Search Results (29)

Planform evolution and terrestrial habitat health of two representative mid-channel bars (Baishazhou bar and Tianxingzhou bar) in the urban reach of the Middle Yangtze River in Wuhan City have not been understood under the combined influences of natural forcing and human activities. Using dry-season Landsat imagery (1989–2020), hydrological records from the Hankou gauging station (1990–2019), and field surveys, we quantified bar-morphology changes and examined the mechanisms underlying their differentiated scouring. We also developed an indicator system to evaluate terrestrial habitat health on mid-channel bars. Indicator weights were determined using a combined weighting approach integrating the Analytic Hierarchy Process and the entropy weight method. Since the Three Gorges Dam began operation, the runoff in the Wuhan reach has decreased only slightly (6.72%), whereas sediment load decreased sharply (69.88%), causing net scouring of both bars. Baishazhou bar, in a straight anabranching reach, lost 43.83% of its area (1989–2020), with erosion concentrated at the head and main channel margin and caving. Tianxingzhou bar, in a mildly curved reach, had moderate shrinkage (26.33%, 1992–2022) as revetments curbed head/right margin retreat. Both bars were “very healthy” in natural attributes, with the Baishazhou bar showing longer water–land ecotone exposure (217 d) and higher vegetation cover (92%). Socially, Baishazhou bar was “sub-healthy” due to unprotected shrinkage, and Tianxingzhou bar was “unhealthy” due to area loss and low permeability of hard works. Overall, both bars were “healthy”. These findings provide a basis for ecological conservation and habitat restoration of bar wetlands. Full article

The Lower North River (LNR) exhibits a distinctive anabranching pattern in the Pearl River Basin, China. However, research has predominantly focused on vertical channel adjustments relying on in situ measurements, while the large-scale spatiotemporal dynamics of the anabranching planform have received limited attention. To address this gap, this study quantified the evolution of the anabranching planform from 1990 to 2022 using remote sensing images, focusing on anabranching intensity and island morphology, and analyzed driving factors using hydrological observations. Results revealed three evolutionary phases driven by shifting dominance of human interventions. During the first phase (1990–2004), the LNR experienced a moderate decline in anabranching intensity and widespread shrinkage of river islands, primarily attributed to sediment starvation induced by upstream dams. In the second phase (2004–2013), the decline in anabranching intensity accelerated and the proportion of expanding islands increased, driven by unregulated sand mining and channel regulation. In the third phase (2013–2022), the rapid decline in anabranching intensity decelerated and the islands shifted from a shrinkage-dominated to a stable-dominated state following the implementation of strict mining management and the physical confinement imposed by engineering structures. These findings reveal distinct morphological responses of the LNR to flow–sediment regimes and anthropogenic physical interventions, offering insights into the sustainable management of large anabranching rivers worldwide in the Anthropocene. Full article

Climate change is impacting rivers worldwide, with a reduction in normal flow conditions in temperate regions like Poland. Such changes might have a significant influence on riparian vegetation and channel planform dynamics. To better understand how these changes impact the river morphology, this research focuses on a 250 km-long reach of the Polish Vistula River and investigates variations of monthly maximum discharges and vegetation conditions over the period 1984–2023 by means of Landsat satellite images. These satellite data were handled via Google Earth Engine, looking at a common index such as the Normalized Difference Vegetation Index, considered as a proxy of vegetation coverage variations. Results point out an increase in the median NDVI over the study area from 0.2 in 1984 to 0.3 in 2023, connected with a reduction of monthly discharge from around 920 m³/s to 880 m³/s. This suggests that changes in flow discharge are associated with a process of riparian vegetation growth, leading to a reduction of planform and bars dynamics and closure of secondary channels (i.e., oversimplification). This is particularly evident over the last couple of decades, during which water availability has decreased significantly, as more humid years in the middle of the study period are now no longer existing, with an observed decrease in the maximum monthly discharge during the last 20 years, likely connected with a more severe impact of climate change. This reduction in flooding events allows more time for vegetation to establish on river bars and banks, eventually creating new islands and causing the observed oversimplification of the active channel. In summary, using the Vistula River as an exemplary case study, this research suggests that prolonged dry periods, more common in recent decades due to climate change, might impact large rivers located in temperate climates, favouring the development of vegetation on exposed sandbars, eventually resulting in a less dynamic active channel. Full article

To investigate the erosion and deposition evolution characteristics of the Xinqiman–Kelelik reach along the main stem of the Tarim River, this study analyzed river channel dynamics and planform morphological changes using Landsat satellite imagery (1993–2024) and hydrological data (water discharge and sediment load) from gauge stations. The results show that the thalweg line swings indefinitely in the river. The thalweg length increased by 29 km, while the mean channel width decreased by 0.28 km. The sinuosity index rose from 1.95 to 2.34, indicating a gradual intensification of channel curvature. The north bank is in a state of siltation, while the south bank is in a state of erosion. The riverbank exhibited an overall southward migration. The farmland area in the study area increased from 1510 hectares in 1993 to 5140 hectares in 2024. During this period, the thalweg near the water-diversion sluice continuously shifted toward the sluice side. To ensure flood protection safety for farmlands and villages on both banks, as well as ecological water diversion, river channel regulation and channel pattern control should be implemented. Full article

As the threat of unstable braided river geomorphology to the resilience of local communities grows, a better understanding of the morphological changes in a river subject to climate is essential. However, little research has focused on the long-term planform change of the braided reaches and its response to hydrological changes. The reach around Majuli Island (Majuli Reach), the first and typical braided reach of the Brahmaputra River emerging from the gorge, experiences intense geomorphological change of the channels and loss of riparian area every year due to the seasonal hydrological variability. Therefore, focusing on the Majuli Reach, we quantitatively investigate changes in its planform morphology from 1990 to 2020 using remote sensing images from the Landsat dataset and analyze the influence of discharge in previous years on channel braiding. The study shows that the Majuli Reach is characterized by a high braiding degree with an average Modified Plan Form Index (MPFI) of 4.39, an average reach width of 5.58 km, and the development of densely migrating bars and active braided channels. Analysis shows a control point near Borboka Pathar with little morphological change, and the braided channel shows contrasting morphological changes in the braiding degree, bars, and main channel between the reach upstream and downstream of it. The area of the riparian zone of the Majuli Reach decreased by more than 50 km² during the study period due to migration of the main channel toward the island. The braiding degree of Majuli Reach is positively correlated with the discharge in previous years, with the delayed response time of the MPFI to discharge being just 3–4 years, indicating the unstable feature of the Majuli Reach with varied hydrology conditions. Full article

In the Loess Plateau of China, loess is widely distributed and forms a unique geomorphic feature of the world. Meanwhile, the Yellow River water and sediment regulation system is under construction. Nonetheless, the morphological characteristics of constrained meandering rivers in the Loess Plateau are still unknown due to the difficulty of extracting the sediment-laden water body. An improved method is proposed based on Landsat 8 imagery, which automatically extracts the multi-band spectral relationship of high-sediment-concentration rivers in valleys. This study analyzes the morphological characteristics of constrained meandering rivers in the middle reaches of the Yellow River Basin, including their sinuosity, periodicity, curvature, and skewness based on the deflection points bend segmentation and continuous wavelet transform methods. These characteristics are then compared with those of other constrained meandering rivers and alluvial meandering rivers. The results show that the sinuosity of the constrained river bends is generally low (with an average of 1.55) due to limitations imposed by the riverbanks, which prevent full development. The average dimensionless curvature radius of the constrained rivers is 18.72, lower than that of alluvial rivers. The skewing angle of the constrained river bends typically inclines upstream, with a proportion reaching 59.44%. In constrained river bends, as the sinuosity increases, the proportion of bends skewing upstream initially increases and then gradually decreases. This indicates that constrained river bends can develop similarly to alluvial bends at lower sinuosity but are limited by the mountains on both sides at medium sinuosity. The analysis of river characteristics in regions with different geological structures reveals the effect of geological structures on the formation of constrained rivers in the Loess Plateau. These findings can provide a reference for selecting reservoir dam sites and are important for the dredging engineering layout in the middle reaches of the Loess Plateau. They also offer quantitative explanations for the meandering characteristics of these rivers. Full article

Vegetation plays a key role in trapping sediments and further controlling pollutants. However, few studies were conducted to clarify the erosion and deposition laws of sediments and the influence factors caused by vegetation patch properties, which is not conducive to the revelation of riverbank protection and erosion prevention. Therefore, this study investigated the change in scouring and deposition characteristics around submerged vegetation patches of nine kinds of typical configurations and their influencing factors. Vegetation patches were assembled from three vegetation densities (G/d = 0.83, 1.3, and 1.77, representing dense, medium, and sparse, respectively), and three vegetation patch thicknesses (dn = 170, 400, and 630, representing narrow, usual, and wide, respectively), to measure vegetation patch property influences. Flow velocity, scouring, and deposition characteristics under nine patches were determined by a hydraulic flume experiment, three-dimensional acoustic Doppler velocimetry (ADV), and three-dimensional laser scanner, and then ten geometry and morphology indices were measured and calculated based on the results of laser scanning. Results showed that both vegetation patch density and thickness were positively related to the turbulence kinetic energy (TKE) above the vegetation canopy, and only vegetation patch density was negatively related to the flow velocity above the vegetation canopy. The relation between the product of density and vegetation patch thickness and erosion area in planform (EA) showed a power function (R² = 0.644). Both density and vegetation patch thickness determined the scouring degree, but deposition location and amount did not rely on each one simply. On average, medium density showed the smallest maximum erosion length (MEL), EA, deposition area in planform (DA), and average deposition length (ADL) and a minimum of the above parameters also occurred at narrow vegetation patch thickness. The shape factor of the erosion volume (SFEV), the shape factor of the deposition volume (SFDV), ADL, and MEL of medium density and narrow thickness vegetation patch (G/d = 1.3, dn = 170) were significantly smaller than that of other types of patches. DA and equivalent prismatic erosion depth on the erosion area (EPED) were significantly linearly related (R² = 0.766). Consequently, most sediment was deposited close to the vegetation patch edge. It is suggested that vegetation patch thickness and density should be given to control sediment transport. In particular, natural vegetation growth changes vegetation patch density and then alters vegetation patch thickness. Management and repair need to be first considered. The results of this study shed light on riparian zone recovery and vegetation filter strip mechanism. Full article

Predicting morphological adjustments in alluvial meandering streams remains a challenging task due to the complex nature of the governing inter-related dynamic flow and sediment transport processes. This difficulty is increased in streams with irregular single-channel planform geometries, such as skewed meanders, where the meander apex is shifted in either the up-valley or down-valley direction relative to the meander centroid. Research in confined bank flume experiments has shown that the geometry difference affects flow characteristics and streambed development. The present study extends upon these findings by being the first to investigate the effects of skewness orientation in a wide-channel flume with a fully unconfined bed and banks. Three experiments were completed with an up-valley skewed, a down-valley skewed, and a non-skewed symmetrical channel, using well-sorted coarse sand and no sediment feed. The results had some variabilities in erosion and magnitude of morphological developments due to initial experimental conditions, but our analysis of the bedform positioning showed notable similarities and differences between the geometries. Bedforms typically formed upstream of the apex, with differences in their stream-wise direction extents. This research highlights how channel width-to-depth ratio and bank erodibility significantly impact river evolution, offering new insights into the dynamics of skewed meandering river channels. This study is a novel step towards a better understanding of skewed meandering rivers in unconfined alluvial channels and highlights opportunities for further research. Full article

This review presents a synthesis of the interaction between the hydro-morphological processes on interfluves and channels within fluvial catchments in permafrost regions. Both in modern and ancient permafrost catchments, this integrated landscape is quite diverse because of a variegated extent of frozen ground, density of vegetation cover, snow thickness, and other local factors. Moreover, temporal changes in environmental conditions are expressed in the morphological evolution of catchments. Channel patterns vary between single- and different multi-channel forms while the interfluves show a high diversity ranging from complete stability to intense denudation by surface runoff. It appears that braided channels, despite their high energy, were only significant during short intervals of peak discharge and transported only limited amounts of eroded sediment, while other channel patterns required more subdued annual discharge variability. Further, denudational processes on interfluves were a specific characteristic of landscape evolution during subsequent ice ages, especially in conditions of snow-rich and poorly vegetated, seasonal frost, or discontinuous permafrost resulting in the formation of extended planforms (cryopediments). In contrast, interfluves appeared to be rather stable on continuously frozen soils. Full article

The morphology of some lithified wind-blown, carbonate dunes in The Bahamas preserves the signature of erosion from paleo-marine processes: wave-induced swash, scarping, and longshore transport. Digital elevation models were used to distinguish between two dune morphotypes—those disconnected versus connected to beach processes. Dune sinuosity and upwind slope were quantified and used to interpret which dunes remained beach-attached and subject to marine erosion and processes versus dunes that became disconnected from the shoreline via inland migration or shoreline regression. Disconnected dunes possess low slopes over stoss surfaces with sinuous planforms mimicking their crestlines. Beach-connected foredunes preserve steep, kilometers-long linear upwind faces, which are interpreted to be signatures of beach-dune morphodynamics. Foredune morphology serves as a proxy for shoreline position during past sea-level high-stands, while the basal elevations of their stoss dune toes provide an upper limit on the beach and adjacent sea level. A growing library of digital topography will allow for this tool to be used to interpret global paleo-shoreline positions through time and space. Full article

Assessing the vulnerability of low-lying coral reef islands is a global concern due to predictions that climate and environmental change will increase reef island instability and cause reef island populations to be among the first environmental refugees. Reef islands in the Pacific and Indian Oceans are highly dynamic environments that morphologically adjust to changing environmental conditions over annual-decadal timescales. However, there is a paucity of reef island shoreline change data from the Caribbean where sea-level rise, ecological and environmental disturbance and hydrodynamic regimes are considerably different than in other oceans globally. Here we present shoreline change analysis of 16 reef islands in northern Honduras, at the southern end of the Mesoamerican Barrier Reef. Satellite imagery from a maximum period of 12.4 years from Utila (2006–2019), and 2.4 years from Cayos Cochinos (2018–2021) was analysed to quantify island shoreline change and planform morphological adjustments. We identified accretion as the dominant island behaviour in Utila, where 5 of 7 islands increased in area and 61.7% of shorelines accreted, contributing to an overall net area increase of 9.4%. Island behaviour was more variable in Cayos Cochinos, where 55.7% of shorelines eroded, 5 of 9 islands remained stable, and net island area change was insignificant (2%). Conversely, the 4 smallest Cayos Cochinos islands (all <1500 m²) experienced significant shoreline change, potentially highlighting a new size threshold for considering reef island evolution. Across both sites, reef islands demonstrated a range of modes of planform change, including lateral accretion and erosion, and migration. Consequently, we provide the first empirical evidence of the dynamic nature of Caribbean reef islands during a period coincident with sea-level rise and highlight the heterogeneous nature of reef island evolution between and within two neighbouring sites at timescales relevant for island adaptation efforts. Full article

Anegada, the easternmost island of the Virgin Islands group (Caribbean Sea), is a low Pleistocene carbonate platform surrounded by Horseshoe Reef, the world’s third-largest fringing reef. The western part of the island consists of an extensive beachridge plain (>40 ridges). The sandy carbonate shoreline exists in three morphodynamic domains that exhibit distinctive behaviour over the 59-year study period (1953 to 2012). The northern shore is dominated by westerly longshore drift under fair-weather conditions and cross-shore sediment transport during high-energy events. Storm wave run-up and high nearshore sediment availability contribute to the construction of shore-parallel beachridges. The western end of the island is affected by refracted waves that drive strong erosion and sediment transport. This is reflected in a succession of alternating rapid shoreline recession and progradation phases over the study period. The south–central shoreline is exposed to low wave energy and is stable and colonised by mangroves. The fringing reef plays a dominant role in mesoscale shoreline morphodynamics, both as a sediment source and in wave energy dissipation. Quasi-stable points and embayments suggest a strong influence of the reef framework in controlling the shoreline’s morphology and position. Sediment transfer from the reef to the shoreline appears to take place via shore-oblique, linear sediment transport pathways that develop across the lagoon in response to the modification of incoming waves. Cannibalisation of the shoreline sediment over the past 50 years is leading to straightening of the shoreline planform. This is counter to the long-term (Holocene) development of beachridges and suggests a change from a strongly positive to negative sediment budget. Full article

To quantitatively study the hydrodynamic changes in different river morphologies and clarify the impact of morphological changes on river ecosystems, this study examined a section of the Nansha River near Laoniuwan in the Haidian District, Beijing, and characterized different river morphologies by river sinuosity. The River 2D model was used for simulation and analysis, and the depth and velocity diversity indices were introduced to quantify the distribution of depth and velocity under different sinuosities. Cyprinus carpio was selected as the target fish in this study, and its suitability curve was determined using literature and field surveys. Combined with the simulation results, a weighted usable area curve was established to identify its inflection point and maximum value and determine the ecological flow in the river under different sinuosities, that is, to clarify the relationship between sinuosity and ecological flow. The results showed that the lower the sinuosity, the worse the depth and velocity diversity, but a greater sinuosity did not lead to better depth and velocity diversity. The depth and velocity diversity of a sinuosity of 1.5 were better than those of 1.89 in general, except for low flow conditions (Q = 5 m³/s). For rivers with water use restricted by nature and society and where ecological needs exist, ecological engineering that appropriately changes the planform of rivers can be considered to increase the diversity of river/channel geometry and provide a basis for the ecological restoration of rivers. Full article

This study investigates the contribution of river morphology towards the occurrence of manganese (Mn) in both sediment and surface water (SW), considering the temporal climatic and spatial conditions. The Boac and Mogpog rivers on the island province of Marinduque, Philippines, were examined in this study. These rivers are downstream of the two abandoned open mine pits at San Antonio and Tapian, where mining disasters occurred in 1993 and 1996, respectively. Field sampling programs were conducted in 2019, 2021 and 2022 to measure the Mn concentrations in sediment and SW, and the physicochemical parameters in SW during the same sampling event. Geographic Information System (GIS) tools were employed to characterize the morphology of each river, specifically river slope, river bends, sinuosity, and channel width and length. The Boac and Mogpog rivers were divided into 22 and 15 river segments, respectively, to account for spatial heterogeneity of all parameters. Correlation (r) analysis on the average Mn concentration and river morphology within each segment was performed and indicated that river bends (Boac r = 0.421, Mogpog r = 0.356) and sinuosity (Boac r = 0.403, Mogpog r = 0.352) had the highest correlation with Mn concentrations in sediment. While river slope (Boac r = 0.716, Mogpog r = 0.282) and sinuosity (Boac r = 0.505, Mogpog r = 0.257) were the highest for Mn in SW. This confirmed that the planform of the river affected the accumulation of Mn due to its effect on sediment deposition along the river and its potential to adsorb and/or desorb metals. Furthermore, the pH of SW also directly correlated with sediment Mn (r = 0.293), and inversely correlated with SW Mn (r = −0.465), which was expected as acidic water promotes the release of metals from sediments to SW. The results from this study will aid local government, environmental engineers and managers in their mitigation program through identification of the areas and segments in the river that contain the highest and the least contamination. This is to optimize financial and human resources during river system remediation and monitoring. Data and information extracted from this study are useful in other areas of similar condition. Full article

Detached breakwaters are widely used for shore protection. The planforms of tombolos or salients behind structures have also been used to provide a recreational and sustainable coastal environment. In this study, the comprehensive XBeach model was used to numerically simulate the evolution of wave transformation, nearshore current, and morphological changes in tombolo planforms behind detached breakwaters. Given various gap spacings between consecutive breakwaters, the numerical results indicated that both equilibrium bay-shaped shorelines and bottom profiles form in the lee of detached breakwaters after long-term persistent wave action. These equilibrium shorelines and bottom profiles were verified using well-known empirical formulas. Post-wave-action retreat displacement to the initial shoreline was analyzed, and an empirical relationship was proposed for predicting the equilibrium bay-shaped shoreline. By associating the empirical formula with a parabolic bay-shape equation, some actual beaches were evaluated to validate the predictions of equilibrium shorelines behind detached breakwaters. In conclusion, to appropriately plan the layouts of breakwaters, bay-shaped shorelines of tombolo planforms in the lee of detached breakwaters can be predicted at the design stage by using the proposed relationship. Full article