred with the gradually increasing tidal range and demonstrated the role of the limited river flow on the tidal asymmetry at this tidal junction. This study advances the understanding of river flow dynamics in shallow tidal junction systems.
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•Six fluvial acoustic tomography (FAT) systems were deployed at a tidal junction.•Monitored 2D tidal current and salinity distributions at a shallow tidal junction.•FAT is useful for mapping 2D currents and salinity at shallow tidal junctions.•Findings advance the understanding of river flow dynamics in shallow tidal systems.
Understanding the streamflow hydrodynamics is important for forecasting flooding phenomena in mountainous rivers. Accordingly, based on long‐term runoff observations obtained using diverse runoff ...techniques (i.e., rating curves and fluvial acoustic tomography (FAT)), the authors (1) evaluated and explored flood phenomena, (2) discussed the effects of dams on flood hydrograph, (3) and revealed backwater effects caused by river channel bends, sand bars, and floodplains. The duration and slope of the falling limb of the hydrograph were directly influenced by the catchment characteristics that affected runoff recession, whereas the behaviour of the rising limb of the hydrograph was directly influenced by rainfall. A weaker correlation between discharge and rainfall in higher flood events indicates that rainfall events were strongly altered by water released from dams in the basin. Additionally, because of the backwater effects, the rate at which the flow velocity and boundary shear stress changed with the increasing discharge was reduced, potentially slowing the pace of erosion. Our findings are relevant for managing mountain rivers, particularly in river bend reaches prone to backwater effects. The FAT method could help increase the ability to monitor short‐term fluctuations in floods and associated hazards.
Fluvial acoustic tomography system was used to determine key streamflow characteristics (i.e., rainfall, backwater effects) based on a high temporal resolution of 10 min and long‐term observations of streamflow in a mountainous river.
To assess the dynamics of rivers, a reliable characterization of river streamflow during unsteady flow regimes is of paramount importance. In this work, we aimed at investigating the characteristics ...of turbidity–discharge (T–Q) dynamics corresponding to annual artificial dam flush release in a mountainous stream. Two methods for evaluating discharge were used in this study: the classical rating curve and the fluvial acoustic tomography (FAT) system that was developed by Hiroshima University. Interestingly, during dam flush, the discharge records obtained by FAT showed striking features of unsteady streamflow behavior, such as discharge shoulders and, in some events, secondary discharge peaks. According to the T–Q hysteresis loops, the common type of T–Q observed patterns were anticlockwise loops. During the studied DF events, sediment was supplied by river banks located at different sites along the river channel.
•Short-scale streamflow variations during dam flush events were monitored by a novel acoustic tomography system.•Distinctive features were observed in the discharge hydrographs, which differed from the original flush patterns.•Turbidity–discharge hysteresis due to artificial dam flush was studied.
A novel acoustic tomographic measurement system capable of resolving sound travel time in extremely shallow rivers is introduced and the results of an extensive field measurements campaign are ...presented and further discussed. Acoustic pulses were transmitted over a wide frequency band of 20–35 kHz between eight transducers for about a week in a meandering reach of theBāsen River, Hiroshima, Japan. The purpose of the field experiment was validating the concept of acoustic tomography in rivers for visualizing current fields. The particular novelty of the experiment resides in its unusual tomographic features: subbasin scale (100 m × 270 m) and shallowness (0.5–3.0 m) of the physical domain, frequency of the transmitted acoustic signals (central frequency of 30 kHz), and the use of small sampling intervals (105 s). Inverse techniques with no a priori statistical information were used to estimate the depth‐average current velocity components from differential travel times. Zeroth‐order Tikhonov regularization, in conjunction with L‐curve method deployed to stabilize the solution and to determine the weighting factor appearing in the inverse analysis. Concurrent direct environmental measurements were provided in the form of ADCP readings close to the right and left bank. Very good agreement found between along‐channel velocities larger than 0.2 m/s obtained from the two techniques. Inverted quantities were, however, underestimated, perhaps due to vicinity of the ADCPs to the banks and strong effect of river geometry on the readings. In general, comparing the visualized currents with direct nodal measurements illustrate the plausibility of the tomographically reconstructed flow structures.
Key Points:
Array of tomographic sensors is deployed in a 270x100m domain of a shallow river
Horizontal flow field is reconstructed using 15 paths and inversion techniques
Comparison with stationary ADCPs denotes the plausibility of reconstructed flow
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•Monitoring river dynamics using three underwater tomographic systems.•Estimating continuous cross-sectional mean velocity and runoff based on travel-time.•Proposing new equations to ...estimate continuous mean flow direction using travel-time.•Flow direction in unidirectional river can be estimated using three acoustic stations.
Monitoring flood dynamics is important to provide optimal flood mitigation practices and understand their hydrological responses. Recently, applications of travel time principles have gained a growing interest in hydrological research and river engineering. In this study, flood dynamics were monitored using the fluvial acoustic tomography system (FAT), based on travel time principles. The primary objective of this study is to continuously measure the mean cross-sectional velocity, river flow direction, and river discharge using an innovative tomographic system during two flood events. In this regard, three FAT systems were placed in a gravel bed stream forming a triangle shape to measure stream velocity along two cross-sections. By investigating the magnitude of the cross-sectional mean velocity vectors and the cross-sectional areas, we proposed new equations to evaluate the expected flow direction. The performance of flow measurement by the FAT system was verified with another reference record. Importantly, we demonstrated that the minimum number of acoustic stations to determine river flow direction in unidirectional streams can be reduced to three stations which can be more practical and easier. Further, one of the novel aspects of this study is offering new guidelines to continuously estimate flow direction using a triangular distribution of tomographic systems. In general, this study presents a promising method for monitoring flow dynamics in rivers.
Given the changing climate, understanding the recent variability in large-scale rainfall patterns is a crucial task in order to better understand the underlying hydrological processes that occur ...within a watershed. This study aims to investigate how rainfall events in western Japan have changed due to climate change and how these changes have affected runoff–turbidity dynamics during the rainy season. To address the research objectives, we analyzed two decades of precipitation records in the Gōno River watershed and examined the associated runoff–turbidity dynamics during floods using turbidity–discharge (T-Q) loops, quantified using an enhanced hysteresis index. Our findings revealed a kind of intense rainfall event occurring every 3 to 4 years. Additionally, spatial pentad analysis showed varying intensities of accumulated precipitation, indicating that extreme rainfall is not confined to a specific spatial zone. Regarding turbidity–discharge behavior, we found that clockwise hysteresis patterns were caused by sediment sources from near-channel areas, while anticlockwise patterns were caused by soil erosion from nearby areas. Another notable finding was that turbidity peaks during floods may represent the earlier (or later) arrival of turbid water from distant upstream sources due to intense precipitation. One of the key challenges in quantifying hysteresis patterns is that there is no agreed-upon definition for how to determine the start and end of a flood event. This can lead to bias in the quantification of these patterns.
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