Search Results (24)

The Clearwater River, located in western Washington, USA, is a free-flowing river with high precipitation rates impacted by spatially extensive logging throughout the 1900s. Declining salmon productivity within the watershed has been linked to the effects of legacy deforestation, including increased fine sediment loads, a lack of large wood and physical habitat complexity, and potential channel incision coupled with side channel and floodplain disconnection. To test a conceptual model positing that the river’s geomorphic diversity was declining, potentially due to anthropogenic incision, we employed a dual approach, combining historical geomorphic mapping and current-condition hydraulic modeling using SRH-2D. A dual approach allows us to identify mainstem river reaches with the greatest potential for floodplain and side channel reconnection by utilizing increased roughness as a proxy for large wood effects on the river stage. Based on our geomorphic mapping, the area occupied by the mainstem river and surrounding geomorphic units has remained relatively stable through time. However, there was a marked decrease in the side channel connections within the downstream-most 30 river kilometers, confirmed through the hydraulic modeling results. Between river kilometers 10 and 20, river stages at 2-year recurrence interval peak discharge are located over 2 m below young Holocene terraces and could indicate a recent anthropogenic incision contributing to side channel disconnection. A decrease in unvegetated alluvium through time also indicates that there could be less dynamic lateral channel movement and overbank inundation between 1980 and 2017, despite a similar history of high peak flows. Overall, even though the river is able to balance the loss of the active geomorphic unit area with the incorporation of new geomorphic units through lateral channel changes, this area is likely concentrated in a smaller number of individual channels and floodplains, specifically in the lower 30 river kilometers. This study provides a framework for a site-screening-level analysis in impacted watersheds, using a watershed impacted by legacy logging without flow regulation, where the impacts are often less pronounced than in dammed river systems. Full article

River embankments are critical flood defense structures, stretching for thousands of kilometers across alluvial plains. They often originated as natural levees resulting from overbank flows and were later enlarged using locally available soils yet rarely designed according to modern engineering standards. Substantially under-characterized, their performance to extreme events provides an invaluable opportunity to highlight their vulnerability and then to improve monitoring, management, and reinforcement strategies. In May 2023, two extreme meteorological events hit the Emilia-Romagna region in rapid succession, causing numerous breaches along river embankments and therefore widespread flooding of cities and territories. These were followed by two additional intense events in September and October 2024, marking an unprecedented frequency of extreme precipitation episodes in the history of the region. This study presents the methodology adopted to create a regional database of 66 major breaches and damages that occurred during May 2023 extensive floods. The database integrates multi-source information, including field surveys; remote sensing data; and eyewitness documentation collected before, during, and after the events. Preliminary interpretation enabled the identification of the most likely failure mechanisms—primarily external erosion, internal erosion, and slope instability—often acting in combination. The database, unprecedented in Italy and with few parallels worldwide, also supported a statistical analysis of breach widths in relation to failure mechanisms, crucial for improving flood hazard models, which often rely on generalized assumptions about breach development. By offering insights into the real-scale behavior of a regional river defense system, the dataset provides an important tool to support river embankments risk assessment and future resilience strategies. Full article

The morphological characteristics of catchments are key controls on how flow is routed through catchments and the spatial and temporal dynamics of floods, therefore influencing the shape of hydrographs at any location. Here, we developed a hydro-morphic catchment classification to understand the extent to which various catchment characteristics act as controls on flood behaviour. The catchment characteristics include: size (as measured by gauge position in catchment and valley confinement at the gauge site), shape (elongation ratio and form factor), topography (catchment relief and longitudinal slope), and drainage network structure (drainage density). A total of 2452 high flow (near bankfull) and overbank flood hydrographs from rivers in 17 coastal catchments of New South Wales (NSW), Australia were used. Cluster analysis on hydrograph shape metrics of kurtosis, skewness, and rate-of-rise was performed to identify classes of hydrographs and their median shape. Three statistically distinct clusters were delineated for both high flows and overbank floods, and categorised as flashy, intermediate, and broad. Topographic characteristics of catchments (i.e., relief and longitudinal slope) were commonly among the dominant controls for all high flow and overbank flood hydrographs, excluding broad overbank floods. Drainage network structure (i.e., drainage density) also controlled flashy and intermediate high flows, and intermediate and broad overbank floods, while catchment size (i.e., gauge position in the network) influenced broad high flows. Catchment shape (i.e., elongation ratio) influenced broad overbank floods, and is a dominant control on flashy high flows, and intermediate and broad overbank floods. Overall, topographic controls were more useful for differentiating the hydrological behaviour of high flows relative to overbank floods. Understanding the relative control of different catchment morphometric characteristics on flow and flood behaviour can be used to identify the aspects of flood behaviour that are set by imposed controls and cannot therefore be realistically manipulated in management. A hydro-morphic classification can also be used in the design and calibration of hydrological models, tailoring their use to hydro-morphic catchment class. Full article

The exchange of water, sediment, and nutrients in wetlands occurs through a complex network of channels and overbank flow. Although optical sensors can map channels at high resolution, they fail to identify narrow intermittent channels colonized by vegetation. Here we demonstrate an innovative application of rapid-repeat interferometric synthetic aperture radar (InSAR) to study hydrologic connectivity and tidal influences in Louisiana’s coastal wetlands, which can provide valuable insights into water flow dynamics, particularly in vegetation-covered and narrow channels where traditional optical methods struggle. Data used were from the airborne UAVSAR L-band sensor acquired for the Delta-X mission. We applied interferometric techniques to rapid-repeat (~30 min) SAR imagery of the southern Atchafalaya basin acquired during two flights encompassing rising-to-high tides and ebbing-to-low tides. InSAR coherence is used to identify and differentiate permanent open water channels from intermittent channels in which flow occurs underneath the vegetation canopy. The channel networks at rising and ebbing tides show significant differences in the extent of flow, with vegetation-filled small channels more clearly identified at rising-to-high tide. The InSAR phase change is used to identify locations on channel banks where overbank flow occurs, which is a critical component for modeling wetland hydrodynamics. This is the first study to use rapid-repeat InSAR to monitor tidal impacts on water flow dynamics in wetlands. The results show that the InSAR method outperforms traditional optical remote sensing methods in monitoring water flow in vegetation-covered wetlands, providing high-resolution data to support hydrodynamic models and critical support for wetland protection and management. Full article

The floodplain transverse slope is a significant parameter reflecting the degree of development of a secondary suspended river, as well as a crucial index of the flood risk in the river channel. Clarifying the factors that influence the evolution of the floodplain transverse slope has always been a hot and difficult topic for researchers working on the Yellow River management. We took the severe section of the secondary suspended river from Dongbatou to Gaocun in the lower Yellow River as the research object, selecting the annual runoff, annual sediment load, annual sediment coefficient, and the intensity of flood-season flow scouring at the Huayuankou station in the downstream as the water–sediment indexes. The correlation between different water–sediment indexes and the floodplain transverse slope under three modes: interannual, flood season, and flood-season overbank was studied through methods such as cross-wavelet transform and wavelet coherence analysis. The results showed that under the three modes, the annual sediment load and annual sediment coefficient had a high correlation with the evolution cycle of the transverse slope, followed by the intensity of flood-season flow scouring, and the annual runoff had the lowest correlation. Meanwhile, the change in the transverse slope had a good correlation with the flood-season overbank mode, indicating there was a high similarity between the water–sediment characteristics of floodplain flooding and the evolution cycle of the transverse slope; that is, the change in the transverse slope is greatly influenced by floodplain flooding events. Full article

As a prerequisite and foundation for studying the evolution mechanism of river channels, an in-depth understanding of the cross-sectional morphology adjustment is required. As a starting point, it is crucial to systematically summarize and generalize the research findings on channel morphological adjustment obtained to date, particularly in the context of the significant changes in the water and sediment conditions of large rivers that have occurred worldwide. This paper provides a comprehensive review of the research findings on the three following aspects of the Lower Yellow River: the transverse distribution of overbank flow velocity, the transverse distribution of suspended sediment concentration, and the morphological adjustment of the river cross-section. There are various equations available to predict the lateral depth–average flow velocity distribution. These equations are classified into the two following categories: empirical and theoretical formulas. Theoretical formulas are obtained through consideration of the cross-sectional morphology, accounting for inertial force terms caused by secondary flow, and momentum transfer between the main channel and its floodplain. Similarly, empirical equations and theoretical formulas for sediment concentration transverse distribution are also summarized, given the different influencing factors and assumptions. We also discuss the morphological adjustment of river cross-sections based on the analysis of measured data, mathematical model calculation, and the physical model test. In particular, we propose the idea of revealing channel cross-section morphology evolution mechanisms from the theoretical level of water and sediment movement and distribution. This review aims to enhance understanding of overbank flow, sediment transport, and channel morphology in the Lower Yellow River and may also serve to some extent as a reference for the evolution and management of channels in other rivers. Full article

Environmental flow assessment is an essential tool in water resource management. This study employs a holistic approach to evaluate the environmental flow in the Yen Basin, Thanh Hoa, Vietnam. Based on information gathered from a field survey, the Yen River system is divided into five reaches, and environmental objectives and ecological assets are identified in each reach. Hydrological and hydraulic mathematical models are applied to simulate the flow regime in the river, demonstrating their potential to assess environmental flow, especially in basins with limited data. The detailed results from the mathematical model facilitate selecting environmental flow components to address specific objectives for each river reach. By analyzing and selecting the flow regime, this study aims to ensure environmental protection while also considering basin development requirements, laying the groundwork for defining prescribed flow regimes in basin water management. Full article

The dynamic behavior of flood waves on rivers is essential to flood prediction. Natural flood waves are complex due to tributary inputs, rainfall variations, and overbank flows, so this study examines hydropower dam releases, which are simpler to analyze because channel effects are isolated. Successive arrival times and heights of peaks along 9 rivers with multiple stream gauges downstream of hydroelectric dams show that flow peaks typically become exponentially lower and wider with distance. The propagation velocity of peaks increases with water depth and channel slope but decreases with downstream distance and greater channel tortuosity. A rich hierarchy of velocities was found. Hydropower pulses progress at or in slight excess of the theoretical celerity, which is faster than the propagation rate of average natural floods, which in turn exceeds the mean velocity of water in the channel, yet the water moves faster than the peaks of record floods. The progressive changes to the height, shape, and velocity of hydropower flow peaks are simulated by the first analytical solution to the convolution integral for a rectangular source pulse that is based on diffusion-advection theory. Available data support some widely held expectations while refuting others. An expanded definition of “water mining” is proposed. Full article

The origin and dynamics of a 2010 pluvial flood in the valley of a large European river are described. In order to study how local people perceive this catastrophic event a small administrative unit (rural municipality) within the Holocene floodplain (thus flooded to 90%) was chosen. Using a questionnaire a human-research survey was performed in the field among 287 people living in flood-prone areas. Almost half of the interviewees feel safe and do not expect a flood recurrence (interpreted as a levee effect). Seventeen percent believe the levee was intentionally breached due to political issues. Six percent of interviewees link the breach with small mammals using levees as a habitat, e.g., beavers, moles, and foxes. The sex and age of interviewees are related to these opinions. Most interviewees (39%) think that flooding was a result of embankment (dyke) instability. The spatial distribution of the survey results are analyzed. Maps presenting: inundation height, economic loss, attitude to geohazards and perception of possible flood recurrence were drawn. Causes of the flood as viewed by local inhabitants and in the context of the riverine geological setting and its processes are discussed. Particular attention is paid to processes linking the levee breach location with specific geomorphic features of the Holocene floodplain. A wide perspective of fluvial geomorphology where erosive landforms of crevasse channels (and associated depositional crevasse splays) are indicators of geohazards was adopted. This distinct geomorphological imprint left by overbank flow is considered a natural flood mark. Such an approach is completely neglected by interviewees who overestimate the role of hydrotechnical structures. Full article

The physical and biological structure of riparian vegetation fundamentally influences floodplain roughness, and thus the flood velocity and flood levels of a river. The study aims to provide detailed spatial data on the vegetation density of a floodplain, and to model the effect of the actual vegetation and various scenarios on flow conditions. LiDAR data were applied to evaluate the density and roughness of the submerged understory vegetation over the densely vegetated floodplain of Lower Tisza, Hungary. Then, HEC–RAS 2D modelling was applied to analyse the effect of the actual vegetation on flow conditions. Further scenarios were also created to predict the effect of (i) invasive plant control, (ii) no maintenance, and (iii) riparian vegetation restoration (meadows). According to the results, since the 19th Century, the increased vegetation density is responsible for a 17-cm flood level increase, and if the vegetation grows even denser, a further 7 cm could be expected. As the vegetation density increases, the overbank flow velocity decreases, and the crevasses and flood conveyance zones gradually lose their function. Simultaneously, the flow velocity increases in the channel (from 1 m/s to 1.4 m/s), resulting in an incision. Applying LiDAR-based 2D flow modelling makes it possible to plan sustainable riparian vegetation maintenance (e.g., forestry, invasive species clearance) from both ecology and flood control perspectives. Full article

Abandoned channels are essential in the Quaternary floodplains, and their infill contains different paleoenvironment recorders. Grain-size distribution (GSD) is one proxy that helps characterize the alluviation and associated sedimentological processes of the abandoned channels. The classic statistical methods of the grain-size analysis provide insufficient information on the whole distribution; this necessitates a more comprehensive approach. Grain-size endmember modeling (EMM) is one approach beyond the traditional procedures that helps unmix the GSDs. This study describes the changes in the depositional process by unmixing the GSDs of a Holocene abandoned channel through parameterized EMM integrated with lithofacies, age–depth model, loss-on-ignition (LOI), and magnetic susceptibility (MS). This approach effectively enabled the quantification and characterization of up to four endmembers (EM1-4); the characteristics of grain-size endmembers imply changes in sedimentary environments since 8000 BP. EM1 is mainly clay and very fine silt, representing the fine component of the distribution corresponding to the background of quiet water sedimentation of the lacustrine phase. EM2 and EM3 are the intermediate components representing the distal overbank deposits of the flood. EM4 is dominated by coarse silt and very fine sand, representing deposition of overbank flow during the flood periods. This paper demonstrates that the parametrized grain-size EMM is reasonable in characterizing abandoned channel infill sedimentary depositional and sedimentation history. Full article

The Inka site of Tipon had many unique hydraulic engineering features that have modern hydraulic theory counterparts. For example, the Tipon channel system providing water to the Principal Fountain had a channel contraction inducing critical flow as determined by CFD analysis- this feature designed to induce flow stability and preserve the aesthetic display of the downstream Waterfall. The Main Aqueduct channel sourced by the Pukara River had a given flow rate to limit channel overbank spillage induced by a hydraulic jump at the steep-mild slope transition channel location as determined by use of modern CFD methods- this flow rate corresponds to the duplication of the actual flow rate used in the modern restoration using flow blockage plates placed in the channel to limit over-bank spillage. Additional hydraulic features governing the water supply to agricultural terraces for specialty crops constitute further sophisticated water management control systems discussed in detail in the text. Full article

We examined riparian system responses to an extreme rainfall event on 1–4 December 2007, in eleven small watersheds (mean area—13.2 km²) from 2008–2016 at debris flow, high flood, and low flood reaches (all extended overbank flows). Macroinvertebrate responses followed expected outcomes after extreme disturbance including increasing chironomids and other multi-voltine species. A core assemblage of twenty abundant and common species-maintained populations even after debris flow (likely by recolonizing quickly) with total richness during project of 253 including 183 rare species (<0.01 total abundance) supporting an annual turnover of species from 22 to 33%. Primary disturbance changes to habitat were declines in shade and in-channel wood at all reaches, more strongly at debris flow reaches. Macroinvertebrate communities across disturbance intensities became increasingly similar after the storm. Combined effects of the flood reducing channel complexity and previous logging decreasing in-channel wood recruitment from riparian systems, limits habitat complexity. Until this feature of forested watershed streams returns, there appears to be a ceiling on reach scale aquatic biological diversity. Full article

River deltas have received considerable attention due to coastal land loss issues caused by subsidence, storms, and sea level rise. Improved understanding of deltaic processes and dynamics is vital to coastal restoration efforts. This paper describes the application of process-based morphodynamic models to a prograding river delta. The analysis focuses on the flow and sediment dynamics amongst the interconnected channel network of the delta. The models were validated against observations of velocity and sediment concentrations for the Wax Lake Delta (WLD) of the Atchafalaya River system in Louisiana, USA. The WLD provides an opportunity as a natural laboratory for studying the processes associated with river dominated deltaic growth. It includes a network of bifurcated channels that self-organize and dynamically adjust, as the delta grows seaward to the Gulf of Mexico. The model results for a flood event show that 47% of the flow exits the system as channelized flow and the remaining 53% exits as overbank flow. The fine sediment (silt and clay) distribution was proportional with water fluxes throughout the channel network, whereas sand distribution was influenced by geometric attributes (size, invert elevation, and alignment) of the distributary channels. The long-term deltaic growth predicted by the model compares well with the observations for the period 1998–2012. This paper provides insights on how the distribution of flow and sediment amongst the interconnected delta channels influences the morphodynamics of the delta to reach a dynamic equilibrium within this relatively young deltaic system. Full article

Connectivity metrics for surface water are important for predicting floods and droughts, and improving water management for human use and ecological integrity at the landscape scale. The integrated use of synthetic aperture radar (SAR) observations and geostatistics approach can be useful for developing and quantifying these metrics and their changes, including geostatistical connectivity function (GCF), maximum distance of connection (MDC), surface water extent (SWE), and connection frequency. In this study, we conducted a geostatistical analysis based on 52 wet and dry binary state (i.e., water and non-water) rasters derived from Sentinel-1 A/B GRD products acquired from 2015 to 2019 for China’s Momoge National Nature Reserve to investigate applicability and dynamics of the hydrologic connectivity metrics in an ungauged (i.e., data such as flow and water level are scarce) multi-lake system. We found: (1) generally, the change of GCF in North–South and Northeast–Southwest directions was greater than that in the West–East and Northwest–Southeast directions; (2) MDC had a threshold effect, generally at most 25 km along the W–E, NW–SE and NE–SW directions, and at most 45 km along the N–S direction; (3) the flow paths between lakes are diverse, including channelized flow, diffusive overbank flow, over-road flow and “fill-and-merge”; (4) generally, the values of the three surface hydrological connectivity indicators (i.e., the MDC, the SWE, and the conneciton frequency) all increased from May to August, and decreased from August to October; (5) generally, the closer the distance between the lakes, the greater the connection frequency, but it is also affected by the dam and road barrier. The study demonstrates the usefulness of the geostatistical method combining Sentinel-1 SAR image analysis in quantifying surface hydrological connectivity in an ungagged area. This approach should be applicable for other geographical regions, in order help resource managers and policymakers identify changes in surface hydrological connectivity, as well as address potential impacts of these changes on water resources for human use and/or ecological integrity at the landscape level. Full article