Search Results (11)

The ICESat-2 and SWOT satellite earth observation missions have provided highly accurate water surface slope (WSS) observations in global rivers for the first time. While water surface slope is expected to remain constant in time for approximately uniform flow conditions, we observe time varying water surface slope in many river reaches around the globe in the ICESat-2 record. Here, we investigate the causes of time variability of WSSs using simplified river hydraulic models based on the theory of steady, gradually varied flow. We identify bed slope or cross section shape changes, river confluences, flood waves, and backwater effects from lakes, reservoirs, or the ocean as the main non-uniform hydraulic situations in natural rivers that cause time changes of WSSs. We illustrate these phenomena at selected river sites around the world, using ICESat-2 data and river discharge estimates. The analysis shows that WSS observations from space can provide new insights into river hydraulics and can enable the estimation of river discharge from combined observations of water surface elevation and WSSs at sites with complex hydraulic characteristics. Full article

Lake Konin is a small and shallow lake under the influence of highly eutrophic riverine waters. Feeding the lake as a backwater during high water level periods, the River Obra had exerted a decisive impact on lake water quality, and thus a new dike with a closing device was created. Protective measures were followed by the application of Effective Microorganisms (EM), aiming at a reduction in nutrient concentrations and CyanoHABs. Positive changes in the ecosystem were initiated (increased phytoplankton diversity), but cyanobacteria blooms were still present due to high nutrient content. Some changes were observed in the lake sediments (phosphorus (P) and its fractions, P in pore waters, organic matter and experimental assessment of internal P loading) studied before and during treatment. A slight increase in P content in sediments was noted, as a result of an increase in the Res-P fraction. Simultaneously, a decrease in the most mobile fractions was observed. Summer internal P load was reduced from 5.4 kgP d⁻¹ before the treatment to less than 1 kgP d⁻¹ in the first year, but increased again in the second year to 4.5 kgP d⁻¹. Similarly to lake water quality, positive changes were induced in the lake sediments; nevertheless, they still acted as an important source of nutrients for primary producers. Additional restoration methods shall be considered, as combined treatments used simultaneously are reported to be the most effective for water quality improvement. Full article

This article provides a comprehensive overview of ice-jam flood forecasting methodologies applicable to rivers during freezing. It emphasizes the importance of understanding river ice processes and fluvial geomorphology for developing a freeze-up ice-jam flood forecasting system. The article showcases a stochastic modelling approach, which involves simulating a deterministic river ice model multiple times with varying parameters and boundary conditions. This approach has been applied to the Exploits River at Badger in Newfoundland, Canada, a river that has experienced several freeze-up ice-jam floods. The forecasting involves two approaches: predicting the extent of the ice cover during river freezing and using an ensemble method to determine backwater flood level elevations. Other examples of current ice-jam flood forecasting systems for the Kokemäenjoki River (Pori, Finland), Saint John River (Edmundston, NB, Canada), and Churchill River (Mud Lake, NL, Canada) that are operational are also presented. The text provides a detailed explanation of the processes involved in river freeze-up and ice-jam formation, as well as the methodologies used for freeze-up ice-jam flood forecasting. Ice-jam flood forecasting systems used for freeze-up were compared to those employed for spring breakup. Spring breakup and freeze-up ice-jam flood forecasting systems differ in their driving factors and methodologies. Spring breakup, driven by snowmelt runoff, typically relies on deterministic and probabilistic approaches to predict peak flows. Freeze-up, driven by cold temperatures, focuses on the complex interactions between atmospheric conditions, river flow, and ice dynamics. Both systems require air temperature forecasts, but snowpack data are more crucial for spring breakup forecasting. To account for uncertainty, both approaches may employ ensemble forecasting techniques, generating multiple forecasts using slightly different initial conditions or model parameters. The objective of this review is to provide an overview of the current state-of-the-art in ice-jam flood forecasting systems and to identify gaps and areas for improvement in existing ice-jam flood forecasting approaches, with a focus on enhancing their accuracy, reliability, and decision-making potential. In conclusion, an effective freeze-up ice-jam flood forecasting system requires real-time data collection and analysis, historical data analysis, ice jam modeling, user interface design, alert systems, and integration with other relevant systems. This combination allows operators to better understand ice jam behavior and make informed decisions about potential risks or mitigation measures to protect people and property along rivers. The key findings of this review are as follows: (i) Ice-jam flood forecasting systems are often based on simple, empirical models that rely heavily on historical data and limited real-time monitoring information. (ii) There is a need for more sophisticated modeling techniques that can better capture the complex interactions between ice cover, water levels, and channel geometry. (iii) Combining data from multiple sources such as satellite imagery, ground-based sensors, numerical models, and machine learning algorithms can significantly improve the accuracy and reliability of ice-jam flood forecasts. (iv) Effective decision-support tools are crucial for integrating ice-jam flood forecasts into emergency response and mitigation strategies. Full article

The backwater lowland habitats of large rivers, like the Mississippi River in North America, present complex and often inaccessible environments for traditional capture-based fish biodiversity sampling. Our knowledge of the assemblages of the fishes that occupy such habitats is often incomplete, and this can compromise management efforts. We employed environmental DNA (eDNA) metabarcoding methods to sample a Mississippi River bottom wetland system to assess the ichthyofaunal diversity and the assemblage structure across habitat types, and we compared our results with capture-based survey records for the same habitats. We collected water samples in the spring and fall of 2022 from slough, ditch, shallow lake, and bayou habitats that varied in depth, vegetation, seasonal variability, and connectivity to the Mississippi River channel. We detected a diverse array of fish species that included 51 taxa. Nearly all the species previously documented in the habitats were detected using eDNA metabarcoding, and we increased the number of documented species by more than a third. Most of the species were ubiquitous across the range of habitats, but there was also a substantial assemblage structure, with some species exhibiting clear habitat specificity. Fall sampling was limited to the deeper bayou habitats where seasonal variation between the spring and fall was minimal. eDNA metabarcode sampling was demonstrated to be effective at detecting invasive species as well as uncommon species, which included several species of conservation concern. Full article

Since the impoundment of the Three Gorges Project, the downstream hydrology and river dynamics have been modified. The Yichang–Chenglingji Reach (YCR), as a part of the mainstream of the Middle Yangtze River, has consequently been significantly scoured, which has resulted in stream trenching and section enlargements, without showing any obvious trend in flood level variation, however. This phenomenon can be caused by the increase in riverbed resistance due to river geomorphological change and bottomland vegetation development and the backwater effect of Dongting Lake. To investigate how these factors influence the flood water levels, this study analyzed the variations in the influencing factors based on observational data, theoretical analysis and mathematical modelling, including river channel scouring, riverbed resistance, and the influence of Dongting Lake backwater. Then, the impact of these factors on flood levels was evaluated, followed by a comparative analysis of the effects of various factors. The results show that both the flood backwater height (ΔZ) and the backwater influence range (L) are positively correlated with the outflow intensity (T) at the Chenglingji station. The backwater effect decreases gradually with increasing upstream distance, and the influence on the upstream reach can extend up to Shashi city. It was also indicated that the increase in riverbed resistance due to bottomland vegetation development and river geomorphology are dominant factors in inhibiting flood level declines in the YCR, while the backwater of Dongting Lake just affects local regions. This study can provide a better understanding of the flood level changes of the YCR and thus contribute to flood control and riverbank protection of the Yangtze River in the future. Full article

In the context of global climate change, the frequency of watershed flooding events resulting from extreme rainfall has significantly increased. Especially at river or lake confluences, the presence of backwater effects greatly amplifies the flood risk. To investigate the influence of backwater effects on the hydraulic characteristics of rivers and lakes, this study focuses on the Dongping Lake in China. An enhanced two-dimensional hydrodynamic model was employed to simulate and analyze three different degrees of backwater effects. The results indicate that, compared to the working conditions without the backwater effect, the highest lake water level increased by 1.0 m and 0.1 m under severe and moderate backwater effect conditions, respectively. The total outflow flood volume decreased by 30.1% and 2.3%, respectively. The demolition time for the Jinshan Dam needs to be advanced by 12.5 h and 10.0 h, respectively, and the inundation area in the western region expanded by 2.73% and 0.32%. Additionally, the average inundation depth increased by 0.93 m and 0.08 m, respectively. These results provide valuable data support for the safe operation of Dongping Lake, the formulation of flood defense strategies, and, likewise, offer valuable insights into the risk management of flood events in other rivers and lakes with backwater effects. Full article

The hydrological characteristics of the river–lake connecting section are determined by their interaction and studying them can help to understand the changing relationship between these two water bodies over time. The Lujiao–Luosan section is the connecting section of Dongting Lake and the Yangtze River, and the hydrological data for this section over the past 70 years has been analyzed. It has been found that the lowest water level is consistently rising at the same discharge at Chenglingji station, which is the joint point of Dongting Lake and the Yangtze River. While this could alleviate the drought situation in the Dongting Lake area during dry seasons, it could pose a more significant flood-control challenge during high water levels in the flood season. The water surface slope shows a decreasing trend especially during the dry season, except for the high flood period (July–September), which indicates that the water slope in the connecting section of Dongting Lake has become flatter. The backwater effect of the Yangtze River on Dongting Lake becomes increasingly stronger as the water surface slope difference between the Chenglingji–Luoshan section and the Lujiao–Chenglingji section changes from negative to positive between January and April. Full article

Some lakeside cities may suffer from urban waterlogging owing to the backwater effect caused by the rise of lake water levels under a extreme rainfall scenario in the basin, but it is not suitable for large-scale gray drainage infrastructure upgrading in high-density lakeside urban built-up areas. This study, as per this, constructs the blue-green-gray infrastructure reconstruction planning and design mode to alleviate the waterlogging in the extreme rainstorm scenario of the lakeside city. Extending the Shiwuli River Basin in Hefei City, Anhui Province, China as an example, this study uses SWMM software to simulate the waterlogging situation in the study area under an extreme rainstorm under the urban planning scenario. According to the waterlogging situation, different hydrological scenarios (scenarios where the pipe network can and cannot discharge normally) are used to plan and design the blue-green-gray infrastructure reconstruction of the study area with both constructed land and non-constructed land. The research results show that just the planning and design of blue and green space can effectively reduce the degree of urban waterlogging, and with the cooperation of artificial pre-drainage, its own hydrological characteristics and geographical conditions can be used to prevent urban waterlogging caused by the backwater effects of a lake. In this study, the blue-green-gray transformation planning and design model of lakeside cities can deal with the complex urban waterlogging caused by extreme rainstorms, and the model could be extended to other cities along rivers or lakes with similar conditions. Full article

In a previous study two pairs of paleo-landslides within an 8 km reach of the upper Yellow River were studied and dated back to ca. 80 ka, however the relationship between these two pairs of paleo-landslides were not explored. This study inferred that the initial pair of landslides (Dehenglong and Suozi) appearing contiguously and forming an upstream 46 km-long lake along the river may be triggered by earthquake events from nearby capable faults. Subsequently, backwater inundating the valley floor as the dammed lake formed may cause shear stress of sediments lowered on steep slopes adjacent to the River, and eventually induce the other two additional landslides (Xiazangtan and Kangyang) ~8 km upstream. This could be inferred from two optically stimulated luminescence (OSL) samples yielding ca. 80 ka also, which were collected from asymmetric folds 10 to 30 cm in amplitude within the bedding plane between lake/lakeshore sediment and landslide mass at the front lobes of the two additional landslides. We estimated the maximum volume of this dammed lake was 38 km³ and may generate an outburst flood with an estimated peak discharge of 6.1 × 10⁵ m³/s, which may cause massive geomorphic effects and potential disasters upstream and downstream. It is important to better understand the geomorphic process of this damming event in mountainous area with respect to reflecting tectonic uplift, paleoclimatic change and forecast and mitigate hazards on the northeast Tibetan Plateau. Full article

We investigated how hydro-climatological changes would affect fluvial forces and inundated area during a typical high-flow situation (MHQ, mean high discharge), and how adaptive regulation could attenuate the climate change impacts in a low-relief river of the Southern Boreal climate area. We used hydrologically modeled data as input for 2D hydraulic modeling. Our results show that, even though the MHQ will increase in the future (2050–2079), the erosional power of the flow will decrease on the study area. This can be attributed to the change of timing in floods from spring to autumn and winter, when the sea levels during flood peaks is higher, causing backwater effect. Even though the mean depth will not increase notably (from 1.14 m to 1.25 m) during MHQ, compared to the control period (1985–2014), the inundated area will expand by 15% due to the flat terrain. The increase in flooding may be restrained by adaptive regulations: strategies favoring ecologically sustainable and recreationally desirable lake water levels were modeled. The demands of environment, society, and hydropower are not necessarily contradictory in terms of climate change adaptation, and regulation could provide an adaptive practice in the areas of increased flooding. Full article

An integrated hydrological-hydraulic model employing the 2-D local inertial equation as the core is established for effective numerical simulation of surface water flows in a great lake and its floodplain. The model is a cascade of validated hydrological and hydraulic sub-models. The model was applied to simulating the surface water flows of the Tonle Sap Lake and its floodplain in Cambodia using the roughness coefficient value calibrated comparing with a remote-sensing data set. The resulting model reasonably handles backwater flows during the rainy season and simulates the propagations of wet and dry interfaces without numerical instability, owing to a proper setting of time step supported by a novel numerical stability analysis. Sensitivity analysis of the surface water dynamics focusing on the setting of roughness coefficient and the backwater effect was also carried out. Overall, utilizing the 2-D local inertial equation in the assessment of lake water dynamics is a new modelling approach, which turns out to be an efficient simulation tool. Full article